NGL trains description.pdf

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Issued: APR 2006 Revised: SEP 2006 Job No: 0-3850 Doc No: S-660-1283-001

CONTENT

This instruction outlines the process descriptions of NGL trains. There are three (3) NGL trains,

which are identical. The description is mentioned based on train number 1. All instrument tag

numbers on this section is prefixed “41-“ for Train 1 and “42-“ and “43-“ for Train 2 and 3 unless

otherwise noted.

The text includes:

1. INTRODUCTION

2. DESIGN BASIS

3. PROCESS DESCRIPTION AND CONTROL

4. OVERALL PLANT CONTROL

5. PROCESS CONTROL

6. COMPLEX CONTROL

7. REGENERATION /ABSORPTION LOGIC SEQUENCE DESCRIPTION

8. PROCESS THEORY

9. PROCESS VARIABLE

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1 INTRODUCTION

The NGL Recovery Trains recover ethane and heavier hydrocarbons. The ethane recovery

is limited only by the minimum gross heating value specification on the residue gas of 930

BTU/SCF. The carbon dioxide content of the ethane plus NGL is specified as less than 1500

ppmv.

The NGL recovery unit consists of three identical trains; each designed to handle 33.3% of

the peak total inlet gas flow rate. The capacity of each train is 1333 MMSCFD.

Although the Haradh and Hawiyah inlet gas streams to each NGL recovery unit have been

dew-point controlled, it contains impurities such as nitrogen, carbon dioxide, mercury and

water, which adversely affect cryogenic processing to recover ethane and heavier

hydrocarbons (ethane plus).

The Haradh and Hawiyah inlet gas streams to each NGL recovery unit will be mixed inside

the train and then pre-cooled before passing through the molecular sieve beds for

dehydration and the activated carbon beds for mercury removal. The water is removed

using a molecular sieve dehydration system, since cryogenic temperatures are required to

recover ethane product and water freezing and hydrate formation shall be prevented. Since

brazed aluminum heat exchangers (BAHE) are used in the cryogenic process; mercury that

could attack the aluminum material removed in the activated carbon beds.

The ethane and heavier hydrocarbons are extracted from the methane component of the inlet

gas by fractionation in a demethanizer column. This is accomplished by liquefying the gas

streams using heat exchangers, turbo expanders, or Joule-Thompson (JT) valves before it

enters the demethanizer column. The demethanizer column operates at a controlled

pressure with heat being added to the bottom by means of reboilers and overhead

temperature being controlled by the cold feed stream. The overhead residue gas stream is

essentially ethane free and passes to the sales gas compression unit (B68) after

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recompression by brake compressors.

The nitrogen is not removed from the inlet gas and simply passes through the plant with the

residue gas unaffected by the process.

The NGL products coming off the bottom of the demethanizer are primarily ethane, heavier

hydrocarbon liquids. Major part of carbon dioxide (CO2) in Haradh gas is removed in B65,

and remaining CO2 in Haradh gas and CO2 containing in Hawiyah gas pass through the

process with the ethane plus product and is send to NGL surge spheres (B67) as part of the

ethane plus liquid.

A simplified block diagram of the NGL trains is shown on the next page and Attachment 10.

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The following is a brief description of the main facilities included in each NGL Train:

• Precondition System

Two Feed Gas enters this system, one from HUG-1 and the other from HDUG-1. The Dry

Hawiyah Feed Gas is coming from HUG-1 after filtration in B64. The Hawiyah gas inlet

does not have to be treated as the Carbon dioxide (CO2) was removed at the existing

Hawiyah Gas Plant. The Hawiyah gas goes through two heat exchangers which will lower

its temperature from 139 °F to 80 °F.

The Haradh Gas is wet gas because it is coming from DGA gas treating facility (B65) after

removing CO2. The wet Haradh gas enters a heat exchanger and a separator where the

temperature is reduced to 80 °F and the condensed liquid separated. Both Gas will then join

in a Static Mixer and fed to the Dehydration System.

• Molecular Sieve Gas Dehydration

The Feed Gas Dehydration Beds contain the molecular sieve used to dehydrate the feed gas.

There are 6 beds per train, 5 beds are on absorption and one is on regeneration/stand-by at

any time.

• Mercury Removal

The Mercury Removal Beds use activated carbon to remove the mercury from the feed gas.

The carbon beds are disposable, and when fully loaded with mercury, must be replaced with

fresh material.

The dehydrated mercury free gas flows to the dust filters where it is filtered to remove any

entrained fine dust and particles.

• Regeneration Gas System

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Sales gas heated to 550 °F is used to regenerate the beds. The regeneration gas is heated in

two Heaters. The first heater utilizes medium pressure hot water to heat the regeneration

gas to 400 °F. The second heater utilizes electricity to further heat the regeneration gas to

550 °F.

• Cryogenic System

The gas is cooled through the Brazed Aluminum Heater Exchanger to approximately -55 °F,

and separated liquids are routed to the Demethanizer.

Gas from the expander feed separator is split into two streams. One stream (28 %vol) is fed

to the Demethanizer Overhead Exchanger where it is cooled and passes through an

expansion valve where the pressure is dropped to 259 psig. This stream is then fed to the top

separator section of the Demethanizer.

The remaining gas (72 %vol) from the expander separator is fed to the turbo expanders. The

gas exits the turbo expanders at approximately 260 psig and -124 °F and is fed to the top tray

of the Demethanizer.

Power recovered from the expanders is utilized in the brake compressor portion to increase

the pressure of the residue gas. There are two 50% capacity Turbo-Expanders in each NGL

train.

The Demethanizer distills the liquefied NGLs to produce an ethane rich NGL product that

meets the required specifications.

It is required to have a CO2 content of less than 1500 ppmv, and no more than 2.5% methane

in ethane. (The NGL liquid produced as bottoms product is pumped to the surge spheres).

• Demethanizer

The Demethanizer overhead gas stream (Residue Gas) flows through a series of Brazed

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Aluminum Heat Exchanger and is routed to the suction of the Brake Compressors where

those are compressed and sent to the Sales Gas Compression trains (Plant B68).

There are three reboilers on the Demethanizer, two side reboilers and a bottom reboiler with

auxiliary reboiler.

• Propane Refrigeration

Propane Refrigeration is used to assist in cooling the feed gas stream. Each NGL train has a

dedicated system and consists of two-motor driven, two-stage centrifugal compressors.

2 DESIGN BASIS

The NGL recovery unit consists of three identical trains that include the following main

facilities. The description is mentioned based on train number 1. All instrument tag

numbers on this section is prefixed “41-“ for Train 1 and “42-“ and “43-“ for Train 2 and 3

unless otherwise noted.

2.1 SYSTEM CAPACITY

The NGL recovery unit consists of three identical trains; each designed to handle 33.3% of

the peak total inlet gas flow rate. The capacity of each train is 1,323 MMSCFD. Turndown

capability is a minimum of 50% of design capacity.

The HNRP will recover from the inlet gases approximately 310,000 BPD of C2+ NGL

(180,000 – 185,000 BPD), whose ethane content is 60 mol%.

Each NGL train consists of the follows:

• six 20% capacity molecular sieve beds per train – 5 beds are on adsorption and one

is on regeneration at any point in time.

• five 20% capacity activated carbon beds for mercury removable system

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• two 50% capacity turbo expander / brake compressors (50% x 2, no spare)

• one demethanizer column with reboilers

• two 50% capacity two-stage refrigerant compressors (no spare)

• Pre-coolers and Brazed aluminum heat exchangers, etc.

2.2 FEED AND PRODUCT DATA

The ethane recovery is limited only by the minimum gross heating value specification on the

residue gas of 930 BTU/SCF. The CO2 content of the C2+ NGL is specified as less than

1500 ppmv.

The design parameters of the NGL unit are as follows:

• Capacity of each train: 1,323 MMSCFD

• Turndown capability: to a minimum of 50% of design capacity

1) Feed Gas Pre-cooling

• Dry inlet gas temperature of Hawiyah gas stream: 140 ºF

• Wet inlet gas temperature of Haradh gas downstream of gas treating: 146 ºF

(water saturated)

• Pre-cooling temperature for dehydration: 80 ºF

2) Molecular Sieve Gas Dehydration

• Design water content of the wet gas for molecular sieve: 20 lb/MMSCF at

1,323 MMSCFD and saturated at 680 MMSCFD (Haradh gas only case)

• Water content of the dehydrated gas: less than 0.1 ppmv.

• Designed bed life is 3 years

• Regeneration gas temperature: 550 ºF (heating) and 90 ºF (cooling)

• Regeneration gas flow rate: Maximum 60 MMSCFD

3) Mercury Removal

• Design mercury content of the inlet gas: 70 micrograms/ Nm3

• Mercury content of the dehydrated gas: less than 0.01 microgram/Nm3 of

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gas.

• Designed bed life is 3 years

4) C2+ NGL recovery

• Heat content of residue gas 930 BTU/SCF (minimum gross heating value)

• NGL liquid produced as a bottoms product when processed at Saudi

Aramco’s NGL Fractionation plants to meet the following ethane

specifications:

- CO2 content of less than 1500 ppmv

- No more than 2.5% mole methane in ethane.

5) Propane Refrigeration

• Refrigeration design levels:

(1) 1st suction: -14 ºF at 13 psig

(2) side stream: economizer 52 ºF at 83 psig, chillers 55 ºF at 83 psig and 75

ºF at 118 psig

(3) condenser 140 ºF at 302 psig

• The heat gain in the propane refrigeration system is 2% of the chiller duties in

summer operation and 1% of the chiller duties in winter operation.

3 PROCESS DESCRIPTION AND CONTROL

The following description is based on train 1 (Unit 41), but is also applicable to train 2 & 3

(Unit 42 & 43).

3.1 FEED GAS PRE-COOLING

The pre-cooling area equipment is used to lower the temperature of the feed gas stream to

80 °F, which is based on hydrate formation temperature of approximately 62 °F plus 18 °F

margin, before it passes into the Molecular Sieve Dehydrators. The feed gas streams are

Hawiyah gas and Haradh gas. Haradh gas is coming from gas tearing trains (B65) and water

saturated, although Hawiyah gas is dry.

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The Feed Gas/Residue Gas Exchanger (B66-E-0101 A/B) is the first set of shell-and-tube

type heat exchangers on Hawiyah feed gas lines in the NGL recovery process. It is used to

cool the Hawiyah inlet gas to 90 °F. Due to the presence of mercury in the gas, this

exchanger is a shell-and-tube type heat exchanger of steel material.

After the Feed Gas/Residue Gas Exchanger, the Hawiyah gas is fed to the Hawiyah Gas

Chiller (B66-E-0102). It is a steel tube bundle inside a propane-bath kettle-type heat

exchanger and is used to cool the gas to 80 °F. The propane refrigerant for this chiller is fed

from the propane sub-cooler (B66-E-0117 A/B). The outlet gas from this chiller is fed to the

static mixer where it is mixed with the chilled Haradh gas.

The Haradh Gas Chiller (B66-E-0108) is a steel tube bundle inside a propane-bath

kettle-type heat exchanger and is used to cool the wet Haradh gas from 146 °F to 80°F and

condense the majority of the water vapor. The propane refrigerant for this chiller is fed from

the propane sub-cooler (B66-E-0117 A/B).

Gas from the Haradh Gas Chiller is fed to Haradh Gas Chiller Separator (B66-D-0101)

to remove the water/entrained DGA condensed in the Haradh Gas Chiller. The

condensed is recycled back to the gas treating trains (B65) where the water/entrained

DGA is reused by adding it to the Diglycolamine (DGA) solution to minimize DGA

loss.

The chilled Hawiyah gas and the chilled Haradh gas are commingled and mixed in the static

mixer (B66-SM-001). The purpose of this mixer is to ensure the mixture is homogeneous

and is without stratification, which could cause unequal loadings of water in the molecular

sieve dehydration beds.

If temperature of Hawiyah gas is lower than that of Haradh gas, Condensation of water may

take place and, thereby, performance of molecular sieves dehydrator worsens. Therefore,

the differential temperature between Hawiyah and Haradh gas at mixer inlet is monitored

and the alarm signal is initiated when warmer Haradh gas (i.e. lower Hawiyah gas) is

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detected.

3.2 MOLECULAR SIEVE GAS DEHYDRATION

The Feed Gas Dehydration Beds (B66-D-0102A/B/C/D/E/F) contain the molecular sieve

used to dehydrate the feed gas to 0.1 ppmv (0.1 ppmV water content corresponds to less than

-174degF at 263psig which is the operating condition of demethanizer reflux line). This low

water content is required to prevent hydrate formation in the cryogenic section of the plant.

There are 6 beds per train – 5 beds are on adsorption and one is on regeneration or stand-by

at any point in time. Each bed is sized to process 20% of the inlet gas flow. Adsorption is

done with the gas flowing vertically down through the bed. Regeneration gas is lean sales

gas and taken from the discharge of each sales gas compressors (B68) and flowing vertically

up through bed.

Once a bed has adsorbed as much water as the molecular sieve can handle, it is placed on

regeneration. Sales gas heated to 550 °F is used to regenerate the beds. Following

regeneration, the bed is cooled down to 90 °F, which is the normal operating temperature

plus 10 °F, using cooled lean sales gas.

Sequencing of the dehydration bed switching valves is to be controlled by timer sequencers

programmed into the DCS control system.

The water content of the dehydrator outlet gas will be monitored with an on-line moisture

analyzer. The time span the beds are on adsorption shall be adjusted to ensure that the beds

are on adsorption as long as possible while ensuring that water break-through does not

occur.

The outlet gas from the Feed Gas Dehydration Beds is fed to the Mercury Removal Beds.

During the regeneration heating cycle, the sales gas is heated in two regeneration gas heaters.

The first of the heaters, the Regen Gas Hot Water Heater (B66-E-0103A/B), utilizes

medium pressure hot water to heat the regeneration gas to 400 °F. The second heater, the

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Regen Gas Electric Heater (B66-E-0105 A/B), utilizes electricity to further heat the

regeneration gas to 550 °F.

The regeneration gas can be automatically heated in two steps by activating or deactivating

the electric heater and by controlling the hot-water flow rate.

During the regeneration cooling cycle, the Regen Gas Cooling Cycle Chiller (B66-E-0104)

cools the sales gas to 90 °F using propane refrigerant.

Two coolers in series cool the regeneration gas from the gas dehydration beds. The first

cooler is the Regen Gas Air Cooler (B66-E-0106), a fin-fan cooler that cools the gas to

approximately 145 °F. The second cooler, the Regen Gas/Propane Chiller (B66-E-0107),

cools the gas to 80 °F using propane refrigerant. This is to condense as much water vapor as

practicable. Hydrate formation temperature is approximately 51 °F. The gas is then routed

to the Regen Gas Separator.

The Regen Gas Separator (HP) (B66-D-0105) separates any water that condenses out of the

regeneration gas stream as it is cooled. The gas from B66-D-0105 is then routed to sales gas

pipeline via the regeneration gas blowers KO drums and Blowers (B64). The water from

B66-D-0105 is flashed to the Regen Gas LP Knock Out Drum (B66-D-0106) to

depressurize it to 5 psig. Condensed water is routed to the Oily Water Sewer (OWS) and the

flashed gas is routed to LP flare.

3.3 MERCURY REMOVAL

The gas from the Dehydration Beds passes through the Activated Carbon Beds

(B66-D-0107A/B/C/D/E). Flow direction is vertically down through the beds. The beds

contain an activated carbon that removes the mercury from the feed gas. The activated

carbon is disposable, and when fully loaded with mercury, the bed must be replaced with

fresh material.

There are five beds for each NGL train. Each is sized for 20% of the inlet-gas flow.

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The Carbon Bed Outlet Dust Filters/Basket Strainers (B66-D-0103A/B/C/D/E and

B66-D-0104 A/B/C/D/E) are used to remove the fine dust and particles to prevent foiling or

plugging of the downstream brazed aluminum heat exchangers. Each dust filter/basket

strainer is dedicated to one of the activated-carbon beds.

3.4 C2+ NGL RECOVERY

The NGL Recovery Area equipment is used to lower the temperature of the gas stream to

liquefy and distill the NGLs.

The Feed Gas Exchanger (B66-E-0110 A/B) receives gas from the molecular-sieve

dehydration unit. The gas is fully dehydrated and is free of mercury. The exchanger is a

brazed aluminum heat exchanger (BAHE) and has three sections (passes) – the feed gas

section (Pass A), a residue gas section (Pass B), and the Demethanizer reboiler section (Pass

C). It is used to cool the feed gas to approximately 30 ºF.

Two 50% units (A &B) have been provided to allow one unit to be taken out of service for

maintenance (back puffing) without shutting down the entire train.

Following this exchanger, the gas is split into two streams, approximately 42% being fed to

the Second Stage Feed Gas Chiller (B66-E-0114), and the remaining 58% being fed to the

Warm Gas Exchanger (B66-E-0111).

The Second Stage Feed Gas Chiller (B66-E-0114) is a BAHE (core) inside a propane-bath

kettle-type heat exchanger and is used to cool the gas to approximately -9 ºF. The propane

refrigerant for this chiller is fed from the Refrigerant Economizer (B66-D-0115).

The Warm Gas Exchanger (B66-E-0111) receives gas from the Feed Gas Exchanger. The

exchanger is a brazed aluminum heat exchanger (BAHE) and has three sections (passes) –

the feed gas section (Pass A), a residue gas section (Pass B), and the Demethanizer bottom

side reboiler section (Pass C). It is used to cool the inlet gas to approximately -9 ºF.

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The feed gas fluid stream from the Warm Gas Exchanger is commingled with the feed gas

fluid stream from the Second Stage Feed Gas Chiller and is routed to the Chiller Separator.

The Chiller Separator (B66-D-0110) receives a two-phase fluid stream from the Second

Stage Feed Gas Chiller and from the Warm Gas Exchanger. The separator is designed with

a single inlet, a single liquid outlet and two vapor outlet connections, one vapor outlet at

each end of the vessel. Each of these vapor outlet connections is provided with a mist

eliminator pad. Liquids separated are routed to the Demethanizer as a side feed. The

remaining gases are fed to the Cold Gas Exchanger.

The Cold Gas Exchanger (B66-E-0112) receives feed gas from the Chiller Separator. The

exchanger is a brazed aluminum heat exchanger (BAHE) and has three sections (passes) –

the feed gas section (Pass A), a residue gas section (Pass B), and the Demethanizer top side

reboiler section (Pass C). It is used to cool the inlet gas to approximately -56 ºF.

The Expander Feed Separator (B66-D-0111) receives a two-phase stream from the Cold Gas

Exchanger. The separator is designed with a single inlet, a single liquid outlet and two

vapor outlet connections, one vapor outlet at each end of the vessel. Each of these vapor

outlet connections is provided with a mist eliminator pad. Liquids separated are routed to

the Demethanizer as a side feed.

Following this separator, the gas is split into two streams, approximately 28% being fed to

the Demethanizer Overhead Exchanger (B66-E-0113), and the remaining 72% being fed to

the Turbo-Expanders.

The Demethanizer Overhead Exchanger (B66-E-0113) receives feed gas from the Expander

Feed Separator. The exchanger is a brazed aluminum heat exchanger (BAHE) and has two

sections (passes) – the feed gas section (Pass A), and a residue gas section (Pass B). It is

used to cool the feed gas to approximately -159 ºF.

The liquid stream exiting the exchanger is passed through a Joule-Thompson (J-T)

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expansion valve where the pressure is dropped to 264 psig and the temperature is decreased

to -174 ºF. The fluid is then fed to the top packed section of the Demethanizer.

The Turbo-Expander/Brake Compressor Units (B66-K-0110A/B) receive gas from the

Expander Feed Separator. The two-phase fluid stream exits each of the expanders at

approximately 276 psig and -123 ºF, and are fed individually to the top tray of the

Demethanizer. Power recovered in the expander portion of the Turbo-Expander is utilized

in the compressor portion to increase the pressure of the residue gas.

There are two 50% capacity Turbo-Expanders in each NGL train; there are no spare or

stand-by units. The Turbo-Expander/Brake Compressor units are connected in parallel.

The Demethanizer (B66-C-0110) is used to distill the recovered liquid NGLs and produce

an ethane rich NGL product, which meets the methane and carbon dioxide content

specifications. The Demethanizer receives a two- phase (gas and liquid) feed from the

Demethanizer Overhead Exchanger and from the two Turbo-Expanders. It also receives

flashed liquid NGLs from the Expander Feed Separator and from the Chiller Separator.

The demethanizer smaller diameter section has 34 Flexitrays (Valve trays) with four

chimney trays and larger diameter section has random packing with two chimney trays.

There are three reboilers on the Demethanizer. The bottom reboiler is heated by the Feed

Gas Exchanger, the bottom side reboiler is heated by the Warm Gas Exchanger, and the top

side reboiler is heated by the Cold Gas Exchanger.

The NGL liquid produced as a bottoms product shall meet the ethane product specification

when further processed at Saudi Aramco’s NGL Fractionation plants.

A Demethanizer Auxiliary Reboiler (B66-E-0118) is provided for one JT / one

Turbo-Expander operation mode so that the produced NGL liquids meet the required

specifications.

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3.5 PROPANE REFRIGERATION

Propane Refrigeration is used to supply the cold source for heat removal. The Propane

Refrigeration system in each NGL train has two 50% (Unit A & Unit B) capacity

compressors, suction drums, condensers and accumulators. The sub-cooler and economizer

are common to both Unit A and Unit B.

The Propane Refrigerant Compressors (B66-K-0111A/B) are centrifugal compressors and

have two stages. The low pressure stage takes propane vapors from the Second Stage Feed

Gas Chiller (B66-E-0114) and the high pressure stage takes propane vapors from the

Refrigerant Economizer (B66-D-0115), Hawiyah Gas Chiller (B66-E-0102), Regen Gas

Cooling Cycle Chiller (B66-E-0104), Regen Gas/Propane Chiller (B66-E-0107), and

Haradh Gas Chiller (B66-E-0108).

The discharge from the compressors is routed to the Refrigerant Condensers (B66-E-0115

A/B).

The Refrigerant Compressors are equipped with anti-surge flow-control loops on the first

and second stages. Each recycle-gas stream is temperature controlled by quenching (i.e.,

mixing) with liquid refrigerant.

The Refrigerant First Stage Compressor Suction Drums (B66-D-0112A/B) and the

Refrigerant Second Stage Compressor Suction Drums (B66-D-0113A/B) are intended to

prevent any liquid propane from entering the suction of the compressors. Each of the drums

is equipped with a mist eliminator pad and heating coil in the bottom of the drum used to

vaporize any liquid propane which accumulates in the drum. The coils are heated using hot

refrigerant compressor discharge gas.

Each compressor discharges into a Refrigerant Condenser (B66-E-0115A/B). This is a

battery of air cooled heat exchangers. Condensed propane refrigerant from the condenser is

combined and fed to the Refrigerant / Water Sub-cooler (B66-E-0117 A/B).

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A Refrigerant Accumulator (B66-D-0114A/B) is installed between the Refrigerant

Condenser and the common sub-cooler. System liquid fluctuations will be accommodated

in the accumulator. In order to ensure there is always sufficient pressure in the accumulator

to allow flow through the chillers, a hot gas by-pass is installed around the Refrigerant

Condenser. This maintains pressure in the Refrigerant Accumulator when ambient

temperatures decrease.

A Refrigerant / Water Sub-cooler (B66-E-0117 A/B) is installed downstream of the

Refrigerant Accumulators. The Refrigerant / Water Sub-cooler uses chilled cooling water

that has been further cooled by the export NGL in the Product Surge area (B67).

The compressors are equipped with a common Refrigerant Economizer (B66-D-0115) to

reduce the overall load on the compressors.

Propane refrigerant transferred from the storage facility in Plant B67 to Plant B66 is filtered

through a Refrigerant Filter (B66-D-0116) before being distributed into the refrigerant

circuit. During a unit shutdown, propane refrigerant is transferred from Plant B66 to B67 via

the Refrigerant Return Pump (B66-G-0114) from economizer and accumulators.

During Haradh gas only operation, refrigerant compressors' side stream duty is almost same

as that of normal operation, however, 1st suction stream duty is reduced to less than 45% of

normal and possible minimum flow recycle is required for 1st stage only. To prevent

minimum flow recycle and save energy consumption, side stream flow is bypassed to 1st

suction via letdown valve.

4 OVERALL PLANT CONTROL

On the main gas line, there are five control valves for overall plant control as below:

1. Hawiyah Feed Gas Line, 41/42/43-FV-001

2. Haradh Feed Gas Line, 31/32-FV-003

3. 41/42/43-HV-311/330 (Expander inlet guide vane) and FV-238 (DeC1 reflux)

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4. 41/42/43-PV-537 (DeC1 overhead)

5. 61/62/63/64-FV-001, Sales Gas Compressor Inlet

The detail of control is mentioned the following section and B74-J-BE530023

(S-741-1371-101), Specification for Complex Control Strategies, para 6.

4.1 PURPOSE

The priority of purpose is the follows.

a. To maintain inlet pressure to turbo expander (K-0110A/B, K-0210A/B,

K-0310A/B).

b. To maintain constant pressure in both inlet pipelines (to match the plant

processing rate to the supply from both pipelines).

c. To provide flexibility of evenly splitting both Hawiyah and Haradh gas flows

between all three NGL recovery trains.

d. To limit gas flow through each NGL train to the train design capacity and to

allow any single train capacity testing during multi-train operation, also to

limit Hawiyah gas flow through a single line train.

e. To automatically perform all the above independently of number DGA, NGL

and sales compression trains in operation.

f. To ensure priority of operation with Haradh gas, over Hawiyah gas, in case of

reduced plant capacity.

g. To perform all the above with minimum pressure drop to the gas flow.

Demethanizer overhead pressure is controlled by 4x-PV-537 during normal operation.

During JT operation, Demethanizer overhead pressure is depend on sales gas

compressor master pressure control and pipeline pressure.

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4.2 STRADDLE CONTROL (PLANT BYPASS): (GTCC PORTION.)

This control loop operates the plant bypass on the Haradh & Hawiyah sales gas lines. In the

event of a plant trip or emergency, gas feed is bypassed around the Hawiyah NGL plant.

This loop is controlled by continually monitoring the Pressure in the HUG-1 and HDUG-1

pipelines In and Out of the plant.

If the Hawiyah gas supply header pressure exceeds its preset value, Hawiyah Gas supply

header high pressure protection controller 21-PIC-005 opens pipeline bypass valves,

21-PV-005A/B to reduce the header pressure.

Differential Pressure 21-PDI-007 will provide permissive-to-open bypass valves,

21-PV-005A/B via DCS logic. If the pressure difference between supply header pressure

and return pressure becomes less than preset value, this DCS logic will close the pipeline

bypass valves to avoid reverse flow. A 48 inches check valve is also available to

mechanically ensure that no back flow will occur.

If the Haradh gas supply header pressure exceeds its preset value, Haradh Gas supply header

high pressure protection controller 22-PIC-105 opens pipeline bypass valves,

22-PV-105A/B to reduce the header pressure.

Differential Pressure 22-PDI-008 will provide permissive-to-open bypass valves,

22-PV-105A/B via DCS logic. If the pressure difference between supply header pressure

and return pressure becomes less than preset value, this DCS logic will close the pipeline

bypass valves to avoid reverse flow. A 48 inches check valve is also available to

mechanically ensure that no back flow will occur.

4.3 HAWIYAH GAS AND HARADH GAS FLOWRATE CONTROL

Nitrogen component of Hawiyah feed gas is higher than that of Haradh feed gas. If

Hawiyah gas is only feed to DeC1, Nitrogen content of sales gas is increased and possible

off-spec sales gas occurs. In view of keep the heating value of sales gas as minimum 930

MMBTU/SCF, Hawiyah gas is to be reduced first in case of reduced plant capacity.

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For C2 recovery rate, the difference between the Hawiyah gas maximum case and Haradh

gas maximum case is +/- 0.3% and negligible.

Therefore, ratio control for Haradh gas and Hawiyah gas flow rate is not required and

Haradh feed gas flow to each NGL train is controlled by balance of NGL train Maximum

total flow controller (41/42/43-FIC-237) and Hawiyah gas flow controller

(41/42/43-FIC-001).

Haradh gas and Total NGL feed gas flow ratio of each NGL train is calculated

(41/42/43-FY-009) and indicated in DCS (41/42/43-FI-009) as a reference for operator.

4.3.1 Maximum Flow Limit Control on Total Hawiyah and Total Haradh Feed Lines

The maximum total feed gas flow from Hawiyah can be set through 40-HIC-004. When

measured total gas feed flow from Hawiyah gas pipeline exceeds this limit, 40-HIC-004 will

override signal from 21-PIC-006 via low signal selector, 40-PY-036 and thus limit the

setpoint of 40-FIC-002.

The maximum total feed gas from Hawiyah and Haradh to NGL train is limited by

41/42/43-FIC-237. 41/42/43-FIC-237 setpoint is about 1,400 MMSCFD in consideration of

the Demethanizer, B66-C-0*10 capacity. When this value is exceeded, 41/42/43-FIC-237

will manipulate the expander Inlet guide vane to close via low signal selector,

41/42/43-PY-499A and override signals from 41/42/43-PIC-499A.

The maximum total Haradh feed gas to DGA units is around 1,700 MMSCFD in

consideration of the DGA unit capacity of 816 MMSCFD per DGA unit. This maximum

limit can be set through 22-HIC-004. When this limit is exceeded, 22-HIC-004 will override

signal from 22-PIC-004 via low signal selector, 22-PY-004 and thus limit the setpoint of

22-FIC-003.

When one or two NGL trains are shutdown, the total Haradh gas max total flow limit will be

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calculated by 40-FY-004. When 41/42/43-FIC-004 process value read lower than a preset

value, 40-FY-004 will consider that train to be blocked/shutdown and reduce 22-FIC-003

setpoint via low signal selector 22-PY-004 and override signal from 22-PIC-004 and

22-HIC-004.

No. of Running Trains Max. Total Haradh Gas Feed Flow Rate

0 or 1 900 MMSCFD

2 or 3 1700 MMSCFD

The set point of maximum feed gas rate of total feed gas (Hawiyah and Haradh) and Haradh

gas is calculated from the number of operating trains as below:

NGL train # Hawiyah + Haradh Gas output Haradh Gas (10-FY-004)

1 1,400 MMSCFD 900 MMSCFD

2 2,800 MMSCFD 1,700 MMSCFD

3 4,380 MMSCFD 1,700 MMSCFD

Logic for 40-FY-004 output is as follows:

Three NGL Trains in operation

If 41-FIC-004.PV >= X and 42-FIC-004.PV >= X and 43-FIC-004.PV >= X

Then 40-FY-004.MV= 1700

Two NGL Trains in operation

If 41-FIC-004.PV < X and 42-FIC-004.PV >= X and 43-FIC-004.PV >= X or

If 41-FIC-004.PV >= X and 42FIC004.PV< X and 43-FIC-004.PV>=X or

If 41-FIC-004.PV >= X and 42-FIC-004.PV >= X and 43-FIC-004.PV < X

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Then 40-FY-004.MV= 1700 (MMSCFD)

One NGL Train in operation

If 41-FIC-004.PV < X and 42-FIC-004.PV<X and 43-FIC-004.PV>= X or

If 41-FIC-004.PV < X and 42-FIC-004.PV>= X and 43-FIC-004.PV<X or

If 41-FIC-004.PV >= X and 42-FIC-004.PV< and 43-FIC-004.PV<X

Then 40-FY-004.MV= 900 (MMSCFD)

Where “X” is low flow value to consider that the train is blocked or shutdown.

The DCS logic shall be provided to set the Max Total Haradh Gas Feed Flow Rate to

22-HIC-004 as one shot action in case of the number of running NGL train becomes less

than 2.

A rate of change limiter in “SCFD/ sec” shall be provided for 22-HIC-004 output signal to

change gradually when number of NGL trains running is changed.

4.3.2 Equal Distribution of Total Haradh Flow on NGL Trains

NGL trains are to have same flow rate for all 3 Hawiyah feed flow to NGL trains, and all 3

Haradh feed also at the same flow rate which is mixed with Hawiyah feed gas on each Train.

The ratio of Hawiyah to Haradh gas feed is not really a main concern but an unevenly

distributed Hawiyah & Haradh feed flows may shorten the running time of Dehydration

system on NGL Trains, and may cause operation problem.

At normal operation, where 3 NGL trains are operating, to avoid overloading the

dehydration systems by uneven distribution of Haradh feed, Hawiyah ratio setter,

41/42/43-FY-001B will be automatically adjusted by 41/42/43-FDC-010 to maintain a set

value on Haradh flow to each NGL train. Process value of 41/42/43-FIC-004.PV will be

averaged, 40-FY-003 and the calculated value will then be compared to individual NGL

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train process value, 41/42/43FIC004.PV. The difference between process value and average

value (41/42/43-FIC-004.PV-Average) will then be used to automatically adjust the ratio set

via 41/42/43-FY-001B on corresponding Hawiyah flow.

DCS logic will disable this control by changing the mode of 41/42/43-FY-001B Ratio Setter

from “CAS” to “AUTO” when one of NGL trains is shutdown and keep the last ratio

setpoint.

4.3.3 Hawiyah Gas Feed Flow Control & Supply Header Pressure Control

During normal plant operation, Hawiyah gas supply header pressure controller, 21-PIC-006

will control the header pressure by manipulating the setpoint of total Hawiyah feed gas flow

controller, 40-FIC-002 via low signal selector, 40-PY-036. The total Hawiyah feed gas

flowrate is then equally distributed by controller, 40-FIC-002 by manipulating the setpoint

of 41/42/43-FIC-001 for each NGL train via ratio setter, 41/42/43-FY-001B. Hawiyah feed

gas flow to each NGL train is controlled by 41/42/43-FIC-001 that manipulates control

valve, 41/42/43-FV-001. The total Hawiyah gas feed flow rate is calculated from the PV

value of 41/42/43-FIC-001 and used as process value of total Hawiyah gas feed flow rate

controller 40-FIC-002.

If operator would like to limit the maximum total flow rate through the NGL trains, operator

can set the maximum flow limit to the 40-HIC-004 connected with the total Hawiyah gas

feed flowrate setpoint via low signal selector, 40-PY-036.

21-PIC-006 to be “non-linear gain PI controller” will minimize the change of feed flow to

NGL unit under small Hawiyah Gas header pressure changes. The non-linear gain PI

controller will lower the proportional gain to moderate the 41/42/43-FV-001 movement

when the pressure variation is within a range (Gap). This Gap will be decided at later and

can be modified during plant commissioning.

The total gas flowrate, Hawiyah and Haradh gas to NGL train is limited by total feed gas

max flow limit controller (DCS) described in section 4.2.

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If the operator would like to operate one or two NGL trains in FIC (Stable feed flow) mode

and the remaining trains by PIC - FIC cascade control, the DCS operator can disconnect the

cascade connection of each train to be run in FIC mode by changing Hawiyah gas

41/42/43-FIC-001 on each NGL train to Auto mode.

If the expander suction pressure exceeds the preset value, the High Pressure protection

controller, 41/42/43-PIC-499B will reduce feed gas flow rate from Hawiyah gas header via

41/42/43-HIC-014 and low signal selector, 41/42/43-FY-001. Even if the gas feed from

Hawiyah pipeline is reduced but the expander suction pressure still exceeds its preset value,

41/42/43-PIC-499B will then reduce feed gas from Haradh gas supply header.

If the Hawiyah gas supply header pressure exceeds its preset value, Hawiyah gas supply

header high pressure protection controller 21-PIC-005 opens pipeline bypass valves to

reduce the header pressure via low signal selector.

4.3.4 Haradh Gas Feed Flow Control & Supply Header Pressure Control

During normal plant operation, Haradh gas supply header pressure controller 22-PIC-004

will control the header pressure by manipulating the setpoint of the total Haradh gas feed

flow controller, 22-FIC-003 via low signal selector, 22-PY-004. The total Haradh feed gas

is then equally distributed to two DGA trains by controller, 22-FIC-003 by manipulating the

setpoint of controller, 3*-FIC-003 to each DGA via ratio setter, 3*-FY-036/039. Haradh

feed gas flow to each DGA train is controlled by 3*-FIC-003 that manipulates control valve,

3*-FV-003. The total Haradh gas feed flow rate is calculated from the PV value of

3*-FIC-003 and used as process value of total Haradh gas feed flow rate controller

22-FIC-003.

If operator would like to limit the maximum total flow rate through the DGA trains, operator

can set the maximum flow limit to the 22-HIC-004 connected with the total Haradh gas feed

flowrate setpoint via low signal selector, 22-PY-004.

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22-PIC-004 to be “non-linear gain PI controller” will minimize the change of feed flow to

DGA units under small Haradh Gas header pressure changing. The non-linear gain PI

controller will lower the proportional gain to moderate the 3*-FV-003 movement when the

pressure variation is within a range (Gap). This Gap will be decided at later and can be

modified during plant commissioning.

The total Haradh gas max flow rate to NGL trains via DGA trains is limited by total Haradh

gas max flow limit controller (DCS) described in section 4.3.1.

If operator would like to operate one DGA train in FIC (Auto mode) and other train by PIC

- FIC cascade control, DCS operator can disconnect the cascade connection by changing the

mode of Haradh gas 3*-FIC-003 on DGA train to Auto mode which the operator would like

to operate the train in FIC mode, i.e. stable feed flow rate.

If the expander suction pressure exceeds the preset value, the expander suction header high

pressure protection 41/42/43-PIC-499B will reduce feed gas flow rate from Hawiyah gas

header first, and if the header pressure is still higher than the preset value, the

41/42/43-PIC-499B will reduce the gas flow rate from Haradh gas pipeline via

3*-HIC-AAA and low signal selector, 3*-FY-003.

If the Haradh gas supply header pressure exceeds its preset value, the High Pressure

protection controller 22-PIC-105 opens pipeline bypass valves to reduce the header pressure

via low signal selector. Refer to Section 4.2.

4.4 EXPANDER INLET HEADER PRESSURE CONTROL AND NGL TRAIN

MAXIMUM TOTAL GAS FLOW LIMIT

At normal operation, the turbo expander inlet header pressure is controlled at a pseudo

setpoint value via 41/42/43-PIC-499A. 41/42/43-PIC-499A output goes through low signal

selector, 41/42/43-PY-499A to manipulate the 2 set of Turbo Expanders’ IGVs

(41/42/43-HV-311, 330) or Expander bypass JT valves (41/42/43-FV-237A, C) via

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expander/compressor control system.

The Demethanizer overhead feed flow controller, 41/42/43-FIC-238 receives its setpoint

from total feed flow 41/42/43-FIC-237 via fixed flow ratio setter, 41/42/43-FY-238. By this

ratio setter, the Demethanizer overhead (OVHD) feed flow through the DeC1 OVHD

exchanger (B66-E-*13) via 41/42/43-FV-238 is maintained at a preset flow ratio of total gas

flow to the NGL train.

The 41/42/43-PIC-499A pseudo pressure set point value is calculated via

41/42/43-PY-499C which consider the following:

P499A setpoint = Higher Signal ((P499A (PFD Value) - PDEH), PFIC004.MV)

1. P499A (PFD Value) = 748 psig as per PFD

2. PDEH = a manual term to allow bias for aging desiccant higher pressure drop

If Pressure drop on dehydrators is increased, the operator have to compare PDEH with

other trains and determine a PDEH bias value (from zero to a certain value) in order to

have same operating pressure at mixing point of Hawiyah and Haradh Gas on three

NGL trains. Same pressure at mixing point of Hawiyah and Haradh Gas on three NGL

trains means that the gas flow from Haradh gas pipeline will be equalized.

3. PFIC004 = 41/42/43-FIC-004 output value in psig

If 41/42/43-FIC-004.PV exceed its set point (Maximum Haradh Gas flow limit per

train), 41/42/43-FIC-004 output value will be increased. If 41/42/43-PIC-499A.SP is

increased and 41/42/43-PIC-499A.PV is increased, the Haradh gas flowrate will be

decreased because the Haradh flowrate is determined by the pressure balance between

DGA outlet header pressure and mixing point pressure between Hawiyah and Haradh

gas.

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Haradh gas distribution to each NGL trains is by hydraulic balancing by the piping and

resistance (dehydrator pressure drops). Hawiyah flow to each NGL train is controlled

by 41/42/43-FV-001. The Haradh gas must be balanced to avoid overloading the

dehydrators in the units (Max = 680 MMSCFD @ Haradh only case). The overall flow

distribution must be biased to prevent possible crushing the dehydrator beds as the

desiccant ages.

Total gas flow rate to Demethanizer (DeC1) is also limited by NGL train total flow

controller (41/42/43-FIC-237) via low signal selector, 41/42/43-PY-499A. When the

limit setpoint around 1,400 MMSCFD is exceeded, 41/42/43-FIC-237 will override

41/42/43-PIC-499A to manipulate the Turbo expander IGVs (41/42/43-HV-310,330).

This is to protect DeC1 from operating at over the design capacity.

If the sales gas (SG) compressor suction pressure exceeds its preset value due to one or

more of SG compressor trip, the SG suction header high pressure protection 90-PIC-016

via SG compressor master pressure validation controller will override the signals from

41/42/43-PIC-499A and 41/42/43-FIC-237 via low signal selector, 41/42/43-PY-499A.

In this case, 60-PIC-016 will manipulate the opening of the turbo expander IGVs to

reduce DeC1 overhead flow.

If the expander suction pressure exceeds the preset value, the Header High Pressure

protection, 41/42/43-PIC-499B will reduce feed gas flow rate from Hawiyah gas

pipeline first and if the header pressure is still higher than the preset value, the

41/42/43-PIC-499B will reduce the gas flow rate from Haradh gas pipeline (especially

for Haradh Gas Only Operation).

The control action of the SG suction Header High Pressure protection 60-PIC-016 and

expander suction header High Pressure protection 41/42/43-PIC-499B are reverse (the

output of the controller will decrease if suction pressure measurement increases) and the

expander suction header pressure controller 41/42/43-PIC-499A is direct (output of the

controller will increase if pressure measurement increases).

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Operator can limit the NGL train total gas flow rate during start-up or during normal

operation by changing the controller 41/42/43-FIC-237 setpoint.

4.5 DEMETHANIZER OVERHEAD PRESSURE CONTROLLER

In normal operation, i.e. two expanders in operation, Demethanizer overhead pressure is

controlled by manipulating 41/42/43-PV-537 at common suction line of brake compressors.

If one of turbo expander/ compressor tripped, the Demethanizer will operate at a higher

pressure. The Demethanizer overhead pressure controller 41/42/43-PIC-537 kept in AUTO

mode will fully open 41/42/43-PV-537. In this case, Demethanizer overhead pressure is not

controlled by 41/42/43-PIC-537, rather it would be determine by the hydraulic balance from

the suction pressure controller of the Sales Gas Compressor. All Demethanizer overhead gas

can be sent to SG compressor via running brake compressor and bypass line.

If two set of Expander / compressor trip, it is possible to produce off-specification of NGL,

operator should take appropriate action, e.g., shut down the train or reduce the NGL feed gas

rate.

4.6 ONE NGL RECOVERY TRAIN SHUTDOWN

When one of NGL trains is shutdown, Hawiyah and Haradh feed gas rate controlled by the

Total Feed gas flow limit controller. Refer to section 4.3.1.

5 PROCESS CONTROL

5.1 SALES GAS RECYCLE FOR START-UP

During Process Dry-out and Start-up, Sales Gas Recycle is utilized first before introducing

Haradh Gas (coming from DGA) to the Unit. To ensure that enough Sales Gas is used,

Selective Control method is applied. With this method the low Signal Selector 41-FY-002

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shall select the lower manipulative value between the input signal from pressure controller

41-PIC-003 and flow controller 41-FIC-002 (Both are located at the Sales Gas Line). Output

signal from 41-FY-002 is then used to manipulate control valve 41-FV-002 which controls

the flow rate of Sales Gas Recycle entering the Unit. Note that this line is normally no flow.

5.2 HAWIYAH FEED GAS FLOW RATE

Actual Hawiyah feed gas flow rate is measured by 4-*FIC-001. To get an accurate flow

indication, temperature 4*-TI-008 and pressure 4*-PI-014 is accounted for (calculated in

4*-FY-001A). Hawiyah feed gas flow rate indicated in 4*-FY-001A is pressure and

temperature compensated.

5.3 HARADH FEED GAS FLOW RATE

Actual Haradh feed gas flow rate is measured by 4-*FIC-004. To get an accurate flow

indication, temperature 4*-TI-015 and pressure 4*-PI-033 is accounted for (calculated in

4*-FY-004). Haradh feed gas flow rate indicated in 4*-FY-004 is pressure and temperature

compensated.

5.4 REGEN GAS FROM SALES GAS COMPRESSOR

Sufficient Regeneration Gas Flow is necessary to make sure that the Feed Gas Dehydrators

(B66-D-0102A~F) are effectively regenerated within the required Regeneration time. To

achieve this, during normal operation, flow controller 4*-FIC-101A will control the regen

gas flow rate. If the regen system pressure exceeds the preset value, pressure controller

4*-PIC-228 will reduce regen gas flow rate via low signal selector 4*-FY-101. Output

signal from 4*-FY-101 is then used to manipulate control valve 4*-FV-101 which controls

regen gas flow rate to B66-E-0103A/B or B66-E-0104. Note that during stand-by period (i.e.

no flow of regen gas), PIC-228 will close FV-101.

5.5 PROPANE REFRIGERANT FEED TO B66-E-0104

Temperature controller 4*-TIC-182 on regen gas line to B66-D-0102A~F is cascaded to

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slave level controller 4*-LIC-033 which manipulates control valve 4*-LV-033 at Regen

Gas Cooling Cycle Chiller (B66-E-0104) shell side inlet line. B66-E-0104 outlet Regen gas

temperature is controlled by maintaining the propane level and pressure in the exchanger

and hence its rate of boiling.

TC-LC cascade will be disconnected by dehydrator sequence via HS-173 except for cooling

period.

5.6 PROPANE VAPOR TO COMPRESSOR SUCTION DRUM

The Low Signal Selector 4*-TY-195 shall select the lower manipulative value between the

input signal from temperature controller 4*-TIC-195 on the Regen gas line or temperature

controller 4*-TIC-196 on the liquid propane line. Output signal from 4*-TY-195 is then

used to manipulate control valve 4*-TV-195 which controls the flow rate of propane vapor

from Regen Gas/Propane Chiller (B66-E-0107) to Refrigerant 2nd Stage Compressor

Suction Drum (B66-D-0113AB). Outlet Regen gas temperature is controlled by maintaining

the propane vapor pressure in the exchanger and hence its rate of boiling.

5.7 DEMETHANIZER RESIDUE GAS FLOW RATE

Actual residue gas flow rate from Demethanizer is measured by 4*-FI-289A. To get an

accurate flow indication, temperature (average between upstream, 4*-TI-431 and

downstream, 4*-TI-364 of FE-289) and pressure 4*-PIC-608 located in Demethanizer

overhead line is accounted for (calculated in 4*-FY-289). Residue gas flow rate from

Demethanizer indicated in 4*-FI-289B is pressure and temperature compensated.

5.8 DEMETHANIZER BOTTOMS

Level of Demethanizer (B66-C-0110) Bottoms is maintained by level controller

4*-LIC-127A by manipulating control valve 4*-FV-341 by cascade control with flow

controller 4*-FIC-341. 4*FV-341 located at Demethanizer Bottoms Pumps

B66-G-0113A/B discharge line controls the flow rate of NGL going to Surge Spheres

B67-D-0101A/B.

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At process upset, with Demethanizer bottoms level exceeding LIC-127A high set point,

level controller 4*-LIC-127B will open control valve 4*-LV-127B to divert NGL to

Cryogenic Burn Pit. Further increase in liquid level (exceeding LIC-127B high set point),

level controller 4*-LIC-127C will open control valve 4*-LV-128C to divert NGL to

Cryogenic Burn Pit.

5.9 DEMETHANIZER CHIMNEY TRAY #3

Level Controller 4*-LIC-123 cascades onto flow controller 4*-FIC-303 with positive bias

(calculated in 4*-FY-303). This controls the level in Demethanizer Chimney Tray 3 by

manipulating control valve 4*-FV-303. 4*-FV-303 located at Demethanizer Top Side

Reboiler Pumps (B66-G-0112A/B) discharge line controls the HC Liquid flow rate going to

Cold Gas Exchanger, B66-E-0112.




manipulating control valve 4*-FV-316. 4*-FV-316 located at Demethanizer Bottom Side

Reboiler Pumps (B66-G-0111A/B) discharge line controls the HC Liquid flow rate going to

Warm Gas Exchanger, B66-E-0111.




manipulating control valve 4*-FV-329. 4*-FV-329 located at Demethanizer Reboiler

Pumps (B66-G-0110A/B) discharge line controls the HC Liquid flow rate going to Feed Gas

Exchanger, B66-E-0110A/B.

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5.12 CHILLED COOLING WATER FOR B66-E-0117A/B

50-TE-018 is installed on NGL/Water Exchanger B67-E-0101A~E in order to have stable

NGL Product temperature. 50-TIC-018 output signal is split range:

a) X% - This signal is cascaded to slave flow controller 4*-FIC-404 to manipulate

control valve 4*-FV-404 located on the Chilled Cooling Water line from

Refrigerant / Water Subcooler, B66-E-0117A/B to B67-D-0103. This controls the

temperature of propane from B66-E-0117A/B by varying the flow rate of Chilled

Cooling Water.

b) X-100% - This signal is used to control the Chilled Water (Warm) Supply bypass

control valve 50-TV-018 to the chilled water return header.

On Temperature increase, first close 4*-FV-404 to reduce water flow to minimum flow of

B67-G-0105ABC, then open bypass control valve 50-TV-018.

Close

Open

TC-018

TV018FV404

0 X 100

5.13 HAWIYAH GAS CHILLER B66-E-0102 OUTLET TEMPERATURE CONTROL

(BA-543210.005)

The 41-TIC-003 cascades onto 41-LIC-002 to control 41-LV-002. Also 41-TIC-003 process

value is passed to 41-TY-005 to compare with 41-TIC-016. The temperature difference

between 41-TIC-003 and 41-TIC-016 will be shown on 41-TDI-005. If the temperature of

the Haradh stream to the mixer gets significantly warmer than the temperature of the

Hawiyah stream, condensation of water may take place. Any liquid water going to the

dehydrator beds will damage the mol sieve material. Therefore, the temperature difference

between the Hawiyah and Haradh streams going to the mixer is monitored by 41-TDI-005

and an alarm signal is initiated when the Haradh stream is more than 9 degF warmer than the

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Hawiyah stream.

5.14 HARADH GAS CHILLER B66-E-0108 OUTLET TEMPERATURE CONTROL

(BA-543210.005)

Either lower MV of 41-TIC-018 or 41-TY-016 is selected at 41-TY-005 to control

41-TV016. During ESD condition, 41-TV-016 and 41-TXV-016 behave as well as control

description for control valve with SOV in 2.15.

5.15 TEMPERATURE CONTROL WITH WARM GAS EXCHANGER (B66-E-0111) &

2ND STAGE GAS CHILLER (B66-E-0114) (BA-543212.001/003/004)

The 2nd Stage Gas Chiller (B66-E-0114) outlet temperature (41-TI-312) cascade on outlet

temperature (41-TIC-292) of Warm Gas Exchanger (B66-E-0111) to control 41-TV-292.

During ESD condition, 41-TV-292 and 41-TXV-292 behave as well as control description

for control valve with SOV in 2.15.

6 COMPLEX CONTROL

6.1 NGL RECOVERY AREA B66 (3 TRAINS)

NGL Trains High Pressure Protection Control

Refer to P&ID: B66-A-BA-543210-001, B66-A-BA-543213-001, B65-A-BA-540691-002

and Figure 4.13.1 of this document.

Objective

Protect each NGL Train feed gas header from over-pressure by reducing the feed gas flow

rate from Hawiyah gas pipeline first and if the header pressure is still higher than the set

value, reduce the feed gas flow rate from Haradh gas pipeline.

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Functional Description

The controls description that follows is for the NGL recovery Train1 only, but the control

scheme is the same for NGL Train 2 and NGL Train 3 only with different prefix for

instrument tag identifications.

The NGL train feed gas header High Pressure protection controller 41-PIC-499B receives

its PV from the Expander suction header pressure measurement 41-PT-499. The output of

41-PIC-499B is split via a split range calculator. Two outputs of the split range calculator

are connected to blocks 41-HIC-014 and 40-PY-499B.

Higher range split control signal to reduce feed gas flow rate from Hawiyah gas pipeline will

adjust setpoint of Max Hawiyah train feed flow limit controller, 41-HIC-014, when it is in

Cascade mode. Output of 41-HIC-014 will then pass through low signal selector,

41-FY-001 to finally control 41-FV-001.

When 41-HIC-014 is in Auto mode, the operator can set the maximum feed gas flow rate for

NGL train 1 at the SP of 41-HIC-014.

When 41-HIC-014 is in Manual mode, the operator can manually change HIC output signal

to override the output signal from 41-FIC-001 via low signal selector 41-FY-001.

Lower range split control signal from 41/42/43-PIC-499B to reduce feed gas flow rate from

Haradh gas pipeline will pass through low signal selector, 40-PY-499B. Output of

40-PY-499B will then adjust the SP of both 31-HIC-003 and 32-HIC-003 when it is in

Cascade mode. Output of 31/32-HIC-003 will then pass through low signal selector switch

31/32-FY-003 to finally control 31/32-FV-003.

When 31/32-HIC-003 is in Auto mode, the operator can set the maximum feed gas flow rate

for DGA train 1/2 at the SP of the HIC.

When 31/32-HIC-003 is in Manual mode, the operator can manually change HIC output

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03-OCT-2006




signal to override the output signal from 31/32-FIC-003 via low signal selector

31/32-FY-003.

Operational and Implementation Aspects

NGL Train Header High Pressure Protection control scheme is required to be operational

during start up and normal operation.

In normal steady state, for Hawiyah pipeline feed gas control, low signal selector

41-FY-001 is cascaded to 41-HIC-014, which in turn cascaded to NGL Train High pressure

controller, 41-PIC-499B. While for Haradh pipeline feed gas control, low signal selectors

31/32-FY-003 are cascaded to low signal selector 40-PY-499B via 31/32-HIC-003

respectively. Low signal selector 40-PY-499B will select the lower value from

41/42/43-PIC-499B lower range output signals to control the feed gas rate to DGA trains

when one or more NGL Trains header pressure is too high.

NGL Train Header High Pressure Protection Controller: Operator to be able to decrease SP

down to an enforced low limit. The operator shall not have access to 41-PIC-499B

controller’s mode or set point enforced low limit. Only engineer can change the controller

mode or set point enforced low limit.

Crippled Mode Operation

Failure of the NGL Train gas inlet pressure input signal from 41-PIT-499, identified as a

“Bad Value” status in DCS, will cause an alarm and high pressure protection controller

41-PIC-499B to go to MANUAL mode, with the output remaining at the last good value

previous to transferring to MANUAL mode.

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_____INDRA

03-OCT-2006




Figu

re 4

.13.

1: H

NG

L Tr

ain

Hig

h Pr

essu

re P

rote

ctio

n C

ontr

ol

Feed

Gas

from

Haw

iyah

AO/A

FS

42FV

-001

43FV

-001

41FY 001

42FY 001

43FY 001

41FI

C00

1

42FI

C00

1

43FI

C00

1

31FV

-003

32FV

-003

DG

A-1

B65

-C-1

01

DG

A-2

B65

-C-X

XX

31FY 003

32FY 003

31FI

C00

3

32FI

C00

3

Feed

Gas

from

Har

adh

41PI

C49

9A41

PIC

499B

41HI

C01

4

42HI

C01

4

43HI

C01

4

SR (N

OTE

1)

42P

IC49

9B

43P

IC49

9B

31HI

C00

3

32HI

C00

3

HN

GL-

1B

66-C

-110

0-X

%

X-10

0 %

NO

TES

: 1.

Typ

ical

for

HN

GL

Trai

n 1,

2 a

nd 3

Hig

h P

ress

ure

Pro

tect

ion

Con

trolle

r 4*P

IC-4

99B

.

Valv

eO

peni

ng [%

]

0

100

100

4*P

IC-4

99B

MV

[%]

x

4*FV

-001

31/3

2FV

-003

SR (N

OTE

1)

SR (N

OTE

1)

40PY

499B

HN

GL

Trai

n-2

HN

GL

Trai

n-3

HN

GL

Trai

n-2

HN

GL

Trai

n-3

X-10

0 %

0-X

%

X-10

0 %

0-X

%

SP SP SP

SP

SP

41FV

-001

AO/A

FS

AO/A

FS

AO/A

FS

AO/A

FS

Rev

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03-OCT-2006




Calculation

41-PIC-499B Output Split Range Calculation

When 41-PIC-499B.PV is less than the setpoint value, the High Pressure protection

controller, 41-PIC-499B, output signal is on the high side, 100%.

When process value is greater than or equal to the set value, Split range calculation block

should convert 41-PIC-499B higher range output signal, X% ~ 100% to 0% ~ 100% as input

signal to 41-HIC-014, and lower range output signal, 0% ~ X% to 0% ~ 100% as input

signal to low signal selector switch, 40-PY-499B.

Initializations

NGL Train Header High Pressure Protection controller, 41-PIC-499B SP shall not track PV

when it is in MANUAL mode.

Output of 41-PIC-499B should be configured to track the 41-HIC-014 setpoint, when HIC is

placed in MANUAL or AUTO mode. Upon switching 41-HIC-014 to CASCADE mode,

41-PIC-499B output should be initialize to 41-HIC-014 setpoint to prevent bumping of the

process.

No output pushback shall be configured for low signal selector 40-PY-499B when any of the

31/32-HIC-003 switched from AUTO or MAN mode to CASCADE. Upon switching

31/32-HIC-003 from AUTO or MAN mode to CASCADE, HIC SP should ramp slowly to

match MV of 40-PY-499B.

Anti reset windup (ARWU) shall be configured for NGL train feed flow controller

41-FIC-001 and feed flow override controller 41-HIC-014 to ensure bumpless transfer in

case HIC is overriding the FIC as follows:

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03-OCT-2006




Normally, 41-FIC-001 in control, 41-HIC-014 MV shall be initialized to the low selector

output value (41-FY-001.MV). When 41-HIC-014 in control, the NGL train feed flow

controller 41-FIC-001 MV shall be initialized to the low selector output value

(41-FY-001.MV)

Anti reset windup (ARWU) shall be configured for DGA feed flow controller

31/32-FIC-003 and Maximum DGA feed flow limit controller 31-HIC-003/32-HIC-003 to

ensure bumpless transfer in case HIC is overriding the FIC as follow:

Normally, 31/32-FIC-003 in control, 31/32-HIC-003 MV shall be initialized to the low

selector output value (31/32-FY-003.MV). When the 31/32-HIC-003 in control, the DGA

train feed flow controller 31/32-FIC-003 MV shall be initialized to the low selector output

value (31/32-FY-003.MV)

Special Consideration

Upon 41-FY-001 selecting signal from 41-HIC-014 for more than 10 seconds, and the mode

of 41-HIC-014 is in CASCADE, 42-FIC-001 and 43-FIC-001 will set to AUTO mode (one

shot signal) if it is in CASCADE. The Operator is responsible to switch 42/43-FIC-001

back to CASCADE when the operating condition is back to normal.

Maximum Hawiyah train feed flow limit controllers, 41/42/43-HIC-014, and Hawiyah train

feed flow controllers, 41/42/43-FIC-001 must have the same process variable range.

Similarly, Maximum DGA feed flow limit controller, 31/32-HIC-003, and DGA feed flow

controller, 31/32-FIC-003 must have the same process variable range.

6.2 NGL TRAIN EXPANDER INLET PRESSURE CONTROL

Refer to P&ID: B66-A-BA-543213-001/ 002/003/004, B68-BA-540838-003 and Section

9.2, 9.3 & 9.4: Appendix , Figure 7.2.2 & Attachment 1 & 2 of this document.

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03-OCT-2006




The anti-sure control system for Brake Compressor will be implemented in the Unit Control

Panel (PLC) by compressor vendor (MTC) and the control narrative for its compressor will

be described in the vendor’s documents.(V-2158-201A-050).

Refer to P&ID: B66-A-BA-543213-001/ 002/003/004, B68-BA-540838-003 and Figure

4.13.2 of this document.

Objective

To maintain constant Inlet pressure to each NGL Train turbo expander by regulating the

total gas flow to expander and Demethanizer overhead feed flow through DeC1 Overhead

Exchanger via fixed flow ratio setter.


The controls description that follows is for the NGL recovery Train1 only, but the control

scheme is the same for NGL Train 2 and NGL Train 3 only with different prefix for

instrument tag identifications.

41/42/43-PIC-499A output goes through low signal selector, 41/42/43-PY-499A to

manipulate the 2 set of Turbo Expanders’ IGVs (41/42/43-HV-311, 330) or Expander

bypass JT valves (41/42/43-FV-237A, C) via expander/compressor control system.

The Demethanizer overhead feed flow controller, 41/42/43-FIC-238 receives its setpoint

from total feed flow 41/42/43-FIC-237 via fixed flow ratio setter, 41/42/43-FY-238. By this

ratio setter, the Demethanizer overhead feed flow through the DeC1 OVHD exchanger

(B66-E-0*13) via 41/42/43-FV-238 is maintained at a preset flow ratio of total gas flow to

the NGL train.

Total gas flow rate to Demethanizer (DeC1) is also limited by NGL train total flow

controller (41/42/43-FIC-237) via low signal selector, 41/42/43-PY-499A. When the limit

setpoint around 1,400 MMSCFD is exceeded, 41/42/43-FIC-237 will override

41/42/43-PIC-499A to manipulate the Turbo expander IGVs. This is to protect DeC1 from

operating at over the design capacity.

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_____INDRA

03-OCT-2006




If the sales gas (SG) compressor suction pressure exceeds its preset value due to one or more

of SG compressor trip, the SG suction header high pressure protection 90-PIC-016 via SG

compressor master pressure validation controller will override the signals from

41/42/43-PIC-499A and 41/42/43-FIC-237 via low signal selector, 41/42/43-PY-499A. In

this case, 90-PIC-016 will manipulate the opening of the turbo expander IGVs via

expander/compressor control system to reduce DeC1 overhead flow.

The control action of the SG suction header High Pressure protection 90-PIC-016 and

expander suction header High Pressure protection 41/42/43-PIC-499B are reverse (the

output of the controller will decrease if suction pressure measurement increases) and the

expander suction header pressure controller 41/42/43-PIC-499A is direct (output of the

controller will increase if pressure measurement increases).

Operator can limit the NGL train total gas flow rate during start-up or during normal

operation by changing the controller 41/42/43-FIC-237 setpoint.

The turbo expanders inlet header pressure is controlled at a pseudo setpoint value via

41/42/43-PIC-499A.

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_____INDRA

03-OCT-2006




Exp

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66-K

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A/B

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AC/A

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AO/A

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AO/A

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499A

41PY

Max

Tot

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as

300

41HI

C30

141

HIC

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EHB

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PP

FD

Har

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Lim

it

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: PY

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.MV

= P P

FD -

P DE

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ias

whe

re: P

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as p

er P

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P

DE

H =

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pre

ssur

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op o

n de

hydr

ator

(-)

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Rev

41HV

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41HV

-330

499C

41PY

41PY

Figu

re 4

.13.

2: H

NG

L Tr

ain

Expa

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Inle

t Pre

ssur

e C

ontr

ol

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_____INDRA

03-OCT-2006




Operation and Implementation Aspects

The Turbo Expander/Brake Compressor Control System (CCS) is required to be operational

during start-up and normal operation.

During the plant start-up, flow controller, 41-FIC-238, may be operated in MANUAL mode

until the flow indication has stabilized. Once the gas flow to DeC1 Overhead Exchanger can

be reliably controlled in AUTO mode, 41-FIC-238 can be placed in CASCADE to the Ratio

setter, 41-FY-238.

In normal operation, turbo expanders inlet header pressure is controlled at a pseudo setpoint

value via 41/42/43-PIC-499A. 41/42/43-PIC-499A output goes through low signal selector,

41/42/43-PY-499A to manipulate the 2 set of Turbo Expanders’ IGVs (41/42/43-HV-311,

330) or Expander bypass JT valves (41/42/43-FV-237A, C) via expander/compressor

control system. The Demethanizer overhead feed gas flow controller, 41-FIC-238, is in

CASCADE mode with ratio setter 41-FY-238.


Crippled mode operation occurs when some instrument fails. Usually this will be a failure of

feed flow or pressure measurement, as described below.

Failure of total DeC1 feed flow transmitter, 41-FIT-237

Failure of the flow signal resulting in a "Bad Value" parameter in DCS will result in placing

affected flow controller 41-FIC-237 and ratio setter block, 41-FY-238, in MANUAL, with

the output remaining at the last good value prior to transferring to MANUAL, and initiating

an alarm.

Failure of DeC1 Overhead feed gas flow transmitter, 41-FIT-238

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_____INDRA

03-OCT-2006




Failure of the flow signal resulting in a "Bad Value" parameter in DCS will result in placing

affected flow controller 41-FIC-238 in MANUAL, with the output remaining at the last

good value prior to transferring to MANUAL, and initiating an alarm.

Failure of Expander Inlet pressure transmitter, 41-PT-499

Failure of the pressure signal resulting in a "Bad Value" parameter in DCS will result in

placing affected pressure controller 41-PIC-499A in MANUAL, with the output remaining

at the last good value prior to transferring to MANUAL, and initiating an alarm.

Calculation

DeC1 Overhead Feed Gas Flow Ratio Setter, 41-FY-238

Demethanizer overhead feed gas flow ratio setter, 41-FY-238 calculates the set point signal

for expander bypass flow controller 41-FIC-238 using the operator inputted ratio value and

the filtered process value of total gas flow rate to Demethanizer, 41-FIC-237.

[ ]PVFRMV 237-FIC41*1][238-FY-41 −=

where:

41-FY-238.MV = calculation block outputs to 41-FIC-238.SP

FR1 = calculation block input, ratio set by operator

41-FIC-237.PV = filtered NGL total gas flow rate to train 1

Note: Low pass filter shall be used for the process value of each NGL train feed flow

controller.

41/42/43-PIC-499A pseudo pressure setpoint value setter, 41-PY-499C

The 41/42/43-PIC-499A pseudo pressure set point value is calculated via

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03-OCT-2006




41/42/43-PY-499C which consider the following:

41/42/43-PY-499C.MV = P499A (PFD Value) – PDEH

1. P499A (PFD Value) = 748 psig as per PFD

Engineer to provide input through 41/42/43-HIC-300

2. PDEH = a manual term to allow bias for aging desiccant higher pressure drop

If pressure drop on dehydrators is increased, the operator has to compare PDEH with

other trains and determine a PDEH bias value (from zero to a certain value) in order

to have same operating pressure at mixing point of Hawiyah and Haradh Gas on

three NGL trains. Same Pressure at mixing point of Hawiyah and Haradh Gas on

three NGL trains means that the gas flow from Haradh gas pipeline will be

equalized.

Operator to input through 41/42/43-HIC-301

PFIC004 = 41/42/43-FIC-004 output value (MV) in psig (the same range as

41-PIC-499A.SP)

If 41/42/43-FIC004.PV exceed its set point (Maximum Haradh Gas flow limit per

train), 41/42/43FIC004 output value will be increased. Via high signal selector,

41/42/43-PY-49D, 41/42/43-PIC499A.SP will increase to adjust the expander’s

IGVs to close. When expander IGVs adjust to close, 41/42/43-PIC499A.PV will

be increased to meet the setpoint. At the same time, Haradh gas flowrate will be

decreased. This control limits the maximum flow rate of Haradh gas to protect

from moisture of Haradh gas.

Initialization

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_____INDRA

03-OCT-2006




Anti-reset windup (ARWU) shall be configured for NGL train expander inlet pressure

controller, 41-PIC-499A , SG compressor suction header pressure protection controller,

90-PIC-016, and NGL Train Max Total Feed gas flow controller, 41-FIC-237 to ensure

bumpless transfer in case one controller is overriding the other controllers as follows;

With 41-PIC-499A in control, SG suction header pressure control, 90-PIC-016 and NGL

Train Max Total Feed gas flow controller, 41-FIC-237 shall be set using the MV value of

41-PY-499A for ARWU.

With 90-PIC-016 in control, NGL train expander suction header pressure controller,

41-PIC-499A and NGL Train Max Total Feed gas flow controller, 41-FIC-237 shall be set

using the MV value of 41-PY-499A for ARWU.

With 41-FIC-237 in control, NGL train expander suction header pressure controller,

41-PIC-499A and SG suction header pressure controller, 90-PIC-016 shall be set using the

MV value of 41-PY-499A for ARWU.


41-FIC-004 shall be a direct acting controller. 41-PIC-499A shall be forced to CASCADE

mode. Engineer and NOT Operator shall have access to 41-HIC-300 PFD set value and

41-PIC-499A controller’s mode. Operator shall have access to 41-HIC-301 set value as

Dehydrator’s pressure bias.

6.3 EQUAL DISTRIBUTION OF TOTAL HARADH FLOW ON NGL TRAINS

Refer to P&ID B66-A-BA-543210-001, and Figure 4.13.3 of this document.

Objective

To avoid overloading of the dehydration system by evenly distributing the total Haradh feed

gas to the three (3) NGL trains.


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_____INDRA

03-OCT-2006




[ ])67.459(*)6959.14.01441()67.459.00841(*)6959.14(*004-FIC41][004-FY-41

++−−+−−+−=

D

D

TMVPIMVTIPPVMV

At normal operation, where 3 NGL trains are operating, to avoid overloading the

dehydration systems by uneven distribution of Haradh feed, Hawiyah ratio setter,

41/42/43-FY-001B will be automatically adjusted to maintain a set value on Haradh flow to

each NGL train. Pressure and temperature compensated flow of 41/42/43-FIC-004 will be

calculated via 41/42/43-FY-004. Compensated flow from each NGL trains will be averaged

via 40-FY-003 and the calculated value will then be compared to individual NGL train

process value, 41/42/43-FY004.MV. The difference between compensated flow value and

average value (41/42/43-FY-004.PV-40FY-003) will then be used to automatically adjust

the ratio set via 41/42/43-FY-001B on corresponding Hawiyah flow through

41/42/43-FDC-010 controllers. For example, incase of Haradh gas flow exceeds above the

setpoint, ratio for setpoint of Hawiyah gas flow will be increased. By the pressure from

Hawiyah gas will control the Haradh gas flow rate to reduce Haradh flow to avoid over flow.

During Start-up, NGL train Hawiyah gas ratio setter, 41/42/43-FY-001B will be operated in

Auto mode and operator will set the initial ratio. Once the Three NGL trains are running and

operating in stabilized condition, the 41/42/43-FY-001B can be switch from Auto to

Cascade mode so that controller 41/42/43-FDC-010 will set the Hawiyah feed ratio.


Failure of Haradh feed gas to NGL train flow signal, 41/42/43-FIT-004 resulting in a "Bad

Value" parameter in flow controller, 41/42/43-FIC-004, and will result in placing the

controllers 41/42/43-FIC-004 and 41/42/43-FDC-010 and calculation blocks,

41/42/43-FY-004, 41/42/43-FY-010 and 40-FY-003 in MANUAL mode, with the output

remaining at the last good value prior to transferring to MANUAL mode and initiating an

alarm.

Calculation

41-FY-004 Pressure and Temperature Flow compensation Calculation Block

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_____INDRA

03-OCT-2006




where;

41-FY-004.MV = P,T compensated volumetric Flow rate [MMSCFD]

41-FIC-004.PV = Raw measured volumetric Flow rate [MMSCFD]

41-PI-014.PV = measured pressure [psia]

41-TI-008.PV = measured temperature [degF]

DP = Orifice Design Pressure [psia]

DT = Orifice Design Temperature [degF]

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_____INDRA

03-OCT-2006




Figu

re 4

.13.

3: E

qual

Dis

trib

utio

n of

Tot

al H

arad

h Fl

ow o

n N

GL

Trai

ns

Feed

Gas

from

Haw

iyah

Feed

Gas

from

DG

A1&

2(H

arad

h)

HN

GL

Trai

n-1

Har

adh

Max

Flow

lim

it

Rat

ioC

alcu

lato

r

RS41

FY00

1B NOTE

3

NOTE

3

NOTE

3

42FY

001B

43FY

001B

41FD

C01

0

42FD

C01

0

43FD

C01

0

41FY 010

42FY 010

43FY 010

40FY 003

AVE

42FI

C00

4.PV

43FI

C00

4.PV

NOTE

2

NOTE

1

3. D

CS

Log

ic s

hall

disa

ble

this

con

trol b

y ch

angi

ng th

em

ode

of ra

tio s

ette

r, 4*

FY00

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om C

AS

to A

UTO

and

keep

the

last

ratio

whe

n on

e N

GL

train

is s

hutd

own

2. 4

*FY

010

= 4*

FIC

004.

PV

-40F

Y00

3

NO

TES

: 1.

40F

Y-0

03(A

vera

ge) =

(41F

IC00

4.P

V +

42F

IC00

4.P

V +

43FI

C00

4.P

V) /

3

Ratio

SP

Dir

Dir

Dir

(-) (+)(-) (+)(-)(+)

40FI

C00

2

40FY

004

41FI

C00

4Re

v41

PI03

341

TI01

5

41FY 004

41PY

499C

Har

adh

Gas

Tota

l Flo

w

41FY

009

41FI

C00

1

AO/A

FS

SP41

FY 001

PV

41H

IC01

4

Rev

41PI

014

41TI

008

41FY

001A

40FY

002

Flow

Total

izer

Rat

ioC

alcu

lato

r

41FY

009

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_____INDRA

03-OCT-2006





40-FY-003 Calculation Block

This calculation block computes for the average feed gas flow rate to NGL trains.

40-FY-003.MV = (41-FY-004.PV + 42-FY-004.PV + 43-FY-004.PV) / 3

41/42/43-FY-010 Calculation Block

This calculation block computes for the difference between the process value of Haradh

feed gas to each NGL and the calculated average value, 40-FY-003.MV.

41-FY-010.MV = 41-FY-004.PV- 40FY-003.MV

42-FY-010.MV = 42-FY-004.PV- 40FY-003.MV

43-FY-010.MV = 43-FY-004.PV- 40FY-003.MV


This control scheme is only functional when three NGL trains are all in operation.

When at least one train is shutdown or if the difference of the process value of one train from

the average value is more than 10%, DCS logic will disable this control by changing the

mode of 41/42/43-FY-001B Ratio Setter from “CAS” to “AUTO” and keep the last ratio

setpoint.

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_____INDRA

03-OCT-2006




6.4 DEMETHANIZER OVERHEAD PRESSURE AND BOTTOMS TEMPERATURE

CONTROL

Refer to P&ID B66-A-BA-543213-003/005/008/010, B66-A-BA-543212-001 and Figure

4.13.4 of this document

Objective

Maintain and adjust the overhead pressure and bottom temperature of the Demethanizer to

maximize NGL recovery with on-specification overhead and bottom products.


The controls description that follows is for Demethanizer, 41-B66-C-110, on NGL recovery

Train1 only, but the control scheme is the same for NGL Train 2 and NGL Train 3 only with

different prefix for instrument tag identifications.

The Demethanizer overhead pressure is controlled at preset value via 41-PIC-537 by

manipulating the control valve, 41-PV-537 at common suction line of the break

compressors, B66-K-0110A/B.

The Demethanizer bottom temperature and chimney tray #1 level is controlled by a

decoupling scheme. With this decoupling control scheme, the LIC125A-FIC329 cascade

controller with positive bias calculated by 41-FY-329 will simultaneously adjust TV-429A

and TV-429C in the same direction. When liquid level becomes higher than level set point,

LIC-125A will increase the set point of FIC-329 that will result in increased opening of both

valves. This way, chimney tray 1 level can be controlled without disturbing the liquid flow

ratio distribution between inlet to B66-E-0110A/B, pass C and its bypass line. Thus,

maintaining control of DeC1 bottom temperature.

The temperature controller, TIC-429, will simultaneously adjust TV-429A and TV-429C

but in opposite direction by equal flow amount. In this way, the flow liquid distribution can

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03-OCT-2006




be adjusted between inlet to B66-E-0110A/B, pass C, and its bypass line without changing

the total flow. Thus, maintaining control of Demethanizer chimney tray 1 level.

When more duty is required, TIC-429 will open TV-429B (TV-429A is fully open and

TV-429C is fully close). In this case, DeC1 chimney tray 1 level may be affected.

41-LIC-125B low level over ride signal via low signal selector, 41-TY-429B will close

TV-429B.


During the plant start-up, DeC1 overhead pressure controller, 41-PIC-537 and DeC1 bottom

temperature controller, 41-TIC-429, shall be operated in AUTO mode.

In normal operation, i.e, two expanders in operation, DeC1 overhead pressure controller,

41-PIC-537 and DeC1 bottom temperature controller, 41-TIC-429, shall be operated in

AUTO mode with preset value as set points

If the one of expander / compressor tripped, the Demethanizer will operate in a higher

pressure. The Demethanizer overhead pressure controller 41/42/43-PIC-537 kept in Auto

mode will fully open 41/42/43-PV-537. In this case, Demethanizer overhead pressure is not

controlled by 41/42/43-PIC-537, rather it would be determined by the hydraulic balance

from the suction pressure controller of the Sales Gas Compressor. All Demethanizer

overhead gas can be sent to SG compressor via running brake compressor and bypass line.

In normal operation, 41-TIC-429 output pass through a split range calculator, 41-TY-429

which converts lower range signal 0~50% to 0~100% and higher range signal 50~100% to

0~100%. The higher range signal will manipulate 41-TV-429B via low signal selector,

41-TY-429B.The lower range signal will manipulate 41-TV-429A and 41-TV-429C via

decoupling control scheme. The decoupling control scheme is controlling the Demethanizer

bottom temperature via 41-TIC-429 and Demethanizer chimney tray # 1 liquid level via

41-LIC-125.

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The decoupling control modes operate as follows:

Control Mode Valve Manipulated

TIC LIC-FIC TV-429A TV-429C

Man Man Operator via TIC.MV Operator via LIC-FIC.MV

Auto Man TIC FIC.MV jumps to TV-429C

position and FIC.MV connects

to TV-429C.

Man Auto/Cascade TIC.MV jumps to

TV-429A position and

TIC.MV connects to

TV-429A

LIC-FIC

Auto Auto/Cascade TIC and LIC-FIC TIC and LIC-FIC

In the case that one expander/ compressor trips, a trip signal will activate logic, to

automatically ramp up the setpoint of DeC1 bottom temperature controller, 41-TIC-429 to

produce on-spec bottoms products. If the tripped Expander/Brake Compressor is recovered

from trip condition and put back on service, the Operator is responsible to ramp the set point

of TIC-429 toward normal operating point.

If two sets of the expander/compressor trip, it is possible to produce off-specification NGL.

The operator should take the appropriate action such as reducing the NGL feed gas rate and/

or shutting down the NGL train.

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Figu

re 4

.13.

4: D

emet

hani

zer O

verh

ead

Pres

sure

and

Bot

tom

Tem

pera

ture

Con

trol

Expa

nder

B66-

K-01

10A/

B

DeC

1 O

VH

D E

xch

B66-

E-01

13

B66-

D-0

111

Exp

Feed

Sep

a

SG C

ompr

esso

rB6

8-K-

0101

A~D

41FV

-238

41FV

-237

A/C A&

B

B66-

E-10

1A/B

Brak

e C

ompr

esso

rB6

6-K-

110A

/B

NN

F

A

B

ESD

Log

icZC

AO/A

FS

537

41PI

C

34 23 19

Chi

m1

Tray

1 -

10

Chi

m2

Tray

11

- 18

Chi

m3

Chi

m4

Chi

m5

#1#6#10

#10

#11

#15

#20

B66-

G-0

110A

/BD

eC1

Reb

oile

r Pum

p

Feed

Gas

Exc

hB

66-E

-011

0A/B

429

41TI

C

Aux

iliary

Reb

oile

rB

66-E

-011

8

125A

41LI

C

AC/A

FO

AO/A

FC

41PV

-537

Dir

Dir

Rev

Feed

Gas

(Hot

Gas

)

41FV

-326

A/32

7AAC

/AFO

326A

/7A41

FIC

RevNN

F

B66-

E-01

11/0

112

B66-

D-0

110

NOTE

1

AC/A

FS41

TV-42

9A

AO/A

FC

Hot

Ref

riger

ant

Ref

riger

ant

NNF

429B

41TY

41LIC

125B

LL

329

Rev

41FI

C

SP

AC/A

FS41

TV-4

29C

41TV

-429

B

NOTE

1

NOTE

1 100%

100% 0

X %

100 %

TIC-

429.M

V [%

] X %

0

TV-4

29A

FIC3

29.M

V [%

]

VALV

EOP

ENIN

G[%

]

VALV

EOP

ENIN

G[%

]

30 d

egF

49 de

gF

78 de

gF

63 de

gF23

degF

Dem

etha

nize

rB6

6-C

-011

0

Low

Leve

l Ove

rride

TV-4

29C

TV-4

29A

TV-4

29B

TV-4

29C

SR

429

41TY

429A

41TY

429C

41TY 50

-100

%

0-50

%

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Crippled mode operation occurs when some instrument fails. Usually this will be a failure of

pressure or temperature measurement, as described below.

Failure of Demethanizer overhead pressure transmitter, PIT-537

Failure of the pressure signal resulting in a "Bad Value" parameter in DCS will result in

placing affected DeC1 overhead pressure controller, PIC-537, in MANUAL, with the output

remaining at the last good value prior to transferring to MANUAL, and initiating an alarm.

Failure of Demethanizer bottom temperature transmitter (TT-429) or RTD

Failure of the temperature signal resulting in a "Bad Value" parameter in DCS will result in

placing affected DeC1 bottom temperature controller, 41-TIC-429, in MANUAL, with the

output remaining at the last good value prior to transferring to MANUAL, and initiating an

alarm.

Failure of Flow transmitter (FIT-329)

Failure of the Flow signal resulting in a "Bad Value" parameter in DCS will result in placing

affected flow controller, 41-FIC-329, in MANUAL, with the output remaining at the last


Failure of DeC1 Chimney Tray #1 Level transmitter (LIT-125)

Failure of the DeC1 Chimney Tray #1 level signal resulting in a "Bad Value" parameter in

DCS will result in placing affected level controller, 41-LIC-125A and 41-LIC-125B, in

MANUAL, with the output remaining at the last sound value prior to transferring to

MANUAL, and initiating an alarm.

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Calculation

41-TY-429 Split Range Calculation Block

Split range calculation block, 41-TY-429 shall convert 41-TIC-429 higher range output

signal, 50~100% to 0~100% as input signal to low signal selector, 41-TY-429B and lower

range output signal, 0~50% to 0~100% as input signal to calculation blocks, 41-TY-429A

and 41-TY-429C.

41-TY-429A Calculation Block

100/).42941*100(.32941.42941 MVTYkMVFICMVATY −−∗−−=−−

where :

designA

designB

PP

CvACvBk

∆∆

= = 0.24

429A-TV-41 of valueCvCvA = = 550

429C-TV-41 of valueCvCvB = = 130

drop pressure 42941 designATVP designA −−=∆ = 500 psi

drop pressure 42941 designCTVP designB −−=∆ = 500 psi

41-TY-429C Calculation Block

100/).42941.32941(.42941 MVTYMVFICMVCTY −−∗−−=−−

41 FY-329 Calculation Block

41 –FY-329.MV = 41-LIC-125A.MV * Positive Bias (Range: 0.5 ~ 1.5)

Initialization

PV tracking option shall be provided for both 41-TIC-429 and 41-FIC-329 to initialize the

SP by PVs when the controllers are in Manual mode.

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If first controller (TIC or LIC-FIC) mode is changed from Manual to Auto, both controller

output values shall be back calculated from the current valve opening value for bumpless

transfer.

If next controller (LIC-FIC or TIC) mode is changed from Manual to Auto, the controller’s

output value shall be kept at current value and only the SP shall be initialized by its PV.


Upon one expander/ compressor trip, a logic block, 41-ZC-427/432 will automatically ramp

up the setpoint of DeC1 bottom temperature controller, 41-TIC-429 to77degF at a rate of

measuring Temperature valve

6.5 B66-E-102 CHILLER OUTLET TEMPERATURE CONTROL

Refer to P&ID: B66-A-BA-543210-002/005 and Figure 4.13.5 of this document.

Objective

To maintain temperature of Hawiyah Feed gas at B66-E-102 chiller outlet.


The chiller outlet temperature is maintained by heat transfer rate of the chiller. The heat

transfer rate is controlled by varying the level of chiller refrigerant (propane), thus changing

surface area of gas carrying tubes in contact with the boiling liquid refrigerant. The chiller

level control is cascaded with chiller Hawiyah gas outlet temperature control. A change in

the process gas feed rate to the chiller will result in a change in chiller Hawiyah gas outlet

temperature. The chiller Hawiyah gas outlet temperature controller, 41-TIC-003 will then

change the setpoint of chiller propane refrigerant level controller, 41-LIC-002 to adjust the

propane refrigerant flow to chiller.

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The temperature of Hawiyah gas is compared to Haradh gas temperature where the

difference is calculated by 41-TY-005. When warmer Haradh gas is detected, alarm via

41-TDI-005 will be initiated.


B66-E-102 chiller outlet temperature control scheme is required to be operational during

start up and normal operation

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Figu

re 4

.13.

5: B

66-E

-102

Hea

t Chi

ller O

utle

t Tem

pera

ture

Con

trol

C3

Ref

riger

ant

B66-

E-11

7A/B

41LV

-002

Haw

iyah

Gas

B66-

E-10

1A/B

Haw

iyah

Gas

to S

tatic

Mix

er

C3

Vapo

rto

B66

-D-1

13A

/B

003

41TI

C

002

41LIC

Haw

iyah

Gas

Chi

ller

B66-

E-10

2

SP

MV

AO/A

FS

005

41TY

41TI

C-0

16.P

V

Note

1

005

41TD

IH

NO

TE 1

: Com

pare

the

tem

pera

ture

bet

wee

n H

awiy

ah a

nd

H

arad

h G

as. W

hen

war

mer

Har

adh

gas

is d

etec

ted,

Ala

rm v

ia T

DI-0

05 w

ill b

e in

itiat

ed.

PV

From

Fig.

7.2.

6

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Failure of chiller level signal resulting in a "Bad Value" parameter in DCS will result in

placing level controller 41-LIC-002 in MANUAL, with the output remaining at the last


Failure of chiller exit temperature signal resulting in a "Bad Value" parameter in DCS will

result in placing temperature controller 41-TIC-003 in MANUAL, with the output


Calculations 41-TY-005 Calculation Block 41-TY-005.MV = 41-TIC-016.MV – 41-TIC-003.MV Where: 41-TIC-016.MV = Hawiyah gas chiller outlet temperature 41-TIC-003.MV = Haradh gas chiller outlet temperature

Initializations

The output of 41-TIC-003 shall track SP of 41-LIC-002 when 41-LIC-002 is placed in

MANUAL or AUTO mode. When 41-LIC-002 is placed in CASCADE, 41-TIC-003 MV

initializes to 41-LIC-002 SP to prevent bumping of the process.

6.6 B66-E-108 CHILLER OUTLET TEMPERATURE CONTROL

Refer to P&ID: B66-A-BA-543210-002/005, Figure 4.13.6 of this document.

Objective

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To maintain temperature of Haradh process gas at B66-E-108 chiller outlet.


The chiller outlet temperature is maintained by heat transfer rate of the chiller. The

B66-E-108, chiller heat transfer rate is controlled by varying the propane refrigerant vapor

outlet rate to B66-D-113A/B. The refrigerant level is maintained constant by 41-LIC-013,

while the propane refrigerant vapor pressure (and associated refrigerant boiling rate) is

varied by the outlet gas temperature control loop 41-TIC-016 via the chiller backpressure

valve, 41-TV-016.

A change in Haradh feed gas flow rate to the chiller will result in a change in chiller Haradh

gas outlet temperature as detected by 41-TIC-016 as process value. The chiller Haradh feed

gas outlet temperature controller, 41-TIC-016 controls the valve position for C3R

backpressure control valve, 41-TV-016 via low signal selector, 41-TY-016.

To prevent hydrate formation in Haradh Gas due to low temperature, the propane refrigerant

inlet temperature controller 41-TIC-018, will also manipulate 41-TV-016 via the low signal

selector, 41-TY-016. When 41-TIC-018.PV (refrigerant temperature) becomes less than

41-TIC-018.SP, 41-TIC-018 closes 41-TV-016 via LSS (41-TY-016).

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C3

Ref

riger

ant

B66-

E-11

7A/B

41LV

-013

Haw

iyah

Gas

to S

tatic

Mix

er

C3

Vapo

rto

B66

-D-1

13A/

B

016

41TI

C

013

41LI

C

Har

adh

Gas

Chi

ller

B66

-E-1

08H

arad

h Fe

edG

as

AO/A

FS

018

41TI

C

MV

41TV

-016

Dir

Dir

AO/A

FS

016

41TY

41TY

-005

Note

1

PVTo

Fig

. 7.2

.5

NO

TE 1

: Min

imum

C3

Ref

riger

ant T

empe

ratu

re O

verr

ide

Con

trolle

r

t

o av

oid

hydr

ate

form

atio

n in

Har

adh

Gas

.

Figu

re 4

.13.

6: B

66-E

-108

Hea

t Chi

ller O

utle

t Tem

pera

ture

Con

trol

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B66-E-108 chiller outlet temperature control scheme is required to be operational during

start up and normal operation


Failure of chiller exit temperature signal resulting in a "Bad Value" parameter in DCS will

result in placing temperature controller 41-TIC-016 in MANUAL, with the output


Initializations

B66-E-108 chiller outlet temperature controller 41-TIC-016 and C3 refrigerant inlet

temperature controller 41-TIC018 shall be configured with anti reset windup (ARWU)

function. The function allows the output of 41-TIC-016 to track MV of Lower Signal

Selector (LSS) 41-TY-016 when 41-TY-016 is placed in MANUAL mode. When

41-TY-016 is placed in AUTO, 41-TIC-016 [MV] initializes to 41-TY-016 MV to prevent

bumping of the process.

6.7 TEMPERATURE CONTROL WITH B66-E-111 EXCHANGER AND B66-E-114

CHILLER

Refer to P&ID: B66-A-BA-543212-001/002/003/004/005, Figure 4.13.7 of this document.

Objective

To control NGL trend pressure, and to extract cooling from residue gas at B66-E-0111 up to

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a level to achieve the same B66-E-0111 feed gas outlet temperature as the outlet

temperature of Core-In-Kettle Chiller, B66-E-0114.


The NGL Feed gas trend pressure is controlled at preset value via 41-PIC-362 by

manipulating the feed gas flow to 2nd stage feed gas chiller B66-E-0114 via 41PV-362.

To match the outlet temperature of the 2nd stage feed gas chiller, B66-E-0114 and the outlet

temperature of pass A of B66-E-0111 warm gas exchanger, the setpoint of TIC-292 is set by

the 2nd stage feed gas chiller outlet temperature, 41-TI-312.

The control valve 41-TV-292 located on the inlet of pass A line of B66-E-0111, is

manipulated by the temperature controller 41TIC-292.

Temperature of the mixed feed gas is measured at the inlet to the chiller separator

B66-D-0110 via 41-TI-308 with high alarm.

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Chi

ller

Sep

arat

orB6

6-D

-011

0

B66-

E-01

01A/

B

Feed

Gas

Exc

hB6

6-E-

0110

A/B

Figu

re 4

.13.

7: T

empe

ratu

re C

ontr

ol w

ith B

66-E

-011

1 H

eat E

chan

ger a

nd B

66-E

-011

4 C

hille

r

41TV

-292

287

41TI

AC/A

FO

2nd

Stag

e Fe

edG

as C

hille

rB6

6-E-

0114

War

m G

as E

xch

B66-

E-01

11

41PI

T

163B

41FI

163

41FI

362

41PI

C

B66-

D-0

104A

~E

C3

Econ

omiz

erB6

6-D

-011

541

LV-0

88

088

41LIC

B66-

E-01

12

41PV

-443

A

AC/A

FO

AO/A

FC

Dir

Rev

C3

Ref

riger

ant

Con

dens

erB6

6-E-

0115

A

1st S

tage

Cap

acity

& L

oad

Shar

eC

ontro

ller

1st S

tage

Suct

ion

Dru

mB6

6-D

-011

2A

B66-

K011

1A

41PV

-362

AC/A

FO

B A C

B A C

+63°

F

+78°

F+3

0°F

+23°

F-1

3°F

-9°F

-9°F

-14°

FAC

/AFO

41PV

-443

B

C3

Ref

riger

ant

Con

dens

erB6

6-E-

0115

B

1st S

tage

Suct

ion

Dru

mB6

6-D

-011

2B

B66-

K011

1B

443

41TI 308

443

41PI

41TI

312

Rev

41TI

C29

2

H

SP

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During Start-up, Operator will manipulate 41-TV-292 and 41-PV-362 in manual mode until

the mixed flow temperature on 41-TI-308 reads acceptable temperature. Once the system

stabilizes, 41-TIC-292 will be changed from Manual mode to Auto mode and control

41-TV-292. 41-PIC-362 in Auto mode will control 41-PV-362. High Pressure protection

will be dependent on the Over all master control.

When mixed flow temperature reading on 41-TI-308 exceeds the acceptable temperature

range, High alarm will be enabled and operator to change the C3 refrigerant compressor

suction pressure controller’s setpoint to adjust the C3 refrigerant temperature.

NGL trend pressure control and B66-E-0111 and B66-E-0114 gas outlet temperature

control scheme is required to be operational during normal operation.


Failure of dehydrated gas pressure signal 41-PIT-362 resulting in a "Bad Value" parameter

in dehydrated gas pressure controller, 41-PIC-362, and will result in placing the controller

41-PIC-362 in MANUAL, and initiating an alarm.

Failure of warm gas exchanger B66-E-0111 feed gas exit temperature signal 41-TIT-292

resulting in a "Bad Value" parameter in DCS will result in placing temperature controller

41-TIC-292 in MANUAL, and initiating an alarm.

7 REGENERATION /ABSORPTION LOGIC SEQUENCE DESCRIPTION

There are six (6) Feed Gas Dehydrators (B66-D-0102A/B/C/D/E/F) in the NGL train.

During normal operation, Five (5) Beds are in Absorption Mode and one (1) in Regeneration

Mode. For instance, while dehydrators A/B/C/D/E are in normal operation (adsorption

mode), dehydrator F is in regeneration mode.

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The major process variables, which control and optimize the process in the dehydration

section, are described below.

Feed Gas Flow Rate

The water to be adsorbed during an adsorption cycle of the Dehydrators is directly

proportional to the flow rate of the feed gas. At low feed flow rates the accumulation of

water on the molecular sieve beds will occur more slowly and could theoretically allow for

longer adsorption cycle times. However, in practice the adsorption time will normally be

kept constant.

Feed Gas Temperature

The temperature of the mixed-feed gas exiting the static mixer directly influences the water

load on the Dehydrators. An increase in the temperature of the feed gas leaving the mixer

increases the water contents in the vapor phase (kg-H2O/m3), and therefore, this influences

adsorption cycle time.

The outlet temperature of the mixed-feed gas is controlled by two temperature controllers

located on separate feed gas chillers. Propane cooled chiller is provided each for the Haradh

feed gas and the Hawiyah feed gas. The temperature of each feed gas is maintained at 80

degF. After cooling the two streams, they are mixed in the static mixer.

Feed Gas Pressure

If the feed pressure is increase, the water content remaining in the feed gas leaving the

chiller is reduced. In normal operation, however, the pressure is stable and the pressure

fluctuation effects can be ignored.

Operational Description

For Ease of understanding, the discussion below describes steps undergone specifically by

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Feed Gas Dehydrator A (B66-D-0102A) but also applies to Dehydrators B/C/D/E/F.

The dehydrators sequence consists of the following operation.

7.1 ADSORPTION PHASE: 54 HOURS

The wet gas enters the dehydrator and flows downwards; this step lasts 54 hours.

A water analyzer (4*-AI-045) is installed at the outlet of each dehydrator with a high alarm

keeping the operator informed about the water concentration in the dry gas, and avoiding

water breakthrough in the Gas Chilling section.

7.2 PRESSURIZATION: 10 MINS

a. Disconnect dehydrator from Adsorption (Step1)

At the end of the adsorption phase, the dehydrator-A is isolated by closing the KV valves

(41/42/43-KV-043, 41/42/43-KV-055, 41/42/43-KV-046 and 41/42/43-KV-057) at

dehydrator inlet/outlet lines at the same time. Also, AXV-045 at the sampling line for

41/42/43-AI-045 closes at the same time.

b. Dehydrator pressurization (Step2)

Then the inlet KV valve (41/42/43-KV-147) of Regen Gas Hot Water Heater

(B66-E-0103A/B) and outlet KV valves (41/42/43-KV-160 and 41/42/43-KV-165) of

Regen Gas Electric Heater (B66-E-105A/B) will be opened. The dehydrator is then

slowly pressurized to the regeneration gas operating pressure by opening the pressuring

line through pressure control valve (41/42/43-PV-075) thus preventing any bed

movement. Dehydrator pressure, controlled by pressure controller 41/42/43-PIC-075,

will increase (ramp up: 10 minutes) set point from 780 psig to 902 psig.

41/42/43-PIC-079 set point for 41/42/43-PV-079 is 991 psig to prevent PV-079 opening.

41/42/43-PIC-075 and 41/42/43-PIC-079 set pressure are changed by DCS Dehydrator

Logic for regeneration operation when KV make up is finished. Pressurization of

dehydrators is complete when PDIT (41/42/43-PDI-565) measures a 15 psi or less

difference between dehydrator and the Regen Gas pressure. The PV (41/42/43-PV-075)

is only used for pressurization and will be closed by controller when 902 psig is reached.

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The close limit switch of 41/42/43-PV-075 is included to permissive to go to next step.

c. Connect dehydrator to Regeneration (Step3)

Then the regeneration gas inlet (41/42/43-KV-047 and 41/42/43-KV-058) will be opened

at first, and outlet KV valves (41/42/43-KV-056 and 41/42/43-KV-044) of the dehydrator

will be opened next and heating step will proceed. Regeneration gas flow to the

dehydrator is up-flow (from bottom to top). Change TIC152 SP from 43 degF to 144

degF when this step is started. Also it overrides 41/42/43-PIC-075 SP to 780 psig to keep

close 41/42/43-PV-079.

7.3 HEATING: 385 MINS

a. 1st Ramp-up temperature (Step4): 10mins

After the pressurization of the dehydrator and connected dehydrator to regeneration,

regeneration gas temperature (41/42/43-TIC-152) set point is increased (ramp up: 10

minutes) from 144°F to 248°F using the Regen Gas Hot Water Heater (B66-E-103A/B).

Regeneration gas flow rate is controlled by low selection of either flow controller

(41/42/43-FIC-101A) or pressure controller (41/42/43-PIC-228) located on the inlet line

to B66-E-0103A/B. Temperature of Regen gas is controlled by temperature controller

(41/42/43-TIC-152) by varying the flow rate of MP hot water through control valve

41/42/43-TV-152 on the MP hot water line. During this step, Regen Gas Electric Heater

(B66-E-105A/B) is not on service. Also, inlet and outlet KV valves (41/42/43-KV-175

and 41/42/43-KV-176) of Regen Gas Cooling Cycle Chiller (B66-E-0104) are closed.

With the increase in Regen gas temperature, the dehydrator temperature

(41/42/43-TI-082) will also increase. The dehydrator temperature will increase from

79°F to 200°F.

b. 1st Stage Regeneration (Step5): 30 mins

When the temperature reaches 248°F at B66-E-103A/B outlet, which is controlled by

41/42/43-TIC-152, it is kept at this temperature for 30 mins before proceeding to 2nd

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Ramp-up

c. 2nd Ramp-up temperature (Step6): 15mins

At 2nd Ramp-up Regen Gas temperature (41/42/43-TIC-152) set point at B66-E-103A/B

outlet is ramped up from 248°F to 400°F within 10 mins.

Regen Gas Electric Heater (B66-E-0105A/B) is also started via 41/42/43-HY-158/163

after 10mins of Step 6, and Regen Gas temperature (41/42/43-TI-164/169) is increased

further from 400°F to 550°F.

Note: The temperature control of B66-E-0105A/B is performed by Control Panel

supplied by Heater Vendor.

d. 2nd Stage Regeneration (Step7): 320 mins

When the temperature reaches 550°F at B66-E-0105A/B outlet (41/42/43-TI-164/169), it

is kept at this temperature for 320 mins. The regeneration gas flow rate is maintained as

the previous step. As Hot Regen Gas passes through the dehydrator, water adsorbed in

the bed is evaporated and mixed with the Hot Regen Gas. PV of 41/42/43-TI-082 should

be higher than 528°F and keeps the temperature 5 min within 320 min before go to next

step.

Before step-7 Dehydrator Heating is completed, the Dehydrator outlet temperature

(41/42/43-TI-082) to the Regen Gas Air Cooler (B66-E-0106) shall be confirmed in DCS

that it is sufficiently heated up to 528°F and the Heating Completed status

(41/42/43-YL-104) shall be indicated in DCS. In case it is below 528°F after step-7, the

Heating Not Completed and message “Please confirm to continue the dehydrator

sequence” shall be generated in DCS. Operation mode shall be changed to MANUAL

mode automatically. After then the operator can select from the three types of operation.

One is to stop the sequence. Other is to continue the sequence without excess Heating

Step. The other is to continue the Heating Step. In order to stop the sequence, the Stop

Sequence (41/42/43-HS-103) shall be used. To continue sequence without excess

Heating Step, operator shall change operation mode to AUTO mode. To continue

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Heating Step, an operator shall keep the MANUAL mode and Heating step manually

e. Ramp down (Step8): 10 mins

Once the 2nd Stage Regeneration step is over, Regen Gas Electric Heaters

(B66-E-0105A/B) are turned off and 41/42/43-TIC-152 set point is decreased (ramp

down:10 minutes) from 400°F to 144°F.

7.4 COOLING (STEP9): 133 MINS

Once the heating step is over, the regen gas is then diverted to Regen Gas Cooling Cycle

Chiller (B66-E-0104) by opening KV valves (41/42/43-KV-175 and 41/42/43-KV-176).

Also, 41/42/43-LIC-033 cascade to 41/42/43-TIC-182.

After confirming that these KV valves at inlet and outlet of B66-E-0104 are completely

open, KV valves (41/42/43-KV-147, 41/42/43-KV-160 and 41/42/43-KV-165) around

B66-E-0103A/B and B66-E-0105A/B are closed. The regeneration gas flow rate is

maintained as the previous step. Regen Gas temperature (41/42/43-TIC-182) from Sales

Gas Compressor is cooled down from 144°F to 90°F and will be used to cool the dehydrator

for 133 mins.

The set point of 41/42/43-TIC-152 is changed to 43°

7.5 DEPRESSURIZATION

a. Disconnect dehydrator from Regeneration (Step10)

At the end of the cooling phase, the dehydrator is disconnected from the regeneration gas

line by closing the relevant KV valves (41/42/43-KV-044, 41/42/43-KV-058,

41/42/43-KV-044 and 41/42/43-KV-056) at dehydrator inlet/outlet. Also,

41/42/43-TIC-182/41/42/43-LIC-033 cascade is disconnected.

b. Dehydrator Depressurization (Step11): 10 mins

The dehydrator is then depressurized to the Feed gas operating pressure by opening the

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depressuring line through changing set point of pressure control valve

(41/42/43-PV-079) to residue gas header. Dehydrator pressure should be carefully

decreased (ramp down: 10 minutes) from 991 psig to 821 psig to prevent any bed

movement. The PV is only used for depressurization and will be closed when 821 psig is

reached. Dehydrator pressure is controlled by pressure controller 41/42/43-PIC-079. Set

pressure is changed by DCS Dehydrator Logic for adsorption operation.

Depressurization of dehydrator is complete when PDIT (41/42/43-PDI-077) measures a

15 psi or less difference between dehydrator and the Feed Gas pressure. When this

pressure difference is reached the system will now proceed to stand-by mode.

7.6 STAND-BY TIME: 110 MINS (STEP12)

The system will wait until 110mins have elapsed before going to adsorption mode. 110 mins

of stand-by time will be changed and will depend on operating conditions because starting

time of next Step 13 is fixed. During sequence Manual mode, the operator can skip this step

anytime when operator pressed Go to Next step “41/42/43-HS-105” under his responsibility.

Such kind of operation is considered when one of dehydrator regeneration time exceeds 10.8

hr.

7.7 CONNECT DEHYDRATOR TO ADSORPTION (STEP13)

Prior to opening of the Feed Gas inlet and outlet KV valves (41/42/43-KV-043,

41/42/43-KV-055, 41/42/43-KV-046 and 41/42/43-KV-057), blowdown KV valve

(41/42/43-KV-053) will open to the wet hydrocarbon burn pit after 648 mins later starting

from Step 1. The 41/42/43-KV-053 will be closed after 30 second pass from detecting open

limit switch. This will ensure that accumulated free water, if any, in the Feed Gas line is

flushed out from the feed gas system. This will protect the dehydrator bed from degradation

due to free water carry-over.

Normal operation

1) Regeneration and Adsorption sequence step

One cycle of the regeneration is 648 minutes (10.8 hrs) and consists of the following 14

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steps. Once sequence passes through Step 0, the Step 0 cannot be reached again during

normal sequence operation in Auto Mode except in case of 5 Dehydrators modes and

skipped.

Step Description Regen Gas

Temp. (°F)

Time

(Minutes)

0 Initialization - -

1 Disconnect Dehydrator from

Adsorption

- -

2 Dehydrator Pressurization - 10

3 Connect Dehydrator to Regeneration - -

4 Dehydrator Heating – Ramp up (1st

stage)

144 248 10

5 Dehydrator Heating (1st stage) 248 30

6 Dehydrator Heating – Ramp up (2nd

stage)

248 400

550

15

7 Dehydrator Heating (2nd stage) 550 320

8 Disconnect Regen Gas Electric Heaters

(B66-E-0105A/B) from Regeneration

- -

9 Dehydrator Heating – Ramp down 400 144 10

10 Dehydrator Cooling 90 133

11 Disconnect Dehydrator from

Regeneration

- -

12 Dehydrator Depressurization - 10

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13 Standby time - Approx.

110-

14 Connect Dehydrator to Adsorption -

Total - 648

NOTE 1: Each step timers can be extended anytime.

NOTE 2: Standby timers can be skipped by the operator when it is manual mode.

2) Automatic operation

The dryer sequence shall have two operation modes, Auto and Manual selectable by the

Auto/Man Selector Switch (41/42/43-HS-104). When it is in Auto position, Start

Sequence (41/42/43-HS-100) shall start the sequence, which always starts from

Dehydrator A in regeneration and Dehydrator B, C, D, E and F in adsorption mode. The

regeneration process shall move from one step to another in sequential order from A, B,

C, D, E and F and continue until it is stopped by the Stop Sequence (41/42/43-HS-101).

As the sequence starts in Auto mode, all the sequence related valves are initialized to

close position and then the sequence continues step by step. During AUTO sequence

operation, sequence gives open/close command to KV, change the controller setpoint

and turn on/off electric heater automatically. When a sequence is in Auto mode, the

operator must not manually manipulate any sequence valve. If operator wants to

manipulate the discrepancy valve, the Sequence Manual mode should be selected by

operator and changes controller mode to Manual individually. The timer for each step is

keep counting to proceed to next step. The transition to next step will be done

automatically if all permissive condition is cleared.

All individual valve position status, both open and close, shall be repeated to DCS and

the sequence monitors all the time that they are in the appropriate position as the

sequence programmed. If there is a discrepancy between the sequence command and the

actual valve position or a discrepancy between the start/stop command for Electric

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Heater and it’s feed back, the sequence shall be turned to Sequence Manual mode and

allow to proceed the sequence manually by operator. The timer keeps counting and

generate the discrepancy alarm in DCS. It will continue to sending command to valves

until operator disconnect the valve from sequence by changing controller mode to

manual. After DCS receives the expected feedback of the sequence and all controller

modes is in AUTO, operator is able to put back Sequence mode to AUTO.

If the operator wants to stop the sequence intentionally by any reason, it is allowed to

stop the sequence using the Stop Sequence Switch (41/42/43-HS-101). In order to

resume the sequence from the stopped position, the Start Switch (41/42/43-HS-100)

shall be used.

The status of the Sequence Stopped (41/42/43-YL-102) shall be indicated in DCS when

it is stopped by the Stop Switch. (41/42/43-HS-101)

The mode status of each dehydrator if it is in regeneration or adsorption modes shall be

indicated in DCS by the Dehydrator Status (41/42/43-YI-100A/B/C/D/E/F). The timers

shall be indicated with the unit of “minutes”.

All timers and counters shall be available for operator in DCS graphic by the Phase

Timer.

The duration after depressurization to adsorption operation of the dehydrator is called

“Stand-by” mode, and therefore it is called Available Stand-by Time (41/42/43-KI-008).

The Stand-by time finishes by means of the timer when the total regeneration time is

expired (648 min. = 10.8 hrs).

3) Manual operation

During sequence Manual mode, the sequence also sends command to valves as well as

AUTO mode unless controller mode is changed to Manual by operator. The operator can

also change setpoint and MV.

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This manual mode operation is provided for trouble shooting of the sequence valve

position and for a step by step operation and not intended to manipulate a manual

operation of all the sequence valves. The step by step operation means the sequence can

not proceed to the next step automatically. Therefore, the Go to Next Step HS

(41/42/43-HS-105) shall be highlighted in DCS once all valve position matches to the

expected position in each step. The HS is not to be pressed until all permissive condition

is cleared, including timer. The sequence can start and stop during this manual mode.

Also, a series of the regeneration mode from step-1 through step-14 can be performed in

auto by the regen start switch (41/42/43-HS-100) without operator’s interference in this

manual mode.

4) Five (5) dehydrator’s operation (one dehydrator is out of service)

When one dehydrator is out of service, four (4) beds are in adsorption mode and one (1)

in regeneration mode. In this operation, the adsorption mode lasts for 54 hours, and one

cycle of the regeneration is 13.5 hours (Only stand-by time changes to 4.7 hours instead

of 110 minutes.) The total feed gas flow rate shall be reduced to 80% in this operation.

To change to the five dehydrator’s operation, the selector switch for five dehydrator’s

operation (41/42/43-HS-107) and the selector switch for a skipped dehydrator

(41/42/43-HS-108 A/B/C/D/E/F) shall be used any time. Once the selector switch for

five dehydrator’s operation is initiated, the DCS logic will be ready for switching, and

the five dehydrator’s operation starts when one of the dehydrators goes to step 13 “stand

by time” in regeneration mode by final command before step is moved to step 13, i.e.,

step-1. Any of five dehydrator operation command or skipped dehydrator command

during step 13 will be applied when next dehydrator’s step 13 is started.

8 PROCESS THEORY

The purpose of the Dehydration section is to remove water from the feed gas sent from the

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Haradh and Hawiyah plants.

Feed gas drying is required:

• to meet the dryness specification for sales gas, i.e., water dew point.

• to prevent ice and hydrate formation in the Cryogenic section, which will cause

blockages in piping and equipment.

Dehydration section uses molecular sieves to remove the water from the feed gas.

Molecular sieves are a crystalline form of sodium alumina silicate (zeolite). They can be

manufactured with very specifically sized pore openings into their lattice structure. This

sizing can make the sieve very selective to which particular molecule it adsorbs.

Type 4A molecular sieves, which have a pore diameter of approximately 4 Angstroms

(100,000,000 A = 1 cm), are used in the Gas Dehydration section. They will basically adsorb

molecules with a nominal diameter less than 4A. The internal surfaces of molecular sieves

are electrically charged and are attracted to dissimilar changes on polar molecules. Water

molecules have a strong polarity and can be adsorbed onto 4A molecular sieves. It is

possible to reduce the water content in the outlet gas to less than 0.1 ppmv.

The purpose of the Mercury (Hg) Removal section is to remove trace quantities of mercury

present in the feed to the Cryogenic section, and this protects the Cold Box and

Turbo-Expander impeller made of aluminium against corrosion.

Eliminating mercury from hydrocarbon gas requires the use of a mercury trapping material

such as Activated Carbon. Mercury is trapped in the activated carbon and it is possible to

reduce the mercury content to less than 0.01 microgram/Nm3 of feed outlet gas. The

activated carbon is disposable, and when fully loaded with mercury, the bed must be

replaced with fresh material.

The purpose of the Cryogenic section and Demethanizer (C-0110) is to extract ethane and

heavier components as NGL from the Feed gas and at the same time to control High Heating

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Value of the residue gas to satisfy the sales gas specification. One of the cryogenic

expansion processes with parallel Turbo-Expanders (K-0110 A/B) is used for this unit. In

the cryogenic expansion process, a feed gas stream under high pressure is cooled by Brazed

Aluminum Heat Exchangers (BAHEs) with core in kettle type C3 Refrigerant Chiller

(E-0114). As the feed gas is cooled, liquids are partially condensed and collected in

separators as high-pressure liquids containing some of the desired ethane and heavier

components.

9 PROCESS VARIABLE

9.1 JOULE-THOMSON OPERATING MODE

The unit will be normally operated with two 50% Turbo-Expander. In case of one 50%

Expander shutdown, the Joule-Thompson valve installed on the by-pass line of the

Expander will be commissioned. The unit is designed to produce on-specification Sales Gas

considering one normal Expander operation and the other in Joule-Thomson operation.

1) Demethanizer Temperature

The operating temperatures of the train increases comparing with the normal 2

Turbo-Expander operation because of the lower thermal expansion effect through

Joule-Thomson valve.

2) Demethanizer Pressure

Since one of the Brake Compressor is bypassed in the residue gas line and the suction

pressure of Sales Gas Compressor in Unit B68 is maintained by a pressure controller, the

system operating pressure downstream of Joule-Thompson valve is higher than the

normal operation.

3) Demethanizer Feed Liquid Flow Rate

Liquid flow rate coming from the Chiller Separator and Expander Feed Separator

decreases due to higher temperature level in the Unit.

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For One JT Operation 100% feed flow rate can handled in One JT operation.

Two JT operation is unstable operation with the current design. In order to satisfy the NGL

product specification of C1/C2 less than 2.5%, the feed gas rate at static mixer is reduced to

594.3 MMSCFD (44.9 % of design), because the current UA of B66-E-118 (0.274

MMBtu/F-hr including margin) is bottleneck. At this flow rate, tray load of Demethanizer

is significantly less than Demethanizer minimum turndown ratio (about 20% of normal

flowrate).

Therefore, during start-up, off-spec condensate is possible to be produced before one

expander is started-up. When two Expander/Compressors are tripped, off-spec condensate

is possible to be produced and unit shutdown will be initiated by operator manually.

9.2 FLOWRATE AT MIXER TO JT TRAIN (MMSCFD)

Flow/MMSCFD Total Hawiyah Haradh Normal 1322.9 100.0% 789.5 533.4 One JT 1322.9 100.0% 789.5 533.4 Two JT 594.3 44.9% 60.9 533.4

For Two JT operation, total 594.3 MMSCFD (44.9 % of design) can only be handled by design limit of Demethanizer auxiliary reboiler.

9.3 PRODUCT SPECS OF JT TRAIN

Normal One JT Two JT Heat content of residue gas BTU/SCF 930.0 960.9 997.0 Residue gas lbmol/hr 126,472 131,321 60,661 C1/C2 in NGL % 2.302 2.375 2.375 CO2 in NGL ppmV 464.1 175.0 179.5

% 95.65 56.28 27.62 Ethane Recovery lbmol/hr 18,730 13,881 4,543

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9.4 DEMETHANIZER

The temperature within the demethanizer will have a significant increase compared to normal

operation. Its overhead temperature will increase from -162.7 °F during normal to -125.4/

-104.9 °F (one/Two JT) and the bottom from 45.3 °F to 76.5/ 106.1 °F during One/ Two JT

Operation. This in turn will affect the whole train where residue gas is used as a cooling medium to

other streams.

The Overhead Pressure of the Demethanizer will increase from 263.1 psig during normal operation

to 307.7 psig during One & Two JT operation.

1) Temperature and pressure

OVHD Press(psig): 263.1 (Nor), 307.7 (One & Two JT)

OVHD Temp (degF): -162.7 (Nor), -125.4 (One JT), -104.9 (Two JT)

Bottom Press(psig): 267.5 (Nor), 312.1 (One & Two JT)

Bottom Temp (degF): 45.3 (Nor), 76. 5 (One JT), 106.1 (Two JT)

2) Feed Flow (Normal/One JT/Two JT):

From OVHD exchanger, E-0113/ lbmol/hr) 35,896/ 37,499/ 17,003

From Expander and/or JT valves, K-110/ lbmol/hr) 92,764/ 96,425/ 43,723

From Exp. Feed separator, D-111 / lbmol/hr) 12,013/ 7,866/ 3,422

From Chiller separator, D-110 / lbmol/hr) 4,529/ 3,412/ 1,055

3) Outlet Flow (Normal/One JT/Two JT):

C-110 OVHD/ lbmol/hr) 126,472/ 131,321/ 60,661.

C-110 Bottom/ lbmol/hr) 18,730/ 13,881/ 4,543.

4) Reboilers (Normal/One JT/Two JT):

B66-E-112 / lbmol/hr) 29,850/ 20,540/ 6,321

B66-E-111/ lbmol/hr) 23,585/ 18,133/ 5,949

B66-E-110A/B / lbmol/hr) 24,893/ 15,640/ no use

B66-E-118 / lbmol/hr) no use/ 3,203/ 5,109

For Two JT operation, tray load of Demethanizer is significantly lower than that of normal case and less than Demethanizer minimum turndown ratio. Therefore, Demethanizer cannot be stable

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operation with this conditions.

9.5 BLAZED ALUMINUM HEAT EXCHANGERS

The following figures shall be used for long period One/Two JT operation.

B66-E-0110A/B Hot gas outlet (degF): 30.0 (Nor), 39.2 (One JT), 50.0 (Two JT)

B66-E-0111&0114 Hot gas outlet (degF): -8.65 (Nor), -2.46 (One JT), 6.00 (Two JT)

Sprit flow ratio to E-114 (mol%): 41.61 (Nor), 41.90 (One JT), 48.00 (Two JT)

B66-E-0112 Hot gas outlet (degF): -56.56 (Nor), -41.70 (One JT), -35.00 (Two JT)

B66-E-0113 Hot gas outlet (degF): -159.3 (Nor), -110.4 (One JT), -97.0 (Two JT)

Sprit flow ratio to Expander & JT valve (mol%): 72.1 (Nor), 72.0 (One & Two JT)

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Documents

NGL trains description.pdf