Basic Process Design Requirements and Criteria (2)

8/20/2019 Basic Process Design Requirements and Criteria (2)

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Project N° Unit Document Code Serial N° Rev. Page

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BASIC PROCESS DESIGN REQUIREMENTS AND CRITERIA

1. INTRODUCTION

The purpose of this document is to define the requirements and criteria, which have tobe followed to perform a Process Engineering Design for this specific Project, in theabsence of specific requirements on the subject in the Contract.

When such requirements exist, they have to be followed and the present documentshall be modified accordingly.

In case of licensed units, the rules of the Process Licensor will be generally followed for equipment to be added, in order to have a consistent design, unless otherwise dictatedby the Contract.


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2. DESIGN TEMPERATURE

2.1. EQUIPMENT OPERATING AT TEMPERATURE ABOVE 0 °C

As a general rule the design temperature will be:

TD = TMCO + 15 °C as minimum requirement

The design temperature shall not be lower than 60 °C.

Where:

TD = Design temperature (°C)TMCO = Maximum continuous operating temperature (°C). Its selection must take

into account some specific operating conditions: turndown conditions,different feed and operating cases, etc.

The accidental temperatures, which can occur in emergency situations such as loss of utilities, valve failure or during start-up, shut-down or any abnormal operationcorresponding to a short duration are not taken into account as long as the temperatureincrease does not exceed codes limits (investigation has to be followed withspecialists).

However, equipment containing parts, which can be damaged by abnormal hightemperature, has to be designed for this temperature. It concerns column internals,desalter internals, heat exchanger or air coolers tubes with polymer coating. For thistype of equipment, steam out delivery conditions have to be reconsidered in order toremain below the maximum acceptable temperature.For piping, accidental temperatures are not considered for piping class selection, butare considered for pipe flexibility study.

Alternate or transient operations, such as regeneration, dry out, have to be considered,the duration of the corresponding operations exceeding a total of 100 hours per year. If there is no change in operating pressure, the process design temperature will be the

maximum of the two values:

• Either the maximum temperature for alternate transient operation

• Or the maximum continuous operating temperature + 15 °C minimum.

If there is a significant change in operating pressure for these exceptional operatingconditions (for example reaction loops with in-situ catalyst regeneration), another set of design temperature and pressure has to be specified corresponding to these operatingconditions.

2.2. SPECIAL CASES

• Condensing service by air coolers (column overhead, air condenser in reactionloop etc.).Design temperature downstream the air cooler is equal to air condenser normal


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inlet temperature decreased by expected cooling due to natural draught throughthe air cooler.

• Air cooler on product final cooling step. A similar approach can be taken for thedesign temperature of downstream equipment. But the design temperature of off-site lines will not be increased beyond the application of the general rule.

• If for process reasons, a specified maximum operating temperature must not beexceeded, this maximum possible operating temperature is used as designtemperature (ex catalytic reforming reactors).

• For heat exchanger trains with by-pass of individual exchanger, the design

temperature (hot side) of the downstream exchanger will be the normal operatingtemperature of the by-passed exchanger assuming that shells are by-passedpiece by piece (simultaneous by-pass of several exchangers in series is notconsidered), same philosophy will be applied to a trim cooler downstream air fin.

2.3. STEAM OUT

The steam out conditions (using LP steam) for vessels are as follows:

• 110 °C as minimum requirement

• Atmospheric pressure.

2.4. EMERGENCY DEPRESSURISING

The exceptional temperature generated by depressurising of equipment or completesystem will be indicated with the related residual pressure in order to select thematerial accordingly.

Only depressurising actions, clearly identified in the operating manual for process or safety reasons are considered. Accidental depressurising, due to single controlvalve/safety valve failure or operator error for example are not taken into account.Indeed these potential cases can be faced by:

• Closing the block valves associated to the control valve

• Clear instruction/procedure within the operating manual to avoid such operator error.

The equipment has to be reheated and slowly repressurised according to a writtenprocedure.When immediate repressurisation is required, a second set of design pressure/designtemperature shall be specified.

2.5. VACUUM CONDITIONS

A specific design temperature will be associated to specified vacuum design pressure.


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2.6. EQUIPMENT OPERATING AT A TEMPERATURE BELOW 0 °C

As a general rule the design temperature will be:

TD = TMCO – 10 °C (3)

Where:

TD = Design Temperature (°C)TMCO = Minimum continuous operating temperature (°C) taking into account minimum

operating pressure except depressurisation.

Notes:

(1) If a piece of equipment normally operated below 0 °C can be submitted totemperature above ambient during particular operating phases (dry out, start-up,regeneration, …) or accidental causes (except fire), a hot design temperature willbe indicated with associated design pressure. Such a data can have an impacton insulation type selection.

(2) For depressurising, see paragraph 2.4.

(3) If such temperature cannot be reached due to intrinsic process limits, the lowestpossible temperature will be selected.

(4) Equipment in stand-by at ambient low temperature that can be pressurised for process reasons shall be specified with a second set of design conditions.

2.7. DISCONTINUOUS PROCESSES

Conditions of P and T will be specified for each phase and must be considered assimultaneous design conditions. Mixing of extreme conditions of pressure andtemperature shall not be considered.For cyclic operation, cycle duration is to be specified.


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3. DESIGN PRESSURE

Design pressure for columns, vessels, heat exchangers, reactors, and lines shall beestablished as follows:

Max. operating pressure Design pressure

Atmospheric storage facilities- Cone Roof Hydrostatic pressure and + 50 / – 25 mm H2O- Down Roof Hydrostatic pressure and + 250 / – 50 mm H2O

Atmospheric pressure

(Pressure vessels)

0.5 barg

Vacuum Full vacuum and 3.5 barg min. (1)

Between 0 and 10 bargMax. op. press. + 1 bar as minimum requirement(3.5 barg min.) (2)

Between 10 barg and 35 barg Max. op. press. + 10 % min.

Between 35 barg and 70 barg Max. op. press. + 3.5 bar min.

Above 70 barg Max. op. press. + 5 % min.

Notes:

(1) Full vacuum design conditions will be applied to equipment that fulfil one of thefollowing conditions:

• Normally operates under vacuum• Is subject to vacuum during transient operation or regulation.• Normally operates full of liquid and can be blocked in and cooled down• Can undergo vacuum through the loss of heat input (to be studied case by

case. Vacuum prevention systems are also acceptable.

Partial vacuum design conditions are normally not considered, except for thefollowing cases:

• When the subatmospheric pressure is determined by the vapour pressure of the vessel contents. Then consider the vapour pressure associated with theminimum ambient temperature.

• When the thickness of equipment is determined by external pressurecalculation instead of internal pressure. Then it has to be considered case bycase.

Design pressure for equipment shall consider vacuum condition which can occur due to equipment elevation: an example is given by exchangers in cooling water service normally (provided with vacuum breaker).

(2) For equipment in equilibrium with flare, the design pressure is the flare designpressure.


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For equipment provided with safety valve discharging to a flare system, thedesign pressure cannot be lower than the flare network design pressure.For equipment provided with safety valve discharging to atmosphere the designpressure is 2.5 barg.

(3) Short time conditions for line design, as per ANSI B31.3 and 31.4, can be appliedwhen:

• allowed by contract• for pressure surges due to water hammer • for decoking operations.

(4) Alternate operations, such as regeneration, dry-out, start-up, shut-down etc. shallbe considered in determining the design pressure.

3.1. DESIGN PRESSURE PROFILE FOR COLUMNS AND S YSTEMS

The design pressure at the bottom of a fractionation column will be determined asfollows:

PDB = PDT + ∆P1

Where:

PDB : Design pressure at the bottom (vapour phase)PDT : Design pressure at the top calculated as per paragraph 3.

∆P1 : Column pressure drop and/or hydrostatic head.

The liquid flowing density and the maximum liquid height will be indicated on theProcess Data Sheet.

3.1.1. Liquid head has to be considered in defining the design pressure of natural circulationreboilers.

3.1.2. If a reflux drum is protected by a safety valve at top of the column, its design pressure

must take into account the pressure difference between the drum and the safety valveduring relieving conditions attached to fire case. Such pressure difference must alsointegrate possible liquid leg between the safety valve and the drum if this one has afeeding device completely flooded.

3.2. DESIGN PRESSURE AT THE DISCHARGE OF A PUMP

In principle design pressure for lines and equipment located on the pump dischargeshall be equal to pump process design pressure down to the last block valve locatedbefore a section protected by a safety valve.

The design pressure at the discharge of the pump will be set as follows, before pumpselection:

10.2

dHKPP maxRDSDD

⋅⋅+=


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PDD : Design pressure at the discharge of the pump (barg)PDS : Design pressure at the suction of the pump (barg)HR : Differential head at rated point (m)dmax : Maximum specific gravity of pumped fluid (out of precommissioning phase

when pumps can be tested with water)K : 1.2 for motor driven pump / 1.4 for turbine driven pump

No provision has to be taken for maximum impeller diameter except client requirement. After pump selection and finalisation of all operating cases with final suction designpressure, it will be checked that the design pressure calculated with the previousformula with updated values does not exceed the one of previously selected; otherwiseit will be verified against the following operating conditions:

• Maximum operating pressure at suction nozzle in conjunction with head at noflow conditions and maximum specific gravity of pumped fluid.

• Design pressure at the suction nozzle of the pump in conjunction with differentialhead at rated point and maximum specific gravity of pumped fluid.

For these two conditions, head is multiplied by (1.05)² if pump is driven by steamturbine (maximum continuous turbine speed = 105 % of the speed at rated point).

In case of two pumps in series, the maximum differential head will be the sum of themaximum differential head of each pump if there is no pressure relief valve betweenthe pumps.

3.2.1. Positive Displacement Pump

Design pressure for positive displacement pumps (reciprocating and rotary) is given by:discharge vessel’s maximum operating design pressure + pressure drop along thedischarge line + static head or design pressure of suction vessel plus suction liquidhead (whichever is greater). If required for Process reasons or to fulfil some specificregulations, the maximum operating pressure can be equal to equipment designpressure.Said pressure increased with a margin as per para. 3. shall be the set pressure for thepump’s safety valve.For reciprocating pump, however, the following values shall be considered as minimum

for setting the safety valve.

P operating (barg) P Setting (barg)

≤ 10

10 – 20

20 – 50

> 50

Pop. + 2.5

1.25 · Pop.

Pop. + 5.0

1.10 · Pop.

3.3. DESIGN PRESSURE FOR COMPLEX S YSTEMS

For systems such as reaction loops protected by one safety valve, the design pressure

of equipment on which this pressure safety valve is located is calculated as per paragraph 3 or with consideration of the system settling out pressure.


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For any piece of equipment in the loop, the design pressure will be equal to the designpressure of the equipment where the safety valve is located plus ∆P where ∆P is thepressure drop under S.V. discharge conditions, between this item and equipmentprotected by the safety valve.

A pressure profile taking into account all operating conditions will be drawn.

3.4. TUBE RUPTURE FOR HEAT EXCHANGERS

This concerns TEMA and multitubes heat exchangers.

The installation of safety valves for reason of tube rupture must be avoided as much as

possible for the following reasons:

• Their sizing is not always easy

• They can discharge liquid, or important quantity of water into hydrocarbon flaresystem with possible liquid accumulation

• Freezing risk for some stream (cooling water, etc.)

The recommended practice consists in oversetting, if necessary, the design pressure of low pressure side of heat exchangers in order to have:

side) pressure(highP (1)side) pressure(lowP DTEST ≥

• In all cases up to the limit acceptable of the 150 lbs piping class• After analysis, case by case, for higher pressures.

This rule, while avoiding the installation of safety valve on exchanger low pressure sidefor tube rupture, does not eliminate the possibility of tube rupture itself; the relevantconsequences on the entire low pressure system should be therefore evaluated caseby case.Double pipe type heat exchangers are not concerned.

(1) When using ASME code, the hereabove relation becomes:

side) pressure(highP side) pressure(lowP130% DD ≥

While being the above 130% value generally on the safe side, this point will needto be analysed case by case with vessel specialist when other codes are used(British Standards, CODAP, etc.) to maintain the same philosophy; for projects inEurope the Pressure Equipment European (PED) will need also to be taken intoaccount.

3.5. STEAM CONTAINING EQUIPMENT

As a general rule, full vacuum conditions should be added to design conditions of asteam containing equipment under normal operation, since vacuum can happen duringcooling of such equipment, if it is not connected to atmosphere or equipped withspecial protection device.

Steam out operation is not to be included in that rule.


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4. MATERIALS & CORROSION ALLOWANCE (FOR PIPING AND EQUIPMENT)

4.1. MATERIALS

Preliminary selection of materials to be used at low temperature to avoid embrittlementis the following:

- Low Temperature Carbon Steel ≥ – 50 °C

- 3.5 Nickel ≥ – 80 °C

- 9 Nickel or Stainless Steel


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- welded or non-removable parts: the 100 % of the specified value

- bolted or removable parts (including trays): the 50 % of the specified value.

4.3. H YDROGEN SERVICE

4.3.1. Definitions

Hydrogen service refers to hydrogen or its gaseous mixtures having a partial pressureof hydrogen equal or higher than 7 bara.

4.3.2. Requirements

In hydrogen service, the following engineering design recommendations shall beapplied.

- Screwed connections are not to be used.

- On heat exchanger nozzles, when connections for PI, TI are to be provided per TEMA, 1" minimum size flanged and blinded nozzles are to be foreseen. Onintermediate nozzles of multiple shell heat exchangers, pressure and temperatureconnections shall be not installed.

- The number of vent and drain connections is to be minimised; in any case, their valves shall be blanked. Hydraulic test vents (not valved) shall be sealed after hydraulic test.

- The minimum size of small connections on process lines (excluding orifice flangeand carrier ones), and equipment is to be 1" for strength.

- In order to isolate equipment which can be idle during normal plant operation,double block and bleed valves shall be provided.

- In case of permanent connections to process, normally isolated (as nitrogenpurging connections), double block and bleed valves shall be provided.

- For material selection, refer to Nelson curves (note: KCS must be used instead of CS).

- Nozzle flange facing shall be raised face with 125 – 250 RMS finish and gasketsshall be retained spiral wound type.

- For heat exchangers, tubes shall be seal welded to tube sheet.

4.3.3. Information on process documents

- Process data sheets shall include a note to identify the hydrogen service.

- Mechanical line list will generally have a note for the lines in hydrogen service,unless a dedicated piping class is used for it.


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4.4. WET H YDROGEN SULPHIDE SERVICE

4.4.1. Definition

Metallic materials in presence of H2S in the aqueous phase, may be subject to either hydrogen induced cracking (HIC) and/or Sulphide Stress Cracking (SSC). The sulphidestress cracking is associated with high hardness. Wet hydrogen sulphide service isdefined according to NACE, as per attached table.

4.4.2. Requirements

• All equipment in wet hydrogen sulphide service is to be stress relieved regardless

of plate thickness.

• All carbon steel materials shall be fully killed. All metallic materials shall be specified to be HIC resistant.

• Material shall also conform to recommendation of NACE standard TM 0175 in itslast edition.

• Material selection for H2S service at high temperature shall be according toCOUPER/GORMAN curves.

4.4.3. Information on Process Documents

• Process data sheets of any piece of equipment (including instrumentation) shallinclude a note to identify the wet H2S service.

• Mechanical line list will generally have a note for lines in wet H2S service (sour service), unless a dedicated piping class is used for it.


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DETERMINATION OF WET H2S SERVICE ACCORDING TO NACE

(NACE MR – 01.75, 2000 Rev. )

OIL, WATER AND(WET) GAS SYSTEM MULTIPHASE SYSTEMS

NOTE 1 GOR = Gas to Oil Ratio.


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4.5. POSTWELD HEAT TREATMENT

For caustic soda service, a postweld treatment for stress relief will be specified to avoidcracking when:

• Steam tracing is foreseen, whatever its operating temperature

• Operating temperature in °F is higher than:

170 – B

Where: B is “Baumé”

gravityspecific

145145B −=

For example, a solution of caustic soda at 20 % wt corresponds to a specificgravity of about 1.2. In this case:

242.1

145145B =−=

A postweld heat treatment is required if the operating temperature is above:

170 – 24 = 146 °F (63 °C).

• Transient Operation or misoperation shall also be considered to decide aboutPWHT.

• For lean and rich amine service, a postweld treatment for stress relief will also bespecified.

4.6. TEMPERATURE LIMIT FOR CARBON STEEL IN ENVIRONMENT OF H YDROCARBONSCONTAINING SULPHUR COMPOUNDS

As a general rule, to be verified according to the related corrosion curves, carbon steelwill be used up to 280 °C (normal operating temperature).For pressure vessels including fractionation columns, above a normal operating

temperature of 280 °C carbon steel with 3 mm minimum cladding 11/13 Cr will be used.Cladding should be considered as corrosion allowance.

For heat exchangers, same as for pressure vessels, except for tube bundles for which4/6 Cr will be used.


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5.COLUMNS & TRAYS

5.1. DIAMETER

Normal operating flow rates of liquid from the tray and of vapours to the tray shall notbe increased.Tray load specifications shall indicate normal liquid from tray and vapour to trayoperating flow rates.Column diameter will be calculated accordingly.

5.2. T YPES OF TRAY AND TRAY SIZING

In general, valve trays shall be used. Sieve trays may be used in fouling service.Tray columns will be specified with the following max. flooding factors at max specifiedload:

77 % for Vacuum Tower 82 % for other services65 to 75 % for column diameter under 900 mm

Tray hydraulic calculations and hence column diameter confirmation shall beperformed by the tray vendor. The following sizing criteria shall be recommended totray vendors.

5.2.1. Tray loading margin & flexibility

Required tray flexibility shall be 50 – 110 %, unless otherwise specified.

5.3. COLUMN INTERNALS, CONNECTIONS, HOLD-UPS, COLUMN HEIGHT

Thermowells shall usually be located at feed trays, side stream trays and trays for reboiler control and shall be installed in the vapour phase 200 mm (8”) below upper tray.

The minimum number of manholes to be installed is:

Head, bottom, feed, side streams.

In addition, depending on the service, the following table applies:

Service Additional Manhole location

Clean 1 manhole every 15 traysFouling 1 manhole every 10 traysSevere Fouling 1 manhole every 4 trays

and at any other tray where removable internals are located.

Hold-up times for sizing column bottoms shall be in accordance with the table in Annex1.


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6.VESSELS

6.1. T YPES OF VESSELS

Horizontal vessels shall be preferred for services with high liquid volumes, such ascolumn feed accumulators, recycle accumulators, liquid separators, etc. Verticalseparators shall be preferred when liquid flow-rate is low and vapour phase prevails, or when an accurate level control is required for reduced liquid flow-rates.

6.2. VESSEL SIZING

Vessels with proprietary internals may be considered, in such a case sizing will be inaccordance with vendor guarantee, otherwise the following guidelines shall be used.Vessel sizing will be performed as follows:

• The recommended hold-up times shall be in accordance with the table in Annex1.

• The diameter of horizontal vessels is defined, after calculating the volume tosatisfy normal hold-up time, by adding a height of 300 mm (12”) or 20 % of thediameter, whichever is larger, to the high liquid level, and a height of 300 mm(12”) minimum below the low level.

• Vessel length will normally be between 2 – 4 times vessel diameter.

• Vertical vessels shall be sized in order to keep vapour velocity sufficiently lowand facilitate the separation of the two phases, based on the "critical velocity".

• The installation of a high-high liquid level alarm shall be considered on thecompressor suction separators. If the high-high level alarm is not provided with ashutdown device, an additional 1 minute minimum will be allowed between thehigh level limit (HLL) and the bottom of the feed inlet nozzle. The same hold-uptime value will be provided for vessels with a low/low level alarm.

• For level position see also paragraph 9.


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7.EQUIPMENT NOZZLES

7.1. MINIMUM CONNECTION SIZE WILL BE

• 1” for flanged or welded connections.

7.2. NOZZLE SIZES

1¼”, 2½”, 3½”, 5”, 7”, 9”, 22”, and 26” shall be avoided.

7.3. SIZE OF MANHOLES:

• 20” (DN 500) nominal diameter for vessel diameter larger than 1 000 mm

• 18” (DN 450) nominal diameter for vessel diameter between 800 mm to1 000 mm.

For diameters smaller than 800 mm, a handhole will be provided unless a suitablenozzle for other service exists.

Size of internals shall also be taken in consideration in sizing manhole.

Drums will be provided with one manhole and a 6” ventilation nozzle on the oppositeside.

7.4. PREFERRED SIZE OF HANDHOLES

• 8” (DN 200) nominal diameter

They will be installed on vessel with diameter lower than 800 mm (one or twohandholes).

7.5. VENT, DRAIN, AND UTILITY CONNECTIONS FOR VESSELS SHALL BE SIZED AS FOLLOWS ANDPOSSIBLY LOCATED AT INLET /OUTLET LINES OF EQUIPMENT.

Volume of the vessel (m³) Vent size Drain size Utility connection (steam out) size

V ≤ 75 2” 2” 2”

75


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7.6. VESSEL INTERNALS

Liquid discharge nozzles shall be provided with vortex breakers in the following cases:

• connection to pump suction

• connection to reboiler inlet

• liquid draw-off from trays

• connection to control valve

Mist eliminator shall be installed whenever liquid droplets must be removed fromvapour to the maximum extent.


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8.HEAT EXCHANGERS

8.1. HEAT EXCHANGER T YPE AND ARRANGEMENT

TEMA “R” will be generally used for shell and tubes and hair pin heat exchangers.TEMA “C” can be used when acceptable.

8.1.1. In general, no overdesign shall be required for heat exchangers. As an exception,column reboilers, condensers and pumparound coolers shall have the sameoverdesign as the column itself.

For the design of expansion joints on fixed tube sheet heat exchangers, special

operating conditions not covered by TEMA shall be highlighted as a note in the processdata sheet.For heat exchangers in cyclic service, a specific note shall be added to the processdata sheet.

8.1.2. Exchanger with a shell side fouling factor greater than 0.000 35 °C·m²/W shall havesquare pitch. Triangular pitch shall be used for shell side fouling factor of 0.000 35 °C·m²/W or lower.

8.1.3. U tube exchanger can be used when tube side fouling factor is equal or lower than0.000 18 °C·m²/W and/or when required by the process service.

Exceptionally (Client agreement) U tubes can be provided with tapping for ChemicalCleaning in case of higher fouling factors values.Exceptionally (Client agreement) U tube exchanger can be used in cooling water service where tubes are to be Mechanically Cleaned by High Pressure Jetting.

8.1.4. Floating head type exchanger will be specified for fouling services on both sides.

Fixed tube sheet exchanger will be used for service when shell side fluid is not fouling(lower than 0.000 18 °C·m²/W) or when shell side fluid is fouling (0.000 35 °C·m²/W or lower) and fouling can be removed by Chemical Cleaning.

8.1.5. For plate and spiral heat exchanger, the fouling factor shall be according to

manufacturer experience. The overdesign of such equipment will be defined case bycase.

8.1.6. Tube bundle diameter and length shall be in accordance with T.E.M.A. standardrecommended dimensions.

For removable bundle the following limits apply:

Tube bundle diameter shall be 1 500 mm maximum.Tube length shall be 9 150 mm maximum.Exception can be considered for special cases i.e.:

- Kettle type diameter - Feed/Effluent exchanger length.


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8.1.7. TEMA Head type selection shall be performed following the criteria in Annex 3A or in Annex 3B.

8.2. AIR COOLERS

Air coolers induced draft type are not recommended for air outlet temperature over 80 °C.Normal tubes length is 9.14 m (30 ft). Maximum recommended tube length is 12.2 m(40 ft).50 % of fans equipped with auto-variable pitch control will be specified when processcontrol is required. Action on louvers is considered for specific cases.

8.3. FOULING FACTORS

Fouling factor are selected according to:

- TECHNIP experience or feed back- TEMA recommended figure- Licensor’s experience.


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9.EQUIPMENT LEVEL POSITIONS

The lower level control will be at a minimum of 300 mm from the bottom tangent line.

Unless otherwise specified by Process Licensor, the following alarm and cut-off settingwill be used:

HLCO from 1 to 2 minutes residence time between HLCO and HLL (*) (locatedabove HLL)

HLL at 100 % of the level controller range

HLA at 90 % of the level controller range

NLL at 50 % of the level controller range

LLA at 10 % of the level controller range

LLL at 0 % of the level controller range

LLCO from 1 to 2 minutes residence time between LLL and LLCO (*) locatedbelow LLL)

The trip connections will be independent from other instrument connections.

(*) Mini: 200 mm.


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10.PUMPS

10.1. PUMP SIZING CRITERIA

Pump design flowrates shall include a minimum of 10 % margin on max. operatingflowrate unless in the following cases:

- intermittent service- recirculation

for which design flowrate will equal operating one.

For reflux and pumparound pumps, design flow-rate shall be at least 120 % of operating flowrate.BFW pump shall be sized as per applicable code.Pump differential head indicated in the specification shall be calculated at designflow-rate.

Note: When a permanent recirculation flow for mini flow protection is installed,extra flow must be added to the net process flow.

10.2. SEALS

Pump seal minimum requirements for safety shall be according to the Table 10 – 1.

10.3. GENERAL RECOMMENDATIONS

• Positive displacement pumps shall normally be provided with a relief valve.

• Reciprocating pumps shall have pulsation dampeners on the suction anddischarge side whenever liquid pulsation is detrimental to process operation.

End of curve operation will be specified on pump data sheet for the following cases:

• pumps in auto start service (remote control, sequence activation, etc.)

• pumps without control valve at discharge

• pumps under level control• pumps in parallel operation.


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TABLE 10 – 1

SEAL TYPE SELECTION CRITERIA FROM SAFETY ASPECT

Category Example Seal Type

A - Fluids at temperature lower than flashpoint.

Fuel Oil Single seal with throttle bushing.

B - Fluids reaching a temperature lower than0 °C after expansion at atmosphericpressure.

LPG Unpressurised dual type safety seal withvessels vented to flare containing liquidantifreeze (as alternative solution a dry gasseal as a back-up seal can also be considered).

The vessel shall be equipped with low pressurealarms.(see Annex n. 18).

C - Fluids at temperature over flash point andlower than SIT (Self IgnitionTemperature), not belonging to categoryB.

Gasoline Single seal with lipseal graphoil packing,floating carbon bushing.

D - Fluids at temperature higher than SIT andlower than initial boiling point (IBP).

Unpressurised dual seals (as alternativesolution a dry gas seal as a back-up seal canalso be considered).

E - Fluids at temperature higher than SIT andIBP.

Pressurised dual seals.

F - Dangerous fluid:- where leakage cannot be tolerated.

Acid Pressurised dual seal, unpressurised dualseals, (as alternative solution a dry gas seal asa back-up seal can also be considered), or auxiliary shaft sealing devices.

G - H2S in fluid Pressurised dual.

H - Fluid which solid particles Single seal with external flush.


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11.COMPRESSORS

11.1. CENTRIFUGAL COMPRESSORS

A 5 % minimum margin will be assumed over the operating flow rate for eachcentrifugal compressor except recycle compressors in reaction loops that will have 0 %margin.

11.2. RECIPROCATING COMPRESSORS

Flow-rate control on process compressors shall have the following points of reference:

0 %, 50 %, & 100 %, or else in accordance with process requirements and number of cylinders per stage.Provide at least 10 % oversizing for pressure regulation in case recycle to suction sideis provided.Compressors on refrigeration cycle: thermal losses are generally not included in normalflowrate. They are included in rated flow.


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12.HEATERS

Design duty for process heater shall be:

- 110 % of normal duty or

- normal duty + 5 % of exchanger train duty upstream the heater

whichever is greater.


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13.MOTORS & TURBINES

13.1. ELECTRIC MOTOR SELECTION CRITERIA

Electric motors for centrifugal pumps shall be sized according to API, while taking thefollowing into account:

- for fluids with a specific weight ≤ 0.6 motor shall have sufficient power to operatewith water at minimum flow rate.

- motors with automatic start-up shall be indicated in the specification of the driven

machine.

- end-of-curve operation with rated impeller shall be considered when specified onpump data sheet.

Electric motors for centrifugal or reciprocating compressors shall be sized inaccordance to the applicable API code.

13.2. STEAM TURBINE SELECTION CRITERIA

Turbines shall be selected to cover all the operating points of the driven machine andwill meet API recommendations.

Back-pressure turbines shall be specified for discharging into closed system, but shallalso be checked for discharge to the atmosphere.


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14.LINE SIZING CRITERIA

14.1. LINE SIZING CRITERIA FOR LIQUIDS

PRESSURE DROPbar/kmSERVICE LINE SIZE

MAXIMUMVELOCITY

m/s Normal Max.

≤ 2” 0.6

3” – 10” 0.9

12” – 18” 1.2Pump suction, bubble point (1)

≥ 20” 1.5

0.6 0.9

≤ 2” 0.9

3” – 6” 1.2

8” – 18” 1.5Pump suction, subcooled

≥ 20” 1.8

2.3 3.5

Pump discharge: - P ≤ 50 barg 3.5 4.5

- P > 50 barg1.5 to 3 (8)

7.0 9.0

Gravity flow 0.6 (3) 0.25 0.45

≤ 2” 0.6Side-stream draw-off (2)

≥ 3” 0.9

0.6 0.9

Rich Amine, sour water, caustic soda 2.0 (9)

Cooling water (7): - sub-header 2.5 3.5

- main header 2.5

0.6 – 1.5 (4)

Sea Water 2 m/s min.2.5 to 3.5

Kerosene jet fuel (5) 3.0 (max)

Hot oil 1.0 (min)

Notes:

(1) Applicable to liquid containing dissolved gas.(2) Provide a vertical run of 3 metres minimum from nozzle, at nozzle size, before

reducing the size of the line.(3) Normal velocity.(4) To be analysed case by case.(5) 50 to 100 m upstream tank inlet or loading facilities, the velocity shall be reduced

to 1 m/s limit risks associated with static electricity.(6) Pressure Drops for liquid to thermosiphon reboiler are 0.2 – 0.4 bar/km to be

checked by heat exchanger section.(7) Use Hazen-Williams formula for calculation.(8) For off sites large lines velocity criteria can be increased

(9) Rich Amine velocity limitation to be set-up case by case


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14.2.GAS & VAPOURS

ρ

v² (max)Pa

Pressure Dropbar/km

MaximumVelocity

m/s

1. VACUUM SERVICE 4 % Abs. Press. Max. 90

2. COMPR. SUCT. 0.2 – 0.7 (2)

3. COMPR. DISCH. GAS 0.4 – 1.0 (2)(2)

4. STEAM (sub-headers)

a) 1 barg 0.4 – 1.0

b) 10 – 40 barg 1.0 – 2.0

c) > 40 barg

15 000

(5)

(3)

5. STEAM (long lines)

a) 1 barg 0.1 – 0.2

b, c) > 10 barg

15 000

0.2 – 1.0

(3)

6. KETTLE REBOILER OR NATURALCIRCULATION RETURN LINE

0.2 – 0.4 (4)

7. OVHD VAPOUR FROM STRIPPER 0.2 – 0.45 (4)

8. COLUMN OVHD (P ≥ atm) 15 000 0.3 – 0.6 (1)

9. COLUMN OVHD (vacuum) TOTAL = 5 mm Hg max 90

10. GAS LINES

P ≤ 20 barg 6 000

20<

P≤

50 barg7 500

50 80 barg 15 000

(4)

Notes:

(1) See figure in Annex 2(2) See figure in Annex 5(3) The following table applies to set the velocity:

STEAM CONDITIONSPIPE SIZE

SATURATED SUPERHEATED

10” 40 m/s 60 m/s

(4) For large diameter lines of over 300 mm, it should be verified that the followingvelocities are not exceeded:

Pressure (barg) Max. Velocity (m/s)0.1 or lower 60.0Up to 1.0 40.0Up to 2.5 30.0Up to 10.0 15.0

Up to 20.0 10.0Up to 40.0 7.0

(4) to be analysed case by case


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14.3.EROSIONAL SERVICES

14.3.1. Mixed phase

Pressure Dropbar/km

vm/s

1. MIXED PHASE CONDENSATES 0.2 – 0.3 10 – 20

2. REBOILER RETURN LINE (N ATURAL CIRCULATION) 0.2 – 0.4

3. P ARTIAL CONDENSER OUTLET 0.3 – 0.6

4. MIXED PHASES AT COMPRESSOR DELIVERY 0.4 – 1.0

Vertical and horizontal pipes should not be affected by slug flow.

In a first step, the following criteria can be used:vm = 10 to 23 m/s

2mmvρ = 5 000 to 10 000 Pa

(15 000 Pa Max)

where:

mρ= density of mixed phase

vm = velocity of mixed phase (equal to 10 to 23 m/s)

14.3.2. High velocity services

In offshore facilities piping handling gaseous and mixed phase (gas/vapour + liquid)streams, velocity shall be lower than the erosional velocity defined in API RP-14E/3,that is:

S

CVe =

Where:

Ve = ft/sS = lbs/ft³

C = refer to the following table

“C” VALUES

CONTINUOUS SERVICE

150 For high alloy/corrosion resistant material.

100For uniform corrosion with rates lower than 0.3 mm/a, or when acorrosion inhibitor is used.

80 For uniform corrosion with rates higher than 0.3 mm/a.

DISCONTINUOUS SERVICE

200 For all cases.


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Velocity shall be in any case lower than 50 m/s in continuous services except vacuumservices, while for discontinuous services (as safety valve discharges to flare) velocityshall be lower than:

- 0.75 MACH for individual users- 0.50 MACH for flare header.

In case of solid particle entrainement, limitations for discontinuous services shall beused.

14.3.3. Liquid and gas with solids

v

(m/s)1. Liquid + solids 1 ≤ v ≤ 3 (1)

2. Gas + solids (pneumatic conveying) 20 ≤ v ≤ 30 (1)

Notes:

1. For licensed plants, refer to Licensor requirements.


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15.SAFETY VALVES

15.1. T YPES OF SAFETY VALVE

Safety valves shall be generally balanced for discharge into closed systems andnot-balanced for discharge to the atmosphere.Lines filled with liquid which may be blocked-in between two isolation devices shall beprotected by safety valves for liquid expansion (see diagram Annex 4).

15.2. SAFETY VALVE SIZING

Safety valves shall be sized according to API-ASME standards and/or localregulation/codes.Use of T-size valves should be avoided.

For each safety valve, the applicable causes for relief and the resulting relief requirements shall be determined.The following general emergencies shall be considered separately, unless oneemergency will precipitate the other:

- Total cooling water failure- Total electricity failure - Partial electricity failure, that is failure of one cable or

transformer

- Steam failure, total or partial- Instrument power supply failure- External fire, for each probable fire area.

In particular, the following hypotheses shall be applied to determine vapour relief requirements for external fire exposure:

Flame height: 8 metres (from ground level or any grade at which a fire may besustained).

External insulation: (if per API RP-521):

Environment factor (F):

- 1.0 for not fire resistant insulated or for bare equipment.

- refer to formula (9) and table 5, API RP-521, for insulated equipment (insulationspecified as fire resistant).

Safety valve design temperature

Definition of safety valve (SV) design temperature:

A) "Hot" T: design T is SV inlet temperature during releasing or equipment

design temperature, whichever is greater.

B) "Cold" T: design T is SV outlet discharge T, or the protected equipment designtemperature, whichever is lower.


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Materials shall be selected according to design T.

Setting of single and multiple safety valves

Refer to API RP-520 or local regulations/codes.


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16.CONTROL VALVES

16.1. PRESSURE DROP

Unless established by process requirements, control valve pressure drop values shallbe calculated as the sum of the following two items, at normal flow rate:

a) 20 % of circuit pressure drop, excluding the valve

b) 10 % of the static pressure of the system which the circuit discharges into, for pressures up to 15 barg (220 psig); 1.5 barg (22 psig) for pressures from 15 barg

(220 psig) to 30 barg (440 psig); 5 % for pressures over 30 barg (440 psig)(unless the pressure of the system which the circuit discharges into is directlyconnected with the suction circuit, e.g. reflux pumps).

However, the following minimum values shall be specified at design flow rates:

- Control valves on liquid lines

A) If upstream and downstream pressure are interdependent: 10 % of circuitpressure drop, or 0.7 bar (10 psi), whichever is greater;

B) In all other cases: 5 % of pressure in discharge vessel, or 0.7 bar (10 psi).

- Control valves on gas lines: ∆Pmin = 0.2 bar (3 psi)

Control valves on reflux and recycle lines where static pressure variations influence thewhole circuit shall be sized according to the same minimum values.

The ∆P for the closed valve shall be preliminary assumed as being equal to upstreamdesign pressure, except for recycle lines such as reflux and recycle Hydrogen.

16.2. FLOW-RATE

As a general rule, control valves shall be specified for the following operatingconditions:

a) maximum flow rate: 110 % of max. operating flow rate or according to connectedequipment.

b) minimum flow rate: 50 % of minimum operating flow rate, in order to guaranteecorrect functioning at the extremes of the operating range.

Control valves shall also be checked in order that allowable noise levels are notexceeded.

16.3. CONTROL VALVE MATERIALS

Control valve materials shall be selected according to line materials, taking intoaccount valve operating conditions (flash).


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16.4.SEAT LEAK REQUIREMENT

All the control valves discharging to atm, flare, fuel gas or similar system must bespecified as tight shut-off (TSO) type (ANSI Class V for liquids, VI for gases).

Control valves in services other than the above shall be specified with a seat leakstandard.


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17.ANNEXES

1A) Hold up volumes for process drums

1B – C) Reference sketches

2) Allowable ∆P for Column OVHD

3A) TEMA Head type selection

3B) Selection of Exchanger TEMA Type

4) Rule for installation of thermal relief on piping

5) Recommended velocity for inlet/outlet lines of compressors.


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ANNEX N. 1A

HOLD UP VOLUMES FOR PROCESS DRUMS

HOLD UP VOLUME (whichever is larger )LEVEL EMERGENCYSPAN (note 2)

SERVICEREFERENCESKETCH

VESSELS TYPENORMALLY USED

LEVEL NORMALSPANHL – LL HHL – HL LL – LLL

REFLUX DRUM

- Liquid product to storage 1 Horizontal 5R or 2P note 3 1 (P + R)

- Liquid product to fractionator or to Unitwithout surge drum

2 Horizontal 5R or 10P note 3 1 (P + R)

- Vapour product 3 Horizontal 5R 1R

LIQUID SURGE DRUM

- Feed to Unit 4 Horizontal or vertical 10P 2P 2P

- Feed to critical equipment (furnace, column) 5 Horizontal or vertical 5P 2P 2P

VAPOUR / LIQUID SEPARATOR

- Compressor, suction - Vertical 2P (note 4) 2P -

- Refrigeration compressor, interstage - Vertical 3P (note 4) 2P -

- Process compressor, interstage:

- liquid to storage 6 Vertical 5P 2P

- liquid to fractionator 7 Vertical 5P 2P 2P

- Fuel gas KO drum - Vertical 5P (note 5) - -

- Steam gas KO drum - Vertical 5P (note 5) - -

- Steam drum (boiler) - Horizontal (note 6) - -

LIQUID / LIQUID SEPARATOR HorizontalTime required for separator (note 7)

- -

COLUMNS BOTTOMS

- Btms to Unit or heat recovery train 8 - 5P 2P 2P

- Btms to storage 8 - 2P 2P 2P

- Fired coil reboiler product draw off 9 - 5P - 2P

- Btms to fractionator manual level control 10 - 15P 1P 1P

- Fired coil preheater 11 - 5P to 10P 1P 1P

- Fired coil preheater product draw off 12 - 5 to 10 (F + P) 1 (F + P) 1 (F + R)

- Kettle type reboiler 13 -

• btms to unit - 10P - 2P

• btms to storage - 5P - 1P

- Min. hold-up in tar pot 14 -5 - 10 seconds onP (note 9)

- -

- Amine absorber - - 5P 2P 2P

- Amine stripper - - 5P (note 8) 2P 2P


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ANNEX N. 1A

HOLD UP VOLUMES FOR PROCESS DRUMS

Notes:

1. P = Liquid product (m³/min.)R = Reflux (m³/min.)F = Feed (m³/min.)

2. Above or below level control span, when HHL or LLL gives shutdown for flooding or emptying.

3. At least 2R or 1P (whichever is larger) before the flooding.

4. P is max. liquid flowrate or 10 % of vapour flowrate (whichever is larger).

5. P is max. liquid flowrate or a liquid volume equivalent to 3 m of feed pipe (whichever islarger) and however not less than 600 mm from BTL to the highest liquid level.

6. 2F or 1/3 of boiler volume.

7. or, for each liquid phase, 2P (product to storage) and 15P (product to fractionator)whichever is larger.

8. If the amine unit includes a surge tank with a hold up volume 15P min., the level normalspan can be reduced to 2P; otherwise the level normal span of the stripper btm is to bedesigned for 2 – 4 days of amine make-up.

Hold-up volumes for huge plants to be set-up case by case.

9. Without quench facilities.


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ANNEX N. 1B

REFERENCE SKETCHES


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ANNEX N. 1C

REFERENCE SKETCHES


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ANNEX N. 2

ALLOWABLE P FOR COLUMN OVHD

0.1

1

10

100

0.1 1 10∆P admissible bar/km

P

b a r a b s .


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ANNEX N. 3A

TEMA HEAD TYPE SELECTION

TEMA HEAD T YPE SELECTION

TEMA head type should be selected as follows for normal ranges pressures & temperatures:

Fouling Factors°C·m²/W

CleaningMethod (1)

Tube Side Shell Side

BundleType

Tube Shell

TEMA Head TypesStationary (2)

(Channel)

Rear

(Shell)

≤

0.000 18 All U-Tube — — A or B (3) —

C — A or B (3) —U-Tube

M (4) — A —

C C A or B (3) S or T (5, 6)

M C A S or T (5, 7)

C M A or B (3) S or T (5)

All

Removable

M M A S or T (5)

C C A, B or C (8) L, M or N (9, 10)

≤

0.000 35

≤ 0.000 35 FixedM C A L

U-Tube M (4) — A —

M A S or T (5) AllRemovable —

C A S or T (5)

0.000 35

≤ 0.000 35 Fixed — C A L

Notes:

(1) C - Chemical, M - Mechanical including High Pressure Water Jetting

(2) A - Head preferred when tube side or shell side CA 3 mm

(3) B - Head normally more economical

(4) Only used in cooling water service where tubes are to be cleaned by HighPressure Jetting

(5) Use S - Head unless T - Head is preferred

(6) Integral shell cover may be used with T - Rear when shell side fouling factor

≤ 0.000 35 °C·m²/W

(7) Integral shell cover may be used with T - Rear when shell side fouling factor

≤ 0.000 35 °C·m²/W and tube side to be cleaned by High Pressure Water Jetting

(8) B or C - Heads normally more economical than A - Head

(9) M or N - Heads normally more economical than L - Head

(10) L - Head preferred when tube side CA 3 mm


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ANNEX N. 3B

SELECTION OF EXCHANGER TEMA TYPE

FRONT HEAD SELECTION

Most common heads are the types A and B.Selection follows the next diagram.

NOTA:

* - If tubes side ≥ DP 150b, type D is selected whatever the other criterias.

* - For type N, see third diagram

A TYPE B TYPE

YES

NO

NO

START

YES YES

YES NO

NO

Dirty fluidon

tubes side

Tubes sidedesign pressure

≤ 60 bars

Channel nozzle

≤ 10”

Tubes sidedesign pressure

≤ 60 bars


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ANNEX N. 3B


SHELL SELECTION (Current uses)

NO

YES

E TYPE J TYPE X TYPE K TYPE J or X TYPEG or H

if requiredby licensor

NO

NO YES

YES

Very lowallowed

pressure drop inshell and low

operatingpressure

START

Large flow or low allowed

pressure dropin shell

Vaporized %

≤ 30%

Thermosiphonreboiler

(shell side)

NO YES


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ANNEX N. 3B


REAR HEAD TYPE SELECTION

(1) Feed/effluent for instance (hydrogenservices)

(2) * ∆T between tubes skin T° and

shell ≥ 50°F (YES)

* ∆T between tubes skin T° andshell


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ANNEX N. 4

RULE FOR INSTALLATION OF THERMAL RELIEF ON PIPING


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ANNEX N. 5

RECOMMENDED VELOCITY FOR INLET/OUTLET LINES OF COMPRESSORS

RECOMMENDED GAS VELOCITY

FOR LINES ATTACHED TO COMPRESSORS

10

100

G ( / ³)

G a s V e l o c i t y ( m / s )

1

2

3

Axial compressors: acceptable velocity in area delimited by lines 1 and 2.

Reciprocating and Centrifugal compressors: acceptable velocity in area delimited by lines 2 and 3.

1

2

3