Conversion of SulfinolSM to BASF’s aMDEA

7/24/2019 Conversion of SulfinolSM to BASFs aMDEA

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Conversion of SulfinolSM

to BASFs aMDEA

Incitec Pivot has converted the carbon dioxide (CO2) removal system in its Gibson Island

ammonia plant from SulfinolSM

to aMDEA

in early 2007. SulfinolSM

solution is a mixture of

DIPA (di-isopropanolamine), sulfolane (tetrahydrothiophene dioxide) and water. The SulfinolSM

system had been used for more than 35 years and a solvent change was needed to reduce ongoing

chemical costs of the ammonia plant.

The sequence of project implementation, challenges encountered in design, commissioning and

operation of BASFs aMDEA

system (activated methyl di-ethanol amine) is explained in detail in

this paper.

Venkat Pattabathula, Incitec Pivot LtdGibson Island, Brisbane, Australia

Dr. Torsten Katz

BASF East Asia Regional Headquarters Ltd., Hong Kong

Introduction

ncitec Pivot operates an ammonia plantoriginally of 600 mtpd, designed by J.F.

Pritchard, which has been upgraded to 800mtpd over the years since its commissioning in

the late sixties. The unique features of thisammonia plant are a low pressure (450 psig, 32

bar) front-end, a high-pressure back-end (2600psig, 182 bar), a medium pressure steam system

(400 psig, 28 bar, 750 F, 400 C), a closed looprefrigeration system and a jet engine that drives

a reaction turbine, which in turn drives thesynthesis gas (syngas) compressor. The site also

has a urea plant of Vulcan Cincinnati design,which has also been upgraded over the years to

about 850 mtpd. The urea prilling section was

replaced with a Hydro Agri (now Yara)fluidised bed granulation unit in 1999.

The plant is located at Gibson Island (GI) in the

suburbs of Brisbane City on the East Coast ofAustralia.

Background

In ammonia plants, the carbon dioxide (CO2)

removal section is a key part of the ammoniaplant front-end where CO2 from process gas isseparated to provide more pure hydrogen (H2)

and nitrogen (N2) for the ammonia synthesisreaction. The recovery of CO2 is also required

as a supply for the production of granular ureaand liquid CO2. The economics of the ammonia

plant heavily depends on the efficiency of

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solvent systems used for the removal of CO2from process gas. Over the last five decades,

there have been many industry innovations fromordinary water wash to potassium solutions to

primary, secondary and tertiary amines.

The SulfinolSMCO2removal solution consists of

sulfolane (tetrahydrothiophene dioxide) andDIPA (di-isopropanol amine) up to a total

concentration of 65% in the system. SulfinolSM

was the preferred solvent when the Gibson

Island (GI) ammonia plant was built in the latesixties.

The CO2 removal system at GI is a single stagelean/rich solvent system (Figure 1) that consists

of major unit operations such as an absorber,

stripper and several heat exchangers. The leanSulfinol

SM solvent is fed to the CO2 absorber

where CO2 in process gas is absorbed in

SulfinolSM solution to produce CO2 richsolution. The rich solution is sent to the CO2

stripper after exchanging heat with the leansolution from the stripper in the lean/rich

solution exchangers.

A HP flash drum was installed as part of earlier

plant upgrade to remove inert gases from the

solution. The lean solution is further cooledagainst cooling water (CW) where remainingheat is removed. This additional heat load on the

cooling tower consumes a significant amount ofcity water, which has special importance due to

water supply restrictions from Brisbane CityCouncil. The Sulfinol

SM solvent is circulated

between absorber and stripper by two parallelpumps and a third pump is standing by.

The ammonia plant has a SulfinolSM reclaimer

where degraded chemical product known asoxazolidone is removed through vacuumdistillation and the sludge is used to coat a

product to suppress dust in the granulation plant.About 6 tonnes per day of steam are used in the

reclaimer reboiler.

An arsenic based solution that acts as acorrosion inhibitor is added on weekly basis to

maintain its levels in the system. The SulfinolSM

system had been very reliable with corrosion-

free operation ever since arsenic was added tothe system. Antifoam was also injected on a

needs basis to deal with foaming issues in the

CO2 stripper and absorber. The Sulfinol

SM

chemical makeup rates were quite high due todegradation of the solution to oxazolidone and

the costs were on an increasing trend due tohigher chemical prices.

Many SulfinolSM

systems in natural gas plants

have changed over to aMDEA

solvent forcapacity increases and reduced chemical costs.

The GI plant could be one of the few NH3plants in the world operating with SulfinolSM.

Typical composition of Sulfinol

SM

solution:- DIPA: 50-55%; Sulfolane: 10-15%;

Oxazolidone: 10-15%; water: 20-25%.

aMDEAProcess Simulation andDesign

BASF carried out an initial simulation of the

CO2 removal section. The recommendedstrength of aMDEA

was 40 wt%. BASF

identified the need to replace the randompacking with structured packing in the CO2

stripper (D601), as it was very short (5 m or 17ft) compared to their earlier plant retrofits.

Sulzer performed design checks on the stripperinternals and supplied the new internals.

Orica Engineering Services were involved in the

initial design checks and prepared engineeringspecifications for the side stream filtration unit.

Lean solution pump (P604s) curves werechecked and found suitable for the aMDEA

conversion. The Stripper overhead reflux pump,

(P603s) curves were also checked & found to beadequate, but new valve trim was required for

the stripper reflux drum (T604) level controlvalve, LCV602A.

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BASF advised on the solvent piping stress-relieving requirements for aMDEA

system.

Fortunately, no stress relieving measures wererequired for using aMDEA.

Modifications to ExistingSulfinolSMSystem

The following changes were made to the CO2stripper:

1. Replacement of current random packingwith high efficiency structured packing

(Figure 2) of Sulzer Mellapakto

increase mass transfer efficiency and

capacity.

a. Bottom 11 layers, Mellapak170X for higher capacity (of that3 layers thicker sheet material for

added strength).b. Top 13 layers, Mellapak M2X

for higher efficiency.2. Replacement of liquid downcomers with

envelope type downcomers for top washtrays.

3. Replacement of the flash gallery (Figure3) to conform to BASF design

requirements.4. Replacement of the liquid distributor

(Figure 4) to improve liquid distributionin the column.

5. New support grid (Figure 5) that issuitable for structured packing.

6. Opening up of all bubble caps (Figure 6)on the wash trays: some caps previouslyhad been blanked off.

7. Installation of stiffening plates (Figure7) on two wash trays in order to prevent

any damage to the wash trays duringoperation. This had become necessary,

as the distance between the flash galleryand trays was only 300 mm versus an

optimum design of 500 mm.8. A new side stream filtration unit and an

improved antifoam dosing system werealso installed as part of the project. The

side stream filtration is a common

feature that is required for this type ofsolvent system. Since the new system

requires lower circulation rates withaMDEA

as compared with Sulfinol

SM,

most of the existing equipment was

adequate.9. Corrosion coupons in rich & lean

solution lines.

No changes were made to the absorbercolumn and its internals already had SS

random packing.

Risk Assessments and HAZOP Study

This project was justified based on the reducedchemical costs, and savings from cooling water

and steam.

All phases of this project posed risk - design,engineering and implementation. Poor

implementation could have resulted in delays tothe plant start up due to the extension of the

post-2007 shutdown period. These risks wereminimised by the following:

- Choosing BASFs aMDEA

process withmore than 200 plants in operation.

- The supplier of chemical plant internals forabsorption and desorption columns, Sulzer,

carried out design checks and also suggestedmodifications suitable for the GI application.

Sulzer has been a main vendor for many ofBASFs designed plants & retrofit applications.

- Orica Engineering Shared Services (OESS)

reviewed the BASF and Sulzer designs, and allother existing equipment. OESSs expertise in

the design review of the packed columns furthermitigated risks to the project.

- Design reviews, risk assessments and HAZOP

studies were carried out.



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- Visits were made to existing ammonia plantsin the US and Western Australia that have

successfully changed over their SulfinolSM

systems to aMDEA. The long operating

experience gained at these plants was applied to

GI design and implementation.

- BASF provided classroom training to all shiftoperating teams prior to shutdown where unit

operations of CO2 removal system werediscussed in detail.

- Based on BASF information, a comprehensivetraining package for the new aMDEA

system

was developed for the ammonia plant operators.

- Incitec Pivot laboratory was supplied with new

analytical procedures by BASF and discussionswere held with BASF regarding tests foraMDEA

strength and foam.

The Project schedule was as follows:

Capital approval: May 2006Detail design: June 2006

Order material: June 2006Delivery of material: December 2006

Installation & Commissioning:February/March 2007.

Pre-Commissioning/Commissioning

During shutting down of the plant, all the

SulfinolSMsolution was transferred to its storagetank, T605. Then, the system was flushed with

condensate (demin water) by circulating withthe lean solution pumps. First wash water was

recovered to use it in another plant and 2nd

washwater that had very low levels of SulfinolSMwas

drained to plant effluent system. To insure thathydrogen was removed from the SulfinolSM

solution, the solution was regenerated by usingthe auxiliary steam reboiler prior to draining to

storage tank.

All new internals for the CO2 stripper werechemically cleaned prior to shutdown by

submerging them into a 3 wt% caustic solutionin a warmed-up bath outside the plant. The

purpose of the chemical cleaning is to remove

manufacturing oils, which are responsible forfoaming of the amine solution. After thechemical cleaning, the internals were rinsed

with demin water and it was confirmed therewas no potential for foaming in the rinse water.

The old internals such as flash gallery, liquid

distributor and SS random packing (raschigrings) were removed and the vessel was

inspected. We observed heavy scale build up onthe CO2 stripper vessel walls and as much of it

as possible was removed within the maintenancewindow by chipping it from the vessel. Then the

vessel was cleaned.

Extensive scale build up was also noticed on thebubble caps of stripper top wash trays and they

were sandblasted prior to reinstallation (Figures8 and 9).

The tube bundles of process gas reboilers,

E602A/B were removed and hydro blasted andthe shells, which had Sulfinol

SMsludge deposits,

were flushed with demin water.

Also inspected were the CO2 absorber (D602),vapour lines from E602s/E678, tube sheets of

solvent/solvent exchangers (E604s) and D601solution outlet lines.

Old packing support clips were removed and

new shims were provided prior to theinstallation of new internals.

New internals were installed in the CO2 stripper

under the supervision of a Sulzer field engineer.This took about a week.

Once the unit was handed back from

maintenance, the system was flushed withdemin water twice to ensure that suspended



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solids & iron levels were within BASFrecommendations.

For commissioning, the system demin water

was first added to the system and circulation

was established after pressuring the CO2absorber with nitrogen. Then aMDEA wasadded to the water and solvent circulation was

established in early March 2007, well ahead ofgas introduction to the CO2 absorber while the

reformer and shift converters were being heatedup. Finally, process gas was introduced to the

absorber and the entire aMDEA system was

run for a week at reduced gas rates during

synthesis converter catalyst reduction.

The side stream filter was first commissionedwith 20-micron polypropylene cartridge filters

and then switched to 5-micron filters. About 10litres of antifoam were injected to the system as

an initial charge prior to gas feed.

Operating Experience

The ammonia plant was initially operated at 600

mtpd until all the catalysts were reduced. Noissues were observed with the aMDEA

system.

Plant rates were then raised to 740 mtpd for few

days where the system was steady and finally,the plant rates were raised to a maximum of

860-865 mtpd.

At about 860 mtpd carryover of aMDEA

solution was experienced from the CO2 stripperinto the top reflux drum and then into the urea

plant. It was brought under control by dosingantifoam. Initially, it was necessary to dose

antifoam almost every 2 hours. The systemstrength was about 38% and it was brought up

to 40% by adding more aMDEA. We then

started isolating the side stream filter during thedosing of antifoam. Both these conditions

helped us to reduce foaming.

Overall, the aMDEA system has been fairly

steady except for the need to dose slightly more

antifoam than was originally anticipated.Overall, there are more benefits than originally

envisaged from this change to aMDEA, such

as reduced solvent circulation rates, lowerregeneration heat load and reduced heat

rejection to cooling tower.

N2blanketing system

A new nitrogen blanketing system (Figure 10)was installed on aMDEAsolution storage tank,

as it was not there on the original SulfinolSM

solution tank. As part of this, a pressure

regulator in the N2 supply line, a pressure reliefcoupled with vacuum breaker and a rupture disc

in the old tank vent line were installed (Figure10). The anchor plates of the tank foundation

were reinforced with additional supports andthis has helped to improve tank safety and

integrity.

Operating procedures were also modified toensure that, during plant outages, only lean

aMDEAis transferred to the storage tank after

regeneration of solution.

Summary

SulfinolSM conversion to aMDEA was a

successful project that helped to reduce

operating costs of the Gibson Islandammonia plant.

Significant energy savings were achieved bynot using the 2 bar (30psig) steam auxiliaryreboiler (E678), and by complete isolation

of the old SulfinolSM reclaimer system that

consisted of a steam reboiler, condenser andsludge handling system.

Handling of heavy metals such as arsenicbased corrosion inhibitors have been

discontinued with aMDEA, as the system

no longer requires a corrosion inhibitor.

The water make up to the CO2 removalsection was reduced from 2 Tonnes/hr to

0.75 Tonnes/hr.



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The previous very frequent manual handling

of chemical drums is no longer required.

The aMDEA

makeup requirements are

quite negligible in comparison to the

SulfinolSM

system. The aMDEA

solvent circulation rates were

reduced by about 25% v/s SulfinolSM

and

hence, there are energy savings from

reduced heat load on the cooling tower and

also from the lean solvent pumps.

The CO2 removal system with aMDEA

will allow us to operate the plant as high as

900 mtpd provided we dont have any other

constraints in the plant. This will be a

significant benefit for the long-term

operation of the plant.

A systematic approach to process design,risk assessments, design reviews, hazop

study, shutdown plans for the installation of

new internals in the CO2 stripper, reference

plant visits, operator training, pre-

commissioning and commissioning of the

new system has paid off well. There were nomajor hiccups after change over of the

solvent.

Authors Acknowledgment

The authors acknowledge the support providedby Agrium Kenai Nitrogen Operations (Bill

Switzer etal), Alaska for having shared their

experience in converting SulfinolSM

to

aMDEA

.

Also thanks is given to Yaso Vesely and Terry

Moses of Sulzer, Govind Mudaliar of Orica, GI

ammonia plant operations, the maintenance,

project engineering and laboratory teams, and

GI 2007 Shutdown team, who were involved inthe successful completion of this project from

conceptual stage to commissioning.

Table 1. Physical properties SulfinolSM

v/s aMDEA

SulfinolSM

aMDEA

pH: 10.7 10.1

Density, gm/ml 1.064 1.055

Viscosity, cP 92 6.4

Boiling point

of water free amine

mixture, C (oF) 285 (545) 247 (477)

Combustible No NoFlammable No No



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Table 2. Operating conditions SulfinolSM

v/s aMDEA

SulfinolSM

aMDEA

Production mtpd 820 860Lean solvent

Circulation flow, 705 535Tonnes/hr

Lbs per hour x 1000 1,554.5 1,179.6

CO2 stripper, D601Overhead temp, C (F) 87 (188) 77 (170)

CO2 slip ppm, D602 200 130

CO2 stripper, D601 5.5 2

Reflux flow, Tonnes/hr

Water make up to 2 0.75aMDEA

system,

Tonnes/hr

Regeneration heat load 121 (114) 92 (87)GJ/hr (BTU/hr)



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Figure 1: Flow sheet of CO2 removal system

Figure 2. New structured packing and locating grid

Feedgas

Treated Gas

AbsorberC1

Lean SolutionCooler

E-605 A/B

Make-Up

Water

Lean SolutionPump

Acid Off-Gas

StripperC9

CondenserE-606

Reboiler

E-602 A/B E-678

Solvent/SolventHeat Exchanger

E-604 A/B

Flash Gas

hp flashC4

E-604 C/D/E/F



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Figure 3. New flash gallery

Figure 4. New liquid distributor in CO2 stripper



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Figure 5. New support grid for packing in stripper

Figure 6. Wash tray on top of CO2 stripper



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Figure 7. New stiffening plates on the bottom of wash trays

Figure 8. Scale build up on old bubble caps from old trays



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Figure 9. Bubble caps after sand blasting

Figure 10. Nitrogen blanketing system for aMDEAstorage tank


Documents

Conversion of SulfinolSM to BASF’s aMDEA