2000: kaap converters: inspection, remediation, and

KAAP Converters: Inspection,Remediation, and Modification

The operating experience is discussed concerning two ammonia converters that experienced anincrease in pressure drop across the KAAP beds after startup.

Kenneth Blanchard, Steve Noe, and Ellis PlaxcoKellogg Brown & Root, Houston, TX 77001

Introduction

EHogg Brown & Root (KBR) designed andonstructed two 1850 MTPD ammonialants utilizing the proprietary KBR

Advanced Ammonia Process (KAAP) technology forFarmland MissChem Ltd. (FMCL) and PCS Nitrogen(PCS). Both facilities are located in Point Lisas,Trinidad and were commissioned in 1998.

After startup, the Ammonia Converters in both facil-ities experienced an increase in pressure drop acrossthe KAAP beds. The trend began at different times anddeveloped at different rates in each facility, whilekinetic performance remained stable for both plants.When the pressure drop reached levels that impactedplant capacity, each plant was shut down to inspect theconverter internals, remediate the cause of the pressuredrop, and make modifications as required to preventrecurrence.

The converters were shut down and inspected indi-vidually. All activities including inspection, catalysthandling, internals cleaning, and catalyst reloadingwere conducted under an inert environment. Severalscenarios of possible causes were developed and ana-lyzed, and inspection findings were consistent with one

of the potential scenarios. Modifications were imple-mented to address key issues associated with the exces-sive pressure drop.

Both plants are currently operating at design capaci-ty, and pressure drops across the ammonia convertersare within the design values.

Description of KAAP Ammonia Converter

The grassroots KAAP ammonia converter is a 4-bed,intercooled, radial-flow design as illustrated in Figure1. Bed No. 1 is a conventional magnetite catalyst bedand beds No. 2, No. 3, and No. 4 utilize KBR's propri-etary KAAP catalyst. The gas flow path through theconverter is generally downward, with feed enteringthe top head and the converter effluent exiting the bot-tom head.

Bed No. 1 utilizes a standard radial flow design. Thegas flows through the magnetite bed from outside toinside with the catalyst contained in an annular spaceformed by two concentric profile wire screen baskets.The gas exiting bed No. 1 is cooled against the con-verter effluent in a shell-and-tube heat exchanger cen-tered in bed No.l prior to entering bed No. 2, the firstof the three KAAP beds.

AMMONIA TECHNICAL MANUAL 284 2001

CONVERTERFEED

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BED#1IV1AGNETITECATALYST

BED #4KAAP

CATALYST

CONVERTEREFFLUENT

Figure 1. Grassroots KAAP ammonia converter.

During the KAAP development work, it was recog-nized that the unique properties of KAAP catalystrequired specific design considerations for a commer-cial-scale reactor. The small particle size, the low bulkdensity, and the relatively small bed volumes associat-ed with the high catalyst activity required considerationfrom both kinetic and hydraulic perspectives. In addi-tion to the sizing requirements, low flow zones had tobe eliminated throughout the catalyst bed to avoid hotspots. These design requirements led to development ofa patented radial flow bed design tailored specificallyfor the KAAP process, as shown in Figure 2.

The KAAP bed design is composed of three majorsections: freeboard, chute, and main bed. The freeboardsection is subdivided into two portions: a freeboard cat-alyst zone and a freeboard bypass zone, as shown inFigure 3. The purpose of the freeboard catalyst bed istwofold: to provide a hydraulic seal on the main bed toeliminate gas bypass and to provide a reservoir of cat-alyst for main bed filling as the initial charge compactsand settles over the life of the bed. The chute section isthe conduit, whereby freeboard catalyst is conveyed tothe main bed as settling occurs.

The unique design provides for 100% volume uti-lization of all catalyst loaded. Conventional radial bedsrequire a sealing volume and a settling volume abovethe "main" bed which are only partially effective sincethey are outside of (and parallel with) the main gasflow path. A KAAP bed, however, allows for full vol-ume utilization by placing the freeboard catalyst inseries flow with the main bed section. A portion of thefeed gas passes through the freeboard catalyst zone,mixes with the balance of feed gas from the freeboardbypass zone, and the combined gas stream then flowsthrough the main bed section. Increased gas bypassacross the top of the freeboard zone during catalyst set-tling therefore has little effect on bed performance,since all the gas continues to flow through the main bedsection below. By interconnecting the two beds via achute, the volume in the freeboard bed is available tothe main bed as needed, and all catalyst is fully utilizedthroughout the life of the bed.

Gas flows between beds via two downcomer pipesdischarging into a plenum chamber. The plenum feedsgas radially outward into a freeboard section, which isan integral part of the KAAP bed. Gas exiting the free-


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board is deflected up into the interbed space for mixingand temperature blending. From the interbed space, itpasses down to the main bed via an outer annulusformed by the converter shell and the outer basket. Thegas flows radially through the main beds from outsideto inside, with the catalyst contained in an annularspace formed by two concentric profile wire screenbaskets. After exiting beds No. 2 and No. 3, the syn-thesis gas is cooled against converter feed in shell-and-tube exchangers situated in the center of each bed.

Operation and Converter Performance

The FMCL and PCS plants were designed and con-structed simultaneously as near duplicate facilities.The plants achieved mechanical completion and werecommissioned in 1998, and each plant passed its per-formance test shortly after commissioning.

FMCL

During startup of the FMCL facility, pressure dropacross the KAAP converter was seen to be slightlygreater than expected. A plot giving the ratio of meas-ured to expected pressure drop vs. time is shown inFigure 4. During the commissioning and plant per-formance test, the pressure drop trended upward at arate so gradual that it was not immediately detected.

The plant performance test was successfully com-pleted on July 29, 1998, and operation continued, at orabove, nameplate capacity through summer and earlyfall. By November, the pressure drop had risen signifi-cantly and studies were begun to determine potentialcauses. Data gathered via plant DCS indicated theexcessive pressure drop was distributed in the flow cir-cuits for beds No. 2, No. 3, and No. 4. Although con-version across the reactor remained good, the continu-ing upward trend in pressure drop indicated that reduc-tions in capacity would eventually be required to avoiddamage to converter internals.

Based on a design review of the converter internals,it was determined that one of the bellows expansionjoints limited the allowable pressure drop across theconverter. FMCL was informed of these results andadvised to reduce plant capacity as required to staywithin this limitation. In mid-November 1998 the lim-itation was reached, and thereafter plant capacity was

gradually reduced until the shutdown and inspection inMarch 1999.

PCS

The test run for the PCS plant was successfully com-pleted on July 6, 1998. In contrast with the FMCLoperation, converter pressure drop during the earlystages of operation and the performance test was at, orslightly below expected, as shown in Figure 5. Theslight difference in pressure drop between the two reac-tors was noted but attributed to the differences in start-up history and operation between the two "duplicate"facilities. Throughout the commissioning and test run,the converter pressure drop showed essentially nochange, and operation continued in this fashion untilApril 1999.

During restart after a plant trip-out in mid April,high-temperature syngas was inadvertently introducedto the top of bed No. 2, bypassing bed No. 1 and theinternal heat exchanger. Immediately after this restart,pressure drop across the KAAP beds was seen to behigher than during earlier operation. Over the follow-ing days, a rate of increase in pressure drop signifi-cantly higher than the gradual increase seen at FMCLwas observed, although conversion and overall plantcapacity were still within design. KBR relayed to PCSthe limitation on converter pressure drop previouslydeveloped for FMCL, and in early May plant capacitywas reduced to stay within this limitation. Capacitywas gradually reduced until the shutdown and inspec-tion in July 1999.

Root Cause of Pressure Drop

The first commercial demonstration reactor utilizingKAAP catalyst was installed in 1992 as part of a plantexpansion project. The converter was inspected in 1996after about three years of operation. Circumstances ini-tiating the inspection were that magnetite catalyst hadleaked from an upstream converter and entered theKAAP reactor, plugging the main bed inlet distributorand profile wire screen basket and inducing high con-verter pressure drop.

During this inspection, the two grassroots KAAPreactors for FMCL and PCS were in the design stage.The bed designs in these reactors were geometrically


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similar to the beds in the first commercial unit, includ-ing an open face (no screen) at the inlet to the freeboardbypass zone. To prevent future instances of catalystleakage plugging a main bed inlet basket, the decisionwas made to add profile wire screen to the bypass zoneinlet. Figure 3 illustrates the freeboard design includingthe "new" bypass zone inlet screens.

Although calculations were made to confirm mini-mal impact on overall converter pressure drop whenthe new profile wire screen was added, the effects ongas distribution within the freeboard section were notfully recognized. The design of the freeboard outletdistributors sets the flow requirements through thebypass and catalyst zones; by design, the major flow isthrough the bypass zone with the remaining flow pass-ing through the freeboard catalyst bed.

In the original design the flow of gas through the"open" bypass zone inlet induced minimal pressuredrop, but the addition of the profile wire screen intro-duced a new restriction resulting in a small pressuredrop. Gas flow to the lower catalyst zone inlet screenswas correspondingly increased due to the gas redirec-tion away from the bypass zone inlet. The redistribu-tion of pressure drop was sufficient to reverse the lowdifferential pressure across the horizontal screen panelsfrom downward to upward. The upward differentialpressure resulted in gas upflow, which induced catalystfluidization.

From the initial startup of the two converters, flu-idization with catalyst milling was occurring and fineswere being generated and carried out of the freeboardbed. Based on the pressure drop vs. time plots shown inFigures 4 and 5, and observations made during con-verter inspections, a scenario was developed to explainthe differences in behavior between the two units.

Access to the KAAP beds requires that the horizon-tal screens be removed and reinstalled in the field aftercatalyst loading. The screen panels were specified aspart of the design to contain catalyst in the event offlow reversal and thus a seal fit at the screen supportrings was not required. Although the screen panels atboth sites were reinstalled per the fabrication drawingsafter catalyst loading, fitup of the panels appears tohave been better at PCS than at FMCL. The PCS bedsprobably had no gaps between panel sections orbetween panel sections and the support rings, which

would allow whole catalyst to escape. Therefore, atPCS, only the fines created by milling escaped thefreeboard and made their way into the main bed, wherethe pressure drop impact was minimal. During therestart in mid-April 1999, large thermal gradients dueto uneven heatup of the converter baskets likely creat-ed gaps in the horizontal screen panels which allowedwhole catalyst particles to escape and plug the down-stream main bed inlet baskets.

At FMCL, it is believed that gaps were left in thescreen panels after catalyst loading. These gaps, cou-pled with fluidization in the freeboard, allowed carry-over of whole catalyst particles to the main bed inletscreens from the initial converter startup, causing pro-gressive plugging of the baskets.

Analysts of Root Cause

CFD modeling

During the initial stages of analyzing the high pres-sure drop, the possibility of catalyst fluidization in thefreeboard bed was investigated by CFD modeling.FLUENT, a commercial CFD software, was used tomodel the freeboard bed sections of the converter.

Models of the original KAAP reactor (with no free-board bypass inlet screens) showed no tendency forupflow, consistent with the inspection observations inthe first commercial unit after 3 years of operation.CFD models of the same reactor with freeboard inletscreens added showed upflow in the freeboard bed.Models of the Trinidad reactors also confirmed upflow,consistent with the inspection findings.

Cold-flow modeling

To confirm the CFD modeling, a program was devel-oped to verify results of the CFD simulations using acold-flow model of a KAAP bed. A new cold-flow testunit based on a full-scale, 18 in. wide section of agrassroots converter bed was designed and constructedat the KBR Technology Development Center (KBRT-DC) at Park 10 in West Houston.

The cold-flow unit is shown in Figure 6. The modelincluded profile wire screens and distributors identicalto the commercial designs, except the new freeboardbypass zone inlet screen in question was made fully


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removable. Plexiglas windows were installed in thesides of the model to allow observation of catalystbehavior during operation. Nonimpregnated KAAPbase material was used to test catalyst behavior. Airwas used for the flowing medium, with flow rates set togive the same pressure profile as in the commercialunit. Openings with slide valves were installed in thebottom of the main bed to allow catalyst to be drainedunder flowing conditions to simulate main bed settlingand the resultant freeboard catalyst behavior corre-sponding to years of commercial operation.

Initially, the model was used to confirm fluidizationin the existing unit as predicted by CFD analysis. Testsboth with, and without, the freeboard bypass zone inletscreen confirmed the destabilizing effect of the newscreen. The model was then used to investigate poten-tial methods of stabilizing the freeboard bed.

KAAP Converter Enhancements

A key goal of the turnaround program at both plantswas to implement modifications to insure that the cata-lyst fluidization leading to carryover and plugging

would not reoccur. Two areas required addressing:(1) catalyst fluidization due to the added screens at

the freeboard bypass zone inlet; and(2) gaps in the horizontal screen panels which

allowed whole catalyst to be carried out of the free-board as a result of the fluidization.

Note the screen panel gaps could also pass catalystduring an upset with reverse flow, so resolution of thisissue would still be required even after eliminating thefluidization.

FMCL

Options for eliminating upflow were evaluated usingCFD and the cold flow model. For each option CFDruns were made for the range of freeboard catalyst lev-els from full to near empty. If the option appearedpromising, cold flow modeling was then used to con-firm stability of the bed surface over the range of cata-lyst levels.

Installation of solid plates in place of the existinghorizontal screen panels was selected as the most posi-tive means of preventing upflow and the simplest to

Freeboard OutletDistributor

Cover Plate (Solid)

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Bypass ZoneInlet Screen

Freeboard CatalystZone Inlet Screen

Figure 7. Solid plate retrofit option.


implement in the field. The solid plates simply blockthe gas upflow path causing the catalyst fluidization asshown in Figure 7. In addition, extra steps were takenduring installation to insure the new plates were com-pletely sealed around the perimeter and stiffened toprevent gas upflow and catalyst escape.

PCS

The FMCL converter was modified to stop the unin-tended gas upflow through the top horizontal screen.However, it was recognized that a design that forceddownflow through the existing screens would be moreeffective in establishing the intended flow patternthrough the freeboard. Work therefore continued afterthe FMCL turnaround on developing a more funda-mental approach for stabilizing the bed.

When the pressure drop began to climb at PCS, thesolid plate retrofit was initially planned to address thecatalyst fluidization and carryover. However, based onthe inspection findings at PCS and the mixed results for

bed No. 3 at FMCL (discussed later), the decision wasmade to implement an alternate modification plan toensure downflow through the existing horizontalscreens. The proposed modifications were fully inves-tigated via both CFD modeling and the cold flowmodel. From the test program, an enhanced freeboarddesign emerged that could be implemented readily inthe field under an inert environment.

The design enhancements focused on eliminating theupward pressure gradient across the horizontal screenswhile providing a reduction in total gas flow throughthe freeboard section. This was achieved by relocatingthe freeboard bypass zone to upstream of the freeboardinlet basket, thereby moving the bypass takeoff fromdownstream to upstream of the bypass zone inletscreen. The changes are shown in Figure 8.

The reconfiguration may be summarized in threeparts:

(1) An annular gap with the proper flow area was cutin the plenum dome around the exchanger outlet pipe.

(2) The holes in the freeboard bypass outlet distribu-

PLENUM DOME CUT-OUTW/SUPPORT RIHO

(NEW fa BYPASS ZONE)

Figure 8. Freeboard bypass modification option.


tor were blanked off.(3) The horizontal screen panels were reinstalled.The reconfiguration reduces gas flow through the

freeboard inlet screens, thereby reducing the hydraulicforces acting on the catalyst. By blanking off the holesin the bypass zone outlet distributor and reinstalling thehorizontal screen panels, all gas entering the freeboardbypass zone inlet screen is forced down through thehorizontal screen, thereby eliminating the potential forgas upflow.

The modifications were designed for easy fieldimplementation. Figure 8 highlights the conceptualchanges and key details of the enhancements.

Converter Remediation

Inspection philosophy, timing, and approach

Plans were developed with FMCL in November 1998to open and inspect the reactor. Arrangements weremade to mobilize catalyst handling subcontractor per-sonnel and equipment from the U.S. and to source N2

for reactor purging. A guiding philosophy for theinspection program was developed in conjunction withFMCL management:

(1) All work was to be performed in a safe manner.(2) Find and correct the cause of the high converter

pressure drop.(3) Minimize downtime consistent with the first two

objectives.The PCS inspection was mobilized after the FMCL

effort since the high pressure drop did not develop atPCS until the FMCL reactor had been returned to serv-ice for several weeks. The same logistical arrange-ments were made as had been done for FMCL, includ-ing mobilizing personnel and equipment from the U.S.The guiding philosophy behind the PCS inspectionprogram was the same as at FMCL - safety first.

Inspection activities for each bed followed the samegeneral sequence at both sites:

(1) Preliminary inspection for gross damage.(2) Bed isolation to permit work in adjacent beds

without chimney effect.(3) Detailed mechanical inspection.(4) Disassembly of the bed top closures to gain

access to the catalyst.

(5) Inspection of catalyst bed conditions and deter-mination of bed level.

(6) Catalyst removal by vacuuming with samplingduring removal.

(7) Basket cleaning.(8) Catalyst screening in enclosed, purged shelter

(simultaneous with step No. 7).(9) Bed mechanical modifications and catalyst

reloading.(10) Bed top closure reassembly.(11) Removal of bed isolation.

N'2 usage

Because catalyst activity showed no evidence ofdeterioration in either reactor, a major criteria of theinspection program was to maintain an inert environ-ment on the catalyst at all times to insure the activitywas not adversely affected by oxide contaminants. Inaddition to the catalyst preservation aspect, an inertatmosphere mitigated the safety risks inherent in han-dling the pyrophoric catalyst.

From the outset, the decision was made to keep theconverter fully inert throughout the duration of theturnaround, even after the catalyst was unloaded. Thiswas done primarily to eliminate the possibility of abreach in safety protocol by switching back and forthbetween inert and air environments, as the extendedshutdown and round-the-clock shifts could bring onfatigue and inattentiveness on the part of the subcon-tractor technicians.

Other uses of N2 during the inspection program

were:(1) As inert blanketing on the catalyst storage drums.(2) As purge on the fully enclosed shelter during cat-

alyst screening.(3) As purge on the screening equipment.(4) As motive gas for the drum vacuums during cata-

lyst removal (at FMCL).

Catalyst handling subcontractor staffingand protocol

A catalyst specialty subcontractor was retained for allcatalyst handling, inspection, and remediation activi-ties for both turnarounds. Specialized skills, training,


and life support equipment were needed for the inspec-tion and remediation work due to the continuous N2

purge present on the vessel and the catalyst.The vessel technicians operated under life support

equipment for all reactor entries and all catalyst han-dling activities at both sites. The equipment for eachtechnician consisted of enclosed helmets with primaryand backup air supplies, a communications line forcontact with supervisory personnel outside the reactorand at the life support monitoring console, and a tetherfor personnel extraction in the event of an emergency.Two technicians were able to work inside at each man-hole entry. A third technician in life support equipmentwas situated outside the reactor to provide workingassistance to the inside technicians and to provide res-cue assistance in the event of an emergency. The threeinert suited workers were linked together and to the lifesupport console supervisor via the communicationslink to facilitate direction of activities.

Converter preparation

Plate flanges and blinds were installed in the down-comer pipes below bed No. 1 to isolate the magnetitecatalyst from the KAAP bed inspection and cleaningactivities. These blinds were removed as the last step ofthe reactor closure after all KAAP-related activitieswere complete. Inflatable bladders were installed in theKAAP bed downcomer pipes to guard against chimneyeffects between access manways.

Inspection

Due to the inert atmosphere inside the reactor and thecatalyst screening tent, client and KBR personnel werenot able to participate directly in any activities involv-ing the reactor internals or the catalyst charge.Management of all inspection activities, includingobservation of internals condition and detailed direc-tion of subcontractor personnel, were conducted viaremote video equipment. Subcontractor vessel entrypersonnel were trained in the operation of the cameraequipment, and monitors were set up at grade for view-ing by KBR and client personnel. Direction of theinspection program was via the communications linkinside the technicians' life support helmets and head-

sets worn by the supervisory personnel stationed at thevideo monitors.

KBR assumed the lead role in directing the inspec-tion and client personnel were kept updated via dailybriefings, as well as frequent visits to the video moni-toring station. Overall direction, status, and goals foreach shift were discussed at shift change meetingschaired by KBR and attended by subcontractor super-visors.

The subcontractor technicians were directed by KBRthroughout each step. Because of the radial design withrelatively shallow bed depths and nested internal heatexchangers, some of the areas in the KAAP converterhave limited access. The inspection and cleanup effortrelied heavily on the remote video equipment, the useof which is as much art as science.

Inspection findings

Findings were generally consistent with expectationsand were very similar at the two sites. The outer profilewire screen baskets were plugged both vertically andcircumferentially with whole KAAP catalyst particlesand fines in all three KAAP beds. The holes in the mainbed distribution grid were largely clear. KAAP catalystwas also found in the bottom of the outer annulus, asexpected with catalyst carryover.

Gaps were found in the horizontal screen panels,both in the butt joints between adjacent panels and inthe joints between panels and the support rings. Thesegaps were sufficient to permit passage of whole cata-lyst due to fluidization of the freeboard catalyst. A fewhorizontal screen panel hold-down bolts were found tobe loose in both reactors, thereby creating additionalgap area for whole catalyst escape. Otherwise, nomechanical anomalies were found in any area of eitherof the two converters.

Catalyst removal

After initial inspection results confirmed that theouter baskets had been plugged by carryover of cata-lyst, the next step was to clean the baskets to eliminateflow restrictions. Since the only practical means ofcleaning the baskets was from the catalyst bed side, thecatalyst charge had to be removed from each KAAP


bed. Since the magnetite bed had previously been iso-lated via plate blinds installed in the downcomer pipes,bed No. 1 was not disturbed.

The catalyst was removed by vacuuming. Removalwas done using drum-top vacuums at FMCL and ahigh-capacity bulk removal system was used at PCS.All vacuuming equipment and the collected catalystwere kept under continuous N2 purge throughout the

removal process.

Catalyst screening

All catalyst removed from the reactor was screenedto minimize the effects of fines on reactor pressuredrop and gas distribution. A fully enclosed screeningshelter was built at both sites to house all screeningequipment and personnel in an inert environment forthe screening operation. This would protect personnelagainst any loss of N2 purge to a component of the

screening equipment or any accident involving drumhandling which could expose personnel to thepyrophoric catalyst as it oxidized.

N2 purging of the shelters and screening equipment

began several hours prior to commencement of screen-ing to purge the enclosure of all O2. The shelter envi-

ronment was monitored continuously during screeningto insure O2 levels were kept at less than 0.5%.

Catalyst drums were stored under cover to protectthem from the elements both before and after screen-ing. All drums were kept under continuous N2 blanket

via a system of manifolds and hoses.Access to the three KAAP beds is through a side

manway located above each bed. Therefore, the cata-lyst had to be transferred through the manways forloading. To facilitate this transfer, the catalyst wasloaded into plastic bags as it was discharged from thescreener. Double bags were used to minimize the riskof puncture and loss of catalyst, and bags were tied shutto minimize the risk of spillage. After each bag wasfilled, it was placed into the receiving drum and, aftereach receiving drum was filled, it was weighed andreconnected to the N2 purge header until ready for

loading. Weights of drums before and after screeningwere recorded and verified against unloading logsheets. This system permitted final reconciliation of

unloaded vs. reloaded catalyst.

Reactor screen cleaning

Following removal of the catalyst charge from thereactor, the screens were fully inspected from the inside(catalyst side) surfaces. When further inspections ofother (but not all) converter internals revealed no othersources of plugging, it was concluded that the source ofthe high pressure drop was the outer baskets and thatcleaning would be required to return the converter todesign performance.

Due to their construction, catalyst trapped in theannular spaces of the basket must be removed by backblowing from the catalyst side through the profile wirescreens. Material would be dislodged and carried out ofthe basket through the inlet distribution grid holes.

Prior testing had confirmed that the most effectivecleaning method was first to use CO2 pellet blasting to

break up the particles locked in the profile wire screengaps. The energy created by the shattering and vapor-ization of the CO2 pellet is transferred to the particles,

effectively breaking them up. Elimination of thisblockage then allows access to material in the annularspaces behind the gaps.

After clearing the profile wire screen gaps, the loosecatalyst behind the screens was removed by blowingwith high-pressure air. To deliver the air, an arc-shapedpipe manifold was constructed with a curvature con-forming to the outer basket inside diameter. Multipleholes were drilled in the manifold to discharge airtoward the basket surfaces and through the gaps in theprofile wire.

For both types of cleaning steps, the vessel entrytechnicians operated the equipment (CO2 nozzle or

blowing manifold) at the end of extension pipes. Eachof the cleaning steps were repeated several times to suf-ficiently clean the baskets.

Catalyst reloading

After completion of screen cleaning and final inspec-tion, the reactor was ready for reloading.

Drums were disconnected from the purge header andtransferred to the reactor only as they were required forimmediate loading. The drum purge pressure was rele-


ased at grade, and the drum to be loaded was lifted tothe scaffold platform by crane.

Catalyst bags were passed manually from the drumthrough the manway to an internal loading hopper posi-tioned above the bed. Regular outages were taken dur-ing loading and vibration was performed as required toinsure the targeted bed densities were reached.

Post-Turnaround Performance

FMCL

Restart of the FMCL plant proceeded smoothly andwithout incident. Upon restart of the converter, pres-sure drops in beds No. 2 and No. 4 were seen to be ontarget for the actual loop flow and composition.Pressure drop in bed No. 3, however, was higher thanexpected. Since the converter pressure drop was nolonger limiting, the plant moved into normal produc-

tion mode and is currently operating at nameplatecapacity.

After several months of operation including somebrief shutdowns and restarts, the pressure drop in bedNo. 3 has been relatively stable and we continue tomonitor it closely.

PCS

The PCS plant was restarted and production resumedon August 7, 1999. After the plant was stabilized, con-verter pressure drop was on target for all three beds.The intermediate pressure taps installed during theturnaround have permitted ongoing monitoring of dif-ferential pressures throughout beds No. 2, No. 3, andNo. 4, and all points analyzed are within calculated val-ues for the loop flow and composition.

Pressure drops for all three beds have been stablesince the restart. The plant is currently operating atslightly above nameplate capacity.

QUESTIONS AND ANSWERSAlexander More, British Sulphur Publishing: (1)

As I understand it, the reason you have to provide sucha large amount of spare catalyst in each KAAP stage ofthe KAAP converter is that the carbon support of theKAAP catalyst is gradually volatized by reaction withhydrogen. If that is indeed the case, can you tell me:what is the initial rate of carbon loss in relation to thetotal catalyst mass? Does it continue at the same ratethroughout the service life of the catalyst; and what isthe fate of the Ruthenium when it loses its support? (2)Is there any risk that cutting a hole in the roof thechamber will give rise to vibration?Kenneth Blanchard, Kellogg Brown & Root: (1) Aswas stated in the article, there is no excess catalyst

added in the KAAP beds. All of the catalyst loaded ineach KAAP bed is counted as active volume; there isno excess catalyst added for settling over the life of thebed. The catalyst does not disintegrate during operationdue to the hydrogen environment. Reactor operatingtemperatures are below the methanation temperature ofthe carbon support. The freeboard catalyst, which iscounted as active volume, is provided to fill in the mainbed settling as the particles orient and realign them-selves during operation. The catalyst is not volatilizedand it does not disappear. It simply compacts in themain bed. (2) As the picture shows, a reinforcing collarwas installed around the annular opening to guardagainst the possibility of vibration.


2000: kaap converters: inspection, remediation, and

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