hydrogen optimization paper

8/12/2019 Hydrogen Optimization Paper

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Optimising hydrogen production and use

Hydrogen plays a criticalrole in the productionof clean fuels, and its

use has increased with theintroduction of low-sulphurgasoline and diesel fuels. Thereduction of benzene in gaso-line via benzene saturation willalso increase hydrogenconsumption, as will the trendtoward diesel cetane improve-ment and aromatics reduction.

Changes in marine fuel oil

specications are also expectedto increase hydrogen demand.In 2008, MARPOL Annex VIregulations were passed, settinga framework for regional andglobal specications on marinefuel oil quality. These regula-tions are expected to furtherincrease the demand for hydro-gen for desulphurising residualfuel oils and, through the

increase in distillate fueldemand, to replace residualfuel oil in marine fuels (seeFigure 1).

The overall reduction indemand for heavy fuel oils hasencouraged many reners toinstall bottoms upgradingcapacity such as delayed cokingunits. The streams produced bycoking typically contain higher

Kwee f hre pru sum press ehes, ssemsses press rs be evere pmse hre use

Ronald long, KatHy Picioccio alan ZagoRia

UOP LLC, A Honeywell Company

contaminant levels (sulphurand nitrogen) than the equiva-lent straight-run streams.Hydrotreating these cokerproducts has also increasedhydrogen consumption.

Hydrocracking has becomeincreasingly important forconverting heavier crude frac-tions into high-quality cleanfuels. Increased reliance onhydrocracking for clean fuelsproduction has also led to arise in hydrogen consumption.A hydrocracking unit is typi-cally the largest hydrogenconsumer in the renery, and

www.eptq.com PTQQ3 2011 1

3.0

5.0

4.0

2.0

1.0

2005 2010 2015 2020 2025 2030

Sulphur,wt%m

ax

0.0

ECA

Global

Global delayed

Fure 1 Bunker fuel oil sulphur specications

Catalyst

1%Utilities

15%

Hydrogen

84%

Fure 2 Typical hydrocrackeroperating costs


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2 PTQQ3 2011 www.eptq.com

ates signicant amounts ofcarbon dioxide (CO

2); the

production of 1 tonne of hydro-gen generates 812 tonnes ofCO

2. Future environmental

legislation may regulate theamount of CO

2 that can be

generated and may increase thecosts of hydrogen production.Availability of hydrogen is a

requirement for the productionof clean fuels, and demand forhydrogen is at an all time high.Anticipated future trends andregulations are expected tofurther increase hydrogenconsumption. At the same time,the production of additionalhydrogen is expected to becomemore expensive.

While it is well understoodthat the ability of a rener toproduce clean fuels depends onhaving sufcient hydrogen,what many reners recogniseis that optimum use of hydro-gen will maximise reneryprots.

Hre ewrk ss

mprvemesRenery hydrogen networkstypically interconnect manyproducers, consumers andpurication units with differentpressures, purities and operat-ing objectives. The networkgrows with each subsequentrenery project, modied inways that minimise complexityand the interruption of existing

units rather than for renery-wide optimisation. Hydrogenproduction costs andconstraints on availability aretypically much greater thanwhen the network was rstenvisioned. All of these factorslead to the conclusion that mostoperating hydrogen networksare not optimised for todaysenvironment not for the

hydrogen can account for morethan 80% of the units operat-ing cost (see Figure 2).

The quality of crude oil isgradually declining. Globally,crude API gravity is decliningand the sulphur content isgradually increasing (see Figure3). Both of these trends in crudequality will contribute toincreased hydrogen consump-tion during rening. The use ofsynthetic crudes derived fromoil sands and other unconven-

tional sources is expected toincrease to 2 million b/d by2020. These synthetic crudeswill require additional hydro-gen to be rened into usableproducts.

One of the major sources ofhydrogen and gasoline pooloctane is the catalytic reformer.The blending of ethanol hasreduced the octane require-

ments from other reneryproduct streams to maintainthe gasoline pool octane; often,reners respond to this situa-tion by reducing the catalyticreformers severity to producea lower-octane reformate prod-uct. However, a lower catalyticreformer severity typicallyproduces less hydrogen. Lowerhydrogen production from a

lower severity operation is inopposition to the increaseddemand for hydrogen in therest of the renery and compelsthe rener to obtain hydrogenfrom other sources. Some ren-ers have decided to operatetheir catalytic reformer forhydrogen production and toler-ate some octane giveaway inthe gasoline pool.

Many reners produce orpurchase hydrogen to have asufcient supply available for

their renery. The steamreforming (SR) process is usedto produce most of the addi-tional hydrogen required byreners. The cost of thehydrogen produced is directlyproportional to the feed costs.In the US, most of the hydro-gen is produced in steammethane reforming (SMR) unitsand the cost is typically tied to

the price of natural gas.The production of hydrogen

by a steam reformer requiressignicant energy; one tonne ofhydrogen produced requires3.5 to 4 tonnes of hydrocarbonsas feed and fuel. Hydrogenproduction can account for upto 20% of renery energyconsumption. Additionally, theproduction of hydrogen gener-

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Fure 3 Global crude quality


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minimal cost of hydrogenproduction, nor for maximisedrenery margins.

opms he hreewrkIn many hydrogen optimisation

schemes, it often occurs that thegreater the number of degreesof freedom, the largerthe improvement that is possi-

ble. The most successfulprogrammes for improving thehydrogen network draw thelargest possible envelope andtake advantage of all theknobs that are available toturn, including network connec-tivity, increased hydrogenproduction capacity, targethydrogen partial pressures,process changes in producersand consumers, catalysts, oper-ating procedures, revamped andnew purication capacity, pres-sure swing absorption (PSA)unit feed to product bypass,feed to hydrogen plant,compressor modications, abil-ity of LP models to accurately

represent hydrogen availabilityconstraints, and header pressurecontrol system improvements.

For the optimisation ofhydrogen use, the benets aredriven by identifying and alle-viating critical constraints inthe renery-wide hydrogennetwork. Every renery isdifferent and, from time totime, the active constraints in a

renery can change with differ-ent crudes or operatingobjectives. A renery networkmay be constrained by totalmoles of hydrogen available,hydrogen purity, hydraulics,purier capacity, compression,H

2S scrubbing, fuel system

constraints or other renery-specic issues.

What is ultimately constrained


is a renerys protability.When there is insufcient quan-tity or purity of hydrogen,charge rates, the processing ofmore difcult feeds or productquality are limited and renerymargins are reduced. When

sufcient hydrogen is available,the effect of inefciencies ishigher operating (hydrogenproduction) costs.

Hre pressperfrmeHydrogen has a signicanteffect on process performanceand protability. Hydrogenpartial pressure, a variablecompletely under theoperators control, can beutilised to increase catalyst lifein hydroprocessing units,increase throughput, increaseconversion, improve productquality, or process more prot-able feeds. The potential

benets of affecting reneryprotability through hydrogenmanagement are much greaterthan those from simply reduc-

ing hydrogen production orpurchase costs. Of course, the

benets must be considered inconcert with the capital andoperating costs of increasingthe hydrogen partial pressurein order to determine the mostprotable targets.

Establishing and faithfullymaintaining the target hydro-gen recycle purity of key

hydroprocessing units is animportant component of effec-tive hydrogen management.For reners who want tomaximise the effectiveness oftheir hydrogen network, furtheroptimisation is possible whentargets for recycle hydrogenpurity are modied throughmajor operating changes, suchas variation in charge rate, feed

properties and severity. Themeasured variable that repre-sents hydrogen partial pressureis recycle purity. Make-uppurity and purge rate can bothaffect the hydrogen partialpressure, but they do not deter-

mine it.

Essee f hre ewrkpmsThe rst step in improving thehydrogen network is to clarifythe objective. The objectiveshould always be overall ren-ery protability rather thanhydrogen production costs.Operating costs, capital costsand renery margins are allpart of the picture.

At a high level, the process ofhydrogen network optimisationis: Identify the constraint that ismost limiting protability Identify ways to alleviate theconstraint and select the mostcost-effective approach.Consider all the options listedabove. Many improvements

can be implemented quicklywithout capital projects. Repeat these steps until aconstraint is reached that cannot be cost-effectively relaxedor alleviated Utilising a broad range oftools makes comprehensiveoptimisation possible.

ts

newrk ssHydrogen network pinch anal-ysis is a valuable analyticalmethod to identify the theoreti-cal minimum hydrogenrequirements for a givennetwork through unconstrainedmodication and connectivity(including turning hydrogenrecycle units into once-throughand cascading the purge to


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For example, in the designwork for a major new reneryfor Petrobras, we had full free-dom to route and recoverstreams, since design pressuresand make-up purities were notyet xed. We set the separator

pressure of one hydrotreatersuch that the ash gas could besent to the suction of the make-up compressor of anotherhydrotreater and the revisedmake-up hydrogen puritycould be taken into account inthe design of the consumingunit. The ash drum in anotherunit was set at a pressure suchthat its ash gas could easily

be puried and recovered in anexisting PSA unit.

Given that no external fuelcould be purchased for thisrenery, the fuel balance wasnot only critical from aneconomic standpoint but itdetermined the feed selectionfor the hydrogen plant. In ourearly estimates, we expectedthat an internally generatedLPG stream would have to be

burned to meet the fuelbalance. After energy optimisa-tion of the preliminary design,the fuel gas balance shifted topositive, and we were able toutilise lower-value fuel gas ashydrogen plant feed. As anadditional benet, we couldisolate hydrogen-rich fuel gasstreams and utilise them ashydrogen plant feed. Not only

is fuel gas less valuable thanLPG, but the hydrogen contentenables a signicant reductionin ring and energy consump-tion in the hydrogen plantfurnace compared to otherhydrocarbon feeds.

opms be hehre ewrkBroadening the optimisation


another unit). It provides atarget and a pinch purity thatcan guide the analyst inproposing changes to the exist-ing network. However, pinchanalysis is limited in a numberof ways. Its key limitations are

that it is not concerned withthe pressures of sources andsinks, it treats all light hydro-carbon components the same(in reality, methane has a muchgreater tendency to build up inthe recycle loop than propane),it does not consider the signi-cant effects on compressors andhydraulics of changing ahydrogen recycle hydroprocess-ing unit into a once-throughunit, nor does it considersulphur levels.

To evaluate potential networkimprovements, a detailed ren-ery-wide model of thehydrogen network should beemployed. One of the criticalfeatures of this model (asopposed to a spreadsheetmodel) is that it simulates thenon-linear relationships

between charge rate, make-uprate, make-up purity, and recy-cle purity (hydrogen partialpressure) and purge rate. Withthis model, potential modica-tions can be tested, such aschanging make-up source, trad-ing off purity against recoveryin an existing purier, addingnew purication, or changingthe target hydrogen partial

pressure in a hydrogen-consuming process unit. Thesame model can be used by therener for operations andproject planning.

Press pur mesProcess models of catalyticreformers enable the analyst tounderstand the effects of oper-ating, mechanical or catalyst

changes on hydrogen yield andpurity.

The hydrogen network modelpredicts the effect of changinga hydrogen consuming unitstarget recycle purity on therequired make-up and purge

rates. A hydroprocessing modelwill predict the effect of chang-ing the hydrogen partialpressure on processperformance (catalyst life,product quality, conversion)and hydrogen consumption.

Purier (PSA and membrane)models are used to predict theimpact of changing a puriersfeed composition and operatingconditions on hydrogen productpurity and recovery. Thesemodels are also used to identifythe potential for debottleneck-ing existing puriers.

Reer emsThe right question to ask is notHow much money am Ispending on hydrogen?, butAm I utilising the rightamount of hydrogen to maxim-

ise my renery margin? Withthe addition of a reneryeconomic model to the toolkit,the analyst can consider howthe addition of lower-value,more difcult feeds affecthydrogen consumption, desiredhydrogen partial pressures, thehydrogen network and renerymargins.

des-phse fu pmsWe have had the opportunity tooptimise grassroots reneries

before individual process unitdesign bases are set. When weoptimise at this stage of aproject, all parameters are avail-able for optimisation and wecan be that much more effectivein minimising capital and opti-mising renery margins.


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envelope even further, it ispossible to consider optimisingmore than just the hydrogensystem at one time. There areoften additional benets whenseveral systems are optimisedtogether. For example, whendesigning a rening complexwith new catalytic reformingand hydrocracking units, it is

possible to consider the hydro-gen and LPG recovery systemsat the same time. As standalonedesigns, each unit would haveits own LPG recovery systemand produce moderate- purityhydrogen to be puried/recov-ered (reformer net gas andhydrocracker ash gas). Thereformer net gas contains therecoverable LPG and hydrogen,

while the recoverable hydrogenand LPG are found in the purgeand ash gas streams of thehydrocracker.

LPG recovery is much moreefcient in the hydrocrackerthan in the reformer becausethe gas stream has a lowerhydrogen concentration. Also,it is more cost effective to proc-ess both hydrogen streams in


one PSA unit. It is possible tointegrate the two systemstogether by designing a singlePSA unit that takes both hydro-gen streams as its feed andsending the PSA unit tail gas tothe LPG recovery system in thehydrocracker. Since the PSAunit concentrates LPG in thetail gas, recovering the LPG

from the tail gas in the hydroc-racker recovery system requiresless energy and capital than ifit was recovered separately inthe reformer. An additional

benet of the integration is thata PSA unit product bypass cannow be integrated with thehydrocracker to enable optimi-sation of the hydrocrackermake-up purity a degree of

freedom that would not other-wise exist.

Hre ewrkmprvemesThe potential for improvinghydrogen efciency is esti-mated by evaluating thehydrogen-containing streamscurrently going to fuel, areand hydrogen plant feed. The

Capital project

66%

No/low cost

34%

Other

operations

15%

Catalyst

2%

Other

25%

H2partial

pressure

12%

Purification

38%

Control

improvements

3%

Change

flow piping

5%

Fure 4 tp resus: summr f bees ws $137 m/ seve sues

potential nancial benets willalso be a function of the valueof hydrogen in a renery. Thepotential benet of improve-ments in process performancethrough hydrogen optimisationcan be estimated roughly byevaluating current constraintsto process performance, ren-ery drivers and renery

economics. Our hydrogenmanagement studies generallyidentify $2 million to $20million in annual benets.

In seven studies, UOP identi-ed a total of $137 million inannual benets. A third of theopportunities identied wereno/low-cost changes and theremainder required capitalprojects (all with a simple

payback of less than two years).While 38% of the opportunitiesfor improvement came fromadding or improving hydrogenpurication capacity, a much

broader scope of evaluation isrequired to achieve these bene-ts. Operating changes and

better management of hydro-gen partial pressure targetswere important, as well as


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valves so that the reactor oper-ating pressure can be increased

by 5%, enabling an increase inhydrogen partial pressure.

ops fr hre rever pur

In the rening industry, high-purity hydrogen can improvethe performance of hydro-processing units (hydrotreatersand hydrocrackers) by increas-ing the recycle gas purity andthe hydrogen partial pressurein these units.

In existing hydroprocessingunits, the use of high-purityhydrogen to increase the reac-tor sections hydrogen partial

pressure can deliver the follow-ing benets: Reduce the quantity of make-up gas required Enable the processing ofmore feed Provide the ability to processmore difcult feeds

Improve product quality,especially distillates Increase catalyst life Reduce the quantity of purgegas required to maintain recy-cle gas purity Debottleneck existing make-up gas compressors.

The design of a new hydro-processing unit can benet inthe following ways from a


many other issues. Some of theimprovements found in theseseven studies include: Operators adjusting the PSAcapacity factor to improvehydrogen recovery Addition of a new purica-

tion unit Cascading the purge from anisomerisation unit to the make-up of another unit Reducing the make-up purityof a hydrocracking unit toreduce hydrogen puricationlosses, while still meeting theminimum hydrogen partialpressure target Increasing the make-uppurity to a diesel hydrotreating

unit to improve processperformance Changing feed streams to anexisting membrane purier toobtain more efcientpurication Sending a hydrogen streamof moderate purity to hydrogen

plant feed rather than fuel,reducing the operating costs ofthe hydrogen plant Modifying a compressor toeliminate hydrogen leakingthrough the seals to are.(Wasting hydrogen to are ismuch more costly than wastinghydrogen to fuel.) Replacing pressure safetyvalves with pilot-operated

higher hydrogen partial pres-sure through the use ofhigh-purity hydrogen as themake-up gas: Reduced capital cost (fromlower total plant pressure,smaller make-up gas compres-

sors, smaller recycle gascompressor, smaller reactorsand less catalyst.) Reduced power and fuelrequirements.

imprve se pruquThere are various technologyoptions for the production ofhigh- purity hydrogen byrecovering hydrogen fromlower-purity streams. Themajor technologies used forhydrogen recovery and puri-cation are PSA and membranes.A few hydrogen cold boxeshave been constructed, but theyare only warranted whenrecovery of a valuable liquidproduct is required. Selectionof technology will be guided

by the specic application.

Table 1 is a guide to selectingbetween PSA and membranetechnologies for hydrogenrecovery and purication.

The UOP Polybed PSASystem is a cyclical process inwhich the impurities in ahydrogen-containing streamare adsorbed at high pressureand subsequently rejected atlow pressure. The hydrogen

produced is at just slightlybelow the feed pressure and istypically upgraded to 99.9+%purity, with hydrogen recover-ies of 6090+%. The PolybedPSA System operates as a batchprocess. Multiple adsorbersoperating in a staggeredsequence are used to produceconstant feed, product and tailgas ows. The vast majority of

Vrbe Pbe PSa Psep MembreProduct purity 9999.999 mol% Up to 98 mol%

Remove CO2, H

2S, H

2O

High product pressure

Economy of scale

Feed pressure 1000 psi

Feed H2 Preferred >50 mol% Preferred >70 mol% Min. 15%

H2recovery 7090% 7097%

Ease of expansion Easy Very easy

cmpr pur ehes

tbe 1


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Polybed PSA Systems havebeen in hydrogen service. Theeconomic justication for a PSAunit will depend on the hydro-gen content of the feed streamand the how the rener valueschemical hydrogen versus

hydrogen as a fuel. Generallythe following rules apply: Hydrogen feed concentra-tions >55% are easilyeconomically justied Between 40 and 50% hydro-gen can be economicallyupgraded dependent on site-specic requirements Below 40% hydrogen,economics become more dif-cult to justify.

The UOP Polysep MembraneSystem separates a gas mixture

by the differences in permeationrates of various gases throughthe polymeric membrane. Themore permeable gas (hydrogen)is enriched on the permeate sideof the membrane, while the lesspermeable gas enriches on thefeed side of the membrane. Themembrane separation of these

gases is a pressure-driven proc-ess and requires a high feedpressure. The hydrogen productstream (permeate) is producedat a lower pressure by taking apressure drop across themembrane. The non-permeatestream is available at essentiallyfeed pressure. The membraneprocess is continuous andproduces permeate and non-

permeate streams at constantow, pressure and purity.

The membrane process is themost economical process forhigh- pressure purge gasupgrading. The membranesystem is normally designed toproduce hydrogen at 300600psig, 9298 vol% purity and 8595% hydrogen recovery. Theproduct delivery pressure is

chosen to allow the product toenter one of the stages of themake-up hydrogen compressors.

In addition to adding a newPSA or membrane unit, thereare often opportunities toimprove the performance of

existing units. PSA andmembrane units are oftenrevamped to increase hydrogenproduction, recovery and/orpurity. These revamps can be assimple as replacing adsorbentsor as complex as adding addi-tional equipment. Frequently,reners elect to perform therevamps in phases, where eachphase adds additional capacity.The following are examples ofrevamps conducted by renersin North America.

cse su 1: srbe reA major North Americanrener started up a plant withtwo identical steam reformerPolybed PSA-based hydrogenunits, each with a productcapacity of 27.5 million scfdand a third Polybed PSA unit

to upgrade net gas from a UOPCCR Platforming Process unitwith a product capacity of 28.3million scfd. The producthydrogen from the three PSAunits was combined and usedas the make-up hydrogen to ahydrocracker.

The rener wanted to processmore crude and, therefore, thedemand for hydrogen

increased. The CCR Platformingunits net gas purity wasgreater than 90% hydrogen andwas deemed acceptable fordirect feed to the hydrocrackerwhen blended with high-purityhydrogen from the PSA unit.Re-routing the net gas from thePSA unit to the hydrocrackerreduced hydrogen loss to thePSA units tail gas but, more

importantly, it freed up thisPSA unit for other uses.

First, the PSA units weremodied in a number of stages.The rener debottlenecked thetwo steam reformers, whichwere then producing over 20%

more raw hydrogen than wasoriginally intended. The CCRPSA unit (that is, the PSA unitprocessing net gas from theCCR Platforming unit) wasrevamped by changing the soft-ware and design conditions toallow it to operate on SMR gasin parallel with the original twoSMR PSA units. The adsorbentin the CCR PSA unit was,however, far from optimum forservice on SMR gas. The threePSA units could easily handlethe amount of ow. Sincecapacity was not a problem, astudy was made with the objec-tive of increasing the amountof hydrogen recovered.

The adsorbent in the PSAunit originally treating the CCRPlatforming net gas wasreplaced with adsorbent opti-

mised for SMR gas. This wasdone in conjunction with therst set of vessel inspections,and the PSA units were

balanced and optimised for therevised ow scheme. Thehydrogen recovery in this PSAunit increased by over 6% andsimultaneously resulted in animproved CO specication onthe product hydrogen.

The next vessel inspectionwas of one of the SMR PSAunits. For the inspection, theadsorbent was again vacuumedfrom the vessel through the topange (manway) and thenscreened and replaced in itsoriginal position. About 15% ofthe adsorbent was lost duringthis procedure due to screeninglosses and interface losses



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between adsorbent layers. Thispresented an opportunity toreplace the existing adsorbentwith higher-performanceadsorbent to provide higherrecovery and capacity.

After reloading with higher-performance adsorbents, thepreviously identical PSA1 andPSA2 units for their respectiveSMR units were in operation

side-by-side with advancedand original adsorbents inservice. PSA1 demonstrated acapacity increase of 10% overthe original adsorbent (stillinstalled in PSA2) as well as a2% increase in hydrogenrecovery.

Figure 5 shows these

improvements as trendsrecorded by the distributedcontrol system. The newadsorbents in PSA1 enabled itto produce more hydrogenfrom the same or less feed.

cse su 2: phse revmpsA large residuum desulphuri-sation (RDS) facility in theAmericas was designed using

hydrogen make-up from asteam reformer hydrogen plantwith a product ow of 55million scfd. The hydrogenplant employed a large ten-bedPSA unit that removed essen-tially all impurities, includingnitrogen, from the steamreformers efuent.

Phse 1As designed, the feed gas tothe steam reformer waspredominantly natural gas, andsupplemental feed was derivedfrom the high-pressure ventand the low-pressure ash

gases of the RDS unit. Thehigh-pressure vent gas wasscrubbed of H

2S and throttled

down to the steam reformersfeed pressure, and the low-pressure vent was compressedto match the steam reformersfeed pressure. Figure 6 showsthe overall ow scheme.

Various revamps have takenplace to meet the renerysincreasing needs for hydrogenover the years (see Table 2).

Phse 2: rs revmp f semrefrmer PSaThe rst plant expansion sawtotal hydrogen productionincreased from 55 million scfdto 70 million scfd. The initialcapacity increase was achievedthrough debottlenecking of thesteam reformer and SMR PSA

unit to increase hydrogenoutput by 18% from 55 millionscfd to 65 million scfd. TheSMR PSA units debottleneck-ing was achieved through aprocess redesign and changesto the control system software,with essentially no hardwaremodications. Reducing the


Steam

reformer PSA ARDS

Fure 6 Case study 2: original ow scheme

30

50

45

40

35

25

20

15

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1 5 9 13 17 21 1 5 9 113 7 11 15 19 23 3 7

MM

SCFD

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Fure 5Comparison of two identical PSA units loaded with different adsorbents


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sending the tail gas to the ren-ery fuel system. This new PSAunit, processing net gas fromthe CCR Platforming unit,added 50 million scfd to thehydrogen balance. Five yearslater, this unit was revamped(see Phase 5).

Phse 4: se revmp fsemrefrmer PSa uA second revamp took place tofurther increase the capacity ofthe steam reformer and itsassociated PSA unit from 65million scfd to 85 million scfd.This additional debottleneckingrequired modications to many

number of pressure equalisa-tions enabled the unit toprocess a much higher feedrate with a small decrease inhydrogen recovery, while stillmaintaining design productpurity. This increase in feed

capacity more than compen-sated for the small decrease inhydrogen recovery; the netresult was an increase in hydro-gen production by 18%.

The high-pressure ventstream (over 2000 psig) wasrouted to a membrane system.The hydrogen product wasdelivered to the suction of thehydrogen make-up compressor.This change added 5 millionscfd of hydrogen to the ren-erys hydrogen header.

Phse 3: ew PSa uNext, a UOP CCR Platformingunit was installed and the netgas was fed to a new 10-bedPSA unit. By compressing thetail gas, it was possible tomaximise the hydrogen recov-ery in the PSA unit while still

of the control valves and pipingon the piping skid, but main-tained the existing adsorbervessels and tail gas mixingtanks. As ow rates hadincreased by over 50% since theoriginal design, pressure dropproblems encountered in thefeed, product and tail gaspiping had to be overcome.This was achieved by installingvalves with larger dischargecoefcients to replace some ofthe existing valves, and pres-sure drops through the unitwere reduced to acceptablelevels.

The new cycle was designed

tbe 2

Phse Sem refrmer Membre ccR t1 55 55

2 65 5 70

3 65 5 50 120

4 85 5 50 140

5 85 5 60 150

6 85 5 75 165

Hsr f hre requreme, m sf


Steam

reformer PSA ARDS

Membrane

Catalytic

reformer PSA

Fure 7 Case study 2: revamped ow scheme after phase 5


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such that any component couldfail and the unit wouldcontinue to operate at designrates and maintain designhydrogen purity. This furtherimproved on-stream factorsand unit reliability, as no single

component would cause a unittrip or reduction in feedcapacity.

Minor modications weremade to the skid instrumenta-tion and the entire controlsystem software was repro-grammed to implement thenew cycle. The revamp, designand hardware was completed,ready for installation, in lessthan six months after theproject was authorised. Alleld modications werecompleted during a two-weekturnaround.

Phse 5: revmp f ccRPSa uNext, the PSA unit processingnet gas from the CCRPlatforming unit was debottle-necked, as additional hydrogen

net gas feed was available fromthe CCR Platforming unit. Byinstalling more tail gascompression and updating thecycle, the PSA units hydrogenproduction was increased to 60million scfd with the designhydrogen purity maintained.Fabrication and installation ofthe new compressors deter-mined the projects overall

schedule, and changes to thePSA unit were implementedwell within the time frame.

Phse 6: pe fuureexpsDue to changing demands, therenery is still short of hydro-gen, and UOP was asked toevaluate options to furtherincrease the CCR PSA units

capacity. The most recent PSAunit revamp resulted in theability to process all of theavailable CCR Platforming netgas and, at the time, there wasstill some spare tail gascompression capacity availa-

ble. The CCR PSA unit can befurther revamped to meetcurrent demand by fully utilis-ing the existing compression.

One approach being consid-ered is to make cycle changessimilar to those implementedin the steam reformer PSA unitat this plant. Future hydrogenproduction is predicted toincrease to 75 million scfd. Thisrevamp would reuse the exist-ing adsorber vessels andadsorbents, but would requirechanges to the existing valvesand piping skid. These changeswould allow the CCR PSA unitto produce 50% more hydrogenthan the original design andmaintain the hydrogen recov-ery already obtained from theprevious revamp. This revampwould fully utilise all the tail

gas compressors to their designcapacities.

Additionally, partial adsorb-ent replacement with thecurrent high performanceadsorbents would allow hydro-gen recoveries of both units toimprove, thereby furtherincreasing hydrogen produc-tion. Implementing Phase 6would bring the total hydrogen

availability for this renery to165 million scfd, three timesthe original capacity.

cse su 3: srbe e hes 30%pA Polybed PSA system wasoriginally designed as a six-bedunit processing 12 million scfdof SMR feed and producing

hydrogen with 10 ppmv CO.The plant needed additionalhydrogen and had available arenery off-gas stream contain-ing ~76% hydrogen andC

1-C

6 hydrocarbons. Two

choices were considered. The

rst was to process the newfeed in the SMR and send thetotal efuent to the PSA unit.The second was to send the gas

blended with the current SMRgas directly to the PSA unit. Inthe rst case, the hydrogenwould pass through the steamreformer on a free ride andthere would be a need for addi-tional modications to the SMRto process the gas. In thesecond case, the SMR ow ratewould stay constant and thePSA unit would need anadsorbent replacement for theheavier hydrocarbons in thefeed, plus a new processdesign.

The rener chose the secondoption, to replace the PSAadsorbents and modify the PSAcycle. This PSA unit revamp

increased hydrogen productionby ~30% from the combinationof a new cycle and new adsorb-ents (see Table 3).

Hre pms:sus he beesIt is one thing to optimise yourhydrogen network on paper. Itis quite another to actually real-ise the benets. Daily operating

targets must be optimised toreect the day-to-day changesof the renery. Operationsmust know the critical operat-ing parameters of thehydrogen network to monitorand manage, and have thatdata readily available. Ideally,one person is responsible forthe network as a whole and canmanage the network to



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maximise the overall renerymargin, to avoid each individ-ual operator making decisions

based on just their own unit.It is common practice to

produce additional expensivehydrogen and burn it, just as a

safety margin in case it isrequired in a hurry. Operatingprocedures, control improve-ments, automation includingmultivariable control and betteroperator communications allcan mitigate this inefciencyand waste.

To optimise the networkcontinually, the rener mustunderstand the key constraintswithin the network (purity,compression and so on) andaim to meet those constraintsevery day. Operations mustunderstand and monitor theseconstraints and know whatadjustments they can make toincrease the hydrogennetworks efciency by pushingcloser to a real networkconstraint. For example, in acascaded system, one might

regularly reduce the DHTmake-up purity (bypass arounda PSA) while increasing themake-up and purge rates andmaintaining target recyclepurity, up until the make-upcompressor is at its maximumcapacity. Monitoring thecompressor spillback andadjusting regularly will mini-mise hydrogen losses in the

PSA under all renery operat-ing conditions.

Every operator should beaware of the value of hydrogen,the costs of sending hydrogento fuel and the penalties foroperating too conservatively.Running a PSA unit so thatthere is no detectable impurityin the hydrogen product is safe,

but it can represent a 110%

decrease in PSA recovery, thuswasting hydrogen. Operating ahydroprocessing unit withhigher than target purity forrecycle hydrogen is safe, but itrepresents unnecessary losses ofhydrogen to fuel, either aspurge or as an excessive feedrate to a purier with associatedhydrogen losses to the tail gas.

When analysis of recycle gaspurity is infrequent or unrelia-

ble, the operator is almostforced to run conservatively. Inthis case, reners shouldconsider installing one of thenew inexpensive, very low

maintenance, direct hydrogen-reading analysers that are nowon the market.

Representation of the hydro-gen network in the reneryslinear programming (LP) modelis an often overlooked opportu-nity to signicantly enhanceprotability while evaluatingthe hydrogen network. This isnot signicant if hydrogen does

not constrain the renery, but ifcharge rate and severity targetsare set in the LP model or in theeld in response to hydrogenconstraints, it is critical that theLP model accurately reects theactual constraints. While, typi-cally, LP models do reect thehydrogen yields in catalyticreformers with feed propertiesand severity, they can be

modied and maintained toreect accurately hydrogencompressor constraints and theimpact of hydroprocessing feedproperties and severity onhydrogen consumption, partialpressure, purge rates and make-up rates. Where even greaterdetail is warranted, the LPmodel can reect the relation-ship between hydrogenconsumption and product prop-erties in these units.

cussHydrogen is an increasinglyimportant component of ren-

ing, particularly in view of theincreased demand for cleanfuels. There are opportunitiesto optimise the use of hydrogenin a renery to maximiseprots: Hydrogen network studiesand ow scheme optimisations PSA and membrane technol-ogies to recover and purifyhydrogen

Reforming process and cata-lyst technologies to producemore hydrogen Hydroprocessing and cata-lyst technologies to consumeless hydrogen.

a Zr is Engineering Fellow in the

Optimization Services Department at

Honeywells UOP. He has spent the last

12 years assisting customers in optimising

or es RevmpPSA type 6 bed 6 bed

Feed SMR 12 MMscfd SMR & ROG 15.5 MMscfd

Product 8 MMscfd 10.5 MMscfd

10 ppm CO max 10 ppm CO max

Off-gas 5 psig 5 psig

Recovery 84.5% 87%

Adsorbent replacement & process cycle changes resulted in 30% greater capacity plus

higher recovery

cse su 3

tbe 3


12/12

their renery hydrogen networks. He

holds a BS chemical engineering from

Northwestern University.

R l is Product Line Manager for

Hydrogen with Honeywells UOP. He

has worked in a variety of elds including

R&D, eld operating services, operating


technical services, Far East and Americas

customer services, engineering project

manager and Americas customer sales.

He holds a BS in chemical engineering

from the Illinois Institute of Technology

in Chicago.

Kh P is a Senior Account

Manager for Gas Purication at

Honeywells UOP, responsible for

continuing support of its installed base

of PSA systems and Polysep membranes.

She holds a BE in chemical engineering

and a Masters in electrical engineering/

computer science from Stevens Institute

of Technology.

hydrogen optimization paper

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