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    Two Approaches to

    Converting Coal

    to a Liquid Fuel

    Indirect

    Gasify coal and

    rebuild small

    molecules to

    desired productDirect

    Break coal down to

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    maximize correct size

    of molecules for

    liquid products

    Direct Liquefaction Reacts coal with H2

    sually in presence of a liquid

    sol!ent

    "##ressi!e reaction conditions $emperatures % &''()

    *ressures % +'' atm

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    "ppropriate catalyst

    *roduces a syncrude

    )an be refined to produce #asolineor

    diesel fuel

    ,ore con!ersion than indirect

    process

    Indirect Liquefaction

    -n!ol!es #asification of coal toproduce a syn#as

    ,ixture of ). and H2

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    /yn#as con!erted into a liquid fuel

    !ia processes

    such as 0ischer1$ropsch 0$3 process

    ,obil ,ethanol1to1Gasoline ,$G3

    process$wo !ery different approaches to pro!idin# fluid fuels

    from coal are described and compared in this paper4 direct

    coal liquefaction 5)63 and indirect coal liquefaction-)637 0or both approaches a ma8or challen#e is to increase

    the hydro#en1carbon ratio7 0or finished hydrocarbon

    fuels such as #asoline and diesel9 H:) 2 molar

    basis37 0or petroleum crude oil9 the ratio ran#es from +7;

    to +7

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    steam reformin# or from coal !ia #asificationI the latter

    is a suitable option for )hina9 where natural #as is scarce7

    $he 5)6 products are only partially refined7 $hey must

    be further refined into finished liquid fuel products at con!entional

    refineries9 where additional H2 is added to

    brin# the H:) up to 2 for the final products39 and ener#y

    is consumed to pro!ide the refineryAs heat and powerneeds7

    Coal is a solid with a high carbon content but with a hydrogen content of~5%.

    Coal may be used to produce liquid fuels suitable for transportationapplications by removal of carbon or addition of hydrogen, either directlyor indirectly. The first approach is usually known as carbonisation orpyrolysis and the second as liquefaction.

    in outh !frica. "ere, with large reserves of coal but no oil or gas, tradeembargoes over three decades to the mid#$&'s drove large#scaleapplication( up to )'% of transportation fuel requirements have been metfrom coal.

    Indirect coal liquefaction first gasifies coal and then converts the coal-

    derived syngas into fuels and petrochemicals using Fischer-Tropsch

    technology. There are several technology and process alternatives for

    this type of approach to CTL.

    Direct liquefaction, by contrast, breas do!n the comple" coal

    structure into smaller component molecules !hich then can be further

    refined into clean liquid fuel products by reducing the contents of

    sulfur and nitrogen.

    #osted by$ %ill &illard' (ov )*, )++ $+$+/ 0&

    I !ould lie to see the environmental outputs from the resultant

    energy products. Coal is largely carbon. 0dd hydrogen, mae

    hydrocarbons, burn them, and you have C1), masses of it. 0nd !hat

    about the energy required in the manufacturing process - does it come

    from burning coal2 I suspect this is no !ay an environmentally friendly

    !ay to mae liquid hydrocarbon fuel3

    #osted by$ 4ugh Collins' (ov )5, )++ 6$)$+ 0&

    4ugh,

    7ou need to read the fine print I guess. Diesel fuel from coal

    mailto:[email protected]:[email protected]:[email protected]:[email protected]
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    gasification 8or 9indirect liquefaction9: is almost ;ero sulfur. It is also

    lo! in aromatics. 4ence there are some air pollution benefits.

    1f course, you could also capture the C1) produced in the liquefaction

    plant and sequester it 8ho!ever you may do that at an inland coalmine:. (o!, I !on? politicians.

    *any different +direct processes have been developed, but most areclosely related in terms of the underlying reaction chemistry. Commonfeatures are the dissolution of a high proportion of coal in a solvent at

    elevated temperature and pressure, followed by hydrocracking of thedissolved coal with hydrogen gas -"/ and catalyst.0irect liquefaction is the most efficient route currently available. 1iquidyields in e2cess of 3'% by weight of the dry, mineral matter#free coal feedhave been demonstrated in favourable circumstances. 4verall thermalefficiencies -% calorific value of the input fuel converted to finishedproducts/ for modern processes are generally in the range )'#3'% ifallowance is made for generating losses and other non#coal energy imports.These processes generally have been developed to process development unit-06/ or pilot plant scale and the main technical issues have been resolved."owever, no demonstration or commercial#scale plant has yet been built.

    The commercial viability of coal liquefaction rests with the overalleconomics of the process. This depends on the availability of significantquantities of poor quality, low cost coal, and the unavailability orotherwise relatively high cost of oil -and gas

    B E N E F I T S O F T H ET E C H N O L O G Y7 Coal liquefaction offers the following benefits87 1argely proven technology for the manufacture of useful liquidproducts.7 !bility to manufacture transportation fuels from abundant coal.7 9nsurance against depleting oil stocks and oil supply problems.

    I N T R O D U C T I O NThe hydrogen content of Transportation fuels varies from ~$.5% in somegasolines to $:.5% in aviation turbine fuels. ;or coal to replace them, itmust be converted to liquids with similar hydrogen content. This can beachieved either by removing carbon or by adding hydrogen, either directly

    or indirectly. The first approach is known as carbonisation or pyrolysis andthe second as liquefaction.1iquid fuels have long been produced from coal. !s the cost ofconverting coal into useful liquid fuels is higher than the cost of refiningcrude oil, it is the relative price of the raw feedstocks that has providedthe main incentive to pursue the technology. The maorld >ar, as did embargoed outh!frica between the mid#$5's and $&'s.

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    *ost development derives from the early $''s, when two distinctapproaches were pursued. The earliest process route involved hightemperatureand high#pressure dissolution of coal in a solvent to producehigh boiling point -bp/ liquids. ?o hydrogen or catalyst was used at thistime. This approach, known as direct liquefaction, was patented by@ergius in $$A and commercialised in the early $'s( it also becameknown as either the ott#@roche or 9 = ;arben process.;rom the mid#$)'s, at a time of mounting environmental concern overemissions from power generation, there was continued interest indevelopments of the original uncatalysed ott#@roche process. *ost workwas carried out in the 6!, where the more developed e2amples were theBC#9 -olvent Befined Coal/ and BC#99 processes, although otherprocesses were also developed to a smaller scale in apan and the 6D. TheBC#9 process was very similar in concept to the ott#@roche process andaimed to upgrade coal to produce a clean boiler fuel with a much lowerash and sulphur content than the original coal. The BC#99 process,however, was to produce distillate products( the distinguishingcharacteristic of the process was the recycle of vacuum bottoms.Two other direct coal liquefaction processes were under development inthe 6! at the same time8 the E22on 0onor olvent -E0/ process and the"#Coal process. The distinguishing feature of the E0 process was a

    separate solvent hydrogenation step to carefully control the hydrogendonor characteristics of the solvent, and the most important feature of the"#Coal process was its use of an ebullated bed reactor.9n the early $3's, political changes in the ma

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    his process has been used to upgrade lo%$ranksub$bituminous coals in the -/ it increasescalorific value and reduces sulphur content.

    "igh#temperature carbonisation is the oldest route for the production ofliquids from coal, wherein hydrocarbon liquid is predominantly a byproductof coke#making. The low yields -G~5%/ of liquid product and

    relatively high upgrading costs mean that traditional high#temperaturecarbonisation is not an option for the production of liquid fuels on acommercial basis.*ild pyrolysis is also a carbonisation technology but with less severeoperating conditions. *ild pyrolysis consists of heating the coal to atemperature in the range ~:5'#)5'HC -compared with ~5'HC in hightemperaturecarbonisation/, driving off volatile matter from the originalcoal and generating other volatile organic compounds formed by thermaldecomposition during the treatment. 1iquid yields are higher than forhigh#temperature carbonisation, but are still no more than $5#'% atmost. The main product is a char with a reduced hydrogen andheteroatom content. The 6! has led the development of this process,primarily as a means to upgrade low#rank sub#bituminous coals andlignites, to increase calorific value -CI/ by re

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    The Cd i "al fed into aperfotatcd mary gtate dryer where it is heated by a hot gas stream. %~tuidena time of thecoal and temperatureo f the inlet gas haveb eens electedto tufttee thomoisturec ontento f thecoal without initiating chemicacl hanges.T he solid bulk temperatureiscontrolleds o that no

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    significanta mounto f methanec, arbonm ono2ideo r >bon diide isrelea2edfr om the coal.The solidsf rom the dryer are then transfertedt o the pyroly2erw bem thetemperatureo f thedried coat is raisedt o about l44JTb y a hot reoycledg ass tream. The

    rate of hating of thesolids i.e., the inlet tempcmtum and flow rate of the hot recycled &asatream, is catd6lycontmlledb ecausiet determinetsh e pmpettieso f the solii andi iquidpmduc~. 9n the pyroly2er.a chemicalr eactionc ccursw hich tests9tsin the mleaseo f volatile&asemmm aterialsf rom thecoal. olidse 2itingt he pyrolyse areq uickly quenchedto ,stopt he pyrolysisreaction. Theya tethenc ooleda ndt ransfFredt o the 0; storages ilo. incet he solidsh aven

    o surfacet t2ristureand, theseforea, re likely to be dusty. a dust suppressnneta liedh :B isaddeda s they leavet he0; product silo as foal product.The gas produced in the pytoly2er is aent through a cyclone for removal ofpyticulates. 9t isthens entt o a quencht ower to stop any secondaryte aetiw end tocondenseth e desired1 iquids.4nly C01 is condensedin this step( the condensationo f water is avoided.The gas stream

    leaving the quench tower may contain some C01 in the form of a fine mist.9n order to receverthe llquld mist,t hreee leotrostatipcr ecipitators-B s/o peratinginpamBewt ereb tsteied.T hefinished C01 product is pumped from the battom of the quench tower tostorage.Tlte residual- earf mm the electrostaticp recipitatorsis dividedi nto threestreams.* ost of it isrecycledd irectly to the pymlyKer, omei s buntedi n the pyrolymrcombuatnar nd then mi2ed

    with the recycledg ast o provideh eat for the mild gpsffiuttionr ation. Theremaindeor f thegasi s burnedi n the dryer combustorw, hich convertss ulfur compoundstosulfur o2ides- 4,/and hydrocarbontso carbono 2ides- Cod. ?itrogeno 2ide -?4 andcarbonm ono2ide- C4/emissionsa n controlledb y appropriated esigno f the combustor. The hotflue gas from the

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    dtyer combustoirs blendedw ith the recycledg asf rom the dryer to provideheatf or drying.Tho off#gas from the dryer tlrst passesth mu&ha cyelonet o removet heentrainedp artieulate2.. 9rte misa tihnedne dri siv itdreeadt iendto w i9twho s sotdreiuammc sa.r

    *boonsat toefs oitl uitsio rna icny cal otdwd oir#esctatl&y etso c trhuebbderyrs eyrs wtehmile. t@hyesprayingt he off#gas with sodiumc arbonates olution, the first stagescrubberc apturesth e finepatticulatesth at escapeth e dryer cyclone,a nd the seconds tages orubberemovesm osto f the

    L sulfur o2ides from the gas streamb y converting it into sadiurns ultlte. lltesultiteisthen

    o2idi2edi nto sodiums ulfate. The treatedg asi s ventedt o theatmospherteh mugha stackw hile

    the spents olutioni s senti nto a nondiirchatgingp ond for evaporation..$ !9B 4169T!?T

    0uring normal opemtkm,m y purgeg as that is dossed to the atmospheremust passt brougkthe destdfubtion unit, and any purge gas that is prmh2ed in the pyrolyKerloop mm be sent tothe Fsulfuhation unit only after it has been incinuatal in the dryercombustor. Therefore, air

    polhnantse mittedh orn the 0; buildings tackc onsisto nly of minoramountso f ?4., 4,, C4,hydrocarbonasn dp articulates.E missionsfo r eachp ollutanta reb elow the$@4to n per year9 evelfor named- fuel conversion/s ources. Bigorousp armittinga nd monltotingrsquimmentsw ere

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    thus avoided. This was achieved through careful sekction of appropriateJbFon eoatro9technologieas nd processc ontrol equipment.?4,, C4, and hydrocarbonse missionsa re minimiKedb y timrmaldecompositionin the dryer

    combustor. 4i and particulatese missionsfr om the processa recontrolledb y the purge gastreatment described in ection ).$A. 9n addition, particulates emissionsfrom thecrushingMscreeninbgu ilding, raw coai storages ilo, and 0; storages iloam controlledb y wetscrubbers.T he effrciencicso f theses crubbersa re over %.).$A 6B=E =! TBE!T*Em

    +9n order to meete nvimnmcntasl tandardst,h ep urgeg asb eingdischargedto the atmospherbeythe 1;C processm ustb e treated. The off#gasf rom the processc,ontainingm ostlyw aterv a~or,

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    nitrogen, carbon dio2ide and small amounts of sulfur o2ides, -Table ).$/ isvcnlcd to aderulfuriKation unit -;igure ).A/ which consists of a wet gas scrubber anda horiKontalto sodiutir sulfF. 9n the wet gas scrubber, dual atomimtion noKKles disperse

    the sodiumcarbonates olutioni nto tine particlesw ith compresseadi r and sprayi t intothe purgeg as streamto reducet he entrainedp articulatesa nds ulfur o2ides, The horiKontalscrubberf urther reducessulfur o2ides in the purge gas as it flows hori2ontaliy through spraycurtains of sodium carbonatesolution. The gas then passesth rough mist eliminators< ust prior to leavingthe horiaomaetsubbituminous coal contains considerable water, and conventional dryingprocesses physicallyremove some of this moisture, causing the heating value to increase. Thedeeper the coal isphysically dried, the higher the heating value and the more the pore structurepermanentlycollapses, preventing resorption of moisture. "owever, deeply driedowder Biver @asin coalse2hibit significant stability problems when dried by conventional thermal

    processes. The 1;Cprocess overcomes these stability problems by thermally altering the solidto create 0; andC01. The 0; is a stable low sulfur, high @T6 fuel similar in compositionand handlingproperties to bituminous coal. C01 is a heavy, low sulfur liquid fuel similar inproperties toa ?umber ) fuel oil.@riefly, in the 1;C technology, coal is first deeply dried to remove waterphysically. The

    temperature is further raised in a second stage which results indecomposition reactions that formthe new products. This chemical decomposition -mild gasification/ createsgases by crackingreactions, leaving residual solids. The soli.ds are cooled and furtherprocessed to make 0;.The gases are cooled, condensing liquids as C01, and the residual gasesare burned in theprocess for heat.

    D I R E C T L I Q U E F A C T I O NDirect LiquefactionH!drogen is added to the organic structureof coal, breaking it do%n to the point %heredistillable liquids are produced.here are a number of different methods,but the basic process involves dissolving coalin a solvent at high temperature and pressurefollo%ed b! the h!drocracking1 "i.e. addingh!drogen over a catal!st#.

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    )iquid !ields can be in e*cess of 20 of the dr!%eight coal feed, %ith thermal efficiencies ofaround (0$20. he liquids produced fromdirect liquefaction are of much higher qualit!than those from p!rol!sis and can be usedunblended in po%er generation or otherstationar! applications. Ho%ever, further

    upgrading is required for use as a transportfuel. here are t%o main groups of directliquefaction processes344 ingle$stage3 provides the distilled liquids"distillates# through one primar! reactor orreactor chain. &ost of these have beensuperseded b! t%o$stage processes toincrease production of lighter oils.44 %o$stage3 provides distillates through t%oreactors or reactor chains. he first reactiondissolves the coal either %ithout a catal!st or%ith a lo%$activit! disposable catal!st,producing heav! coal liquids. hese are furthertreated in the second reactor, %ith h!drogenand a high$activit! catal!st to produceadditional distillate.

    0irect liquefaction processes aim to add hydrogen to the organic structureof the coal, breaking it down only as far as is necessary to producedistillable liquids. *any different processes have been developed, butmost are closely related in terms of underlying reaction chemistry.Common features are the dissolution of a high proportion of coal in asolvent at elevated temperature and pressure, followed by thehydrocracking of the dissolved coal with " and a catalyst. 0irectliquefaction is the most efficient route currently available. 1iquid yields ine2cess of 3'% by weight of the dry, mineral matter#free coal feed havebeen demonstrated for some processes in favourable circumstances.4verall thermal efficiencies for modern processes are generally in the range)'#3'% if allowance is made for generating losses and other non#coal

    energy imports.The liquid products from direct liquefaction processes are of much higherquality than those from pyrolysis processes and can be used unblended formost stationary fuel applications. They do, however, require furtherupgrading before they can be used directly as transportation fuels. Thisupgrading utilises standard petroleum industry techniques, allowing theproducts from a liquefaction plant to be blended into the feedstockstreams of a petroleum refinery.0irect liquefaction processes can conveniently be divided into two maingroups, depending on whether the initial dissolution of the coal isseparated from the conversion of the dissolved coal into distillableproducts87 ! single#stage direct liquefaction process gives distillates via one primaryreactor or a train of reactors in series. uch processes may include anintegrated on#line hydrotreating reactor, which is intended to upgradethe primary distillates without directly increasing the overall conversion.7 ! two#stage direct liquefaction process is designed to give distillate

    products via two reactors or reactor trains in series. The primaryfunction of the first stage is coal dissolution and is operated eitherwithout a catalyst or with only a low#activity disposable catalyst. Theheavy coal liquids produced in this way are hydrotreated in the secondstage in the presence of a high#activity catalyst to produce additionaldistillate.ome processes were designed specifically to co#process coal withpetroleum#derived oils and these may fall into either group. !lso, coalliquefaction processes from both groups have been adapted for coprocessing.

    S i n g l e - s t a g e P r o e s s e s9n the mid# to late $)'s, as interest was growing, all of the available

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    processes were single#stage. *ost development therefore continued toadopt a single#stage approach. ome developers added a second stageduring the $3's, following the oil crisis, to increase the production oflight oils. The single#stage processes developed furthest are87 Dohleoel -Buhrkohle, =ermany/7 ?E041 -?E04, apan/7 "#Coal -"B9, 6!/7 E22on 0onor olvent -E0/ -E22on, 6!/

    7 BC#9 and 99 -=ulf 4il, 6!/7 9mhausen high#pressure -=ermany/7 Conoco Kinc chloride -Conoco, 6!/.*ost of these have since been superseded and abandoned. Twoe2ceptions are the Dohleoel and ?E041 processes, both of which areconsidered ready for commercialisation by their developers.everal other, less important, processes were developed to a modest scalein the 6!. 4ther countries, notably Bussia and oland, also carried outBF0 on single#stage liquefaction at a significant scale( the approachesadopted are believed to be similar in most respects to the Dohleoelprocess.

    T!e "o!leoel ProessThe Dohleoel process -;igure A/ with 9ntegrated =ross 4il Befining -9=4BN/is a relatively recent development, by Buhrkohle != and IE@! 4E1 !=, ofthe process used on a commercial scale in =ermany until $:5.0evelopment proceeded via a '.5 tonnesMday and '. tonnesMdaycontinuous unit at @ergbau#;orschung -now 0*T/ and a '' tonnesMdayplant at @ottrop. The @ottrop plant operated from $&$ to $&3,producing over &5,'''t of distillate products from $3','''t of coal overappro2imately ,''' operating hours. The technology can therefore beconsidered to be fully demonstrated.9n $3 the China Coal Besearch 9nstitute -CCB9/ signed a two#yearagreement with =ermany to carry out a feasibility study for a 5'''tonnesMday demonstration plant. The suitability of sites for a liquefactionplant in Ounnan rovince was investigated, including the potential marketfor products.Coal is slurried with a process#derived recycle solvent and a +red muddisposable iron catalyst, pressurised and preheated. " is added and the0ryerCoalCycloneCycloneCaustic crubber tack=ases0;-Char/C01-1iquids/0ryerCombustoryrolyserCombustorBotary CoolerCondensation EChar 0eactivationyrolyser

    Figure 2. Encoals LFC process

    mi2ture passed to an up#flow tubular reactor, operating typically at A''barand :3'HC. The specific coal feed rate to this reactor is in the range '.5#'.)5 tonnesMmAMhour. roducts from the top of the reactor pass to a hotseparator. The overheads from this separator remain in the gas phase andare hydrotreated at a temperature of A5'#:'HC in a fi2ed#bed reactor atthe same pressure as the main reactor. The hydrotreated products aredepressurised and cooled in two stages. The liquid product from the firstof these stages is recycled to the slurrying step as part of the solvent. Theliquid product from the second stage is routed to an atmosphericdistillation column, yielding a light oil -C5 # ''HC bp/ and a medium oil

    -''#A5PC bp/ product.The bottoms from the original hot separator pass to a vacuum distillationcolumn to recover distillable liquids. These are added to the hydrotreatingreactor feed, and are subsequently largely recycled as solvent. The vacuumcolumn bottoms consist of pitch, mineral matter, unreacted coal andcatalyst, and in commercial operation would be used as a gasifierfeedstock for " production.=reater than '% conversion can be obtained when processingbituminous coals, with liquid yields in the range 5'#)'% on dry ash#freecoal. rocess yields and quality, when using rosper, a =erman bituminouscoal, are summarised in Table $.Table 1. Kohleoel process yields and pr oduct quality with Pr osper coal

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    T!e NEDOL Proess;rom $3& to $&A, three direct coal liquefaction processes weredeveloped by apanese companies ?ippon Dokan, umitomo *etals9ndustries and *itsubishi "eavy 9ndustries under a apanese =overnmentinitiative. The initiative was managed by the ?ew Energy and 9ndustrialTechnology 0evelopment 4rganisation -?E04/. @y $&A these processeshad been tested at scales ranging from '.$ tonnesMday to .: tonnesMday.Bather than support each individually, ?E04 amalgamated features of all

    three processes to produce the ?E041 process -;igure :/, targetedprincipally at sub#bituminous and low#rank bituminous coals. !consortium of ' companies was then established, under the name ?ipponCoal 4il Company 1td, to design, build and operate a 5' tonnesMday pilotplant. "owever, the pro

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    eparation=ases;lasheparatorrimaryBeactionIacuum0istillationBecycle olvent!tmospheric0istillation1=1ight4il*iddle4ilIacuum@ottoms

    Figure . The Kohleoel process"ydrogen "ydrogen BecycleCatalystCoallurry*i2ingrimaryBeactionIacuum0istillationBecycle olvent!tmospheric0istillation=ases1ight0istillate*iddle0istillate"ydrotreated?aphthaIacuum@ottoms

    "ydrogenolvent"ydrogenation

    Figure !. The "E#$L process

    rocess yields Oield"ydrocarbon gases -C$#C:/ $.'1ight oil -C5#''HC/ 5.A*edium oil -''#A5HC/ A.)6nreacted coal and pitch .$roduct quality 1ight 4il *edium 4il"ydrogen -%/ $A.) $$.?itrogen -ppm/ A $3:42ygen -ppm/ $5A &:ulphur -ppm/ $ G50ensity -kg m#A/ 33 $roduct yields vary with the type of coal being processed, although theprimary reaction operating conditions are ad

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    over fi2ed#bed reactors in this, as the reactor contents are well mi2ed andtemperature monitoring and control is more easily effected. !lso,ebullated#bed reactors allow catalyst to be replaced while the reactorremains in operation, enabling a constant catalyst activity to bemaintained. This is particularly important with supported catalysts as,although these have a high initial activity, they deactivate relatively rapidlyat coal liquefaction conditions.The reactor products pass to a flash separator. 1iquids in the overheads

    are condensed and routed to an atmospheric distillation column, producingnaphtha and middle distillate. The flash bottoms are fed to a bank ofhydrocyclones. The overheads stream, which contains $#% solids, isrecycled to the slurrying stage. The underflow is routed to a vacuumdistillation column. olids are removed with the vacuum column bottoms,while the vacuum distillate forms part of the product for e2port.!s with other processes, yields are dependent on the coal. R5% overallconversion can be obtained with suitable coals, with liquid yields up to5'% -dry basis/.

    T!e E##on Donor Sol$ent ProessE22on Corporation started E0 process development in the $3's andprogressed to the construction of a 5' tonsMday pilot plant at @aytown,Te2as, in $&'. !t this point E22on considered that the process -;igure )/was ready for commercialisation, although development was discontinued.1iquid yields were lower than in more recent processes. !s a result theprocess showed relatively high specific capital costs and apparentlyuncompetitive economics. The pilot plant was operated until $&, withfurther research continued until at least $&5.Coal is slurried with a distillable recycled solvent that has beenrehydrogenated to restore its hydrogen donation capacity. This improvesthe effectiveness of the solvent, and this is the key distinguishing featureof the process.

    The slurry is mi2ed with ", preheated and fed to a simple up#flow tubularreactor that operates at :5#:5'HC and $35bar. ?o catalyst is added. Thereactor effluent passes to gas#liquid separators, from which the liquidproduct is fed to a vacuum distillation column. ?aphtha and middledistillate products are recovered, although most of the middle distillate isrecombined with the heavy distillate to form the basis for the recycle

    solvent. The vacuum column bottoms, containing the solid residues, aredischarged and fed to a proprietary E22on +;le2icoker unit. This combinespyrolysis and gasification steps to produce additional distillate product anda fuel gas, which would be used for " production. The pyrolysis step iscarried out at temperatures in the range :&5#)5'HC. ;le2icoking is now incommercial use.Behydrogenation of the recycle solvent is carried out in a fi2ed#bedcatalytic reactor, using either nickel#molybdenum or cobalt#molybdenumon an alumina support. The reactor is operated at conditions in the regionof A3'HCM$$'bar, although conditions are varied to control the degree ofhydrogenation of the solvent and thus maintain its quality.rocess yields are closely related to the characteristics of the coal being

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    processed, but can be varied to some e2tent by altering conditions.Typically, overall liquid yields -including the liquids produced by ;le2icoking/are ~A)% for lignites, ~A&% for sub#bituminous coals and ~A#:)% forbituminous coals -all dry ash#free basis/. 1iquid yields can be increasedfurther by recycling part of the vacuum bottoms stream to the slurryingstep, although this was not tested on the 5' tonsMday plant. 6sing thistechnique, yields of up to :3% for lignites, 5'% for sub#bituminous coalsand )'% for bituminous coals could be achieved.

    The boiling range distribution of the liquid products can also be variedwithin a wide range, depending on market requirements.

    T!e SRC-I an% SRC-II ProessesThe BC processes were originally developed to produce cleaner boilerfuels from coal. ! '.5 tonsMday plant was built in $)5 and scaled up in$3: to two separate pilot plant. These were located at >ilsonville -BC#9,) tonsMday see ;igure 3/ and ;ort 1ewis, >ashington -BC#9, 5' tonsMday/.The ;ort 1ewis plant was later converted to a BC#99 unit, although becauseof the more severe conditions required for BC#99, the capacity wasdowngraded to about 5 tonsMday. The obilsonville plant continued to be funded by the 604E until $ as apilot#scale test facility for the whole 6 direct liquefaction developmentprogramme. The BC processes have now been abandoned in theiroriginal form, but elements have been incorporated in more recent 6processes."ydrogen BecycleCoallurry*i2ingIacuum0istillation!tmospheric0istillation=asesIacuum@ottoms;lasheparatorEbullated@ed"ydrocrackerreheating1ean lurry Becycle"ydrocyclone;resh"ydrogen?aphtharoduct0istillateroduct*iddle 0istillate olvent Becycle

    Figure %. &che'atic diagra' o( the )*Coal process"ydrogen BecycleCoallurry*i2ingIacuum0istillation=asesreheating;resh"ydrogen?aphtharoduct0istillateeparation ;uel 4ilTubularBeactor"ydrogen;le2icokerCoke to=asification;i2ed @ed"ydrotreaterBecycle olvent

    Figure +. &che'atic diagra' o( the E#& process

    T!e I&!a'sen Hig!-(ress're ProessThe development of the 9mhausen high#pressure process commenced in$& and a $''kgMday 06 was commissioned in $&:. The processoperating conditions appear very severe -:3'#5'5PC and )''#$'''bar/.!s a consequence, it seems unlikely that the process could be successfullycommercialised unless yields were e2ceptionally high.

    T!e Conoo )in C!lori%e Proess9n the late $3's and early $&'s Conoco worked on the development ofa process which uses molten Kinc chloride to hydrocrack coal directly togive good yields of gasoline in a single step. This process is one of thevery few direct liquefaction processes that is not a direct derivative of prewartechnology. The process was taken to the $ tonMday pilot plant scale,

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    although this was operated for only a short period and with limitedsuccess. *a

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    boiling up to :''HC are removed. The bottom stream from this columncontains solvent, unreacted coal and mineral matter. These solids areremoved by one of several possible techniques and the solvent is recycledto the slurrying step. 9n some process variants, only part of theatmospheric column bottom stream is routed to the solids removal step,resulting in the recycle solvent containing mineral matter and anydispersed catalyst that may have been used. The process is designed tooperate without the need to remove a separate pitch stream as a product.

    *ost operating e2perience at the >ilsonville plant was gained with theDerr#*c=ee critical solvent de#ashing -C0/ process, also known as theresidual oil solvent e2traction -B4E/ process.ince the process has now been taken back to the developmental stage,recently reported yields vary considerably depending on the coal processed,the process configuration adopted and the particular processingFigure ,. &-C*1 + tonsday direct lique(action plant at /ilson0ille"ydrogen BecycleCoallurry*i2ing=asesreheating;resh"ydrogen1ight0istillateecond#tageEbullatingBeactorBecycle olvent;irst#tageEbullating

    BeactorBesiduesolidseparation*iddle0istillate"eavy0istillate

    Figure . The CT&L process

    conditions. 0istillate product yields of )5% or higher on dry ash#free coalcan be obtained, although the product is relatively high#boiling. Theresidue of unconverted coal and the heavy preasphaltenic material reales -;igure /, but has since beendecommissioned. !n outline design for a )5 tonnesMday demonstrationplant has been produced in sufficient detail to allow a contractor toproceed directly to the detailed design stage. "owever, there are nocurrent plans to construct such a plant.;igure $' shows a schematic diagram of the process. Coal is slurried witha process#derived recycle solvent, preheated and passed to a non#catalyticdigestion step, which consists of two or more continuous#stirred tankreactors in series. These reactors operate at a temperature of :$'#::'HCand a pressure of $'#'bar, required solely to reduce solvent vaporisation.?o " is used in this step, but the solvent acts as a hydrogen donor,transferring up to % by weight of hydrogen to the coal.The digester product is partially cooled and filtered in a vertical#leafpressure filter to remove unreacted coal and ash. The filter cake is washedwith a light recycle oil fraction to recover product and dried under vacuum.The dried filter cake contains only a small proportion of residual nondistillableliquids( the process is therefore relatively insensitive to the ashcontent of the feed coal or the e2tent to which it can be dissolved. 9n

    commercial operation the filter cake would be gasified to produce ".The filtered coal e2tract passes to a distillation column to recover the lightoil wash solvent and is then preheated, mi2ed with " and routed to oneor more ebullating#bed reactors in series. There is no inter#stageseparation and the reactors operate at nominally the same conditions8~''bar, :''#::'HC and a space velocity in the range '.5#$.'h#$ -kg feedper kg catalyst per hour/. The reactor products are cooled, depressurisedand passed to an atmospheric distillation column to recover a distillateproduct. The cut#point of this column is ad

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    column are recombined with the main atmospheric column bottomsstream and recycled as the solvent to the slurrying step.! significant proportion of saturated species may build up in the recyclesolvent under certain conditions, reducing the effectiveness of thee2traction step. Thermal cracking is used to control this aspect of solventquality.The pilot plant operating programme concluded with a steady#statedemonstration run. The results from this run indicate that it would be

    possible to operate the process in an all#distillate product mode, removingthe requirement for a vacuum column. olvent quality was maintainedwithout the need for a separate, thermal cracking step. rimary productqualitydata from this demonstration period are summarised in Table .The total distillate product yield is in the range )'#)5% -dry ash#free coal/,most of which boils below A''HC. The total filter cake yield includes ~3%of undistillable pitch.Table 2. L&E process conditions yields and product quality using Point o( 3yr coal

    daf8 dry ash#free

    T!e Bro*n Coal Li,'eation ProessThe @C1 process -;igure $$/ was developed by ?E04 of apan to a 5'tonnesMday pilot#plant scale, constructed at *orwell in Iictoria, !ustralia.9t was operated over the period $&5#$', processing a total of ~)','''tof coal. 4perations ceased in 4ctober $'. The plant wasdecommissioned in $$ and demolished in $.Coallurry*i2ing

    Becycle olvent0esaturated olventThermalCracking;ilterBecycled"ydrogenolventBecovery;resh"ydrogenEbullated@ed"ydrocracker!tmospheric0istillationIacuum0istillation=ases0istillateroduct;ilterCakeitchCTBBeactors

    Figure 14. The L&E processFigure 5. L&E pilot plant (acility at Point o( 3yr

    4perating conditionsolventMcoal ratio .0igestion pressure -bar/ $50igestion temperature -HC/ :A$?ominal residence time -min/ 5'"ydrocracking pressure -bar/ ''"ydrocracking temperature -HC/ :A:pace velocity -kg feedMkg catMhour/ '.3)roduct yieldC$#C: hydrocarbon gases -% daf coal/ $5.:C5#A''HC distillate product -% daf coal/ :.A''#:5'HC solvent surplus -% daf coal/ $.:itch -R:5'HC/ -% daf coal/ '.&;ilter cake organics -% daf coal/ A.roduct analysis

    "ydrogen -wt%/ $.$:?itrogen -wt%/ '.$:ulphur -wt%/ '.':"ydrogen "ydrogenCatalystCoalIacuum0istillationolvent Becycleolvent Becycle!tmospheric0istillationolvent"ydrogenation>et *illinglurry0ewateringrimary

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    Beaction>ater=ases?aphtha"ydrotreated?aphthaBesidueolvent0eashing

    Figure 11. The 6CL process

    The process is designed specifically to handle very low#rank coals such asthose found in the 1atrobe Ialley of Iictoria, which may contain R)'%

    moisture. !s a result, a crucial aspect is the efficient drying of the coal.The 5' tonnesMday rated throughput of the pilot plant required ~$3'tonnesMday of raw coal to be processed.;ollowing e2tensive pilot plant operation, BF0 using a '.$ tonnesMdaybench#scale continuous liquefaction test facility and related equipmentwas carried out until $3 to improve the reliability, economics andenvironmental compatibility of the coal liquefaction process. @ased on theBF0 results an improved @C1 process was proposed. This comprises slurryde#watering, liquefaction, in#line hydrotreating, and de#ashing, with thefollowing features87 use of a high#active and ine2pensive catalyst such as limonite orepulverised in oil7 use of a heavy fraction solvent -bp A''#:'HC/7 adoption of coal liquid bottom -C1@/ bpR:'HC recycling.Compared with the results of the pilot plant, the increase of oil yield,improvement of product oil quality and suppression of scale formation in

    reactors were proved using the bench#scale unit with G$% -dry ash#freecoal/ catalyst addition. 9t was estimated that the improved process coulddecrease the crude oil equivalent nominal price by :% compared with the@C1 process at the !ustralian pilot plant.

    C o - ( r o e s s i n g+Co#processing is generally a variant on other direct liquefaction processes.9t involves simultaneous upgrading of coal and of a non coal#derived liquidhydrocarbon. The liquid hydrocarbon also serves as the slurrying andtransport medium for the coal. This is usually a low#value high#boilingpointmaterial, such as bitumen, an ultra#heavy crude oil or a distillationresidue or tar from conventional crude oil processing. There is no solventrecycle loop and the underlying process may be either single# or two#stage.9n general, co#processing technologies are based on adaptations of pree2istingdirect liquefaction processes to a once#through non#recyclingbasis. 9n these processes most of the liquid product derives from the oilrather than from the coal.

    The overall aim of co#processing is to upgrade the petroleum#derivedsolvent at the same time as the coal is liquefied, thereby reducing capitaland operating costs per unit of product. "owever, the non coal#derivedsolvents are both poor physical solvents for coal and poor hydrogendonors. This results in a relatively low conversion of the coal to liquidproducts. The economics of co#processing, therefore, dependpredominantly on the differential between the heavy liquid feedstock costand the price of conventional crude oil. The addition of a low#price coalto the feed improves the process economics by reducing the averagefeedstock cost. Compared with other liquefaction routes, capital costs aregenerally significantly lower per unit of product, since most of the productis derived from the oil feedstock. 9n practice, the true competitors for coprocessingare likely to be heavy oil upgrading processes.!lthough some co#processing technologies have been developed to severaltonnesMday 06, or pilot plant scale, they have not been developed to thesame degree as other liquefaction processes. ?one has beendemonstrated at significant -~$'' tonnesMday/ scale.

    rocesses include87 *9T9 *ark 9 -apan/7 *9T9 *ark 99 -apan/7 the Cherry rocess -4saka =as Co., apan/7 olvolysis -*itsubishi "eavy 9ndustries, apan/7 *obil -6!/7 yrosol -aarbergwerke, =ermany/7 Chevron -6!/7 1ummus Crest -6!/7 !lberta Besearch Council -!BC, Canada/7 C!?*ET !4TB! -Canada/7 Bheinbraun -=ermany/

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    7 T6C -Technical 6niversity of Clausthal, =ermany/7 64 lurry#catalysed -64, 6!/7 "T9 -6!/.The most important of these are !BC, C!?*ET, "T9 and 1ummus Crest.

    L'&&'s Crest Co-(roessing1ummus Crest Co#processing was developed to a '.5 tonsMday 06 in theearly and mid#$&'s. 9t is a derivative of the 1ummus 9T1 process. ! keyfeature of the process is that the petroleum heavy oil is hydrogenated prior

    to its use as slurrying solvent for the coal. This generates some hydrogendonor capability, increasing the e2tent to which the coal is dissolved andreducing repolymerisation and coking reactions.Coal is slurried with the hydrogenated petroleum residue and reacted in anuncatalysed, short contact time reactor at a temperature of :A'#:5'HC anda hydrogen pressure of $:'bar. The reactor products pass directly to thesecond stage 1C#;iner ebullated#bed reactor, which operates at the samepressure and a temperature of :''#:A5PC with a supported hydrotreatingcatalyst. !s with many other co#processing options, the intention appearsto be to integrate the process within an e2isting oil refinery. ~'% of thecoal is dissolved in the first stage on a dry ash#free basis, with overallconversions approaching 5%. The overall conversion of heavy material inthe petroleum residue is 3'#&'%. The total net yield of distillable productsis in the range 5'#55% on fresh feed.

    Al.erta Resear! Co'nil Co-(roessing!BC, in collaboration with Canadian Energy 0evelopments, originally

    developed the two#stage Counter#flow Beactor -C;B/ process for upgradingtar#sand bitumen. ubsequently, the process was adapted to co#process subbituminouscoals with bitumen. 9ncorporation of coal is said to increasedistillable oil yields in comparison with those obtainable from bitumen alone.The process is unusual as it uses a C;B and, in place of ", uses C4 andwater in the first stage. The first stage has been tested at a scale of '.5tonsMday for co#processing and 5 tonsMday for bitumen alone.Coal is first cleaned by an oil agglomeration technique and then slurriedwith bitumen, water and a disposable alkali metal catalyst. The mi2ture isfed to the top of the counter#flow reactor, which operates at A&'#:''HCand &3bar. C4 is fed to the base of this reactor and travels upwards, theshift reaction generating ". The high o2ygen content of sub#bituminouscoals is reduced by use of C4 and steam and the process is claimed to bemore effective and lower cost than the direct use of ".The second stage, in principle, consists of a second C;B reactor systemoperated at ~:'#:&'HCM$35bar. Either " or C4Msteam could be used inthis stage. There is no recycle of product from the second stage.

    The conversion of the coal depends primarily on the coal characteristics,but conversions of up to &% on dry, ash#free coal can be obtained insome cases. The overall product yield from the two stages isappro2imately 3'% on the combined weight, dry ash#free coal andbitumen#fed.

    CAN/ET Co-(roessingThe C!?*ET hydrocracking process was intended to hydrocrack heavy oilsand was developed to a 5''' barrels -bbl/Mday commercial scale at theetro Canada *ontreal refinery by $&5. ! variation of the process wasadapted for co#processing and was taken to the '.5 tonsMday pilot plantscale in a three#year BF0 consortium programme sponsored by Bheinbraun!=, !moco Corporation and the !lberta 4il ands Technology andBesearch !uthority -!4TB!/. C!?*ET discontinued BF0 in $A.Coal and a disposable coal#based catalyst are slurried with a petroleumvacuum residue or bitumen, mi2ed with " and fed to a single#stage upflowreactor. Typical operating conditions are reactor temperatures from

    ::'#:)'HC, pressures from $'#$5*a with feedstock coal concentrationsof A'#:'wt% -mineral matter#free basis/.The reactor product is separated and fractionated to recover distillateproducts and an undistillable residue. The e2tent to which coal isconverted is highly dependent on coal characteristics, but may be as highas &% on a dry ash#free basis. The conversion of high#boiling material inthe bitumen or vacuum residue may be up to 3'%, depending on reactionseverity. 4verall net distillable oil yields of up to &'% on dry ash#freeslurry feed are reported.

    HTI Co-(roessing"T9 -previously "B9/ has carried out test work on co#processing since $&5,treating it as a simplified version of the mainstream two#stage direct CT1

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    coal liquefaction process. 9t differs only in that there is no recycle solventloop. *ost work has been carried out with l ignites and other low#rankcoals. Becent work includes the use of "T9s =elCatS, an iron#baseddispersed catalyst .Coal conversions of up to $% -dry ash#free basis/ have been reported.The conversion of heavy material in the petroleum residue varied from&'% to '%, with overall distillable product yields in the range 33#&)%by weight on the total feed.

    I N D I R E C T L I Q U E F A C T I O NThe only +core unit specific to indirect liquefaction is the synthesis reactionstep. "ere, a consensus has developed that slurry#phase fluidised#bedreactors are preferable. The ma

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    catalyst.The "T;T process operates at A''#A5'HC and '#A'bar, again with an ironbasedcatalyst, and produces a lighter, more olefinic product slateincluding gasoline, petrochemicals and o2ygenated chemicals. Thegasoline produced by upgrading the primary products is of particularlygood quality.The 0 process was developed for monetising natural gas and comprisesnatural gas reforming, slurry#phase ;T and mild hydroprocessing to

    produce naphtha and an e2cellent diesel. The 0 process uses a cobaltbasedcatalyst specially developed for the slurry#phase system. Thenaphtha, because of its paraffinic nature, has a low octane number and assuch is poor quality for gasoline, but it is a very good cracker feedstock.tudies carried out by asol have shown that "aldor Topse autothermalreforming, used to reform the natural gas with o2ygen, is the mostappropriate for the ;T process. "ydroprocessing of the products is verymild and the slurry#phase ;T has been demonstrated commercially in a5''bblMday unit at asolburg. asol believes that this relatively simplethree#step process is superior in all aspects and can be built and operatedeconomically.! schematic diagram of the 0 process is shown in ;igure $A.*ethaneBeformingCryogeniceparationeparationand;ractionationlurry

    haseBeactorBectisol?aphtha9somerisation0ewa2ing=asoline0iesel=ases!shCoalBecycled ynthesis =as

    Figure 12. The &asol process!ireparation"ydrogenroduction!irweet ?atural =asweet?atural=asE2ternal Becycle;uel =asTail =as?aphtha0ieselTreated >ater

    42ygenateslant Effluents@;>teamyngasBeaction >ater>a2 NCondlant Condensatesteam F @;> to4ther 6sers4roduct>ork#6p; # Tynthesisynthesis=asower=eneration6tilities EffluentTreatment

    Figure 1. &&P# process

    T!e /o.il /TG ProessThe *obil methanol#to#gasoline -*T=/ process produces gasoline fromcoal or natural gas in two distinct steps. The process has been taken to a

    commercial scale in a $,5''bblMday plant built in ?ew Uealand to processgas from the *aui field. !lthough this plant is still operating, it hasrecently been used solely for methanol production, for which theeconomics are currently more favourable.9n the first step, synthesis gas produced by steam reforming of natural gasor by coal gasification is reacted over a copper#based catalyst to producemethanol in near to $''% yield. The reaction is carried out at )'#A5'HCand 5'#3'bar.The second step involves partial dehydration of methanol to dimethyl etherat A''HC over an activated alumina catalyst, followed by reaction over afi2ed#bed Keolite U*#5 catalyst. These reactions are strongly e2othermic,with the feed entering the reactor at A)'HC and leaving at :$5PC. The

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    reactor pressure is bar. ! series of reactions converts methanol anddimethyl ether to olefins and then to saturated hydrocarbons. Oields ofmaterial in the gasoline boiling range represent ~&'% of the totalhydrocarbon product. >ith alkylation of by#product propane and butane,total gasoline yields of '% at A.3 B4? -octane number/ were achievedat the ?ew Uealand plant. The use of a fluidised#bed reactor offersadvantages for temperature control and maintenance of constant catalyticactivity over a fi2ed#bed system. The fluidised#bed reactor operates at an

    almost isothermal temperature of :$'HC but at a pressure of only Abar.rimary, gasoline#range liquid yields are lower, but there is little differencein final gasoline yields after alkylation.

    T!e S!ell S/DS ProessThe hell *iddle 0istillate ynthesis -*0/ process produces a highqualitydiesel fuel from natural gas. 9t is a process being considered inmany =as#to#1iquids -=T1/ processes in oil production. !s the processproduces liquids from synthesis gas, although the technology is primarilyaimed at a natural gas feedstock, synthesis gas generated from coalgasification would, presumably, be equally suitable. ! schematic diagramof the process is shown in ;igure $:.?atural gas is first partially o2idised in an o2ygen#blown hell gasifier toproduce synthesis gas. This gasification approach is preferred over steamreforming, despite the considerably higher capital cost and lower thermalefficiency, because it produces a synthesis gas with the correct C48" ratioof $8. team reforming produces e2cess ", which in a stand#aloneoperation can only be used as fuel.The cleaned synthesis gas is then reacted over a proprietary hell catalystin a fi2ed#bed tube#bundle reactor that is cooled in boiling water. Theproduct is almost e2clusively paraffinic. The catalyst formulation andoperating conditions in this step are deliberately chosen to give a muchhigher#boiling product than usual, since this minimises the production ofhydrocarbon gases.9n the final step, the wa2y heavy paraffin is catalytically hydrogenated,isomerised and hydrocracked in a single trickle#bed reactor over aproprietary catalyst to give products that are mainly middle distillates. Thereactor operates at A''#A5'HC and A'#5'bar. ! high degree of productrecycle is used to minimise the production of light products and to ensurethat higher bp products are recycled to e2tinction. @y varying thehydrocracking severity and the e2tent of recycle, the product distributioncan be ad

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    Befineries with the necessary thermal or catalytic crackers have claimedthermal efficiencies of A#:% when allowance is made for electricalpower generation. Thus an efficiency of '% may be assumed for ahypothetical refinery producing only transport fuel.The standard coal may be converted to the standard crude oil, by directand indirect liquefaction, at thermal efficiencies of 35% and )$%respectively, with all the carbon in the coal, not ending up in the +crudeoil, converted to C4 -either in power stations or furnaces/. ;or direct or

    indirect liquefaction this amounts to $.&: tonnes or A.''tonnes C4Mtonnecrude. ?ote that, even at $''% thermal efficiency, there is some C4produced because of the release of '.') tonnes of hydrogen from coal.;uel =asBecycled "ydrogen;ractionation"ydrocracking"eavy roduct Becycle?aphthaDerosene0iesel;resh "ydrogenTube#@undleBeactorCleanedynthesis =as

    Figure 1!. &che'atic diagra' o( &8#& process$''% V 5:)$*>.)$3.5"ydrogenroductionCoal E2traction and;iltration

    "ydrocracking1oss1oss1oss

    1oss1oss@utaneBefiningower tation:.)$.3$&.)$.:'.3rincipal)'.3 roducts@y#productsinc. 1= -:.$/ower E2port$''.').) '.$ '.$:..)'.)$.5

    $..5.A:.$5.5

    Figure 1%. Ener gy (low diagra' (or a conceptual L&E plant

    Stan%ar% 'els @ituminous coal Crude oilCarbon -%/ &) &).$"ydrogen -%/ 5.5 $$.&42ygen -%/ ).' #?itrogen and sulphur -%/ .5 .$?et CI -*>hMtonne/ .)) $$.:9n refining crude oil to finished fuels there would be a further '.A tonnesC4Mtonne of crude oil processed, giving $'.A$*>h of CI in the finishedproducts.9n all, ~3#$' times as much C4 is emitted in converting coal to transportfuels, when compared with crude oil.

    P R O S P E C T S F O RI / P L E / E N T A T I O N9n $&5 oil prices fell suddenly and, with brief e2ceptions, have remainedlow since. 9nterest in coal liquefaction for the production of transportationfuels has declined accordingly. !t present, only apan is active in largescaleprocess development, with a $5' tonnesMday plant in operation atDashima near Tokyo, and China is participating in several collaborativefeasibility and process development studies. 9t remains to be seen whethera future increase in oil prices will result in renewed interest and possibly infull#scale commercialisation. 9n the meantime, the emphasis has returnedto coal upgrading.

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    Coal liquefaction, by whichever route, is capital#intensive and thereforebenefits substantially from economies of scale. *ost studies on processeconomics have assumed that a full#scale commercial plant would produce5','''#$'','''bblMday of liquid products. uch a plant would process$5,'''#A5,''' tonnesMday of bituminous coal or up to double thatamount of sub#bituminous coal or lignite. !t the lowest end of this range,the annual consumption would be 5 million tonnesMyear of bituminouscoal. The output from this plant would still be small relative to that from a

    typical modern crude oil refinery, where a throughput of R'','''bblMdayis common.Countries that might implement coal liquefaction must, therefore, haveready access to large quantities of coal. The economics of liquefactiondepend strongly on coal costs and this coal must be delivered to the plantat a low price. ince coal is more difficult to transport than oil, it would,as a general principle, be better for liquefaction to be carried out in thecountry of origin and preferably at the point of origin. There will,however, be e2ceptions to this generalisation, particularly whereconstruction costs near the point of origin are likely to be high due toremoteness or where there are already good rail links.9f liquefaction is to be carried out in the country of origin of the coal,there must be sufficient reserves to last for a pro

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    Bomania A.5

    pain ' ?o oil reserves

    Turkey ' ?o oil reserves

    6D 5. 1ow oil reserves

    ;ormer oviet 6nion 5 olitical and economic considerations

    outh !frica ' ?o oil reserves

    Uimbabwe X ' ?o oil reserves but no demand( economic

    considerations!ustralia & 1ow oil reserves

    China '.5 4il reserves remote from demand

    9ndia $5.) 4il reserves remote from demand

    9ndonesia 1ow oil reserves with increasing domestic demand

    apan ' ?o oil reserves W 4il demand in 6! is ten times that of most other countriesWW @ tatistical Beview of >orld Energy $&Table !. 3nalysis o( potential i'ple'enting countries

    power and chemical feedstock supplies, would be common to both therefining and liquefaction processes, there would be opportunities forsharing some of the necessary facilities. Equally, many of the unitoperations are likely to be similar in both the refinery and the coalliquefaction plant. !gain, this favours implementation by the oil industry.9ntegration may involve simply a shared product#blending and e2portfacility. Even this minimal integration of facilities would offer significant

    capital cost reductions. tudies have shown that a $','''bblMday refinerycould accept the whole output from a 5','''bblMday liquefaction plantwith minimal change in overall product quality, so the typical refinery of'','''bblMday would cope easily.! more comple2 integrated approach could involve the liquefaction plantand the refinery transferring products for further processing. rimarydistillates from the liquefaction plant could be blended and processed withthe equivalent feedstocks in the refinery. 9n addition to capital savings, thegreatest benefits would come from e2porting low#value products from therefinery to the liquefaction plant, for gasification to produce ". Thesematerials may include vistar from a visbreaking unit or high#sulphur cokefrom a delayed coker, for which the refiner may otherwise have no outlet.This also increases fle2ibility in determining the refinery product mi2,possibly by making additional use of coking to increase distillateproduction. The liquefaction plant would no longer require additional coalas a supplemental utility fuel. The

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    and higher carbon content. Coal#to#liquid conversion processes requirehydrogen to be added or, alternatively, carbon to be removed.?umerous +direct and +indirect processes have been developed for thispurpose.7 Considerable BF0 into liquefaction processes was carried out during the$3's and early $&'s, mainly in the 6!, apan, the 6D and =ermanyspurred on by oil price shocks. ince then, development has largelybeen put on hold.

    7 outh !frica is the only country presently operating liquefaction plant.9t has large reserves of coal but no oil and gas. Trade embargoes overthree decades to the mid#$&'s drove large#scale application and up to)'% of transportation fuel requirements have been met from coal.7 Coal liquefaction is now a largely proven technology for themanufacture of useful liquid products.

    Beneits o t!e Te!nolog+7 Coal is abundant but, in comparison with liquid fuels, inconvenient tohandle and unsuited to some applications particularly transport. Coalliquefaction provides the ability to manufacture transportation fuelsfrom coal.7 The technology provides insurance against depleting oil stocks and oilsupply problems.

    Disa%$antages o t!e Te!nolog+7 1iquefaction processes typically achieve an energy conversion -% CI ofthe input fuel converted to finished products/ of )5#3'% -direct

    liquefaction/ and 55% -indirect liquefaction/.7 Converting coal to transportation fuels results in ~3#$' times as muchC4 being emitted, compared with converting crude oil. This increasein C4 emissions at the processing stage has the effect of raising overallC4 emissions from transport by ~5'%, compared with transport basedon conventional, refined petroleum products.

    /ar2et Pros(ets7 resently, only apan is active in large#scale process development, whilstChina -increasingly a net oil importer and containing areas remote fromsources of oil/ presents the strongest adoption prospects.7 The commercial viability of coal liquefaction rests with the overalleconomics of the process. This depends on the availability of significantquantities of poor#quality, low#cost coal, and the unavailability orotherwise relatively high cost of oil -and gas/. !ppropriate marketconditions are likely to emerge around '$'( many countries are thenlikely to be involved.

    A C " N O 3 L E D G E / E N T SThis review was funded by the 0T9s Cleaner Coal Technology rogramme.B I B L I O G R A P H Y7 ynthetic ;uels from Coal8 tatus of the Technology. Bomey, aul and9marisio -Eds/. ublished by =raham and Trotman for the EuropeanCommunities -$&3/. 9@? $#&5AAA#$'A#$.7 Coal 1iquefaction8 ! Besearch ?eeds !ssessment. 604E Beport04EMEB#':'' -$&/.7 604E Coal 1iquefaction and =as Conversion Contractors BeviewConference. roceedings.7 Energy for Tomorrows >orld. >orld Energy Council. ublished byDogan age -$A/. 9@? '#A$#$')5#.7 The Coming 4il Crisis. C Campbell. ublished by *ulti#cienceublishing Co -$3/. 9@? ' ')5#$$#'.7 @ tatistical Beview of >orld Energy -$&/.7 Beport of hases 9#9Ib of @ritish Coal 1iquefaction ro

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    Direct and Indirect Liquefaction

    There are two methods of deriving liquid fuel from coal: direct coalliquefaction (DCL) and indirect coal liquefaction (ICL). The major difference

    between the two is that DCL is the rocess of creating a liquid fuel from coalwhile ICL involves gasif!ing coal first and then using this s!ngas to roduceliquid fuel. "lthough DCL methods are more efficient# the rocess involveslarge amounts of aromatic comounds. "s a result# an! liquid fuels obtainedthrough DCL methods would have worse e$haust emissions from the combustionrocess than etroleum fuels. "lso# DCL does not give an! otions for caturingC%&emissions.

    Li,'eation

    9ncreasing "MC ratio is a must(Two options Be

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    Coal Con$ersion

    Proesses CarboniKation and yrolysisY 1ow severity -*ild =asification/Y "igh temperature0irect 1iquefactionY 4ne stage reactor technologyY Two#stage reactor technology

    Y Co#processingY "ybrid9ndirect 1iquefactionY =as reactorsY lurry reactors

    Coal Li,'eationA((roa!es

    yrolysis or mild gasification0irect coal liquefaction9ndirect coal liquefactionCo#processing

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    @ioliquefaction

    &ubstantial o0erlap in the che'istryo( 'ild gasi(icationdirect coal lique(action and co*processing