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I RELATIONSHIP BETW EEN TH E GASIFICATIONREACTIVITIES O F COAL CHAR AND TH EPHYSICAL AND CHEMICAL PROP ERT IES O FC O A L A N D C O A L C H A RJ a m e s L. Johnson

Inst i tute of G a s Technology3424 S . State S t reetChicago, Il l inois 6061 6

INTRODUCTION

85

A var ie ty of exper imental inves t igat ions have s tudied , a t e levated pr es su re s ,the gas i fica t ion k inet ics of coal c ha rs in hydrogen and in ga ses conta ining steamand hydrogen.conce rned with the cha racter izat ion of gasif icat ion ra te s a s a function of environ-men ta l condi ti ons such a s t emper a tu re , p res su re , and ga s composi ti on, andhave provided l i t t le sy stema tic information concerning rela t ionships betwee ngas i f ica t ion react iv i t i es and the phys ical and chemical pro per t ies of c o a l o r c oa lc h a r .

The bulk of thes e inves tigat ions , however , have been pr i ma r i ly

This s tudy was th ere fore in i ti a ted to evaluate poss ib le re la t ionships betweengas if i ca t ion reac t iv i t ie s and s imp le compos it iona l pa ra me te r s fo r coa l c ha r s de r ivedf r o m a wide varie ty of coa l s and coa l -ma cera l concen tra t es. The i n t e rna l s t ruc tu ra lchanges that occ ur during the c ou rse of gasif icat ion of a few coal ch a rs of vary ingrank we re a l so exp lo red .wer e de t e rmined i n hydrogen o r i n a 50:50 s t eam-hydrogen m ix tu r e at 35 a t m o s p h e r e s ,using a high-pressure thermobalance.a l though, in a specia l se r i es of t es t s des igned to inves t igate the cata ly t ic ef fects ofexchangeable cat ions on lign i te char react iv i t i es , t em pe rat ure s wer e var ie d f r om1400" t o 1700F .

The gasif icat ion react iv i t ies of individual co al c ha rsMos t t e s t s wer e conduct ed a t 1700" F ,

The fo ll owing resu l t s a r e d i s cus sed i n t h i s paper :The relat ionship between the ini t ial carbon content and the gasif icat ion re act ivi t iesde t e rmined i n t he hydrogen a t 1700" F, fo r coa l cha r s de r ived f r om 36 coa l s and

I ma ce ra l concen t ra tes ranging in rank f ro m anthra ci te to l ign i te .I The effect of exchangeable cat ion concentrat ions (so diu m and cal ciu m) ongasification reac tivit ies of l ignite s in hydrogen at 170 0F and i n s team-hydrogenmix tur es a t 1400" to 1700F .

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,

0 The surface area and pore volume var ia t ions that occ ur dur ing gas i f ica t ion inhydrogen and in s team-hydrogen mixtu res a t 1700F of c oa l cha r s de r ived f r omanthrac i te, me tal lur gic al coking coal , high-volat i le A bi tuminous coal , sub-bituminous A coal, and lignite.

EXPERIMENTAL PROCEDUREThe h igh-pressure thermobalance used in th i s work to obta in gasi f icat ion re ac -t iv i ty f a c to r s h as been desc r ibed p rev iously ( 4 ) .app ara tus i s that the weight of a small f ixed-bed sample of co al ch ar ( 1 Z t o 1 g r a m )contained i n a wire -m esh baske t ca n be cont inous ly measu r ed a s it undergoesgasif icat ion i n a des i red gaseous envi ronment at const ant t empera tu re and p res su r e .In al l te s ts conducted, --20+40 U. S. s i eve s i ze pa r t i c l e s wer e u sed, and gas f lowra t e s i n t he r eac to r w er e main ta ined at sufficient ly high valu es to re sul t in nenl i -gible ga s conversion. Under the se condi tions, coal-c har gasif ic at ion could b econside red to occ ur under constant known environ menta l condi t ions.we re produced by in i t ia l ly exposing the raw coals to n i t rogen a t 1 a tmo sphe re for

The mai n feat ure of th i s

Coal cha r s

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8660 minutes , a t the sam e tempe ra tu re to be used dur ing subsequent gas if icat ion inhydrogen o r in s team-hydrogen mi x tur es .te r i s t ic s ob ta ined during gas i f ica t ion in ind iv idual tes ts were then used a s a b a s i sfor computing gasif icat ion reactivi ty factors, using a procedu re d escr ib ed below.

The weight loss ver sus t ime cha rac -

Cer ta i n of the so l id feeds and res idue s wer e analyzed fo r in terna l su r face are a ,pore vo lume, and t r ue densi ty . Sur fac e ar ea s were computed f rom adsorp t ioniso ther ms obtained with a Model 2100 O r r su r face area- pore vo lume analyz ermanufac tured by the Microm ere t ics Corp . , which was a ls o used to obta in t r uedensi t i es in he lium.in terpre ted with the BET equat ion to compute su r face are a , and iso the rms ob tainedin car bo n dioxide at 298K w er e inte rpre ted with the Dubinin-Polanyi equation a smodified by Kaganer ( 7 ) to compute sur face area . In genera l, sur face ar ea scomputed f r om n i trogen and carbon d iox ide adsorpt ion i so the rms w ere no t inagreem ent , and va lues ob tained in carbon d iox ide were considered to be mostref lect ive of equivalent int erna l s urfa ce ar ea , which is consistent with the findingsof ot he r inves tigat ors ( 2, 3 , 6, 7, 12) . Apparen t ly , the penetra tion of nitrogen intothe microp orous s t r uc tu re of c oa ls o r carbonized coal ch ar s i s severe ly l imi ted byslow, act ivated diffusion pr oc es se s at 77"K, eading to very low apparent sur facear ea s : on th e o ther hand, fo r par t ia l ly gas i f ied coal chars hav ing m or e openmic ropo rous structures, cap il la ry condensation of ni trogen can lead to unreasonablyh igh appare n t sur face ar ea s ( 1,8).dioxide a t the h igher tem pera ture of 2 9 8 K faci l i tate act ivated diffusion intomicrop orous s t ruc tur es , and cap i l la ry condensa tion i s inhibited by the low er relat ivep r e s s u r e s e mp lo ye d ( 0 . 0 0 3 to 0 . 0 2 ) . Although there is some question concerningwhether carbon diox ide adsorp t ion i s o the rms should be in terpre t ed in te rm s ofmic ropo re volume (8,9, 0, 11) r a th e r than mic ropo re su r f ace area (2 , 3 , 6, 7 , 1 2 ) ,the dist inction is not of impor t ance in em pir ica l cor re la t ions with gas if ica t ion k ine t icp a r a m e t e r s .va lues of m icropore vo lume and micr opo re sur fac e a re a a r e v ir tua l ly ident ical ,differ ing only i n th e numer ic a l constan ts used .po re vo lumes can be conver ted to cor responding va lues of microp ore sur fac e ar e aby a f ixed constant. In this study we have chosen to compute surface ar e a values,favoring the argument that car bon dioxide adsorption on a carbon sur face should beres t r i c t ed to a monolayer th ickn ess , as a re su lt of the quadruple intera ction of thecarb on dioxide molecules with the v-bonds of the carbon sur fac e ( 2 , 7).

Adsorption iso the rm s obtained in ni trogen a t 77K we re

Adsorption iso the rms obtained with carbon

This is becau se the ca lcu la tion methods used to compute numer i ca lThus, reported values of mi cr o-

An Aminco mer cury in t rus i on poro sim ete r capable of a hydrosta t ic p r es su re of15, 000 ps i was used to obta in po re vo lume d is t r ibu tions fo r pores having d iame tersgr ea te r than about 120 ang st ro ms. Po re vo lume d is t r ibu t ions for pore s be tweenabout 12 and 300 ang st ro ms w er e ob ta ined f ro m adsorp tion i so the rms ob ta ined innitrogen at 77K a t r e la t ive p r e s su re s up to abou t 0 . 9 3 .obtained with these two met hod s in the overlap region from 180 to 300 angs t roms ,s imilar to resu l ts repor te d by Gana.3 ) .

Good ag ree men t wa s

DEFINITION O F RELATIVE REACTIVITY FACTOR, f,Weight loss vers us t ime cha rac t er is t ics ob ta ined in individual thermobalancete s t s we re in terpre ted to ob ta in re la t ive reac t iv i ty fac tors fo r the coal cha rs used ,b a s e d o n a quantitative model developed previously at the In stitu te of G as Technologyto d esc r ibe the gas i fica tion k ine t ics of b i tuminous coal ch ar s a s a function oft empera tu re , p r e ssu re , ga s composi tion, p r e t r ea tmen t t empera tu re , and ca rbonconversion ( 4 ) .Coal-c har gasi ficat ion i n ga se s conta in ing s team and hydrogen a r e assum ed to

The essen t ia l fea ture s of th is model a r e descr i bed be low.occur v ia th re e main reac t ions:

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I\

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a7kl

React ion 1 C +H,O f CO + H Zk2

k3React ion 11 C + 2Hz f CH,React ion 111 2C + H, + H,O f CO + CH4

where k,, k,, and k, a r e rate const ant s fo r t he t h re e r e ac t i ons shown and a r equant itat ively defined in the mode l a s a funct ion of t emp erat ure , pr es su re , and gascomp osition (acco unting f o r CO, Hz, H,O, and CHI) . The diff ere ntia l coa l-ch arconversion ra t e is exp ress ed by the re la tionship :2 /3-t = f L k T ( l - X ) exp (4z)

w h e r e -X = base carbon convers ion f raction9 = t imefL = re la tive react iv i ty factor for coa l -ch ar gas i f ica t ion , which depends onthe pa r t i cu l a r coa l cha r and on t he p re t r ea tm en t t em pera tu re u sed i nprepar ing the coal cha rkT = k, + k, + k3c1 = kinet ic pa ram ete r def ined as a funct ion of pr es su re and ga s compos i tion .

Ba se carbon, r e fe r r ed t o i n t he above de f in it ion of X, me ans th e nonvolat i lecarbon in raw coal that re main s after standard devolat i l izat ion.conversion f ract ions can be es t imated f ro m weight loss -versus- t ime cur vesobta ined in thermobalance tes t s , us ing the express ion:B a s e c a r b on

w/w, - V M )1 - V M - A=w h e r e -

WIW, = to ta l weight -loss f ract ion ref err ed to or ig inal coalVM = weight los s fract ion during ini t ial devolat i l izat ion in ni t rogen

(approximately equal to s tandard vola ti l e mat ter a t e levatedt e m p e r a t u r e )A = a s h m a s s f r a c t i o n i n f ee d c o al .

The re la t ive react iv i ty factor , fL, depends on the pre t re atm ent t emp era tur e accordingto the expression:fL = f o e x p ( 8 4 6 7 ) ( 1 / T -I/T)P 3 )

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w h e r e - 88foT = p r e t re a t m e n t t e m p e r a t u r e , " RT = gasif icat ion tem pera tur e , "R.

= reactivi ty fa ct or dependent only on the in herent nature of th e coal ch arP

Equation 3 i s only applicable for T > T; for T d T, then f L = fo .P PAt constant environmental condit ions, Equation 1 can be integrated t o yield -

M ( X ) = lxe-dX l - X Z s = f L Te 4 )Base d o n Equation 4, a plot of M ( X ) v e r s u s 0 should yield a straight l in e having as lope equal to the te r m f k .thermobalance data, us& Equation 2 to obtain values of X and using th e definedvalue of a o evaluate th e inte gra l in Equation 4.pu re hydrogen, t he value ofis approximately equal to ( 1 -X ) , over near ly a comp lete rang e of X.M ( X ) = -In( 1 - X ) and va lues of the specif ic gasif icat ion rat e , (dX/d0) /( 1 -X ) ,a r e constan t and equal to f kL T '

F i g u r e 1 shows two types of behavior noted in this study in e xperimental plotsof M(X) versus 8 .of coa l ch ar s tested, with l ine ari ty exhibited over the complete range of bas e carbonconversion. The l ine shown does not extrapolate to the or igin bec aus e char samplesinit ial ly exposed to the gasifying environment in the thermobalance re qu ire 1 to 2minutes t o heat up to r e ac to r t empera tu re . A character ist ic of the type shown fo rC a s e B wa s obtained with so m e coal cha rs, usually low-rank mat er ia ls , indicatinga n in i tia l per iod of t ra ns i en t reac t iv ity , which decrease d dur ing the f irst 5 to 10minut es and remained constan t thereaf te r . F o r coal ch ars exh ibi t ing th is type ofbehavior , only the l in ear port ion of the curv e corresponding to constant reactivi tywas used to evalua te exper iment a l va lues o f f kL T 'by th e value of kT defined i n the mo& l ( 4 ) for the reaction condit ions used.RESULTS

Valu es of M( X ) can b e computed f r om exper imenta lNote that, f o r t e s t s conducted inis 0.97 ; wi th th is va lue , the te rm ( 1 -X)2/3exp( 0.9 7 X')Fo r th is ca se ,

Line A is typical of t he c ha rac t e r i s t i c s cb ta ined with t h e majority

Values of the reactivi ty fa cto r , f we re then obtained by dividing th e te r m fLkT

Cor re la t ion of Reactiv i ty F ac to rs With Carbon Conten t in Raw CoalsThe reac t iv i ty fac tors f o r coa l cha rs der ived f ro m 36 coals and coal macer a lconcentrates were de t ermin ed i n hydrogen a t 1700 F and 35 a tmosphe res .distr ibution of coals used with r es pe ct to rank and li thotype i s desc r ibed in Tab le 1 .In thia study a variety of cor re l a t ions wer e evalua ted in a t tempting t o quanti ta tive lyre la te these react iv ity fac tor s wi th s imple , composi t ional par ame ter s inc luded inu l t imate , p rox imate , and pe t rog raphic analyses of t he r aw coa ls . The be s t success ,however , wa s achieved with one of the simp lest cor rel at io ns considered - a relation-ship between reactivi ty fac tor s and ini t ial carbon contents.i l l u s t r a t ed in F igure 2, whe re the l ine drawn cor respon ds to the express ion :

T he

Th is co r r e l a t ion is

f L = 6 . 2 Y ( l - Y ) 5 )

3

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89where -f L = relat ive react iv i ty fac tor of coal ch arY = concent ra tion of carbon in raw coal (dry , ash -f r ee) , g /g coal .

Ta ble 1. NUMBERS O F EACH COAL TY PE USED IN CORRELATIONWhole Vi t ra in Fus ian Tota l- - -oal Rank

LigniteSubbituminous CSubbituminous BSubbituminous AHigh-Volatile C BituminousHigh-Volatile B BituminousHigh-Volatile A BituminousLow-Volatile BituminousAnthraci te

121311421-

1122212- -

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Total 16 11 9 36F o r r eason s d i scussed below, i t should be emphas ized that, fo r l ign i te coal chars ,the corre la t ion shown in F igur e 2 i s appl icable only when the r aw l igni te i s initiallyt rea ted i n ac id to re move exchangeable cat ions .

The s tand ard deviat ion of experim ental re act ivi ty fac tor s shown in Fi gu re 2 andof react ivi ty fact ors calculated fro m Equation 5 is about 0 . 1, which i s equivalentto the reproducibi l ity of experimental ly determined react ivi ty fac tor s .the correlat ion proposed does not uniquely dis t inguish between m ac er al types.Effects of Exchangeable Cat ion Concentrat ion on Ligni te Char React ivi ty

Interest ingly,

If reactiv ity factors determined for coal ch ar s der ived f r om unt reated rawl igni tes wer e included in F ig ure 2, then a considera ble amount of sc at t er would beapparent above the corre la t ion l ine at low carb on concent ra t ions .s tudy, however, showed that the r eact ivi t ies of l igni te ch ar s obtained fr om l igni tesini t ial ly t rea ted in HC1 o r HCI -HF acid we re general ly s ignificant ly l ess t han t hecorresponding react iv i ti es exhib ited by l ign i te c har s der ived f r om unt re ated l ign i tes .Th is was not observed with seve ral bi tuminous and subbi tuminous coa l cha rs . Thi sbehavior apparently resu l ted f r o m a catalytic ef fect of exchangeable cat ions inherentlypres ent in raw l igni tes in carboxyl funct ional groups , which can be removed in acidby th e following type of reac tion :

One phas e of this

-COONa + H+ = -COOH t Na'With this explanat ion, one can reasonably expect that this catalyt ic effect wouldpredom inate in l igni tes and would de cr ea se rapidly with increasing c oal rank,corresponding to a rapid d ec re as e in th e amount of c oal oxygen combined incarboxyl functional groups.

A s er ie s of tes ts w er e conducted to obtain a quant i tat ive m ea su re of the effectsof exchangeable cat ion concentrat ion (so diu m and calc ium ) on ch ar react ivi ty f ac tor sfo r gasif icat ion in hydrogen and in s team-hy drogen mix tur es .conducted with lign ite ch ars der ived f ro m ra w l ignites , wi th the l ign i te c ha rs der ivedfr om raw l igni tes in it i a lly demineral ized in hydrochlor ic a c id to remo ve exchangeablecat ions and with th e l ign i te cha rs der ived f ro m raw l igni tes in i t i al ly demineral izedin hydrochloric aci d to which vario us amou nts of calcium o r sodium wer e then addedby cat ion exchange in sodium aceta te or ca l c ium aceta te so lu t ions . Resu l t s of one

T h e se t e s t s w e r e

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90se r i es of te s ts cor responding to gas if icat ion in hydrogen at 1700F a r e shown inF igu re 3. The r e su l t s in F i gu r e 3 we re c or re la te d wi th the express ion :

1

f L / f L = 1 + 54.7' YN a + 14.0 YCawhere -

= reactivi ty fac tor of l ignite to which sodium o r calcium was addedf L= reactivi ty f act or of aci d- tr eat ed l ignite (YNa' YCa = O )

YNa, YCa = concentrat ion of exchangeable sodium o r calcium in l ignite beforedevolat i lizat ion in ni trogen, g/g f ixed carbon.Although th e correlat ion given in Equation 6 was developed fro m data obtained withpre pa re d l ignites tha t did not contain both calcium and sodium at the sa me t ime, i tdoe s apply reasonably well to untreated l ignites containing, in some c as es , bothcalci um and sodium. Th is i s demons t r a t ed in Tab le 2.

Table 2. COMPARISON O F CALCU LATED ANDEXP ERIM ENT AL REACTIVITY RATIOS'Ca 'Na fL If.,

Lignite g / g f ixed car bon Calculated ExperimentalSavage Mine, Montana (wh ole ) 0 .043 0.000 2.1 1.7Savage Mine, Montana(v i t ra in ) 0 .019 0 .004 1 . 5 1 .7Glenharold Mine,Glenharold Mine,N. Dakota (who le) 0.0 31 0.009 1.9 2.0N. Dakota (vitrain) 0.019 0.002 1.3 1 . 2

A te s t ser ies wa s a l so conducted to de t ermine ef fec ts of exchangeable ca lc iumand sodium concentrat ions o n the reactivi t ies on a Montana l ignite char i n steam -hydrogen mix ture s at t empera tu re s f ro m 1400F to 1700F. Results obtained arei l lu s t r a t ed in F igure 4, which plots values of the kinetic te rm , f kT, a s a functionof te mp er at ure and catio n concentration. Although th es e resultsLhave not yet beenquanti tatively correl ate d, the y apparently show that sodium and calcium signif icantlyenhance gas if icat ion in s team-hydrogen mix tu res , even m or e so than f or gasificationin hydroge n alone.reactivi t ies i s subs tan t ia l ly the sa me a s the e ff ec t of sodium concentrat ion a tcor responding condi tions (c on tr ar y to the behavior ob tained in pure hydrogen) , andthat relat ive catalytic effects tend to dec rea se with inc rea sin g gasif icat ion temperature.

Fi gu re 4 shows that the effect of calcium concentrat ion on

A significant additional result of the tes t se r i es conducted with steam-hydrogenremai ns constan t fo r gas i fica tion in s team-hydrogen mix t ures over a tempera tur erange f r om 1400" to 1700F. This i s shown in Fig ure 5. which plots experimentalvalues of f k ve rsu s values of k calculated fr om cor rel at io ns developed to d e s -cr ib e b i tuminous co al char gas i f iA t ion k ine t ics (4 ) . The l ine drawn cor res ponds toa constant va lue of f = 1.3, which is about the sa me value obtained fo r gasif icationin pu re hydrogen at k'O0"F.

mi xtu res wa s that the reactivi ty of acid- treated Montana l ignite (YCa, 'N a= O)

L T

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91Var iat ions in In terna l Char Sur face Ar eas Dur ing Gasi fica tion

T he v a ri a ti o ns i n i n t e rn a l s u r f a c e a r e a s w e r e m e a s u r e d f o r s e v e r a l c h a r s atdifferent stag es of gasi fication in hydrogen o r s team-hydrogen mix tures .composi t ions of the coa l s f ro m which these cha r s were p repa r ed a r e g iven inTable 3 .with different bas e carbo n conversion fractions fo r a se r i es of te st s conductedwith Montana l ignite ch ars . Fi gu re 6 shows tha t the in terna l sur fa ce ar ea of theMontana l ignite char tends t o re ma in constant over a maj or range of base carbonconversion fractions and i s essen t ia l ly independent of ch ar p re t re a tme nt o rgasificat ion condit ions. The apparent surfa ce areas of carbo nize d ch ar s ( X = 0 )a r e lower than the nominal va lue of par t ia l ly gasi f ied ch ars . This d i f ference mayreflect that , even with carbon dioxide, p enetrat ion into the mi cr op ore s tru ctu re issomewhat inhibited before the str uct ure i s opened up by par t i al gasif icat ion.

TheFigu re 6 shows the va r i at ions in su r f ace a r ea meas u red in ca rbon d iox ide

F i g u r e 7 shows var ia t ions in apparen t s ur face ar e a meas ure d in n i t rogen fo rMontana l ignite cha rs. The chara cte r is t ic s shown tend to support the suggestionmade previously that , at low levels of conversion, nitrogen penetrat ion into themic ropo re s t ruc tu re is sev erl y inhibited, but that , a t higher ca rbo n conversions,unreasonably h igh apparen t sur fac e ar ea s a r e ob ta ined beca use of cap i l la rycondensation.In Fig ure 8, var ia t ions in su r f ace a r ea meas u red in ca rbon dioxide ( S )obta ined with some o t her coa l c har s a r e compared wi th re su l ts ob ta ined si%Montana lignite chars.anthracite , high-volati le bi tuminous coal, and l ignite remained es sential ly constantduring the cou rse of conversion in hydrogen and steam-hydrogen mi xtu res , surfacear ea s for the subbituminous coal char genera l ly decre ased wi th increas ing carbonconversions during gasif icat ion in hydrogen. Interest ingly, of the fou r coal ch ar stested, only the subbituminous coal cha r exhibited decreasing specif ic gasif icat ion

rates during gasificat ion with hydrogen that paral leled the dec rea se i n surfa ce are a.This i s shown in Fig ure 9.exhibited by only four coal ch ar s ar e not just if ied, the se r esu lts do suggest that afo rm of k ine tic cor re la tion to de scr ib e coal -char gas i fica tion ra t es tha t is m o r emeaningful than that deriv ed f ro m the Equation 1 ma y be the following:

Although sur face ar ea s measu red fo r char der ived f r om

Although generalizat ion s based on the kinetic behaviors

where -X = re la t ive reac t iv ity per un i t of in terna l s ur face ar eaS = i n t erna l su r f ace a r e a pe r m as s of ca rbon p resen t .

With th is interp retation, the constancy of th e values of f L and Sco of anthracite,high-volat i le bi tuminous, and l ignite coal ch ar during gasif icat ion tn hydrogencorresponds to a constant va lue of X fo r each cha r .X i s al so constant , a l though Scapparently beca use of th e grow& of cry st al lit es .used, t hi s growth i s probably unusual and not cha rac ter ist ic of mos t coal ch ars .This i s par ticu lar ly t ru e if the f i r s t -o rde r k ine t ics observed in a variety of previousstudies of the gasification of a fa i r ly la r ge number of coa l cha rs i n hydrogen a r eass um ed to correspond to constant values of X and Stested.

F or the subbi tuminous coal char ,dec rea ses wi th increas ing carbon convers ion ,F o r the gas i fica tion temp era tu res

fo r the individual coal charCOZ

IP

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93Interest ingly, in the kinetic model previously re fer re d to , the value of (Y i nEquation 1 is approxima tely 1 .7 for a varie ty of gas composit ions containingste am and hydrogen a t e levated pre ssu res . Empir ica l ly , th is va lue cor respo ndsto decreasing values of X with increas ing carbon convers ions when in terpr e ted in

terms of Equation 7. Th i s occu r s even when the to t a l i n t erna l su r f ace a r e as re -ma in constant during conversion in steam-hydrogen mix tur es, a s was shown inF i g u r e 6 fo r Montana l ignite char .I

ISome addit ional evidence was obtained in this s tudy that can be in ter pre ted i nte r m s of the formulation given in Equation 7.obtained during gasification of a c o al c h a r d e r iv e d f r o m B r a z i l i a n m e t a l l u r g i d lcoal. at var ious temp era tu res , wi th hydrogen and s team-hydrogen mix tu res . With

th is ma te r i a l , t he cha r su r f ace a r ea , Sco , is not a function of c ar bo n convers ionlevel and is t he s am e in hydrogen and in skam -hydro gen mix tu res , but dec rease swith increasing gasif icat ion tem per atu re. The reactivi ty factor , which i scha rac ter ist ic of res ult s obtained at a spec i fi c t empera tu re , a l s o %creases withinc reas ing t empe ra tu re and i s p ropor t iona l to in t e rna l cha r su r f ace a r ea , a sshown in Figure 11.valu e of A, independent of tem per atu re, conversion, o r gasif icat ion medium, butdoes exhibi: a decreas ing in ternal sur fa ce ar ea wi th increas ing temper a ture , af ea tu r e tha t p robab ly r e f l ec t s i t s u se a s a meta l lu rg i ca l coking coal .

Figure 10 shows values of Sco\t

This pa r t i cu la r cha r then can b e conside red to have a constant

I

I

Variat ions in Char Po re Volumes During Gasif icat ionF i g u r e 1 2 i l l ust rat es typical pore-volume distr ibutions of par t ia l ly gasif ied coalc h a r s .exhibited in Figur e 12 app ear to b e generally sim ila r to the distr ibutions obtained byStacy and Walker ( 9 ) with some coa l ch ar s result ing fr om a fluid-bed hydrogasif icat ion.Whereas Curves A through E tend to show a plateau at a po re dia me te r of about 55an gs tr om s, possibly indicati ve of the lack of development of sig nificant transit iona lpores , Curve F shows a signif icant var iat ion i n po re volume through thi s ran ge of

po re diameters. I t ma y b e pert inent , therefore, that the gasif icat ion ra te s of un-tre ate d Montana l ignite ch ar in a s team-hydrogen mix tu re were about 7 t i m e s f a s t e rthan the largest of the gasif icat ion ra te s obtained with ch ar s corresponding toCurves A through E.ra t es , dynamic modifica tions tha t tend to occur wi th in coal s t ruc ture s a s carbon isremoved a r e inhib ited.

With the exception of untre ated Montana lignite ( Cu rv e F ) , t he f ea tu r e s

It i s thus possible that , with suff iciently lar ge gasif icat ion

The plateau in pore-volume variat ions a t a por e d iame ter of 55 angs t romsexhibited by mos t coals tes ted ha s suggested the following simplif ied repres entat ionof pore-vo lume chara c ter i s t ics : Tota l por e vo lume acces s ib le v ia po re s le ss than55 angst roms i s defined a s "micropore" vo lume, and po re vo lume acce ss ib l e v iapo re openings having dia me ter s between 55 and 20,000 ang str om s i s def ined a s"macropore" volume. Micropore and ma cro po re volumes obtained with differentcoa l cha r s a r e shown in F igu res 13 and 14 a s a function of th e ba se car bon con-vers i on f ract ion.-ni t ia l base carbon ra ther than pe r ma ss of remain ing carbon and, therefore , a repropor t ional to vo lumes on a p e r pa r t i c l e bas i s .l i t t le varia t ion in ma cro por e vo lume wi th increas ing convers ion fo r C urves A throughE. In v iewing these resu l ts , reme mber tha t the t ru e densi ty of ba se c arbon i n thesecoa l cha r s i s about 2 gra ms /cu cm, cor responding to a total volume of 0. 5 cu c m /g r a m of in i tia l ba se carbon . Thus , if the spac e initially occupied by gasified ba secarbo n we re added to the mac rop ore vo lume, ma cro por e vo lumes would inc rea sesignif icantly with increasing carbon conversion. The re su lt s shown in Fi gu re 13,however , indicate that this is not gene rally the case, with the exception of Curv e F,which does show a sha rp inc r ease i n macropo re volume up to conv ersi ons of about0.8.

Note tha t in these f igu res , vo lumes a r e r ep resen ted pe r m as s ofFigu r e 13 shows su rp r i s ing ly

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94F i g u r e 1 4 shows tha t micro por e vo lumes tend to in i t ia l ly inc rea se with increas ingcarbo n convers ion , r each a maximum , and then de cr ea se with increasing conver-sion, approaching ze ro at complete conversion. Interest ingly, the mi cro por e-

volume char act er i st i cs corresponding to untreated Montana l ignite ch ar gasif ied ina s team-hydrogen mixture a r e e ssen t ia l ly iden ti cal to the cha ra c te r i s t i c s fo r theoth er Montana l ignite cha rs , a s opposed to the behavior noted in F igu res 1 2 and 13.Thus, the rapid gasif icat ion r at es that evidently affect struc tura l t ransi t ions at a"macro" leve l apparen t ly do not a ffec t s t ruc tura l t rans i t io ns on a "micro" level . ,T h i s i s consistent with the r es ul ts disc uss ed previously, which showed a n insen-s i tiv ity in l ign i t e - cha r - su r f ace a r ea s to in it i a l ac id t r ea tme n t o r to gasif icat ioncondit ions.The var ia t ions in to ta l par t ic le vo lume with ba se carbon convers ion meas uredwith the m e r c u r y p o r o s i m e t e r a r e s ho wn in F i g u r e 15. The vo lumes represen tthe s u m of solid volume plus por e volumes ac ces sib le via por e openings havingd i a m e t e r s of l e s s t h an 120 m i c r o n s .volumes tend to dec rea se wi th increa s ing ba se carbon convers ion f ract ion, par t i -cular ly at convers ions gr ea te r than about 0. 5.somewh at unexpected when ini t ial ly observed, som e addit ional te st s w ere conductedto obtain photographic evidence of quanti tat ive changes th at oc cu rre d in individualex tern a l coa l -char par t ic le d imensions befor e and af te r gas i fica tion in hydrogena t 1700F. In t h is s e r i e s of tests, a few par t ic les each of anthracite , high-volati leA bituminous coal, and Montana l ignite we re ini t ial ly photographed in s ev er alor ientat ions under optically ca l ib rat ed condit ions; we re gasif ie d in the thermobalanceto relat ively high levels of car bon conversion; and wer e then photographed again.Deta iled exam ination of the photographs obtained did show a signif icant reductionin par t ic le volumes, consis ten t wi th the resu l t s shown in Figur e 15 .of volume redu ction of e ac h ty pe of c ha r was independent of initi al part ic le dia met erin the r ange f r om abou t 200 to 800 micron s .topolog ica l char ac ter i s t ics rema ined unchanged except fo r a diminishment in size

inidicated that the obse rve d shrinkage o ccu rre d throughout individual par t ic les andwa s no t the re su l t of a "shrinking co re" phenomenon.

As ind ica ted i n Figur e 15, to ta l par t ic leBecause these r e su l t s wer e

The fractionTh i s f ac t and the fac t that externa l

SUMMARY AND CONCLUSIONSThe overall evidence obtained in th is study suggests the tentat ive conclusion thatgas if icat ion of coa l c ha rs wi th hydrogen and s team-hydrogen mix tures occ ursp r i m a r i l y at char sur faces loca ted wi th in micro pores . Th is conclusion is supportedby the relat ionships indicated between specif ic gasif icat ion ra te s and internal cha rsu r f ace a r eas , pa r t i cu la r ly for gasif icat ion i n hydrogen. With the ma jo ri ty of coalchars , in terna l sur fa ce a re a rem ains constan t dur ing gas i fica tion and i s independentof gasif icat ion condit ions, possibly indicating an invariance in ave rag e crystal l i ted imensions dur ing the gas i f ica t ion pro ces s . With some coal chars , however, sur facea r ea s t end to dec rea se wi th inc reas ing conve rs ion o r inc reas ing gasi fi cat ion t emper-at ure , which would be indicative of a growth in c rys ta l l i t e d imensions .Pa rt i cl e shr inkage occu rs during coal-char gasif ication.due al mo st solely tocontraction of t he mic ropo rous phase ( so l id s p lu s po res access ib le v ia openingswi th d iame te r s l e s s than 55 ang st r oms ) , poss ib ly becau se of the continuous re-or ien ta tion of ind iv idual carbon crys t a l l i te s . Macropore cav i t ies a l so shr ink a thighe r lev el s of conversion, bu t in a mann er analogous to cav i t ies in a meta l l i cso l id undergoing th er ma l contrac tion .inc rea se somewhat dur ing the in i t ia l s tage s of conversion , th is incre ase may c or res-pond to a n increas ing access ib i l i t y of the macro pore cav i t ies p resen t in i t ia l ly.Although there a r e som e s igni f ican t d i f fere nces in the var ia t ions in sur f ace are asand pore vo lumes for var io us coal cha rs dur ing gas if icat ion, the d i f ferent coa l charst e s t ed exhib it a su rp r i s ing s imi la r i ty in va r ia t ions i n ave rage mic ropo re d iam e te r

wi th increas ing b as e carbon convers ion .

Although access ib le m acr opo re vo lumes may

Th is is shown in F igu re 1 6 , which plots

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95, -1 values of t he average mic rop ore d i amete r , D, ve r s us t he ba se ca rbon conversion\ f ract ion , X. The averag e mic ropore d i amete r was compu ted f ro m the exp res sion -

- 4 vD = -where -

V =Although the rel at i ve gasif icat ion react iv i ty factor, f

micropore vo lume (acces s ib l e po re-open ing d i amete r

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9610. Toda, Y . , Study on Pore Structure of Coals and Fluid Carbonized Produ cts, Report No. 5 of the National Institute fo r Pol luti on and Re so ur ce s. Japan, 1973.1 1 . Toda. Y . , Hatauci, M., Toyoda, S., Yoshida, Y . and Honda, H . , Fuel 50 ( 2 ) ,

187 (1971).12. Walker, P. L. andPate l , R. L . , Fuel 49 ( l ) , 91 (1 9 7 0) .

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98

1400 1500 1600 1700TEMPERATURE. .F .-a

F i g u r e 4. EF FE CT O F CATION

0.0001 I I I 1 1 1 1 1 1 I I I I I l l l l I I I I l U0.m1 0.001 0.01 0.10k, ,min" (Calculated) .,MI,,.,

Fi gu re 5. REACTIVITY O F ACID-TREATEDCONCENTRATION ON REACTIVITY M ~ N T A N A IGNITE CHAR IN STEAM-O F MONTANA LIGNITE CHAR INSTEAM-HYDROGEN MIXTURES AND 35 ATMOSPHERESAT 1400' TO 1700'F AND3 5 ATMOSPHERES

HYDROGEN M IXTU RES AT 1400' T O 1700'F

'---I;?P52ocv)

PRETREATMENT* TEMP,*6 DM t+-HzO 1400DM Hz-HzO 1600DM-CA Hz-HzO 1400

A DM t+-eo 1500* DM t+-&O 1700a DM-CAM OM-CA &H2O'l M-CA +H20 1700RAW t+-H20 I700? DM HZ 1700V RAW HZ 1700E2 1 OM. DEMINERAL IZED IN HCL0Y-W DEMINERALIZED IN HCL WITH SUBSEWENT CATION EXCHAffilRAW. UNTREATEDI I I I I I I I I

BASE CARBON CONVERSION FRACTION, X .,~,.,

i

I

0

F i g u r e 6 . VARIATIONS IN SU RF ACE AREA M EASURED I N CARBON DIOXIDE(Sco,) WITH BASE CARBON CONVERSION F RACTION FO R MONTANALIGNITE CHARS GAS IFIED AT VARIOUS CONDITIONS

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10 0

GASIFICATION

0. 1800OPEN POINTS: HYDROGEN GASIFICATIONCLOSED POINTS: STEAM-HYDROGEN GASIFICATION

00 0.2 04 06 08' ' I ' ' ' ' IBASE CARBON CONVERSION FRAnION, XF i g u r e 10. EFFE CT O F GASIFI-CATION TEMPERATURE ONINTERNAL SURFACE AREA OFCARVAO METALLURGICAL COA LCHAR

9 LIGNITE.ACI0-TREATEDLIGNITE. LWTREATED n, - H ~ O0 12 4 6 8 10 2I" 0 I II1 I I I I 1

IO I IO' 1 10PO RE OP ENIN G D I A M E T E R . D . o ~ ~ ~ ~ o ~ s

. I *O I IO *

F i g u r e 1 2 . TYPICAL PO RE VOLUMEDISTRIBUTIONS FOR D IFF ER EN TCOAL CHARS GASIFIED IN HYDROGENAT 1700F and 35 ATMOSPHERESAND STEAM-HYDROGEN MIXTURES

/o k ' 100 ' 200 I 300 ' 400CHAR SURFACE AREA, Scofsq m/g char (ash- f ree)

Fi gu re 11. RELATIONSHIP BETWEENREACTIVITY FACTOR, fL , and SFOR CARVAO METALLURG ICAL COALCHAR

1-15051144

c 2

0 0. 5EASE CARBON COMERSON FRACTION, X .,,~y,_

Fi gu re 13, RELATIONSHIPBETWEEN MACROPORE VOLUMEAND BASE CARBON CONVERSIONFRACTION FOR DIFFERENT COALCHARS

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10 1

t

4

COAL GASIFICATION M D l U h-0 ANTHRACITE H i H P4 hvAb n 2 - vD SUBBITUMINOUS A H I0 LIGNITE.UNTREATED H I0 LIGNIT6.ACID-TREATED HII LIGNITE.UNTREATED

BASE CARBON CONVERSION FRACTION, X..1,0,1141

F i g u r e 14. RELATIONSHIPBETWEEN MICROPORE VOLUMEAND BASE CARBON CONVERSIONFRACTION FOR DIFFE RENT COALCHARS

o5,r00,,1,.BASE CARBON CONVERSION F RACTI0N .X

Fig ur e 15. RELATIONSHIP BETWEENTOTAL PARTICLE VOLUME AND BASECARBON CONVERSION FR AC TIO N FO RDIF FERE NT COAL CHARS

in 40t10a

w

0

GASIFICATION MEDIUMHI - Hp OHp - Hz O

0 SUBBITUMINOUS A H p0 LIGNITE0 IGNITE,V LIGNITE,

U N T R ~ A T E D H ZACID-TREATED HrUNTREATED H - H.0-O I I I I I I I I I0 0.2 0.4 0.6 0. 8BAS E CARBON CONVERSION FRACTION, X

AT5051140

Figure 16 . RELATION SHIP BETWEENAVERAGE MICROPORE DIAM ETER ANDBASE CARBON CONVERSION FRACTIONFOR D IFFERE NT COAL CHARS

0

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RAPID DEVOLATILIZATION AND HYDROGASIFICATION OF BITUMIKXE COAL.D.B. Anthony, H.C. H o t t e l , J . B . Howard, and H.P. Meissner, Department of ChemicalEngineering, Mass achusetts I n s t i t u t e of Technology, Cambridge, Massachusetts 02139Rapid dev o l a t i l i z a t io n and hydrogas i f ic a t ion o f a Pi tt sb ur gh Seam bituminous co alwere stu di ed and an epproximate co al conv ersion (weight lo ss ) model w a s developed thataccounts fo r secondary char- forming re ac t i on s among vo la t i le s .layer samples ef s m ~ l l cs1 p ar t i c l e s s u p p o r t ed on wire mesh hearing elements wereelectr ical ly heated in hydrogen and hydrogen/hel ium mixtures .

measured as a f u n c t i o n of r e s id en ce t ime (0.05-20 se c. ), te mp er at ure (400-11OO0C),heat ing ra te ( l o 2 - l o 4 'C/sec. ), t o t a l pres sure (0 .001 - 100 atm), hydrogen pa rti al .p r e s s u r e (0 - 1 00 a tn ) , and p a r t i c l e s i z e 50 - 1000pm). Rate of weight l o s s under thesecondi t io ns appears to be cont rol led by thermal decomposit ion rea ct i ons t h a t form vola-t i l e s and i n i t i a t e a s equ en ce of s eco nd a ry r eac t i o n s l ead in g t o ch a r .s i t i o n i s modelled a s a la rg e number of p a r a l l e l f i r s t - o r d e r r e a c t i o n s h av in g as t a t i s t i c a l d i s t r ib u t io n o f a c t i v a t i o n e n e r g i e s (20-89 kcal /mole) .s eco nd a ry r eac t i o n s t o w e ig h t l o s s i s descr ib ed by a s e l ec t i v i ty express ion der ived f romthe assumption th at cha r forma tion by t he se re ac t io ns competes with hydrogenat ionreac t ion s and d i f fus i onal escape of v o l a t i l e s f rom t h e p a r t i c l e .

Approximately mono-Coal weight l o s s was

Thermal decompo-The co ntr i but i on of

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Hydrog asificat ion Kine tics of Biturd nous Coal and Coal CharJ. A. Gray, P. 3. Donatel l i , P . M. Yavorsky

U.S. Energy Research and Development AdministrationPittsburgh Energy Research CenterPi t t sburgh, Pennsylvania 152134800 Forbes Avenue

103

INTRODUCTIONOf th e many proc es se s c u rr en tl y under development which w i l l conver t coa l t oenvironmental ly acceptab le so l id , l iqu i d , and gaseous f ue l s u t i l i z i np pyro l ys i s ,syn t he s i s ga s , so l ve n t e x t r a c t i on , or hydrogenat ion techniques, the di rect hydro-genat ion of coa l to a raw gas that i s e a s i l y upg ra ded t o p i pe l i ne qua l i t y Is apromising approach.Energy Research Center and is known as WDRANE ( 2).Such a process i s under development by t h e E.R.D.A., Pi t t sburgh

IIBr i e f l y , t he HYDRANE f low sheet is as fol lows. Pulver ized r a w c oa l i s f ed t oth e top zone of t he hydrog as i f i e r , ope ra ted a t 70 atm and 750-900" C , where i tf a l l s f r e e l y as a d i l u t e c loud o f pa r t i c l e s t hr ough a hydrogen-r ich gas conta i ningsome methane from th e lower zone. About 2 0 pct of t he carbon in t he r a w c oa l i sc onver te d t o methane, c aus ing t he c oa l pa r t i c l e s t o l o se t h e i r vo l a t i l e matter andagglomera t ing ch ara c te r i s t i c s and to form very porous, react ive c h a r p a r t i c l e s .c ha r f a l l s i n t o t h e lower zone, operated a t 70 atm and 900-980" C , where hydrogenf e ed gas ma in ta in s t h e pa r t i c l e s i n a f l u i d i z e d s t a t e and reacts w i th a n a d d i t i ona l25 pc t of t h e carbon t o make methane.dilute -phas e zone and i s cleaned of ent ra ined sol id s, t a r s and o i l s , and someunwanted gases.carbon monoxide gives a p i pe l i ne qua l i t y , h igh- Bt u, sub s t i t u t e na t u r a l gas . Charfrom the lower zone of th e hydrog asi f ier i s reac ted wi th steam and oxygen t o make

t h e needed hydrogen.

This

The product gas exists from the bottom of t h eAfte r c l eanup, ca ta ly t i c me thanat ion of th e smal l amount o f re s id ua l

This process has the following advantages:

\

1.

2.

3.

4.5 .

6 .

External hydrogen consumption per unit of methane produced i slow because t he hydrogen a l ready i n th e co al i s e f f i c i e n t l yu t i l i z e d ,P rocess cos t s a ssoc ia ted with coa l p re t reatment, inheren t i noth er co al conversion processes based on caking bi tuminous co alfeedstocks, a re e l iminated,95 per cent of th e product methane i s produce d d i r e c t l y i n t h ehydrogas i f i e r thus requi r ing ve ry l i t t l e c a t a l y t i c m e thana ti on ,Simple reactor design,Produces law-su lfur ch ar byproduct f o r hydrogen p ene rati on and low-su l f u r t a r s , andUt i l i z es sens ib le hea t of the re s id ua l cha r from the hydrogas i f i e ri n t he hydrogen generat ion plan t .

Because of these advantages, coa l and oxygen ( th e cos t l ie st items i n g a s i f i c a t i o n )requirements ar e minimized f o r the proc ess, and thermal e f f i c i ency and carbon u t i l i za t i ona r e h i gh a t 78 pc t and 44 pc t , r e spec t ive ly (2, ) .

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Much o f t h e hyd r oga s i f i c a t i on k i n e t i c da t a on t he l a bo r a t o r y sc a l e , f r e e - f a l l ,I n t h i s p ap er w e review previous and some recentd i lu te-phase reac tor has a l ready been publ i shed (5,5) as w e l l as data f rom asemiflow bench-scale r ea ct o r (1).k i n e t i c d a ta w i t h regard t o th e type of reac tor used to ob ta in the da t a , and thee f fe c t o f t he type of re ac to r on the convers ion da ta .m i ner a l e l em e nt s i n t he coal dur ing hyd r oga s i f i c a t i on a nd t h e c ha r y i e l d are shownt o be re l a t ed t o th e ca rbon convers ion regard less o f th e reac tor geometry used, sot h a t the con s t i tu en t convers ions can be ca lcu la t ed once the carbon convers ion i sknown. This s i m p l i f i e s t h e r e a c t o r de s ign i n t h a t onl y t h e c ar bon conve r si on nee db e k i n e t i c a l l y d ef in ed f o r a par t i cu la r reac tor geomet ry .

The conversion of the non-

EXPERIMENTAL REACTORS"Hot-Rod" Reactors (HR)

In 1955 E l Paso Natural Gas Company entered i n t o a coop erativ e agreement wi tht he t he n U.S. Bureau of Mines S yn th et ic Fuel s Research Branch t o i n v e s t i g a t e t h ehydrogenat ion of a subbituminous New Mexico co al t o produce high-Btu ga s and low-bo i l i n g a r om a ti cs . Pa r t o f th e agreement ca l l e d fo r t e s t s i n a reac tor i n which drycoa l could be rap id ly brought to th e de s i red opera t in g t emperature and pressure .normal autoclave requi red over an hour t o reach temperature .of the hea t i ng and cool ing cyc les on t he re ac t ion could no t be d i sce rned .Hiteshue conceived the apparatus known as th e "hot-rod" re ac to r and completed t h e E l Pasop r o j e c t u s i ng i t .Hiteshue, Anderson, and Sch les ing er i n 1957 (i) nd again during 1960-1964 ( 2 ,g ) .

AConsequently, t h e e f f e c tI n l a t e 1955,The appara tus a long wi th convers ion da ta were f i r s t repor ted by

The "hot-rod" re ac to r, shown i n Fi gu re 1, was a 70-inch long s ta in le s s s teeltube (type 304) having a 5/16-inch in s id e diameter and a 5/8-inch ou ts ide diameter.A c o a l o r c h a r sample weighing 8 grams and scre ened t o 30 x 60 U.S. s i e ve s i z e wasi n s e r t e d i n t o t he t ube be tw ee n two por ous s t a i n l e s s s t e e l d i sk s such t h a t a 32-inchl e ng t h w a s a v a i l a b l e t o f l u i d i z e t h e sample.cur rent by connect ing i t t o a t ransformer tha t wae capable of supplying 700 amperesa t 9 vol t s . W i t h t h i s method of h ea t ing , t h e r e a c t o r , sample, and feed gas w e r eheated from room temperature t o 800' C i n a bout 2 minutes and t o 1200' C i n a bo ut4 minutes, A t the end of th e experimen ts, the reactor and sample were cooled t oroom temperature in about 10 seconds by spraying wi th c old water . The f lowsheeto f t he e n t i r e appa ra t u s is shown i n Figu re 2 and ha s bee n di sc us se d i n d e t a i l i nt he p r e v i ous l y c i t e d r e f e r e nc e s ,F ree -Fa l l D i lu te Phase Reactor (FDP)

The tube w a s h e at ed w i th e l e c t r i c a l

The agglomeration of bituminous co al s i n hydrogen i s a major problem i ndesigning a reac tor fo r t h e i r continuous hydrogenat ion t o produce a high-Btu gas.It has been shown t h a t bitumino us co als , both caking and noncaking, w i l l agglomeratewhen r api dly heated i n hydrogen a t 500 psig and 500" C o r a t 6,000 psig and 500 t o800 C (lo,3, 14) .no t agglomerate at 500 p s ig and 500' C. Chars produced from car bo niz ing bituminouscoa ls , cokes, gra phi te and an th rac i te , and a hig hly oxidized hvAb coal did notagglomerate. Feldmenn (i) bse rved tha t e t l e a s t 1 0 p c t of t h e v o l a t i l e matteri n P i t t s b u r gh seam hvAb coa l , or ig in al ly conta ining 36 p c t v o l a t i l e matter, hadt o be removed t o obta in a char th at would no t agglomerate a t 1,000 ps ig and 800 Ci n hydrogen i n subsequent "hot-rod" rea cto r tes ts .

Texas l i gn i t e agglomerated a t 6,000 psig and 800' C b u t d i d

L e w i s and Hiteshue (15) esigned an ent ra in ed flow reac tor fo r cont inuous lyhy dro gen ati ng both ca kin g (hvAb) and noncaking (hvCb) c oa ls .t he su spe ns i on of c oa l i n t h e f e ed ga s w a s di lute enough ( d i l u t e phase ), pa r t i c l e -

They be l i eved tha t i f

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\

pa rt ic le col l i s ion and subsequent agglomerat ion could be avoided.a l /& inc h insi de diameter , 60-foot long he l i ca l tube, and w a s operated a t 600 pSigand 800' C.hydrogen ve lo ci ty was 2 fps.because of so l ids p lwgin g a t about th e 500 t o 550' C zone i n th e he l i c a l tube.Changing t o a s t ra igh t , hor i zonta l tube reac t or hav ing an in te r na l d ian e te r o f 5 /16inches and a length of 20 fe e t d id no t a l l e v i a t e t he p lugging problem.

The reactor was

The coa l was entr ai ne d a t a rate of 60 gr s/ hr i n hydrogen where t h eExper iments wi th the h e l i c a l reac tor were unsuccessful

A 4-inch d iameter ve r t i ca l rea c tor where the coa l p a r t i c l e s would no t contac tt he r e a c t o r w a l l du r i ng de vo l a t i l i z a t i on w a s found to opera te ve ry successfu l ly .It was fur ther shown that reducing the diameter to less than 3 inches caused plugging,aga in due to coa l pa r t i c l e s contac t ing t he r e a c t o r w a l l.l abora tory d ilu te -phase reac to r th a t evolved f ro= these s tud ies .Figure 3 shows th e

A l a r g e a m un t of k t n e t i c da t a ha s bee n r epo rt e d f o r t h i s r e a c t o r u s ingPi tt sb ur gh seam hvAb and Il l i n o i s 1/6 hvCb c oa ls (5,a, l6,lJ).lab or ato ry rea cto r and method of operat ion are di scussed i n the prev ious re fe rences .

D e t a i l s of t he

The pres en t FDP re a ct or i s a 3.26-inch in si de diameter pipe t h a t is heatedthrough t he wal l and conta ined i n a 10-inch diameter pres sur e she l l .in j ec ted in t o the top of t he reac tor through a 5/16-inch in s id e diameter, water-coolednozzle using a rotary feeder and par t of the feed gas.a 5-foot long rea cto r concurrent ly wi th t he feed gas a t a p a r t i c l e r e s i d e n c e t i m eof less tha n a second. Agglomeration i s avoided because the rap id hea t ing dev ol a t i l i z est he pa r t i c l e s be f or e many pa r t i c l e c o l l i s i o ns w it h t he wall o r o t h e r p a r t i c l e s canoccur. The char produ ct i s recovered from a cooled hopper af t e r each experiment andis analyzed. Gas flo ws and compositions ar e measured ove r stead y s ta te per iods ofthe experiment so that mass balances can be calcula ted.Two-Stage In teg ra ted Rea cto r

Coal i sThe coa l f r ee - fa l l s through

I n o r de r t o r e a c t f r e sh d i l u t e pha se c ha r w it h hydrogen a s i n t he i n t e g r a t e drea cto r system descr ibed previously, and t o measure re ac t i vi ty and methane yi e l d a tcarbon converaion l ev el s expected i n a commercial reactor, a two-stage laboratoryhyd r oga s i f i e r w a s b u i l t c o n s i s t in g of a di lu te -phase r eac to r in tegra te d wi th asecond sta ge reac tor th at could be operated as e i th er a moving-bed o r f luid-bedreac tor .th e d iameter of the coa l pa r t i c l e s inc reased subs tan t i a l ly due t o swe l l ing andsome agglomeration during devolati l ization, a char c rushe r was used t o reduce th ep a r t i c l e s i z e t o a level acceptable fo r f lu idi zat ion . In th e moving-bed v ersi on,no crusher was used as shown i n Fig ur e 5.

Figure 4 i l l u s t r a t e s the ve rs ion us ing a f luid-bed second s t age . Because

The t rue composi tion of product gas f rom th e ind ivi du al s tage s could n ot bedetermined directly because a la r g e amount of mixing occurr ed between g as ne ar th e bottomof the d i l u te phase reac tor and gas near t he top of the second sta ge react or .ov er al l methane yi el d f or th e two-stage u ni t was determined i n some cas es , and th eseyie lds were compared t o yie lds f rom previous d i lu t e phase rea cto r experiments .mixing problem was not unexpected since there w a s no gas seal le g used between t hetwo rea ct or s because of th e small sc al e of th e equipment.from convection currents c r e a t e d from t he f a l l i n g c ha r pa r t i c l e s and t he ho t r e a c t o rw a l l s .de ta i l e lsewhere (Is).

TheThe

The mixing was causedThe operati on of t he twc-stage hyd ro gas ifi er is descr ibed i n much greater

KINETIC MODELWithin about the f i r s t few inches of f r ee- fa l l in the FPD rea cto r , the coa lpa r t i c l e s a r e r a p i d l y he at ed and de vo l a t i l i z e d y i e l d i ng a "popcorn" char (E).

i s genera l ly accepted tha t dur ing the pe r iod of devo la t i l i z a t ion , chemical bondsI t

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107fraction of the carbon which i s a v a i l a bl e f o r r e a ct i o n i n the repine being consideredand k t he r e a c t i on ra te constant .devola t i l ized carbon i s not inc luded i n th e f ra c t i on a l ca rbon conversion i sAnother way of w ri ti ng Equation 4 where the

where 2 = (x-E)/(l-E) and B = (a-E)/(l-F).t h a t was devola t i l i zed .reac to r a t t a i n t e rmina l ve loc i ty and th e same t emperature a s th e reac t or wa l l a lmosti w e d i a t e l y , Equation 4 may be ap pl ie d to th e FDP r e a c t o r a s

E cor responds to the f r ac t ion of carbonA s s d n g t h e c o a l p a r t i c l e s b ei ng f e d t o t h e d i l u t e ph as e

'

1

where UT i s t he pa r t i c l e t e rmina l ve loci ty .l ength y ie ld ing Equation 6 i s i n t eg ra ted over the reac tor

Xdx L

'HZE

I n t he i n t e g r a t i on , P B ~ s assumed constant andin the product pas because extensive backmixingand t h e downward flow of char. The fr ac tio n ofin the in tegra t ion . Within the cons t ra in t tha t

7)

e qua l t o t he hydr ogen pa r t i a l p r es su r eoccurs due t o t he ho t r eac to r wa l l sType 1 carbon i s accounted for a s E0 < a I 1. t h e b e s t f i t of carbonconversion data f rom th e FDP r e a c t o r is obtained when a = 1 - ( 2 ) .e s se n t i a l l y a l l of t he c arbon i s ava i l ab le for hydrogas i f i ca t ion . Thi s means th atThe hydr ogas i f ica t ion of char i n a "hot-rod", moving-bed, o r fluid-bed reactorfol lows the 8am.e rate exp res sio n given by Equation 4 , however, t he rea cti on i smuch slower because most of the carbon that i s reac t ing i s of the Type 3 va r i e t y .Application of Equation 4 t o fluid-bed and moving-bed re ac to rs ha s been discuss edelsewhere (E).The rate express ion does no t t ake in to account t r an s i t io ns between the va r iousreac t ive types of ca rbon i n th e coa l nor mass t r an sf e r re s i s t anc e .hydrogasi f ica t ion of char i s so complex because of the change i n carbon s tr u ct ur edur ing reac t ion , th a t the above s imple c l as s i f i c a t i on of carbon may no t apply i n a l lcasea.char bu t a160 adds anothe r cons tan t in t o th e wde lw hi ch m st be e va l ua t e d u s ingexperimental data. Generally the more const ants the re are i n a m.odel, th e b e tt er

the model w i l l f i t regar dles s of the accuracy of the proposed react ion mechanism, andthe pore experimental data i s needed to eva lua te the cons tan t s . For th i s reason ,Equation 4 was kept simple so th at data f rom various r eac tor s could be e as i l y cor,pared.With t h i s persp ective, th e data from each of th e reac tor systems will now be discussed.

I n f a c t t h e

Johnson's model (23) akes int o account the cont inuous dea ct i vat ion of the

EWERIMENMI, RESULTSFLIP Reactor

Using Equation 7 and a term inal ve lo ci ty of 9 fp s, Feldmann (2) determinedE and k values f o r carbon conversion data a t 900' C and 725' C. These values arel i s t e d in Table 1.a s a functio n of hydrogen pa r t i a l pre ss ur e and presented rec ent 850"-900 C ( t o t a lI n a l a t e r publication, Feldmann (2) reanalyzed the 725" C data

k

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TABLE 1.- FDP Reactor k in et ic d at a (2)~ ~~

Reactor Wall Tot al Reactor kTemp., O C Press. , a t m E , % atrn-lhr-l725 103,2 05 22 6900 205 1 4 21

TABLE 2 . - U l t i m a t e and proximate analyses of feedsCoals CharsRun S e r i e s HR-1 IIR-2 FDP HR-1c HR-2C

W t . % Pgh hvAb Pgh hvAb Pgh hvAb I l l . (16 hvCb Pgh hvAb I l l . C6 hvCb~ ~~~~

C 74.2 74.1 78.1 74.4 78.8 83.9H 5.1 5. 1 5.3 5.2 1 . 9 2.8N 1.5 1.5 1.6 1 . 7 1.6S 1.9 1.5 1.1 1.3 1.10 8.8 7. 6 8.2 11.5 1.9

---------Ash 8.5 10.2 5.7 5.9 14.7 10.2

100 100 10 0 100 100Moisture 1.9 1.4 1 . 2 1.4 0 0.926.0M 33.9 35.3 36.4 36.8 ---FC 56.5 53 .1 56.7 55.9---

--- ---

TABLE 3.- FDP Re ac to r k i n e t i c d a t aReactor Wall, To ta l Reactor LcTemp., C Press. , a t m E, % atm-lhr-'

725 103 ,205 23.1 5.3*725 103,205 9.4 14.7850-900 69-108 21.5 24. 7*850-900 69-108 12.2 33.0 I

*Total carbon conversion.

,

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pr es su re 69-108 atm) d at a (k).a r e shown in Table 2 f o r th e FDP and "hot-rod" re ac to rs .carbon conversion data as t o t a l carbon conversion and as carbon conversion t oequ iva len t methane (carbon in methane and ethane).The ult imat e and proximate analys es of t he feed co al sFigures 7 and 8 show the

The d iff ere nce between t o t a l carbon conver sion and carbon conversion t o methaneis due mainly to the production of carbon oxides and oil .i s a l s o in troduced in measuring the f low rat e and composition of t h e feed and prod uctgases, and in recovery and analysis of the so l i d and l iqu id produc t s .run t imes were not lo ng enough t o c o ll ec t enough oil so t he y ie ld could be accura te lymeasured (2).much lower than 100 pct .w e l l as reac tor temperature gre at l y inf luences the anount of o i l produced, es peci a l lybelow a p a r t i a l p r es s u r e of 30 a t m .p a r t i a l pressure agrees wi th t he divergence of the two carbon conversion curves i nFigures 7 and 8.hydrocracking of the o i l products .r e a ct o r a l s o a f f e c t s t h e o i l y i el d causinp lower amounts of o i l a t i nc r e a s i ngresidence t ime as shown in Figure 10.determined by recovery from the gas sample and main t a i l gas streams.of t he o i l w a s lost by condensation on t he char r ece iv e r wa l l and t o some ex ten ton the char in t he r e c e i ve r .where t he y ie l d in the gas sample stream is m ul t i p l i e d by t he r a t i o o f t he t o t a lp r oduct ga s f l ow r at e t o t he s ample ga s f l ow r a t e i n o r de r t o e s t i m a t e t o t a l o i l y i e l d .These values w i l l probably be higher than th e rep orte d values.

Some experimental error@f t e n t he

These e r ro r s becove obvious when th e carbon and ash re cov eri es a r eFigure 9 i nd i c a t e s t h a t t he hyd roge n pa r t i a l p r e s su r e asThe increase in oil yield wi th decreasing hydrogen

Apparent ly th e higher hydrogen p a r t i a l press ures enhance th eResidence time of the hydrocarbon vapors in t heA s i nd i c a t e d in F i gu r e 5 , t h e o i l y i e l d wasHowever, some

Therefore the oil y i e l d d a t a are now beinp reexamined

The values of th e ki ne t i c parameters in Equation 7 for t h e d a t a in Figures 7and 8 are l i s t e d i n T ab le 3.conversion and fo r carbon conversion to equ ivalent methane. The va lue of a - 1gave t he be s t f i t of t he t o t a l c a rbon c onve rs ion da t a and w a s subsequent ly used t of i t th e carbon conversion to methane data . The t e rmina l ve loc i ty of a s in g l e cha rpa r t i c l e was ca lcu la ted us ing the equa t ion

= [ p g g 3 .These parameters were e va l ua t e d bo t h f o r t o t a l

3.1g(Ps-P )ZP 1 / 2 8)-d p Uf o r 500 < ReD = peT C 200,000 (z),nd- c o r r e c t i ng t h i s va l ue f o r t he e f f e c tU,' 5of the cloud oi p a r t i c l e s (25).t he t e rmina l ve loc i t i e s .900' C da ta and 10.7 fp s ( avera ge of 9.9 and 11.5) for the 725" C da ta .Table 4 l i s t s t he pa rameters used fo r ca lcu la t ingA terminal velo ci ty of 16.5 f ps w a s use d f o r t he 850'-

The t o ta l reac to r p ressure has a l a r ge i n f l ue nc e on t he t e rm i na l pa r t i c l eve lo c i ty because the pressure de te rmines for th e most pa r t th e s i ze of the charpa rt ic le s produced and hence t he bulk a n d p a r t i c l e d e n s i t i es . T hi s i s i l l u s t r a t e din Figure 11 where th e char bulk dens i ty is p l o t t e d ve r sus t o t a l r e a c t o r p r es su re .A s the pres sur e incr ease s, the bulk dens i ty increases. The bulk densi ty is higherwhen the feed gas contains about 50 pct methane instead of pure hydrogen.increasing th e reac tor pres sur e dampens the explosive e niss ion of gases during ther a p i d de vo l a t i l i z a t i on r e a c t i on . A high concentra t ion of hydrogen i n th e rea cto rcauses more of the carbon t o be reacted out of t h e p a r t i c l e s t r u c t u r e r e s u l t i n g ina lower bulk dens i ty char (and lower pa r t ic le den si ty ) than is obt ain ed when t h erea cto r feed gas contains about 50 pc t Eethane. Some char pa r t i c l e s i z e da ta isl i s t e d in Table 5 showing how inc rea ses i n re ac to r temp erature and pres su re causedecreases in the mean char pa r t ic le diameter .

Apparently,

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TABLE 4.- Para mete rs used t o ca lc ul at e term ina l ve lo ci ty~~ ~~

Temperature,Pressure, a t m-, l b / h r f t 2dp, in.Pb , lb / f t3ps*, l b / f t 3

~~~ ~

C 7252051650.052113.3336.81.4080.057453.312643.09.9

7251031280.06678.022.10.70740.057454. 110102.811.5

~~

90020514512.2933.91.1990.064092.85423.08.4

0.0345

900692070.06605.816.00.40350.064094.65733.616.5

~~ ~ ~~* Estimated by the ra t io o f b u lk d en s i t i e s and p a r t i c l e d en s i t y o f 16.0 l b / f t 316 I 6.8.26) or cha r produced a t 85O0-9OO0 C and 69 atm, e.g.,

* *Ratio of t e r min a l v e l o c i t y t o s i n g l e p a r t i c l e t e rmin al v e lo c i t y a t a s p e c i f i cmass f ee d r a t e p e r u n i t area (25).

TABLE 5.- Effe c t o f r eac to r tempera tu re and p ressureon average char pa r t i c l e s i z eAverape Char Par t icle Diameter*. i n .

Press., atm/Temp., C 750 -00 850 -0069 - 0.0735 0.0628 0.05378 3 -- I- .0566 0.0501103 0.0667 -- -- 0.0485

205 0.0521 0.0492 0.0529 0.0345

, Pi t t s b u r g h seam hvAb coal, 50 x 100mesh feed.

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The e f f e c t of f e e d r a t e p e r u n i t r e a c t o r c r o s s s e c t i o n on t he average charp a r t i c l e d i a m e t e r i s s h a m i n F i g u re 12.rea cto r d iameter , th e number of p ar t i c l e co l l i s io ns incre ase and hence the mean charp a r t i c l e s i z e i n c r e a s e s d ue t o a g gl om e ra ti on . At a mass f e e d rate of 2 2 1 W h r f t 2 ,Pi t t sbu rgh seam coa l y i e lded an average char par t i c l e d i ameter o f 1 .70 mm (0.0669inc he s) compared t o 0.487 mm (0.0192 inche s) fo r char produced fron: I l l i n o i s #6 hvCbcoa l under i den t i ca l r eac to r cond i t i ons .sec t i on o f t he two-s tage i n t eg ra t ed r ea c to r i s l i m i t e d by t h e s i z e o f t h e c h a rp roduced in t he d i l u t e phase sec t i on t ha t may be f l u id i zed adequa t e ly i n t he second-s t age f lu id-bed s ec t i on .h i gh e r f o r I l l i n o i s c o a l t h an f o r P i t t s b ur g h c o a l b e ca u se of t h e smaller s i z e c ha rPar t ic les produced.

A s t h e f e e d r a t e i s i n c r e a s e d f o r a f i x e d

The maximum c ap ac i ty i n th e di lute-phase

Therefo re , t he di l u te -phase r eac to r capac i ty w i l l be much

The feed rates p e r u n i t a r e a i n F i g u r e 1 2 a re probably low because t he coa l i sA s mentionedno t comple te ly d i s t r i b u t ed across t h e d i lu t e -phase r eac to r c ross s ec t i o n befo re r ap idheat-up and de vo la t i l iz at io n, when the coal i s s u s c e p t i b l e t o c a k in p .

e a r l i e r , t h e c o a l i s fe d by a 5/16 inch diameter tube in t o a 3.26 i nch d iameter reactor .The p a r t i c l e s h i t t h e w a l l of t he r eac to r about 12 i nches down from t h e end of t he f eednozzl e . I f devo la t i l i z a t i on i s completed wi th in 6 inche s f rom th e end o f th e nozzle ,a f e e d r a t e c a l c u la t e d t o b e 300 l b s / h r f t 2 of r e a c t o r CKOSS sec t i on ac tua l l y co r respondst o a r a t e of 1000 l b s / h r f t 2 of c ross - sec t i ona l a rea occup ied by t he pa r t i c l es . Datafrom a f r e e - f a l l c a r b o n i z e r (c),2 i nches i n d i ameter, a t the Morgantown EnergyResearch Center , show tha t Pi t t s bur gh coal w a s processed a t 1000 lb s / hr f t 2 and y ieldedcha r with a mean dia mete r of about 0.508 m (0.02 inches).through 200 mesh.

1f The feed coal w a s 70 p c t

The react ion rate cons tant s for the FDP rea cto r are shown on a n Arrhenius p lo ti n Figure 13 .r eac t ed appear s t o i n d i c a t e t ha t t he r eac t i on may be con t ro l l ed by mass t r a ns fe rof hydrogen to the react ion s i t e s and no t by t he r a t e o f hydroga s i f i ca t i on .(2) has sugges t ed t ha t i n t he h igher t empera tu re range t he r a t e may be be t t e rdescr ibed as pro po rt i ona l t o kgPH2, where khydrogen through the gas f i lm surrounding t8e p a r t i c l e .a s t r a i g h t l i n e c ou ld ha ve j u s t as e a s i l y f i t t h e t o t a l c a rb on co nv er si on d a t a i nFigures 7 and 8.f low reactor was determined by Zahradnik and Glenn (2)o be 15 kcal /mole, i nagreement wi th th e value obtained i n t h i s work.energy r ep resen t s t he d i f f e renc e i n ac t i v a t i on energy between the hydrogas i f i c a t i onand polymer izat ion rea ct io ns .c a l c u l a t e s k by i nt eg ra t in g Equation 7 from zero t o x ins tea d of from E t o x, showssome low temperature FDP dat a. The a c ti v a ti o n energy i s 29.8 kcal/ mole f o r temper-atures below 580' C , and decreas es t o 6.4 kcal/mole fo r temperatures above 580' C .The k values were ca lc ula ted t h i s way because E could not be determined frog theavai lab le data and because P H ~a s approximately constant .energy supports Feldmann's suggest ion th at th e rea ct i on i s mass t r a n s f e r c o n t r o l l e d .More comments w i l l be made on thes e r e su l t s a f t e r rev iewing some low-temperature"hot-rod" re ac to r dat a.

The re la t i v e ly low ac t i va t io n energy of 15.1 kcal/mole of carbonFeldmann

i s a mass t r a n s f e r c o e f f i c i e n t f o rThis seems r easonab le s i nceThe ac t i va t i o n energy f o r ca rbon hydroga s i f i ca t i on i n an en t r a ined

They sugges t t h a t t h i s ac t i v a t i onAn Arrhenius pl o t of Feldmann's (L) n which he

Th i s change i n ac t i va t i on

The.data presente d f or th e FDP rea ct or a r e based mainly on P i t t s b u r g h seam hvAbcoal .a t i n g p r o p e r ti e s .could ea s i l y handle mi ld ly caking coals .FDP r e s u l t s on t h i s c o a l are shown i n Fi gur e 14.has not been s tu died over a wide range of hydrogen p a r t ia l pressu re as h a s t h ePi t t s burg h coal , but does appear t o be more re ac t iv e based on comparison of th etwo coals in Figure 14 a t t h e same r eac to r cond i t i ons .

This coa l was s tud ied e xten sive ly because of i t s extreme swelling and agglomer-If t he r eac to r cou ld p rocess badly cak ing coa l t han s u re ly i tI l l i no i s 16 hvCb coa l i s mild ly caking andThe convers ion of I l l i n o i s coal

i

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112"Ho -Rod" ReactorsThe resul ts from th e "hot-rod" re ac tor t es t s of Hiteshue, Friedman, and Madden(L) w i l l b e r ef er re d t o a s HR-1 series when coal is u sed a s t h e s t a r t i n g r e a c t a n tand HR-1C when char i s used.r e f e rr e d t o as HR-2 and HR-2C series. The weight lo ss and carbon conversion dataa r e shown i n F igures 1 5 and 16, re spec t ive ly . fo r the HR-2 series e xpe r i r e n t s . I nmost of t h e HR-2 t es t s th e r ea c to r temperature was maintained low enough t h a t Type 2carbon conversion appeared to occur over a period of about 6 minutes. Once t h etemperature exceeded about 600" C, Type 3 carbon w a s rapidly formed.a t which t he c u rve s i n F i gu r e 15 o r 16 appe ar t o l e v e l o f f c or re spond t o t het r a n s i t i o n p o in t s a t which th e hydrog asific ation occu rs predominately with Type 3carbon. For th e tes ts a t 800 C, the devola t i l iza t ion and Type 2 carbon conversionboth occur i n less than a minute .a r e p l o t t e d on t h e same Arrhenius graph with t he FDP da ta in Figure 13. For th e da taup t o 600" C , Equation 4 w a s int eg rat ed s ta r t in g from zero carbon conversion, and theva l ue s of k and a were determined from a least -squares f i t of t he data ( E w a s foundto be ve ry c lose t o ze ro i n th e regress ion ana l ys i s fo r t emperatures below 520' C).For the 800" C d a ta , t h e i n t e g r a t i o n was s t a r t e d from E with a = 1, and aga in k and

E were determined from a least -squares ana lys is of the data . The val ues of the separameters are l i s t e d i n T ab le 6.d a t a in Figu re 15. As i s obvious in Figure 16, the carbon conversions calcula tedfrom th e carbon analys es were no t c ons i s t e n t a t 425" C and 69 atm w i th e i t h e r t h eto ta l convers ion data i n F i g u r e 1 5 o r d a t a a t 35 a t m . Therefore, th e ca rbon gas i f i -c a t i o n r a t e c o n s ta n t a t 425' C w a s ca lcu la ted by ex t rapo la t ing the l i n e ob ta ined whenk i s p l o t t e d ve r sus $ ( r a t e c o n s t an t f o r t o t a l c on ve rs io n) .can al s o be estimate d by assuming the cu rve must pass through 0.0588 (average of twoda t a po i n t s ) a t 6 minutes. This method giv es a k va lu e of 0.255 atm-l hr-' comparedto 0.365 arm-? 'nr-lby extrapolation,

Unpublished data of Feldmann and Williams w i l l be

The conversions

This is m re c l e a r l y v i s i b l e when t he r a t e c ons ta n ts

The model was a l s o f i t t o t h e t o t a l weig ht l o s s

The k v alu e a t 425' C

In the Arrhenius p l o t o f F igu re 13, th e low temperature "hot-rod" re ac to r dataappears to be cons i s t en t wi th the d i lu te -phase reac tor da ta . Unfortunate ly , lowtem per atu re FDP d at a is ve r y d i f f i c u l t t o ob t ai n i n o r de r t o ve r i f y t he low temper-a t u r e "hot-rod' ' re ac to r da ta because of agglomer ation and plugging.temperature "hot-rod" re ac to r d at a cannot ve ri fy th e FDP da ta because th e heat-upr a t e and res idence t i m e s a r e suc h t ha t t hey ope r a t e in di f f e r en t carbon convers ionregimes. The key di ff er en ce between th e FDP re ac to r and th e "hot-rod" re ac to r ist he co a l heat -up ra te .whereas in the "hot-rod" re ac to r the ra te i s about 7 C/sec.temperature quickly enough, th e ki ne t i cs of Type 2 carbon hydro gas i f i c a t ion can beobserved.

The high

I n th e FDP reac tor t h i s ra te is on the or der of 1000 C/secBy achiev ing rea cti on

The carbon conversion data for the HR-1 series e xp e r b e n t s a r e shown i n F i gu re 1 7 .I n t he se t e s t s t he de vo la t i l i z a t io n and Type 2 ca rbon convers ion occur red in lessthan a minute because of th e high temperatures.pa r t represen t Type 3 carbon conversio n. Johnson (23) has observed i n thermobalanceexper iment s tha t devola t i l i za t ion and Type 2 carbon convers ion a re e s se n t i a l l y completew i t h i n 2 minutes a t temperatures above about 800" C.b a l a n c e t e s t s was about the same as in th e "hot-rod" re ac to r tests . The HR-1 s e r i e sd a t a were f i t u si ng E qu ati on 4 with a = 1 and in tegra t ion s t a r t ing f rom E.p ar am et er s a r e l i s t e d i n T a bl e 7.the carbon beyond the fract ion E is Type 3.an d 2 carbon.

Therefore the curves f o r the most

The heat-up r a t e i n th e thermo-The kineticChoosing a = 1 s im pl y means t ha t e s s e n t i a l l y a l lHere E r e p r e se n t s t he sum of Types 1

F i gu r e 18 i l l u s t r a t e s the e f f ec t o f the reac to r t empera ture on the amount ofcarbon that can be hydrogasi f ied as Types 1 and 2. High temperatures and hydrogen

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TAELC 6. - K i ne t i c pa r a a e t e r s f o r UR-2 series data

Temp., * C42547 049 05206 0 06 0 0800800

PI! , a t n6 96 96 96 96 96 96 96 9

a.071*.189.199.179.2321.0.3151.0

E00000.1750.243

- 1atv-lhr-l0.383*0.4470 .6251.470.9760 .007511 .220 .0123

UT**

.099.261.278.264.272

.344

-

------

%**a t r - l hr- 0.5100.5040.8382.071.08

1.66----

* Extrapola ted usinp t o t a l conversion kT values.is 0.255 atn-lhr- . Ey an ot he r method, t h e k value** Subscript T i nd i c a t e s t o t a l c onver s ion pa r a pe t e r s ( t o t a l w ei ph t loss).

TABLE 7.- K i ne t i c pa r a ue t e r s f o r ER-1 s e r i e s d a ta1.a E atv- lhr- lH , a t r -enp., a C800 18.0 1.0 .252 0 .0282800 35.0 1.0 .355 0 . 0 1 5 4800 69.0 1.0 .A50 0.01601 2 0 0 4 .1 1.0 . 298 0 . 3 6 31200 18.0 l.@ .377 0.1371 2 0 0 35.0 1.0 .514 0 .350

TABLE 8.- E f f e c t of hydropen p a r t i a l p ressur e on ca r ton conversionin t he ho t rod reac to r

TestBR-1HR-1HR-1m-2m-2ER-2IIR-2HR-2HR-2HR-2

- enp.. C8008008005004 9 06 0 06 0 07 0 0800800

Fp,, ata1835693569356935356 9

Carbon Conversion, pet1 p i n . 2 pin. 5-6 c i n .--- --- 30.7.25.7--- --- 39.4,40.4--- --- 52 .0 ,55 .5 ,52 .6 ,54 .69.10 12.1 ---10.4 14.5 ---17.6 18.4 ---17.5 17.9 ------ 21.0 ---23.7 24.3 31.225.6 25.8 33.9

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p a r t i a l p r es su re s result i n a la rg e amount of carbon being hydrogasif ied i n t he Types1 an d 2 regime..p a r t i a l p r es s ur e of 500 a m and 900' C, the carbon is r ap i d ly ga s i f i ed t o comple tion .

There is a l a r g e d i ff e r e n c e i n t h e l e v e l of Types 1 and 2 carbon conversion

In f a c t Moseley and Paterson (22) have shown th at a t a hydrogen

between the HR-1 d a t a a t 800' C and the corresponding HR-2 tests .is s h a m i n Table 8 and is es p ec i a l l y n o t i ceab l e a t 800" C and 69 atm.condi t i ons the conver s ions from th e HR-1 t e s t s range f rom 52 to 54.6 pc t a t ares idence t i m e of 5 minutes whereas the corresponding convers ions fo r the HR-2tests ranged from 31.2 t o 33 .9 pc t a t a res idence time of 6 minutes.r esponse o f convers ion t o changes i n hydrogen pa r t ia l p ressure i n th e HR-2 tes tss ug g es ts t h a t t he r e a c t i o n r a t e was s t rong ly mass t r an s fe r con t ro l led .v e r i f i ed b y comparing t h e g as v e lo c i t i e s i n t h e HR-1 and HR-2 experime nts i n Tabl e9. In t h e HR-1 t e s t s t h e s u p e r f i c i a l hy dro gen f eed g as v e lo c i t y was 36 cm/seccompared t o a v e lo c i t y o f 1 t o 2 cm/sec i n th e HR-2 tes ts . Apparently the pasv e l o c i t y w a s low enough i n t h e HR-2 t e s t s t h a t a t t h e h igh e r t emp er a tu re s t h e masst r a n s f e r r e s i s t an ce t hr ou gh th e p a r t i c l e g as fi lm was s ig n i f i ca n t .s lower pa r t ic le heat-up r a t e may have con t r ibu ted t o t he d i f f ere nce i n convers ions .Anthony (2)as demonstrated, however, th a t varying the he at in g ra t e from 180 t o10,000" C/sec has no e f f ec t on t he coa l conversion.and more highly dispe rsed samples t o be extremely importa nt because th e f l u x ofvolat i les emerging f rom the coal p a r t i c l e may l i m i t th e counter d if f usi on of hydrogeni n t o t h e p a rt i c l e .r eac t ion t o compete wi th po lymeriza t ion r eac t ions th a t p roduce a r e la t i ve ly in ac t i vechar .

This discrepancyUnder these

The lack ofThis can be

In ad d i t i o n , t h e

H e found smal ler par t i c l e sizes

This r e s t r i c t i o n makes i t d i f f i c u l t f o r t h e h y d ro g as i fi c at i on

In Table 10 the Types 1 an d 2 carbon conversio n f o r FDP and "hot-rod" re ac to rt e e t e ere coxqare:. The HR-2 t e s t s were d e f i n i t e l y mass t r an s f er con t ro l le d whereasi t is d i f f i c u l t t o conclude th i s i n the FDP tests compared t o t h e HR-1 tests becauseo f t h e l a r g e d i f fe r e n ce i n r e s i d e n ce t i m e .w a s less than 1 second and i n t h e "hot-rod" re ac to r it was two orders of magnitudeg r e a t e r .a f t e r a b ou t 3 seconds a t 69 arm, 900' C, and a heat ing r a t e of 750' C/sec.c o al p a r t i c l e s i z e w a s 70 micr ons compared t o about 220 microns i n t h e FDP experiments.Therefore Types l a n d 2 carbon conver s ion i n the FDP tes t s probably di d not rea chcompletion.

In the FDP re ac tor the res idenc e t i m eAnthony (2)as s h am th a t T y p es 1 and 2 carbon conversions are completeHis s t a r t i n g

Photographs of some of th e ch ar s under a scanning el e c tr o n microscope reve al theporous s tr uc tu re produced i n th e FDP and "hot-rod" re ac to rs under various con ditions.F ig u r e 19 compares chars produced i n th e FDP re ac to r a t 725' C , 205 a t m ( top- lef t ) , anda t 850 C, 69 a t m (bottom-left) . The ch ar produced a t 69 a t m app ea rs t o be much moreporous and less dense than the char made a t 205 atm. As discussed previously , thiseffect shows up as a l a r g e d i f f e r e n c e i n b u lk d e ns it y.

Figure 20 compares chars produced i n th e "hot-rod" re ac to r a t 600' C , 69 a t m(bottom) and a t 800 C, 69 a t m ( t o p ) a t d i f f e r e n t r es id e nc e times. The low temperaturechar has nuch la rg er pores whi le th e h igh temperatu re char has a l a r g e r number of v erysmall pores.r a t e o f v o l a t i l e ma tt er f rom t h e p a r t i c l e s r e a c te d a t 800' C. In add i t i on , th e super -f i c i a l h ydrogen v e l oc i t y i n t h e 600 C te s t was 0.9 cm/sec versus 1.1 cm/sec i n t h e800' C t e s t .co u n te r d i f f u s io n of h yd ro gen i n to t h e ch a r s t r u c t u r e r e s u l t i n g i n l e s s Compe ti ti onf o r t h e polym eriza tion re ac ti on . Comparison of t he FDP and "hot-rod" cha r Samplesi n d i ca t e s t h a t t h e p o re s t r u c tu r e o f t h e FDP ch ar is more highly developed with poreshav ing t h i n wal l s.t h a t t h e g r o s s po re s t r u c t u r e is n o t a s clear as p o s s ib l e .

This d i f fe r e n ce i n t h e p o re size is probab ly r e la te d t o the h igher emission

Both these cond i t ions (h igh vo la t i l es emiss ion , low gas ve loc i ty ) l i m i t

The samples i n Figure 20 were crushed t o 100 pct th ru 60 mesh 8 0

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TABLE 9.- Effect of hydrogen velocity on carbon conversionin the hot rod reactor at 800' CpH , atm 132 velocity Average CarbonSeries Sample 2 cmf ec Conv.. %

HR-1 Pgh. hvAb Coal 35 36.6 39.9HR-1 Pgh. hvAb Coal 69 36.6 53.7HR-2 Pgh. hvAb Coal 69 1.11 33.9HR-2- Pgh. hvAb Coal 35 2.19 31.2HR-lC Pgh. hvAb Char 69 36.6 31.4HR-2C Ill. 16 hvCb Char 69 1.11 31.2

ResidenceTime, min.56561515

TABLE 10.- Comparison of types 1 and 2 carbon conversionin the FDP and "Hot-Rod" ReactorsCarbon Conv., %H , atmTests

FDP* 35.0 27.2pDP* 69.0 32.2HR-1** 35.0 33.2, 32.8HR-1** 69 n 38.5, 40.3HR-2** 35.0 23.7HR-2** 69.0 25.6

-

*From Figure 8, 850'-900" C.**800 C.

TABU 11.- Kinetic parameters for HR-1C series datak

7 a E atm-lhr''PH , atm -emp,, C800 18.0 1.0 .009 .0234800 35.0 1.0 .027 .0178800 69.0 1.0 .144 .0110800 69.0 1.0 .136 .0137*

*HR-SC data.

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116Fi gu re 21 shows th e ch ar samples from FDP te s ts a t 850 C and 69 a t m using a

l i g n i t e co a l f e e d ,s t ru c t u r e obta ined wi t h b i tuminous coal.w i th l i g n i t e ( co a l p a r t i c l e a l s o i n F ig u re 2 1), t h e p en e t r a t i o n o f h ydrogen i n t o th ep a r t i c l e i s poorer compared t o bituminous coa l.have an even s tronge r inf lue nce on the hydrogas if icat ion of l igni te than with bituminouscoals .

The por e s tr uc tu re appears very undeveloped compared t o th eBecause of the lac k o f pa r t ic le swel l ingConsequen tly, pa r t ic le s i ze shou ld

The char data i n Table 9 are very in te res t in g because the su pe r f i c i a l hydrogenvel oc i ty had no ef f ec t on t he carbon convers ion .char pa r t ic le s must be la rg e compared to th e char-hydrogen re ac t i on rate. This i sn o t s u r p r i s i n g since t h e r ea c t i o n r a t e o f Type 3 carbon i s very slow, probably muchs lower than t he d i f f us ion ra tes of hydrogen and gaseous re ac ti on produ cts.

The mass t r a n s f e r rate i n t o t h e

The results o f HR-1C series experiments with char produced from Pi tts bur gh seamhvAb co a l are shavn i n F igur e 22.ex cep t f o r a smal l amount o f r ap id i n i t i a l conver sion. The k i ne t i c parareters f o rth es e d a t a are l i s t e d i n T ab le 11.al so shown i n Table 11 and Fi gu re 22, and agree w e l l w i th t h e HR-1C data. The twochar s are d i f f e r e nt i n tha t t h e HR-2C char w a s produced from I l l i n o i s #6 hvCb c oa li n t h e d i l u t e phase r e a c t o r a t 585' C whereas the HR-1C ch ar was produced fromPi t t sburgh seam hvAb coal by ba tch carbon iza t ion fo r 2 hours in he lium a t 600 C.The HR-2C ch ar conta ined about 26 p c t v o l a t i l e matter compared t o the or ig in al 36.5p c t vola t i le m a tt er i n t h e s t a r t i n g c oa l.n ea r ly eq u a l d ev o la t i l i za t i o n t emp era tur e s, t h e r ea c t i v i t i e s o f t h e two ch a r s aree s s e n t i a l l y t h e same.cou ld have r e s u l t ed i n t h e ch a r s having d i f f e r i n g r e ac t i v i t i e s (23,2).

The carbon conversion i s of t he Type 3 spec ie sThe results o f t h e HR-2C series experiments are

Despi te these d i f f erences , ex cep t f o r t h eA s i g n i f i c a n t d i f fe r e n ce i n t h e d e v o l a t i l i z a t i o n t em pe ra tu re s

The Arrhenius graph i n F igur e 13 summarizes t he r e s u l t s f o r a l l the coals andchars tes ted and Includes some of Johnson's data (23)which was a d ju st e d t o c a l c u l a t ek values according t o Equ at ion 4. Assuming th a t i t i s v a l i d t o r ep res en t t h e l owtemperature "hot-rod" re ac to r da ta by t he same Arrhenius l i n e as th e FDP dat a, t h eac t iv a t i on energy f o r hydrogas i f ica t ion o f Type 2 carbon i s 15.1 kcal/mole of carbong as i f i ed .magnitude lower than the rate of hydrogas i f ica t ion o f Type 2 carbon. The ac t iva t ionene rg y f o r t h e HR-1, HR-lC, and HR-2C d a t a i s 24.7 kcal/mole of carbon gasified (Type 3carbon) compared to a value of 47.1 kcal/mole obtained by Johnson (23) us ing a thermo-balance. A t 600Oand 800' C , th e HR-2 da ta was complicated by th e tr an si ti on t o Type 3carbon c onversion and a s i gn i f ic an t amount of mass t r a n s f e r r e s i s t a n ce .tempera tu res the apparen t ac t iv a t io n energy fa l l s o f f considerab ly as shown i n F igu re13.Two-Stage I nt eg rat ed Reac tor

The hydrogasif icat ion ra t e of Type 3 carbon i s about th ree o rder s o f

A t these higher

The results of t h e two-stage tes ts w here t h e f i r s t - s t ag e was a FDP r eac to r andthe second-stage e it he r a moving-bed o r fluid-be d re ac to r have been pres ente d else-where @).plo t te d .in F igure13 .caused th e t r ue p ar t i cl e temperature t o be higher than the measured temperature,the ac t i va t i on energy of the moving bed da ta is low, and the r a te cons tan t va lues arer e l a t i v e l y h i gh a t t h e lower reactor temperatures .Cor rel ati on of Char Yie ld and Coal H. N, S. and 0 Conversion Data

The ki ne t i c r e su l t s a re summarized i n Tab les 12 , 13, and 14 and are a l s oBecause h ea t t r a n s f e r l im i t a t i o n s w i th in t h e ch a r p a r t i c l e s

I n o r d e r t o p r ed i c t t h e co nv e rs io n o f o th e r co n s t i t u en t s i n t h e co a l d u ringhydrogas i f ica t io n bes ides carbon convers ion, results from nin ety -fiv e experiments

1II1

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b./

TABLE 12.- Kinetic results from two-stage integrated reactorexperiments (18) at 69 atmkoving FluidTotal C Bed C Bed C Bed-un Conv., X Conv., Z* Conv., Z* Temp., O K atm-lhr-l

2 0.552 --- 0.378 1158 0.01453 0.536 --- 0.356 1158 0.02845 0.558 --- 0.345 1158 0.031611 0.608 --- 0.419 1073 0.045012 0.551 --- 0.335 1118 0.020213 0.556 --- 0.383 1113 0.021814 0.537 --- 0.357 1183 0.013933 0.620 0.457 --- 1178 0.057337 0.392 0.131 --- 1173 0.036038 0.485 0.264 --- 1148 0.039639 0.417 0.167 --- 918 0.044943b 0.430 0.186 --- 1038 0.039544b 0.391 0.130 --- 923 0.02604 b 0.406 0.151 --- 933 0.030746a 0.399 0.151 --- 957 0.030548 0.511 0.301 --- 1073 0.029949 0.536 , 0.337 --- 988 0.0358

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TABLE 13.- Hyd roga sifi cat ion of I l l i n o i s 16 hvCb c oa l i n a two-stager e a c t o r a t 1000 p s i g - run condit ionsTes t 46 48 49Re ac to r Zone FDP* MB* FDP MB FDP MBTemp., C 850 684 850 800 850 715Coal o r Char Rate, lb (d ry )/ hr 10.51 6.68 10.26 5.08 10.32 5.0136ed Height, i n . --- 0 - 36 -Residence Time, min. -- 0 -- 10.4 -- 10.4Feed Gas, SCFH 164.4 141.4 181.7 152.0 166.2 150.7Vol. Pct. H2 56.2 99.4 52.0 99.0 50.9 98.637.2 -- 42.1 --- 42.8 -4 1.05 0.50 1.10 1.00 1.50 1.30

He 5.45 -- 4.70 -- 4.70 --2Product Gas, SCFH** 168.6 141.4 179.0 124.6 169.8 130.3Vol. Pct. H2 34.8 99.4 32.4 54.2 30.1 58.0CH4 55.1 -- 57.2 43.5 58.0 39.0Run Time, min. 187 19 3 187

* FDP:**For runs 48 and 49, th e ind iv id ua l product pas f lowrates and the composition of the

f r ee -f a l l d i l u t e p h as e r eac to r ( 3 f o o t h ea ted l en g th ) ; MB: moving-bed reactor.MB product gas p r i o r t o mixing were es t imated using t he hel ium tra ce r data ,

TAB