Experimental and numerical investigation on the pyrolysis of single coarse lignite particles

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1 Korean J. Chem. ng., 29(4, (2012 DOI: /s INVITD RVIW PAPR xpermental and nmercal nvestgaton on the pyrolyss of sngle coarse lgnte partcles Ka Zhang, Changf Yo, and Yle L Key Laboratory for Thermal Scence and Power ngneerng of Mnstry of dcaton, Department of Thermal ngneerng, Tsngha Unversty, Bejng , Chna (Receved 8 December 2010 accepted 3 Agst 2011 Abstract Ths paper reports on the mathematcal modelng of the pyrolyss of sngle coarse lgnte partcles sng a knetcs model copled wth a heat transfer model. The parallel reacton knetcs model of the lgnte pyrolyss makes no assmptons abot the actvaton energy dstrbton and the converson of sb-reactons. The pyrolyss knetcs parameters were obtaned on the bass of expermental data from thermogravmetrc analyss (TGA tests. The heat transfer model ncldes dffsve, convectve and radatve heat transfer modes. The expermental nvestgatons were carred ot for sngle lgnte partcles n an electrcally heated reactor. Measrements of the temperatre and mass loss were performed drng the pyrolyss n a ntrogen atmosphere. The model predctons for the temperatre and mass loss hstores agree well wth the expermental data, verfyng that the mathematcal model accrately evalates the pyrolyss of lgnte partcles. The effects of temperatre and partcle sze on the pyrolyss tme and fnal resdal mass fracton were evalated sng the nmercal model. Key words: Lgnte, Coarse Partcle, Pyrolyss, Knetcs Model INTRODUCTION Lgnte as a prmary energy sorce wll become ncreasngly mportant n energy spples n the ftre becase of ts abndance, easy access and low mnng costs. At the end of 2005, worldwde lgnte reserves amonted to bllon tons and acconted for 17.7 percent of total coal resorces [1]. The enormos resorces of low-rank coal as an abndant fel have become the focs of development for power generaton [2-4]. Fldzed-bed combston and gasfcaton have been a recognzed means of technology for power generaton de to ther nherent operatng flexblty [5-7]. The se of low-rank coals s strongly dependent pon the behavor of the volatle matter, whch can accont for p to 50% of the specfc energy for low rank coals. Ths, nderstandng of the volatle release s of paramont mportance. However, pyrolyss and devolatlzaton, lke other coal processng methods and coal propertes, have been manly nvestgated sng fnely plverzed (mcrometer gran sze samples [8-14]. Larger, centmeter sze coal partcles have sometmes been consdered, for example, n fldzed bed combston stdes, bt the behavor of a sngle coal lmp has rarely been nvestgated [15]. Small partcles are lkely to more qckly release the volatle matter, wth very dfferent release characterstcs for the volatle matter n coarse partcles becase they are heated at a slower rate than the smaller partcles [16-20]. Coarse partcle coal pyrolyss s controlled by three man factors: the heat transfer to and wthn the coal partcle, the chemcal knetcs, and the mass transfer of the volatle speces wthn the coal partcle [21,22]. Several mathematcal models have been developed to descrbe the devolatlzaton of coarse coal partcles showng that To whom correspondence shold be addressed. -mal: yocf@tsngha.ed.cn Ths work was presented at the 8 th Kore-Chna Workshop on Clean nergy Technology held at Daejeon, Korea, Nov , the heat transfer and chemcal knetcs domnate the overall reacton mechansm [21-23]. Koch et al. [24] sggested that the char layer whch forms arond the pyrolyzng coal partcle provdes no resstance to the ot-flowng volatles, whle the data of Anthony et al. [25] ndcated that the effect of pressre on the devolatlzaton of a Montana lgnte s neglgble. These reslts tend to spport the assmpton that the effect of mass transfer s neglgble for low-rank coals, hence, t wll not be consdered n the crrent nvestgaton. The prpose of ths work s to frther advance the stdy of the pyrolyss mechansm of coarse coal partcles (centmeter sze whch are sed n some gasfcaton processes. A model was developed to predct the temperatre response and the evolton of volatles from coarse coal partcles drng pyrolyss. The model s based on the nsteady state heat condcton eqaton n sphercal coordnates and ses a new parallel reacton model to predct the volatles evolton. The model s valdated wth expermental reslts wth smlaton stdes condcted to predct the pyrolyss behavor over a wde range of pyrolyss parameters and process condtons. MATHMATICAL MODL Drng pyrolyss, fne coal partcles are generally assmed to be sothermal. The assmpton of an sothermal partcle reqres that the heat transfer Bot nmber s less than However, for coarse coal partcle (>1 mm wth the larger Bot nmbers, the nternal temperatre gradents mst be consdered [26,27]. xstng gassold heat transfer correlatons and thermophyscal propertes can be sed to show that the heat transfer Bot nmber vares from 1 to 20 for partcle szes >1 mm. Ths, modelng of the pyrolyss of coarse coal partcles mst consder heat transfer processes nsde the partcles. The heat transfer starts at the partcle srface where the coal partcle receves energy from the srrondng gas va convecton and radaton heat transfer modes. The heat s sbseqently transferred by condcton to the partcle nteror. volton of volatle 540

2 Investgaton of the pyrolyss of sngle coarse lgnte partcles 541 matter from the coal partcle therefore depends on the relatve rates of convecton and radaton heat transfer to the srface and condcton heat transfer nto the nteror. The loss of partcle mass also creates a gas flow away from the partcle, whch s detrmental to the convecton heat transfer. The pyrolyss model for a coarse coal partcle conssts of a reacton knetcs model and a heat transfer model. 1. Knetcs Model Many knetcs models have been reported for the pyrolyss of fne coal. There s the sngle knetcs rate model [8], the two competng rates model [9], the dstrbted actvaton energy model (DAM [10], the mltple parallel reacton model (MPRM and others. Fne coal pyrolyss models have been revewed by Saxena [11], Solomon et al. [12], ssenhgh [13] and Anthony and Howard [14]. The dstrbted actvaton energy model (DAM assmes a Gassan actvaton energy dstrbton or sb reacton converson of The mltple parallel reacton model assmes a sb-reacton converson of However, there s no theoretcal spport for these assmptons of the actvaton energy dstrbton or the sb-reacton converson. Ths stdy presents a parallel reacton model to descrbe the pyrolyss knetcs wthot assmptons for the actvaton energy dstrbton and the converson of sb-reacton. The model assmes that at each converson only one frst-order sb-reacton domnates the overall mass loss. Ths, at a gven converson of α *, the th sb reacton s the only reacton takng place at ths converson: = A exp ( 1 α RT dα dt W where α = 0 W t W 0 W Integratng q. (1, reslts n t 1 α * exp A exp( /RTdt 0 If the converson n two separate experments at dfferent heatng rates, β 1 and β 2, s consdered A T 1 T 2 exp ---- exp( /RTdT = exp ---- exp( /RTdT β 1 T 0 Takng logarthms on each sde yelds T 0 exp β 1 RT 0 R /RT 0 A β 2 exp( d T 1 exp RT exp( d R = ---- T /RT 1 exp β 2 RT exp( d T 2 R exp RT /RT 0 R T 0 /RT 2 exp( d (1 (2 (3 (4 Ths s a nonlnear eqaton, whch can be solved for the nknown. Once s known from q. (4, A can be calclated from A Ln( 1 α * = T 0 exp β 1 RT R T 1 exp RT R /RT 1 /RT 0 exp( d Once each vale of and A s known, at each tme: Where f s the contrbton rate of the sb-reacton. q. (6 may be wrtten as a matrx eqaton, where, for any set of temperatres T 0, T 1, T 2, etc., the mass of coal remanng, M(T, s gven by 2. Heat Transfer Model The convectve heat transfer between the volatles and the solds s ncorporated nto the governng eqaton. Usng an nfntesmal exp( d M =1 α = f exp A exp( /RTdt MT ( 0 MT ( 1 MT ( 2 = all reactons ψ 1 ( T 0 ψ 2 ( T 0 ψn ( T 0 ψ 1 ( T 1 ψ 2 ( T 1 ψn ( T 1 ψ 1 ( T 2 ψ 2 ( T 2 ψn ( T 2 A where ψ ( T = exp ---- exp( /RTdT ρ s M = ρ s0 V t t β 1 T T 0 t 0 Table 1. Parameters sed n the smlatons Parameter Correlaton/vale Sorce C ps (Jkg 1K 1 C ps =c P_daf w daf +c P_ash w ash [28] C p_daf (Jkg 1K T [29] +( Tw v C p_ash (Jkg 1K T [30] λ s (Wm 1K w C w H T [31] ε 0.95 σ (Wm 2K H (kjkg ρ s0_ho (kgm ρ s0_ha (kgm f 1 f 2 f n (5 (6 (7 (8 Table 2. Ultmate and proxmate analyses of the raw lgnte Samples Ultmate analyss (wt% a Proxmate analyss (wt% a Proxmate analyss (wt% b C H O N S V FC A M Holnhe lgnte Halaer lgnte a Dry bass b As receved bass Korean J. Chem. ng.(vol. 29, No. 4

3 542 K. Zhang et al. control volme n the radal drecton of the sold partcle, the energy balance eqaton n sphercal coordnates s: --- ( ρ s C ps T ( ρ g C pg T r = λ (9 t r r 2 s r 2 T r r H ρ s t XPRIMNT 1. Materals The two knds of Chnese lgnte sed n these experments were 4πr 2dρ s dr 0 dt where r = πr 2 r ρ g (10 The ntal and bondary condtons are T t=0 = T 0 T r r=0 = 0 λ T = h( T f T + εσ( T f T 4 r r=r Drng pyrolyss the resdal mass fracton s calclated on a dry sample bass and expressed as follows: resdal mass fracton sample weght at any pyrolyss tme t = ntal dry sample weght (11 The parameters sed n the model are lsted n Table 1. Fg. 1. Schematc dagram of the expermental system. Table 3. Pyrolyss knetc parameters of Halaer lgnte N J/mol A s-1 f / N J/mol A s-1 f / Aprl, 2012

4 Investgaton of the pyrolyss of sngle coarse lgnte partcles 543 Holnhe lgnte and Halaer lgnte. The ltmate and proxmate analyses of the raw lgnte are lsted n Table 2. Lgnte fnes n the sze range of µm were sed to stdy the pyrolyss knetcs. The lgnte lmps were dred at a temperatre of 105 o C for at least 10 h before the pyrolyss experments to remove mostre. Then the lgnte lmps were grond nto sphercal partcles (20 mm and 30 mm dameter to facltate comparson of the expermental and nmercal reslts. 2. Thermogravmetrc xperments wth Fne Gran Lgnte The thermogravmetrc experments were carred ot n a TGA/ Q600. The nert gas sed for the pyrolyss was ntrogen wth a flow rate of 100 ml/mn. The ntal mass of the samples was abot 10 mg. Before the experment was started, the frnace was prged for 30 mntes at room temperatre. The frnace was then heated to 105 o C at a heatng rate of 10 K/mn and held at 105 o C for 10 mntes to evaporate external mostre. The frnace was sbseqently heated from 105 o C to 900 o C at dfferent heatng rates (30 K/mn, 50 K/ mn, 80 K/mn, 100 K/mn and 150 K/mn and held at ths fnal temperatre for 20 mntes. 3. Pyrolyss xperment for a Sngle Coarse Lgnte Partcle A schematc dagram of the pyrolyss expermental system for coarse lgnte partcles s shown n Fg. 1. The nsde dameter of the tblar reactor was approxmately 70 mm and the length was 1,400 mm. The tbe was nslated by a thck layer of plaster of Pars arond whch heatng wre was wond, formng the heatng element of the reactor. The temperatre arond the partcle was mantaned at the desred vale by the temperatre control sbsystem and measred by a K-type thermocople wth an accracy of ±0.75%. An electrcal sngle-pan balance was provded to contnosly montor the sample mass. The reactor was flshed contnosly wth nert ntrogen gas at a rate of 10 L/mn nsde the reactor. The flow rate was not hgh enogh to nterfere wth the mass-loss measrement. The temperatres at the center of the lgnte sphere were measred drng the pyrolyss by sng K-type thermocoples. Ths type of thermocople provdes an accracy of ±0.75% of the measred vale. The electronc balance sed to montor the partcle mass had an accracy of ±0.1 mg. All experments were performed at atmospherc pressre wth the weghts and temperatres recorded every 10 seconds. The electrcal otpts for these two measrements were contnosly logged by a data acqston nt. RSULTS AND DISCUSSION 1. Pyrolyss Reacton Knetcs Parameters The knetcs parameters lsted n Tables 3 and 4 were obtaned sng an establshed knetcs model and thermogravmetrc expermental data at heatng rates of 50 K/mn and 100 K/mn. xcldng sb-reactons wth a dstrbton rate of 0, The Halaer lgnte knetcs model contans 30 sb-reactons, and the Holnhe lgnte knetc model contans 24 sb-reactons. The calclated actvaton energes ( were manly n the range of KJ/mol, wth preexponental factors (A of s 1, whch agree wth the reslts Table 4. Pyrolyss knetc parameters of Holnhe lgnte N J/mol A s-1 f / N J/mol A s-1 f / Korean J. Chem. ng.(vol. 29, No. 4

5 544 K. Zhang et al. Fg. 2. xpermental data and model predctons for the normalzed mass of Halaer lgnte: (a β=50 k/mn and 100 K/mn; (b β=30 k/ mn, 80 k/mn and 150 K/mn. Fg. 3. xpermental data and model predctons for the normalzed mass of Holnhe lgnte: (a β=50 k/mn and 100 K/mn; (b β=30 k/ mn, 80 k/mn and 150 K/mn. Fg. 4. xpermental data and model predctons for the pyrolyss rate: (a Halaer lgnte; (b Holnhe lgnte. of Mra et al. [32,33] for coal pyrolyss knetcs. The expermental and calclated reslts for the normalzed mass and the pyrolyss rate profles for Holnhe fne lgnte and Halaer fne lgnte are compared n Fgs. 2, 3 and 4. The reslts show that the resdal mass and the weght loss rate are accrately predcted. 2. Valdaton of the Pyrolyss Model for the Sngle Coarse Lgnte Partcles The effects of nternal convecton arsng from the volatles evolton and the heat of reacton were nvestgated sng for models: (1 wth nternal convecton and wthot heat of reacton, (2 wthot nternal convecton and wthot the heat of reacton, (3 wth nternal convecton and wth the heat of reacton, and (4 wthot nternal convecton and wth the heat of reacton. The reslts n Fg. 5 show that the predcted centre temperatre s lower n the presence of heat of reacton snce the pyrolyss reactons absorb heat from the partcle. Fg. 5 also shows that the nternal convecton has only slght nflence on lgnte partcle pyrolyss. The reslts n Fg. 6 show that the crves (wth the heat of reacton have better agreement wth the expermental reslts for both the resdal mass fracton profle and the center temperatre profle. Ths, ths nvestgaton Aprl, 2012

6 Investgaton of the pyrolyss of sngle coarse lgnte partcles 545 Fg. 5. Model comparson for Holnhe lgnte, T f =713 K, D 0 =20 mm: (a Varatons of the resdal mass fracton; (b Varatons of partcle temperatre. Fg. 6. xpermental data and model predctons for the resdal mass fracton: (a Holnhe lgnte, T f =713 K; (b Holnhe lgnte, T f = 823 K; (c Halaer lgnte, T f =713 K; (d Halaer lgnte, T f =823 K. nderlnes the mportance of ncorporatng the heat of reacton n the pyrolyss model. The model has been valdated wth expermental reslts for large sphercal lgnte partcles at temperatres of 713 and 823 K. Fgs. 6(a and 6(c show the expermental and predcted center temperatre and resdal mass fracton profles for Holnhe and Halaer lgnte partcles at 713 K. The agreement between the expermental data and model predcton s good wth respect to both the resdal mass fracton and center temperatre. Fgs. 6(b and 6(d show smlar trends at 823 K. The reslts n Fg. 6 show that at the lower pyrolyss temperatre the mass loss s more gradal whle at the hgher temperatre the pyrolyzng partcle loses mass rapdly and qckly reaches the fnal resdal mass fracton. Ths, as the pyrolyss temperatre ncreases, the tme needed to attan a gven converson level decreases. The reslts also show that the fnal resdal mass fracton decreases as the pyrolyss temperatre ncreases. 3. Smlaton Stdes Nmercal smlaton can provde a better way to acqre more detaled nformaton nsde the partcle, whch s dffclt to measre bt very mportant. The nmercal reslts agree well wth the expermental data, verfyng that the mathematcal model can evalate the pyrolyss performance of lgnte partcles and obtan more detaled nformaton nsde the partcle ffect of Partcle Sze and Pyrolyss Temperatre The effects of the pyrolyss condtons sch as the partcle sze, the pyrolyss temperatre on the pyrolyss process were evalated sng the nmercal model. The nflence of partcle sze on the resdal mass fracton s shown n Fgs. 7(a and 7(c for Holnhe and Halaer lgnte partcles. Nearly the same fnal resdal mass fractons are obtaned for all partcle szes at a gven temperatre, Korean J. Chem. ng.(vol. 29, No. 4

7 546 K. Zhang et al. Fg. 7. Model predctons for the resdal mass fracton: (a Holnhe lgnte, T f =773 K; (b Holnhe lgnte, D 0 =30 mm; (c Halaer lgnte, T f =773 K; (d Halaer lgnte, D 0 =30 mm. Fg. 8. Model predctons for the partcle temperatre: (a Holnhe lgnte, T f =773 K, D 0 =30 mm; (b Halaer lgnte, T f =773 K, D 0 = 30 mm. whch s the prmary factor controllng the pyrolyss. However, the resde profles over tme dffer for dfferent partcles, and the strong nflence of sample sze s readly observed wth a more rapd declne n average mass wth tme for the 10 mm partcle compared wth the 20 mm, 30 mm, 40 mm, and 50 mm partcles, snce a smaller partcle has a larger specfc srface area for pyrolyss. The varaton of the resdal mass fracton wth tme s shown n Fgs. 7(b and 7(d for dfferent pyrolyss temperatres for Holnhe and Halaer lgnte partcles. These show that ncreasng pyrolyss temperatres redces the pyrolyss tme and a hgher pyrolyzng temperatre leads to a lower fnal resdal mass fracton Profles of Temperatre and Resdal Mass Fracton The detaled nformaton abot temperatre and the resdal mass fracton nsde the partcles drng the pyrolyss process was evalated sng the nmercal model. Fg. 8 shows the smlated temperatres profles at 773 K for pyrolyss of a lgnte sphere wth a 15 mm rads. When a partcle s ntrodced nto the reactor, the srface heats very qckly, dependng on the convectve heat transfer and the radaton flx. The center temperatre s lower de to addtonal dffson heat transfer resstance nsde the partcle. Fg. 8 also shows that the srface temperatre reaches the blk temperatre after a sgnfcant length of tme, whch sggests that the external heat transfer resstance cannot be neglected for these partcles. The reslts also show that the temperatre at r 0 /2 from the center always les between the center and the srface temperatres. Radal profles of the resdal mass fracton (Fgs. 9(a and 9(b Aprl, 2012

8 Investgaton of the pyrolyss of sngle coarse lgnte partcles 547 Fg. 9. Model predctons for the radal profle of the resdal mass fracton: (a Holnhe lgnte, T f =773 K, D 0 =30 mm; (b Halaer lgnte, T f =773 K, D 0 =30 mm. Fg. 10. Model predctons for the radal profle of the partcle temperatre: (a Holnhe lgnte, T f =773 K, D 0 =30 mm; (b Halaer lgnte, T f =773 K, D 0 =30 mm. and partcle temperatre at 773 K (Fgs. 10(a and 10(b show the gradal heatng and transformaton of the lgnte partcle wth a sgnfcant tme lag for the reacton to start. These varatons of the resdal mass fracton n the partcles are not well reported n the lteratre. Drng the pyrolyss, the otsde temperatre s hgher than the nsde temperatre, so resdal mass fracton at the srface s lower than at the center. A large resdal mass fracton gradent appears n the partcle for the pyrolyss process. Ths, the nternal heat transfer resstance sgnfcantly affects the partcle pyrolyss process. At hgher temperatre (773 K the resdal mass fracton profles reveal that at the srface the lgnte has already pyrolyzed and char s formed; at the center pyrolyss reacton s on progress, whle the sold stll contans a large amont of volatle matter. The resde profle s, however, almost flat at the completon of the reacton. CONCLUSIONS A mathematcal model was developed to descrbe the pyrolyss of sngle coarse lgnte partcles sng a knetcs model copled wth a heat transfer model. The parallel reacton knetcs model of the lgnte pyrolyss makes no assmptons abot the actvaton energy dstrbton and the converson of sb-reactons. The knetcs parameters were then obtaned from sothermal mass-loss stdes of lgnte fnes n a TGA. The effect of heat of reacton s fond to be sgnfcant, whle ntra-partcle convecton has lttle nflence on the lgnte partcle pyrolyss. xcellent agreement s fond between the model predcton and the expermental data for two dfferent lgntes. The smlated temperatre profles show that the srface temperatre reaches the blk temperatre after a very long perod; ths, the external heat transfer resstance s qte mportant n the model. As the blk temperatres ncrease, the fnal resdal mass fracton decreases, whch ndcates hgher volatle yelds. At the same blk temperatre, the fnal resdal mass fracton s not sgnfcantly affected by the partcle sze. ACKNOWLDGMNTS Ths research was spported by the Natonal Natral Scence Fondaton of Chna (No and the Specal Fnds for Major State Basc Research Projects Natonal 973 Project (No. 2006CB NOMNCLATUR A : pre-exponental factor [s 1 ] C ps : specfc heat of dry coal [J kg 1 K 1 ] C p_daf : specfc heat of dry, ash-free coal [g] C p_ash : specfc heat of coal ash [g] D 0 : lgnte partcle dameter [mm] : actvaton energy [J mol 1 ] Korean J. Chem. ng.(vol. 29, No. 4

9 548 K. Zhang et al. f : contrbton rate of sb-reacton [dmensonless] R : deal gas constant [J mol 1 K 1 ] t : tme [s] T : temperatre [K] T f : pyrolyss temperatre [K] w daf : mass fracton of dry, ash-free coal n dry coal [dmensonless] w ash : mass fracton of coal ash n dry coal [dmensonless] w v : mass fracton of volatle matter n dry coal [dmensonless] w C : mass fracton of carbon n dry coal [dmensonless] w H : mass fracton of hydrogen n dry coal [dmensonless] W 0 : fne coal weght after dryng [mg] W t : weght at tme t [mg] W : fnal weght of fne coal [mg] H : heat of reacton [kj kg 1 ] Greek Letters α : converson [dmensonless] 1 α : normalzed mass [dmensonless] dα/dt : pyrolyss rate [s 1 ] β : heatng rate [K/mn] ε : emssvty coeffcent [dmensonless] λ : thermal condctvty [J m 1 s 1 K 1 ] ρ : densty [kg m 3 ] σ : Stefan-Boltzmann constant [J m 2 s 1 K 4 ] Sbscrpts ash : coal ash daf : dry ash-free bass ha : Halaer lgnte ho : Holnhe lgnte RFRNCS 1. T. Thomas, S. J. Sandro and G. Peter, Int. J. Coal Geol., 72, 1 ( S. Z. Sn, J. W. Zhang, X. D. H, P. H. Qo, J. Qan and Y. K. Qn, Korean J. Chem. ng., 26, 554 ( J. M. Lee, D. W. Km and J. S. Km, Korean J. Chem. ng., 26, 506 ( Y. J. Hang, B. S. Jn, Z. P. Zhong, R. Xao and H. C. Zhong, Korean J. Chem. ng., 24, 698 ( J. W. Zhang, S. Z. Sn, X. D. H, R. Sn and Y. K. Qn, nergy Fels, 23, 2376 ( F. Fang, Z. S. L and N. S. Ca, Korean J. Chem. ng., 26, 1414 ( C. Prompbess, L. Mekast, P. Pmsomboon and P. Kchontara, Korean J. Chem. ng., 24, 989 ( S. Badzoch and P. G. Hawksley, Ind. ng. Chem. Proc. Des. Dev., 9, 521 ( H. Kobayash, J. B. Howard and A. F. Sarofm, Sxteenth symposm (nternatonal on combston, Cambrdge, U.K. ( D. B. Anthony and J. B. Howard, AICh J., 22, 625 ( S.C. Saxena, Prog. nergy Combst. Sc., 16, 55 ( R. P. Solomon, M. A. Sero and. M. Sberg, Prog. nergy Combst. Sc., 18, 133 ( R. H. ssenhgh, Chemstry of coal tlzaton, John Wley & Sons Inc., New York ( D. B. Anthony, J. B. Howard, H. C. Hottel and H. P. Messer, Fel, 55, 121 ( A. K. Sadhkhan, P. Gpta and R. K. Saha, J. Anal. Appl. Pyrol., 81, 183 ( A. K. Sadhkhan, P. Gpta and R. K. Saha, Boresor. Technol., 100, 3134 ( J. Larfeldt, B. Leckner and M. C. Melaaen1, Fel, 79, 1637 ( C. A. Hedenrech, H. M. Yan and D. K. Zhang, Fel, 78, 557 ( J. S. Chern and A. N. Hayhrst, Combst. Flame, 157, 925 ( W. C. Park, A. Atreya and H. R. Bamb, Combst. Flame, 157, 481 ( P. K. Agarwal, W.. Genett and Y. Y. Lee, Fel, 63, 1157 ( J. F. Stbngton and K. Smaryono, Fel, 63, 1013 ( J. Tomeczek and J. Kowol, Can. J. Chem. ng., 69, 286 ( Koch, H. Jntgen and W. Peters, Brennstoff Cheme, 50, 366 ( D. B. Anthony, J. B. Howard, H. C. Hottel and H. P. Messner, Ffteenth symposm (nternatonal on combston, Tokyo, Japan ( B. A. Adesanya and H. N. Pham, Fel, 74, 896 ( Y. Zhao, M. A. Sero and P. R. Solomon, Twenty-Sxth symposm (nternatonal on combston, Naples, Italy ( D. Merrck, Fel, 62, 540 ( V. Strezov, J. A. Lcas, T. J. vans and L. Strezov, J. Therm. Anal. Calorm., 78, 385 ( F. Hanrot, D. Abltzer, J. L. Hozelot and M. Drand, Fel, 73, 305 ( A. Volborth, Coal scence and chemstry, lsever, Amsterdam ( K. Mra and T. Mak, nergy Fels, 12, 864 ( K. Mra, nergy Fels, 9, 302 (1995. Aprl, 2012