Modelling of a solar-powered supercritical water biomass gasifier

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1 Modellng of a solar-powered supercrtcal water bomass gasfer Laurance A Watson 1, John D Pye and Gregory J Burgess 3 1 BEng student, Research School of Engneerng (RSE), Australan Natonal Unversty, (ANU) Lecturer, RSE, ANU, Canberra, AC, 000, Australa. Phone: , john.pye@anu.edu.au 3 Research Offcer, RSE, ANU 1. Abstract hs paper presents the results of a rgorous modellng exercse to desgn a solar supercrtcal water gasfcaton (SCWG) reactor. A formatve reactor concept model has been developed. hs model ncorporates a solar recever/reactor operatng at condtons of 8 MPa and K. An ntal heat exchange unt s ncorporated to preheat the bomass, usng the waste heat (steam) of a downstream Fscher- ropsch process. An ntermedate heat exchange unt s ncorporated that recovers the waste heat proceedng bomass gasfcaton. Under the deal assumptons appled, the predcted thermal energy effcency of the reactor s 53%. Keywords: Bomass, gasfcaton, supercrtcal water, reactor modellng.. Introducton Gasfcaton descrbes the endothermc reacton between a hydrogen lean feedstock (such as coal or bomass) and steam, wth substantal heat nput and potentally also oxygen, to produce synthess gas (CO, H, CH 4, CO ). If oxygen s suppled to the gasfcaton reactor, a porton of the feedstock undergoes combuston to supply the heat requrement; otherwse an external heat exchange mechansm must be employed. Synthetc chemcals and fuels derved from the converson of a synthess gas, va the Fscher-ropsch (F) reacton as a syncrude, represent an attractve replacement to fosslzed crude ol [1]. he F reacton nvolves the converson of CO and H to a hydrocarbon mxture (C x H y ) and byproduct gases CO and/or H O, wth assocated heat rejecton. he ablty to effcently gasfy bomass would offer one potental source of sustanable hydrocarbons and delver desrable envronmental outcomes. he ndustral focus on gasfcaton to date has predomnantly centred on the converson of fosslsed feedstocks (partcularly natural gas) to produce synthess gas for subsequent F lquds converson. here are three key reasons for the lack of ndustral nterest n bomass gasfcaton. Frstly, bomass s a hydrogen lean feedstock and has a lower specfc energy content than CH 4. Accordngly more external heatng must be suppled to drve the gasfcaton reacton. Secondly, exstng gasfcaton processes result n the adverse formaton of char and tar by-products. hese by-products represent nherent carbon neffcency and rapdly foul process equpment. hrdly, conventonal gasfcaton reactors requre low mosture content feedstock. hs ether elmnates numerous bomass sources, or undesrably, nvolves pre-heatng the feedstock to reduce the mosture content. Gasfcaton of bomass by means of supercrtcal water gasfcaton (SCWG) presents a promsng avenue for utlsaton of wet and/or woody bomass that s not so attractve for other methods of gasfcaton, and an exctng opton for producton of solar-boosted hydrocarbon fuels at moderate scales [][3]. It has been found that when bomass gasfcaton s completed n a supercrtcal water medum ( c K, P c.09 MPa), gasfcaton proceeds rapdly and cleanly (char free) yeldng a gas rch n H, CH 4, CO and CO [3][4]. Moreover, as a wet-process, SCWG process effcency s nvarant of mosture content of the bomass [5]. Lterature reports on lab-scale SCWG reactors however dentfy a number of techncal ssues pertnent to an ndustral-scale SCWG reactor. hese nclude reactor pluggng/foulng, heat transfer rates, hgh hoop stress, and ensurng complete feedstock converson. o date SCWG reactor modellng remans undeveloped, although there s an emergng body of work regardng expermental and thermodynamc SCWG process analyses. In ths study, a reactor model s developed for nvestgatng ndustral-scale SCWG.

2 3. System descrpton Our concept for an ndustral scale SCWG reactor ncorporates the ntegraton of three heat-exchange/reactor unts (Fgure 1). hs sequence of unts s ntegrated nto the overall Bomass-to-Lquds process plant. hs ntegraton s realsed n the producton of an unprocessed synthess gas, and the exchange of heat wth a downstream F reactor. In the current case a low-temperature F slurry bubble column reactor (LF-SBCR) was selected. he SBCR has found extensve use n ndustry for F. Modellng of SBCR Fgure 1: Solar SCWG Reactor Concept operaton has been well documented n lterature [6][7][8][9], and s contnued as part of the current work []. For the current model, the LFSCBR operatng condtons were selected, whch n turn determned the F waste heat flows assocated wth the coolant; saturated steam at 5 K. Regeneratng ths coolant flud as saturated water at 5 K and recoverng energy, for contnuous F coolng and maxmzng thermal effcency, are key process requrements. In commercal applcatons ths s ordnarly acheved by passng the coolant through a medum pressure turbne [11], thereby recoverng some work from the waste heat. In the current context of wet bomass gasfcaton, and gven the low exergy of the steam, t was felt that ths heat source was more valuable for use n preheat treatment. Accordngly, the frst unt of the SCWG reactor s a preheat unt. Preheatng of bomass, also known as hydrothermal pulpng, causes the structural decomposton of cellulosc materal [1]. Experments conducted by Kato et al. reveal that precedng lqudsaton treatment at 43 K promoted subsequent gasfcaton of bomass n supercrtcal water [1]. he second unt n the unt sequence s a secondary heat exchanger to recover the waste heat of gasfcaton, and to further heat the bomass slurry. In the context of reactor desgn, Matsumura et al. [3] suggested the bomass slurry should be pre-heated to a temperature of 73 K pror to enterng a gasfcaton reactor, to mtgate the rsk of foulng the reactor surface. he rate of heat transfer should also be hgh to avod foulng of the heat exchange surfaces. Matsumura et al. [3] suggested a heatng rate of ~300 K mn-1 was requred to prevent foulng of the reactor surfaces. Heat recovery s also dentfed n the lterature as an ssue of mportance for thermally effcent process desgn [3][13]. Wth the bomass slurry requrng a large excess of water, as the gasfcaton temperature s ncreased the SCWG thermal effcency falls. he heat recovery performed by ths heat exchange unt s necessary to maxmze process thermal effcency. he thrd unt s the gasfcaton reactor. hs unt rases the flud temperature up to the requred K to allow gasfcaton to proceed rapdly, and provdes suffcent resdence tme for ths reacton to proceed to completon. he gasfcaton reactor s formed of an arrangement of numerous vertcal tubes, whch n parallel conducts the preheated bomass slurry flow, and whch are drectly heated by concentrated solar rradance. he desgn assumes a hgh-temperature solar heat nput from a helostat feld or dsh collector (Fgure ). hese solar thermal concentrators operate over sutable temperature range ( K and K respectvely) [14] for hgh-temperature supercrtcal gasfcaton. Solar drven supercrtcal gasfcaton of bomass has been demonstrated at a small scale (16 kw thermal nput to the SCWG stage)[15][16]. hs heated tube gasfcaton reactor concept was chosen for two key reasons. Frstly, Matsumura et al. [13] dentfed that drect heatng of the bomass slurry medum had hgher thermal effcency, as compared to mxng bomass slurry wth an excess of supercrtcal water. Secondly, as a tubular desgn lmts the maxmum hoop stress t reduces the requred tube thckness, and therefore presents a more materally effcency reactor desgn.

3 A supercrtcal water reactor s nevtably mpacted by the confluence of hgh pressures and hgh temperatures n the context of fundamental materal constrants. he corrosve envronment consttuted by water n the supercrtcal state further lmts the materal choces. he alloy used n ths reactor model (Inconel 65 ) begns to rapdly loose mechancal ntegrty above 973 K. Accordngly the desgn substtuted an ncreased reactor length and more tubes Fgure : Solar SCWG Helostat-Recever Concept for a more moderate nternal dameter, to both reduce the hoop stress and ncrease resdence tme. Reducng the tube thckness, n the context of poor heat conducton of Inconel 65, s of crtcal mportance for the maxmzng the rate of heat exchange. hese concepts n tube szng were appled n the desgn across all three unts. For the purposes of smulatng the SCWG reactor model, the set of unoptmsed reactor geometrc parameters lsted n able 1 were used. able 1: SCWG Reactor Geometrc Parameters ( kg s-1 flow; 1.6% mol C6H1O6) Inner Radus (m) Outer Radus (m) Stress (MPa) FOS Length (m) Number Preheat Vessel* Preheat ubes* Recycle Vessel Recycle ubes * *3 Gasfer ubes*,4 *1: Factor of safety (FOS) based on maxmum temperature attaned of 500 K (σy = 660 MPa at 500 K). *: Factor of safety (FOS) based on maxmum temperature of 973 K (σy = 640 MPa at 973 K). *3: Reactor modelled as sobarc, hoop stress should be neglgble across tube-sde. *4: Gasfer tube has a 5 m-heated length (at 973 K), the remanng 5 m s perfectly nsulated. 4. Model descrpton he reactor model mplements a one-dmensonal non-sothermal plug flow reactor (PFR) representaton. hs smplfed reactor representaton allows for change n concentraton of flow consttuents by ether reacton or change n flud densty. In ths case mass transfer s by advectve means only, and the model makes no admsson for mass flow by axal mxng (drven by concentraton gradents). hs smple model descrpton has been prevously appled for supercrtcal reactor modellng by Cocero et al. [17]. Cocero publshed a smple supercrtcal water oxdaton reactor (SCWO) model for the destructon of pollutant speces (acetc acd or DMSO (dmethyl sulfoxde)). he dfferental equaton for mass balance as presented by Cocero et al. [17] s shown below. he concentraton of the -th component (C) s recovered from the molar flux rate (F), usng the contnuty of mass and the calculaton of flud densty. df = Ar dx F F C = = = v m / ρ F ( F MW ) / ρ(f,f...,f,p,h ) 1 n dh U o P(1 ) r Δhr A = dx m Whereas Cocero et al. used a temperature explct form for energy balance, the current model s explct n specfc enthalpy (H) for energy balance. It was found that the enthalpy explct form was more numercally

4 tractable n the current case. he above dfferental equatons requre a mathematcal descrpton of fve key aspects of reactor behavour. hese are the heat transfer behavour, gasfcaton knetc behavour, thermodynamc propertes, reacton thermodynamcs, and transport propertes. he proceedng sectons brefly outlne the theoretcal bass for these sub-models and there numercal ncorporaton nto the overall SCWG reactor model. 4.1 Reactor Heat ransfer A descrpton of heat transfer requres the elucdaton of three heat transfer terms. hese are the radal conducton and the nner and outer convectve heat transfer terms. he radal conducton term s assumed constant over the axal dmenson (k x = 9.8 W m -1 K -1 ). However, gven the dramatc change n flud propertes (temperature and composton) and flow propertes (velocty and vscosty) both the convectve heat transfer term must be evaluated locally (h and h o ). Once these terms have been elucdated, these are reduced to the sngle local heat transfer constant (U o ) as defned over the outer exchange surface (A o ). For modellng the tube-sde F-steam at the pre-heat unt the model assumes that the convectve heat transfer behavour s well modelled by bolng heat transfer correlaton presented n [18]. hs necesstates the solvng for an unknown nner-wall temperature ( wall, ) teratvely along the axal dmenson. hs was mplemented n smulaton usng a drect root solvng method. For modellng the convectve heat transfer over the remanng four transfer surfaces, the model mplements a set of emprcal relatons for forced-convecton heat transfer [18]. hs set of relatons covers all physcal contngences (Reynolds number). he correlatons mplemented are the Eckert-Drake relaton and Churchll-Bernsten relatons. Where d s the characterstc length over whch transfer occurs, and havng determned the conductvty of the flud (see transport propertes sub-model), the convectve heat transfer can be determned from the defnton of Nusselt number. 1 < Re d < 3 Nu = hd k = Re0.5 Pr 1/ 3 [ 1+ ( 0.4 Pr) / 3 ] Nu = hd k = Re0.5 Pr 1/ 3 [ 1+ ( 0.4 Pr) / 3 ] Re 8 3 Re / 8 4 / < Re d < 7 4 < Re d < Gasfcaton Knetc Behavour For the desgn of a reactor, the rate laws and assocated knetc parameters are essental elements of modellng. Unfortunately there are only a few rate laws for bomass gasfcaton under supercrtcal condtons. As bomass covers all manner of carbonaceous feedstock, these are lmted n lterature to key model compounds. After an extensve lterature search these were found to nclude only cellulose and lgnn [19], xylose [0], glycerol [1] and glucose []. Of these however only the knetcs for glucose are mmedately useful. he frst-order rate law of Lee et al. [] for glucose gasfcaton embodes the complete reacton network, from glucose nput through ntermedates to product gases. Glucose as the monomer of cellulose and prmary consttuent of hem-cellulose s hghly plentful source bomass and thus an attractve bomass model. 8 MPa, 753 3K

5 he envsaged gasfcaton reacton represents two consecutve reactons, an ntal glucose reformng reacton that s nstantly followed by the water gas shft reacton (WGSR). he succeedng WGSR recognses that ths reacton s rapd and that the equlbrum poston nherently favours the formaton of H and CO. However, beng a reversble reacton, the gaseous product balance may later changng under altered reactor condtons, and accordngly ths and other gas-phase chemstry should be accounted for. In addton to the WGSR, the most other relevant gas product reacton s the methanaton reacton. Much lke the gasfcaton chemstry however, there are few rate relatonshps avalable for descrbng the knetcs of gaseous products under supercrtcal condtons. o our current knowledge there are no publshed methanaton reacton rate laws coverng supercrtcal condtons. WGSR rate laws under supercrtcal condtons are also lmted to frst-order CO relatonshps as revewed by Sato et al. [3]. None of these publshed rate laws were mmedately useful for modellng the reversble reacton. Under a set of assumptons outlned n our orgnal work [], the followng reversble rate law was used for modellng. he rate of the methanaton reacton s more relably assumed as zero as evdenced by the reactor experments of alyor et al. [4]. aylor reported on experments on methanol reformng n supercrtcal water at K under 7.6 MPa n a tubular Inconel-65 reactor. aylor reported that the producton of methane was suppressed, and the WGSR was accelerated. It was concluded that Inconel-65 knetcally nhbts the formaton of methane from achevng thermodynamc equlbrum. Dscountng the possblty that the glucose precursor undergoes hydrogasfcaton to produce methane drectly, ths elmnates the methane component from further analyss. he reacton equlbrum poston under sothermal and sobarc assumptons s requred to account for the reversblty of the WGSR (K wgs ). hs s calculated from the deal gas mxture Gbbs free energy and the non-deal contrbuton to the Gbbs free energy. hs s calculated usng NASA polynomals [5], and the resdual Gbbs free energy of reacton (see reacton thermodynamcs sub-model). 4.3 hermodynamc Property Model K = G ξ p, = exp Δ r g R he model mplements the Peng-Robnson Equaton-of-State (PR-EoS) flud model [6] to predct the thermodynamc propertes of the mxture propertes. he p-v- relatonshp s charactersed by the cubc equaton wth the equaton parameters a (temperature dependent attracton parameter) and b (temperature ndependent repulson parameter). he defnton of these parameters s gven n terms of the mxture components crtcal propertes ( c, P c, ω ) s left to reference [7]. he model apples Van der Waals oneflud theory classcal mxng rules, wth bnary nteracton parameters calculated accordng to the method of Praustntz and Cheuh [8]. he crtcal propertes were taken from Red et al. [9]. p = R ( v b) a v( v + b) + b( v b) By takng the partal thermodynamc dervatves of the PR-EoS, provdes the means to evaluate the remanng thermodynamc propertes of nterest (U, S, H, G, C V, C P ). he resdual quantty of any thermodynamc property descrbes dfference between that of the real flud mxture and the deal gas mxture, and s descrbed by the departure functons of the appled equaton of state. Melham et al. [30]

6 provdes a full dervaton of the requred analytcal thermodynamc dervatves of the PR-EoS, whch were mplemented n ths model. he deal thermodynamc quanttes of an deal gas mxture were establshed usng NASA polynomals assumng a lnear mxture model. he flud enthalpy at s referenced to a common enthalpy datum at the reference condton (98.15 K, 1 bar). h = x h 0,ref + x c 0 p, d + R Z 1 ref ( ) + da a d ln Z + ( 1+ )B b Z + ( 1 )B he molar entropy, nternal energy and Gbbs free energy (and the specfc equvalents; U, S, G) each have forms smlar of that gven above for molar enthalpy. he molar heat capactes c v and c p (and ther specfc equvalents) can be obtaned drectly by dfferentaton of u and h respectvely. Lastly, as the energy balance s gven n terms of specfc enthalpy (H) the model must at each spatal locaton determne the flud temperature for the gven composton and pressure. hs temperature s found by solvng the non-lnear equaton posed by the resdual equaton form of the above enthalpy equaton (n specfc form). A Brent solver method was mplemented. 4.4 Reacton hermodynamc Model he enthalpy changes resultng from chemcal reactons (the breakng and formaton of chemcal bonds) are calculated usng Hess s Law. In ths model, ths process shall be consdered as both sothermal and sobarc. he deal component of the heat of reacton (deal-gas to deal-gas enthalpy of reacton; Δ r h 0 ) s calculated usng NASA polynomals and a referenced enthalpy datum (98.15 K, 1 bar). o observe energy balance durng the chemcal reacton at condtons other than deal gas condtons, the reacton enthalpy must also nclude the enthalpy change resultng from the reacton of real compounds at hgh pressure. hs can nclude the enthalpy dfference resultng of any phase changes. hs enthalpy dfference s the resdual enthalpy of reacton. Applyng the same summaton under Hess s law, ths can be evaluated from the component resdual partal molar enthalpes. Partal molar enthalpes were calculated usng the Peng-Robnson equaton of reacton (PR-EoR) presented by Marroqun de la Rosa et al. [31]. he spontanety and drectonalty of a chemcal reacton can be ascertaned by evaluatng the Gbbs free energy of reacton. he deal Gbbs free energy s convenently evaluated from NASA polynomals referenced to the Gbbs free energy datum of each speces. he resdual contrbuton to the Gbbs free energy s determned from the respectve partal molar Gbbs free energy of each component. A key thermodynamc requrement s realzed n the Second Law of hermodynamcs, whch dctates that, under sothermal and sobarc condtons, only a reacton wth free energy change Δ r G < 0 s spontaneous. he model calculates the respectve values for Δ r G gasfy and Δ r G wgsr to zero out the gasfcaton reacton rate (f the reacton s entropcally prohbted) and to determne the equlbrum constant (drectonalty) of the WGSR. Δ r g = n =1 4.5 ransport Property Model 0 ν Δ f g ref + c 0 p, d ref ref 0 c p, ( ) d R ln P P g IG g o n,p,n k ransport propertes such as vscosty (µ) and conductvty (λ) exhbt strong composton, temperature and pressure dependency. Whlst an sobarc assumpton s made, the flud experences wde temperature varaton ( K), and radcal flud composton varance, such that the transport propertes shall vary sgnfcantly. A flexble transport property model was requred to calculate flud transport propertes.

7 he pure component vscostes and conductvtes are determned usng the method of Chung et al. [3]. he method of Chung s vald for the calculaton of hgh-pressure, hgh-densty gases. hs s acheved by a correspondng states method to correlate the change n transport propertes accordng to the change n PV propertes. he method also accounts for molecular propertes; ncludng molecular weght, dpole moment and assocaton factor to characterze molecular effects upon transport propertes. he method frst establshes the low-pressure gas transport property value (µ *, λ *). Further gven relatons map the component low-pressure transport property to the hgh-pressure regon (µ, λ ). Mxture vscosty and conductvty are determned usng the mxng rule methods of Wlke (for µ) and Wassljewa (for λ) as reported by Red et al. [9]. hese methods are applcable for dense gas mxtures and report good results for polar-polar mxtures. 5. Results he ordnary dfferental equatons for mass and energy balance for each reactor unt were solved smultaneously usng MALAB (009). Intal value problems (preheat and gasfer unts) were solved usng the ode15s routne. he two-pont boundary value problem posed by the heat recovery exchanger unt was solved usng BVP5c routne. he ssue presented by the unknown rght-sde boundary condton was resolved by applyng a tearng process across the gasfer outlet stream and the heated tube-sde heat recovery unt. A maxmum absolute devaton between these streams, n any component or stream enthalpy, of ε 1-5 % was allowed. he system rapdly converged upon the fnal soluton after several teratons. he SCWG reactor was smulated under kg s -1 mass flow rate wth a 60:1 H O:glucose molar excess. Departure functons of PR-EoS for enthalpy were adapted to model the requred pumpng work requred to compress the nlet mxture from ambent pressure to 8 MPa at room temperature (98 K). Subsequent performance analyss of SCWG reactor was based on three metrc categores. hese are bomass converson, the heatng effects, and SCWG energy effcency. he converson of bomass (X) s defned as the percentage of bomass nput havng undergone gasfcaton. Attanng near complete gasfcaton should clearly be a key process goal so as to mnmze the complexty of the downstream processng operatons for the reactor lqud effluent stream. he current SCWG reactor confguraton ndcates that 97% of the glucose shall gasfy. hs would suggest that the resdence tme, and by consequence the scale of the reactor tube unts, are close to deal under the smulated mass flow., able : Summary of Energy Flows Fgure 3: Heat recovery and gasfer unts temperature profle Energy Flow Power (MW) C 6 H 1 O 6 LHV 1.3 W comp 0.5 Q F 7.1 Q sol 13.5 CO Fuel LHV H Fuel LHV.3 he heatng metrcs utlsed are the pre-gasfcaton temperature and the heatng rate. he mean heatng rate over the heat recovery exchange unt was calculated from the temperature lft and resdence tme. he smulated desgn fals to lft the flud temperature to the suggested pre-gasfcaton temperature of 73 K suggested by Matsumura et al. [3] (modelled to reach 703 K). However, the recycle heat exchange surface s predcted to provde the requred rapd heatng rate n excess of 300 K mn -1 (smulated to proceed at 3 K mn -1 ). Whle ths goes some way to allevate the aforementoned pluggng ssues, optmsaton should be completed to enhance the heatng rate and boost the temperature lft acheved by the heatng transfer surface.

8 d dt mean = out recover n recover τ = Δ recover V V = Δ recover V m 1 L L ( ) ρdx he energy effcency (η) has been defned analogously to that of Calzavara et al. [33]. hs relates the thermomechancal energy nputs (compresson work, preheatng, solar heatng) and chemcal energy (heatng value of glucose) and relates ths to the recovered thermomechancal energy (expanson work and heat recovery) and chemcal energy (heatng value of CO and H ). he current study makes no consderaton of the potental thermomechancal energy recoveres from the reactor effluent. hese energy flows are presented n able, and gve an overall energy effcency of 53% (subsequent to further energy recovery). 0 F outlet CO LHV CO + F outlet H η = LHV H Χ F nlet Glu LHV Glu + Q sol + Q F + W comp W recvover Q recover he reactor energy effcency was compared to the 8 MPa SCWG model of Calzavara et al. (able 3). he current model presents an ntermedate energy effcency between the two deal zero-dmensonal models of Calzavara et al. n whch energy s not recovered (33 %) and n whch energy recovery s performed (76%). A key dfference s the lower requred external heat per unt bomass nput (50% less) as drven by the nternal heat recovery. he means to derve addtonal effcences can only be realsed by consderng subsequent heat and work recovery. he extent to whch the water effluent (whch retans the bulk of the waste heat) could be drected towards useful heatng purposes, such as a heat source to drve the water gas shft reacton n the post-processng of the generated syngas, s an avenue of potental further nvestgaton. able 3: Current model n comparson to the zero-dmensonal models of Calzavara et al. [33] Expermental [33] hermodynamc [33] hs Model Unts Bomass C 6 H.5 O 5.4 C 6 H.5 O 5.4 C 6 H 1 O 6 C x H y O z rate kg/s H O:C x H y O z 60:1 60:1 60:1 mol/mol X % Conv Energy Input MJ/kg C x H y O z η (no recovery) % η (recovery) % 6. Conclusons A solar powered F-SCWG ntegrated process presents a potentally attractve opton for the sustanable producton of hydrocarbon chemcals and solar boosted fuels. SCWG has been demonstrated as a vable means for the converson of a woody bomass resource to an ndustrally useful synthess gas n laboratory reactor scale experments. hs work descrbes modellng of a new solar reactor based upon reported laboratory scale expermental data and emprcal relatons. A one-dmensonal non-sothermal plug-flow reactor model was developed for the purpose of nvestgatng SCWG reactor behavor, and provdes an ntal bass for desgnng a SCWG reactor. Specfc model attrbutes ncluded accountng for gasfcaton knetcs, heat transfer, and a broad range of thermo-physcal propertes. he work also addresses many ssues dentfed n the lterature, ncludng hgh hoop stress, hghtemperatures, the effects of a corrosve water medum, achevng hgh heat transfer rates, mtgatng reactor pluggng/foulng, and ensurng near complete bomass gasfcaton. Further optmzaton of the SCWG reactor desgn and ntegraton wth a solar feld has yet to be completed. he energy effcency of the SCWG reactor, before addtonal energy recovery, was 53%. he majorty of the unrecovered waste heat, that emboded of the reactor effluent stream, s assocated wth the water fracton due to t s large excess n the bomass slurry. In a combned F-SCWG system t s qute possble that ths waste heat resource can be appled to a downstream process, whch would n turn drve enhanced process

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