CET vol 99 DOI: 10.3303/CET2399116 Paper Received: 28 February 2023; Revised: 14 March 2023; Accepted: 6 May 2023 Please cite this article as: Detchusananard T., Wiranarongkorn K., Im-Orb K., 2023, Process Analysis of Integrated Biomass Gasification and Solid Oxide Electrolysis Cell (SOEC) for Syngas Production, Chemical Engineering Transactions, 99, 691-696 DOI:10.3303/CET2399116 A publication of The Italian Association of Chemical Engineering Online at www.cetjournal.it CHEMICAL ENGINEERING TRANSACTIONS VOL. 99, 2023 Process Analysis of Integrated Biomass Gasification and Solid Oxide Electrolysis Cell (SOEC) for Syngas Production Thanaphorn Detchusananarda, Kunlanan Wiranarongkornb, Karittha Im-orbc,* a Center of Excellence in Process and Energy Systems Engineering, Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand b Department of Basic Science and Physical Education, Faculty of Science at Sriracha, Kasetsart University Sriracha Campus, Chonburi 20230, Thailand c Program in Food Process Engineering, School of Food-Industry, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand karittha.im@kmitl.ac.th The integrated biomass gasification and SOEC process (IBG-SOEC), which O2 from SOEC was used as gasifying agent while the separated H2 could be used for H2/CO adjustment or sell as a valuable byproduct, was studied to find the sustainable syngas production process. The model of IBG-SOEC was developed in Aspen Plus. The parametric analysis was performed to investigate the effect of operating conditions of SOEC (i.e., cell temperature and number of cells) on the overall process performance. For energy performance, the total energy demand decreased as cell temperature increased while increased with number of cells. The changes in cell temperature had no effect on the yield and composition of syngas from gasifier. The maximum yield of syngas, with H2/CO of 0.96, of 1.9 kmol/h was achieved at cell temperature of 790 °C and number of cells of 600. At this condition, the overall efficiency of IBG-SOEC of 63 % was achieved and H2 byproduct of 1 kmol/h could obtained from SOEC. 1. Introduction Biomass gasification is a promising technology for converting biomass into syngas (mainly contain H2 and CO) which can be direct used as a fuel gas or as an intermediate for several chemical synthesis. In the process, biomass reacts with gasifying agent, which can be air, steam, O2, CO2 or the mixture of them, to produce syngas. The use of different gasifying agents provides syngas with different H2/CO ratios. Islam (2020) reported that using steam as gasifying agent offered the syngas with the highest H2/CO ratio followed by using H2O2, air, O2 and CO2, respectively. Commercially, although the use of air and O2 as gasifying agent were preferred due to the high energy demand of steam generation, it provides low H2/CO syngas. Therefore, the water gas shift (WGS) and the carbon capture and utilization system (CCUS) units were needed to increase H2 and decrease CO2, respectively. However, this practice offered lower carbon conversion efficiency of the total system (Sun and Tang, 2023). In addition, direct feeding H2 to the syngas can be another option. However, H2 was mainly produced from fossil fuel via steam reforming of natural gas or coal gasification which causes an increase in atmospheric CO2 level. The water electrolysis is an interesting technology for green H2 production as it uses renewable electric energy to separate water into H2 and O2. There are several types of water electrolyzer including alkaline electrolyte membrane (AEL), polymer electrolyte membrane (PEM) and solid oxide electrolysis cell (SOEC). As the SOEC operated at high temperature (600-800 °C) closed to gasifying temperature (Im-orb et al., 2018), the integration of biomass gasification and SOEC could provide the more energy efficient and sustainable syngas production process. In addition, this integrated system could consequently integrate with some chemical synthesis. For example, Giglio et al. (2021) studied the integration of biomass gasification, SOEC and methane synthesis. They found that the process without additional WGS and CCUS offered high overall process efficiency of 71.7 %. Clausen et al. (2019) reported that 70 % of energy efficiency was achieved when using the integration of steam electrolysis and biomass gasification for synthetic natural gas (SNG) production. Guest Editors: Sauro Pierucci, Flavio Manenti Copyright © 2023, AIDIC Servizi S.r.l. ISBN 978-88-95608-98-3; ISSN 2283-9216 691 Ali et al. (2020) studied an integration of oxygen blown biomass gasification, SOEC and methanol synthesis. In their result, the thermal efficiency of 72.08 % was obtained by using oxygen generated form SOEC as gasifying agent. Previously, most studies focused on the process analysis of the overall process of biochemicals (e.g., methane, methanol and DME) production in several aspects. Nevertheless, the intensive study on the syngas production part via the integrated biomass gasification and SOEC still lack of study. Therefore, the objective of this study is to perform the process analysis of the integrated biomass gasification and SOEC process (IBG- SOEC) for syngas production. The effect of cell temperature of SOEC and number of cells on the overall IBG- SOEC performance was investigated. The simplify process of IBG-SOEC was shown in Figure 1. GasificationSOEC O2 Renewable electricity H2O Syngas H2 Syngas Figure 1: Simplify diagram of the IBG-SOEC. 2. Model development In this study, the renewable electricity was supplied to SOEC to separate H2O into O2 and H2. Then O2 was fed to gasifier as gasifying agent and reacted with biomass to produce syngas. The H2 derived from SOEC was separated as valuable byproduct. The model of the IBG-SOEC, developed in Aspen Plus software version 10, consisted of two-main parts, i.e., biomass gasification and SOEC (Figure 2). The empty fruit branch (EFB) of oil palm was used as biomass feedstock and its proximate and ultimate analyses was shown in Table 1. Figure 2: Aspen plus model flowsheet of the IBG-SOEC. Table 1: Ultimate and proximate analyses of EFB (Uthaikiattikul et al., 2011) Ultimate Analysis (wt.% dry biomass) Proximate Analysis (wt.% dry biomass) Carbon 43.78 Fixed carbon 13.31 Hydrogen 6.2 Volatile matter 79.82 Oxygen 42.62 Ash 6.87 Nitrogen 0.44 Moisture 12.5 Sulfur 0.09 692 2.1 Biomass gasification As shown in Figure 2, the model of biomass gasification comprised of four major sections, i.e., pyrolysis, decomposition, combustion, and reduction. Biomass (S-101) was fed to the pyrolysis section (PYRO), modeled by RYIEL to produce the pyrolysis product containing of H2, CO, CO2, CH4 C2H4, C2H6, C6H6, C7H8, C6H6O, C10H8 and H2O (Eq(1)). The yields of pyrolysis product were calculated from the correlations of yield of pyrolyzed products and pyrolysis temperature, and the yield of biochar was derived from mass balance (Abdelouahed et al., 2012). Then non-conventional biochar was separated at a separator (SEP) before it was converted to conventional components, including C, O2, N2, H2, S and ash at decomposition section (DECOM), modelled by RYIELD, in which the yield distribution based on ultimate and proximate analyses was specified. The pyrolysis gases (S-103) and biochar (S-105) reacted with O2 from the SOEC at the combustion section (COMB), modelled by RPlug, in which the oxidation reactions occurred (Eq(2)-Eq(7)). Then, the product gases from this section were sent to the reduction section (REDUCT), modelled by RPlug, in which the reduction reactions occurred (Eq(8)-Eq(14)). The composition of syngas from the combustion and reduction sections was determined based on the kinetic data of related oxidation and reduction reactions (Puig-Gamero et al., 2021). The reactions considered in gasification section were summarized in Table 2. In this study, the developed gasification model was validated with the experimental data reported by Pio et al. (2017) and offered comparable results with the root mean square error of 1.09%. Table 2: The related reactions in gasification process Reactions Pyrolysis section Biomass pyrolysis 4 2 2 4 2 6 6 6 7 8 6 6 6 10 8 2 Biomass CH H CO C H C H C H C H C H O C H H O biochar → + + + + + + + + + + (1) Combustion section Partial oxidation of C 2 2( ) 2( 1) (2 )+ → − + −αC s O α CO α CO (2) Partial oxidation of CH4 4 2 21/ 2 2CH O CO H+ → + (3) Total oxidation of CO 2 21/ 2CO O CO+ → (4) Hydrogen oxidation 2 2 21/ 2H O H O+ → (5) Partial oxidation of benzene 6 6 2 29 / 2 6 3C H O CO H O+ → + (6) Partial oxidation of phenol 6 6 2 24 6 3C H O O CO H O+ → + (7) Reduction section Water gas shift 2 2 2CO H O CO H+ → + (8) Water gas 2 2C H O CO H+ → + (9) Boudouard 2 2C CO CO+ → (10) Steam reforming 4 2 23CH H O CO H+ → + (11) Decomposition of phenol 6 6 10 8 6 6 4 20.4 0.15 0.1 0.75C H O CO C H C H CH H→ + + + + (12) Decomposition of naphthalene 10 8 6 6 4 26.5 0.5 0.5 1.5C H C C H CH H→ + + + (13) Steam reforming of phenol 6 6 2 2 4 4 23 4 0.5 3C H O H O CO C H CH H+ → + + + (14) 2.2 Solid oxide electrolysis cell The SOEC consisted of an electrolyte, a cathode and an anode, which were normally constructed from yttria- stabilized zirconia cermet (YSZ), Ni-yttria-stabilized zirconia cermet (Ni-YSZ) and lanthanum strontium manganite-YSZ (LSM-YSZ), respectively. The model of SOEC was developed based on the same approach as reported in previous work (Im-orb et al., 2018). The RSTOIC reactor represented the cathode (CATHODE), in which the electrochemical reaction of the steam was occurred at specified reaction temperature to produce H2 and O2. Then, O2 was separated from H2 through an electrolyte (ELECT), which was modelled by SEPARATOR, and completely permeated into the anode channel (ANODE). The electrolysis reactions occurred in SOEC were shown in Table 3. The equations used to calculate the SOEC performance and the overall efficiency of the process were summarized in Table 4. As shown in Eq(17), the cell voltage of SOEC calculated by the summation of the equilibrium voltage and all overpotential, i.e., ohmic overpotential (Eq(20)), activation overpotential (Eq(21)-Eq(23)), and concentration overpotential (Eq(24)-Eq(26)). The total electricity requirement for the SOEC can be computed by multiplying of the current density (J), cell voltage (V), cell area (A), and number of cells (N) in the SOEC stack as shown in Eq(27). For the IBG-SOEC performance, the overall efficiency could be evaluated by the lower heating value (LHV) of the products (e.g. syngas and H2) divided by total energy input (Eq(30)). 693 Table 3: The electrolysis reactions in SOEC Reactions Cathode 2 2 22H O e H O− −+ → + (15) Anode 2 2 1 2 2 O O e− −→ + (16) Table 4: The equations for calculation of SOEC and overall IBG-SOEC performance Equations Cell voltage (V) ( )  = + + +ohmic act concV E (17) Equilibrium voltage (E) 2 2 2 1 2 1 2 0 2 / / ln    = +       H O H O x x PRT E E F x (18) Standard potential (E0) 0 41 253 2 4516 10. .E T−= −  (19) Ohmic overpotential ( ohmic ) 5 10300 2 99 10. expohm JL T  −   =      (20) Activation overpotential ( act ) , ,act act a act c  = + (21) 2 0 0 1 2 2 , , , ln , a or cact i i i RT J J i F J J      = + + =        (22) 0 , , exp , a or cact i i i E J i RT    = − =    (23) Concentration overpotential ( conc ) , ,conc conc a conc c  = + (24) ( ) ( ) 2 2 2 0 0 2 4 , / ln O a g conc a O P JRT d FBRT F P     +  =       (25) ( ) ( ) 2 2 2 2 2 2 2 2 2 , / ln / eff H c H O H O conc c eff H O c H O H P JRTd FD PRT F P JRTd FD P   +   =  −    (26) Power (W) W J V A N=    (27) Thermal energy for SOEC ( T,SOECQ ) T,SOEC r ovgQ Q Q W= − − (28) Heat of overpotential ( ovgQ ) ( )ovg ohmic act concQ J A N  = + +    (29) Overall efficiency ( en ) 2 2 100 SYGN SYGN H H en T,SOEC T,GAS EFB EFB N LHV N LHV W Q Q M LHV  + =  + + + (30) 3. Results and discussions 3.1 Effect of cell temperature of SOEC on overall IBG-SOEC performance In this section, the effect of cell temperature of SOEC on the IBG-SOEC performance was investigated by varying the cell temperature in a range of 700-850 °C at constant number of cells of 400. Figure 3a showed that the activation overpotential and ohmic overpotential decreased whereas the concentration overpotential increased as the cell temperature increased. This was due to an increase in the rate of electrochemical reaction and oxygen ion conductivity of electrolyte at elevated cell temperature. Moreover, the equilibrium voltage decreased when cell temperature increased resulting in lower cell voltage. This led to lower electrical demand as shown in Figure 3b. Although thermal energy demand increased, the total energy demand slightly decreased. The overall efficiency of IBG-SOEC was found to increase as cell temperature increased from 700 to 790 °C and reached the maximum value of 63 % before it started to decrease when the cell temperature higher than this range. At the cell temperature higher than 790 °C, the overall efficiency decreased due to the increase in 694 thermal energy demand. It was noted that the cell temperature had no effect on the yield and composition of syngas produced from gasifier. Figure 3: Effect of cell temperature on a) overpotential, equilibrium voltage and cell voltage, and b) energy demand and overall efficiency 3.2 Effect of number of cells of SOEC on overall IBG-SOEC process performance The effect of number of cells of SOEC on the IBG-SOEC performance was studied by varying the number of cells between 400-600 cells at constant temperature of 790 °C. Figure 4a indicated that increase in number of cells enhanced O2 produced from SOEC leading to more gasifying agent fed to the gasifier. As a result, the amount of CO, CO2 and H2 produced from gasifier increased whereas CH4 decreased due to the domination of oxidation reactions (Eq(2)-Eq(7)). Consequently, this increased the yield (H2+CO) and the H2/CO ratio of syngas as shown in Figure 4b. Moreover, H2 from the SOEC, which could be sold as high value product or used to adjust the H2/CO ratio of syngas to satisfy each chemical synthesis specification, was found to increase. The maximum yield of syngas of 1.9 kmol/h was achieved at number of cells of 600. At this condition, the H2/CO ratio of 0.96 was obtained. Regarding the energy performance of the proposed process, the electricity demand increased while thermal energy demand decreased when number of cells increased resulting in an increase in the total energy demand. However, the overall efficiency was found to increase with number of cells caused by the reduction in thermal energy requirement (Figure 4c). Figure 4: Effect of number of cells on a) syngas composition and H2 and O2 from SOEC, b) syngas yield and H2/CO ratio, and c) energy demand and overall efficiency 695 4. Conclusions The effect of operating conditions of SOEC i.e., cell temperature and number of cells, on the overall performance of the IBG-SOEC integrated process was investigated using process model developed in Aspen Plus. The overall energy demand was found to decrease when cell temperature increased whereas it increased with number of cells. The maximum efficiency of the IBG-SOEC of 63 % was achieved at cell temperature of 790 °C. Regarding the syngas production, the cell temperature had no effect on the yield (H2+CO) and the H2/CO ratio of syngas while the increase in number of cells could increase the yield and H2/CO ratio of syngas. When the SOEC was operated at the cell temperature of 790 °C and the number of cells was maintained at 600, the maximum yield of syngas of 1.9 kmol/h obtaining H2/CO ratio of 0.96 was achieved. Nomenclature A – cell area, m2 Bg – flow permeability, m2 2 eff H OD – effective diffusion coefficient of steam, m2/s ad – thickness of the anode, m cd – thickness of the cathode, m E – equilibrium voltage, V E0 – standard potential, V actE – activation energy, J/(mol·K) F – Faraday's constant, C/mol J – current density, A/m2 J0 – exchange current density, A/m2 L– thickness of the electrolyte, m N – number of cells, cells M – mass flow rate, kg/hr N – molar flow rate, kmol/hr P – operating pressure, atm Pi – partial pressure of component i, Pa rQ – heat required for the reaction, kW T,GASQ – thermal energy for gasification, kW T,SOECQ – thermal energy for SOEC, kW ovgQ – heat of overpotential, kW T – cell temperature, K V – cell voltage, V W – power, V x – mole fraction, - act – activation overpotential, V conc – concentration overpotential, V en – overall efficiency, % ohmic – ohmic overpotential, V Acknowledgments This work was supported by King Mongkut’s institute of Technology Ladkrabang (KREF046606). 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