Chapter 14 - Biomass Gasification Integrated Fischer-Tropsch Synthesis: Perspectives, Opportunities and Challenges

98/02189 Chemistry of tar formation and maturation in the thermochemical conversion of biomass

Highly efficient liquid fuel production can be expected by integrating the Fischer-Tropsch (FT) synthesis process at the latter stage of the solid oxide electrolysis cell (SOEC) process and integrating the heat transfer between the processes. However, it is difficult to achieve the high efficiency and durability conditions in SOEC process with the high-yield conditions in FT synthesis process. In this study, the SOEC operating conditions were investigated to improve the efficiency and durability of the integrated production process by thermodynamic equilibrium calculations of the gas composition at the SOEC outlet (FT synthesis inlet) and experiments using a single cell.Gas compositions of H2/CO=2.0 and high H2 and CO production are favorable for FT synthesis. To achieve these conditions at the SOEC outlet, the SOEC inlet gas must be close to (H2+H2O)/CO2=2.0, and reactant utilization must be high. However, these conditions are likely to cause carbon deposition in SOEC, which can lead to cell damage. An effective way to prevent carbon deposition is to increase the cell temperature because carbon deposition is an exothermic reaction. High temperature conditions have the advantage of lowering the cell voltage in co-electrolysis and preventing carbon deposition, but the life of the cell components may be shortened. Promoting methanation was also an effective way to prevent carbon deposition because of consuming CO, but it may cause lower yields of liquid fuel from FT synthesis. Under pressurized conditions, the volume reduction reaction which includes methanation and carbon deposition is accelerated Therefore, the risk of carbon deposition under pressurized conditions has become highly dependent on the SOEC operating conditions which determine whether methanation or carbon deposition is more promoted. These results clarify the risks associated with changing the operating conditions by co-electrolysis in SOEC and can be used to guide the optimum operating conditions.

OutlineSOEC (Solid Oxide Electrolysis Cell) in the co-electrolysis of H2O and CO2 can produce syngas and, when integrated with Fischer-Tropsch (FT) synthesis, liquid fuel can be obtained in a clean and efficient process. Pressurizing SOEC in co-electrolysis can potentially enhance SOEC performance and improve efficiency in an integrated process with FT synthesis. However, pressurizing SOEC may lead to issues such as carbon deposition in the fuel electrode, which can damage the electrode microstructure, and the undesired promotion of methanation reaction. In this study, SOEC operating conditions which prevent these problems were determined by thermodynamic equilibrium calculations under pressurized conditions. In addition, the performance of the SOEC single cells, including the gas manifold and end separator, which are the same as those in a stack, was evaluated under pressurized conditions to examine the performance factors of the SOEC.Thermodynamic equilibrium calculationIn this study, the water gas shift reaction and methanation reaction were only considered in the thermodynamic equilibrium calculations of the gas composition in SOEC. In fact, the outlet gas composition at the fuel electrode was analyzed experimentally, and it was confirmed that it was almost at equilibrium. Therefore, the outlet gas composition was assumed to be in thermodynamic equilibrium. In this calculation, it was considered that carbon deposition occurred when the calculated pressure equilibrium constants of Boudouard reaction (Kb) from the equilibrium gas composition were smaller than the calculated Kb from thermodynamic parameters.Water-gas shift reaction: CO2+H2=CO+H2O, Kw = [CO]×[H2O] / ([CO2]×[H2])Methanation reaction: CO+3H2=CH4+H2O, Km = [CH4]×[H2O] / ([CO]×[H2]3×P 2)Boudouard reaction: 2CO＝C+CO2, Kb = [CO2] / ([CO]2×P)K: pressure equilibrium constant, P: gas pressurePerformance evaluation methodTo examine the performance factors of SOEC, the performance evaluation method of SOEC has been already developed based on Eq. (1)-(4) in Central Research Institute of Electric Power Industry (CRIEPI)[1]. Eq. (2) can be applied in the region of the linear relationship in the current-voltage (IV) characteristics under a constant gas utilization rate, as shown in Fig. 1. In Eq. (3), the fuel electrode reaction resistance depends on the partial pressures of hydrogen and steam in the fuel electrode. These partial pressures were calculated by assuming the equilibrium between the water-gas shift reaction and methanation reaction. V = E +η ne+η ir+η f+η o (1)≈ E +η ne+ (R ir+ R f+ R o) × J (2) R f = f 0 × P H2 α × P H2O β (3) R o = o 0 × P O2 γ (4) V: cell voltage, E: OCV, η ne: Nernst loss, η ir: internal resistance loss, η f, η o: fuel, oxygen electrode overvoltage, R ir: internal resistance, R f, R o: reaction resistance at fuel, oxygen electrode, J: current density, f 0,o 0: resistance parameter, P i: gas partial pressure of “i”, α, β, and γ: degree of gas partial pressureThe values of α, β, and γ were determined by obtaining the gas partial pressure dependencies. These values change depending on the cell specifications but do not change with the cell degradation. To evaluate the SOEC performance, it is necessary to measure the cell voltages under approximately ten different conditions, including variations in the inlet gas composition at the fuel electrode, reactant gas utilization (U re) at the fuel electrode, and inlet gas composition at the oxygen electrode. The R ir was measured using electrochemical impedance spectroscopy (EIS). The R ir value is defined as the intersection of the real axis and the measurement result of the highest-frequency side in the Cole-Cole plot. Performance was evaluated by calculating the current density and gas partial pressure distribution in the cell based on the measured values.Results and discussionThe following criteria were used in this study to determine the SOEC operating conditions: Gas compositions in SOEC outlet were H2/CO≈2.0 (for FT synthesis)High yield of H2 and CO (for FT synthesis)Low methane formation (for FT synthesis)No carbon deposition in SOEC (for SOEC) From these criteria and the results of the thermodynamic equilibrium calculations, the SOEC operating conditions in this study were determined as follows: Fuel inlet gas composition: H2O/CO2/H2 = 56.7/33.3/10% ((H2+H2O)/CO2=2.0) U re at the fuel electrode: 70%Operating temperature: 750-800 ˚C The SOEC performance under various pressures based on the determined operating conditions was evaluated using the performance evaluation method. The results indicated that the open-circuit voltages under pressurized conditions increased but the fuel electrode overvoltage and oxygen electrode overvoltage decreased under the same conditions. It was revealed that SOEC performance was also improved under pressurized conditions, which is favorable for SOEC and FT synthesis.These results of this study suggest that the efficiency of the integrated SOEC and FT synthesis processes can potentially be enhanced under pressurized conditions.AcknowledgementThis work is based on results obtained from project, JPNP16002, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

In this work, the “HRSC Optimizer”, a recently developed optimization methodology for the design of Heat Recovery Steam Cycles (HRSCs), Steam Generators (HRSGs) and boilers, is applied to the design of steam cycles for three interesting coal fired, gasification based, plants with CO2 capture: a Fischer-Tropsch (FT) synthesis process with high recycle fraction of the unconverted FT gases (CTL-RC-CCS), a FT synthesis process with once-through reactor (CTL-OT-CCS), and an Integrated Gasification Combined Cycle (IGCC-CCS) based on the same technologies. The analysis reveals that designing efficient HRSCs for the IGCC and the once-through FT plant is relatively straightforward, while designing the HRSC for plant CTL-RC-CCS is very challenging because the recoverable thermal power is concentrated at low temperatures (i.e., below 260 °C) and only a small fraction can be used to superheat steam. As a consequence of the improved heat integration, the electric efficiency of the three plants is increased by about 2 percentage points with respect to the solutions previously published.

00/01720 Indirect coal liquefaction — where do we stand?

Conversion of synthesis gas into clean diesel fuel from natural gas (Gas-to-Liquids - GTL) via a Fischer-Tropsch synthesis (FTS) process can provide an economical way to create value from unconventional, remote and problem gas. However, conventional processes, fixed-bed and slurry phase, are not economically viable for the smaller plants required for processing stranded natural gas fields. On the other hand, a microchannel reactor for FTS offers the opportunity for a small, modular, less expensive and high efficiency facility. Over the past several years Velocys has been engaged in not only the development of microchannel reactor technology for FTS, but also supported cobalt catalysts that provide the necessary level of C5+ productivity for an economically viable process. The influence of support properties, synthesis methodology, cobalt loading and promoters on catalyst performance has been studied. For example, it has been determined that both the support surface chemistry and the Co particle size distribution have a strong effect on the rate of catalyst deactivation for Co loadings >40%. In this presentation the authors will show how the structural properties of a Co/SiO2 catalyst are influenced by both the surface chemistry of the support and the method of synthesis. Catalyst characterization data will be used to explain observed FTS performance in a microchannel reactor. Introduction For most of its nearly 100 year history, the considerations for deployment of the Fischer-Tropsch (FT) synthesis have focused on either conventional multi-tube fixed-bed or slurry bubble-column reactors. As catalyst development offered catalysts with increasing activity, the need to shed the high heat of the hydrogenation reactions was a much greater focus of process designers. Dramatic advances in metal fabrication techniques in recent decades have now allowed for a further reactor option for deploying FT technology, the microchannel fixed-bed reactor. In such microchannel devices, both process and coolant channels have dimensions which are factors of 10–100 smaller than their traditional technology counterparts. [1] These short transport distances make it possible to remove much higher heats of reaction per unit area of cooled wall, thereby making it possible to shrink the overall dimensions of the process reactors quite dramatically. Velocys was founded on the basis of innovative microchannel reactor designs for process technologies where heat transfer is a critical aspect of process and has been a leader in the deployment of such reactors for application to the FT synthesis. Successful and cost-effective deployment of a FT process requires more than just the microchannel reactor itself. At every step of the process design, attention must be paid to the particular characteristics of the microchannel reactor environment. These microchannel systems are ideal platforms for the development of highly modularized process designs, since capacity can be tailored by discreet units of output. Velocys has brought together companies which are leaders in their market areas in order to provide customers with smaller gas holdings plant designs which achieve favorable economic returns at production scales well below those required by conventional reactor technologies. An example is shown in Figure 1 using a range of potential costs for microchannel-based installations. While the microchannel and slurry reactor facility costs per unit of output converge at larger capacity, the microchannel-based facility achieves significant advantages at lower capacity. Even more importantly, the rate at which costs rise as capacity decreases is sufficiently modest that even much smaller plants can potentially meet the requirements for market-based economic returns. This opens a much wider range of gas sources to potential development than would be possible using only traditional slurry or tubular reactor designs.

Hydroxyapatite as a new support material for cobalt-based catalysts in Fischer-Tropsch synthesis

Numerical optimization of steam cycles and steam generators designs for coal to FT plants

The biomass-to-liquid (BtL) process is a promising technology to obtain clean, liquid, second-generation biofuels and chemicals. The BtL process, which comprises several steps, is based upon the gasification of biomass and the catalytic transformation of the syngas that is obtained via the Fischer-Tropsch synthesis (FTS) reaction, producing a hydrocarbon pool known as syncrude. The FTS process is a well-established technology, and there are currently very large FTS plants operating worldwide that produce liquid fuels and hydrocarbons from natural gas (NG) (gas-to-liquids, GtL process) and coal (coal-to-liquids, CtL process). Due to the limited availability of local biomass, the size of the BtL plants should be downscaled compared to that of a GtL or CtL plant. Since the feasibility of the XtL (X refers to any energy source that can be converted to liquid, including coal, NG, biomass, municipal solid waste, etc.) processes is strongly influenced by the economies of scale, the viability of small-scale BtL plants can be compromised. An interesting approach to overcome this issue is to increase the productivity of the FTS process by developing reactors and catalysts with higher productivities to generate the desired product fraction. Recently, by integrating membrane reactors with the FTS process the gas feeding and separation unit have been demonstrated in a single reactor. In this review, the most significant achievements in the field of catalytic membrane reactors for the FTS process will be discussed. Different types of membranes and configurations of membrane reactors, including H2O separation and H2-feed distribution, among others, will be analyzed.

Optimization of coal-to-liquid processes; A way forward towards carbon neutrality, high economic returns and effective resource utilization. Evidences from China

99/00547 Scale-up of a dedicated biomass feedstock system for production of ethanol and electricity

This work makes thermodynamic analysis and optimization for the coal-based Fischer-Tropsch (FT) process. The thermodynamic analysis results show that under standard conditions the maximum effective carbon conversion is 50% from raw coal (CH0.8O0.1) to hydrocarbon products, and at least 50% carbon is converted into CO2 emission in the coal-based FT process. Subsequently, a new coal-based FT synthesis process is proposed to get minimum water consumption, minimum wastewater emission and maximum energy efficiency. The process contains a pulverized coal gasification unit, water-gas-shift unit and iron-based FT synthesis unit with 50% CO2 selectivity. The H2/CO molar ratio of fresh syngas to the FT synthesis unit is 0.5. The carbon and water footprints analysis results indicate that the effective carbon conversion from raw coal to hydrocarbon products is about 46.0%, and it only consumes 0.102 molar water and generates 0.032 molar wastewater when converts 1 molar coal to hydrocarbon products in the process.

Further Investigation into the Formation of Alcohol during Fischer Tropsch Synthesis on Fe-based Catalysts

Fischer-Tropsch (FT) wax is an important material produced from FT synthesis reactions. In this study, an improved separation and identification method for FT wax by high temperature gas chromatography (HTGC) coupled with cold-on-column (without pretreatment) was developed. In our improved separation procedure, the carrier gas was changed to helium and a long chromatographic column was adapted for use at high temperature. The n-alkanes in FT wax were well separated from other unknown components and the heavy components with carbon numbers higher than C90 could be eluted. Unknown components of the FT wax fraction were confirmed as alkanes, alkenes and oxygenated compounds by using HTGC-mass spectrometry. These results improve our understanding of the FT synthesis process and increase our detailed knowledge of FT products.

In the Fischer–Tropsch (FT) synthesis, a mixture of CO and H2 is converted into hydrocarbons and water with diluted organics. This water fraction with oxygenated hydrocarbons can be processed through aqueous-phase reforming (APR) to produce H2. Therefore, the APR of FT water may decrease the environmental impact of organic waters and improve the efficiency of the FT process. This work aimed at developing a kinetic model for the APR of FT water. APR experiments were conducted with real FT water in a continuous packed-bed reactor at different operating conditions of temperature (210–240 °C), pressure (3.2–4.5 MPa) and weight hourly space velocity (WHSV) (40–200 h−1) over a nickel-copper catalyst supported on ceria-zirconia. The kinetic model considered C1-C4 alcohols as reactants, H2, CO, CO2 and CH4 as the gaseous products, and acetic acid as the only liquid product. The kinetic model included seven reactions, the reaction rates of which were expressed with power law equations. The kinetic parameters were estimated with variances and confidence intervals that explain the accuracy of the model to estimate the outlet liquid composition resulting from the APR of FT water. The kinetic model developed in this work may facilitate the development of APR to be integrated in a FT synthesis process.