Evaluation of energy integration aspects for IGCC-based hydrogen and electricity co-production with carbon capture and storage

Integrated Gasification Combined Cycle (IGCC) is a power generation technology in which the solid feedstock is partially oxidized with oxygen and steam to produce syngas. In a conventional IGCC design without carbon capture, the syngas is purified for dust and hydrogen sulphide removal and then sent to a Combined Cycle Gas Turbine (CCGT) for power generation. Carbon capture technologies are expected to play an important role in the coming decades for reducing the greenhouse gas emissions. In a modified IGCC design for carbon capture, the syngas is catalytically shifted to maximize the hydrogen level and to concentrate the carbon species in the form of carbon dioxide which can be later captured in a pre-combustion arrangement. After carbon dioxide capture, the hydrogen-rich syngas can be either purified in a Pressure Swing Adsorption (PSA) unit and exported to the external customers (e.g., chemical industry, PEM fuel cells) or used in a CCGT for power generation.     

Thermodynamic analysis of syngas production from biodiesel via chemical looping reforming

In this study, thermodynamic analysis of the syngas production using biodiesel derived from waste cooking oil is studied based on the chemical looping reforming (CLR) process. The NiO is used as the oxygen carrier to carry out the thermodynamic analysis. Syngas with various H₂/CO ratios can be obtained by chemical looping dry reforming (CL-DR) or steam reforming (CL-SR). It is found that the syngas obtained from CL-DR is suitable for long-chain carbon fuel synthesis while syngas obtained from CL-SR is suitable for methanol synthesis. The carbon-free syngas production can be obtained when reforming temperature is higher than 700 °C for all processes. To convert the carbon resulted from biodiesel coking and operate the CLR with a lower oxygen carrier flow rate, a carbon reactor is introduced between the air and fuel reactors for removing the carbon using H₂O or CO₂ as the oxidizing agent. Because of the endothermic nature of both Boudouard and water-gas reactions, the carbon conversion in the carbon reactor increases with increased reaction temperature. High purity H₂ or CO yield can be obtained when the carbon reactor is operated with high reaction temperature and oxidizing agent flow.     

Simulation of a fuel reforming system based on catalytic partial oxidation

Catalytic partial oxidation (CPO) has potential for producing hydrogen that can be fed to a fuel cell for portable power generation. In order to be used for this purpose, catalytic partial oxidation must be combined with other processes, such as water-gas shift and preferential oxidation, to produce hydrogen with minimal carbon monoxide. This paper evaluates the use of catalytic partial oxidation in an integrated system for conversion of a military logistic fuel, JP-8, to high-purity hydrogen. A fuel processing system using CPO as the first processing step is simulated to understand the trade-offs involved in using CPO. The effects of water flow rate, CPO reactor temperature, carbon to oxygen ratio in the CPO reactor, temperature of preferential oxidation, oxygen to carbon ratio in the preferential oxidation reactor, and temperature for the water-gas shift reaction are evaluated. The possibility of recycling water from the fuel cell for use in fuel processing is evaluated. Finally, heat integration options are explored. A process efficiency, defined as the ratio of the lower heating value of hydrogen to that of JP-8, of around 53% is possible with a carbon to oxygen ratio of 0.7. Higher efficiencies are possible (up to 71%) when higher C/O ratios are used, provided that olefin production can be minimized in the CPO reactor.     

Conversion of fossil and biomass fuels to electric power and transportation fuels by high efficiency integrated plasma fuel cell (IPFC) energy cycle

The IPFC is a high efficiency energy cycle, which converts fossil and biomass fuel to electricity and co-product hydrogen and liquid transportation fuels (gasoline and diesel). The cycle consists of two basic units, a hydrogen plasma black reactor (HPBR) which converts the carbonaceous fuel feedstock to elemental carbon and hydrogen and CO gas. The carbon is used as fuel in a direct carbon fuel cell (DCFC), which generates electricity, a small part of which is used to power the plasma reactor. The gases are cleaned and water gas shifted for either hydrogen or syngas formation. The hydrogen is separated for production or the syngas is catalytically converted in a Fischer–Tropsch (F–T) reactor to gasoline and/or diesel fuel. Based on the demonstrated efficiencies of each of the component reactors, the overall IPFC thermal efficiency for electricity and hydrogen or transportation fuel is estimated to vary from 70 to 90% depending on the feedstock and the co-product gas or liquid fuel produced. The CO₂ emissions are proportionately reduced and are in concentrated streams directly ready for sequestration. Preliminary cost estimates indicate that IPFC is highly competitive with respect to conventional integrated combined cycle plants (NGCC and IGCC) for production of electricity and hydrogen and transportation fuels.     

Conversion of jet fuel and butanol to syngas by filtration combustion

Replacing batteries with fuel cells is a promising approach for powering portable devices; however, hydrogen fuel generation and storage are challenges to the acceptance of this technology. A potential solution to this problem is on-site fuel reforming, in which a rich fuel/air mixture is converted to a hydrogen-rich syngas. In this paper, we present experimental results of the conversion of jet fuel (Jet-A) and butanol to syngas by non-catalytic filtration combustion in a porous media reactor operating over a wide range of equivalence ratios and inlet velocities. Since the focus of this study is the production of syngas, our primary results are the hydrogen yield, the carbon monoxide yield, and the energy conversion efficiency. In addition, the production of soot that occurred during testing is discussed for both fuels. Finally, an analysis of the potential for these fuels and others to be converted to syngas based on the present experiments and data available in the literature is presented. This study is intended to increase the understanding of filtration combustion for syngas production and to illuminate the potential of these fuels for conversion to syngas by non-catalytic methods.     

Mini CHP based on the electrochemical generator and impeded fluidized bed reactor for methane steam reforming

The paper presents a configuration of mini CHP with the methane reformer and planar solid oxide fuel cell (SOFC) stacks. This mini CHP may produce electricity and superheated steam as well as preheat air and methane for the reformer along with cathode air used in the SOFC stack as an oxidant. Moreover, the mathematical model for this power plant has been created. The thermochemical reactor with impeded fluidized bed for autothermal steam reforming of methane (reformer) considered as the basis for the synthesis gas (syngas) production to fuel SOFC stacks has been studied experimentally as well. A fraction of conversion products has been oxidized by the air fed to the upper region of the impeded fluidized bed in order to carry out the endothermic methane steam reforming in a 1:3 ratio as well as to preheat products of these reactions. Studies have shown that syngas containing 55% of hydrogen could be produced by this reactor. Basic dimensions of the reactor as well as flow rates of air, water and methane for the conversion of methane have been adjusted through mathematical modelling.The paper provides heat balances for the reformer, SOFC stack and waste heat boiler (WHB) intended for generating superheated water steam along with preheating air and methane for the reformer as well as the preheated cathode air. The balances have formed the basis for calculating the following values: the useful product fraction in the reformer; fraction of hydrogen oxidized at SOFC anode; gross electric efficiency; anode temperature; exothermic effect of syngas hydrogen oxidation by air oxygen; excess entropy along with the Gibbs free energy change at standard conditions; electromotive force (EMF) of the fuel cell; specific flow rate of the equivalent fuel for producing electric and heat energy. Calculations have shown that the temperature of hydrogen oxidation products at SOFC anode is 850 °C; gross electric efficiency is 61.0%; EMF of one fuel cell is 0.985 V; fraction of hydrogen oxidized at SOFC anode is 64.6%; specific flow rate of the equivalent fuel for producing electric energy is 0.16 kg of eq.f./(kW·h) while that for heat generation amounts to 44.7 kg of eq.f./(GJ). All specific parameters are in agreement with the results of other studies.     

Potential of molten lead oxide for liquid chemical looping gasification (LCLG): A thermochemical analysis

Molten lead oxide is revealed to have favourable thermodynamic performance for gasification in a new process employing chemical looping of a molten liquid metal oxide. In this process, the feedstock is partially oxidized with molten lead oxide in the fuel reactor, while the reduced molten lead is oxidized in the air reactor. As with other chemical looping processes, this avoids direct contact between air and fuel, which prevents the undesirable dilution of the gaseous product with nitrogen. The Gibbs minimization method was employed together with thermo-chemical equilibrium analysis to assess the feasibility of the gasification process using graphite as a surrogate for more realistic, but complex carbonaceous fuels, together with steam and/or carbon dioxide as the gasifying agent. It was found that both the reduction and oxidation reactions of molten lead oxide with carbonaceous fuel are spontaneous. Likewise, the ratio of H₂:CO can be as high as 2.5, while the carbon conversion can reach 94% based on the thermochemical analysis. An energetic performance analysis was also employed for the case of a supercritical steam turbine cycle to extract work from the hot gaseous co-products. On this basis, the first law efficiency of the power cycle was estimated to be up to 33.8%, while the syngas co-product stream for applications such as Fischer-Tropsch synthesis has a chemical exergy efficiency of 41%.     

Assessment of calcium-based chemical looping options for gasification power plants

This paper evaluates various calcium-based chemical looping concepts to be applied in Integrated Gasification Combined Cycle (IGCC) plants for decarbonised energy vectors poly-generation (with emphasis on power generation and hydrogen and power co-generation). Two calcium-based chemical looping configurations were analysed. The first concept is based on post-combustion capture using the flue gases resulted from the power block (combined cycle gas turbine). The second concept is based on pre-combustion capture, the calcium-based chemical looping systems being used simultaneous to capture carbon dioxide (by sorbent enhanced water gas shift) and to concentrate the syngas energy in the form of hydrogen-rich gas.     

Hydrogen production from fossil fuels with carbon capture and storage based on chemical looping systems

This paper analyzes innovative processes for producing hydrogen from fossil fuels conversion (natural gas, coal, lignite) based on chemical looping techniques, allowing intrinsic CO₂ capture. This paper evaluates in details the iron-based chemical looping system used for hydrogen production in conjunction with natural gas and syngas produced from coal and lignite gasification. The paper assesses the potential applications of natural gas and syngas chemical looping combustion systems to generate hydrogen. Investigated plant concepts with natural gas and syngas-based chemical looping method produce 500 MW hydrogen (based on lower heating value) covering ancillary power consumption with an almost total decarbonisation rate of the fossil fuels used.The paper presents in details the plant concepts and the methodology used to evaluate the performances using critical design factors like: gasifier feeding system (various fuel transport gases), heat and power integration analysis, potential ways to increase the overall energy efficiency (e.g. steam integration of chemical looping unit into the combined cycle), hydrogen and carbon dioxide quality specifications considering the use of hydrogen in transport (fuel cells) and carbon dioxide storage in geological formation or used for EOR.     

Evaluation of power generation schemes based on hydrogen-fuelled combined cycle with carbon capture and storage (CCS)

IGCC is a power generation technology in which the solid feedstock is partially oxidized to produce syngas. In a modified IGCC design for carbon capture, there are several technological options which are evaluated in this paper. The first two options involve pre-combustion arrangements in which syngas is processed, either by shift conversion or chemical looping, to maximise the hydrogen level and to concentrate the carbon species as CO₂. After CO₂ capture by gas-liquid absorption or chemical looping, the hydrogen-rich gas is used for power generation. The third capture option is based on post-combustion arrangement using chemical absorption.Investigated coal-based IGCC case studies produce 400-500 MW net power with more than 90% carbon capture rate. Principal focus of the paper is concentrated on evaluation of key performance indicators for investigated carbon capture options, the influence of various gasifiers on carbon capture process, optimisation of energy efficiency by heat and power integration, quality specification of captured CO₂. The capture option with minimal energy penalty is based on chemical looping, followed by pre-combustion and post-combustion.     

High temperature steam gasification of wastewater sludge

High temperature steam gasification is one of the most promising, viable, effective and efficient technology for clean conversion of wastes to energy with minimal or negligible environmental impact. Gasification can add value by transforming the waste to low or medium heating value fuel which can be used as a source of clean energy or co-fired with other fuels in current power systems. Wastewater sludge is a good source of sustainable fuel after fuel reforming with steam gasification. The use of steam is shown to provide value added characteristics to the sewage sludge with increased hydrogen content as well total energy. Results obtained on the syngas properties from sewage sludge are presented here at various steam to carbon ratios at a reactor temperature of 1173 K. Effect of steam to carbon ratio on syngas properties are evaluated with specific focus on the amounts of syngas yield, syngas composition, hydrogen yield, energy yield, and apparent thermal efficiency. The apparent thermal efficiency is similar to cold gas efficiency used in industry and was determined from the ratio of energy in syngas to energy in the solid sewage sludge feedstock. A laboratory scale semi-batch type gasifier was used to determine the evolutionary behavior of the syngas properties using calibrated experiments and diagnostic facilities. Results showed an optimum steam to carbon ratio of 5.62 for the range of conditions examined here for syngas yield, hydrogen yield, energy yield and energy ratio of syngas to sewage sludge fuel. The results show that steam gasification provided 25% increase in energy yield as compared to pyrolysis at the same temperature.     

Assessment of hydrogen and electricity co-production schemes based on gasification process with carbon capture and storage

Through gasification, a solid feedstock is partially oxidized with oxygen and steam to produce syngas which can be used for conversion into different valuable compounds (e.g. hydrogen) or to generate power in a combined cycle gas turbine (CCGT). Integrated gasification combined cycle (IGCC) is one of power generation technologies having the highest potential for carbon capture with low penalties in efficiency and cost.     

Fuel saving, carbon dioxide emission avoidance, and syngas production by tri-reforming of flue gases from coal- and gas-fired power stations, and by the carbothermic reduction of iron oxide

Flue gases from coal, gas, or oil-fired power stations, as well as from several heavy industries, such as the production of iron, lime and cement, are major anthropogenic sources of global CO₂ emissions. The newly proposed process for syngas production based on the tri-reforming of such flue gases with natural gas could be an important route for CO₂ emission avoidance. In addition, by combining the carbothermic reduction of iron oxide with the partial oxidation of the carbon source, an overall thermoneutral process can be designed for the co-production of iron and syngas rich in CO. Water-gas shift (WGS) of CO to H₂ enables the production of useful syngas. The reaction process heat, or the conditions for thermoneutrality, are derived by thermochemical equilibrium calculations. The thermodynamic constraints are determined for the production of syngas suitable for methanol, hydrogen, or ammonia synthesis. The environmental and economic consequences are assessed for large-scale commercial production of these chemical commodities. Preliminary evaluations with natural gas, coke, or coal as carbon source indicate that such combined processes should be economically competitive, as well as promising significant fuel saving and CO₂ emission avoidance. The production of ammonia in the above processes seems particularly attractive, as it consumes the nitrogen in the flue gases.     

Performance of hydrogen and power co-generation system based on chemical looping hydrogen generation of coal

An integrated hydrogen and power co-generation system based on slurry-feed coal gasification and chemical looping hydrogen generation (CLH) was proposed with Shenhua coal as fuel and Fe₂O₃/MgAl₂O₄ as an oxygen carrier. The sensitivity analyses of the main units of the system were carried out respectively to optimize the parameters. The syngas can be converted completely in the fuel reactor, and both of the fuel reactor and steam reactor can maintain heat balance. The purity of hydrogen produced after water condensation is 100%. The energy and exergy analyses of the proposed system were studied. Pinch technology was adopted to get a reasonable design of the heat transfer network, and it is found pinch point appears at the hot side temperature of 224.7 °C. At the given status of the proposed system, the hydrogen yield is 1040.11 kg·h⁻¹ and the CO₂ capture rate is 94.56%. At the same time, its energy and exergy efficiencies are 46.21% and 47.22%, respectively. According to exergy analysis, the degree of exergy destruction is ranked. The gasifier unit has the most serious exergy destruction, followed by chemical looping hydrogen generation unit and the heat recovery steam generator unit.     

Design of highly efficient coal-based integrated gasification fuel cell power plants

Integrated gasification fuel cell (IGFC) technology combining coal gasification and solid oxide fuel cell (SOFC) is believed to be the only viable solution to achieving U.S. Department of Energy (DOE)’s performance goal for next generation coal-based power plants, producing electricity at 60% efficiency (coal HHV-AC) while capturing more than 90% of the evolved CO₂. Achieving this goal is challenging even with high performance SOFCs; design concepts published to date have not demonstrated this performance goal. In this work an IGFC system concept consisting of catalytic hydro-gasification, proven low-temperature gas cleaning and hybrid fuel cell-gas turbine power block (with SOFC operating at about 10 bar) is introduced. The system is demonstrating an electricity efficiency greater than 60% (coal HHV basis), with more than 90% of the carbon present in the syngas separated as CO₂ amenable to sequestration. A unique characteristic of the system is recycling de-carbonized, humidified anode exhaust back to the catalytic hydro-gasifier for improved energy integration. Alternative designs where: (1) anode exhaust is recycled directly back to SOFC stacks, (2) SOFC stack operating pressure is reduced to near atmospheric and (3) methanation reactor in the reactor/expander topping cycle is removed, have also been investigated and the system design and performance differences are discussed.     

联合CO2捕集的生物质化学链气化制备合成气系统分析

本文提出以Fe₂O₃为载氧体、以CaO捕集CO₂的生物质化学链气化系统,利用Aspen Plus软件对该系统进行了模拟,以合成气组成（干基）、合成气氢碳比、含碳产物的碳摩尔分布、冷气效率及收率等为系统性能评价指标,重点分析了燃料反应器温度（T_FR）、载氧体Fe₂O₃与生物质碳摩尔比（Fe₂O₃/C）、水蒸气与生物质碳摩尔比（Steam/C）、CaO与生物质碳摩尔比（CaO/C）等系统参数对固体生物质化学链气化系统的影响。结果表明,在T_FR = 825℃、Fe₂O₃/C = 0.5、Steam/C = 0.71和CaO/C = 0.26条件下,合成气制备系统性能较优,合成气中H₂和CO₂含量分别为55.2%和15.4%,氢碳比为1.93,冷气效率为78.2%,被CaCO₃捕集的生物质碳为18.2%,收率（湿气基）为1.95 Nm³/kg_biomass,其中合成气中H₂和CO收率为1.24 Nm³/kg_biomass。     

Hydrogen-rich syngas production through coal and charcoal gasification using microwave steam and air plasma torch

In the present study, microwave plasma gasification of two kinds of coal and one kind of charcoal was performed with various O₂/fuel ratios of 0–0.544. Plasma-forming gases used under 5 kW microwave plasma power were steam and air. The changes in the syngas composition and gasification efficiency in relation to the location of the coal supply to the reactor were also compared. As the O₂/fuel ratio was increased, the H₂ and CH₄ contents in the syngas decreased, and CO and CO₂ increased. When steam plasma was used to gasify the fuel with the O₂/fuel ratio being zero, it was possible to produce syngas with a high content of hydrogen in excess of 60% with an H₂/CO ratio greater than 3. Depending on the O₂/fuel ratio, the composition of the syngas varied widely, and the H₂/CO ratio necessary for using the syngas to produce synthetic fuel could be adjusted by changing the O₂/fuel ratio alone. Carbon conversion increased as the O₂/fuel ratio was increased, and cold gas efficiency was maximized when the O₂/fuel ratio was 0.272. Charcoal with high carbon and fixed carbon content had a lower carbon conversion and cold gas efficiency than the coals used in this study.     

Detailed kinetic modelling of non-catalytic ethanol reforming for SOFC applications

Ethanol is a particularly attractive alternative fuel for automotive and stationary applications. Due to its high hydrogen content, ethanol can also be utilized for hydrogen production in SOFC systems. The present study assesses the potential of non-catalytic ethanol reforming using a detailed chemical kinetic approach. A recently developed comprehensive detailed mechanism for ethanol oxidation, pyrolysis and combustion is implemented and validated against data from ethanol reformers. Comparisons between computations and experimental major and intermediate species data are shown to be satisfactory. Chemical aspects of the fuel reforming process are thoroughly investigated through rate-of-production and sensitivity analyses with particular emphasis on syngas and potential carbonaceous deposit formation. An assessment of ethanol as a primary fuel versus conventional fuels with similar hydrogen content is also numerically performed. It is shown that ethanol features higher conversion efficiency to syngas than methane. Soot precursor chemistry is shown to be largely dependant both on fuel and reactor operating conditions. Finally, the work demonstrates the limitations of the thermodynamic equilibrium approach.     

Modeling electrochemical partial oxidation of methane for cogeneration of electricity and syngas in solid-oxide fuel cells

This paper uses computational models to evaluate strategies for scaling electrochemical partial oxidation (EPOX) processes from the laboratory scale to practical application. In addition to producing electrical energy alone, solid-oxide fuel cells (SOFC) can be operated with hydrocarbon fuel streams to produce synthesis gas (H₂ and CO) as well. SOFC systems are usually operated to consume most of the fuel and produce electricity. However, by operating with a hydrocarbon fuel at relatively high flow rates, the exhaust-gas composition can be predominantly syngas. In this case the steam (and CO₂), produced from electrochemical and thermal reactions, reacts to reform the hydrocarbon fuel within the catalytic anode support structure. A practical limitation of electrochemical partial oxidation operation is the fact that carbon tends to deposit on Ni-based anode catalysts. The present paper explores the use of barrier layers to prevent carbon deposits. The results show that a tubular cell can be designed to deliver syngas and electricity using methane as the primary fuel.     

New concept for soot removal from a syngas mixture

A new concept for soot removal from inside a syngas environment has been studied. Particulate emissions are retained in a soot trap downstream from a thermal partial oxidation (TPOX) reformer, while the syngas atmosphere itself is utilized as a gasification agent to achieve continuous and passive trap regeneration. This work analyses the performances of the loading and the regenerating phases of a wall flow soot trap in a syngas environment in an ad hoc developed test rig. A balance point between filtered and removed soot was actually reached at trap temperatures in the 800-1000 °C range with soot abatement efficiencies above 95 wt%. The particulate is obtained from a TPOX reactor operating in very rich fuel conditions, using methane as fuel. The final application of the reactor and trap assembly is a micro CHP system, based on an SOFC fed by a TPOX reformer. However, application to larger contexts (e.g. biomass gasification plants) can be envisaged.