Exergetic analysis of solid oxide fuel cell and biomass gasification integration with heat pipes

This paper presents an exergetic analysis of a combined heat and power (CHP) system, integrating a near-atmospheric solid oxide fuel cell (SOFC) with an allothermal biomass fluidised bed steam gasification process. The gasification heat requirement is supplied to the fluidised bed from the SOFC stack through high-temperature sodium heat pipes. The CHP system was modelled in AspenPlus™ software including sub-models for the gasification, SOFC, gas cleaning and heat pipes. For an average current density of 3000 A m⁻² the proposed system would consume 90 kg h⁻¹ biomass producing 170 kW_e net power with a system exergetic efficiency of 36%, out of which 34% are electrical.     

Energy absorption characteristics and kinetics of carbonaceous solid waste gasification with copper slag as heat carrier

High energy consumption is the bottleneck for gasification technology of carbonaceous waste. Exactly, copper slag has such cheap and huge energy that can be used. Copper slag waste heat can provide energy and metallic oxide in copper slag has catalytic effect on carbonaceous solid waste gasification reaction. The gasification energy absorption characteristics and kinetics of typical solid waste, sludge, enteromorpha and lignite with air as oxidation agent has been studied using copper slag as heat carrier. Gasification reaction of waste is scored as multi-stage reactions. For sludge and enteromorpha gasification reactions, there are two and three reaction stages respectively. Gasification reaction rate becomes unstable when copper slag added. The addition of copper slag has little effect on the peak value and peak temperature. Pyrolysis reaction rate of heat absorption is controlled by material diffusion. At medium and high temperature, the limitation of gasification endothermic reaction of sludge and enteromorpha is chemical reaction rate. When copper slag added, the total energy absorption of lignite, sludge and enteromorpha are 11285.8 mw/mg, 8994.2 mw/mg and 9461.7 mw/mg respectively. Copper slag has catalytic decomposition effect on the gasification reaction at high and medium temperature, and improves the heat exchange rate.     

Application of a detailed dimensional solid oxide fuel cell model in integrated gasification fuel cell system design and analysis

Integrated gasification fuel cell (IGFC) systems that combine coal gasification and solid oxide fuel cells (SOFC) are promising for highly efficient and environmentally sensitive utilization of coal for power production. Most IGFC system analysis efforts performed to-date have employed non-dimensional SOFC models, which predict SOFC performance based upon global mass and energy balances that do not resolve important intrinsic constraints of SOFC operation, such as the limits of internal temperatures and species concentrations. In this work, a detailed dimensional planar SOFC model is applied in IGFC system analysis to investigate these constraints and their implications and effects on the system performance. The analysis results further confirm the need for employing a dimensional SOFC model in IGFC system design. To maintain the SOFC internal temperature within a safe operating range, the required cooling air flow rate is much larger than that predicted by the non-dimensional SOFC model, which results in a larger air compressor design and operating power that significantly reduces the system efficiency. Options to mitigate the challenges introduced by considering the intrinsic constraints of SOFC operation in the analyses and improve IGFC design and operation have also been investigated. Novel design concepts that include staged SOFC stacks and cascading air flow can achieve a system efficiency that is close to that of the baseline analyses, which did not consider the intrinsic SOFC limitations.     

Effect of gasification agent on the performance of solid oxide fuel cell and biomass gasification systems

In this paper, an integrated solid oxide fuel cell (SOFC) and biomass gasification system is modeled to study the effect of gasification agent (air, enriched oxygen and steam) on its performance. In the present modeling, a heat transfer model for SOFC and thermodynamic models for the rest of the components are used. In addition, exergy balances are written for the system components. The results show that using steam as the gasification agent yields the highest electrical efficiency (41.8%), power-to-heat ratio (4.649), and exergetic efficiency (39.1%), but the lowest fuel utilization efficiency (50.8%). In addition, the exergy destruction is found to be the highest at the gasifier for the air and enriched oxygen gasification cases and the heat exchanger that supplies heat to the air entering the SOFC for the steam gasification case.     

Steam catalytic gasification of municipal solid waste for producing tar-free fuel gas

In the paper, a two-region municipal solid waste (MSW) steam catalytic gasification process was proposed. The gasifier was composed of two individual reactors: one is the gasification reactors and the other is the catalytic reactor. The MSW was initially gasified and the produced tar was gasified in the gasification reactor, and further, the tar not gasified entered the catalytic reactor together with the fuel gas and was catalytically decomposed to fuel gas. The influences of the catalysts, steam and temperature on the content of tar, dry gas yield and composition, and carbon conversion efficiency were studied. The results indicated that under the optimum operating conditions, the dry gas yield can be up to 1.97 Nm³/kg MSW and the tar in the product can be completely eliminated. The concentration of hydrogen, carbon monoxide and methane in the fuel gas produced was 50.8%, 9.32% and 13.3%, respectively.     

The interaction of biomass gasification syngas components with tar in a solid oxide fuel cell and operational conditions to mitigate carbon deposition on nickel-gadolinium doped ceria anodes

The combination of biomass gasification with solid oxide fuel cells (SOFCs) is gaining increasing interest as an efficient and environmentally benign method of producing electricity and heat. However, tars in the gas stream arising from the gasification of biomass material can deposit carbon on the SOFC anode, having detrimental effects to the life cycle and operational characteristics of the fuel cell. This work examines the impact of biomass gasification syngas components combined with benzene as a model tar, on carbon formation on Ni/CGO (gadolinium-doped ceria) SOFC anodes. Thermodynamic calculations suggest that SOFCs operating at temperatures > 750 °C are not susceptible to carbon deposition from a typical biomass gasification syngas containing 15 g m⁻³ benzene.However, intermediate temperature SOFCs operating at temperatures < 650 °C require threshold current densities well above what is technologically achievable to inhibit the effects of carbon deposition. SOFC anodes have been shown to withstand tar levels of 2-15 g m⁻³ benzene at 765 °C for 3 h at a current density of 300 mA cm⁻², with negligible impact on the electrochemical performance of the anode. Furthermore, no carbon could be detected on the anode at this current density when benzene levels were <5 g m⁻³.     

Exergy analysis of updraft and downdraft fixed bed gasification of village-level solid waste

The most commonly used for gasification of village-level solid waste is the fixed-bed gasifier, but there is no reasonable method to evaluate the gasification process. This paper attempts to find a gasifier that is most suitable for gasification of village-level solid wastes through exergy analysis method. Based on experimental data from literature, the exergy efficiencies and LHV(Low Heat Value) of product gas from updraft and downdraft fixed bed gasifier are studied in this paper. The results show that the updraft fixed bed gasifier has higher exergy efficiency, and the gas produced by the downdraft fixed bed gasifier has a higher heating value. Air gasification has higher exergy efficiency than steam gasification and pure oxygen gasification. The highest exergy efficiency at a gasification temperature of about 1000 °C and ER (Equivalence Ratio) value in the range of 0.33–0.36. The volatile content of gasification raw materials is higher, and the gasification efficiency is higher. Through the research of this paper, a new path to reasonably evaluate the gasification process is obtained.     

生物质气化—燃料电池发电系统性能分析

建立了基于热力学平衡的生物质气化模型,利用平衡模型分析了气化过程的特性,研究了气化过程的反应规律及各种因素对气化性能指标的影响,详细分析了当量比及物料湿度对气体产物成分及气化产物热值的影响.同时,建立了以生物质气为燃料的固体氧化物燃料电池的数学模型,该模型考虑了燃料电池的能斯特电动势及各种极化损失.利用建立的模型分析了操作参数以及物料湿度和生物质种类对生物质气化—燃料电池发电系统性能的影响.结果表明,生物质气化—燃料电池发电系统的发电效率可达30％,热电联产效率最高可达95％以上.     

Hydrogen-rich syngas production from municipal solid waste gasification through the application of central composite design: An optimization study

This study aims to investigate the influence and interaction of experimental parameters on the production of optimum H₂ and other gases (CO, CO₂, and CH₄) from gasification of municipal solid waste (MSW). Response surface method in assistance with the central composite design was employed to design the fifteen experiments to find the effect of three independent variables (i.e., temperature, equivalence ratio and residence time) on the yields of gases, char and tar. The optimum H₂ production of 41.36 mol % (15.963 mol kg-MSW⁻¹) was achieved at the conditions of 757.65 °C, 0.241, and 22.26 min for temperature, ER, and residence time respectively. In terms of syngas properties, the lower heating value and molar ratio (H₂/CO) ranged between 9.33 and 12.48 MJ/Nm³ and 0.45–0.93. The predicted model of statistical analysis indicated a good fit with experimental data. The gasification of MSW utilizing air as a gasifying agent was found to be an effective approach to recover the qualitative and quantitate products (H₂ and total gas yield) from the MSW.     

Process analysis of a novel coal-to-methanol technology for gasification integrated solid oxide electrolysis cell (SOEC)

China's carbon peaking and carbon neutrality goals present a significant challenge for coal chemical technology, which is critical to securing the energy structure. Combining coal chemical industry technology with new energy is an effective approach to transform the development of the coal chemical industry. This paper proposes and studies a novel coal-to-methanol (CTM) technology of gasification integrated solid oxide electrolysis cell (SOEC). SOEC electrolytic hydrogen production technology is an advanced electrolytic water technology with the advantages of large scale and high efficiency, which is very suitable to be combined with industrial technology and can solve the painful problem of H₂ deficiency in the conventional coal to methanol process. In this study, from mechanistic analysis and model simulations, it is observed that by increasing the SOEC capacity, the novel CTM system can create more methanol at the same coal consumption and simultaneously reduce CO₂ emissions. The novel CTM system can produce up to 2.2 times more methanol and reduce CO₂ emissions by 94% by replacing the water-gas-shift (WGS) process with the SOEC unit. The novel CTM increases energy consumption. In addition, the novel CTM technology will effectively improve the economics of coal to methanol, taking into account the carbon tax. At the methanol price of 2900 RMB/t and SOEC capacity of 250 MW, the economic benefits of novel CTM were 2.1 times greater than CTM technology.     

Micro-cogeneration based on solid oxide fuel cells: Market opportunities in the agriculture/livestock sector

Bio-waste embeds an extraordinary renewable potential, and it becomes a source of energy savings when transformed into a valuable resource, like biogas. Cogeneration (CHP) from biogas employing high-temperature Solid Oxide Fuel Cells (SOFCs) scores a high sustainability level, thanks to improved environmental and energy performances. The synergy between the niche market of small/micro biogas producers and SOFCs might act as a springboard to open market opportunities for both SOFC commercialization and business upgrade of small farms. However, local regulations, waste management, renewable energy subsidies and, above all, availability of eligible sites, determine real chances for on-the-ground implementation.Through a detailed analysis of the application scenario, this research aims at investigating opportunities for the experimentation of SOFC–CHP in small biogas plants and identifying the possible bottlenecks for future deployment. When it becomes relevant, energy conversion of livestock (especially cattle and swine) and agriculture waste requires SOFC modules from 10 kW_e to 35 kW_e. This is in line with the current status of SOFC suppliers. Moreover, considering the fuel cell market roll-out, the average levelized cost of electricity is expected to decrease from 0.387 €/kWh to 0.115 €/kWh, when electricity is produced from livestock waste available on-site.     

Hydrogen-rich gas production by steam gasification of municipal solid waste (MSW) using NiO supported on modified dolomite

NiO on modified dolomite (NiO/MD) catalysts were developed for hydrogen-rich gas production from steam gasification of municipal solid waste (MSW). The catalysts were prepared through deposition-precipitation method and characterized by various characterization methods. The activity of NiO/MD on the steam gasification of MSW was investigated in a lab-scale fixed bed. The results indicated that the catalysts could significantly eliminate the tar in the gas production and increase the hydrogen yield. In addition, higher temperature contributed to higher hydrogen production and gas yield, meanwhile, the optimal ratio of steam to MSW (S/M) was found to be 1.23. In the experimental conditions, the NiO/MD catalysts showed a good performance over a long lifetime test.     

Modelling of electrical energy recovery from urban solid waste system: The case of Dhaka city

This paper presents a system dynamics computer model to predict population growth, solid waste production, electricity generation from solid waste and percentage of total electricity demand supplied from the solid waste of Dhaka, Bangladesh. Simulated solid waste generation in Dhaka agrees well with values reported by the Dhaka City Corporation. Simulated results show that population, solid waste generation and electricity generation potential from solid waste all increase with time, but percentage of total electricity demand supplied from solid waste decreases with time. However, MSW could still supply a significant portion of the electricity demand of Dhaka. Adoption of policy for electricity recovery from urban solid waste should be dictated by the economic adoption of the technology for electricity generation from the waste and the environmental implications. The model can be used for analysing electrical energy recovery from urban solid waste management.     

Effect of selected representative biomass gasification tar compounds on Ni-GDC solid oxide fuel cells

Contaminants as particulate matter, sulfur, chlorine and tar should be removed from biosyngas to avoid damaging solid oxide fuel cells. However, there is no sufficient information on tar effect since they might be potentially used as a fuel, or they might cause performance losses and irreversible damages. Therefore, this study aims to assess whether tar can be reformed inside the SOFC and used as fuel. Short-duration experiments were conducted on Ni-GDC cells operating with simulated biosyngas containing different concentrations of representative tar compounds from biomass gasification. While benzene and ethylbenzene could be regarded as additional fuels even at concentrations as high as 15 g/Nm³, naphthalene and phenanthrene act as contaminants for the SOFC electrochemical and catalytic reactions, even at concentrations of 0.3 and 0.05 g/Nm³. However, the effect on these reactions appeared almost completely reversible. Solid carbon deposited on the SOFC ceramic housing in proximity of the inlet. Post-mortem analysis should be performed to asses the tar effect on the cell anode.     

Modeling design and analysis of multi-layer solid oxide fuel cells

The thermo-mechanical analytical model proposed for different solid oxide fuel cell (SOFC) designs addresses the deformation behavior and mechanical stability of SOFCs at various thermal stresses, specifically the creep resistance and the long-term endurance beyond the elastic limit.The model considers the deformation of multi-layer SOFC in the temperature range of 600-800 °C and presents the combination of the correlated parameters for SOFC performance evaluation, stability and long-term endurance under realistic operating conditions and temperature gradients. The numerical analysis of the thermo-mechanical properties of the SOFC materials is presented in terms of mechanical behavior at failure conditions and the influence of rheological and structural properties on SOFC long-term endurance. The SOFC thermal behavior, creep parameters of the SOFC materials and long-term stability are analyzed in terms of stresses, deformations and displacements.In terms of broader impact, the algorithms for Maurice-Levi and Voltaire theorems and their validity for non-elastic, e.g. viscous-elastic, viscous-plastic, and elastic-plastic deformations were confirmed. This result allowed us to apply the stress condition of non-elastic body to the stress condition of the elastic body which is relevant to the SOFC operation at elevated temperatures.     

Supplying hydrogen vehicles and ferries in Western Norway with locally produced hydrogen from municipal solid waste

Gibbs free energy minimization has been used to estimate the hydrogen production potential of air gasification of the wet organic fractions of municipal solid waste available in the Bergen region in Western Norway. The aim of this work was to obtain an upper limit of the amount of hydrogen that could be produced and to estimate of the number of vehicles: passenger ferries and cars that could be supplied with an alternative fuel. The hydrogen production potential was investigated as function of waste composition, moisture content, heat loss, and carbon conversion factor. The amount of hydrogen annually available for both gasification and gasification combined with water-gas-shift-reaction was calculated for different scenarios. Up to 2700 tonne H₂ per year could be produced in the best case scenario; which would, if only utilised for maritime operations, be enough to supply nine ferries and ten fast passenger boat connections in the Hordaland region in Western Norway with hydrogen.     

Sensitivity analysis for solid oxide fuel cells using a three-dimensional numerical model

A three-dimensional numerical solver is developed to model complex transport processes inside all components of a solid oxide fuel cell (SOFC). An initial assessment of the accuracy of the model is made by comparing a numerically generated polarization curve with experimental results. Sensitivity derivatives of objective functions representing the cell voltage and the concentration polarization are obtained with respect to the material properties of the anode and the cathode using discrete adjoint method. Implementation of the discrete adjoint method is validated by comparing sensitivity derivatives obtained using the adjoint technique with results obtained using direct-differentiation and finite-difference methods.     

Thermodynamic analysis of an integrated gasification solid oxide fuel cell plant combined with an organic Rankine cycle

A 100 kW_e hybrid plant consisting of gasification system, solid oxide fuel cells and organic Rankine cycle is presented. The nominal power is selected based on cultivation area requirement. For the considered output a land of around 0.5 km² needs to be utilized. Woodchips are introduced into a fixed bed gasification plant to produce syngas which fuels the combined solid oxide fuel cells – organic Rankine cycle system to produce electricity. More than a hundred fluids are considered as possible alternative for the organic cycle using non-ideal equations of state (or state-of-the-art equations of state). A genetic algorithm is employed to select the optimal working fluid and the maximum pressure for the bottoming cycle. Thermodynamic and physical properties, environmental impacts and hazard specifications are also considered in the screening process. The results suggest that efficiencies in the region of 54–56% can be achieved. The highest thermal efficiency (56.4%) is achieved with propylcyclohexane at 15.9 bar. A comparison with the available and future technologies for biomass to electricity conversion is carried out. It is shown that the proposed system presents twice the thermal efficiency achieved by simple and double stage organic Rankine cycle plants and around the same efficiency of a combined gasification, solid oxide fuel cells and micro gas turbine plant.     

Integration of a municipal solid waste gasification plant with solid oxide fuel cell and gas turbine

An interesting source of producing energy with low pollutants emission and reduced environmental impact are the biomasses; particularly using Municipal Solid Waste (MSW) as fuel, can be a competitive solution not only to produce energy with negligible costs but also to decrease the storage in landfills. A Municipal Solid Waste Gasification Plant Integrated with Solid Oxide Fuel Cell (SOFC) and Gas Turbine (GT) has been studied and the plant is called IGSG (Integrated Gasification SOFC and GT). Gasification plant is fed by MSW to produce syngas by which the anode side of an SOFC is fed wherein it reacts with air and produces electricity. The exhausted gases out of the SOFC enter a burner for further fuel combusting and finally the off-gases are sent to a gas turbine to produce additional electricity. Different plant configurations have been studied and the best one found to be a regenerative gas turbine. Under optimized condition, the thermodynamic efficiency of 52% is achieved. Variations of the most critical parameters have been studied and analyzed to evaluate plant features and find out an optimized configuration.     

Towards a high fuel utilization and low degradation of micro-tubular solid oxide fuel cells

This work evaluates the relevance of the carrier gas in the performance of micro-tubular SOFCs and describes its role in improving the fuel cell efficiency of these systems. Initial dual operation mode analyses revealed a strong influence of the carrier gas flow on the fuel cell degradation rate, showing a higher degradation rate when low fuel utilization (FU) conditions were employed under low total flow conditions. These experiments evidenced that a suitable fuel-to-carrier gas ratio must be satisfied in order to avoid mass transport limitations. A decrease of this relation, accomplished in this case by an increase in the amount of gas carrier flow (high total flow conditions), allowed to reduce the degradation rate even at high fuel utilization conditions (80%), breaking the limitations traditionally observed for this technology. This approach improves system efficiency –in terms of fuel consumption– while decreases the degradation rate.