Biomass-based hydrogen for oil refining: Integration and performances of two gasification concepts

In this work, two biomass-to-hydrogen concepts are designed and their integration with a large European refinery is investigated. One concept is based on indirect, atmospheric steam gasification while the second is based on pressurized direct oxygen-steam-blown gasification. The technologies chosen for gas cleaning, upgrading and hydrogen separation also differ in the two concepts. Heat integration and poly-generation opportunities are identified by means of process integration tools and four system configurations are identified. These are compared in terms of energy and exergy performances and potential for reduction of fossil CO₂ emissions at the refinery. It is found that the performance of the biomass-to-hydrogen concepts can be improved by up to 11% points in energy efficiency and 9% points in exergy efficiency. The design based on indirect gasification appears the most efficient according to both energy and exergy efficiencies. All configurations yield potential significant reductions of fossil CO₂ emissions at the refinery.     

Thermodynamic modeling of an integrated biomass gasification and solid oxide fuel cell system

An integrated process of biomass gasification and solid oxide fuel cells (SOFC) is investigated using energy and exergy analyses. The performance of the system is assessed by calculating several parameters such as electrical efficiency, combined heat and power efficiency, power to heat ratio, exergy destruction ratio, and exergy efficiency. A performance comparison of power systems for different gasification agents is given by thermodynamic analysis. Exergy analysis is applied to investigate exergy destruction in components in the power systems. When using oxygen-enriched air as gasification agent, the gasifier reactor causes the greatest exergy destruction. About 29% of the chemical energy of the biomass is converted into net electric power, while about 17% of it is used to for producing hot water for district heating purposes. The total exergy efficiency of combined heat and power is 29%. For the case in which steam as the gasification agent, the highest exergy destruction lies in the air preheater due to the great temperature difference between the hot and cold side. The net electrical efficiency is about 40%. The exergy combined heat and power efficiency is above 36%, which is higher than that when air or oxygen-enriched air as gasification agent.     

Performance analysis of a CCHP system based on SOFC/GT/CO2 cycle and ORC with LNG cold energy utilization

An innovative CCHP system based on SOFC/GT/CO₂ cycle and the organic Rankine cycle (ORC) with LNG cold energy utilization is proposed to achieve cascade energy utilization and carbon dioxide capture. The mathematical models are developed and the system performance is analyzed using the energy and exergy methods. The results illustrate that the comprehensive energy utilization, the net power generation and the overall exergy efficiencies of the system can reach about 79.48%, 79.81% and 62.29%, respectively, while the power generation efficiency of the SOFC is 50.96% and the CO₂ capture rate of the proposed CCHP system is 79.2 kg/h under the given conditions. It shows that the proposed CCHP system can reach a high energy utilization efficiency with near zero emissions. The influence of some key parameters, such as the fuel utilization factor, the air-fuel ratio, the oxygen concentration in the cathode feed and the compression ratio of the SCO₂ turbine on the performance of the entire system is studied.     

Conceptual design and analysis of a novel system based on ash agglomerating fluidized bed gasification for co-production of hydrogen and electricity

In this paper, a novel system with ash agglomerating fluidized bed gasification and CO₂ capture to produce hydrogen and electricity is firstly designed in Aspen Plus. The newly-proposed system is composed of eight subsystems, namely air separation unit, gasification unit, water gas shift unit, Rectisol unit, CO₂ compression unit, Claus unit, pressure swing adsorption unit, gas and steam turbine unit. The thermodynamic performance and hydrogen to coal ratio of the new proposed system are investigated. The results demonstrate that the hydrogen to coal ratio, energy efficiency, net electricity power and exergy efficiency of the overall system for Yangcheng anthracite are 0.096 kg/kg, 46.52%, 1.71 MW and 43.92%, respectively. Additionally, the exergy destruction ratio and exergy efficiency of each subsystem are researched. More importantly, the influences of the oxygen to coal ratio, steam to coal ratio and coal types on the hydrogen to coal ratio, energy efficiency and exergy efficiency are also studied.     

A review on biomass‐based hydrogen production and potential applications

In this paper, a detailed review is presented to discuss biomass‐based hydrogen production systems and their applications. Some optimum hydrogen production and operating conditions are studied through a comprehensive sensitivity analysis on the hydrogen yield from steam biomass gasification. In addition, a hybrid system, which combines a biomass‐based hydrogen production system and a solid oxide fuel cell unit is considered for performance assessment. A comparative thermodynamic study also is undertaken to investigate various operational aspects through energy and exergy efficiencies. The results of this study show that there are various key parameters affecting the hydrogen production process and system performance. They also indicate that it is possible to increase the hydrogen yield from 70 to 107 g H₂ per kg of sawdust wood. By studying the energy and exergy efficiencies, the performance assessment shows the potential to produce hydrogen from steam biomass gasification. The study further reveals a strong potential of this system as it utilizes steam biomass gasification for hydrogen production. To evaluate the system performance, the efficiencies are calculated at particular pressures, temperatures, current densities, and fuel utilization factors. It is found that there is a strong potential in the gasification temperature range 1023–1423 K to increase energy efficiency with a hydrogen yield from 45 to 55% and the exergy efficiency with hydrogen yield from 22 to 32%, respectively, whereas the exergy efficiency of electricity production decreases from 56 to 49.4%. Hydrogen production by steam sawdust gasification appears to be an ultimate option for hydrogen production based on the parametric studies and performance assessments that were carried out through energy and exergy efficiencies. Finally, the system integration is an attractive option for better performance. Copyright © 2012 John Wiley & Sons, Ltd.     

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.     

Global warming,environmental and sustainability aspects of a geothermal energy based biodigester integrated SOFC system

In this study, global warming, environmental and sustainability aspects of a geothermal energy based biodigester integrated SOFC system are parametrically analyzed. In this regard, a system is designed, consisting of three main subsystems such as Solid Oxide Fuel Cell, Anaerobic Digester, and a Heat Recovery Steam Generator. In order to investigate the global warming, environmental and sustainability aspects of the system, the energy and exergy analyses are performed, and the following indicators are taken into consideration, which are i) unit CO₂ emission, ii) environmental effect factor, iii) waste exergy ratio, iv) exergy destruction ratio, v) exergy recovery ratio, vi) exergetic sustainability index. Accordingly, the maximum exergetic sustainability index and exergy efficiency of the integrated system are calculated to be 0.486 and 0.367, respectively, in case the SOFC inlet temperature is equal to 633.3 °C while electric current density is 5500 A/m². On the other hand, the minimum exergy destruction ratio and the minimum environmental effect factor are obtained to be 0.74 and 2.33 while SOFC inlet temperature is 633.3 °C and SOFC current density is 8000 A/m². The minimum unit CO₂ emission of the whole system is determined to be 368.4 kg/MWh at 5500 A/m² of SOFC current density and 727 °C of SOFC inlet temperature while determined as 258.3 kg/MWh at 8000 A/m² of SOFC current density and 680 °C of SOFC inlet temperature. Thus, it can be said that such a system may be applied for reducing the CO₂ based global warming effects and improving the environmental sustainability.     

Study on a zero CO2 emission SOFC hybrid power system integrated with OTM using CO2 as sweep gas

A new zero CO₂ emission solid oxide fuel cell (SOFC) hybrid power system integrated with the oxygen ion transport membrane using CO₂ as sweep gas is proposed in this paper. The pure oxygen is picked up from the cathode outlet gas by the oxygen ion transport membrane with CO₂ as sweep gas; the oxy‐fuel combustion mode in the afterburner of SOFC is employed. Because the combustion product gas only consists of CO₂ and steam, CO₂ is easily captured with lower energy consumption by the condensation of steam. With the aspen plus soft, this paper builds the simulation model of the overall SOFC hybrids system with CO₂ capture. The exergy loss distributions of the overall system are analyzed, and the effects of the key operation parameters on the overall system performance are also investigated. The research results show that the new system still has a high efficiency after CO₂ recovery. The efficiency of the new system is around 65.03%, only 1.25 percentage points lower than that of the traditional SOFC hybrid power system(66.28%)without CO₂ capture. The research achievements from this paper will provide the valuable reference for further study on zero CO₂ emission SOFC hybrid power system with higher efficiency. Copyright © 2013 John Wiley & Sons, Ltd.     

Energy and exergy analyses of an integrated SOFC and coal gasification system

This paper examines an integrated gasification and solid oxide fuel cell (SOFC) system with a gas turbine and steam cycle that uses heat recovery of the gas turbine exhaust. Energy and exergy analyses are performed with two different types of coal. For the two different cases, the energy efficiency of the overall system is 38.1% and 36.7%, while the exergy efficiency is 27% and 23.2%, respectively. The effects of changing the reference temperature on the exergy destruction and exergy efficiency of different components are also reported. A parametric study on the effects of changing the pressure ratio on the component performance is presented.     

A novel hydrogen production system based on the three-step coal gasification technology thermally coupled with the chemical looping combustion process

Coal gasification technology is a significant process for the coal-based hydrogen production system and is considered as a key technology in the transition to “Hydrogen Economy”. To decrease the exergy destruction and enhance the cold gas efficiency of the coal gasification process, a novel three-step gasification technology thermally coupled with the chemical looping combustion process is proposed. And the hydrogen production system with CO₂ recovery is integrated based on the three-step gasification technology. Results indicated that the cold gas efficiency of the three-step coal gasification technology is 86.9%, which is 10.1% points enhanced compared with GE gasification technology. Besides, the novel system has an energy efficiency of 62.3%, which is 3.1% higher than that of the reference system. Exergy analysis presented that the employment of the three-step gasification technology contributed to the reduction of system exergy destruction by 4.2%. Furthermore, the energy utilization diagram (EUD) suggested that matching between endothermic reactions and exothermic reactions plays important role in the enhancement of cold gas efficiency.     

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.     

Thermodynamic performance comparison of SOFC-MGT-CCHP systems coupled with two different solar methane steam reforming processes

Multi-energy complementary distributed energy system integrated with renewable energy is at the forefront of energy sustainable development and is an important way to achieve energy conservation and emission reduction. A comparative analysis of solid oxide fuel cell (SOFC)-micro gas turbine (MGT)-combined cooling, heating and power (CCHP) systems coupled with two solar methane steam reforming processes is presented in terms of energy, exergy, environmental and economic performances in this paper. The first is to couple with the traditional solar methane steam reforming process. Then the produced hydrogen-rich syngas is directly sent into the SOFC anode to produce electricity. The second is to couple with the medium-temperature solar methane membrane separation and reforming process. The produced pure hydrogen enters the SOFC anode to generate electricity, and the remaining small amount of fuel gas enters the afterburner to increase the exhaust gas enthalpy. Both systems transfer the low-grade solar energy to high-grade hydrogen, and then orderly release energy in the systems. The research results show that the solar thermochemical efficiency, energy efficiency and exergy efficiency of the second system reach 52.20%, 77.97% and 57.29%, respectively, 19.05%, 7.51% and 3.63% higher than those of the first system, respectively. Exergy analysis results indicate that both the solar heat collection process and the SOFC electrochemical process have larger exergy destruction. The levelized cost of products of the first system is about 0.0735$/h that is lower than that of the second system. And these two new systems have less environmental impact, with specific CO₂ emissions of 236.98 g/kWh and 249.89 g/kWh, respectively.     

Proposal and thermodynamic performance study of a novel LNG-fueled SOFC-HAT-CCHP system with near-zero CO2 emissions

The cold energy in many liquefied natural gas (LNG) satellite stations is directly carried away by air or seawater. This causes cold energy waste and environmental cold pollution. To solve this problem, a combined power, heating and cooling system (CCHP) driven by LNG is established based on solid oxide fuel cell (SOFC) and humid air turbine (HAT), namely SOFC-HAT-CCHP system, in which, not only can the waste cold energy cool compressor inlet air to decrease power consumption, but supply cold energy for the cold storage and CO₂ recovery. Based on FORTRAN and Aspen Plus, the thermodynamic performance calculation models and the simulation work of the new system are carried out, such as the exergy and energy analysis, as well as the effects of the selected important variables. The results indicate that total exergy efficiency and total power efficiency are 64.7% and 54.4%, and the total thermal efficiency is 79.1%. Besides, the capture rate and purity of the CO₂ are 98.7% and 98.9% respectively. The novel system is environmental protective, energy-saving and efficient, which may provide a new direction to reasonably utilize the waste cold energy in LNG satellite stations.     

Performance analysis and optimization of a trigeneration process consisting of a proton-conducting solid oxide fuel cell and a LiBr absorption chiller

In this work, the trigeneration system, consisting of a proton-conducting solid oxide fuel cell (SOFC–H⁺) and a single-stage LiBr absorption chiller, was proposed. The SOFC–H⁺ and single-stage LiBr absorption chiller models were developed through Aspen Plus V10. From the sensitivity analysis, the results show that increases in temperature and fuel utilization can improve the performance of the SOFC–H⁺. Conversely, the air to fuel (A/F) molar ratio and pressure negatively affect the electrical efficiency and overall system efficiency. In the case of the absorption chiller, the coefficient of performance was increased and made stable according to a constant value when the generator temperature was increased from 90 to 100 °C. When the optimization was performed, it was found that the SOFC–H⁺ should be operated at 700 °C and 10 bar with fuel utilization of 0.8 and A/F molar ratio of 2 to achieve a maximum overall efficiency of 93.34%. For the energy and exergy analysis, a combined heat and power SOFC–H⁺ was found to have the highest energy and exergy efficiencies, followed by the trigeneration process. This indicates that the integration of the SOFC–H⁺ and LiBr absorption chiller is possible to efficiently produce electricity, heating and cooling.     

Performance assessment of hydrogen production from a solar-assisted biomass gasification system

In this study, we investigate a solar-assisted biomass gasification system for hydrogen production and assess its performance thermodynamically using actual literature data. We also analyze the entire system both energetically and exergetically and evaluate its performance through both energy and exergy efficiencies. Three feedstocks, namely beech charcoal, sewage sludge and fluff, are considered as samples in the same reactor. While energy efficiencies vary from 14.14% to 27.29%, exergy efficiencies change from 10.43% to 23.92%. We use a sustainability index (SI), as a function of exergy efficiency, to calculate the impacts on sustainable development and environment. This index changes from 1.12 to 1.31 due to intensive utilization of solar energy. Also, environmental impact of these systems is evaluated through calculating the specific greenhouse gas (GHG) emissions. They are determined to be 17.97, 17.51 and 26.74 g CO₂/MJ H₂ for beech charcoal, sewage sludge and fluff, respectively.     

A parametric study on thermodynamic performance of a SOFC oriented hybrid energy system

In this paper, a parametric study of the performance of a SOFC system for several types of supplied fuels is carried out. A SOFC system which is assisted by some energy resources, namely biomass, solar energy and natural gas, i.e. methane, is designed in order to realize this study.This system consists of four main components which are Solid Oxide Fuel Cell (SOFC), Proton Exchange Membrane Electrolyser (PEME), Photovoltaic system (PV), and Anaerobic Digester for biogas production (AD). The system is designed by considering three fundamental operation modes which are day-time (M1), night-time (M2), and winter-time (M3), in accordance with the duration of solar irradiation period. In order to evaluate the performance of the system, comprehensive energy and exergy analyses are performed, as major system parameters are changed for the operation modes considered. In this study, maximum total energy and exergy efficiency values of 0.60 and 0.49, respectively, are achieved when the overall energy and exergy performance of the system is evaluated, at 5500 A/m² current density for M3 operation mode among the three operation modes considered. Finally, the maximum net electrical energy and exergy efficiencies are achieved for 633 °C SOFC fuel inlet temperature and 8000 A/m² current density, in this study.     

Exergy analysis in the assessment of hydrogen production from UCG

The demand for H₂ increases rapidly with the gradual recognition of the potential of H₂ as an important secondary energy. At present, coal gasification is the main way to obtain hydrogen on a large scale and at a low cost in China. The underground coal gasification (UCG), as a kind of in-situ utilization technology that can exploit the unreachable deep coal resources, could become an alternative H₂ production pathway. This paper presents comparative study of energy utilization and resource consumption in H₂ production by UCG and typical surface coal gasification (SCG) technology, namely Lurgi fixed bed gasification, with 1.2 billion Nm³/a throughput of H₂ as example, to offer corresponding data support. The efficiency and the amount of resources consumed in constructing and operating each coal-to-hydrogen system under different conditions have been researched from exergetic point of view, which is not reported in existing literatures. In this paper, the exergy efficiency is calculated to be 40.48% and 40.98% for hydrogen production using UCG and SCG. The result indicates the competitiveness of UCG in the field of hydrogen production comparing with widely used coal gasification technology. The resource consumption is measured by cumulative exergy consumption (CExC), which is 8.17E+10 MJ and 6.57E+10 MJ for H₂ production from UCG and SCG. The result shows that although the H₂ production from UCG has higher CExC, it can significantly reduce the resource consumption of equipment comparing with H₂ production from SCG, indicating its advantage in total investment. It is found that the exergy efficiency increases with the rise in H₂O-to-O₂ and O₂-to-CO₂ ratio, while the value of CExC decreases with the appreciation of H₂O-to-O₂ ratio yet increases as the O₂-to-CO₂ ratio rises. In addition, the sensitivity analysis of production capacity reveals that the exergy efficiency gap and CExC gap between hydrogen production by UCG and SCG diminishes at smaller scale production capacities, showing that UCG is more suitable for small-scale hydrogen production.     

Exergy analysis of hydrogen-reduction based steel production with coal gasification-shaft furnace-electric furnace process

Carbon-free energy utilization in steel production is an effective way for China's iron and steel industry to achieve low carbon development. Thus, coal gasification-shaft furnace-electric furnace (CSE) technology, which use hydrogen-enriched gas for steel production, has recently become a sustainable topic of great concern. In the current study, the material flow analysis (MFA) and exergy assessment of the CSE process are conducted to investigate the material consumption and energy efficiency of this new steelmaking process. The exergy efficiency of the CSE process is calculated to be 50.11%, indicating a great potential for energy-saving. The results indicate that the coal gasification & gas purification that responsible for hydrogen-enriched gas production is the system with the largest exergy loss (account for 23.13% of the total exergy input), while the pelletizing system has the lowest efficiency (13.33%) due to heat loss. The key to further improve the thermal performance of this process lies in the heat recovery of the coal gasifier and pelletizing. It is also found that when the H₂ content in reducing gas rise from 57.00% to 100.00%, the exergy efficiency of the shaft furnace is only increased by 1.58%, while the demand volume of reducing gas significantly increases from 1326.30 Nm³/t to 2201.50 Nm³/t. The environmental benefits of hydrogen reduction based steelmaking must be considered together with energy utilization and production cost. The present work should do helpful effort for the application and further improvement of the CSE process in China.     

Exergoeconomic analysis of a hybrid system based on steam biomass gasification products for hydrogen production

In this paper, a conceptual hybrid biomass gasification system is developed to produce hydrogen and is exergoeconomically analyzed. The system is based on steam biomass gasification with the lumped solid oxide fuel cell (SOFC) and solid oxide electrolyser cell (SOEC) subsystem as the core components. The gasifier gasifies sawdust in a steam medium and operates at a temperature range of 1023-1423 K and near atmospheric pressure. The analysis is conducted for a specific steam biomass ratio of 0.8 kmol-steam/kmol-biomass. The gasification process is assumed to be self-thermally standing. The pressurized SOFC and SOEC are of planar types and operate at 1000 K and 1.2 bar. The system can produce multi-outputs, such as hydrogen (with a production capacity range of 21.8-25.2 kgh⁻¹), power and heat. The internal hydrogen consumption in the lumped SOFC-SOEC subsystem increases from 8.1 to 8.6 kg/h. The SOFC performs an efficiency of 50.3% and utilizes the hydrogen produced from the steam that decomposes in the SOEC. The exergoeconomic analysis is performed to investigate and describe the exergetic and economic interactions between the system components through calculations of the unit exergy cost of the process streams. It obtains a set of cost balance equations belonging to an exergy flow with material streams to and from the components which constitute the system. Solving the developed cost balance equations provides the cost values of the exergy streams. For the gasification temperature range and the electricity cost of 0.1046 $/kWh considered, the unit exergy cost of hydrogen ranges from 0.258 to 0.211 $/kWh.     

Thermodynamic modeling and exergy investigation of a hydrogen-based integrated system consisting of SOFC and CO2 capture option

The current study deals with the thermodynamic modeling of an innovative integrated plant based on solid oxide fuel cell (SOFC) with liquefied natural gas (LNG) cold energy supply. For the suggested innovative plant the energy, and exergy simulations are fully extended and the plant comprehensively analyzed. According to mathematical simulations of the proposed plant, a MATLAB code has been extended. The results indicate that under considered initial conditions, the efficiencies of SOFC and net power generation calculated 58% and 78%, respectively and the CO₂-capture rate is obtained 79 kg/h. This study clearly shows that the integrated system reached high efficiency while having zero emissions. In addition, the efficiencies and net amount of power generation, cooling or heating output and SOFC power generation are discussed in detail as a function of different variables such utilization factor, air/fuel ratio, or SOFC inlet temperature. For enhancing the power production efficiency of SOFC, the net electricity, and CCHP exergy efficiency the plant should run in higher utilization factor and lower air/fuel ration also it's important to approximately set SOFC temperature to its ideal temperature.