Comparison by the use of numerical simulation of a MCFC-IR and a MCFC-ER when used with syngas obtained by atmospheric pressure biomass gasification

In order to realize biomass potential as a major source of energy in the power generation and transport sectors, there is a need for high efficient and clean energy conversion devices, especially in the low-medium range suiting the disperseness of this fuel. Large installations, based on boiler coupled to steam turbine (or IGCC), are too complex at smaller scale, where biomass gasifiers coupled to ICEs have low electrical efficiency (15-30%) and generally not negligible emissions.This paper analyses new plants configurations consisted of Fast Internal Circulated Fluidized-Bed Gasifier, hot-gas conditioning and cleaning, high temperature fuel cells (MCFC), micro gas turbines, water gas shift reactor and PSA to improve flexibility and electric efficiency at medium scale. The power plant feasibility was analyzed by means of a steady state simulation realized through the process simulator Chemcad in which a detailed 2D Fortran model has been integrated for the MCFC. A comparison of the new plant working with external (MCFC-ER) and internal (MCFC-IR) reforming MCFC was carried out. The small amount of methane in the syngas obtained by atmospheric pressure biomass gasification is not enough to exploit internal reforming cooling in the MCFC. This issue has been solved by the use of pre-reformer working as methanizer upstream the MCFC. The results of the simulations shown that, when MCFC-IR is used, the parameters of the cell are better managed. The result is a more efficient use of fuel even if some energy has to be consumed in the methanizer. In the MCFC-IR and MCFC-ER configurations, the calculated cell efficiency is, respectively, 0.53 and 0.42; the electric power produced is, respectively, 236 and 216 kW_e, and the maximum temperature reached in the cell layer is, respectively, 670 °C and 700 °C. The MCFC-ER configuration uses a cathode flowrate for MCFC cooling that are 30% lower than MCFC-IR configuration. This reduces pressure drop in the MCFC, possible crossover effect and auxiliaries power consumption. The electrical efficiency for the MCFC-IR configuration reaches 38%.     

Performance of sorption-enhanced chemical looping gasification system coupled with solid oxide fuel cell using exergy analysis

Coal gasification system integrated with solid oxide fuel cell (SOFC) provides a promising energy conversion way owing to its high efficiency. To get a deep insight into the energy performance of this system, a thermodynamic evaluation is implemented. Meanwhile, the technologies of chemical looping and CO₂ sorption are introduced into this integration system. It is found that the addition of oxygen carrier and sorbent into coal gasification system can promote the output power of the SOFC with a higher exergy destruction, where the exergy efficiency of most modules in the system can reach 80% except tar separation. The results also reveal that a suitable improvement of gasifying agent amount is beneficial to the energy performance of the system. When the H₂O/C molar ratio is increased to 3.0, the SOFC exergy efficiency of 97% can be achieved.     

Energy,exergy, and environmental (3E) assessments of an integrated molten carbonate fuel cell (MCFC), Stirling engine and organic Rankine cycle (ORC) cogeneration system fed by a biomass-fueled gasifier

In this paper, a novel syngas-fed combined cogeneration plant, integrating a biomass gasifier, a molten carbonate fuel cell (MCFC), a heat recovery steam generator (HRSG) unit, a Stirling engine, and an organic Rankine cycle (ORC), is introduced and thermodynamically analyzed to recognize its potentials compared to the previous solo/combined systems. For the proposed system, energetic, exergetic as well as environmental evaluations are performed. Based on the results, the gasifier and the fuel cell have a significant contribution to the exergy destruction of the system. Through a parametric study, the current density and the stack temperature difference are known as the main effective factors on the plant performance. Meanwhile, dividing the whole system into three sub-models, i.e., model (1): power production plant including the gasifier and MCFC without including Stirling engine, HRSG, and ORC unit, model (2): the cogeneration system without ORC unit, and model (3): the whole cogeneration system, an environmental impact assessment is carried out regarding CO₂ emission. Considering paper as biomass revealed that maximum value of exergy efficiency is 50.18% with CO₂ emissions of 28.9 × 10⁻² t.MWh⁻¹ which compared to the solo MCFC system indicates 28.40% increase and 13.3 × 10⁻² t.MWh⁻¹ decrease in exergy efficiency and CO₂ emission, respectively.     

Performance evaluation of a novel CCHP system integrated with MCFC,ISCC and LiBr refrigeration system

This paper proposes a novel combined cooling, heating, and power (CCHP) system integrated with molten carbonate fuel cell (MCFC), integrated solar gas-steam combined cycle (ISCC), and double-effect absorption lithium bromide refrigeration (DEALBR) system. According to the principle of energy cascade utilization, part of the high-temperature waste gas discharged by MCFC is led to the heat recovery steam generator (HRSG) for further waste heat utilization, and the other part of the high-temperature waste gas is led to the MCFC cathode to produce CO₃^2?, and solar energy is used to replace part of the heating load of a high-pressure economizer in HRSG. Aspen Plus software is used for modeling, and the effects of key factors on the system performances are analyzed and evaluated by using the exergy analysis method. The results show that the new CCHP system can produce 494.1 MW of electric power, 7557.09 kW of cooling load and 57,956.25 kW of heating load. Both the exergy efficiency and the energy efficiency of the new system are 61.69% and 61.64%, respectively. Comparing the research results of new system with similar systems, it is found that the new CCHP system has better ability to do work, lower CO₂ emission, and can meet the cooling load, heating load and electric power requirements of the user side at the same time.     

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 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.     

Economic analysis of hydrogen production from wastewater and wood for municipal bus system

The levelized cost of hydrogen for municipal fuel cell buses has been determined using the DOE H2A model for steam methane reforming (SMR), molten carbonate fuel cell reforming (MCFC), and wood gasification using wastewater biogas and willow wood chips as energy feedstocks. 300 kg H₂/day was chosen as the design capacity. Greenhouse gas emissions were calculated for each for the three processes and compared to diesel bus emissions in order to assess environmental impact. The levelized cost per kilogram for SMR, MCFC, and gasification is $5.12, $8.59, and $10.62, respectively. SMR provided the lowest sensitivity to feedstock price, and lowest levelized cost at various scales, with competitive cost to diesel on a cost/km basis. All three technologies provide a reduction in total greenhouse gases compared to diesel bus emissions, with MCFC providing the largest reduction. These results provide preliminary evidence that small scale distributed hydrogen production for public transportation can be relatively cost-effective and have minimal environmental impact.     

Metal sulfide-based process analysis for hydrogen generation from hydrogen sulfide conversion

Fossil fuel power plants often generate sulfur species such as hydrogen sulfide or sulfur dioxide due to the sulfur content of the raw feedstocks. To combat the associated environmental, processing, and corrosion issues, facilities commonly utilize a Claus process to convert hydrogen sulfide (H₂S) to elemental sulfur. Unfortunately, the potential for H₂ production from H₂S is lost in the Claus process. In this study, two chemical looping process configurations utilizing metal sulfides as chemical intermediates for sulfur recovery are investigated: (1) sulfur recovery (SR) system for sulfur production; (2) sulfur and hydrogen (H₂) recovery (SHR) system for sulfur and H₂ and production utilizing staged H₂ separation. Since, H₂ yield and sulfur recovery in a single thermal decomposition reactor is limited by low H₂S equilibrium conversion, a staged H₂ separation approach is used to increase H₂S conversion to H₂ using the SHR system. Steady-state simulations and optimization of process conditions are conducted in Aspen Plus (v10) simulation software for the chemical looping process configurations and the Claus process. An energy and exergy analysis are done for the Claus and chemical looping processes to demonstrate the relative contribution to exergy destruction from different unit operations as well as overall exergy and energy efficiency. The two chemical looping process configurations are compared against the conventional Claus process for similar sulfur recovery in a 629 MW_e integrated gasification combined cycle power plant. The SHR system is found to be the most efficient option due to a 97.11% exergy efficiency with 99.31% H₂ recovery. The overall energy and exergy efficiencies of this chemical looping system are 14.74% and 21.54% points higher than the Claus process, respectively, suggesting more efficient use of total input energy.     

Economic and environmental impact assessments of hybridized aircraft engines with hydrogen and other fuels

Hybridized engines have become the focus of research nowadays in order to update the existing engines in different transportation sectors. This paper presents a hybridized aircraft engine consisting of a molten carbonate fuel cell system and a commercial turbofan system. The MCFC units are connected to a steam reforming and a water gas shift system. Also, five clean fuels are selected, such as dimethyl ether, hydrogen, ethanol, methane, and methanol, which are combined with different mass ratios to form five different fuel blends. The hybridized aircraft is investigated using three approaches: exergy analysis, exergoeconomic analysis, and exergoenvironmental analysis. It is found that the proposed engine has an average exergetic efficiency of 88% and an average exergy destruction ratio of 12%. The specific exergetic cost of electricity of the engine has an average value of 710 $/GJ for the high-pressure turbine and 230$/GJ for the intermediate and low-pressure turbines, as well as 50 $/GJ for the MCFC. The average specific exergoenvironmental impact of electricity is 14 mPt/MJ for turbines and 4 mPt/MJ for the MCFC. In addition, a blend of ethanol and hydrogen appears to be a viable option economically and environmentally.     

First and second law thermodynamic analysis of air and oxy-steam biomass gasification

Gasification is an energy transformation process in which solid fuel undergoes thermochemical conversion to produce gaseous fuel, and the two most important criteria involved in such process to evaluate the performance, economics and sustainability of the technology are: the total available energy (exergy) and the energy conserved (energy efficiency). Current study focuses on the energy and exergy analysis of the oxy-steam gasification and comparing with air gasification to optimize the H₂ yield, efficiency and syngas energy density.     

Thermodynamic and economic optimization of a MCFC-based hybrid system for the combined production of electricity and hydrogen

In this paper, a biogas fuelled power generation system is considered. The system is based on a molten carbonate fuel cell (MCFC) stack integrated with a micro gas turbine for electricity generation, coupled with a pressure swing absorption system (PSA) for hydrogen production.     

Thermo-environmental analysis of a new molten carbonate fuel cell-based tri-generation plant using stirling engine,generator absorber exchanger and vapour absorption refrigeration: A comparative study

This study aims to present a novel tri-generation plant consisting of a molten carbonate fuel cell (MCFC) unit coupled with a Stirling engine (SE), a heat recovery steam generator (HRSG), and two types of absorption refrigeration cycles (ARCs), i.e., Generator Absorber eXchanger (GAX) and Vapour Absorption Refrigeration (VAR). The proposed system is evaluated from energy, exergy, as well as environmental impact (3E) points of view. To carry out the parametric study, three sub-models are also introduced for the whole system. The sub-model (1) investigates the solo MCFC with the new configuration. In the sub-model (2), the SE and HRSG are added to boost the power generation and overall system efficiency through employing the heat wasted in the sub-model (1). In the last sub-model, for cooling purposes, the surplus heat of MCFC is reutilized using an absorption refrigeration cycle. Besides, to make a comparative study between GAX and VAR systems, the sub-model (3) is classified into two different schemes: (a) with a VAR cycle, and (b) with a GAX cycle. The results reveal that the exergy efficiency and CO₂ emissions of the sub-models (1), (2), and (3) are 48.04%, 51.24%, 52.35% (VAR cycle), 52.12% (GAX cycle), 0.388 t/MWh, 0.364 t/MWh, 0.357 t/MWh (VAR cycle), and 0.358 t/MWh (GAX cycle), respectively. Either with GAX or VAR cycle, the proposed system indicates an acceptable standard of functionality in thermodynamic and environmental perspectives.     

Steady state simulation of energy production from biomass by molten carbonate fuel cells

This paper presents an integrated approach to the steady state simulation of biomass gasification, fuel cells and power generation processes. Attention is devoted to molten carbonate fuel cells (MCFC) due to the relative low cost, simpler construction and flexibility in the use of fuel. A steady state model simulating a global MCFC power plant based on real plants data is described and the simulations are selected according to real operating conditions. The software developed allows to study ‘ìn silico’ the effect of variations of the process conditions as well as modification of the input fuel, thus providing a useful tool for supporting technical decisions and feasibility study on the use of fuel cells in developing countries. The paper reports results of computer simulation focusing on macroscopic quantities of interest such as stack efficiency, global process electrical efficiency, cogenerative efficiency. The computer simulation is applied to a feasibility study of a MCFC coupled with a biomass gasification module focusing on the energy consumption of the process and reporting comparison of the energy efficiency for three kinds of biomass.     

Exergoeconomic analysis of hydrogen production from biomass gasification

In this study, we investigate biomass-based hydrogen production through exergy and exergoeconomic analyses and evaluate all components and associated streams using an exergy, cost, energy and mass (EXCEM) method. Then, we define the hydrogen unit cost and examine how key system parameters affect the unit hydrogen cost. Also, we present a case study of the gasification process with a circulating fluidized bed gasifier (CFBG) for hydrogen production using the actual data taken from the literature. We first calculate energy and exergy values of all streams associated with the system, exergy efficiencies of all equipment, and determine the costs of equipment along with their thermodynamic loss rates and ratio of thermodynamic loss rate to capital cost. Furthermore, we evaluate the main system components, consisting of gasifier and PSA, from the exergoeconomic point of view. Moreover, we investigate the effects of various parameters on unit hydrogen cost, such as unit biomass and unit power costs and hydrogen content of the syngas before PSA equipment and PSA hydrogen recovery. The results show that the CFBG system, which has energy and exergy efficiencies of 55.11% and 35.74%, respectively, generates unit hydrogen costs between 5.37 $/kg and 1.59 $/kg, according to the internal and external parameters considered.     

Gasification characteristics of organic waste by molten salt

Recently, along with the growth in economic development, there has been a dramatic accompanying increase in the amount of sludge and organic waste. The disposal of such is a significant problem. Moreover, there is also an increased in the consumption of electricity along with economic growth. Although new energy development, such as fuel cells, has been promoted to solve the problem of power consumption, there has been little corresponding promotion relating to the disposal of sludge and organic waste. Generally, methane fermentation comprises the primary organic waste fuel used in gasification systems. However, the methane fermentation method takes a long time to obtain the fuel gas, and the quality of the obtained gas is unstable. On the other hand, gasification by molten salt is undesirable because the molten salt in the gasification gas corrodes the piping and turbine blades. Therefore, a gasification system is proposed by which the sludge and organic waste are gasified by molten salt. Moreover, molten carbonate fuel cells (MCFC) are needed to refill the MCFC electrolyte volatilized in the operation. Since the gasification gas is used as an MCFC fuel, MCFC electrolyte can be provided with the fuel gas. This paper elucidates the fundamental characteristics of sludge and organic waste gasification. A crucible filled with the molten salt comprising 62 Li₂CO₃/38 K₂CO₃, is installed in the reaction vessel, and can be set to an arbitrary temperature in a gas atmosphere. In this instance, the gasifying agent gas is CO₂. Sludge or the rice is supplied as organic waste into the molten salt, and is gasified. The chemical composition of the gasification gas is analyzed by a CO/CO₂ meter, a HC meter, and a SO_x meter gas chromatography. As a result, although sludge can generate CO and H₂ near the chemical equilibrium value, all of the sulfur in the sludge is not fixed in the molten salt, because the sludge floats on the surface of the carbonate by the specific gravity of sludge lighter than the carbonate, and is not completely converted into CO and H₂. Moreover, the rice also shows good characteristics as a gasifying agent. Consequently, there is high expectation to using the organic waste as a molten salt gasifying agent. However, this requires lengthening the contact time between the organic waste and the molten salt.     

Exergy, exergoeconomic and environmental analyses and evolutionary algorithm based multi-objective optimization of combined cycle power plants

A comprehensive exergy, exergoeconomic and environmental impact analysis and optimization is reported of several combined cycle power plants (CCPPs). In the first part, thermodynamic analyses based on energy and exergy of the CCPPs are performed, and the effect of supplementary firing on the natural gas-fired CCPP is investigated. The latter step includes the effect of supplementary firing on the performance of bottoming cycle and CO₂ emissions, and utilizes the first and second laws of thermodynamics. In the second part, a multi-objective optimization is performed to determine the “best” design parameters, accounting for exergetic, economic and environmental factors. The optimization considers three objective functions: CCPP exergy efficiency, total cost rate of the system products and CO₂ emissions of the overall plant. The environmental impact in terms of CO₂ emissions is integrated with the exergoeconomic objective function as a new objective function. The results of both exergy and exergoeconomic analyses show that the largest exergy destructions occur in the CCPP combustion chamber, and that increasing the gas turbine inlet temperature decreases the CCPP cost of exergy destruction. The optimization results demonstrates that CO₂ emissions are reduced by selecting the best components and using a low fuel injection rate into the combustion chamber.     

Energy and exergy analyses of a hybrid system containing solid oxide and molten carbonate fuel cells,a gas turbine,and a compressed air energy storage unit

Design of a hybrid system composed of a solid oxide fuel cell (SOFC), molten carbonate fuel cell (MCFC), gas turbine (GT), and an advanced adiabatic compressed air energy storage (AA-CAES) based on only energy analysis could not completely identify optimal operating conditions. In this study, the energy and exergy analyses of the hybrid fuel cell system are performed to determine suitable working conditions for stable system operation with load flexibility. Pressure ratios of the compressors and energy charging ratios are varied to investigate their effects on the performance of the hybrid system. The hybrid fuel cell system is found to produce electricity up to 60% of the variation in demand. A GT pressure ratio of 2 provides agreeable conditions for efficient operation of the hybrid system. An AA-CAES pressure ratio of 15 and charging ratio of 0.9 assist in lengthening the discharging time during a high load demand based on an electricity variation of 50%.     

A novel MCFC hybrid power generation process using solar parabolic dish thermal energy

In this paper, a novel molten carbonate fuel cell hybrid power generation process with using solar parabolic dish thermal energy is proposed. The process contains MCFC, Oxy-fuel and Rankine power generation cycles. The Rankine power generation cycles utilized various types of working fluid to emphasize taking advantage of the cycles in different thermodynamic conditions. The required hot and cold energies are provided from solar dish parabolic thermal hot and liquefied natural gas (LNG) cold energies, respectively. The carbon dioxide (CO₂) from MCFC effluent stream is captured from the process at liquid state. The process total heat integrated and in this regards, no need to any hot and cold external sources with the net electrical power generation. The energy and exergy analysis are conducted to determine the approaches to improve the process performance. This integrated structure consumed 2.30 × 10⁶ kg h⁻¹ of air and 2.67 × 10⁶ kg h⁻¹ of LNG to generate 292597 kW of net power. The products of this integrated structure are 6.25 × 10⁴ kg h⁻¹ of condensates, 183 kg h⁻¹ of water vapor, 2.20 × 10⁶ kg h⁻¹ of MCFC effluent stream, 2.60 × 10⁶ kg h⁻¹ of natural gas and 1.10 × 10⁵ kg h⁻¹ of CO₂ in liquid state. The presented new integrated structure has overall thermal efficiency of 73.14% and total exergy efficiency of 63.19%. Also, sensitivity analysis is performed for determination of the process key parameters which affected the process operating performance.     

Thermodynamic analysis and assessment of novel ORC- DEC integrated PEMFC system for liquid hydrogen fueled ship application

Proton-exchange membrane fuel cell (PEMFC) and liquid hydrogen are gaining attention as a power generation system and alternative fuel of ship. This study proposes a novel PEMFC system, integrated with the organic Rankine cycle–direct expansion cycle (ORC-DEC), which exploits cold exergy from liquid hydrogen and low temperature waste heat generated by the PEMFC for application in a liquid hydrogen fueled ship. A thermodynamic model of each subsystem was established and analyzed from the economic, energy, and exergy viewpoints. Moreover, parametric analysis was performed to identify the effects of certain key parameters, such as the working fluid in the ORC, pressure exerted by the fuel pump, cooling water temperature of the PEMFC, and the stack current density on the system performance. The results showed that the proposed system could generate 221 kW of additional power. The overall system achieved an exergy and energy efficiency of 43.52 and 40.45%, respectively. The PEMFC system had the largest exergy destruction, followed by the cryogenic heat exchanger. Propane showed the best performance among the several investigated ORC working fluids and the system performance improved with the increase in the cooling water temperature of the PEMFC. The economic analysis showed that the average payback time of ORC-DEC was 11.2 years and the average net present value (NPV) was $295,268 at liquid hydrogen costing $3 to $7, showing the potential viability of the system.     

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.