Energy and exergy analysis of syngas production from different biomasses through air-steam gasification

Gasification is a thermo-chemical reaction which converts biomass into fuel gases in a reactor. The efficiency of conversion depends on the effective working of the gasifier. The first step in the conversion process is the selection of a suitable feedstock capable of generating more gaseous fuels. This paper analyses the performance of different biomasses during gasification through energy and exergy analysis. A quasi-equilibrium model is developed to simulate and compare the feasibility of different biomass materials as gasifier feedstock. Parametric studies are conducted to analyze the effect of temperature, steam to biomass ratio and equivalence ratio on energy and exergy efficiencies. Of the biomasses considered, sawdust has the highest energy and exergy efficiencies and lowest irreversibility. At a gasification temperature of 1000 K, the steam to biomass ratio of unity and the equivalence ratio of 0.25, the energy efficiency, exergy efficiency and irreversibility of sawdust are 35.62%, 36.98% and 10.62 MJ/kg, respectively. It is also inferred that the biomass with lower ash content and higher carbon content contributes to maximum energy and exergy efficiencies.     

Steam and air fed biomass gasification: Comparisons based on energy and exergy

Results are reported of thermodynamic analyses of a biomass gasification unit in which sawdust is the biomass feed and the gasifying medium is either air or steam. Energy and exergy analyses are performed for the system and each of its components. A parametric study reveals the effect of design and operating parameters on the system's performance and energy and exergy efficiencies. The results show that the adiabatic temperature of biomass gasification significantly changes with the type of the gasifying medium. In addition, the exergy and energy efficiencies are observed to be higher when air is the gasifying medium rather than steam, while the system performance and exergy efficiencies are dependent on the moisture content of the feed biomass. The results are significant because they quantify the strong dependence of biomass gasification, which can be used for syngas or hydrogen production, on moisture content, and gasifying medium.     

Energy and exergy analysis and optimization of biomass gasification process for hydrogen production (based on air,steam and air/steam gasifying agents)

Growing the consumption of fossil fuels and emerging global warming issue have driven the research interests toward renewable and environmentally friendly energy sources. Biomass gasification is identified as an efficient technology to produce sustainable hydrogen. In this work, energy and exergy analysis coupled with thermodynamic equilibrium model were implemented in biomass gasification process for production of hydrogen. In this regard, a detailed comparison of the performance of a downdraft gasifier was implemented using air, steam, and air/steam as the gasifying agents for horse manure, pinewood and sawdust as the biomass materials. The comparison results indicate that the steam gasification of pinewood generates a more desired product gas compositions with a much higher hydrogen exergy efficiency and low exergy values of unreacted carbon and irreversibility. Then the effects of the inherent operating factors were investigated and optimized applying a response surface methodology to maximize hydrogen exergy efficiency of the process. A hydrogen exergy efficiency of 44% was obtained when the product gas exergy efficiency reaches to the highest value (88.26%) and destruction and unreacted carbon efficiencies exhibit minimum values of 7.96% and 1.9%.     

Investigation of a multi-generation system using a hybrid steam biomass gasification for hydrogen, power and heat

In this paper, an integrated process of steam biomass gasification and a solid oxide fuel cell (SOFC) is investigated energetically to evaluate both electrical and energy efficiencies. This system is conceptualized as a combined system, based on steam biomass gasification and with a high temperature, pressurized SOFC. The SOFC system uses hydrogen obtained from steam sawdust gasification. Due to the utilization of the hydrogen content of steam in the reforming and shift reaction stages, the system efficiencies reach appreciable levels. This study essentially investigates the utilization of steam biomass gasification derived hydrogen that was produced from an earlier work in a system combines gasifier and SOFC to perform multi-duties (power and heat). A thermodynamic model is developed to explore a combination of steam biomass gasification, which produces 70–75 g of hydrogen/kg of biomass to fuel a planar SOFC, and generate both heat and power. Furthermore, processes are emerged in the system to increase the hydrogen yield by further processing the rest of gasification products: carbon monoxide, methane, char and tar. The conceptualized scheme combines SOFC operates at 1000 K and 1.2 bar and gasifier scheme based on steam biomass gasification which operates close to the atmospheric pressure, a temperature range of 1023–1423 K and a steam-biomass ratio of 0.8 kmol/kmol. A parametric study is also performed to evaluate the effect of various parameters such as hydrogen yield, air flow rate etc. on the system performance. The results show that SOFC with an efficiency of 50.3% operates in a good fit with the steam biomass gasification module with an efficiency, based on hydrogen yield, of 55.3%, and the overall system then works efficiently with an electric efficiency of ∼82%.     

Study of synthesis gas composition,exergy assessment,and multi-criteria decision-making analysis of fluidized bed gasifier

A system based a fluidized bed gasifier with steam as a gasifying agent is investigated in details. Comparing the synthesis of gas compositions with experimental data available in the literature is used to validate the model. The synthesis of gas composition and efficiencies of the system is investigated respect to different biomasses considered as gasification fuels. The results indicate that the molar fractions of hydrogen and carbon dioxide are increased and the molar fraction of carbon monoxide is reduced with steam to biomass ratio (STBR). The hydrogen and cold gas efficiencies are improved with decreasing STBR. Hydrogen, cold gas, and exergy efficiencies are enhanced with temperature. The results illuminate that pine sawdust and straw have the highest hydrogen production and legume straw produces the lowest CO molar fraction. Straw has the highest hydrogen efficiency, eucalyptus and straw have the highest cold gas efficiency, and eucalyptus has the highest exergy efficiency. A systematical analytical hierarchy process (AHP)/technique for order preferences by similarity to ideal solution (TOPSIS) couple method are utilized to select the best alternative. The results illuminate that eucalyptus, straw, and pine sawdust are the best candidates, respectively as gasification fuel based on the considered criteria.     

Exergy analysis of hydrogen production from steam gasification of biomass: A review

Exergy analysis of hydrogen production from steam gasification of biomass was reviewed in this study. The effects of the main parameters (biomass characteristics, particle size, gasification temperature, steam/biomass ratio, steam flow rate, reaction catalyst, and residence time) on the exergy efficiency were presented and discussed. The results show that the exergy efficiency of hydrogen production from steam gasification of biomass is mainly determined by the H₂ yield and the chemical exergy of biomass. Increases in gasification temperatures improve the exergy efficiency whereas increases in particle sizes generally decrease the exergy efficiency. Generally, both steam/biomass ratio and steam flow rate initially increases and finally decreases the exergy efficiency. A reaction catalyst may have positive, negative or negligible effect on the exergy efficiency, whereas residence time generally has slight effect on the exergy efficiency.     

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.     

Sustainable hydrogen production options and the role of IAHE

In this paper, some potential sustainable hydrogen production options are identified and discussed. There are natural resources from which hydrogen can be extracted such as water, fossil hydrocarbons, biomass and hydrogen sulphide. In addition, hydrogen can be extracted from a large palette of anthropogenic wastes starting with biomass residuals, municipal wastes, plastics, sewage waters etc. In order to extract hydrogen from these resources one needs to use sustainable energy sources like renewables and nuclear. A total of 24 options for sustainable hydrogen production are then identified. Sustainable water splitting is the most important method of hydrogen production. Five sustainable options are discussed to split water, which include electrolysis, high temperature electrolysis, pure and hybrid thermochemical cycles, and photochemical/radiochemical methods. Other 19 methods refer to extraction of hydrogen from other materials than water or in conjunction with water (e.g., coal gasification with CO₂ capture and sequestration). For each case the achievable energy and exergy efficiency of the method were estimated based on state of the art literature screening for each involved process. In addition, a range of hydrogen production capacity is determined for each of the option. For a transition period to hydrogen economy nuclear or solar assisted coal gasification and fossil fuel reforming technologies – with efficiencies of 10–55% including CO₂ sequestration – should be considered as a viable option. Other “ready to be implemented” technology is hydro-power coupled to alkaline electrolysers which shows the highest hydrogen generation efficiency amongst all electrical driven options with 60–65%. Next generation nuclear reactors as to be coupled with thermochemical cycles have the potential to generate hydrogen with 40–43% energy efficiency (based on LHV of hydrogen) and 35–37% exergy efficiency (based on chemical exergy of hydrogen). Furthermore, recycling anthropogenic waste, including waste heat, waste plastic materials, waste biomass and sewage waters, shows also good potential as a sustainable option for hydrogen production. Biomass conversion to hydrogen is found as potentially the most efficient amongst all studied options in this paper with up to 70% energy efficiency and 65% exergy efficiency.     

Decentralized generation of electricity from biomass with proton exchange membrane fuel cell

Biomass can be applied as the primary source for the production of hydrogen in the future. The biomass is converted in an atmospheric fluidized bed gasification process using steam as the gasifying agent. The producer gas needs further cleaning and processing before the hydrogen can be converted in a fuel cell; it is assumed that the gas cleaning processes are able to meet the requirements for a PEM-FC. The compressed hydrogen is supplied to a hydrogen grid and can be used in small-scale decentralized CHP units. In this study it is assumed that the CHP units are based on low temperature PEM fuel cells. For the evaluation of alternative technologies the whole chain of centralized hydrogen production from biomass up to and including decentralized electricity production in PEM fuel cells is considered.Two models for the production of hydrogen from biomass and three models for the combined production of electricity and heat with PEM fuel cells are built using the computer program Cycle-Tempo. Two different levels of hydrogen purity are considered in this evaluation: 60% and 99.99% pure hydrogen. The purity of the hydrogen affects both the efficiencies of the hydrogen production as well as the PEM-FC systems. The electrical exergy efficiency of the PEM-FC system without additional heat production is calculated to be 27.66% in the case of 60% hydrogen and 29.06% in the case of 99.99% pure hydrogen. The electrical exergy efficiencies of the whole conversion chain appear to be 21.68% and 18.74%, respectively. The high losses during purification of the hydrogen gas result in a higher efficiency for the case with low purity hydrogen. The removal of the last impurities strongly increases the overall exergy losses of the conversion chain.     

Thermodynamic analysis of hydrogen production from biomass gasification

An investigation is reported of the thermodynamic performance of the gasification process followed by the steam-methane reforming (SMR) and shift reactions for producing hydrogen from oil palm shell, one of the most common biomass resources. Energy and exergy efficiencies are determined for each component in this system. A process simulation tool is used for assessing the indirectly heated Battelle Columbus Laboratory (BCL) gasifier, which is included with the decomposition reactor to produce syngas for producing hydrogen. A simplified model is presented here for biomass gasification based on chemical equilibrium considerations, with the Gibbs free energy minimization approach. The gasifier with the decomposition reactor is observed to be one of the most critical components of a biomass gasification system, and is modeled to control the produced syngas yield. Also various thermodynamic efficiencies, namely energy, exergy and cold gas efficiencies are evaluated which may be useful for the design, optimization and modification of hydrogen production and other related processes.     

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.     

生物质费托合成制取液体燃料的仿真及分析

以生物质费托合成制取液体燃料工艺为基础,利用Aspen Plus软件建立其流程的仿真模型,研究各单元操作参数变化对航空煤油产量的影响,并在最优工况下对系统进行能量分析.结果表明:生物质气化单元对航油产量的影响主要来自产物合成气中H2与CO物质的量之比(H2/CO),最优操作条件为T=750℃,P=0.1 MPa,进口水...     

Exergy analysis of hydrogen production plants based on biomass gasification

Biomass gasification is a promising option for the sustainable production of hydrogen rich gas. Five different commercial or pilot scale gasification systems are considered for the design of a hydrogen production plant that generates almost pure hydrogen. For each of the gasification technique models of two different hydrogen production plants are developed in Cycle-Tempo: one plant with low temperature gas cleaning (LTGC) and the other with high temperature gas cleaning (HTGC). The thermal input of all plants is 10 MW of biomass with the same dry composition. An exergy analysis of all processes has been made. The processes are compared on their thermodynamic performance (hydrogen yield and exergy efficiency). Since the heat recovery is not incorporated in the models, two efficiencies are calculated. The first one is calculated for the case that all residual heat can be applied, the case with ideal heat recovery, and the other is calculated for the case without heat recovery. It is expected that in real systems only a part of the residual heat can be used. Therefore, the actual value will be in between these calculated values. It was found that three processes have almost the same performance: The Battelle gasification process with LTGC, the FICFB gasification process with LTGC, and the Blaue Turm gasification process with HTGC. All systems include further processing of the cleaned gas from biomass gasification into almost pure hydrogen. The calculated exergy efficiencies are, respectively, 50.69%, 45.95%, and 50.52% for the systems without heat recovery. The exergy efficiencies of the systems with heat recovery are, respectively, 62.79%, 64.41%, and 66.31%. The calculated hydrogen yields of the three processes do not differ very much. The hydrogen yield of the Battelle LTGC process appeared to be 0.097 kg (kg_{(dry biomass)})⁻¹, for the FICFB LTGC process a yield of 0.096 kg (kg_{(dry biomass)})⁻¹ was found, and for the Blaue Turm HTGC 0.106 kg (kg_{(dry biomass)})⁻¹.     

Comparative assessment of hydrogen production methods from renewable and non-renewable sources

In this study, we present a comparative environmental impact assessment of possible hydrogen production methods from renewable and non-renewable sources with a special emphasis on their application in Turkey. It is aimed to study and compare the performances of hydrogen production methods and assess their economic, social and environmental impacts, The methods considered in this study are natural gas steam reforming, coal gasification, water electrolysis via wind and solar energies, biomass gasification, thermochemical water splitting with a Cu–Cl and S–I cycles, and high temperature electrolysis. Environmental impacts (global warming potential, GWP and acidification potential, AP), production costs, energy and exergy efficiencies of these eight methods are compared. Furthermore, the relationship between plant capacity and hydrogen production capital cost is studied. The social cost of carbon concept is used to present the relations between environmental impacts and economic factors. The results indicate that thermochemical water splitting with the Cu–Cl and S–I cycles become more environmentally benign than the other traditional methods in terms of emissions. The options with wind, solar and high temperature electrolysis also provide environmentally attractive results. Electrolysis methods are found to be least attractive when production costs are considered. Therefore, increasing the efficiencies and hence decreasing the costs of hydrogen production from solar and wind electrolysis bring them forefront as potential options. The energy and exergy efficiency comparison study indicates the advantages of biomass gasification over other methods. Overall rankings show that thermochemical Cu–Cl and S–I cycles are primarily promising candidates to produce hydrogen in an environmentally benign and cost-effective way.     

Exergy evaluation of biomass steam gasification via interconnected fluidized beds

This paper presents the thermodynamic assessment of biomass steam gasification via interconnected fluidized beds (IFB) system. The performance examined included the composition, yield and higher heating value (HHV) of dry syngas, and exergy efficiencies of the process. Two exergy efficiencies were calculated for the cases with and without heat recovery, respectively. The effects of steam‐to‐biomass ratio (S/B), gasification temperature, and pressure on the thermodynamic performances were investigated based on a modified modeling of the IFB system. The results showed that at given gasification temperature and pressure, the exergy efficiencies and dry syngas yield reached the maximums when S/B was at the corresponding carbon boundary point (S/B_CBP). The HHV of the dry syngas continuously decreased with the increase of S/B. Moreover, the exergy efficiency with heat recovery was averagely a dozen percentage points higher than that without heat recovery. Under atmospheric conditions, lower gasification temperature favored the yield and HHV of dry syngas at various S/B. In addition, it also favored the exergy efficiencies of the process when S/B is approximately larger than 0.75. Under pressurized conditions, higher gasification pressure favored both the yield and HHV of dry syngas, as well as the exergy efficiencies at different S/B. Copyright © 2013 John Wiley & Sons, Ltd.     

Industrial emergy evaluation for hydrogen production systems from biomass and natural gas

Fossil fuel resources are the main source for hydrogen production, and hydrogen production by renewable energy, such as biomass, is under development. To compare the performance in natural resource utilization for different hydrogen production systems, in this paper, two laboratorial hydrogen production systems from biomass and one industrial hydrogen production system from natural gas are analyzed by using industrial emergy evaluation indices. One of the laboratorial systems is a continuous supercritical water gasification system from glucose, and the other is a batch supercritical water gasification system from sawdust. The industrial system adopts American Brown technology. The evaluation results show that although the industrial emergy efficiency (IEE) of the industrial system from natural gas is higher than that of the laboratorial systems from biomass, the industrial emergy index of sustainability (IEIS) of the two laboratorial systems are higher than that of the industrial system. To make the laboratorial biomass system become an industrial system, the system should improve its yield, and reduce its capital investment.     

Exergy analysis of renewable light olefin production system via biomass gasification and methanol synthesis

The conceptual light olefin production system from biomass via gasification and methanol synthesis was simulated and its thermodynamic performance was evaluated through exergy analysis. The system was made up of gasification, gas composition adjustment, methanol synthesis, light olefin synthesis, steam & power generation and cooling water treatment. The in-depth exergy analysis was performed at the levels of system, subsystem and operation component respectively. The gasifier and the tail gas combustor were the main sources of irreversibility with exergy destruction ratios of 17.0% and 16.8% of the input exergy of biomass. The steam & power generation subsystem accounted for 43.4% of the overall exergy destruction, followed by 41.0% and 5.69% in the subsystems of gasification and gas composition adjustment respectively. The sensitivity evaluation of the operation parameters of gasifier indicates that the system efficiency could be improved by enhancing syngas yield and subsequent yield of light olefins. The overall exergetic efficiency of 30.5% is obtained at the mass ratios of steam to biomass and O₂-rich gas (95 vol%) to biomass (S/B and O/B) of 0.26 and 0.14 and gasification temperature at 725 °C.     

Biomass-based hydrogen production: A review and analysis

In this study, various processes for conversion of biomass into hydrogen gas are comprehensively reviewed in terms of two main groups, namely (i) thermo-chemical processes (pyrolysis, conventional gasification, supercritical water gasification (SCWG)), and (ii) biological conversions (fermentative hydrogen production, photosynthesis, biological water gas shift reactions (BWGS)). Biomass-based hydrogen production systems are discussed in terms of their energetic and exergetic aspects. Literature studies and potential methods are then summarized for comparison purposes. In addition, a biomass gasification process via oxygen and steam in a downdraft gasifier is exergetically studied for performance assessment as a case study. The operating conditions and strategies are really important for better performance of the system for hydrogen production. A distinct range of temperatures and pressures is used, such as that the temperatures may vary from 480 to 1400 °C, while the pressures are in the range of 0.1–50 MPa in various thermo-chemical processes reviewed. For the operating conditions considered the data for steam biomass ratio (SBR) and equivalence ratio (ER) range from 0.6 to 10 and 0.1 to 0.4, respectively. In the study considered, steam is used as the gasifying agent with a product gas heating value of about 10–15 MJ/Nm³, compared to an air gasification of biomass process with 3–6 MJ/Nm³. The exergy efficiency value for the case study system is calculated to be 56.8%, while irreversibility and improvement potential rates are found to be 670.43 and 288.28 kW, respectively. Also, exergetic fuel and product rates of the downdraft gasifier are calculated as 1572.08 and 901.64 kW, while fuel depletion and productivity lack ratios are 43% and 74.3%, respectively.     

Exergy analysis of hydrogen production from biomass gasification

For a given set of operating conditions, the hydrogen production from biomass gasification can be improved through optimization of the operating parameters and efficiencies. The present approach can predict hydrogen production via biomass gasification in a range of 10–32 kg/s from biomass (sawdust wood). The biomass is introduced to a gasifier at an operating temperature range of 1000–1500 K. Also, 4.5 kg/s of steam at 500 K is used as gasification medium. Results indicate that improvement in hydrogen production from biomass steam gasification depending on the amount of steam and quantity of biomass feeding to the gasifier as well the operating temperature. Over the range of feeding biomass, the hydrogen yield reaches 80–130 g H₂/kg biomass while in the operating temperature examined, the hydrogen yield reaches 80 g H₂/kg biomass. On mole basis it is found that, in the first range of H₂ varies from 51 to 63% in the studied range of feeding biomass in existing 4.5 kg/s from steam while H₂ gets to 51–53% in existing of 6.3 kg/s from steam.     

Continuous hydrogen production by biomass gasification in supercritical water heated by molten salt flow: System development and reactor assessment

Hydrogen production by biomass gasification using solar energy is a promising approach for overcoming the drawbacks of fossil fuel utilization, but the storage of discontinuous solar flux is a critical issue for continuous solar hydrogen production. A continuous hydrogen production system by biomass gasification in supercritical water using molten-salts-stored solar energy was proposed and constructed. A novel double tube helical heat exchanger was designed to be molten salts reactor for hydrogen production. Model compounds (glycerol/glucose) and real biomass (corn cob) were successfully gasified in this molten salts reactor for producing hydrogen-rich gas. The unique temperature profiles of biomass slurry in the reactor were observed and compared with that of conventional electrical heating and direct solar heating approaches. Product gases yield, gasification efficiency and exergy conversion efficiency of the reactor were analyzed. The results showed that the performances of reactor were determined by feedstock style, biomass concentration, residence time and biomass slurry temperature profiles.