Hydrogen and syngas production from biomass gasification for fuel cell application

Gasification process is being developed to produce a clean and efficient gas flue from fuels such as coal, biomass, and solid/liquid wastes for power generation. In this work, a biomass gasification kinetic model that can predict reaction temperature, gasification performance, and gas composition has been developed for a circulating fluidized bed (CFB). Experimental data from a CFB power plant have been used to validate the model. It is confirmed that the addition of steam is important for increasing the hydrogen concentration and syngas caloric value. Based on the predicted results, an optimal condition is suggested for air and steam gasification in the CFB gasifier.     

Hydrogen and syngas production from sewage sludge via steam gasification

High temperature steam gasification is an attractive alternative technology which can allow one to obtain high percentage of hydrogen in the syngas from low-grade fuels. Gasification is considered a clean technology for energy conversion without environmental impact using biomass and solid wastes as feedstock. Sewage sludge is considered a renewable fuel because it is sustainable and has good potential for energy recovery. In this investigation, sewage sludge samples were gasified at various temperatures to determine the evolutionary behavior of syngas characteristics and other properties of the syngas produced. The syngas characteristics were evaluated in terms of syngas yield, hydrogen production, syngas chemical analysis, and efficiency of energy conversion. In addition to gasification experiments, pyrolysis experiments were conducted for evaluating the performance of gasification over pyrolysis. The increase in reactor temperature resulted in increased generation of hydrogen. Hydrogen yield at 1000 °C was found to be 0.076 g_gas g_sample⁻¹. Steam as the gasifying agent increased the hydrogen yield three times as compared to air gasification. Sewage sludge gasification results were compared with other samples, such as, paper, food wastes and plastics. The time duration for sewage sludge gasification was longer as compared to other samples. On the other hand sewage sludge yielded more hydrogen than that from paper and food wastes.     

Potential applications of high-temperature air/steam-blown gasification and pyrolysis systems

Several aspects of using the advanced, high-temperature air/steam-blown gasification and pyrolysis technologies for converting solid fuels into syngas are examined. The gasification/pyrolysis systems, known as Multi-staged Enthalpy Extraction Technology (MEET), employ high-temperature air and steam as oxidizer agents for converting the solid fuels into syngas and have many features that are advantageous for power generation. The low-cost gasifier/pyrolyzer is extremely compact and flexible, capable of operating efficiently on a wide range of low-caloric-value fuels. Potential uses of this technology range from large-scale integrated gasification power plants to small-scale waste-to-energy applications. Present R&D status of the MEET technology are summarized and its main components are described. Major fuel resources for the different markets are explored. The performance and feasibility of diverse power conversion systems to couple with MEET gasifier/pyrolyzer for combined heat and power applications are assessed.     

高效低污染燃烧及气化技术的最新研究进展

根据参加2003日本神户国际动力工程会议的情况,着重评述了化石燃料低NOX燃烧、固体废弃物焚烧、煤及固体废弃物气化等技术领域的最新研究进展。目前烟气脱硝成为中国电厂技术革新的热点问题,炉内高效低NOX燃烧是一种适于我国国情的高效廉价的技术路线。热解和焚烧相结合的固体废弃物利用技术在日本已得到较为广泛的应用,但是它利用蒸汽轮机发电对于未来小型发电系统而言效率较低,而热解和气化相结合的固体废弃物利用技术是利用内燃机或燃气轮机发电,对于日处理废弃物量小于200t d的发电系统其效率较高,因此成为下一代分布式能源利用系统的良好选择。图7参1     

Enhancement of hydrogen production in a modified moving bed downdraft gasifier – A thermodynamic study by including tar

A new approach on thermodynamic simulation of the gasification process is conducted by considering the formation of tar using Aspen Plus. The present model shows higher accuracy as compared to the conventional model in term of the composition of producer gas. The tar from pyrolysis process is successfully reduced with high reaction temperature in the combustion zone. A parametric study is performed by varying the split ratio of gasifying agents (steam/oxygen) through three different zones: (i) combustion zone, (ii) counter-current reduction zone, and/or (iii) co-current reduction zone. Introduction of the gasifying agents through the counter-current reduction zone has positive effects on the gasification performances in term of hydrogen concentration, cold gas efficiency, and gasification system efficiency. The effects of O₂ equivalence ratio and steam to carbon ratio (S/C) on the performance of gasification are also investigated. The gasification with oxygen provided the highest cold gas efficiency. A remarkable hydrogen production is achieved from gasification with both oxygen and steam.     

Integrated adsorption steam gasification for enhanced hydrogen production from palm waste at bench scale plant

The generation of hydrogen-enriched synthesis gas from catalytic steam gasification of biomass with in-situ CO₂ capture utilizing CaO has a high perspective as clean energy fuels. The present study focused on the process modeling of catalytic steam gasification of biomass using palm empty fruit bunch (EFB) as biomass for hydrogen generation through experimental work. Experiment work has been carried out using a fluidized bed gasifier on a bench-scale plant. The established model integrates the kinetics of EFB catalytic steam gasification reactions, in-situ capturing of CO₂, mass and energy balance calculations. Chemical reaction constants have been calculated via the parameters fitting optimization approach. The influence of operating parameters, mainly temperature, steam to biomass, and sorbent to biomass ratio, was investigated for the hydrogen purity and yield through the experimental study and developed model. The results predicted approximately 75 vol% of the hydrogen purity in the product gas composition. The maximum H₂ yield produced from the gasifier was 127 gH₂/kg of EFB via experimental setup. The increase in both steam to biomass ratio and temperature enhanced the production of hydrogen gas. Comparing the results with already published literature showed that the current system enables to produce a high amount of hydrogen from EFB.     

Hydrogen-rich gas production by air–steam gasification of rice husk using supported nano-NiO/γ-Al2O3 catalyst

The air–steam catalytic gasification of rice husk for hydrogen-rich gas production was experimentally investigated in a combined fixed bed reactor with the newly developed nano-NiO/γ-Al₂O₃ catalyst. A series of experiments have been performed to explore the effects of catalyst presence, catalytic reactor temperature, the equivalence ratio (ER), and steam to biomass ratio (S/B) on the composition and yield of gasification gases. The experiments demonstrated that the developed nano-NiO/γ-Al₂O₃ catalyst had a high activity of cracking tar and hydrocarbons, upgrading the gas quality, as well as yielding a high hydrogen production. Catalytic temperature was crucial for the overall gasification process, a higher temperature contributed to more hydrogen production and gas yield. Varying ER demonstrated complex effects on rice husk gasification and an optimal value of 0.22 was found in the present study. Compared with biomass catalytic gasification under air only, the introduction of steam improved the gas quality and yield. The steam/biomass ratio of 1.33 was found as the optimum operating condition in the air–steam catalytic gasification.     

An experimental study on air gasification of biomass micron fuel (BMF) in a cyclone gasifier

Biomass micron fuel (BMF) produced from feedstock (energy crops, agricultural wastes, forestry residues and so on) through an efficient crushing process is a kind of powdery biomass fuel with particle size of less than 250 μm. Based on the properties of BMF, a cyclone gasifier concept has been considered in our laboratory for biomass gasification. The concept combines and integrates partial oxidation, fast pyrolysis, gasification, and tar cracking, as well as a shift reaction, with the purpose of producing a high quality of gas. In this paper, characteristics of BMF air gasification were studied in the gasifier. Without outer heat energy input, the whole process is supplied with energy produced by partial combustion of BMF in the gasifier using a hypostoichiometric amount of air. The effects of equivalence ratio (ER) and biomass particle size on gasification temperature, gas composition, gas yield, low-heating value (LHV), carbon conversion and gasification efficiency were studied. The results showed that higher ER led to higher gasification temperature and contributed to high H₂-content, but too high ER lowered fuel gas content and degraded fuel gas quality. A smaller particle was more favorable for higher gas yield, LHV, carbon conversion and gasification efficiency. And the BMF air gasification in the cyclone gasifier with the energy self-sufficiency is reliable.     

Optimization of a combined heat and power system based gasification of municipal solid waste of Urmia University student dormitories via ANOVA and taguchi approaches

Municipal solid waste (MSW) of Urmia University student dormitories was utilized to trigger a co-generation system. The combined heat and power system consisted of a gasifier, a micro gas turbine, an organic Rankine cycle, a heat exchanger, and a domestic heat recovery. The system performance was validated by comparing the results with experimental results available in the literature. Air, steam, and oxygen were considered as different gasification mediums. Hydrogen content in the case of the steam medium was higher at all gasification temperatures and low moisture contents. However, hydrogen content of the system based oxygen medium was higher at high moisture contents. The system performances from power generation and hot water flow rate viewpoints were assessed versus the MSW flow rate, gasification temperature, pressure ratio, and turbine inlet temperature. Taguchi approach was employed to optimize the generated power in air, steam, and oxygen medium cases. The optimum conditions were the same for all cases. The optimum powers were 281.1 kW, 279.4 kW, and 266.9 kW for the system based steam, air, and oxygen gasifying agents, respectively.     

Modelling of biomass gasifier and microturbine for the olive oil industry

The olive oil industry generates several solid wastes. Among these residues are olive tree leaves, prunings, and dried olive pomace (orujillo) from the extraction process. These renewable energy sources can be used for heat and power production. The aim of this paper consists of modelling and simulation of a small‐scale combined heat and power (CHP) plant (fuelled with olive industry wastes) incorporating a downdraft gasifier, gas cleaning and cooling subsystem, and a microturbine as the power generation unit. The gasifier was modelled with thermodynamic equilibrium calculations (fixed bed type, stratified and with an open top). This gasifier operates at atmospheric pressure with a reaction temperature about 800°C. Simulation results (biomass consumption, gasification efficiency, rated gas flow, calorific value, gas composition, etc.) are compared with a real gasification technology. The product gas obtained has a low heating value (4.8–5.0 MJ Nm^?3) and the CHP system provides 30 kW_e and 60 kW_th. High system overall CHP efficiencies around 50% are achievable with such a system. The proposed system has been modelled using Cycle‐Tempo software^®. Copyright © 2010 John Wiley & Sons, Ltd.     

Existing large steam power plant upgraded for hydrogen production

This paper presents and discusses the results of a complete thermoeconomic analysis of an integrated power plant for co-production of electricity and hydrogen via pyrolysis and gasification processes fed by various coals and mixture of coal and biomass, applied to an existing large steam power plant (ENEL Brindisi power plant – 660 MW_e). Two different technologies for the syngas production section are considered: pyrolysis process and direct pressurized gasification. Moreover, the proximity of a hydrogen production and purification plants to an existing steam power plant favors the inter-exchange of energy streams, mainly in the form of hot water and steam, which reduces the costs of auxiliary equipment. The high quality of the hydrogen would guarantee its usability for distributed generation and for public transport. The results were obtained using WTEMP thermoeconomic software, developed by the Thermochemical Power Group of the University of Genoa, and this project has been carried out within the framework of the FISR National project “Integrated systems for hydrogen production and utilization in distributed power generation”.     

Distributed power generation via gasification of biomass and municipal solid waste: A review

The access to electricity has increased worldwide, growing from 60 million additional consumers per year in 2000–2012 to 100 million per year in 2012–2016. Despite this growth, approximately 675 million people will still lack access to electricity in 2030, indicating that electricity demand will continue to increase. Unfortunately, traditional large fossil power technologies based on coal, oil and natural gas lead to a major concern in tackling worldwide carbon dioxide emissions, and nuclear power remains unpopular due to public safety concerns. Distributed power generation utilizing CO₂-neutral sources, such as gasification of biomass and municipal solid wastes (MSW), can play an important role in meeting the world energy demand in a sustainable way. This review focuses on the recent technology developments on seven power generation technologies (i.e. internal combustion engine, gas turbine, micro gas turbine, steam turbine, Stirling engine, organic rankine cycle generator, and fuel cell) suitable for distributed power applications with capability of independent operation using syngas derived from gasification of biomass and MSW. Technology selection guidelines is discussed based on criteria, including hardware modification required, size inflexibility, sensitivity to syngas contaminants, operational uncertainty, efficiency, lifetime, fast ramp up/down capability, controls and capital cost. Major challenges facing further development and commercialization of these power generation technologies are discussed.     

Biomass integrated gasification fuel cell systems-Concept development and experimental results

The link-up of wood gasification with high temperature solid oxide fuel cells (Biomass-Integrated Gasification Fuel Cell System, B-IGFC) is a promising approach to reach high electrical efficiencies in small-scale biomass fuelled combined heat and power plants (CHP). The main technical challenge is the adjustment of the three main system components gasification, gas processing and fuel cell. A B-IGFC concept has been developed based on the findings that producer gas originating from the updraft gasification of wood can be electrochemically converted in a SOFC whereby tars are degraded to hydrogen and carbon monoxide and contribute to the electrochemical reactions and power generation. Important unit operations of the B-IGFC system were characterised experimentally. During a long-term test of the complete B-IGFC demonstration unit, the gasifier and the catalytic partial oxidation could be operated without problems, delivering a fuel gas to the SOFC system with relatively constant composition and properties. Compared to methane operation, the SOFC system delivered approx. 40% less current. With the chosen operating conditions, carbon deposition was effectively prevented. Ash deposits were identified as major obstacle for a smooth SOFC system operation.     

Thermodynamic optimization of biomass gasification for decentralized power generation and Fischer–Tropsch synthesis

In recent years, biomass gasification has emerged as a viable option for decentralized power generation, especially in developing countries. Another potential use of producer gas from biomass gasification is in terms of feedstock for Fischer–Tropsch (FT) synthesis – a process for manufacture of synthetic gasoline and diesel. This paper reports optimization of biomass gasification process for these two applications. Using the non–stoichometric equilibrium model (SOLGASMIX), we have assessed the outcome of gasification process for different combinations of operating conditions. Four key parameters have been used for optimization, viz. biomass type (saw dust, rice husk, bamboo dust), air or equivalence ratio (AR = 0, 0.2, 0.4, 0.6, 0.8 and 1), temperature of gasification (T = 400, 500, 600, 700, 800, 900 and 1000 °C), and gasification medium (air, air–steam 10% mole/mole mixture, air–steam 30%mole/mole mixture). Performance of the gasification process has been assessed with four measures, viz. molar content of H₂ and CO in the producer gas, H₂/CO molar ratio, LHV of producer gas and overall efficiency of gasifier. The optimum sets of operating conditions for gasifier for FT synthesis are: AR = 0.2–0.4, Temp = 800–1000 °C, and gasification medium as air. The optimum sets of operating conditions for decentralized power generation are: AR = 0.3–0.4, Temp = 700–800 °C with gasification medium being air. The thermodynamic model and methodology presented in this work also presents a general framework, which could be extended for optimization of biomass gasification for any other application.     

Comparison between externally fired gas turbine and gasifier-gas turbine system for the olive oil industry

The olive oil industry generates during the extraction process several solid wastes as olive tree leaves and prunings, exhausted pomace and olive pits. These renewable wastes could be used for power and heat applications. The aim of this paper is to compare the performance of two small-scale CHP systems: a gasification- gas turbine system and an EFGT (externally fired gas turbine system). For this reason, several parameters have been calculated: generated heat and power, electric and overall efficiencies, biomass consumption, exergy efficiency, optimum pressure ratio, etc. These systems provide 30 kW_e and about 60kW_th. Simulation results show that the electrical and overall efficiencies achieved in EFGT system (19.1% and 59.3%, respectively) are significantly higher than those obtained in the gasification plant (12.3% and 45.4%). The proposed CHP systems have been modeled using Cycle-Tempo^® software.     

Performance of active nickel loaded lignite char catalyst on conversion of coffee residue into rich-synthesis gas by gasification

Performance of nickel-loaded lignite char catalyst on conversion of coffee residue into synthesis gas by catalytic steam gasification was carried out at low reaction temperatures ranging from 500 °C to 650 °C in the two-stage quartz fixed bed reactor. The effects of steam pressures (30, 36 and 50 kPa corresponding to S/B = 2.23, 2.92 5.16, respectively) and catalyst to biomass ratios (C/B ratio = 0, 1, 3) were considered. Nickel-loaded lignite char was prepared as a catalyst with a low nickel loading amount of 12.9 wt%. The gas yields in the catalytic steam gasification process strongly depended on the reaction temperature and C/B ratio. The total gas yields obtained in catalytic steam gasification was higher than that of catalytic pyrolysis, steam gasification and non-catalytic pyrolysis with steam absence by factors of 3.0, 3.8 and 7.7, respectively. To produce the high synthesis gas, it could be taken at 600 °C with total gas yields of 67.13 and 127.18 mmol/g biomass-d.a.f. for C/B ratios of 1.0 and 3.0, respectively. However, the maximum H₂/CO ratio was 3.57 at a reaction temperature of 600 °C, S/B of 2.23 and C/B of 1.0. Considering the conversion of coffee residue by catalytic steam gasification using the nickel-loaded lignite char catalyst, it is possible to covert the coffee residue volatiles into rich synthesis gas.     

Research and development of a low-BTU gas-driven engine for waste gasification and power generation

Combustion characteristics of low-BTU gases (about 1000 kcal/N m³) were experimentally investigated in order to develop engine generators for waste gasification and power generation systems. Two simulated low-BTU gases, obtained from one-step high temperature gasification (hydrogen rich) and two-step pyrolysis/reforming gasification (methane rich), as well as natural gas, were tested in a small-scale spark ignition engine. Compared to the natural gas driven engine, the hydrogen rich low-BTU gas driven engine showed similar thermal efficiency but with significantly lower NO_x and hydrocarbon emissions and wider equivalence ratio range for stable engine operation. On the other hand, the methane rich low-BTU gas engine showed narrower equivalence ratio range for stable operation. The test results show engine performance more depends on combustion characteristics than on the heating value of the fuel gas. For better engine performance, hydrogen rich fuel gas is desirable.     

Comparisons of MHD topping combined power generation systems

The efficiencies of six MHD topping combined power generation systems and one gas turbine topping combined system driven by different combinations of fuel and oxidant supply schematics were compared and classified on the bases of overall chemical reaction models for the combustion and gasification processes. The primary fuel was carbon that modeled a coal. The fuel types considered were coal and coal-synthesized gases which were provided by either conventional top gasification or by the tail gasification process. The oxidant was either pure oxygen, oxygen enriched air or air. In the MHD topping cases, the oxidant was preheated to each appropriate temperature. The enthalpy extraction of the corresponding power generation units in the topping and bottoming systems and the temperatures at the inlets of regenerators as well as at the stacks were assumed to be identical in all cases, except the inlet temperatures at the recuperative air heaters and the steam generators. We showed that the tail gasification system with an MHD topping and a combined gas turbine and steam turbine bottoming exhibited the highest plant efficiency insofar as it was based on the state-of-the-art technology of the power generation units and the heat exchanger.     

Plasma fixed bed gasification using an Eulerian model

Gasification of solid waste is considered as a green and sustainable solution to perform energy recovery from several waste streams. This work aims to adapt an Euler-Euler multiphase mathematical model to understand the effects of physical and chemical factors, i.e. equivalence ratio (ER), steam to fuel ratio (SFR), and input plasma power of municipal solid waste (MSW) fixed bed gasification. The model is capable of simulating temperature and velocity fields, as well as gas and solid composition variations inside the reactor. A two-step pyrolysis model is used considering the pyrolysis mechanism of cellulose and plastic components. Drying, pyrolysis, homogeneous gas reactions, and heterogeneous combustion/gasification reactions were also included in the model. It was shown that the proposed model could provide accurate predictions against experimental data with a deviation generally lesser than 10%. Conclusion could be drawn that an ER of 0.3 and an SRF of 0.5 seems to be the most favourable conditions in order to obtain a high-quality syngas. Higher plasma power is favourable to obtain a high-quality syngas. However, the high electric power required penalizes the process efficiency and may compromise the economic viability of a plasma gasification project.     

Hydrogen-rich gas production by steam gasification of palm oil wastes over supported tri-metallic catalyst

The catalytic steam gasification of palm oil wastes for hydrogen-rich gas production was experimentally investigated in a combined fixed bed reactor using the newly developed tri-metallic catalyst. The results indicated that the supported tri-metallic catalyst had greater activity for the cracking of hydrocarbons and tar in vapor phase and higher hydrogen yield than the calcined dolomite in catalytic steam gasification of palm oil wastes. A series of experiments have been performed to explore the effects of temperature, steam to biomass ratio (S/B) and biomass particle size on gas composition, gas yield, low heating value (LHV) and hydrogen yield. The experiments demonstrated that temperature was the most important factor in this process; higher temperature contributed to higher hydrogen production and gas yield, however, it lowered gas heating value. Comparing with biomass catalytic gasification, the introduction of steam improved gas quality and yield, the optimal value of S/B was found to be 1.33 under the present operating condition. It was also shown that a smaller particle size was more favorable for gas quality and yield. However, the LHV of fuel gas decreased with the increasing S/B ratio and the decreasing biomass particle size.