SOFC分布式热电联供系统的性能研究

对固体氧化物燃料电池(SOFC)热电联供系统(CHP)进行了研究,建立了各个组件的数学模型,并应用Matlab软件实现了系统的计算机模拟。以发电规模为20 kW的系统为研究对象,对其设计工况和运行工况进行了性能模拟,模拟结果表明,在设计点工况,系统的联供效率可达89%,系统中空气侧压缩机的功率消耗最大;在运行工况下,减小燃料利用率或增加过量空气比率均使系统的热、电效率下降,两参数对系统热效率的影响程度相当且较为显著,而燃料利用对发电效率的影响更为敏感,若需获得较高的发电效率,建议系统采取高燃料利用率的操作策略,若需获得较高的热效率,建议采取高燃料利用率或者在电堆允许的温差应力下降低过量空气比率的操作策略。整个研究工作为固体氧化物燃料电池热电联供系统的设计和操作提供了指导。     

Application of bacteria involved in the biological sulfur cycle for paper mill effluent purification

In anaerobic wastewater treatment, the occurrence of biological sulfate reduction results in the formation of unwanted hydrogen sulfide, which is odorous, corrosive and toxic. In this paper, the role and application of bacteria in anaerobic and aerobic sulfur transformations are described and exemplified for the treatment of a paper mill wastewater. The sulfate containing wastewater first passes an anaerobic UASB reactor for bulk COD removal which is accompanied by the formation of biogas and hydrogen sulfide. In an aeration pond, the residual COD_organic and the formed dissolved hydrogen sulfide are removed. The biogas, consisting of CH₄ (80-90 vol.%), CO₂ (10-20 vol.%) and H₂S (0.8-1.2 vol.%), is desulfurised prior to its combustion in a power generator thereby using a new biological process for H₂S removal. This process will be described in more detail in this paper. Biomass from the anaerobic bioreactor has a compact granular structure and contains a diverse microbial community. Therefore, other anaerobic bioreactors throughout the world are inoculated with biomass from this UASB reactor. The sludge was also successfully used in investigation on sulfate reduction with carbon monoxide as the electron donor and the conversion of methanethiol. This shows the biotechnological potential of this complex reactor biomass.     

Effects of Sn doping on the manufacturing,performance and carbon deposition of Ni/ScSZ cells in solid oxide fuel cells

This work demonstrates the effect of tin (Sn) doping on the manufacturing, electrochemical performance, and carbon deposition in dry biogas-fuelled solid oxide fuel cells (SOFCs). Sn doping via blending in technique alters the rheology of tape casting slurry and increases the Ni/ScSZ anode porosity. In contrast to the undoped Ni/ScSZ cells, where open-circuit voltage (OCV) drops in biogas, Sn–Ni/ScSZ SOFC OCV increases by 3%. The maximum power densities in biogas are 0.116, 0.211, 0.263, and 0.314 W/cm² for undoped Ni/ScSZ, undoped Ni/ScSZ with 3 wt% pore former, Sn–Ni/ScSZ and Sn–NiScSZ with 1 wt% pore former, respectively. Sn–Ni/ScSZ reduces the effect of the drop in the maximum power densities by 26%–36% with the fuel switch. A 1.28–2.24-fold higher amount of carbon is detected on the Sn–Ni/ScSZ samples despite the better electrochemical performance, which may reflect an enhanced methane decomposition reaction.     

On the feasibility of on-farm biogas-to-electricity conversion: To what extent is solid oxide fuel cells durability a threat to break even the initial investment?

Despite their promising features, adverse economic feasibility still hamper SOFCs wide implementation and this effect is emphasized as long as the system size is reduced. According to previous investigations, the biogas pre-treatment section represents a burden for the economic viability. Aiming at reducing the extent of installation costs in SOFC-based configurations, biogas partial upgrading through CO₂ gas-separation membranes is put forth as innovative solution against reforming. This innovative system concept is expected to make SOFCs more cost-effective, yet resulting feeding gas might cause a quicker SOFC performance decay. Besides solving this trade-off, the economic viability results strongly sensitive to subsidiary electricity prices in force according to the regulatory framework.This paper presents a comparative economic assessment regarding biogas-to-electricity conversion via Solid Oxide fuel cells (SOFCs) and mature technologies as internal combustion engines (ICEs). Results highlighted that, the innovative SOFC system is far more viable than reforming-based one, exhibiting a reasonable payback time, with an adequate subsidized electricity sale price (4 and 5 years for small/medium and large-size plants respectively when subsidy is 0.28 €/kWh), up to 1%_1000h degradation rate. On the other hand, whilst considering a SOFC degradation rate of 0.03%_1000h, the reforming-based system appears feasible only on large-size plants, yet recovering the initial capital expenditure in 9 years. Moreover, once the break-even point is reached, the gain in the net revenue produced by the innovative system is amplified in the event of small-size installation. This allows the possibility to undertake the risk of higher degradation rates (up to 2%_1000h) without jeopardizing the economic profitability. Therefore, in the present regulatory framework and under current capital costs projections, the innovative SOFC system appears as much profitable as ICE mature technology. Such effort in the design of the fuel pre-treatment unit can lever SOFC broad spreading into the market of small biogas producers.     

H2S removal from biogas for fuelling MCFCs: New adsorbing materials

Cu and Zn modified 13X zeolites prepared by ion exchange or impregnation and activated carbons (ACs) treated with KOH, NaOH or Na₂CO₃ solutions were studied as H₂S sorbents for biogas purification for fuelling molten carbonate fuel cells. H₂S sorption was studied in a new experimental set-up equipped with a high sensitivity potentiometric system for the analysis of H₂S. Breakthrough curves were obtained at 40 °C with a fixed bed of 20 mg of the samples under a stream (6 L h⁻¹) of 8 ppm H₂S/He mixture. The adsorption properties of 13X zeolite improved with addition of Cu or Zn:Cu exchanged zeolite showed the best performances with a breakthrough time of 580 min at 0.5 ppm H₂S, that is 12 times longer than the parent zeolite. In general, unmodified and modified ACs were more effective H₂S sorbents than zeolites. Treating ACs with NaOH, KOH, or Na₂CO₃ solutions improved the H₂S adsorption properties: AC treated with Na₂CO₃ was the most effective sorbent, showing a breakthrough time of 1222 min at 0.5 ppm, that is twice the time of the parent AC.     

Short contact time catalytic partial oxidation of biogas – A comprehensive study on CO2 and N2 dilution

The short contact time catalytic partial oxidation of methane diluted with nitrogen and/or carbon dioxide to act as a surrogate for biogas conversion was carried out. Experiments were carried out under varying operating conditions to determine the possible use of the products in pyrolysis.Carbon dioxide has a larger effect on the product selectivities and back face temperature of the catalyst compared to nitrogen for equal dilutions. Carbon dioxide is consumed in the reactor whereas nitrogen is not. Since carbon dioxide likely takes part in endothermic reactions, the temperature of the catalyst is lower as is the conversion of methane and selectivity to carbon monoxide and hydrogen.The product stream is at an appropriate composition and temperature for subsequent use in a pyrolysis reactor. The presence of hydrogen and carbon monoxide will result in the removal of oxygen from bio-oils that are produced in the pyrolysis reactor.     

Enhancement of biogas production by addition of hemicellulolytic bacteria immobilised on activated zeolite

Biogas from agricultural biomass and residues is a valuable source of renewable energy. However, recalcitrant plant cell structures represent a barrier in the fermentative biodegradation process in single- and two-stage reactors. Therefore, approaches concerning a more efficient de-polymerisation of cellulose and hemicellulose to monomeric sugars are required amongst others in order to optimise the fermentation efficiency and to increase methane yields. Here we show a new strategy for the enhancement of biogas production from hemicellulose-rich substrates. Hemicellulolytic populations from a common biogas fermenter consortium were successively enriched in batch-cultures using a synthetic medium containing xylan powder as single carbon source under anaerobic mesophilic conditions. Enriched hemicellulolytic bacteria were immobilised on trace metal activated zeolite to ensure a stable storage and easy application. Xylanase activity increased continuously during subsequent enrichment cycles by up to 162%. In batch-culture experiments we were able to observe an increase of methane by 53% compared to controls without additionally introduced microorganisms immobilised on zeolite. Specific enrichment of hemicellulolytic bacteria during the process was confirmed by using single strand conformation polymorphism (SSCP) analysis based on amplification of the eubacterial 16S rDNA fragments. Using sequence analysis conspicuous bands from SSCP patterns could be identified as belonging to the groups Bacteroides sp., Azospira oryzae (Dechlorosoma sp.) as well as to a wide spectrum of diverse species within the order of Clostridiales (Firmicutes).     

SI engine assessment using biogas,natural gas and syngas with different content of hydrogen for application in Brazilian rice industries: Efficiency and pollutant emissions

After Asia, Brazil is the world's largest rice producer. During the processing of the grain, large amounts of husk are generated, corresponding to 22% of its weight. On the other hand, in the process of parboiling, in turn, the final result is considerable volumes of effluents rich in organic matter, generating large amounts of methane gas through anaerobic treatment. Therefore, the SI engine can operate with mixtures of biogas and syngas, generating electricity and heat in the Brazilian rice industries. In addition, it reduces the emissions of polluting gases that are generated with a direct burning of the husks instead of their gasification, as well as the use of methane gas. Accordingly, in this work, it was used the spark-ignition engine operating with one of the typical biogas and syngas compositions generated in the rice industries, named Bio65 (containing 65% of CH₄ by vol.), syngas1 (containing 18,3% of H₂ by vol.), and syngas2 (containing 13,5% of H₂ by vol.), respectively. Additionally, the tests with natural gas as a reference fuel have been performed. It was evaluated the emissions of polluting gases such as CO, NO_x and HC, as well as the thermal and electrical efficiency of all tested fuels. An important result that could be observed was that for both natural gas and biogas fuel, the increase in excess ratio (λ) value from 1 to 1.5 led to lower NO_x and CO emissions, even if with increased HC emissions. On the other hand, the Indicated Specific Energy Consumption increased to all the fuels tested in lean conditions in almost all ignition advances angles. The research tried to show that biogas and syngas can be used in parboiling rice industries, taking the advantage of the generated gases for energy self-sufficiency as well as reducing emissions.     

Multicarrier energy systems: Optimization model based on real data and application to a case study

Multicarrier energy systems are increasingly used for a number of applications, among which the supply of electricity, heating, and cooling in buildings. The possibility of switching between different energy sources is a crucial advantage for the optimal fulfillment of the energy demand. The flexibility of these systems can benefit from the integration with smart grids, which have strong variations in time during their operation. The energy price is the parameter that is usually considered, but also the primary energy factor and the greenhouse gases emissions need to be accounted. This paper presents an application of an operational optimization method for a multicarrier energy system, based on real data–driven model and applied to different countries. The generation plant of a hospital is considered as case study, coping with multiple energy needs by relying on different conversion technologies. The optimal operation of the system shows a wide range of variability, depending on the chosen objective function, the hour of the day, the season, and the country. The results are affected mostly by the energy mix of the electricity supplied from the power grid, which has a direct influence on the primary energy consumption and the greenhouse gases emissions and an indirect influence on the electricity prices.     

Effect of some operating parameters on biogas production rate

In order to enhance the performance of a biogas generation process and prevent process failure, certain operataing parameters need to be controlled. This article presents the results of a series of studies in which the effect of temperature, pH, carbon -nitrogen ratio and retention time on biogas production from cowdung were investigated