生物质水蒸气气化制氢模拟研究

利用ASPEN PLUS软件建立了生物质水蒸气气化制氢模型,对各种影响因素进行了深入分析。结果表明:随着碳转化率的增加,H2浓度略有降低,H2产量大幅增加,在碳转化率为1时达到最大值142.54 g/kg;随着水蒸气/生物质质量比的增加,H2浓度和产量大幅增加,而后趋于稳定,水蒸气/生物质质量比取2比较适宜。适当的升温和低压对制备H2有利,在加压条件下,H2浓度与产量达到最大值的温度升高。     

Catalytic steam reforming of tar for enhancing hydrogen production from biomass gasification: a review

Presently, the global search for alternative renewable energy sources is rising due to the depletion of fossil fuel and rising greenhouse gas (GHG) emissions. Among alternatives, hydrogen (H₂) produced from biomass gasification is considered a green energy sector, due to its environmentally friendly, sustainable, and renewable characteristics. However, tar formation along with syngas is a severe impediment to biomass conversion efficiency, which results in process-related problems. Typically, tar consists of various hydrocarbons (HCs), which are also sources for syngas. Hence, catalytic steam reforming is an effective technique to address tar formation and improve H₂ production from biomass gasification. Of the various classes in existence, supported metal catalysts are considered the most promising. This paper focuses on the current researching status, prospects, and challenges of steam reforming of gasified biomass tar. Besides, it includes recent developments in tar compositional analysis, supported metal catalysts, along with the reactions and process conditions for catalytic steam reforming. Moreover, it discusses alternatives such as dry and autothermal reforming of tar.     

水蒸气氛围下甘蔗渣热解气化条件的研究

在试验条件下，考察反应温度、升温速率、物料颗粒大小等因素对蔗渣在水蒸气中的热解气化特性的影响。试验结果表明，热解终温越高，物料粒径越小，越有利于产生高质量的热解气。热解终温是热解气化过程主要的决定因素，在先到达热解终温，再通入水蒸气的操作条件下，升温速率的改变对气化效果的影响并不突出。试验在最佳条件(采用粉末物料，在1000℃下进行热解)下，可以得到高热值(10MJ／m^3)合成气和较高的产气率(1．7m^3／kg)。     

Oxy–steam gasification of biomass for hydrogen rich syngas production using downdraft reactor configuration

The paper focuses on the use of oxygen and steam as the gasification agents in the thermochemical conversion of biomass to produce hydrogen rich syngas, using a downdraft reactor configuration. Performance of the reactor is evaluated for different equivalence ratios (ER), steam to biomass ratios (SBR) and moisture content in the fuel. The results are compared and evaluated with chemical equilibrium analysis and reaction kinetics along with the results available in the literature. Parametric study suggests that, with increase in SBR, hydrogen fraction in the syngas increases but necessitates an increase in the ER to maintain reactor temperature toward stable operating conditions. SBR is varied from 0.75 to 2.7 and ER from 0.18 to 0.3. The peak hydrogen yield is found to be 104 g/kg of biomass at SBR of 2.7. Further, significant enhancement in H₂ yield and H₂ to CO ratio is observed at higher SBR (SBR = 1.5–2.7) compared with lower range SBR (SBR = 0.75–1.5). Experiments were conducted using wet wood chips to induce moisture into the reacting system and compare the performance with dry wood with steam. The results clearly indicate the both hydrogen generation and the gasification efficiency (η_g) are better in the latter case. With the increase in SBR, gasification efficiency (η_g) and lower heating value (LHV) tend to reduce. Gasification efficiency of 85.8% is reported with LHV of 8.9 MJ Nm^?3 at SBR of 0.75 compared with 69.5% efficiency at SBR of 2.5 and lower LHV of 7.4 at MJ Nm^?3 at SBR of 2.7. These are argued on the basis of the energy required for steam generation and the extent of steam consumption during the reaction, which translates subsequently in the LHV of syngas. From the analysis of the results, it is evident that reaction kinetics plays a crucial role in the conversion process. The study also presents the importance of reaction kinetics, which controls the overall performance related to efficiency, H₂ yield, H₂ to CO fraction and LHV of syngas, and their dependence on the process parameters SBR and ER. Copyright © 2013 John Wiley & Sons, Ltd.     

生物质气化(干馏)过程的物料衡算分析

生物质干馏气化是将秸秆、薪柴等农林剩余物在一定的热力学条件下转化为可燃气、固体炭、液体产物(木醋液和木焦油)的过程.该反应过程受原料特性、反应温度等诸多因素影响,同时各产物间有不同程度的转换.文章结合北京联合创业建设工程有限公司建设的多个工程实例,以实际生产数据为基础,对生物质干馏气化过程进行物料衡算,运用spas对生产数据进行分析处理,并与理论计算数据进行比较,以期为生物质干馏气化技术的实际应用提供可靠的理论依据.     

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.     

生物质水蒸气气化利用过程数学模型的建立

分析了甘蔗渣的水蒸气气化过程,基于气化过程的物料平衡和化学平衡关系,建立了一种生物质气化过程的数学模型。用该模型模拟计算甘蔗渣在水蒸气氛围下气化后的气体成分,计算结果与试验数据基本相符,尤其在温度950℃之后,计算值和测量值更接近。以甘蔗渣和木薯渣为例,研究该气化模型的特性。甘蔗渣和木薯渣水蒸气气化的最佳水蒸气/燃料值(S/B)分别为0.3和0.2。气化气组分和气化效果随温度和S/B变化的结果表明:提高温度有利于气化反应的进行,提高S/B,可以增加气体产率,气体热值有所降低。     

生物质在高频耦合等离子体中的热解气化研究

采用高频电容耦合等离子体热解技术对生物质原料进行了热解气化试验，研究气体产物产率、成分随反应条件的变化规律。反应在3000-8000Pa的真空范围内进行，热解温度为1000～2000K。该技术可大幅度提高生物质气的热值及产率，本试验中产气率达到了66％以上，并且还有提高的潜力。     

Inhibition of steam gasification of biomass char by hydrogen and tar

The influence of hydrogen and tar on the reaction rate of woody biomass char in steam gasification was investigated by varying the concentrations in a rapid-heating thermobalance reactor. It was observed that the steam gasification of biomass char can be separated into two periods. Compared with the first period, in the second period (in which the relative mass of remaining char is smaller than 0.4) the gasification rate is increased. These effects are probably due to inherent potassium catalyst. Higher hydrogen partial pressure greatly inhibits the gasification of biomass char in the first and second periods. By calculating the first-order rate constants of char gasification in the first and second periods, we found that the hydrogen inhibition on biomass char gasification is caused by the reverse oxygen exchange reaction in the first period. In the second period, dissociative hydrogen adsorption on the char is the major inhibition reaction. The influence of levoglucosan, a major tar component derived from cellulose, was also examined. We found that not only hydrogen but also vapor-phase levoglucosan and its pyrolysates inhibited the steam gasification of woody biomass char. By mixing levoglucosan with woody biomass sample, the pyrolysis of char proceeds slightly more rapidly than with woody biomass alone, and gas evolution rates of H₂ and CO₂ are larger in steam gasification.     

Experimental research for biomass steam gasification in a fluidized bed

A fluidized bed gasification system was built to investigate the biomass steam gasification performance in different conditions. Medium heating value syngas with 34% H₂ content and no more than 20 g/Nm³ tar content could be obtained under 800°C with a S/B (steam vs. biomass ratio) of 0.9 by using olivine as bed material. The results indicated that syngas quality (including H₂ content, gasification efficiency, tar reduction, etc.) is in a positive correlation with temperature and S/B, but has a negative correlation with fluidization number (FN). Compared with quartz sand and dolomite, olivine is more suitable for fluidized bed because of its catalytic ability and good abrasion performance for fluidized bed gasifier. As a result, a set of optimum parameters is recommended with S/B of 0.9~1.0, FN of 1.4, and temperature of 800°C in this study.

Tar is a by-product from the gasification process, which will cause the pipeline congestion, reduce the gasification efficiency, and deteriorate the working condition. According to this experiment, the temperature and S/B both have a negative effect on tar content, while tar content increased with increase in the FN. Dolomite and olivine both have an inhibition function on tar, and the olivine is considered the best choice of bed material because of its good anti-wear properties.     

Experimental investigation of a multi‐stage air‐steam gasification process for hydrogen enriched gas production

To achieve hydrogen‐rich and low‐tar producer gas, multi‐stage air‐blown and air‐steam gasification processes were studied in this research. Results showed that the tar content from multi‐stage air‐blown and air‐steam gasification were lower, compared to the average value of that from downdraft gasification. In the cases of air supplies of 80, 100 l min^?1 and 100, 100 l min^?1 with steam, hydrogen yields were increased by 40.71 and 41.62%, respectively, compared to that without steam. These were about 1.6 times of hydrogen flow rate of the base case (S/B = 0). However, it was found that too much steam added to the process was disadvantageous. The equilibrium model was also applied to predict the hydrogen production and the composition of producer gas obtained from the multi‐stage air‐blown and air‐steam gasification processes. The predicted result showed a better match for the case of multi‐stage air‐blown gasification process. Copyright © 2010 John Wiley & Sons, Ltd.     

Novel hydrogen‐rich gas production by steam gasification of biomass in a research‐scale rotary tubular helical coil gasifier

The concept of biomass steam gasification offers platform for production (i) of hydrogen, (ii) hydrocarbons and (iii) value added chemicals. Majority of these developments are either in nascent or in pilot/demonstration stage. In this context, there exists potential for hydrogen production via biomass steam gasification. Gaseous products of biomass steam gasification consist of large percentage of CO, CH₄ and other hydrocarbons, which can be converted to hydrogen through water‐gas‐shift reaction, steam reforming and cracking respectively. Although there are many previous research works showing the potential of production of hydrogen from biomass in a two stage process, challenges remain in extended biomass and char gasification so as to reduce the amount of carbon in the residual char as well as improve conversion of heavy hydrocarbon condensates to hydrogen rich gas. In the current work, the characteristics of biomass steam gasification in an in‐house designed rotary tubular helical coil reactor at temperatures less than 850 °C, in the presence of superheated steam, were presented. The objectives were to obtain high carbon conversion in the primary biomass steam gasification step (upstream) and high product gas yield and hydrogen yield in the secondary fixed bed catalytic step (downstream). The influence of temperature, steam‐to‐biomass ratio and residence time on product gas yield in the rotary tubular helical coil gasifier was studied in detail using one of the abundantly available biomass sources in India‐rice husk. Further, enhancement of product gas yield and hydrogen yield in a fixed bed catalytic converter was studied and optimized. In the integrated pathway, a maximum gas yield of 1.92 Nm³/kg moisture‐free biomass was obtained at a carbon conversion efficiency of 92%. The maximum hydrogen purity achieved under steady state conditions was 53% by volume with a hydrogen yield of 91.5 g/kg of moisture‐free biomass. This study substantiates overall feasibility of production of high value hydrogen from locally available biomass by superheated steam gasification followed by catalytic conversion. Copyright © 2016 John Wiley & Sons, Ltd.     

Neural network modeling of biomass gasification for hydrogen production

Hydrogen plays a significant role as an alternative feedstock in the production of several industrial chemicals such as methanol and ammonia; it can also be used as a clean fuel for power generation in the Internal Combustion (IC) engines and Proton Exchange Membrane (PEM) fuel cells. The main objective of this work is to develop a computer-based model based on the experimental data to predict the gasification behavior of biomass particles for hydrogen and syngas production. The results showed that an increase in gasification temperature significantly increased the hydrogen yield and CGE. The maximum CGE also found to be increased by about 230% when the reaction temperature increases from 700 to 900 ^?C.     

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.     

生物质超临界水催化气化制氢实验系统

生物质超临界水催化气化制氢是一项很有价值的离新技术,它有利于开发广泛的生物质资源,为大规模的制氢提供一条高效、清洁的途径。针对生物质超临界水气化制氢,国内外结合工作具体要求和条件,设计出了一系列生物质超临界水催化气化制氢的实验系统。主要对国内外几种较好的生物质超临界水催化气化制氢实验进行了综合评述,分析了各类实验系统存在的问题及待改进之处。     

小型生物质气化发电系统的设计与测试

对小型生物质气化发电系统进行了设计和测试分析,阐述了以农作物秸秆为原料的小型生物质气化发电系统的技术可行性,总结出分散式的生物质能利用模式具有投资少、见效快并且易于操作和管理等优点,认为在未来一段时间内,该系统的推广、应用具有一定的可行性和优越性。     

High temperature steam-only gasification of woody biomass

We have studied a high temperature steam gasification process to generate hydrogen-rich fuel gas from woody biomass. In this study, the performance of the gasification system which employs only high temperature steam exceeding 1200 K as the gasifying agent was evaluated in a 1.2 ton/day-scale demonstration plant. A numerical analysis was also carried out to analyze the experimental results. Both the steam temperature and the molar ratio of steam to carbon (S/C ratio) affected the reaction temperature which strongly affects the gasified gas composition. The H₂ fraction in the produced gas was 35–55 vol.% at the outlet of the gasifier. Under the experimental conditions, S/C ratio had a significant effect on the gas composition through the dominant reaction, water–gas shift reaction. The tar concentration in the produced gas from the high temperature steam gasification process was higher than that from the oxygen-blown gasification processes. The highest cold gas efficiency was 60.4%. However, the gross cold gas efficiency was 35%, which considers the heat supplied by high temperature steam. The ideal cold gas efficiency of the whole system with heat recovery processes was 71%.     

生物质热解制炭与制气一体化研究

在自行设计的管式炉上进行生物质热解制炭与制气一体化研究,对生物质种类和热解终温两个因素进行了实验和分析,得到了生物质热解过程中气体析出的规律和固体炭的产率。当以制炭和制气一体化为目的,在4种生物质原料中选用麦秆,热解终温选择500℃时,可以得到较大的固体炭产率和气体析出浓度。     

污泥热解残渣水蒸气气化制取富氢燃气

采用固定床反应器,进行了污泥热解残渣水蒸气气化制取富氢燃气的研究。考察了反应温度、固相停留时间、水蒸气流量及催化剂对气化效果及气体产物组成的影响。结果表明:随着反应温度的升高,气体产率由0.096 7 m3/kg逐渐增加到0.460 0 m3/kg,燃气中H2含量由17.87%逐渐增加到52.44%;在最佳固相停留时间为15min时,气体产率达到0.540 m3/kg;最佳水蒸气流量为1.19 g/min,此时产气量达到最大值0.61 m3/kg,H2含量为64.7%;添加催化剂有利于气体中H2含量的提高。     

A techno-economic review of biomass gasification for production of chemicals

Gasification is a thermochemical process which can be used as a low-emission and highly efficient method to produce syngas and chemicals such as biomethanol and dimethyl ether (DME). In this paper, a review of technologies and methods for economic production of chemicals through gasification of biomass and other fuels has been carried out. A variety of techno-economic studies and analysis have been proposed in order to better understand the technical and economic assessments during the biomass gasification. Results showed that the methanol production cost for biomass (wood) is from 195 to 935 €/t, for waste residues is from 200 to 930 €/t, for coal is from 160 to 480 €/t, and for natural gas is from 90 to 290 €/t. It also concluded that fuel (wood) cost has positive linear relationship with ethanol production cost, meaning as the feedstock cost increases from 30 to 50 $/day-ton, the ethanol production cost enhances from 1.66 to 1.95 $/gal.