生物质超临界水气化制氢反应建模及数值模拟

建立了管式反应器中生物质超临界水气化制氢反应的数学模型,同时提出了以葡萄糖做为生物质模型化合物的全局气化反应动力学模型。模型计算结果与实验值的比较表明该模型能较好的预测反应器出口温度与气体产物组份分布。利用该模型数值模拟计算得到了反应器中温度场、速度场基本情况以及化学反应速率分布的基本规律。该文通过计算还讨论了反应器入口水温、反应器壁温以及物料和预热水之比对反应器内气化反应的影响,得出一系列重要结论。该模型对生物质超临界水反应器系统的优化设计与化学反应最佳工况的选择有一定的实用价值。     

超临界水中木质素/CMC催化气化制氢

在间歇式高压反应釜中,以碱性化合物K_2CO_3和Ca(OH)_2以及Ru/C为催化剂,对木质素在超临界水中的气化制氢特性进行了实验研究。结果表明:3种催化剂都有较好的催化作用,其中Ru/C的效果最佳,几种催化剂混合使用的效果要比单独一种催化剂使用时好,但是其提高的幅度不很明显。另外,随着温度的升高,H_2和CH_4的产气量以及氢转化率等都相应的升高。     

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。     

多碟太阳能聚热与生物质超临界水气化耦合制氢

搭建了一套连续式多碟太阳能聚热与生物质超临界水气化耦合制氢系统,以生物质模型化合物(乙二醇、丙三醇、葡萄糖)为原料在该装置上进行了气化制氢实验,研究了太阳能直接辐照度(DNI)、物料成分、物料浓度、停留时间对气化效果的影响。实验结果表明:太阳能直接辐照度对太阳能吸收器腔内及反应器壁温的影响较大,进而能影响气化效果,在实验流量、压力范围内当DNI为363～656W/m2时,反应器出口流体温度达520～676℃,可以满足生物质超临界水气化制氢的温度及能量需要。0.1mol/L葡萄糖气化H2体积分数均值超过50%,H2产量为27.2mol/kg,气化率达109.7%。低物料浓度和长停留时间有利于气化效果的提高。实验验证了利用可再生的太阳能聚焦供热耦合生物质超临界水气化制氢是可行的。     

木质素在超临界水中气化制氢的实验研究

以木质素为原料,利用连续管流反应器,首先在反应压力为15.0～27.5MPa、反应器壁温为500～650℃、物料流速为4.7～7.5mL/min的条件下,对质量浓度为1%～3%的木质素在超临界水中进行了气化制氢的实验研究。针对实验中存在的问题,改造了反应器,着重考查壁面温度为700～775℃下高浓度木质素的气化效果。实验表明升高壁温能够极大提高木质素在超临界水中的气化效果,700℃以上木质素可以高效气化;升高压力有利于氢气质量产率的提高,并可促进甲烷化反应;而高浓度不利于木质素气化;降低流速,有利于提高氢气质量产率,但对气态产物中各组分气体的体积百分含量影响不大;相同条件下,木质素较纤维素更难气化,气化率较低。     

玉米芯在超临界水中气化制氢实验研究

以玉米芯为原料,羧甲基纤维素纳(CMC)为添加剂,利用连续管流反应器,在反应压力为22.5MPa~27.5MPa、反应器壁温为550℃~650℃、反应停留时间为0.33min~0.67min、物料浓度为3wt%~6wt%的条件下,对玉米芯超临界水气化制氢进行了实验研究。利用正交实验设计与分析方法,得到实验条件范围内玉米芯超临界水气化制氢的最佳反应参数,同时对气化过程主要操作参数的影响进行了分析。实验表明温度对气化影响最大,高温度有利于产氢,气化制氢的最佳压力为25MPa,反应停留时间越长气化越完全,低浓度生物质比高浓度生物质更容易气化。     

生物质在超临界水流化床反应系统中气化制氢实验研究

以生物质模型化合物葡萄糖为原料,在温度500～600℃,压力23～37胁范围内,利用新研制的超临界水流化床系统对其气化制氧特性进行研究,讨论了过程主要参数温度、压力、物料浓度以及催化剂添加对气化制氢的影响.实验结果表明:温度对气化影响最大,而压力对气化的影响较小,升高温度和压力都有利于产氢.随着物料浓度增加葡萄糖气化效果下降,在超临界水流化床气化制氢系统中实现30%葡萄糖的连续稳定气化.K_2CO_3提高气化率同时降低了产气中CO含量,ZnCl_2的加入虽对气化率影响不大,但大大提高了氢气的选择性.该文的实验研究验证了超临界水流化床气化制氢系统的有效性.     

生物质气化制氢研究现状

重点讨论生物质催化气化制氢的基本原理和基本过程，阐述生物质催化气化制氢、超临界水中生物质催化气化制氢、等离子体热解气化制氢的研究现状，指出生物质气化制氢的广阔前景。     

连续式超临界水中煤/CMC催化气化制氢

在向水煤浆中添加CMC（羧甲基纤维素钠），成功实现水煤浆高压均匀输送基础上，对超临界水中煤／CMC催化气化制氢性能进行了进一步研究。结果表明：在压力20～25MPa、停留时间15～30s、NaOH添加量0．1％、反应器外壁温650℃条件下，超临界水中煤/CMC催化气化制氢气体产物中H2摩尔含量远比常规气化高，主要气体产物是H2、CO2和CH4。增加物料中CMC的含量、升高压力均有利于提高气体产物中心的产量，延长停留时间虽有利于物料气化但不利于氢气的制取。     

串行流化床生物质气化制氢试验研究

基于串行流化床生物质气化技术,以水蒸气为气化剂,在串行流化床试验装置上进行生物质气化制氢的试验研究,考察了气化反应器温度、水蒸气/生物质比率(S/B)对气化气成分、烟气成分和氢产率的影响。结果表明:在燃烧反应器内燃烧烟气不会串混至气化反应器,该气化技术能够稳定连续地从气化反应器获得不含N_2的富氢燃气,氢浓度最高可达71.5%;气化反应器温度是影响制氢过程的重要因素,随着温度的升高,气化气中H_2浓度不断降低,CO浓度显著上升,氢产率有所提高;S/B对气化气成分影响较小,随着S/B的增加,氢产率先升高而后降低,S/B的最优值为1.4。最高氢产率(60.3g H_2/kg biomass)是在气化反应器温度为920℃,S/B为1.4的条件下获得的。     

Experimental research on catalysts and their catalytic mechanism for hydrogen production by gasification of peanut shell in supercritical water

Peanut shell, mixed with sodium carboxymethyl-cellulose, was gasified at a temperature of 450°C and a pressure range from 24 to 27 MPa with the presence of different catalysts, including K₂CO₃, ZnCl₂ and Raney-Ni. The experimental results show that different catalysts have greatly different effects on the reaction. Gasification efficiency (GE), hydrogen gasification efficiency (GHE), carbon gasification efficiency (GCE), yield of hydrogen production and potential yield of hydrogen production are applied to describe the catalytic efficiency. From the result of gaseous components, ZnCl₂ has the highest hydrogen selectivity, K₂CO₃ is lower, and Raney-Ni is the lowest, but Raney-Ni is the most favorable to gasify biomass among the three catalysts, and its G _E, G _HE, G _CE reach 126.84%, 185.71%, 94.24%, respectively. As expected, hydrogen selectivity increased and CH₄ reduced rapidly when the mixture of ZnCl₂ and Raney-Ni is used under the same condition. The optimization mixture appeared when 0.2 g of ZnCl₂ was added to 1 g of Raney-Ni, 43.56 g·kg⁻¹ of hydrogen production was obtained. In addition, the catalytic mechanisms of different catalysts were analyzed, and the possible reaction pathway was brought forward, which helped to explain the experiment phenomena and results correctly. __________ Translated from Journal of Xi’an Jiaotong University, 2006, 40(9): 1 263–1 267 [译自: 西安交通大学学报]     

Review of catalytic supercritical water gasification for hydrogen production from biomass

Hydrogen is defined as an attractive energy carrier due to its potentially higher energy efficiency and low generation of pollutants, which can replace conventional fossil fuels in the future. The governments have invested huge funds and made great efforts on the research of hydrogen production. Among the various options, supercritical water gasification (SCWG) is a most promising method of hydrogen production from biomass. Supercritical water (SCW) has received a great deal of attention as a most suitable reaction medium for biomass gasification because it is safe, non-toxic, readily available, inexpensive and environmentally benign. However, high temperature and pressure are required to meet the minimum reaction condition. Therefore, the high operating cost has become the biggest obstacle to the development of this technology. To overcome this bottleneck, many researchers have carried out intensive research work on the catalytic supercritical water gasification (CSCWG). Based on the previous studies stated in the literature, the authors try to give an overview (but not an exhaustive review) on the recent investigations of CSCWG. Besides, the physicochemical properties of SCW and its contributions in subcritical and supercritical water reaction are also summarized.     

Technical and economic evaluation of solar hydrogen production by supercritical water gasification of biomass in China

A novel thermochemical method for solar hydrogen production was proposed by state key laboratory of multiphase flow in power engineering (SKLMFPE) of Xi’an Jiaotong University. In this paper, a technical and economic evaluation of the new solar hydrogen production technology was conducted. Firstly, the advantages of this new solar hydrogen production process, compared with other processes, were assessed and thermodynamic analysis of the new process was carried out. The results show that biomass gasification in supercritical water driven by concentrating solar energy may be used to achieve high efficiency solar thermal decomposition of water and biomass for hydrogen production. Secondly, the hydrogen production cost was analyzed using the method of the total annual revenue requirement. The estimated hydrogen production cost was 38.46RMB/kg for the experimental demonstration system with a treatment capacity of 1 ton wet biomass per hour, and it would be decreased to 25.1 RMB/kg if the treatment capacity of wet biomass increased from 1 t/h to 10 t/h. A sensitivity analysis was also performed and influence of parameters on the hydrogen production cost was studied. The results from technical and economic evaluation show that supercritical water gasification of biomass driven by concentrated solar energy is a promising technology for hydrogen production and it is competitive compared to other solar hydrogen production technologies.     

Solar receiver/reactor for hydrogen production with biomass gasification in supercritical water

A novel receiver/reactor driven by concentrating solar energy for hydrogen production by supercritical water gasification (SCWG) of biomass was designed, constructed and tested. Model compound (glucose) and real biomass (corncob) were successfully gasified under SCW conditions to generate hydrogen-rich fuel gas in the apparatus. It is found that the receiver/reactor temperature increased with the increment of the direct normal solar irradiation (DNI). Effects of the DNI, the flow rates and concentration of the feedstocks as well as alkali catalysts addition were investigated. The results showed that DNI and flow rates of reactants have prominent effects on the temperature of reactor wall and gasification results. Higher DNI and lower feed concentrations favor the biomass gasification for hydrogen production. The encouraging results indicate a promising approach for hydrogen production with biomass gasification in supercritical water using concentrated solar energy.     

Hydrogen production from co-gasification of coal and biomass in supercritical water by continuous flow thermal-catalytic reaction system

Hydrogen is a clean energy carrier. Converting abundant coal sources and green biomass energy into hydrogen effectively and without any pollution promotes environmental protection. The co-gasification performance of coal and a model compound of biomass, carboxymethylcellulose (CMC) in supercritical water (SCW), were investigated experimentally. The influences of temperature, pressure and concentration on hydrogen production from co-gasification of coal and CMC in SCW under the given conditions (20–25 MPa, 650°C, 15–30 s) are discussed in detail. The experimental results show that H₂, CO₂ and CH₄ are the main gas products, and the molar fraction of hydrogen reaches in excess of 60%. The higher pressure and higher CMC content facilitate hydrogen production; production is decreased remarkably given a longer residence time. Translated from Journal of Xi’an Jiao Tong University, 2005, 39(5): 454–457 [译自: 西安交通大学学报]     

Hydrogen production by supercritical water gasification of biomass: Explore the way to maximum hydrogen yield and high carbon gasification efficiency

Supercritical water gasification (SCWG) is a promising technology for wet biomass utilization. In this paper, orthogonal experimental design method, which can minimize the number of experiments compared with the full factorial experiments, was used to optimize the operation parameters of SCWG with a tubular reactor system. Using this method, the influences of the main parameters including pressure, temperature, residence time and solution concentration on biomass gasification were also investigated. Simultaneously, in order to further improve the gasification efficiency of biomass, acid hydrolysis pretreatment of feedstock, oxidizers addition and increasing reaction temperature were employed. Results from the experiments show that in the range of experimental parameters, the order of the effects of the factors on H₂ yield of corn cob gasification in SCW is temperature > pressure > feedstock concentration > residence time. Temperature and pressure have a significant and complicated effect on biomass gasification. Hydrogen yield increases by the acid hydrolysis pretreatment of feedstock, and oxidizer addition reduces the hydrogen yield but it promotes the increase in carbon gasification efficiency. Biomass feedstock with high concentration was gasified successfully at high reaction temperature.     

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。     

Assessment of sugarcane bagasse gasification in supercritical water for hydrogen production

Sugarcane bagasse is one of the major resources of agricultural biomass waste in the world. In this work, supercritical water gasification characteristics of sugarcane bagasse were investigated. The effect of temperature (600–750 °C), concentration (3–12 wt%), residence time (5–20 min) and catalysts (Raney-Ni, K₂CO₃ and Na₂CO₃) on bagasse gasification were studied. A kinetic study on the non-catalytic and Na₂CO₃ catalytic bagasse gasification was conducted to describe the kinetic information of the bagasse gasification reaction. The results showed that a higher reaction temperature, a lower bagasse concentration and a longer residence time could favor the gasification of bagasse, leading to a higher hydrogen yield. Bagasse was nearly completely gasified at 750 °C without using any catalyst and the carbon gasification efficiency could reach up to 96.28%. The addition of employed catalysts remarkably promoted the bagasse gasification reactivity. The maximum hydrogen yield (35.3 mol/kg) was achieved at 650 °C with the Na₂CO₃ loading of 20 wt%. The experimental data fitted well with a homogeneous model based on a Pseudo-first-order reaction hypothesis. The kinetic study showed that Na₂CO₃ catalyst could lower the activation energy E_a of bagasse gasification from 117.88 kJ/mol to 78.25 kJ/mol.     

生物质热化学转化制氢技术

生物质是一种重要的可再生能源,是氢的载体,与矿物燃料相比,具有挥发分高,硫、氮含量低等优点。无论是从能源角度还是从环境角度,发展生物质制氢技术都具有重要的意义。目前有关生物质制氢方面的研究主要集中在热化学转换法和生物法,文章从热化学转换的角度,进行了几种生物质制氢路线的技术经济分析预测。