褐煤气化及其影响因素分析

文中综述了国外有关褐煤气化影响因素的试验研究成果，并对各种影响因素进行了分析，提出了促进褐煤气化的一些建设性意见。     

煤质对固定床气化炉气化性能影响的工业试验研究

在使用烟煤作为设计气化燃料的Lurgi固态排渣气化炉上,进行了褐煤气化实验,获得了褐煤固定床气化的工业实验数据。通过优化实验,确定了煤质改变条件下的Lurgi固定床气化炉的最佳工艺参数,并获得了褐煤的最佳气化指标。研究表明,针对煤质的特殊性采取一些针对性措施,可以在使用烟煤的固定床气化炉上完成褐煤气化,为设计褐煤固定床气化提供有力的参考。     

褐煤造气锅炉的设计特点

文章主要介绍褐煤气化的产生机理，燃褐煤煤气锅炉的设计构想、设计特点、经济价值。     

CuFe2O4氧载体与小麦秆-煤化学链共气化研究

以小麦秆与印尼褐煤为原料,制备具有尖晶石结构的CuFe₂O₄复合氧载体,在自制多功能反应器上,系统研究了CuFe₂O₄氧载体反应活性及小麦秆和印尼褐煤化学链共气化特性,重点关注小麦秆和煤不同掺混比、气化温度、氧载体过量系数和水蒸气输入量这4个关键运行参数的影响。结果表明：CuFe₂O₄复合氧载体中Cu-Fe的协同作用有助于晶格氧的有效传递和反应活性的提升,而小麦秆和印尼褐煤化学链共气化时碳转化率及冷煤气效率比单一燃料的大,促进了高品质合成气的形成;小麦秆和褐煤在与CuFe₂O₄化学链气化过程中的最优运行参数为共气化温度950℃、氧载体过量系数0.2、水蒸气通入体积流量0.125 mL/min、小麦秆-印尼褐煤掺混质量比1∶1,在此最优条件下,合成气产量高达1.262 m³/kg, H₂与CO体积比为1.69,碳转化率为89.7%,合成气选择性为63.2%。     

锡林浩特褐煤气化特性研究

利用同步热分析仪研究了制焦温度、气化温度以及升温速率等因素对煤焦气化特性的影响。研究结果表明:随着制焦温度的升高,煤焦的气化失重量减少,气化反应的时间延长,气化反应性略有降低。随着气化温度的提高,锡林浩特褐煤煤焦在相同时间内的碳转化率增加,煤焦的气化时间缩短,气化温度对煤焦的气化反应性有较大的影响。随着升温速率的增大,TG曲线、DTG曲线均向高温侧偏移。升温速率越大,相同温度时煤焦的碳转化率越低,气化反应速率达到峰值对应的气化温度随升温速率的增大而升高。随着升温速率的增大,煤焦气化反应活性变好,气化反应进行的更加剧烈。     

立式锅炉燃用褐煤型煤的研究

我国褐煤资源十分丰富。约占煤炭总储量的13.8％。靠近东北地区的内蒙,建的三个大型露天矿均为褐煤矿。吉林省煤炭总产量的三分之一是褐煤。褐煤资源的应用技术在我国发展较慢。目前,褐煤主要用于发电,工业锅炉中的沸腾炉也耗用一部分。由于褐煤散烧着火困难,发热值又较低,层燃锅炉及民用炉灶难以燃用。工业发达国家褐煤资源的利用技术比较发达,除部分气化燃烧外,大部分加工成型煤燃用。据1980年统计,西德年产褐煤1.4亿吨,而褐煤砖产量     

石油焦的气化反应特性

针对3种不同的石油焦，在热天平上考察了不同的化学反应条件，包括温度、压力和气氛等因素对气化反应的影响．研究结果发现，在水蒸气气氛下石油焦具有良好的气化反应活性，而在二氧化碳气氛下石油焦气化反应进行得相当缓慢，相同条件下的C-H2O反应速率是C-CO2反应速率的十几倍，在60％水蒸气的实验温度条件下，每升高50℃，平均气化反应速率提高1倍；1000℃时，水蒸气分压对平均气化反应速率的影响不均匀，分压增加，影响减小．随着反应的不断进行，气化反应速率存在最大值，而出现最大值时的转化率不受反应温度和压力的影响，而与气化介质有关．根据实验结果，分析得到了3种石油焦在水蒸气条件下反应速率与温度、水蒸气分压和转化率的关系式，并得到了3种石油焦气化反应的活化能。     

燃用褐煤气化燃料的燃气轮机电站

对在邱允弗莱索瓦一个现有的褐煤气化厂内装设的两台９Ｅ型燃气轮机联合循环装置的情况作了介绍,特别是在能源利用最佳化,燃料适应性,环保和良好的社会影响等方面进行了描述。     

水分对褐煤燃烧特性及锅炉性能的影响

以660 MW褐煤锅炉为对象,研究了含水量升高对褐煤燃烧特性及锅炉性能的影响。模拟中采用一种特殊的方法来考虑褐煤中水分的存在,计算准确性高。研究结果表明:水分较高的褐煤炉膛温度相对较低,炉内受热面吸热量减少,但气体发射率变大使得屏区的辐射传热差异相比水冷壁减小。水分含量升高对炉内气化反应有促进作用,但总体影响小于温度降低带来的抑制作用。高含水率煤的未燃尽碳浓度升高,煤粉燃尽变差,锅炉整体效率降低。因此,实际锅炉运行时不宜燃用超过设计燃料水分太大的褐煤。     

提质条件对褐煤表观性质的影响研究

在不同的加热温度、保温时间、粒度提质条件下,对内蒙古锡林浩特褐煤进行低温干燥,研究了提质后褐煤的表观性质,分析了提质前后褐煤的水分、挥发分、发热量的变化,得出各提质条件对褐煤表观性质的影响从大到小依次为煤样粒度、加热温度、保温时间.综合考虑提质条件对褐煤表观性质的影响、提质后所需褐煤的水分和挥发分要求以及现有的试验设备和试验条件等因素考虑,最终确定褐煤干燥提质的条件为:煤样粒度6 mm,加热温度200 ℃,保温时间20 min.     

Direct production of hydrogen-enriched syngas by calcium-catalyzed steam gasification of Shengli lignite/chars: Structural evolution

Calcium has been proved to be efficient for the catalytic steam gasification of lignite. In this study, we studied the steam gasification of lignite with Ca(OH)₂ added by wet impregnation for to produce hydrogen. The effect of calcium on the microstructural evolution and char gasification behavior in the presence of steam were studied. The distribution of the gaseous products was examined by using fixed-bed micro reactor equipment for steam gasification. Partially gasified chars obtained at different temperatures (400, 500, 600, and 700 °C) in the gasification process were characterized by scanning electron microscopy coupled with energy dispersive spectroscopy, ¹³C nuclear magnetic resonance, Fourier-transform infrared spectroscopy, and Raman spectroscopy. The results suggested that a “Ca-carboxylate-like structure” was formed due to the addition of calcium to lignite. This Ca-carboxylate-like structure increased the thermal stability of the original carboxylic structure in lignite. As a result, the calcium-added coal retained more oxygen-containing structures, formed more defects, and possessed significantly lower aromatic structures due to the formed Ca-complexes during steam gasification. Therefore, it can be inferred that the Ca-complexes in the lignite char increased the gasification reactivity of char.     

Detailed kinetic analysis and modelling of the dry gasification reaction of olive kernel and lignite coal chars

The dry gasification process of solid fuels is a promising pathway to mitigate and utilize captured CO₂ emissions toward syngas generation with tailored composition for several downstream energy conversion and chemical production processes. In the present work, comprehensive kinetic analysis and reaction modelling studies were carried out for olive kernel and lignite coal chars gasification reaction using pure CO₂ as gasifying agent. Chars reactivity and kinetics of the gasification reactions were thoroughly examined by thermogravimetric analysis at three different heating rates and correlated with their physicochemical properties. The reactivity of olive kernel char, as determined by the mean gasification reactivity and the comprehensive gasification characteristic index, S, was almost three times higher compared to that of the lignite coal char. It was disclosed that the fixed carbon content and alkali index (AI) have a major impact on the reactivity of chars. The activation energy, E_a, estimated by three different model-free kinetic methods was ranged between 140 and 170 kJ/mol and 250–350 kJ/mol for the olive kernel and lignite coal chars, respectively. The activation energy values for the lignite coal char significantly varied with carbon conversion degree, whereas this was not the case for olive kernel char, where the activation energy remained essentially unmodified throughout the whole carbon conversion range. Finally, the combined Malek and Coats-Rendfrem method was applied to unravel the mechanism of chars-CO₂ gasification reaction. It was found that the olive kernel char-CO₂ gasification can be described with a 2D-diffusion mechanism function (D2) whereas the lignite coal char-CO₂ gasification follows a second order chemical reaction mechanism function (F2).     

Towards the improvement of thermal efficiency in lignite‐fired power generation: Concerning the utilization of Polish lignite deposits in state‐of‐the‐art IGCC technology

Integrated coal Gasification Combined Cycle (IGCC) is the most advanced technology for coal‐fired power generation. The two‐stage entrained flow gasification process allows for the use of a wide range of coal, as long as the gasification temperature is above the ash melting point of a used fuel. In this gasification technology, lignite, which often has a low ash melting point, can be preferably utilized. However, ash fluidity is also another importance, because the behaviour of molten slag can diminish a stable ash discharge from a gasifier. As the eligibility of coal ash properties is a considerable factor, water physically and chemically kept in lignite (30 – 60% in mass) attributes to deteriorating gasification efficiency, because it causes significant heat loss and increasing oxygen consumption. Developing a thermal evaporative lignite drying method will be a necessary attempt to apply lignite to the coal gasification process. For those preceded objectives, coal and ash properties and drying characteristics of several grades of Polish lignite, extracted from Belchatow and Turow deposits, have been experimentally investigated in a preliminary study evaluating the applicability and consideration for its utilization in state‐of‐the‐art clean coal technology, IGCC. This paper particularly discusses the eligibility of Polish lignite from the perspective of the fusibility and fluidity of ash melts and the fundamental drying kinetics of lignite in superheated steam in the light of water removal. The viscosity of ash melts is measured at high temperature up to 1700 °C. In the drying tests, the significant influence of structural issues, because of the provenance and origin of lignite on the drying characteristics, was found by applying the method of sensitivity analysis of physical propensity. This paper concludes that the investigated Polish lignite has characteristics favourable for utilization in IGCC technology, once the precautions related to its high moisture have been carefully addressed. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

Petrographic composition of the ex-situ lignite gasification residues

The article presents the results of the petrographic analysis of the lignite from Turów deposit and the residues formed during its ex-situ gasification. The analysis used seven spot samples, representing different transformation areas, collected from the residues. The obtained results, compared with the lignite before the gasification, have shown that changes in the petrographic composition correspond to the temperature distribution during the process. The highest amounts of gasified particles, represented by inertoid-type chars, were observed in samples collected from areas where the temperature exceeded 600°C. The unchanged lignite macerals dominated in samples from areas where the temperature was below 200°C.     

Energy absorption characteristics and kinetics of carbonaceous solid waste gasification with copper slag as heat carrier

High energy consumption is the bottleneck for gasification technology of carbonaceous waste. Exactly, copper slag has such cheap and huge energy that can be used. Copper slag waste heat can provide energy and metallic oxide in copper slag has catalytic effect on carbonaceous solid waste gasification reaction. The gasification energy absorption characteristics and kinetics of typical solid waste, sludge, enteromorpha and lignite with air as oxidation agent has been studied using copper slag as heat carrier. Gasification reaction of waste is scored as multi-stage reactions. For sludge and enteromorpha gasification reactions, there are two and three reaction stages respectively. Gasification reaction rate becomes unstable when copper slag added. The addition of copper slag has little effect on the peak value and peak temperature. Pyrolysis reaction rate of heat absorption is controlled by material diffusion. At medium and high temperature, the limitation of gasification endothermic reaction of sludge and enteromorpha is chemical reaction rate. When copper slag added, the total energy absorption of lignite, sludge and enteromorpha are 11285.8 mw/mg, 8994.2 mw/mg and 9461.7 mw/mg respectively. Copper slag has catalytic decomposition effect on the gasification reaction at high and medium temperature, and improves the heat exchange rate.     

Effect of fuel blend composition on hydrogen yield in co-gasification of coal and non-woody biomass

In this study, torrefaction of sunflower seed cake and hydrogen production from torrefied sunflower seed cake via steam gasification were investigated. Torrefaction experiments were performed at 250, 300 and 350 °C for different times (10–30 min). Torrefaction at 300 °C for 30 min was selected to be optimum condition, considering the mass yield and energy densification ratio. Steam gasification of lignite, raw- and torrefied biomass, and their blends at different ratios were conducted at downdraft fixed bed reactor. For comparison, gasification experiments with pyrochar obtained at 500 °C were also performed. The maximum hydrogen yield of 100 mol/kg fuel was obtained steam gasification of pyrochar. The hydrogen yields of 84 and 75 mol/kg fuel were obtained from lignite and torrefied biomass, respectively. Remarkable synergic effect exhibited in co-gasification of lignite with raw biomass or torrefied biomass at a blending ratio of 1:1. In co-gasification, the highest hydrogen yield of 110 mol/kg fuel was obtained from torrefied biomass-lignite (1:1) blend, while a hydrogen yield from pyrochar-lignite (1:1) blend was 98 mol/kg. The overall results showed that in co-gasification of lignite with biomass, the yields of hydrogen depend on the volatiles content of raw biomass/torrefied biomass, besides alkaline earth metals (AAEMs) content.     

Comparison between isothermal and microwave gasification of lignite char for high syngas production

Using the water of lignite as gasification agent, this paper mainly studies the influence of microwave and isothermal gasification on the syngas production and H₂/CO ratio to obtain the maximum possible amount of high-quality syngas. The results show that microwave heating produced syngas had an immensely superior performance over conventional heating. The total gas yields of 1,000 W microwave gasification is 1.75 times more than that of the 1,000°C isothermal gasification. Moreover, the values of H₂/CO ratio obtained from microwave gasification was higher than 1,000°C isothermal gasification.     

Hydrogen-rich gas as a product of two-stage co-gasification of lignite/waste plastics mixtures

Under atmospheric pressure, mixtures of lignite with waste plastics were gasified on a laboratory scale. The resulting tar was cracked in a thermal cracking reactor. For experiments, low-ash and low-sulfur lignite was used; the percentage of waste plastics in the mixtures was 10 and 20 wt.%. The main product of co-gasification was hydrogen-rich gas, as by-products, soot and non-gasified solid residue were obtained. It was found that the higher heating value of obtained gas is fully comparable with that of industrial gas from lignite gasification. Probably, at least 20 wt.% of lignite can be replaced with mixed waste plastics in this process. The effect of waste plastics addition on properties of the obtained gas and of the non-gasified solid residue was evaluated and discussed.