One step methane production based on catalytic pressurized calcium looping gasification with in-situ CO2 capture and self-sustained heat supply

Catalytic steam hydrogasification of coal is a direct method for methane production. Calcium looping concept is usually used in coal gasification process for in-situ carbon dioxide removal and heat supply. In this paper, a new process combining catalytic steam hydrogasification and calcium looping was proposed and investigated using a self designed instantaneously feeding reactor under high-temperature and pressurized conditions. The effects of operation conditions (including hydrogen concentration with a range of 0–50 vol%, gasification pressure with a range of 0.1–3.5 MPa, gasification temperature with a range of 700–800 °C, and gasification-calcination cycle number up to six) on the performance of the new process have been studied. The results show that: (i) increasing H₂ concentration is beneficial to methane products; (ii) high temperature and low pressure are not conducive to methane production and carbon dioxide capture as well as the self-sustained heat supply in gasifier; (iii) the methane content and carbon conversion can be maintained at 30–40 vol% and 75–80% for the durability tests. According to the performance of gas products, 750 °C 3.5 MPa and Ca/C = 0.5 are suggested for the new process. In addition, the gasification reactivity can be affected by the Ca–K-Char interaction as indicated by the XRD, FT-IR and SEM-EDX analysis.     

零排放煤基发电系统关键设备的化学动力学分析

零排放煤基发电技术是近年来为了克服常规动力系统中煤等化石燃料直接燃烧时存在能源转换率低、环境保护压力大等能源环境问题,和常规煤气化过程中能耗偏大等缺点而出现的一门高效、清洁煤利用技术。在系统概念设计的工作条件下,对实现煤加氢气化零排放发电的四个关键设备(气化炉、碳化塔、煅烧炉和燃料电池)进行了化学动力学分析,研究了温度和压力的变化对其中进行的化学反应的影响,得到了使反应能够进行和维持较高平衡转化率的温度和压力条件。     

Catalytic activities of ion-exchanged nickel and iron in low temperature hydrogasification of raw and modified birch chars

Raw, HNO₃ oxidized and carboxymethylated birch woods loaded with nickel or iron by the ion-exchange method were carbonized at 500 °C in a flow of nitrogen, and the resulting chars were hydrogasified in a thermobalance to examine their reactivities below 700 °C. The amounts of ion-exchanged metals on raw char were too small to give high gasification reactivity. However, oxidized and carboxymethylated woods with increased ion-exchange capacity produced much more reactive chars. Both nickel and iron exhibited larger catalytic activities on carboxymethylated chars than on oxidized chars, because better metal dispersion could be achieved on carboxymethylated wood with its larger cation exchangeability. It was noteworthy that only 1 wt% loading of iron, as well as nickel, on carboxymethylated char was sufficient to attain a gasification of 90 wt% at 700 °C. It was also noted that the catalytic effect, up to 600 °C, of iron on the gasification of oxidized and carboxymethylated chars was larger than that of nickel. This is ascribed to two factors; greater catalytic activity of metallic iron formed during the gasification than that of nickel metal, and low ash level in the chars. Above 600 °C, however, serious loss of activity of the iron was observed in the absence of wood ash. This showed the different influence of wood ash on the catalysis of iron in the low and high temperature regions.     

Chemistry of methane formation in hydrogasification of aromatics. 1. Non-substituted aromatics

The chemistry of the formation of methane in hydrogasification of such unsubstituted aromatics as benzene, naphthalene, phenanthrene, anthracene and biphenyl was studied using a flow tube. Temperatures varied between 800 and 1000 °C. Gases and benzene were analysed by on-line gas chromatography, the tar products being analysed by mass spectrometry. At short residence times up to 10 s, methane yields increase with decreasing stability of the aromatics; that is from benzene to naphthalene, phenanthrene and anthracene. As decreasing thermal stability also promotes carbon formation as a competitive reaction, the methane yields from the less reactive aromatics may exceed those of the reactive aromatics if the residence time is prolonged. In addition to thermal stability the position of the primary bond rupture is important because it determines the structure of intermediate products.     

Synthesis gas production using steam hydrogasification and steam reforming

Experimental work has been carried out on the mixed reforming reaction, i.e., simultaneous steam and CO₂ reforming of methane under a wide range of feed compositions and four different reaction temperatures from 700 °C to 850 °C using a commercial steam reforming catalyst. The experiments were conducted for a CO₂/CH₄ ratio from 0 to 2 and a steam to methane ratio from 3 to 5. The effect of CO₂/CH₄ ratio on the exit H₂/CO ratio and the conversions of the reactants indicate that the dry reforming reaction is dominant under increased carbon dioxide in the feed. Steam reforming of typical steam hydrogasification product gas consisting of CO, H₂ and CO₂ in addition to steam and methane has also been investigated. The H₂/CO ratio of the product synthesis gas varies from 4.3 to 3.7 and from 4.8 to 4.1 depending on the feed composition and reaction temperature. The CO/CO₂ ratios of the synthesis gas varied from 1.9 to 2.9 and 2.0 to 3.3. The results are compared with simulation results obtained through the Aspen Plus process simulation tool. The results demonstrate that a coupled steam hydrogasification and reforming process can generate a synthesis gas with a flexible H₂/CO ratio from carbon-containing feedstocks.     

煤直接加氢制甲烷研究进展

天然气资源短缺、低阶煤资源利用问题突出,开发新型、高效和对环境友好的低阶煤制甲烷工艺成为研究热点。本文分析讨论了以下几方面:温度、压力、催化剂、煤种和气化剂等因素对煤直接加氢制甲烷过程的影响;煤直接加氢制甲烷的反应机理和动力学;3种典型煤直接加氢甲烷化工艺的优缺点;本文作者课题组正在研究开发的低阶煤炭化脱氧、高活性半焦直接加氢制甲烷工艺及其特点。分析认为:以低阶煤(生物质)为原料进行加氢甲烷化生产代用天然气成为新的研究重点,其中又以新型、廉价煤加氢甲烷化催化剂的研制和新型甲烷化反应器的开发最为关键。     

煤的加氢气化研究

在固定床加压反应器和加压热天平上对五种中国气化用煤进行加氢气化试验，探讨了煤在氢气中的气化特性，以及气化条件对气化结果的影响。发现在气化过程中。各类产品气体的生成速率都随温度而变化。甲烷和乙烷的生成速率在600℃左右可达到最大值．在常压到6MPa的压力范围内，气化速率，转化率，甲烷产率都随压力的提高而增加，呈朗格谬尔吸附等温线形状。当压力高于2MPa时，煤气中(不包括H2)烃类化合物的含量达到或超过90%．在850-1000℃的气化温度下．某些煤焦的加氩反应表现活化能为100kJ／mol左右．建立了动力学模型，较好地拟合了各项实验结果．     

Inhibition of hydrogasification of brown coals by moisture: Influence of heating rate, temperature and pressure

Two types of Rheinische Braunkohle with different mineral matter contents, each with two different moisture contents plus a coke produced from the coal with the lower ash content, were gasified at total pressures between 0.2 and 5 MPa with pure or dry hydrogen, hydrogen/water vapour and argon/water vapour mixtures. In studies with controlled heating (4 K min⁻¹ up to 850 °C) it was found that: 1. methane formation rates and methane yields during gasification in dry hydrogen are drastically lowered with increased moisture of the coals but only at high pressures which reduce evaporation of water; 2. methane formation rates and methane yields during gasification with wet hydrogen (x_H2o = 0.02) are generally lowered with all materials; 3. increasing the water content does not further lower the yields or lead to water vapour gasification. Studies at constant temperature (after rapid heating, 100 K s⁻¹) confirmed these results. It was found that increasing the temperature to 950 °C does not eliminate the inhibiting effect of moisture (in hydrogen) if hydrogen pressure is low ≈ ≤ 1 MPa. It was also determined that raising the temperature above 850 °C with a simultaneous increase in pressure up to 5 MPa hydrogen effectively prevented the inhibition by moisture. It was concluded that extremely stable ether bridges are blocking the active sites at the carbon suface and are therefore responsible for the inhibitory effect of moisture in hydrogasification.     

Possibilities and state of development of nuclear coal gasification processes

By the development work of the last years and the successful operation of a experimental reactor it is clear today that the high temperature reactor is capable to produce heat at a temperature level of 950° C. This heat can be used in different industrial processes, especially for coal gasification. The processes of hydrogasification and steam gasification have been tested in large pilot plants in the past and are thought to be feasible today in connection with use of nuclear energy. In this paper the main aspects of these processes, of the nuclear reactor and of the heat exchanger system are presented and discussed. Questions like the choice and qualification of high temperature materials, the tritium contamination of the product gas and the aspects of licensing are key points of the technical realisation of nuclear process heat applications. This paper tries to summarize some of these results of the development programm of the PNP-Project (Prototyp Nukleare Prozeβwärme) in Germany, which is a common Projekt of German Companies financed by the government.     

褐煤分级转化制天然气新方法

我国能源结构和能源消费矛盾日益突出,开发清洁高效煤炭利用技术,成为了调整能源产业结构、实现能源产业可持续发展的有效手段,是增强国家能源安全、落实二氧化碳减排的战略举措。基于分级转化的思想和实验工作基础,提出了低温热解—热解半焦加氢气化制甲烷—甲烷化残渣气化制氢的褐煤分级转化制天然气的新方法,并从物质转化和能量利用的角度与传统煤制甲烷工艺进行分析比较,认为褐煤分级转化新方法通过多联产工艺对褐煤资源进行分质梯级利用,在能源利用效率和物质转化率方面较之传统煤制甲烷工艺具有显著优势,既提高了褐煤资源利用效率和产品资源价值,又增加了整个系统的经济效益。