Study on a multifunctional energy system producing coking heat, methanol and electricity

A multifunctional energy system (MES) capable of consuming coke oven gas (COG) and coal, and simultaneously producing coking heat, methanol and electricity, was subject to an exergy analyses based on Energy Utilization Diagrams (EUDs). In this system a coal-fired coke oven is adopted to produce coke and COG, where non-coking coal is burned to supply thermal energy to the coking process. The COG and coal gas gasified from coal in a gasifier, were mixed to produce syngas for methanol synthesis. Since COG rich in hydrogen and coal gas rich in CO, the mixture of COG and coal gas can easily adjust the mole ratio of CO to H₂ of syngas instead of the conversional reforming and shift processes. The active component of syngas is firstly converted into methanol and then the rest is introduced to a gas turbine for power generation. As a result, the overall efficiency of the MES system is about 62.3%, and its energy savings ratio is about 15% comparing with individual systems. The paper provides a new approach to use coal more efficiently and cleanly.     

气化剂配比对气化炉性能的影响

为了实现能源利用的可持续发展,多联产技术可以对能量进行合理的利用.多联产系统不同于化工或动力分产系统,对气化炉性能有更具体的要求.通过化学平衡和热量平衡方法求解气化炉平衡工作温度以及该温度下的出口煤气成分,研究了气化炉进口气化剂配比对出口煤气成分、冷煤气效率、热效率及火用效率的影响,指出热效率、火用效率最优情况下适应于各煤种的最优氧煤比以及合理的水蒸气耗量,为多联产系统的设计优化提供参考.     

Application of oxygen ion-conductive membranes for simultaneous electricity and hydrogen generation

The high temperature of the air in power generation gas-turbine cycles involving natural gas (mainly methane) oxidation accounts for the utilization of ion-conductive membranes within solid oxide fuel cells (SOFCs) and membrane reactors (MRs). In SOFCs, the electricity is directly derived from the chemical exergy of methane (SOFCs with internal methane reforming are considered here). Within a membrane reactor (MR), which is considered a substitute for combustion chambers in traditional gas-turbine units, the ion-conductive membranes separate oxygen from air and allow the flow of the hot combustion products (carbon dioxide and steam) to be separated from air. It permits the use of combustion products which are not diluted in nitrogen in the process of methane conversion into hydrogen. A modified gas-turbine cycle that includes a SOFC stack, an MR (instead of a traditional combustion chamber), and a catalytic reactor to convert methane to hydrogen is proposed. An exergy analysis of the proposed system is conducted to evaluate its exergy efficiency and the exergy losses for the processes occurring within the system. It is shown that, in comparison to the traditional gas-turbine cycle, there is a significant reduction (more than three times) in the exergy losses for the most irreversible process occurring in the system, natural gas combustion. It is also found that the proposed cogeneration scheme, including both power generation and the industrial catalytic conversion of methane to hydrogen, permits improved efficiencies for both technologies. The efficiency of this cogeneration, as well as the reduction in exergy losses, is demonstrated by the following observation: if the value of energy (exergy) efficiency of hydrogen production is considered equal to that for a traditional process, the corresponding thermal (energy) efficiency for electricity generation would reach values of 80–96% depending on the efficiency of a SOFC stack. The combined SOFC and MR application also eliminates the possibility of toxic nitrogen oxides formation and, at the same time, makes carbon dioxide removal from flue gases feasible (due to its high concentration). The development of the proposed technology is especially important, within the context of the hydrogen economy, if the produced hydrogen is used as a fuel for fuel cell vehicles.     

Electrical efficiencies of methane fired, high- and low- temperature fuel cell power plants

The important system difference between power plants based on low temperature and high temperature fuel cells is that gas reforming and shift conversion is thermally decoupled from the cell in low temperature cell power plants whereas the gas process steps are performed at close to the elevated fuel cell temperatures in high temperature fuel cell power plants. This article elucidates the consequences: assuming equal electrical efficiencies for the respective cells (50%) it is shown that thermal decoupling leads to energy and exergy losses and sizably lower electrical system efficiencies because heat for the generation of the process steam necessitates the combustion of methane. Also hydrogen losses in the step for preferential oxidation of carbon monoxide (Selox process) and several heat transfer steps add to the lower efficiency of low temperature systems. Low temperature fuel cell power plants need 15–17% more fuel than high temperature fuel cell power plants for the same amount of electric energy. The theoretical comparison of an adiabatic LT and HT fuel cell process reveals that, with postulated electrical cell efficiencies of 50%, the theoretical electrical efficiency of the LT process is 6–7% points lower than that for the HT-process (35 vs. 41%). For exergy efficiencies also taking into account rejected heats, the numbers read 43 and 58%.     

煤炭热力学高效和化学高价值利用新工艺

提出一种煤炭热力学高效和化学高价值利用新工艺（TCCUC）,包括煤炭拔头技术-半焦富氧直燃制备燃气轮机高温工质系统-燃气发电-蒸汽发电系统-CO₂捕集技术-干馏拔头产物提质处理技术六个技术模块。该工艺通过煤干馏拔头和焦油加氢等技术,对煤中大分子碳氢化合物进行适当热解和对热解产物焦油加氢处理得到高价值的碳氢液体燃料,实现煤炭的化学高价值利用;通过高温过滤、半焦直燃、燃气轮机与蒸汽轮机相结合等方法,实现对煤炭燃烧过程中高位热能的充分利用,进一步提高热-电联产效率。     

合成气为核心的联供联产系统变工况特性

煤气化合成气为核心的多联供多联产系统是能源化工可持续发展的重要组成部分，联供因子和联产因子是影响多联供多联产系统性能的两个关键因素。以天然气辅助煤多联供甲醇电多联产系统为例，根据其结构特性，提出以甲醇合成模块中未反应合成气进燃气-蒸汽联合循环发电装置的分流比率为联产因子，以进系统天然气的与原煤的的比值为联供因子，考察系统规模、损率、产品成本分别跟随联供因子和联产因子单因素变量变化规律，并讨论煤炭价格和天然气价格对系统产品成本的影响。     

气和煤生产乙二醇合成气的原料路线选择探讨

介绍天然气转化和气煤联产氢碳互补制乙二醇合成气的工艺原理。对天然气部分氧化和气煤联产乙二醇合成气的工艺流程、原料消耗、CO2排放、动力消耗、投资、经济性进行比较。提出气煤联产和天然气部分氧化都是可行的乙二醇合成气生产路线。气煤联产有氢碳互补作用,水煤气无需变换,天然气消耗和氧耗低;天然气部分氧化流程简单、投资省、CO2排放少。经济比较,两种原料路线相差不大。     

Possibility of using paper sludge in co-firing applications

The possibility of co-processing paper sludge with coal in power plants for power production and useful products was investigated as an alternative to the disposal option. The thermal behaviour of the fuels and their blend during pyrolysis and combustion processes was studied, kinetic models were developed and the compatibility of each component in the blend was evaluated. The experiments were conducted in a thermogravimetric analysis system, at non-isothermal heating conditions, over the temperature range 25-850 °C. The effect of the inorganic constituents of the fuels and their mixture on thermal conversion characteristics, reactivity, slagging and fouling propensities and environmental pollution was examined.The thermochemical reactivity of the two fuels was different in both nitrogen and air. Devolatilization of paper sludge occurred earlier and with a higher rate, while its combustion was hindered by the high content of ash. When the two fuels were mixed their pyrolysis or combustion reactivities did not substantially change. A first-order parallel reactions model for pyrolysis and a power low model for combustion fitted the experimental results accurately. The kinetic parameters of the blend could be predicted from the data of the individual components. Co-firing paper sludge with subbituminous coal might somehow improve the slagging/fouling potential of the coal. However, if the mineral matter of paper sludge is partly removed before use, then the combustion behaviour of the mixture could resemble that of coal alone and the overall efficiency of the process would increase.     

低阶煤热解多联产与混合发电系统

中国煤资源中80%以上属于中高挥发分的低阶煤. 将煤炭进行热解分级,液体产物可转化为化学品和燃料油,气体产物可作为燃气或转化为天然气使用,固体半焦是洁净的固体燃料. 中国科学院过程工程研究所自1999年开始对煤热解分级高效利用技术的基础理论、工艺和设备放大等方面进行了系统研究,并在廊坊中试基地建立了煤处理量为10 t/d的煤热解燃烧中试平台. 采用该实验装置对多种低阶煤进行热解,结果表明,在燃用半焦的同时焦油产率为煤干重的6%?10%,热解煤气产率为煤干重的8%?12%. 介绍了过程所煤热解分级混合发电系统,并对该系统在燃煤发电厂的应用进行了技术经济分析.     

Analysis of main gaseous emissions of heavy duty gas turbines burning several syngas fuels

This work presents the development of a simple analytical model of performance for heavy duty gas turbine combustors and its use for the analysis of main emissions for a set of syngas fuels. This set of syngas fuels has been selected as a wide representation of different compositions of syngas fuels, from fossil or vegetal origins. Their combustion processes have been modelled as a set of chemical reactors in serial and a detailed kinetic model, simulating a conventional diffusion flame combustor. In each slice, the thermodynamics and the kinetics have been modelled using perfect stirred reactor models. The combustor model has been validated with the GE MS7001F gas turbine experimental data. From this validation the model applicability range has been established for combustor outlet temperatures above 1200 K. Finally the combustor model has been applied to the comparison of different syngas fuels emissions in three new generation gas turbines.     

基于煤和天然气联合制取合成气工艺研究进展

回顾了以煤和天然气为原料通过不同工艺流程制备合成气用以化工合成或发电的研究进展。介绍了以煤和天然气为原料分别制取合成气后再汇合的工艺流程和共气化技术等不同工艺路线的特点。研究了煤气化和天然气转化制备合成气时不同工艺路线在元素互补、能量利用、杂质混合等方面的表现。结果表明是否考虑煤和天然气的碳氢元素互补以及煤气化热量的有效利用将成为决定工艺流程优劣的重要因素。研究表明,煤气化和天然气转化分别制备合成气后汇合的工艺技术更易实现工业化应用,共气化技术的工业化应用较易受到气化炉反应条件的限制,尤其是内置换热管式的共气化技术。进行比较后,认为以煤和天然气为原料的多原料系统能够降低原料消耗、同时减排二氧化碳,符合煤炭的清洁利用要求,具有一定优势。     

Performance analysis of integrated biomass gasification fuel cell (BGFC) and biomass gasification combined cycle (BGCC) systems

Biomass gasification processes are more commonly integrated to gas turbine based combined heat and power (CHP) generation systems. However, efficiency can be greatly enhanced by the use of more advanced power generation technology such as solid oxide fuel cells (SOFC). The key objective of this work is to develop systematic site-wide process integration strategies, based on detailed process simulation in Aspen Plus, in view to improve heat recovery including waste heat, energy efficiency and cleaner operation, of biomass gasification fuel cell (BGFC) systems. The BGFC system considers integration of the exhaust gas as a source of steam and unreacted fuel from the SOFC to the steam gasifier, utilising biomass volatilised gases and tars, which is separately carried out from the combustion of the remaining char of the biomass in the presence of depleted air from the SOFC. The high grade process heat is utilised into direct heating of the process streams, e.g. heating of the syngas feed to the SOFC after cooling, condensation and ultra-cleaning with the Rectisol^® process, using the hot product gas from the steam gasifier and heating of air to the SOFC using exhaust gas from the char combustor. The medium to low grade process heat is extracted into excess steam and hot water generation from the BGFC site. This study presents a comprehensive comparison of energetic and emission performances between BGFC and biomass gasification combined cycle (BGCC) systems, based on a 4th generation biomass waste resource, straws. The former integrated system provides as much as twice the power, than the latter. Furthermore, the performance of the integrated BGFC system is thoroughly analysed for a range of power generations, ～100–997 kW. Increasing power generation from a BGFC system decreases its power generation efficiency (69–63%), while increasing CHP generation efficiency (80–85%).     

煤在不同氧化氛围中的能量梯级释放

针对传统煤燃烧能量利用效率低、污染严重等问题,将超临界水氧化技术应用于煤的清洁燃烧过程,分析了煤在空气和超临界水两种不同的氧化氛围中的反应特性。进而,基于不同的反应路径,利用图像(火用)分析法,剖析了煤在两种氧化氛围中的能量转换特点,揭示了煤在水相氧化氛围中的能量释放新机理,最后对煤在超临界水氧化反应器和传统锅炉中的实际过程进行了(火用)分析。结果表明,水相氧化将煤的化学能品位从1降低到0.83,并且减小了煤的化学能品位与热源品位之差,从而降低了煤中化学能向物理能转变的不可逆损失,(火用)损失减少了6.04%,热(火用)增加了5.25%,而且水相氧化没有传热(火用)损失;运用(火用)分析理论,计算得到超临界水氧化反应器(火用)效率高达80.1%,高出传统锅炉(火用)效率24.2%。     

Syngas combustion in a chemical-looping combustion system using an impregnated Ni-based oxygen carrier

Chemical-looping combustion (CLC) has emerged as a promising option for CO₂ capture because this gas is inherently separated from the other flue gas components and thus no energy is expended for the separation. This technology would have some advantages if it could be adapted for its use with coal as fuel. In this sense, a process integrated by coal gasification and CLC could be used in power plants with low energy penalty for CO₂ capture. This work presents the results obtained in the combustion of syngas as fuel with a Ni-based oxygen carrier prepared by impregnation in a CLC plant under continuous operation. The effect on the oxygen carrier behaviour and the combustion efficiency of several operating conditions was determined in the continuous CLC plant. High combustion efficiencies (～99%), close to the values limited by thermodynamics, were reached at oxygen carrier-to-fuel ratios higher than 5. The temperature in the FR had a significant influence, although high efficiencies were obtained even at 1073 K. The syngas composition had small effect on the combustion, obtaining high and similar efficiencies with syngas fuels of different composition, even in the presence of high CO concentrations. The low reactivity of the oxygen carrier with CO seemed to indicate that the water gas shift reaction acts as an intermediate step in the global reaction of the syngas in a continuous CLC plant. Neither agglomeration nor carbon deposition problems were detected during 50 h of continuous operation in the prototype. The obtained results showed that the impregnated Ni-based oxygen carrier could be used in a CLC plant for the combustion of syngas produced in an integrated gasification combined cycle (IGCC).     

一种煤基多联产碳循环系统的设计及评价

将高密度三塔式循环流化床(TBCFB)应用于串并联综合型多联产系统,提出一种基于碳循环的流程与参数共优化的煤基多联产系统,促进低阶煤资源的高质高效转化。碳循环体现在两方面,一是系统以热解煤气循环作为热解气氛,提高了焦油产率,实现低阶煤高质化转化;二是在TBCFB使用富氧燃烧,提高了烟气中二氧化碳浓度,将烟气替代氮气直接用于燃气轮机发电工质,减少了氮气消耗。利用Aspen Plus对全系统进行模拟,对多联产系统进行物料、能量和?衡算,研究未反应合成气循环比和烟气注入量对过程的影响;以能量利用效率为优化目标,对煤基多联产碳循环系统的操作条件寻优。结果表明,动力单元注入气体使用烟气时,煤基多联产碳循环系统的能量利用效率达49.7%,高于用氮气作为热解气氛的传统煤基多联产系统,相比传统的单产系统,煤基多联产系统的能量可节约13%,对于年处理30万吨煤的系统,折合减少二氧化碳排放量为14.9万吨/年。     

Catalytic Performance of Coal Char for the Methane Reforming Process

A new concept of combined coal gasification and methane reforming in a single reactor was proposed as an alternative path for syngas production using coal and coalbed methane. Here, the results of this process are summarized. The experimental work was carried out in a fixed‐bed reactor. Methane cracking, CO₂/steam reforming of methane over coal char, and the effects of chars made from different types of parent coal on methane conversion were examined. The catalytic effect of coal char on methane cracking and reforming increased with decreasing coalification degree. A synergistic effect was observed in that, while the coal char catalyzed the methane reforming reactions, gasification of the coal char took place simultaneously, which counter‐balanced the deposition of carbon especially for the methane‐steam‐char system.     

Evaluation of the economic and environmental impact of combining dry reforming with steam reforming of methane

Lately, there has been considerable interest in the development of more efficient processes to generate syngas, an intermediate in the production of fuels and chemicals, including methanol, dimethyl ether, ethylene, propylene and Fischer–Tropsch fuels. Steam methane reforming (SMR) is the most widely applied method of producing syngas from natural gas. Dry reforming of methane (DRM) is a process that uses waste carbon dioxide to produce syngas from natural gas. Dry reforming alone has not yet been implemented commercially; however, a combination of steam methane reforming and dry reforming of methane (SMR + DRM) has been used in industry for several years.     

Oxygen carriers for chemical looping combustion of solid fuels

A thermal analyzer-differential scanning calorimeter-mass spectrometer (TG-DSC-MS) was used to study oxygen carriers (OC) for their potential use for the application of chemical looping combustion (CLC) to solid fuels. Reaction rates, changes in reaction rates with repeated oxidation-reductions, exothermic heats during oxidation, and the effect of changing reduction gas compositions were studied. Oxidation rates were greater than reduction rates and reaction rates were reproducible through multiple oxidation-reduction cycles except where agglomeration occurred with powders. Iron oxide (Fe₂O₃ powder) and iron-based catalysts were found suitable for CLC of solid fuels having rapid reduction rates which increased with higher reducing gas concentrations. Fe₂O₃ powder was used to oxidize a high carbon coal char in an inert gas removing 88% of the carbon from the char. Other properties such as cost and durability indicated iron oxide OCs potential use for CLC of solid fuels.     

生物质型CCHP系统的联合循环仿真及性能分析

利用ASPEN PLUS稳态模拟平台测试修正热力参数、流动过程的作用条件,以建立冷热电联供(CCHP)系统的联合循环,研究了系统中关键单元的热功转换过程,以及物流的流率、压力和温度分布,探讨了各输入参数对系统经济、技术和排放性能等的影响。结果表明:(1)预设工况下,燃气轮机进口温度为340℃,系统总能利用率达到94.65%,经济效率达到67.27%,CO2、CO、NO2、NO、SO2排放量分别为0.5kg·(kW·h)-1、1.025mg·(kW·h)-1、0.15g·(kW·h)-1、6g·(kW·h)-1、3.7g·(kW·h)-1;(2)随着空气流量的增加,燃气轮机和余热锅炉的排气温度急速下降,总能利用率上升,而相对节能率、当量效率和经济效率不断减小。因此,空气的量应控制在理论空气量的20%~40%之间;(3)随着空气温度及环境温度的升高,燃料的气化率会微小地下降,但系统的总体能效性能会提高。     

Combustion behaviour of ultra clean coal obtained by chemical demineralisation

The increasing environmental concern caused by the use of fossil fuels and the concomitant need for improved combustion efficiency is leading to the development of new coal cleaning and utilisation processes. However, the benefits achieved by the removal of most mineral matter from coal either by physical or chemical methods can be annulled if poor coal combustibility characteristics are attained. In this work a high volatile bituminous coal with 6% ash content was subjected to chemical demineralisation via hydrofluoric and nitric acid leaching, the ash content of the clean coal was reduced to 0.3%. The original and treated coals were devolatilised in a drop tube furnace and the structure and morphology of the resultant chars was analysed by optical and scanning electron microscopies. The reactivity characteristics of the chars were studied by isothermal combustion tests in air at different temperatures in a thermogravimetric system. Comparison of the combustion behaviour and pollutant emissions of both coals was conducted in a drop tube furnace operating at 1000 °C. The results of this work indicate that the char obtained from the chemically treated coal presents very different structure, morphology and reactivity behaviour than the char from the original coal. The changes induced by the chemical treatment increased the combustion efficiency determined in the drop tube furnace, in fact higher burnout levels were obtained for the demineralised coal.