Sequentially coupled flow-geomechanical modeling of underground coal gasification for a three-dimensional problem

Underground coal gasification (UCG) has been identified as an environmentally friendly technique for gasification of deep un-mineable coal seams in situ. This technology has the potential to be a clean and promising energy provider from coal seams with minimal greenhouse gas emission. The UCG eliminates the presence of coal miners underground hence, it is believed to be a much safer technique compared to the deep coal mining method. The UCG includes drilling injection and production wells into the coal seam, igniting coal, and injecting oxygen-based mix to facilitate coal gasification. Produced syngas is extracted from the production well. Evolution of a cavity created from the gasification process along with high temperature as well as change in pore fluid pressure causes mechanical changes to the coal and surrounding formations. Therefore, simulation of the gasification process alone is not sufficient to represent this complex thermal-hydro-chemical–mechanical process. Instead, a coupled flow and geomechanical modeling can help better represent the process by allowing simultaneous observation of the syngas production, advancement of the gasification chamber, and the cavity growth. Adaptation of such a coupled simulation would aid in optimization of the UCG process while helping controlling and mitigating the environmental risks caused by geomechanical failure and syngas loss to the groundwater. This paper presents results of a sequentially coupled flow-geomechanical simulation of a three-dimensional (3D) UCG example using the numerical methodology devised in this study. The 3D model includes caprock on top, coal seam in the middle, and another layer of rock underneath. Gasification modeling was conducted in the Computer Modelling Group Ltd. (CMG)’s Steam, Thermal, and Advanced processes Reservoir Simulator (STARS). Temperature and fluid pressure of each grid block as well as the cavity geometry, at the timestep level, were passed from the STARS to the geomechanical simulator i.e. the Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) computer program (from the Itasca Consulting Group Inc.). Key features of the UCG process which were investigated herein include syngas flow rate, cavity growth, temperature and pressure profiles, porosity and permeability changes, and stress and deformation in coal and rock layers. It was observed that the coal matrix deformed towards the cavity, displacement and additional stress happened, and some blocks in the coal and rock layers mechanically failed.     

A life cycle comparison of greenhouse emissions for power generation from coal mining and underground coal gasification

Underground coal gasification (UCG) is an advancing technology that is receiving considerable global attention as an economic and environmentally friendly alternative for exploitation of coal deposits. UCG has the potential to decrease greenhouse gas emissions (GHG) during the development and utilization of coal resources. In this paper, the life cycle of UCG from in situ coal gasification to utilization for electricity generation is analyzed and compared with coal extraction through conventional coal mining and utilization in power plants. Four life cycle assessment models have been developed and analyzed to compare (greenhouse gas) GHG emissions of coal mining, coal gasification and power generation through conventional pulverized coal fired power plants (PCC), supercritical coal fired (SCPC) power plants, integrated gasification combined cycle plants for coal (Coal-IGCC), and combined cycle gas turbine plants for UCG (UCG-CCGT). The analysis shows that UCG is comparable to these latest technologies and in fact, the GHG emissions from UCG are about 28 % less than the conventional PCC plant. When combined with the economic superiority, UCG has a clear advantage over competing technologies. The comparison also shows that there is considerable reduction in the GHG emissions with the development of technology and improvements in generation efficiencies.     

Reaction rate constants in simulation of underground coal gasification using porous medium approach

Underground coal gasification (UCG) is an emerging energy technology for a cleaner type of coal extraction method. It avoids current coal mining challenges such as drastic changes to landscapes, high machinery costs, elevated risks to personnel, and post-extraction transport. UCG has a huge potential to provide a clean coal energy source by implementing carbon capture and storage techniques as part of the process. In order to support mitigation strategies for clean coal production and policy development, much research needs to be completed. One component of this information is the need to understand what happens when the coal burns and a subsurface cavity is formed. This paper looks at the efforts to enhance reliable prediction of the size and shape of the cavities. Reactions are one of the most important mechanisms that control the rate of the growth of the cavities. Therefore, modeling the reactions and precise prediction of reaction kinetics can influence the accuracy of a UCG process. The produced syngas composition during UCG is closely linked to the reactions that take place in this process, the permeability of the coal seam, and the temperature distribution. Since the combination of reactions can influence the distributions of the heat and gas components in the coal seam during UCG or even extinguish the combustion, accurate modeling of the reactions is crucial, particularly when all phenomena affecting the reaction rate are considered in a single set of kinetics. In this study, procedures are proposed to estimate the frequency factor and activation energy of the pyrolysis reaction using a single-step decomposition method, the kinetics of the endothermic direction of homogeneous reversible reactions, and the frequency factor of heterogeneous reactions from experiments or literature data. The estimated kinetics is more appropriate for simulation of the UCG process using the porous medium approach. Computer Modelling Group’s CMG-STARS (Steam, Thermal, and Advanced Processes Reservoir Simulator) software is used in this study.     

Mitigation and adaptation strategies for global change via the implementation of underground coal gasification

Coal is the most abundant hydrocarbon energy source in the world. It also produces a very high volume of greenhouse gases using the current production technology. It is more difficult to handle and transport than crude oil and natural gas. We face a challenge: how can we access this abundant resource and at the same time mitigate global environmental challenges, in particular, the production of carbon dioxide (CO₂)? The editors of this special edition journal consider the opportunity to increase the utilization of this globally abundant resource and recover it in an environmentally sustainable manner. Underground coal gasification (UCG) is the recovery of energy from coal by gasifying the coal underground. This  process produces a high calorific synthesis gas, which can be applied for electricity generation and/or the production of fuels and chemicals. The carbon dioxide emissions are relatively pure and the surface facilities are limited in their environmental footprint. Unused carbon is readily separated and can be geo-sequester in the resulting cavity. The cavity is also being considered as a potential option to mitigate against change impacts of other sources of carbon dioxide (CO₂) emissions. These outcomes mean there is an opportunity to provide developing and developed countries a source of low-cost clean energy. Further, the burning of coal in situ means that the traditional dangers of underground mining and extraction are reduced, a higher percentage of the coal is actually recovered and the resulting cavern creates the potential for a long-term storage solution of the gasification wastes. The process is not without challenges. Ground subsidence and groundwater pollution are two potential environmental impacts that need to be averted for this process to be acceptable. It is essential to advance the understanding of this practice and this special edition journal seeks to share the progress that scientists are making in this dynamic field. The technical challenges are being addressed by researchers around the world who work to resolve and understand how burning coal underground impacts the geology, the surface land, and ground water both in the short and the long term. This special issue reviews the process of UCG and considers the opportunities, challenges, risks, competitive analysis and synergies, commercial initiatives and a roadmap to solutions via the modelling and simulation of UCG. Building and then disseminating the fundamental knowledge of UCG will enhance policy development, best practices and processes that reflect the global desires for energy production with reduced environmental impact.     

褐煤地下气化过程中铅和砷的迁移规律的研究

在煤炭地下气化模型试验的基础上,研究了褐煤原煤及其气化产物中的铅和砷的含量和分布,进行了铅和砷的质量平衡计算,并分析了其析出的反应机理.实验结果表明,铅在原煤中以残渣态23.07%、碳酸盐和铁锰氧化物结合态53.96%、硫化物结合态22.96%存在,而砷则以残渣态47.73%、有机结合态7.95%、硫化物结合态40.90%存在.在气化过程中63.65%的铅和56.23%的砷残存在地下煤灰中,1.15%的Pb和6.62%的As转化到煤气冷凝水中,35.20%的Pb和37.15%的As转化到煤气中.     

On the mitigating environmental aspects of a vertical well in underground coal gasification method

Mitigation and Adaptation Strategies for Global Change - Underground coal gasification (UCG) is an energy production pathway in underground coal deposits with the potential advantage of decreasing...     

基于绿色投入产出模型的资源补偿费及经济影响模拟

在编制的绿色投入产出表基础上,对我国煤炭和石油资源的使用补偿费和理论价格进行计算,并分三种情景对征收资源使用补偿费产生的经济影响进行模拟。模拟结果显示,煤炭和石油资源的使用补偿费分别为623 元/t 和7 688 元/t,其理论价格分别是实际价格的5.3 和3.9 倍,我国煤炭和石油资源的价格偏低。如果征收理论资源使用费用将对石油和天然气开采业、 煤炭开采和洗选业、电力、热力的生产和供应业、黑色金属冶炼及压延加工业、化学原料及化学制品制造业、石油加工及炼焦业等部门的价格影响较大,如果按照新修订的资源税进行征收,将对石油和天然气开采业的影响较大。     

燃料电池汽车氢源生命周期分析

运用生命周期评价方法对使用不同氢源的燃料电池汽车进行了分析.经过目的与范围的确定、清单分析、影响评价和结果解释,表明电解制氢方案的污染排放明显高于甲醇重整和汽油重整方案,而甲醇重整和汽油重整方案又高于天然气制氢和煤制氢方案,对于相同的制氢方案,液氢方案的排放略高于气氢方案.      

民用清洁煤技术的定量评价与筛选

选用合适的民用清洁煤技术是提高居民生活用煤能源利用效率、减少环境污染的重要途径之一,本文利用笔者提出的清洁煤技术定量评价方法对民用清洁煤技术进行了定量评价与筛选,评价结果表明,在标准状态下各种民用适用清洁煤技术的单位综合成本分别为选煤48元/GJ,民用型煤45.73元/GJ,炼焦制气28.53元/GJ,加压气化联产甲醇54.73元/GJ,加压气化联产油蜡50.71元/GJ,两段炉气化88.66元/GJ,直立炉气化38.84元/GJ,其中炼焦制气是单位综合成本最小的民用清洁煤技术．敏感度分析表明,煤气化将是民用清洁煤技术的主要发展方向     

能源资源价格长期关系与短期动态调整研究：1985-2011年

为探讨国际市场上主要能源资源价格之间的长期均衡关系和动态调整规律,论文利用国际货币基金组织官方网站提供的自1985年到2011年的数据,建立向量自回归(VAR)和向量误差修正(VEC)模型,对当前四大主要能源资源煤、石油、天然气和铀的价格序列展开研究。结果表明:①4种主要能源资源价格之间存在稳定的长期均衡关系:铀价格每变化1%,将使煤和天然气的价格分别反向变动2.11%和7.10%,使石油的价格正向变动7.97%。②4种主要能源资源产品价格均会对自身新信息立即产生大幅度反应,但持续时间差异很大:铀在15个月内只有微弱降幅,而煤在6个月,石油在2个月后即开始迅速减弱,天然气则是直接进入下降趋势。③除天然气在长期内会受到石油价格的显著影响外,铀、煤和石油的价格波动主要由自身因素形成。④天然气的误差修正项具有显著的负向调节作用,价格偏离长期均衡关系时,能够很快得到纠正。煤、石油和铀的误差修正项系数很小,且石油和铀不具有任何显著性,说明石油和铀不具备短期动态调节能力。     

基于LCA的稻秸合成甲醇的环境-经济成本分析

以年产5万t甲醇的稻秸气化合成甲醇系统为研究对象,采用生命周期评价方法,对该系统进行了环境-经济成本分析.结果表明,稻秸合成甲醇系统的环境影响成本是284.99元/t(以甲醇计),且主要集中在生产转化过程和下游甲醇燃料消费2个单元阶段.在不同环境影响类型中,温室效应是生命周期最主要的环境影响因素,由于稻秸固碳作用产生的环境成本是-152.79元/t,生产上游温室效应影响负荷为负、总环境影响负荷为负.每t稻秸甲醇的真实成本比煤基甲醇低76.84元.     

Biomass chemical looping gasification for syngas production using modified hematite as oxygen carriers

Syngas is a clean energy carrier and a major industrial feedstock. In this paper, syngas was produced via biomass chemical looping gasification(CLG) process. Hematite, the most common Fe-based oxygen carrier(OC), was modified with different metal oxides(CeO₂, CaO and MgO) by the impregnation method. The hematite modified by CeO₂, CaO and MgO was namely as CeO₂-hematite(CeO₂-H), CaO-hematite(CaO-H) and MgO-hematite(MgO-H), respectively. The introduction...     

国内大城市煤改气工程的费用-效益分析

国内大城市以PM10和SO2为主要污染物的煤烟型污染十分严重,因而天然气作为煤的清洁替代品已越来越受到人们的重视。过去天然气作为宝贵的战略资源多被用作化工原料,而对是否应将其作为城市民用燃料存有争论。本研究以北京和重庆为案例城市,对大城市中实施大规模的“煤改气”工程进行了详尽的费用－效益分析（CBA）。其中,采用Rowe与Ostro的剂量－反应函数详细估算了天然气替代煤后产生的外部效益。结果表明,在人口和经济活动高度集中的大城市,使用天然气作民用燃料能有效降低非点源大气污染物排放和低空污染物浓度,产生明显的环境效益,因而具有显著的效益－费用比较优势。最后,本文对激励天然气在大城市的推广提出了环境经济政策建议。     

Modern Biomass Conversion Technologies

This article gives an overview of the state-of-the-art of key biomass conversion technologies currently deployed and technologies that may play a key role in the future, including possible linkage to CO₂ capture and sequestration technology (CCS). In doing so, special attention is paid to production of biofuels for the transport sector, because this is likely to become the key emerging market for large-scale sustainable biomass use. Although the actual role of bio-energy will depend on its competitiveness with fossil fuels and on agricultural policies worldwide, it seems realistic to expect that the current contribution of bio-energy of 40–55 EJ per year will increase considerably. A range from 200 to 300 EJ may be observed looking well into this century, making biomass a more important energy supply option than mineral oil today. A key issue for bio-energy is that its use should be modernized to fit into a sustainable development path. Especially promising are the production of electricity via advanced conversion concepts (i.e. gasification and state-of-the-art combustion and co-firing) and modern biomass derived fuels like methanol, hydrogen and ethanol from ligno-cellulosic biomass, which can reach competitive cost levels within 1–2 decades (partly depending on price developments with petroleum). Sugar cane based ethanol production already provides a competitive biofuel production system in tropical regions and further improvements are possible. Flexible energy systems, in which biomass and fossil fuels can be used in combination, could be the backbone for a low risk, low cost and low carbon emission energy supply system for large scale supply of fuels and power and providing a framework for the evolution of large scale biomass raw material supply systems. The gasification route offers special possibilities to combine this with low cost CO₂ capture (and storage), resulting in concepts that are both flexible with respect to primary fuel input as well as product mix and with the possibility of achieving zero or even negative carbon emissions. Prolonged RD&D efforts and biomass market development, consistent policy support and international collaboration are essential to achieve this.     

旅行成本法在我国应用中存在的几个问题

我国旅行成本法案例研究多数未分清旅行成本与旅游目的地本身价格的关系,推导的游憩需求曲线是旅行成本-旅游人次模型,而不是旅游目的地本身的价格-旅游人次需求曲线。文章具体说明了区域旅行成本法的基本原理及操作方法,并用乔光华文章数据重新对达里诺尔国家级自然保护区游憩价值进行计算,对旅行成本的构成等问题进行了讨论,得出其消费者剩余为0.9221×108元a/,比原研究中的0.0937×108元a/高出近10倍。认为乔光华等的研究在推断游憩需求曲线时存在方法上的问题,直接将旅行成本和时间价值作为游憩价值不符合旅行成本法的基本原理和公共物品无(或低)市场价格的经济理论。还对调整后的旅行成本数据进行了计算,得到保护区游憩价值为1.3581×108元a/。     

Using activated biochar for greenhouse gas mitigation and industrial water treatment

This study explored the feasibility of using residual biomass to both mitigate greenhouse gas (GHG) emissions and remediate water contaminated by hydrocarbons. Using produced (process-affected) water from Canada’s oil sands operations as a case study, activated biochar (ACB) was found to have a higher affinity to organics than activated coal and removed 75 % of total organic carbon (TOC) from produced water in steam-assisted gravity drainage (SAGD) operations or 90 % of the TOC from synthetic tailings (ST) water sample. Up to 6 Tg dry biomass year^?1 would be required to treat the waters associated with the 93?×?10⁶-m³ of bitumen recovered per year. Landfilling the spent ACB and flaring any biogas produced were estimated to provide a greater GHG benefit than the combustion of the biochar + organics for heat to offset natural gas demand. Net costs for the ACB were about 13.84?$?m^?3 bitumen for SAGD operations and 1.76?$?m^?3 bitumen for mining operations. The values for mining operations justify further work to create a value chain that will integrate bioprocesses into the fossil fuel industry.     

温度对干化污泥水蒸气气化产气特性的影响

采用固定床气化装置,在水蒸气流量为0.32 kg/h条件下进行了污泥水蒸气气化实验。研究了温度对污泥气化气体产率、氢气产率、气体成分与低位热值、气体能源转化率的影响。结果表明:随着反应温度从700℃上升到1 000℃;气体产率从0.39 m3/kg升至0.61 m3/kg;氢气产率从0.18 m3/kg升至0.34 m3/kg;气体能源转化率从54%升至88%;产气的低位热值从10 688.1 kJ/m3提高至11 168.9 kJ/m3。同时产气中H2和CO含量随着温度的升高而增加,CH4、CO2和CnHm含量随温度的升高而减少。因此,为了获得更多的可燃气体,建议在污泥水蒸气气化工艺中,气化温度必须大于800℃。     

废轮胎流化床气化特性试验研究

为了掌握废轮胎在流化床内的气化特性,利用自行设计的小型流化床试验装置系统,对废轮胎在不同的过量空气系数下在400～700℃温度范围内进行了空气气化实验.分析了废轮胎气化效率、固定碳转化率、气化气热值、产气量以及气化气成分随气化温度、过量空气系数的变化规律.结果表明,废轮胎气化的最佳运行条件为气化初始温度700℃,过量空气系数α=0.4.在此条件下得到的气化气成分主要包括CH₄、CO、H₂、C₂H₆和高分子有机化合物,此时的气化效率为47.96%,气化气低位热值为4 804kJ/m³.     

基于Aspen Plus的生活垃圾热解气化模拟及正交优化

热解气化技术作为一种城市固体废弃物(municipal solid waste,MSW)无害化处理的方式,其相关研究具有现实意义.利用Aspen Plus软件建立了 MSW固定床热解气化模型,在模型验证的基础上探讨了气化温度、气化压力和空气当量比对MSW热解气化过程的影响.通过二次回归正交试验法得出MSW热解气化过程中...     

Process conditions for preparing methanol from cornstalk gas

The low-heat-value cornstalk gas produced in the down-flow fixed bed gasifier was tentatively used for methanol synthesis. The cornstalk gas was purified and the technical procedures such as deoxygenation, desulfurization, catalytic cracking of tar, purification and hydrogenation were studied. The catalytic experiments of methanol synthesis with cornstalk syngas were carried out in a tubular-flow integral and isothermal reactor. The effect of reaction temperature, pressure, catalyst types, catalyst particle size, syngas flow at entering end and composition of syngas was investigated. The optimum process conditions and yield of methanol from cornstalk syngas were obtained. The experimental results indicated that the proper catalyst for the synthetic reaction was C301 and the optimum catalyst size was 0.833 mm x 0.351 mm. The optimum operating temperature and pressure were found to be 235癈 and 5 MPa, respectively. The suitable syngas flow 0.9-1.10 mol/h at entering end was selected and the best composition of syngas were CO 10.49%, CO2 8.8%, N2 37.32%, CnHm 0.95% and H2 40.49%. The best methanol yield was 0.418 g/g cornstalk. This study provided the technical support for the industrial test of methanol production from biomass (cornstalk) gas.