Evaluation of Structural Changes in the Coal Specimen Heating Process and UCG Model Experiments for Developing Efficient UCG Systems

Underground coal gasification – A numerical approach to study the formation of syngas and its reactive transport in the surrounding strata

Global and micro/macro structural models simulating the Longwall generator concept for underground coal gasification (UCG) are formulated for several geometric and loading conditions. Dynamic thermal and stress response solutions are computed for axisymmetric boundary value problems represented by a stationary circular cavity model and an expanding radially propagating circular cavity. Static thermoelastic response solutions are presented for circular and elliptical cylindrical presented for circular and elliptical cylindrical cavities in a homogeneous, isotropic medium and layered media. Considerations pertaining to roof collapse and surface subsidence are discussed. The micro/macro modeling investigations include thermorheological representation of Pittsburgh coal at elevated temperature and studies on thermal crack propagation of coal fissures. Finally, the relevance of stress and temperature profiles, fracture permeabilities, and fissure response is discussed in relation to the propagation and stability of the UCG process. Introduction Fossil fuels are currently the main energy resource for the U.S. with coal reserve estimates ranging from 3 to 4 trillion tons. Only one-sixth of this coal can be extracted by state-of-the-art mining techniques. It is anticipated that about one-third of the U.S. total coal energy reserves, particularly thin coal beds and thick-seam deep coal, can be recovered by underground coal gasification (UCG). This process entails ignition of a coal seam and circulation of gas through a controlled path. The resulting chemical reactions produce a gas with calorific value, depending on several process parameters and variables. Their optimization parameters and variables. Their optimization requires sophisticated analytical simulations of the structural, heat transfer, fluid flow, and reaction kinetics aspects along with controlled laboratory experiments and field tests. Descriptions and appraisals of various underground coal pregasification schemes and gasification processes mad a discussion of significant problems, processes mad a discussion of significant problems, such as roof collapse, gas leakage, water control, and surface subsidence, etc., have been given in a detailed report by Arthur D. Little, Inc.. Reports on UCG experiments in the Soviet Union, Great Britian, and other countries have been summarized in excellent monographs. The outlook for UCG in the U.S. was discussed recently at the First Annual UCG Symposium conducted by the Laramie Energy Research Center in Wyo. It appears that several candidate concepts and solutions exist, depending (on the type of coal, coal seam thickness, overburden, and environmental requirements. The concepts currently being investigated by ERDA's research centers and laboratories includethe vertical well to well linking experiments at Hanna, Wyo., for medium seams (Laramie Energy Research Center),the packed-bed concept for thick coal seams (Lawrence Livermore Laboratory), andthe Longwall generator concept for thin seams (Morgantown Energy Research Center). This paper presents results obtained from analytical structural and thermal simulations associated moth the Longwall generator UCG concept. Temperature and stress response solutions are presented for different boundary value problem representations. The results of this study provide fundamental insight to the interpretation of UCG global and micro/macro mechanisms. UCG LONGWALL GENERATOR CONCEPT AND MECHANISMS Morgantown Energy Research Center presently is developing the Longwall generator concept to gasify thin-seam eastern coals (Fig. 1). In this concept, directional holes (6-in. diameter) are drilled from the ground surface with horizontal holes, 500 ft in length, entering through the 6-ft-thick coal seam (1,000-ft overburden) and returning vertically back to the coal surface. The gasification reaction zone propagates horizontally in the coal propagates horizontally in the coal maximum-permeability direction between the parallel horizontal holes drilled approximately in the coal butt-cleat direction. JPT P. 413

Nonlinear-Control-Oriented Modeling of the Multi-Variable Underground Coal Gasification Process for UCG Project Thar: A Machine Learning Perspective

Distributed optical fiber temperature sensor (DTS) for underground coal gasification (UCG) system using is studied in this paper. By measuring temperature of reacting mine gasification process can be controlled. Calibration of DTS and experiment result are introduced. The results show that, DTS can play an important role in UCG systems.

Experimental study of underground coal gasification (UCG) of a high-rank coal using atmospheric and high-pressure conditions in an ex-situ reactor

Kinetics of heterogeneous reactions with coal in context of underground coal gasification

Underground coal gasification (UCG) as a clean energy technology and efficient way for the conversion of the coal resources into energy in-situ has attracted wide public attention in recent years. Laboratory-scale experiments on coal blocks can provide significant insight into UCG process. The main goal of this study was evaluation of the gasification effect applying L-shape linking-hole and Coaxial-hole UCG models. Experimental results show the gas composition, AE activity and the temperature distribution inside the combustion reactors under similar operating parameters. Positive correlation was found between the temperature and cumulative AE events. The results shown that the gasification of L-shape linking-hole model obtained the average calorific value, as high as 11.3 MJ/m3, whereas in the Coaxial-hole model, the average calorific value of gas produced was only 5.79 MJ/m3under the experimental conditions. Even so, the results of conducted Coaxial-hole UCG experiment provide the original and sorely lacking data base for future new-style UCG research.

The wastewater from underground coal gasification (UCG) process has extremely complex composition and high concentrations of toxic and refractory compounds including phenolics, aliphatic and aromatic hydrocarbons, ammonia, cyanides, hazardous metals and metalloids. So, the development of biological processes for treating UCG wastewater poses a serious challenge in the sustainable coal industry. The aim of the study was to develop an innovative and efficient wetland construction technology suitable for a treatment of UCG wastewater using available and low-cost media. During the bioremediation process the toxicity of the raw wastewater decreased significantly between 74%-99%. The toxicity units (TU) ranged from values corresponding to very high acute toxic for raw wastewater to non-toxic for effluents from wetland columns after 60 days of the experiment. The toxicity results correlated with the decrease of some organic and inorganic compounds such as phenols, aromatic hydrocarbons, cyanides, metals and ammonia observed during the bioremediation process. The removal percentage of organic compounds like BTEX, PAHs and phenol was around 99% just after 14 days of treatment. A similar removal rate was indicated for cyanide and metals (Zn, Cr, Cd and Pb). Concluded, in order to effectively assess remediation technologies, it is desirable to consider combination of physicochemical parameters with ecotoxicity measurements. The present findings show that wetland remediation technology can be used to clean-up the heavily contaminated waters from the UCG process. Wetland technology as a nature-based solution has the potential to turn coal gasification wastewater into usable recycled water. It is economically and environmentally alternative treatment method.

Robust tracking of the heating value in an underground coal gasification process using dynamic integral sliding mode control and a gain-scheduled modified Utkin observer

Underground coal gasification (UCG) can be considered as one of the clean coal technologies. During the process, the gas of industrial value is produced, which can be used to produce heat and electricity, liquid fuels or can replace natural gas in chemistry. However, UCG does carry some environmental risks, mainly related to potential negative impacts on surface and groundwater. Wastewater and sludge from UCG contain significant amounts of aliphatic and aromatic hydrocarbons, phenols, ammonia, cyanides and hazardous metals such as arsenic. This complicated matrix containing high concentrations of hazardous pollutants is similar to wastewater from the coke industry and, similarly to them, requires complex mechanical, chemical and biological treatment. The focus of the review is to explain how the wetlands systems, described as one of bioremediation methods, work and whether these systems are suitable for removing organic and inorganic contaminants from heavily contaminated industrial wastewater, of which underground coal gasification wastewater is a particularly challenging example. Wetlands appear to be suitable systems for the treatment of UCG wastewater and can provide the benefits of nature-based solutions. This review explains the principles of constructed wetlands (CWs) and provides examples of industrial wastewater treated by various wetland systems along with their operating principles. In addition, the physicochemical characteristics of the wastewater from different coal gasifications under various conditions, obtained from UCG’s own experiments, are presented.

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. This technology has the potential to decrease greenhouse gas emissions during the development of coal deposits. The environmental benefits of UCG that promote reduction in greenhouse gas emissions include elimination of conventional mining, coal washing and fines disposal, coal stockpiling and coal transportation activities. Additional benefits include; a smaller surface area requirement with minimal surface disruption; removal of CO2 from the syngas at significantly reduced cost as compared to carbon capture and transport from a power plant; and the potential to reduce CH4 emissions, a potent greenhouse gas. UCG utilizes coalbed methane irrespective of its economic value during the burning process and increases energy efficiency. The CH4 in the product gas is consumed completely during power and/or electricity generation, thus reducing overall methane emissions to the atmosphere. This paper compares greenhouse gas emissions from conventional mining methods to UCG for the exploitation of a coal reserve. The findings indicate that UCG reduces greenhouse gas emissions significantly as compared to other competitive coal exploiting technologies. This research may help in the selection of a suitable method to develop coal deposits when the reduction of greenhouse gases is an essential part of planning. Introduction Underground coal gasification (UCG) is a process that involves burning coal in-situ and converting it into a gaseous product, commonly called syngas. This syngas is composed of mixture of gases at elevated temperatures and pressures and can be utilized for various purposes, including electricity and power generation, heat production, and as a chemical feedstock for a variety of chemical products like ethylene, acetic acid, polyolefin, methanol, petrol and synthetic natural gas (Anon, 1977; Burton, Friedmann, & Upadhye, 2006; Courtney, 2009; Liu, Mallet, Beath, Elsworth, & Brady, 2003). A typical composition of syngas includes H2, CO, CO2, CH4, and some traces of tars, NH3 & H2S. The molar percentage of component gases and concentration of NH3, H2S and other traces depends upon the type of oxidant used (air, oxygen, or steam), site characteristics and coal properties (Ahner, 2008; Walker, 1999). UGC is a rapidly developing technology and several projects in different countries are underway. The global attention gained by UCG is due to its potential for harnessing energy from coal deposits in a manner that is more economical and environmentally friendly than conventional mining methods. As stated by Meany and Maynard, UCG provides several environmental and economic benefits, not only over conventional mining methods but also over surface gasification and even coalbed methane drainage (Meany & Maynard, 2009).

Underground Coal Gasification is a method used to convert underground coal seams into a gaseous product commonly called synthetic gas through a flammable chemical process without going through a conventional mining process. The UCG concept was first developed in England which was then continued by the Soviet Union in field trials of UCG which was used as a power plant. In Indonesia, Tekmira has begun to research UCG, but there are very few publications on UCG. Therefore, it is necessary to conduct research on laboratory scale UCG for analysis of gas products to support the study of renewable energy. UCG testing begins with sample preparation followed by laboratory-scale coal gasification testing. There is a sample of coal used in the test, namely Subbituminous Coal from Tanjung Enim, South Sumatra. Initial combustion is carried out by flowing propane gas into the reactor tube using a burner. Furthermore, a mixture of oxygen gas and compressed air is used to keep the coals burning. After obtaining the gas from the combustion, then gas sampling is carried out using a suction pump which will be stored in a tedlar gas bag. Combustion gas products will be checked for syngas concentration using a Gas Chromatography tool to determine the concentration of CH4, CO2 and O2 gases. From the tests that have been carried out, the gas concentrations of O2 are 3.67%, CO2 41.51%, and CH4 6.93%. Coal in the confined test conditions has good conditions with indications of seeing the concentration of CH4, O2, and CO2 gas.

Study on the monitoring method of cavity growth in underground coal gasification under laboratory conditions

The paper describes the results of research on the applicability of the ground penetrating radar (GPR) method for remote sensing and monitoring of the underground coal gasification (UCG) processes. The gasification of coal in a bed entails various technological problems and poses risks to the environment. Therefore, in parallel with research on coal gasification technologies, it is necessary to develop techniques for remote sensing of the process environment. One such technique may be the radar method, which allows imaging of regions of mass loss (voids, fissures) in coal during and after carrying out a gasification process in the bed. The paper describes two research experiments. The first one was carried out on a large-scale model constructed on the surface. It simulated a coal seam in natural geological conditions. A second experiment was performed in a shallow coal deposit maintained in a disused mine and kept accessible for research purposes. Tests performed in the laboratory and in situ conditions showed that the method provides valuable data for assessing and monitoring gasification surfaces in the UCG processes. The advantage of the GPR method is its high resolution and the possibility of determining the spatial shape of various zones and forms created in the coal by the gasification process.

Underground coal gasification (UCG) converts coal in-situ into a gaseous product, commonly known as synthesis gas or syngas through the same chemical reactions that occur in surface gasifiers. Gasification converts hydrocarbons into a synthesis gas (syngas) at elevated pressures and temperatures and can be used to create many products (electric power, chemical feedstock, liquid fuels, hydrogen, synthetic gas). Gasification provides numerous opportunities for pollution control, especially with respect to emissions of sulfur, nitrous oxides, and mercury. UCG could increase the coal resource available for utilization enormously by gasifying otherwise unmineable deep or thin coals under many different geological settings. A 300-400% increase in recoverable coal reserves in the U.S. is possible. For developing countries undergoing rapid economic expansion, including India and China, UCG also may be a particularly compelling technology. UCG has been tested in many different experimental tests in many countries. The U.S. carried out over 30 pilots between 1975 and 1996, testing bituminous, sub-bituminous, and lignite coals. Before that, the Former Soviet Union executed over 50 years of research on UCG, field tests and several commercial projects, including an electric power plant in Angren, Uzbekistan that is still in operation today after 47 years. Since 1991, China has executed at least 16 tests, and has several commercial UCG projects for chemical and fertilizer feedstocks. In 2000, Australia began a large pilot (Chinchilla) which produced syngas for 3 years before a controlled shut-down and controlled restart. As present, multiple commercial projects are in various stages of development in the U.S., Canada, South Africa, India, Australia, New Zealand, and China to produce power, liquid fuels, and synthetic natural gas.