Discussion on Coal Gasification Technology —— Underground Coal Gasification
Abstract: Underground coal gasification is influenced by many objective conditions. Therefore, in order to ensure the safety of underground coal gasification, it is necessary to control the relevant conditions. As a coal-related worker, the author knows the importance of underground coal gasification control. On the basis of systematic research on underground coal gasification, the author comprehensively discusses underground coal gasification combined with his own working experience.
Keywords: underground coal gasification control method
In 1950s, China conducted underground coal gasification technology experiments in Datong Wankuang, Jiaohe Mine and Hegang Xingshan Mine 10. During the period of 1958 ~ 1962, experiments of underground coal gasification under natural conditions were carried out in Datong, southern Anhui, Shenbei and other mining areas in China, and certain results were obtained. 1984, China university of mining and technology (Beijing) underground coal gasification engineering research center began to study underground coal gasification technology. 863? With the support of the planned project, the comprehensive model test-bed and measurement and control system of underground coal gasification with world advanced level have been built, and relevant theoretical research and model test research have been carried out, and the technological parameters of underground coal gasification of lignite, bituminous coal and anthracite coal have been obtained. According to different coal seam occurrence conditions, field tests and production of underground gasification with wells have been carried out successively in Xinhe No.2 Well in Xuzhou, Jiangsu, Liu Zhuang Coal Mine in Tangshan, Hebei, Xinwen Suncun Coal Mine in Shandong, Ezhuang Coal Mine in Xiyang, Shanxi and Xingdanyu Coal Mine. Formed with China's independent intellectual property rights? Long passage, large section, two stages? The new technology of underground coal gasification is the first at home and abroad, which has been proved by the novelty of scientific research results.
Study on the structure of 1. gasifier
The basis of field test is to establish an underground gasifier with reasonable structure according to the occurrence conditions of coal seam. The material layer of underground gasifier can't move, so measures must be taken to control the movement of gasification working face to keep the gasification process continuous. Therefore, the structure of gasifier must adapt to the requirements of gasification process, and adjust the horizontal position and height of gas supply point and exhaust point, that is, realize the two-dimensional control of gas supply point and exhaust point. Therefore, on the basis of field test and according to the occurrence characteristics of steep coal seam, an adjustable push underground gasifier is designed.
Second, the auxiliary channel of aeration.
The operation experience of the existing underground gasifier proves that it is the main condition for the stable gasification of the underground gasifier to uniformly blow air to the coal seam reaction surface at different working stages. Different natural conditions of coal seam burial, different composition and thickness of coal seam, different chemical properties of coal and different roof stability will make uniform air supply to coal seam more or less complicated. But in any case, only by solving this problem smoothly can the stability of underground gas producer be guaranteed. When the auxiliary channel supplies air, it can form a disturbed airflow perpendicular to the main flow direction. This disturbance is distributed in the whole oxidation zone, which undoubtedly improves the diffusion ability of gasification agent to the reaction surface. In order to measure the completeness of the transfer of gasification agent to the surface of reactive coal, it can be expressed by the effective aerodynamic activity coefficient of gas flow, which represents the ratio of the percentage of combustible components produced by reduction as a result of heterogeneous reaction to the percentage of original components in gas.
Thirdly, aeration is carried out by combining pressurization with pumping.
Reducing the pressure of reduction zone and dry distillation drying zone is beneficial to the timely discharge of combustible gas and reduce the leakage rate of combustible gas, but the pressure of oxidation zone should be positive. In order to meet the requirements of oxidation zone and reduction zone at the same time, the gasification scheme combining pressurization and pumping can be adopted. Then the air inlet is used to blow in air, and the air outlet draws out air through the induced draft fan to adjust the blowing pressure and negative pressure, so that the reduction zone is in a lower pressure state. The gasification scheme combining pressure and pumping can be used in two unstable gasification processes. 1 for coal seam caving, roadway resistance increases, resulting in reduced air supply. The calorific value decreases. 2 is the leakage of gasifying agent or gas, which leads to the decrease of gas flow. In the field test, compressed air gasification is generally the main method, but the calorific value of gas fluctuates greatly when the coal seam falls. In this case, the gasification process combining pressurization and pumping can achieve the goal of stable gas production. The air leakage is significantly different due to the different occurrence conditions of coal seams, and the buried depth of coal seams, air permeability and the degree of rock breakage of roof and floor all have influences on the air leakage. Although corresponding measures have been taken when designing the gasifier, such as grouting sealing walls in coal lanes and rock lanes connected with the gasifier, or even enclosing gasification panels with isolation belts, there will still be a small amount of air leakage after the gasifier is ignited, which will affect the aerodynamic conditions in the gasifier to varying degrees, reduce the calorific value of gas, and even affect mine safety when horizontal gasification is abandoned.
Fourthly, reverse gas supply gasification
During forward gasification, the flame working face will gradually move to the gas outlet, and the dry distillation drying zone will be shorter and shorter, and the later reduction zone will be shorter and shorter. Finally, the length of the reduction zone will not meet the needs of carbon dioxide reduction and water vapor decomposition reactions produced in the oxidation zone, and the calorific value of gas will decrease. At this time, the reverse gasification scheme must be adopted, that is, air is blown from the outlet hole, and the original inlet hole is discharged, so that the flame working surface moves in the direction of the inlet hole, and new gasification conditions are formed again. Reverse gasification has advantages and disadvantages for gasification process. The advantages are as follows: firstly, air is preheated in the original high-temperature exhaust hole during air blowing, and the water vapor in the gasifier is additionally decomposed by using this heat energy to improve the hydrogen content. Through the physical heat introduced by blast, approximately equal thermal energy can be obtained in the gas. Secondly, when the air is supplied in the reverse direction, the reduction zone and the dry distillation drying zone are both in the combustion zone when the air is supplied in the forward direction, so the temperature is higher, and the temperature conditions of the reduction reaction and the dry distillation effect are better. Thirdly, the metal oxides in the ash downstream of the airflow play a catalytic role in the reduction reaction. The main disadvantages are: first, the movement of flame working face will be affected by ash. Secondly, dry distillation occurs when the coal seam is blown forward, and the output of dry distillation gas is affected. However, these unfavorable factors can be compensated by the new working face exposed by coal seam caving. Therefore, in reverse gasification, gas with the same calorific value as forward gasification can be obtained. Reverse gasification can realize multi-pass gasification and improve the gasification rate of coalbed methane.
Local reverse gasification can solve the problem of unstable calorific value caused by local blockage of gasification channel, and can also control the combustion height of coal seam locally. Blowing into the air inlet, the gasification working surface moves to the adjacent auxiliary hole. When the end of the oxidation zone is close to the auxiliary hole (the judgment is based on the gradual increase of oxygen content in the gas sample in the auxiliary hole), gas can be supplied from the auxiliary hole and exhausted from the air inlet, thus forming local reverse gas supply gasification.
Verb (abbreviation of verb) conclusion
This paper discusses the development status of underground coal gasification in China, and based on this status, analyzes the relevant contents of underground coal gasification from different angles. Through the above analysis and discussion, the following conclusions are drawn: First, the auxiliary channel air supply can improve the effective aerodynamic coefficient by more than 10%, and when the coal seam falls into the oxidation zone, the auxiliary channel air supply can stabilize the airflow. Secondly, the pressure pumping combined with gasification can appropriately increase the reduction reaction rate and reduce the leakage rate of gasifier by about half. Thirdly, reverse air supply gasification can obtain the same quality gas as forward air supply gasification, and the moving speed of gasification working face is equivalent to forward air supply, which is 0.42m/d under experimental conditions. Reverse gas supply gasification can improve the gasification rate of coalbed methane.
refer to
[1] Zhang Qiang. Underground coal gasification technology [J]. Prospecting Engineering, 200 1, (1): 6-9.
Zhao Shoukun, et al. Progress and reaction process of China underground coal gasification test ship 9 [J]. Gas and thermal power, 20iX), (3): 2 12-2 13.
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