Mining coal by geochemical methods

Abstract

Underground mechanization has greatly increased output per man/shift by reducing the number of men employed underground, but has not led to manless mining. This calls for improved methods for coal extraction.underground gasification is one industrial method of mining in which the state of aggregation of the coal is changed. Other methods currently being tested are the extraction of coal by solvents, its conversion to a plasma, electrochemical attack, and processing by nuclear energy. These methods enables us to convert the solid coal to a liquid state or obtain gaseous products,thereby providing a more effective coal mining technique [1]. t Underground gasification of coal was first suggested by Mendeleev. He gave the process a theoretical basis and showed that it was a practical method. The process is of course essentially as follows: oxygen in various coneentrations and steam are fed to a combustion site in a coal seam, thereby producing a great amount of producer ga.~ which is piped to the surface.Underground gasification makes it far cheaper and easier to utilize the energy in coal. Furthermore, seams too thin to be worked by conventional methods (i.e., less than 0.5 m) can be utilized [2]. Work on underground gasification of coal is in progress in Belgium, Britain, the United States, Italy, France, and Poland. It should be mentioned that many countries are utilizing Soviet experience in this field [3]. There are. already underground gasification sites in the Moscow, Kuznetsk, Uzbekistan, and Donets Coalfields. This method completely eliminates conventional pit work; the men are mainly engaged at handling semiautomated drills, sinking pipes in boreholes, erection and fitting, and inspecting waterpipes and gas pipes [3].The performance of underground gasification plants could be improved by increasing their capacity and the scale of the work, by rational location of sites, and by improving engineering methods and individual stages of the process.Underground gasification is not the only shaftless method for underground processing of solid fuel.For conversion to high-grade liquid fuel, coal is subjected to destructive hydrogenation, one of the most efficient methods of chemical processing of coal.Hydrogenation consists in direct saturation with hydrogen or splitting of high-molecular coal compounds and addition of hydrogen to the products thus obtained. This gives low-molecular hydrocarbons, used as motor fuel. Addition of hydrogen to coal is promoted by high temperature (400-450~ and pressure (up to 700 arm), and hightemperature stable catalysts (nickel sulfide, tungsten sulfide, molybdenum sulfide, etc.). An increase in hydrogen pressure 9 1000 arm greatly increases the velocity and degree of hydrogenation [4]. In the destructive hydrogenation process the coal is precrushed, the powder mixed with heavy oil, and then subjected to hydrogenation in 2 to 3 stages; this makes for more efficient manufacture of liquid fuel.The underground production of liquid fuel from coal by hydrogenation is described in [5]; at a ...