Pressurized coal carbonization

Figure 1, Flow diagram of pressurized coal-carbonization system...

Pressure of Carbonization. The effect of a pressurized carbonization is to create a closed system preventing loss of volatile materials. Hence, carbon yields increase. Further, the material normally lost as volatiles in open systems is now retained and the effect of this, by reducing turbulence and bubble formation, is to enhance the size of resultant optical textures. Hiittinger and Rosenblatt (54) report such effects when gas pressures up to 15 MPa pressure (150 bar) were applied to the carbonization of a coal-tar pitch. If higher pressures are used, the pressure being applied hydraulically to the carbonization system, then the effect of pressures at, say, 300 MPa, is to enhance the viscosity of the total system and this prevents coalescence of the mesophase. The resultant appearance of the carbon has been described as botryoidal (55, 56) and an example is Figure 8. 

Low Sulfur Fuel by Pressurized Entrainment Carbonization of Coal... 

All these projections must be treated with caution since the science involved in the uptake of gases by coal is imperfectly understood and complications may arise. As the concentration and prevailing pressure of carbon dioxide increase, adsorption on the coal surface is replaced by absorption (or dissolution) into the structure of the coal. The coal loses its brittle nature and becomes rubbery the latter, in turn, leads to plastic flow. The extent to which this change in state occurs is dependent upon the carbon dioxide pressure, the temperature and the nature of the coal. A probable consequence of plastic flow would be the sealing of capillary channels in the coal and thereby a reduction in its capacity to absorb more gas. Another pertinent factor is that coal swells as carbon dioxide is absorbed and this, too, would cause a major decrease of permeability and consequent gas uptake. For both of these reasons, present estimates of the capability of coal seams to absorb carbon dioxide should be treated as tentative. 

PCO2 Partial pressure of carbon dioxide in the atmosphere, which was approximately 200 ppm during the last glacial maximum (about 18 ka), 280 ppm prior to the growth of industry in the mid-1800 s, 365 ppm at the end of the twentieth century, and continues to rise as coal and oil are burned. 

Cmde gas leaves from the top of the gasifier at 288—593°C depending on the type of coal used. The composition of gas also depends on the type of coal and is notable for the relatively high methane content when contrasted to gases produced at lower pressures or higher temperatures. These gas products can be used as produced for electric power production or can be treated to remove carbon dioxide and hydrocarbons to provide synthesis gas for ammonia, methanol, and synthetic oil production. The gas is made suitable for methanation, to produce synthetic natural gas, by a partial shift and carbon dioxide and sulfur removal. 

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