Comparison of Combustion and Gasification between Crushed and Block Coals in UCG Model Tests

Abstract

Small-scale underground coal gasification (UCG) model tests with a linking hole were carried out using two types of specimens made of either block coal or crushed coal to clarify their characteristics of combustion and gasification. Many similar characteristics were found between both specimens in terms of temperature change and its spatial distribution as well as concentration and heating value of each gas product as long as the crushed coal specimen was sufficiently consolidated. The shape and dimension of the cavity formed in the both specimens were also similar. Texture of the both specimens was changed after the combustion and gasification. Initiation of radial cracks from the linking hole was found in the both specimens. Within the zone with the radial cracks initiation, grains in the crushed coal were bonded whereas cleats in the block coal were healed. The grain bonding and the cleavage healing can be explained by melting and expansion of coal due to temperature increase. The radial cracks are likely initiated after the grain bonding or the cleavage healing due to tensile thermal stress induced by temperature gradient in the coal specimens. It can be concluded that the characteristics of combustion and gasification of the crushed coal and the block coal are similar because both types of coals become similar in texture through combustion and gasification. These results indicate that characteristics of combustion and gasification of coal seam can be mostly estimated from a model test with artificial coal seam made of crushed coal.

Keywords

• ucg
• crushed coal
• block coal
• combustion cavity
• combustion and gasification
• radial cracks