Carbochemistry

About: Carbochemistry is a research topic. Over the lifetime, 1010 publications have been published within this topic receiving 16626 citations.

The Nature of Coal

Abstract: Coal is used primarily as a fuel, so its most important property is its heat of combustion. Gross calorific value , also known as higher heating value (HHV) , is determined by measuring the heat released when coal is burned in a constant-volume calorimeter, with an intitial oxygen pressure of 2 to 4 MPA, and when the combustion products are cooled to a final temperature between 20 and 35°C. Coal is a porous medium, and these pores, especially in low rank coals, can contain substantial quantities of water even though the coal appears to be dry. In the coalification process, the coal rank increases from lignite to anthracite. Bituminous and subbitumous coals are the primary commercial coals. A relatively small amount of anthracite is available. Some coal, particularly bituminous coal, has the tendency to cake. With increasing temperature, coal particles simultaneously pyrolize and partially melt, causing the coal particles to stick to one another. Some gasification reactors, especially moving bed and fluidized bed gasifiers, are limited to processing coal that does not cake. The melting temperatures of coal ash impose temperature limits for coal gasification. Fluidized bed gasifiers and dry-bottom moving bed gasifiers, such as the Lurgi gasifier, require free-flowing ash. The maximum operating temperature for these gasifiers is the initial deformation temperature.