What are stone coals??
Stone coals they are a black, shiny, homogeneous mass, have a white sheen and are grayish-black in color..
The composition of the working mass of hard coals is approximately the following, %: carbon C = 53.9-74.5, hydrogen H = 3.9-4.8, oxygen O = 9.4-3.9, nitrogen N* = 1.1-0.8, sulfur S = 3-0.6, moisture W = 13-7%, ash A = 15.7-8.4. The heat of combustion of the working mass Qr = 21.1-27.6 mJ/kg (5030-7070 kcal/kg).
How were stone coals formed?
Stone coals formed through the slow decomposition of trees and plant remains buried beneath a layer of soil without air. This formation began many millions of years ago.
How are stone coals classified based on their carbon and volatile matter content?
Depending on their carbon and volatile combustible matter content, hard coals are classified into the following grades: gas coal (G), rich coal (Zh), long-flame coal (D), rich gas coal (GZh), coke coal (K), coke coal (KZh), lean caking coal (OS), weak caking coal (SS), and lean coal (T).
Long-flame and gas coals have the highest yield of volatile combustible matter (over 30%), while lean coals have the lowest (9-17%).
Stone coals ash can be either fusible or refractory.
Stone coals containing low-melting-point ash create difficulties during combustion, as the low melting point of the ash often contributes to the formation of liquid slag, which floods the grates and impairs draft.
