Effects of Cooling Conditions on Surface Properties of Heated Coals

Abstract

Cooling coal mines to prevent spontaneous combustion is usually considered to be one important method to prevent coal combustion. Cooling methods may be divided into two main types, a water cooling method and an isolate cooling method (under a vacuum condition). This investigation is to find out the effects of cooling conditions on surface properties of heated coals. Heated coals were cooled in a vacuum chamber and cooled in water. X-ray photoelectron spectroscopy, scanning electron microscope, and contact angle measurements were used to indicate surface properties of heated coals under different cooling conditions. The results showed that heated coal cooled in water (Coal2) was more hydrophilic than heated coal cooled in a vacuum chamber (Coal1). Coal2 could be oxidized more than Coal1. This paper gives an opinion that cooling heated coals in spontaneous combustion using an isolate cooling method (under a vacuum condition) is useful for the flotation upgrade of fine coals, because the flotation upgrade of fine coals is based on the hydrophobicity of the coal surface. However, cooling heated coals in water reduces this hydrophobicity because an oxidation process can occur on a heated coal surface in water.