Influence of natural weathering and low-temperature oxidation on the combustion behavior of bituminous coals.

摘要

The structural changes caused by natural weathering and low-temperature laboratory oxidation and their effect on subsequent combustion behavior were investigated. The study was conducted on six sets of coals, each comprising a fresh and an outcrop coal from the same seam. The effect of stock-pile storage for up to 30 days on the combustion behavior was also evaluated.;Changes to the organic structure of the coals upon natural weathering and laboratory oxidation, as shown by DRIFT and ;The volatiles release rate, as observed by thermogravimetric analysis (TGA), was slower and the volatiles were released over a wider temperature range for the oxidized coals than was the case for the fresh coals. The volatiles from the outcrop coals were leaner in aliphatic and aromatic hydrocarbons and other combustible gases and richer in oxygenated species (as determined by Py GC-MS) than the fresh coals. The relative ignition temperatures of the outcrop coals were lower than those for the corresponding fresh coals.;Both naturally weathered (outcrop) and laboratory-oxidized coals exhibited better combustion behavior, as evaluated by char reactivity and burning profiles using TGA and combustion efficiency as determined in a drop tube reactor (DTR), than the corresponding fresh coals. Due to some changes to the inorganic phase of the outcrop coals, they were found to be more reactive than the laboratory-oxidized coals. A good correlation between the difference in combustion efficiencies between the outcrop and the fresh coals and the oxygen uptake for the naturally weathered coals, and an inverse correlation between the combustion efficiencies determined in a DTR and the "Initial Temperatures" from the burning profiles obtained in a TGA were observed.