Pyrolysis of high sulphur coals: possible sulphate aerosol formation

Abstract

Sulphate aerosols exist in the atmosphere as a suspension of fine solid particles of sulphates (SO42–) or tiny droplets of a solution of a sulphate or sulfuric acid. The sulphate particles in the atmosphere are about 0.1 to 1.0 micrometer in diameter and are particularly concentrated over industrial areas using coal. The north-eastern region (NER) of India has a substantial deposit of high sulphur (2–8%) coals with low ash, high volatile matter (35–45%) and high vitrinite maceral contents. Coal contains generally three forms of sulphur: sulphate, pyrites and organic sulphur. The majority of sulphur present in these coals is generally in the organic forms which are aliphatic or aromatic disulfides, heterocyclic compounds of the thiophenic types etc. During the combustion and carbonization of these coals, its sulphur is emitted to the atmosphere as sulphur dioxide and forms sulfuric acid in the presence of sunlight. The presence of metal ions such as Fe, Mn etc. in the environment catalyzes the process of SO2 to SO42– conversion. In the present investigation, carbonization study has been done in an experimental coke oven (pilot plant of 100kg/batch capacity) where samples of stack, PM2.5, PM10 and SO2 released were collected and analyzed. Estimation of released SO2 and particulate SO42– formed by secondary air in the environment has been made. Various conversion rates of SO2 to SO42– have also been discussed.