Dynamic behaviour of sulphur forms in rapid hydropyrolysis of coal

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Seven bituminous and sub-bituminous coals were rapidly hydrodesulphurized with a free-fall pyrolyser at atmospheric pressure, temperatures up to 1233 K and a heating rate of ≈ 6000 K s −1. The observed changes in the contents of sulphur forms were successfully simulated kinetically. Organic sulphur content was reduced by 54–92% and pyritic sulphur was almost reduced to ferrous sulphide sulphur in a very short reaction time of < 0.5 s. The release rate of volatile organic sulphur to tar and gas increased with increasing release rate of volatile matter and with increasing internal surface area. As the release rate of volatile matter changed from 8 to 43 s −1 with the increasing ratio of internal surface area of 1–4, the frequency factor of the release rate of volatile organic sulphur to tar and gas increased from 1.1 × 10 5 to 3.4 × 10 5 s −1 and that of organic sulphur to tar increased linearly from 3 × 10 4 s −1 to 2 × 10 5 s −1. The desulphurization results of total sulphur and char yield in rapid hydropyrolysis at atmospheric pressure and those in slow heating hydropyrolysis at high pressure are comparable. Comparing the observed rates of the desulphurization steps to those obtained under slow heating at high pressure treatments, rapid hydropyrolysis increases the frequency factors in the rate of release of organic sulphur to gas and tar by 2.5–10 times, while the frequency factors in the reduction rate of pyrite is suppressed by three to four orders. Rapid hydropyrolysis has potential as a pre-treatment process with high thermal efficiency for coal cleaning.