Effect of alkali carbonates on the formation of H₂S and NH₃ during temperature programmed pyrolysis of brown coal

Using a brown coal from Ximeng mine in Inner Mongolia as raw sample, 3% the carbonates of lithium, sodium or potassium were evenly mixed with raw coal and demineralized coal (the inherent mineral was removed by acid-washing). The effects of the minerals and the alkali carbonates added in raw coal on the formation of H₂S and NH₃ during temperature programmed pyrolysis was studied by a fixed-bed reactor and gas chromatography. The results show that the inherent mineral in Ximeng brown coal can restrain the formation and release of H₂S and NH₃ during pyrolysis. The temperature range of maximum H₂S release from demineralized coal is same to that of raw coal because the organic structure of coal and the form of sulfur are not changed. But the behavior of NH₃ is obviously changed in the different temperature range because the secondary reaction of HCN is also one of main sources for NH₃ formation, which is affected by the pore structure change of coal demineralized by acid-washing. The alkali carbonates added have different effects on the formation of NH₃ and H₂S during pyrolysis. Except for K₂CO₃, the presence of alkali carbonates can prohibit the formation of H₂S. They can promote the formation of NH₃, except for Na₂CO₃ added in demineralized coal.