(678g) Emission of Sulphur and Nitrogen Based Pollutants in Commercial Scale Circulating Fluidized Bed Gasifiers

Coal gasification technology has attracted great attention and a number of commercial coal gasification plants have been in operation. Environmental concerns should been taken as well as gas heat value, cold gas efficiency and carbon conversion in coal gasification. In the next years, Institute of Engineering Thermophysics of Chinese Academy of Sciences have designed the circulating fluidized bed gasification system to produce industrial fuel gas, and about 30 suits of commercial coal gasification system have been built in coking and smelting industry. This paper studied wastewater of three different scale coal gasification system, and the release of minor contaminants (N, S compounds) was studied by sampling and analyzing the feedstock, ash, slag and the producer gas. Little tar and phenol was detectable in the three water samples. The main pollutants were COD_Cr, ammonia nitrogen and sulphate, the concentration of whom were 113mg/L to 890 mg/L, 270 mg/L to 903 mg/L, 14 mg/L to 60 mg/L, respectively detected in the gasification wastewater. There was low toxicity due to low level of complex organics. Ammonia nitrogen should been removed firstly because of the low C/N ratio. The NH₃ and H₂S and COS concentrations in the producer gas were 300ppm, 530ppm and 80ppm. There was little HCN detected in producer gas. The elements analyze of fuel coal, ash and slag indicated that more than 96.61% of fuel-S transferred to H₂S and COS. The conversion of fuel-N to ash and slag was less than 1%. A large portion of NH₃ in producer gas dissolved in water along the gas condensation which made ammonia nitrogen concentration in wastewater cannot reach the discharge standard.