Thermal removal of COD and NH₃N from Lurgi coal-gasification wastewater

In this article, an alternative approach of wastewater utilization in coal-gasification process was proposed and evaluated. With wastewater being heated and sprayed into the gasifier, water vapor is treated as gasification agent and contaminants are thermally decomposed under specific conditions. The lab-scale experiments were performed using entrained-flow reactor system to investigate thermal removal of COD and NH₃N contained in wastewater by changing temperature, reaction atmosphere, oxygen proportion, and residence time. The experimental results show that reaction temperature has a significant effect on COD and NH₃N removal, and removal efficiency is obviously increased with temperature increased from 400 to 1000°C. The removal efficiency of COD and NH₃N in different atmospheres ranks in the order: oxidative > inert > reductive. The thermal decomposition of organic constituents is enhanced by increasing oxygen proportion and residence time. Furthermore, a simplified kinetic study of COD and NH₃N removal efficiency was carried out on the hypothesis of pseudo-first order reaction model. The pre-exponential factor and apparent activation energy for COD and NH₃N removal were obtained in the range of 3.63 × 10³−1.62 × 10⁶, 34.39–58.16 kJ mol⁻¹ and 1.58 × 10⁴−8.71 × 10⁵ s⁻¹, 41.25–61.75 kJ mol⁻¹, respectively.