Concomitant removal of NOx and SOx from a pressurized oxy-fuel combustion process using a direct contact column

Abstract

The simultaneous removal of NOx and SOx using a direct contact column has potential for efficient treatment of the flue gases arising from pressurized oxy-fuel combustion. This study focuses on a parametric analysis of the efficiency of NOx and SOx removal from the flue gas of an oxy-fuel combustion process using an Aspen Plus direct contact column model. The chemistry implemented in this model reflects the state-of-the-art NOx and SOx reaction mechanisms, with particular emphasis on the liquid-phase chemistry, including pH-dependency. The effects of pressure, water flow rate, and recycle ratio on the removal efficiencies of NOx and SOx were evaluated. The evaluation was conducted based on the base case pressurized (15bar) flue gas with a feed rate of 120kg/s and inlet temperature of 40°C before it was supplied to the column. NOx removal efficiency increased from 70% to 97% when the pressure increased from 15bar to 30bar, whereas 99.9% of the SO2 was absorbed from the flue gas at 15bar. We show that the removal efficiency is pH-sensitive and it is directly influenced by the recycle ratio and liquid-to-gas ratio (L/G). As the L/G ratio was increased, the removal efficiency of SOx and NOx increased. On the other hand, when the recycle ratio of bottom liquid was increased, the removal efficiency of SOx and NOx decreased.