Pilot-scale testing of direct contact cooler for the removal of SOx and NOx from the flue gas of pressurized oxy-coal combustion

Abstract

To attain the purity standard for carbon sequestration, SOx and NOx must be removed from the flue gas of pressurized oxy-combustion of coal. Studies suggest that at high pressure SOx and NOx can be simultaneously removed in a single column, with water as the working fluid. Additionally, in pressurized oxy-combustion the moisture in the flue gas can be recovered at high temperature. However, to date, experimental investigations in pressurized oxy-combustion environments have been largely limited to laboratory scale and room temperature. This work demonstrates the operation and parametric testing of an experimental pilot-scale direct contact column with a diameter and packing height of 0.2 m and a 2.3 m, respectively, over a temperature range from 24 to 202 °C, O2 concentration from 1 to 4% v/v, and S/N ratio from 0 to 2. Additionally, a model of the direct contact column is developed and simulated in Aspen Plus to complement and interpret the experimental results. The study reveals that NO oxidation is the controlling reaction in the overall scrubbing of SOx and NOx at gas temperatures up to 200 °C. The NOx scrubbing efficiency depends on residence time in the column, with higher than 90% removal at a residence time of 120 s. Oxygen concentration has little effect above a concentration of 1% v/v. At high temperature, the total NOx scrubbing efficiency is reduced by approximately 10%, as compared to room temperature. SOx removal is higher than 93% under all conditions. Scrubbing efficiency at different S/N ratios demonstrate the importance of NOx in sulfur scrubbing and confirm that a low NOx concentration in the flue gas can lead to a significant reduction in SOx scrubbing.