Modeling and improving the scrubbing efficiency of an intensified ammonia process for coke oven gas purification

Coke oven gas (COG) is a valuable byproduct of coke production in the steel industry. Conventionally, undesired H2S and NH3 in COG are removed in separate columns in an ammonia process. In this work, an intensified ammonia process which removes both H2S and NH3 in a single column with multiple sections is studied. The intensified process occupies less space and is less expensive. A process model is built and validated using plant operating data. The underlying principal of scrubber operation is explained through the simulated concentration profile. The influences of important operating variables such as inlet COG flowrate, strong ammonia liquid flowrate, low ammonia liquid flowrate and concentrated NaOH solution flowrate are studied. It is shown that the H2S removal efficiency is sensitive to inlet COG flowrate, and that the flowrate of low ammonia liquid should be used as manipulate variable to control the outlet COG composition. Furthermore, it is found that to improve the H2S removal efficiency, the flowrate of concentrated NaOH solution should exceed a certain threshold. Otherwise the scrubbing liquid will be neutralized by CO2 in the COG, which will decrease the pH and alkalinity of the scrubbing liquid significantly.