Process Parameters Optimization for Ammonia Decomposition up to 99% in Coke Oven Plants

Abstract

Catalytic ammonia decomposition is carried out in the byproduct-plant of Coke Oven-3. This process is picking up due to its ability to decompose the ammonia recovered from coke oven gas. Because of the corrosive nature of ammonia, its removal is a necessity in coke oven byproduct plants. The process begins with the ammonia vapors coming from the ammonia distillation column. The vapors from the distillation unit flow into a refractory-lined ammonia decomposition furnace. Coke oven gas as a supportive fuel and a stoichiometric amount of combustion air are also fed to the burner, at auto controlled flow rates. Within the reactor is a nickel catalyst bed. In the presence of the nickel catalyst, NH₃ is decomposed into nitrogen and hydrogen at a temperature of 1000 °C. The gas is further cooled to 80 °C through heat exchangers, then at the exit tail gas analysis is done to measure the percentage decomposition of NH₃. According to norms, the NH₃ in the outlet should be 30 to 40 mg/m³; however, in actual practice it is as high as 900 mg/m³, possibly due to increased amount of ammonia vapors in the feed. The present study is aimed at minimizing the NH₃ content at the outlet. Increased NH₃ content at the inlet leads to less residence time of vapors with the catalyst. As per the plant design, 18.46 ton of catalyst is used in the furnace to decompose 4200 kg/h of NH₃ containing vapor. In actual practice, 5200 kg/h of NH₃ vapor is made to flow through the decomposition chamber. The catalyst is not able to effectively process the excess amount of NH3 vapor, resulting in high concentration of NH₃ in the tail gas. 

Keywords: Ammonia decomposition, optimization, coke oven byproduct