SCR DeNOx in new maruzen ethylene plant

Environmental regulations have tightened up during recent years, which requires new methods to reduce NOx emissions from ethylene plant cracking furnace flue gases. The reduction of NOx produced by the burners is reduced to the lowest possible levels, but is still higher than the new regulations require. In the 600 KMTA Maruzen Petrochemical Co. Ethylene Plant using ABB Lummus technology which has been operated since 1994, a Selective Catalytic Reduction DeNOx bed was incorporated in the middle of each SRT V heater convection tube bank. It was designed for reduction of NOx in the flue gas to 30 vppm (6%O-2, dry). This technology has been proven in the power generation industry, but is the first attempt to introduce it into cracking, heaters of an Ethylene Plant. The concept of SCR is to convert the NOx contained in the flue gas by reaction with ammonia to produce non-toxic products. The reaction must take place in a temperature range that requires a detailed heater thermal calculation check to keep catalyst performance. Modular construction including the catalyst bed, steel casing, and insulation allows successful installation in the tight space in the convection bank. It also provides good flexibility for maintenance of the reaction section. After initial startup of the plant, the system has been operated successfully with expected performance for six years over four years' guaranteed life. But it was found out that DeNOx catalyst has been deactivated by condensation of chromium oxides mist on the catalyst surface which has vaporized from radiant coil. This paper discusses the concept of SCR DeNOx, how the system was incorporated into tile Maruzen Ethylene Plant and performance history.