Performance update: Low pressure wet air oxidation unit at grangemouth, Scotland

In response to a requirement to provide a low-capital, low operating cost solution for the treatment of steam cracker spent caustic, BP Chemicals Ltd. (BPCL) and Stone and Webster Engineering Ltd. (SWEL) have jointly developed a Low Pressure Wet Air Oxidation Process. The first of these units has been in operation at the BPCL Grangemouth, Scotland facility for the last three years. In that time, it has demonstrated totally effective sulfide removal, surpassing design targets, and producing a neutralized effluent well within the allowable discharge consents for the site. The Grangemouth unit is designed to treat the spent caustic effluent from two crackers with a combined capacity of 600 KTA (currently being expanded to 700 KTA) from both liquid and gas feedstocks. A significant feature of the installation has been the extremely high level of reliability and availability, ensuring trouble-free operation and full compliance with effluent consent levels mandated by the regulatory authorities. At the same time, the unit has demonstrated very low operating and maintenance costs. The design basis and initial commercial experience was presented at the AIChE Spring National Meeting in April 1994 [1]. This paper concentrates on the operational history of the Grangemouth unit, highlighting the process developments and improvements that have been made in the last three years.