Shell U.K. Ltd. completed its largest single environmental program with inauguration of a 35 million ($52.5 million) water treatment plant at its Stanlow refinery and petrochemical plant, Ellesmere Port, England.
In trials during the first half of this year, the new plant removed 95% of trace oil and dirt from 6,850 metric tons/hr of water discharged to the Manchester Ship Canal, River Gowy and Thornton Brook.
Shell realized the need for a new water treatment plant in 1988 when existing equipment was deemed to be near its operational limits. The main treatment was in 37 interceptor pits, where oil and dirt were skimmed off.
Pollution had occasionally passed National Rivers Authority consent levels, and the equipment could not meet expected tighter environmental standards.
Flow studies involving the site's 12 production units showed water quality management would be simplified by cutting the number of water outlets to four from 21. This involved installing 20 km of piping and 43 pumps.
A total 600 metric tons/hr of process and surface water requires treatment in the interceptor pits. These were refurbished with new plate racks and improved skimmers.
Two dissolved air flotation (DAF) units were installed to improve cleaning and filtering in the interceptors. The DAF units inject tiny air bubbles into the water, which rise to the surface carrying droplets of oil and dirt.
A third DAF unit was installed specifically to treat process water from the site, which Shell said proves most difficult to clean.
Oil and dirt are skimmed off for collection and incineration in a refurbished plant that produces steam for use onsite.
Six oil storage tanks were converted for storage of waste water awaiting treatment. These have total capacity of 55,000 cu m.
Most of the site's water throughput is used for cooling. Cooling water is kept clean and is drawn from and discharged to the canal at a rate of 6,250 metric tons/hr.
Shell has set aside a further 35 million ($52.5 million) for future water treatment improvements at the site. A year long study and performance analysis is under way to assess the need for further refinements such as a biotreater.
Discharges of treated process and surface water into Thornton Brook were said to have improved sufficiently to bring about a return of mute swans, teal, mallard, dabchick, and fish to the brook.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.
