REHABILITATING DETROIT'S CRYOGENIC OXYGEN SUPPLY, WHAT ARE THE OPTIONS?

Author： Hulsey Robert A. Bailey Sidney Korpela Thomas M.

ISSN： 1938-6478

Source： Proceedings of the Water Environment Federation, Vol.2000, Iss.10, 2000-01, pp. : 667-681

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Abstract

The Detroit Water and Sewerage Department (DWSD) provides sewerage services to the City of Detroit and a majority of its suburbs. Facilities at the 5,730 Mld (1,520 mgd) WWTP include primary treatment with chemical addition for phosphorus removal, secondary treatment with high-purity oxygen, chlorination, and sludge processing and disposal. Oxygen for secondary treatment is supplied by two cryogenic distillation plants with capacities of 163 and 363 metric tonnes per day (180 and 400 tons/day). Installed in the 1970's, both of these facilities are in need of rehabilitation and updating.Black & Veatch was retained to conduct a capacity study which included; (1) projecting future oxygen production requirements, (2) evaluating the existing facilities' ability to meet those requirements, (3) determining necessary improvements for both plants, and (4) comparing the upgraded facilities to other options to maintain a reliable, inexpensive oxygen supply. In addition to evaluating oxygen production at the wastewater treatment plant, the addition of a liquefaction process was considered. The liquefier would take excess oxygen production capacity from the cryogenic plants during nine months of the year and convert it from a gas into liquid oxygen (LOX) for storage and use at ozone facilities to be installed at Detroit's water treatment plants.The recommended approach was to rehabilitate the existing cryogenic oxygen plants. This approach minimized capital and operating costs, while keeping DWSD in control of oxygen production. In addition, the incorporation of a 91 mtpd oxygen liquifier was estimated to provide liquid oxygen at approximately 31/metric tonne, which compared favorably to local LOX costs of 88/metric tonne. The installation of an oxygen liquifier would be worthy of further consideration if ozone is used at the water treatment plants.