An Integrated Approach to Evaluating the Technical and Commercial Options for Cogeneration Facilities in the Process Industry

Abstract

Cogeneration under the PURPA law is providing opportunity to the Process Industry not only to conserve fuel and electric costs associated with commercial process production, but effectively to share in the revenue from the sale of consumer power. The law permits release of fuel energy significantly in excess of that required for the process, expressly for the production of export electric power, with only a small required fraction contributing to sequential production of useful heat. The low required thermal energy fraction ostensibly allows systems which are hardly integrated at all with the processes involved, subject to evolving agency/legal interpretations. However, greater degrees of process/power system integration can produce increased conservation, not only of energy but of financial resources. This paper describes an integrated approach wherein technical and economic criteria are applied to size and select candidate cogeneration systems. The approach is integrated with regard to technical, economic and financial considerations, as well as to the determination of the appropriate degree of thermal integration of the power and process subsystems. An overview of steam and gas turbine cycle options for process/power integration typical of the refinery, olefins, and other industry complexes is presented. The cycles described include hot gas and steam heat recovery, going beyond the currently popular gas-turbine/ heat-recovery-steam-generator combination.