Achieving Better Power Plant Guarantees Through a New Exergy-Based Approach for the HRSG

Abstract

The best assurance an owner has to maximize the performance of the entire combined cycle power plant is the perfect alignment of heat recovery steam generator (HRSG) performance guarantee metrics to this goal. Currently, HRSG equipment performance guarantees include steam generation rates and steam temperature at each pressure level plus draft loss and reheater pressure drop. This profusion of guaranteed parameters with multiple bonus/liquidated damages (LD) rates is not always well correlated to the customer's ultimate goal of delivering power from the bottoming cycle since the behavior of each steam generation circuit is a complex function of steam pressure, steam turbine performance, and gas turbine exhaust temperature. This paper proposes a solution that normalizes and combines all HRSG performance measurements into a single value directly and reliably tied to the customer value metric (which may be different for fired and unfired operation or other load points). This is achieved by expressing the HRSG performance guarantee in terms of exergy recovered to steam and plant exergy loss attributable to the HRSG (gas side draft loss). This will be shown, with examples, to serve the goals of the customer to confirm by test that an HRSG delivers the promised steam exergy consistent with the plant level performance requirement.