Slow-Roll of 40 MW Condensing-Extraction Steam Turbines in a 420 MW Cogeneration Plant

Abstract

This paper describes efforts required to operate condensing-extraction steam turbine generators with flexible rotor design on a slow-roll (also called, true stand-by) mode of operation. This mode of operation became necessary as a result of changing steam demand from the refinery and the resulting decreased performance of the existing steam turbine generators and the associated economic losses for the cogeneration facility. Design modifications implemented to achieve slow-roll of steam turbine generators and produce maximum power output obtainable with new steam flow conditions without affecting reliability and availability of the entire cogeneration facility are discussed in this paper. Successful implementation of the proposed design approach was demonstrated through extensive field testing completed in the summer of 2011. A simple life cycle economic analysis shows that the payback period associated with the proposed design modifications implemented to two steam turbine generators at the plant is approximately six (6) months.