Scavenging of throttled msr tube bundles

Abstract

Improved means for substantially eliminating condensate subcooling in single-stage moisture separator reheaters is provided by recirculating large quantities of scavenging steam through the reheater tube bundle. Heating steam for the tubeside (within the tubes of the tube bundle) of the reheater is extracted from the main steam supply upstream of the high-pressure turbine. This main steam is throttled before entering the tube bundle at part load conditions to reduce the temperature differential with respect to the high-pressure turbine exhaust steam which is to be reheated on the shellside. The tubes of the tube bundle are differentially orificed at their inlet to provide sufficient steam to each tube based on complete condensation at tube exit. At throttled, part load conditions, considerable excess scavenging steam is required to correct for the inefficiencies of the fixed orifices at these off-design conditions. Substantial amounts of scavenging steam are recirculated through the tube bundle with the use of a high differential pressure thermocompressor. Unthrottled, high-pressure main steam is isentropically expanded in the thermocompressor, drawing a substantially higher amount of throttled, lower pressure steam from the outlet header of the tube bundle. The combined discharge steam from the thermocompressor is fed to the inlet of the tube bundle, resulting in a recirculation of large quantities of scavenging steam. Minimal thermodynamic loss is achieved since the tube bundle scavenging steam is reused to continually scavenge the tube bundle.