General Electric Company

William G Reed

Russell L Shade, Jr

Jack S Mazer

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.

Scavenging of throttled MSR tube bundles

A Moisture Separator Reheater (MSR) has a plurality of tube bundles which receive high-pressure saturated (tubeside) steam therein. Steam to be reheated (shellside steam) is passed in heat-exchange relationship with the tubes of the first and second reheater tube bundles after first being dried by the panels of a moisture separator. It emerges from the shell of the reheater dried and heated. In the reheater tube bundles saturated steam at temperatures and pressures substantially higher than the shellside steam transfers heat to the shellside steam by condensation within the tubes. The steam in the second stage tube bundle is at a temperature and pressure that is substantially higher than that of the steam in the first stage tube bundle and is heating shellside steam at a higher temperature than the shellside inlet steam to the first stage tube bundle. A greater quantity of tubeside steam than is theoretically necessary is passed through the tube bundles. This excess steam causes scavenging of the tube bundle to substantially eliminate condensate subcooling and related instabilities. Scavenging steam is provided to the first stage tube bundle with essentially no thermodynamic loss by passing the exhausted scavenging steam from the second stage tube bundle through a high differential pressure (.DELTA.P) thermocompressor where it is isentropically expanded. It then entrains a higher rate of exhausted scavenging steam from the first stage tube bundle. The mixed discharge from the thermocompressor is then fed to the inlet of the first stage tube bundle, resulting in a high rate of scavenging steam therein. Minimal thermodynamic loss is achieved since the first stage scavenging steam is reused to continually scavenge the first stage tube bundle, rather than being exhausted to a lower energy point in the system, as is conventionally done, as for example to a feedwater heater.

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Portland, ME, United States of America

William G Reed