Improvements in Thermal Efficiencies with Single-stage Reheating at High Steam Pressures and Temperatures

Abstract

In this paper are supplemented the data given by Baumann and by Finniecome in papers on improvements in thermal efficiencies with high steam pressures and temperatures in non-reheating plant. Except for changes necessary to cover single-stage reheating, the same basic assumptions as listed in Finniecome's paper are followed; a detailed feed-heating heat-balance is included in Appendix II as an example. Curves from Finniecome's paper, extended to higher steam conditions and showing the improvements in thermal efficiencies, non-reheating, at various pressures and temperatures, are included to preserve continuity and for comparison with single-stage reheating cycles on a common basis of 600 lb. per sq. in. gauge, 800 deg. F. non-reheating. With single-stage reheating, the effect of varying the feed-temperature at different reheat pressures is illustrated by the results of typical examples which were calculated to determine the optimum feed-temperatures. The improvements in thermal efficiencies due to reheating at various reheat pressures are plotted for stop-valve steam pressures of 900, 1,200, 1,500, and 2,000 lb. per sq. in. gauge; the loss when reheating to a temperature which is 50 deg. F. below the stop-valve temperature is also indicated. The thermal performances reheating and non-reheating, relative to 600 lb. per sq. in. gauge, 800 deg. F., non-reheating, are included; the improvement in thermal efficiency due to reheating is plotted against stop-valve pressure with initial and reheat steam temperatures as parameters for a reheat pressure which is 25 per cent of the stop-valve pressure. The effects of changing certain basic assumptions (such as the pressure drop across the reheater and the vacuum) are stated; wetness values at exhaust reheating and non-reheating are given for comparison.