Abstract
Sustained high steam temperatures at all operating ratings, not peak readings at one narrow load range, are being sought in the industry’s quest for higher operating efficiencies. Uniform average temperatures, not maximum values, determine commercial economy and even safety of higher steam temperatures. Since premiums are paid for high-temperature equipment on the basis of maximum temperatures, it is important that operating temperatures be uniformly high. Decreasing trends of boiler duty and increasing tendencies of superheater and reheater duty, plus multi-valving of turbines, emphasize the inadequacy of purely convection surfaces for maintaining uniform temperatures. A 200-deg. fahr. drop in reheated-steam temperature from full load to quarter load when using only convection surfaces was diminished to 20-deg. fahr. decrease in the planning of a recent large 1200-lb., 850-deg. fahr., single-turbine, single-boiler installation, simply by prescribing two-thirds radiant-superheating equipment. Objectives of this paper are:
1 To tell of considerable experiences with radiant superheaters in a station operating many since 1923, showing that their design and operation are based upon sound fundamental principles that have been proved by successful service.
2 To give operating data evaluating the desirable “rising” radiant characteristic at lower loads and to state basic differences of radiant and convection superheaters.
3 To treat the proper applications and to list the incidental merits of radiant superheaters.
4 To treat desirable application of radiant superheaters and reheaters in future large high-temperature, high-pressure, single-boiler, single-turbine installations, illustrating with calculated data based upon experience that essentially constant temperature can be obtained at all ratings.
Experiences in only one station are cited, yet developments of the industry prompting use of all designs of radiant superheaters are treated.
