Reheat Steam Temperature Research Articles

Design Features, Operating Experience, and Performance of 100,000-KW Reheat Installation at Potomac River Station

Abstract It is the purpose of this paper to discuss the outstanding features, operating experience, manpower requirements, and performance record of a generating unit with a design capability of 100,000 kw and with steam conditions of 1800 psig pressure, 1050 F primary steam temperature, and 1000 F reheat steam temperature. This design capability of 100,000 kw is somewhat less than the national average of 124,000 kw for all reheat machines purchased in the last 6 years. The initial steam pressure and temperature have been surpassed by other installations, and condenser circulating-water temperature is relatively high, with maximum temperatures of 88 F and a 4-month average of 81 F for June to September, inclusive. Notwithstanding these basic limitations, the over-all thermal efficiency is averaging 37 per cent which is near optimum for conditions below the supercritical. The unit under discussion is the No. 3 unit in a station housing also two 90,000-kw non-reheat machines placed in operation in October, 1949, and June, 1950. The new No. 3 unit was placed in preliminary operation June 30, 1954, and became firm commercial capacity 2 weeks later on July 14, 1954. Unit No. 4, which is a duplicate of No. 3, is under construction and is scheduled for service early in 1956. There is a single boiler per turbine, and fuel used is pulverized coal. Light fuel oil is used for ignition.

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

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.

Some Design Factors Relating to Performance and Operation of Reheat Boilers

Abstract Reheat boilers designed to operate with low furnace exit-gas temperatures and at the same time to provide control of superheater and reheater-outlet steam temperatures over a wide load range are illustrated and described. Various means for controlling primary and reheat-steam temperatures are discussed as are design provisions for some of the operating and maintenance problems peculiar to reheat units. Some advantages and disadvantages of indirect reheating are given.

Radiant-Superheater Developments

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.

Binders for foundry cores

In the present paper, computational fluid dynamic modelings were established to research a newly presented re-heat steam temperature deviation solution on the basis of FLUENT 6.3.26 considering a 700 MWe tangentially fired pulverised-coal boiler, which confronted with severe flue gas and re-heat steam temperature deviation. The model was solidly validated by grid independence test and comparison with the experimental data obtained from a series of on-site measurements. Upon reliable validation, the model was further used to investigate the forming mechanism of re-heat steam temperature deviation as well as the influence of burner tilt angle on it. The conclusions mainly include (1) Residual swirling flow in the upper furnace caused the flue gas velocity and temperature deviations in crossover pass. For a typical anticlockwise tangential firing system, the flue gas velocity and temperature were lower in left part of crossover pass. The deviation of flue gas further generated the convective heat transfer imbalance of final re-heater, therefore, the temperature deviation of re-heat steam was severe. (2) Tilting the burner upward can effectively reduce the intensity of residual flow as well as the flue gas deviation degree. The + 11° tilt angle of burner was relatively optimum considering the flue gas deviation and final re-heater overheating potential. Specifically, the intensity of residual swirl flow dropped 44% with burner tilting upward for + 11°. Practical operation of boiler demonstrated that the reheat steam temperature deviation was reduced from 22 °C to 10 °C in this case. (3) When the tilt angle of additional air (AA) was bias set, the flow field of upper furnace was changed. Consequently, the residual swirl flow intensity and the flue gas deviation were reduced considerably. On-site measurements indicated that the combination of tilting burner upward for + 11° and setting the bias of AA tilt angle for 10° can further reduce the re-heat steam temperature deviation to 4 °C.