Claims
- 1. A method for improving operational efficiency of a steam turbine power plant during power output variations, the plant including a partial-arc steam turbine selectively operable in a sliding pressure mode and a constant pressure mode, power variation in the constant pressure mode being effected by gradual valve closing and opening to vary steam flow to selected arcs of admission to thereby vary steam volume flow into the turbine, each arc of admission being defined by adjacent valve points corresponding to a fully open and a fully closed valve controlling steam admission to a respective one of the arcs of admission, sliding pressure operation being affected by varying steam pressure into a steam chest of the turbine, and efficiency being improved by using sliding pressure operation during at least some part of the power variation and constant pressure operation during another part of the power variation, the method comprising the steps of:
- determining impulse chamber pressure at each of a plurality of valve points during operation of the steam turbine at constant pressure;
- computing for each adjacent pair of valve points, an optimum constant pressure transition point between each pair of adjacent valve points for transitioning from a sliding pressure mode to a constant pressure mode;
- converting the optimum constant pressure transition point to a corresponding sliding pressure transition value;
- transitioning from sliding pressure operation to constant pressure operation when the impulse chamber pressure reaches the sliding pressure transition value; and
- increasing steam pressure concurrently with control valve closing beginning at the step of transitioning.
- 2. The method of claim 1, wherein the step of increasing steam pressure includes the step of increasing pressure at a rate such that nominal steam operating pressure is reached substantially concurrently with full closure of the control valve.
- 3. A method for reducing rotor thermal stress and shock loading of control stage blading in a partial-arc steam turbine in which steam flow is controlled to match power demand, the turbine including a plurality of control valves each arranged for admitting steam to a predetermined arc of admission at the control stage blading, the method comprising the steps of:
- reducing steam pressure at the control valves to a predetermined value corresponding to a heat rate achievable by closing a first control valve to a predetermined steam flow value while operating at constant steam pressure;
- gradually increasing steam pressure from said predetermined value to another value while closing said first control valve to a minimum flow position;
- reducing steam pressure to another predetermined value corresponding to another heat rate achievable by closing another control valve to another predetermined steam flow value while operating at constant steam pressure;
- gradually increasing steam pressure from said another predetermined value to said another value while closing said another control valve to a minimum flow position; and
- repeating the steps of reducing and increasing pressure and closing of the control valves until turbine power matches power demand.
- 4. The method of claim 8 wherein the heat rate is determined by the step of computing, for each adjacent pair of valve points, an optimum constant pressure transition point corresponding to an intersection point on a heat rate graph of a constant pressure valve loop and a sliding pressure plot.
Parent Case Info
This is a continuation in part of U.S. patent application Ser. No. 07, 772,505, filed Oct. 7, 1991, U.S. Pat. No. 5,136,845.
US Referenced Citations (4)
Number |
Name |
Date |
Kind |
4297848 |
Silvestri, Jr. |
Nov 1981 |
|
4320625 |
Westphal et al. |
Mar 1982 |
|
4888954 |
Silvestri, Jr. |
Dec 1989 |
|
5136848 |
Silvestri, Jr. |
Aug 1992 |
|
Non-Patent Literature Citations (5)
Entry |
Stodola; "Steam and Gas Turbines With A Supplement On The Prospects Of The Thermal Prime Mover"; McGraw-Hill Book Co., Inc.; vol. 1, pp. 189-190. |
Erbes & Eustis; "A Computer Methodology For Predicting The Design and Off-Design Performance of Utility Steam Turbine Generators"; Proceedings of the American Power Conference, Illinois Institute of Technology; 1986; vol. 48, pp. 318-320. |
Silvestri, Jr.; "Steam Cycle Performance'"; Power Division, American Society of Mechanical Engineers; pp. 9-10. |
Silvestri, Jr. et al.; "Recent Developments in the Application of Partial-Arc Turbines to Cyclic Service"; Electric Power Institute; Oct. 20-22, 1987; pp. 1-20. |
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Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
772505 |
Oct 1991 |
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