초록 ▼

A component cooling steam flow control scheme for a combined cycle power plant (12). Steam pressure in the steam drum (40) of a waste heat recovery steam generator (36) is controlled by selectively positioning a steam bypass valve (54). The flow of steam from the steam drum through a cooling steam f

A component cooling steam flow control scheme for a combined cycle power plant (12). Steam pressure in the steam drum (40) of a waste heat recovery steam generator (36) is controlled by selectively positioning a steam bypass valve (54). The flow of steam from the steam drum through a cooling steam flow path (46) is controlled by selectively positioning a steam admission valve (50) in the cooling steam flow path. At power levels below a predetermined crossover power level (72), the cooling steam flow is controlled independently from the steam drum pressure, thus assuring good system controllability at the lower power levels where system control is historically a concern. The steam admission valve is maintained fully open at power levels above the crossover power level, so changes in cooling steam flow at these higher power levels are accomplished by regulating steam drum pressure. System efficiency losses resulting from pressure drop across the steam admission valve are thus minimized at the higher power levels where system efficiency is historically a concern.

대표청구항 ▼

1. A method for controlling steam flows in a combined cycle power plant having a heat recovery steam generator, an auxiliary steam circuit including a steam admission valve receiving a first flow of steam from a steam drum of the steam generator, and a steam bypass circuit including a steam bypass v

1. A method for controlling steam flows in a combined cycle power plant having a heat recovery steam generator, an auxiliary steam circuit including a steam admission valve receiving a first flow of steam from a steam drum of the steam generator, and a steam bypass circuit including a steam bypass valve receiving a second flow of steam from the steam drum, the method comprising controlling pressure in and flow from the steam drum as a function of gas turbine power to a value that results in the steam admission valve being at least partially dosed at power levels below a crossover power level and that results in the steam admission valve being fully opened at power levels above the crossover power level, so that the steam bypass valve is crossed over from a pressure control mode at power levels below the crossover power level to a flow control mode at power levels above the crossover power level.2. The method of claim 1, wherein the first flow of steam is directed to a component cooling passage, and further comprising selectively controlling the pressure in the steam drum at power levels above the crossover power level in response to a component cooling demand.3. The method of claim 1, further comprising selecting the crossover power level to be at least 70% power.4. A method of controlling delivery of steam from a steam drum of a heat recovery steam generator in a combined cycle power plant, the method comprising:providing a cooling steam flow path between the steam drum and a downstream location passing through a heat exchange passage, the cooling steam flow path comprising a steam admission valve; providing a steam bypass flow path between the steam drum and the downstream location not passing through the heat exchange passage, the steam bypass flow path comprising a steam bypass valve; controlling flow rate of steam through the cooling steam flow path by partially closing the steam admission valve at power levels below a crossover power level; maintaining the steam admission valve in a full open position at power levels above the crossover power level; and controlling flow rate of steam through the cooling steam flow path by selectively positioning the steam bypass valve at power levels above the crossover power level. 5. The method of claim 4, further comprising selecting the crossover power level to be about 70% power.6. The method of claim 4, further comprising selecting the crossover power level to be at least 70% power.7. The method of claim 4, further comprising forming the heat exchange passage through a portion of a gas turbine component of the combined cycle power plant.8. A method for controlling steam flows in a combined cycle power plant comprising a heat recovery steam generator for generating steam, a component cooling circuit including a steam admission valve receiving a flow of cooling steam from the steam generator, and a steam bypass circuit including a steam bypass valve receiving a flow of bypass steam from the steam generator, the method comprising:selecting a cooling circuit demand pressure curve defining a relationship between power level and steam pressure in the steam generator necessary to produce a desired cooling steam flow rate in the component cooling circuit; selecting a steam bypass valve pressure curve that intersects the cooling circuit demand pressure curve at a crossover point below 100% power; controlling the steam admission valve in response to the cooling circuit demand pressure curve; controlling the steam bypass valve in response to the bypass valve pressure curve at power levels up to the crossover point, thus resulting in the steam admission valve being controlled to a full open position at the crossover point; and controlling the steam bypass valve in response to the cooling circuit demand pressure curve at power levels above the crossover point. 9. The method of claim 8, further comprising selecting the crossover point to be about 70% power.10. The method of claim 8, further comprising selecting the crossover point to be at least 70% power.11. A method for controlling steam flows in a combined cycle power plant comprising a heat recovery steam generator, a component cooling circuit including a steam admission valve receiving a flow of cooling steam from the steam generator, and a steam bypass circuit including a steam bypass valve receiving a flow of bypass steam from the steam generator, the method comprising:selecting a demand value for the steam bypass valve necessary to control steam pressure in the steam generator to a predetermined value as a function of power level; selecting a demand value for the steam admission valve necessary to provide a required cooling steam flow as a function of power level; and determining a flow compensator value for combination with the demand value for the steam bypass valve that results in a steam generator pressure sufficient to produce the required cooling steam flow with the steam admission valve fully open at and above a crossover point power level. 12. The method of claim 11, further comprising selecting the demand values for the steam bypass valve and for the steam admission to have the same value in order to position the steam admission valve in a full open position at the crossover point being between a 70-100% power level.13. A method for controlling steam flows in a combined cycle power plant having a gas turbine, a heat recovery boiler, an auxiliary steam circuit including a steam admission control valve receiving a first flow of steam from the boiler, and a steam bypass circuit including a steam bypass control valve receiving a second flow of steam from the boiler, the method comprising:at power levels below a predetermined value below 100% power, controlling steam bypass control valve position to produce steam pressure in the boiler in excess of a pressure required to produce a desired steam flow value through the auxiliary steam circuit with the steam admission control valve fully open, and controlling steam admission control valve position to a partially dosed position to control steam flow through the auxiliary steam circuit to the desired value; and at power levels above the predetermined value, controlling steam bypass control valve position to produce steam pressure in the boiler to a pressure required to produce the desired steam flow value through the auxiliary steam circuit with the steam admission control valve fully open, and controlling steam bypass control valve position to a fully open position. 14. The method of claim 13, wherein the predetermined power level value is at least 70% power.15. The method of claim 13, wherein the predetermined power level value is at least 80% power.16. The method of claim 13, wherein the predetermined power level value is at least 90% power.