POWER PLANT AND WATER CLEANING METHOD FOR A ONCE-THROUGH WATER/STEAM CYCLE OF A POWER PLANT

Abstract

A power plant with a water-steam-cycle includes a steam generator with a plurality of heating surfaces that carry a fluid and transfer heat to the fluid. The plurality of heating surfaces has an economizer for preheating the fluid and a fluidly connected evaporator for producing steam. A steam turbine receives the steam produced in the steam generator to generate power output. A condenser condenses steam from the steam turbine. The condenser has a hotwell as collection container for condensed steam or water. A polishing plant is arranged fluidly between the hotwell of the condenser and the economizer. A drain line interconnects an outlet of the economizer and the hotwell of the condenser. A fluid line interconnects the outlet of the economizer and the evaporator. The fluid line includes a syphon to hold back water in the economizer.

Claims

1. A power plant with a water-steam-cycle comprising: a steam generator with a plurality of heating surfaces configured to carry a fluid and to transfer heat to said fluid, the plurality of heating surfaces comprising an economizer for preheating said fluid and an evaporator for producing steam, the evaporator being fluidly connected to the economizer, a steam turbine that is configured to receive the steam produced in the steam generator to generate power output; a condenser configured to condense steam from the steam turbine, the condenser comprising a hotwell as collection container for condensed steam or water, a polishing plant that is arranged fluidly between the hotwell of the condenser and the economizer, wherein a drain line interconnects an outlet of the economizer and the hotwell of the condenser and wherein a fluid line interconnects the outlet of the economizer and the evaporator, wherein the fluid line comprises means to hold back water in the economizer, characterized in that the means to hold back water is a syphon.

2. The power plant according to claim 1, wherein the syphon reaches above an inlet header of the economizer.

3. The power plant according to claim 1, wherein at the outlet of the economizer an outlet header for collecting preheated feedwater is arranged and from which the drain line and the fluid line branch off.

4. The power plant according to claim 1, wherein a capacity of the polishing plant in parallel flow to a main condensate line is less than 100% of an amount of water supplied to the economizer at base load.

5. The power plant according to claim 1, wherein a heat source for the steam generator is a gas turbine.

6. A method for starting operation of a power plant with a water-steam-cycle, wherein the power plant comprises a steam generator with a plurality of heating surfaces forming at least an economizer, a steam turbine and a condenser comprising a hotwell, the method comprising: draining water contained in the economizer to the hotwell, where it is diluted, leading water from the hotwell at least in part through a polishing plant in order to clean it, supplying the economizer with water from the hotwell and water from the polishing plant, and starting-up the steam generator as soon as at least a part of the water in the economizer has been replaced by clean water from the hotwell and the polishing plant, wherein water getting over syphon tubes at an economizer outlet into evaporator and superheater tubes is drained by a drip leg at a steam generator outlet and led to the hotwell.

7. The method according to claim 6, wherein water is continuously drained from the economizer, led through the polishing plant and supplied to the economizer in case water from the hotwell and the polishing plant is not of a required quality, until it is clean enough for starting the steam generator.

8. The method according to claim 6, wherein water contained in the economizer is drained by pumping boiler feedwater from the hotwell and the polishing plant into the economizer and, where applicable, by opening a drain at an economizer outlet header.

9. The method according to claim 6, wherein circulation of water is maintained until an iron level is low enough.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings, of which:

[0027] FIG. 1 shows a power plant; and

[0028] FIG. 2 shows a heat recovery steam generator bundle of the inventive power plant.

[0029] The illustration in the drawings is in schematic form. It is noted that in different figures, similar or identical elements may be provided with the same reference signs.

DETAILED DESCRIPTION OF INVENTION

[0030] FIG. 1 illustrates a schematic diagram of a power plant 1 according to the invention. As illustrated in the exemplary embodiment of FIG. 1 the power plant 1 may be a combined cycle power plant 22, including a gas turbine 18. The gas turbine 18 generates power output from combustion of a fuel gas and air mixture. In the embodiment of FIG. 1 the gas turbine 18 is connected to a first generator 23. The gas turbine 18 produces exhaust gas at an exit of the gas turbine 18.

[0031] According to the embodiment of FIG. 1 a combined cycle power plant 22 includes a steam generator 2, or more specifically a heat recovery steam generator 24, which is located downstream of the gas turbine 18. The heat recovery steam generator 24 receives the exhaust gas from the gas turbine 18. The heat recovery steam generator 24 comprises a plurality of heating surfaces 3. A heat recovery steam generator 24 usually includes multiple pressure steam systems. In the illustrated example embodiment of FIG. 1, for the sake of simplicity, the heating surfaces of the heat recovery steam generator 24 belong to only one pressure system and comprise a superheater 19, an evaporator 5 and an economizer 4. The exhaust gas flows across the heating surfaces 3 to produce steam by extracting energy from the exhaust gas.

[0032] According to the embodiment of in FIG. 1, a combined cycle power plant 22 also includes a steam turbine 6 that is configured to receive the steam produced in the heat recovery steam generator 24 to generate power output.

[0033] The combined cycle power plant 22 illustrated in FIG. 1 is in a multi-shaft configuration. The steam turbine 6 is connected to a second generator 25. The invention is of course also applicable to a single shaft configuration.

[0034] According to the embodiment, a condenser 7 is located at an exit of the steam turbine 6 and is configured to condense steam from the steam turbine 6, the condenser 7 comprising a hotwell 8 as collection container for condensed steam or water.

[0035] The power plant 1 of FIG. 1 also shows a main condensate line 17 interconnecting hotwell 8 and economizer 4. In parallel to the condensate line 17 a polishing plant 9 is arranged fluidly between the hotwell 8 of the condenser 7 and the economizer 4. The polishing plant 9 removes impurities, that could cause damage to the steam generator 2 or the steam turbine, from the condensate.

[0036] Condenser 7 (+ polishing plant 9), steam generator 2 and steam turbine 6 form a water-steam cycle.

[0037] FIG. 2 shows a more detailed view of the steam generator 2 for economizer 4 and evaporator 5, where a drain line 10 interconnects an outlet header 14 arranged at an outlet 11 of the economizer 4 and the hotwell 8 of the condenser 7 and where a fluid line 12 interconnects the outlet 11 of the economizer 4 and the evaporator 5. According to the invention the fluid line 12 comprises means 13 to hold back water in the economizer 4 during standstill. The means 13 to hold back water is a syphon 15 that reaches above an inlet header 16 of the economizer 4. In case water is getting over the syphon 15 at the economizer outlet 11 into evaporator 5 and superheater 19 tubes, it is drained by a drip leg 20 at a heat recovery steam generator outlet 21 and led to the hotwell 8.

[0038] Although the present invention has been described in detail with reference to an embodiment, it is to be understood that the present invention is not limited by the disclosed example, and that numerous additional modifications and variations could be made thereto by a person skilled in the art without departing from the scope of the invention.