Increasing power of steam plant with refrigerant cooled condenser at peak loads by using cooling thermal storage

Abstract

A steam powered power plant and method of cooling a steam powered plant. A boiler provides steam to turbine and the turbine drives a generator to produce power. Exhaust steam from the turbine is cooled in a condenser and returns to the boiler. A first dry refrigeration cycle uses a first compressor to compress a first flow of refrigerant and the compressed flow of refrigerant rejects heat to the surrounding through an air cooled condenser and is then expanded in the steam condenser to cool the exhaust steam. A second refrigeration cycle includes a second compressor used to compress a second flow of refrigerant and the second flow of refrigerant is cooled in an air cooled condenser and is expanded to cool water in a storage tank wherein the stored water can be used to cool the condenser and exhaust steam during a peak load condition of the power plant.

Description

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61039980, filed 27 Mar. 2008, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Most of the world electricity supply is covered by steam generating power plants. In these plants, heat from the exhaust steam of the turbine has typically been transferred in a condenser to cooling water from a river, lake, sea or some other natural water supply. However, with the increased number of power plants, the number of natural sources of cooling water decreased, necessitating the use of wet cooling towers, where the supply of natural cooling water is insufficient. With developing and foreseeable shortages of adequate water sources in the arid regions alternate technologies are being sought for heat rejection.

United States Patent application US 2007/0137205 A1 to Brown proposed to combine the conventional steam cycle with a conventional refrigeration cycle and to replace the once through cooling water condenser of the steam cycle with a refrigerant cooling condenser. The refrigerant is heated in the steam condenser while condensing the steam. It then completes the refrigeration cycle to be cooled and recirculated through the steam condenser. In a conventional steam plant, nearly double the rate of net-power generation is rejected as waste heat. Nearly 80% of this rejection occurs in the steam condenser, and accordingly plenty of cooling is required. This calls for consuming a substantial portion of power generated by the steam plant to drive the compressor of the refrigeration machine. As a result, a material amount of reduction in total net power of the plant is brought about. Hence, the net power generated by the plant would be considerably less than the demanding load of the end-users during the peak-loads.

As can be seen, there is a need for an improved apparatus and method of cooling the exhaust steam from the turbine of a steam power plant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of the system of the present invention, and

FIG. 2 shows a flow chart of the method of operation of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An emerging alternative to the traditional water consumptive water-cooling technology is dry cooling, where the heat is rejected to air, directly or indirectly without any loss of water. The steam condensing pressures and temperatures of a dry cooled unit are significantly higher than a wet cooled unit, due to the low transfer rates of dry cooling and operation at the dry bulb temperature. This results in a reduction in net power output of the steam plant. The current invention combines a conventional steam plant cycle having a refrigerant-cooled condenser with two conventional refrigeration cycles and a cooling thermal storage container. Both refrigeration cycles are operated during part-loads. The first one is used to cool directly the steam plant condenser by cooling and condensing the refrigerant vapor and re-circulating it back through the steam condenser. The other machine serves for producing cooling to be stored in the cooling storage container. During the period of peak-loads, both refrigeration cycles are stopped, and the refrigerant vapor exiting the steam condenser is condensed in the cooling storage container and re-circulated through the refrigerant-cooled steam condenser. In this way, the power generated during the peak loads is fully made available to the end users.

The main intent of this invention is to maintain the net power output of a steam plant, using refrigerant-cooled condenser, at its maximum value during peak-loads. Dissipation of heat absorbed by the cooling refrigerant in the steam condenser tubes necessitates circulating it through a complete refrigeration cycle. An appreciable portion of the steam plant power output is consumed to operate the refrigeration compressor. To save the compressor power at peak-loads for use by the end user, it is proposed in this invention to produce excess cooling during the part-loads and store it to be used over the peak-loads period for cooling the refrigerant getting out of the steam condenser. Hence, the refrigerant compressor is stopped during the peak loads period, and the whole power generated by the steam plant is made available to cover the demand of the end users at this period. This invention saves investments in building new units for meeting the increasing demands of the end users through the period of peak-loads.

The configuration of the proposed combined steam power plant and cooling thermal storage system 100 is shown schematically in FIG. 1. This system 100 consists of three cycles and a cooling storage container. The three cycles are a steam power plant cycle 101 and two refrigeration cycles 103, 105 each cycle shown in a dashed line box. The steam cycle 101 can comprise the components of which a modern steam power plant is composed. Of these components only the boiler 1, steam turbine 2, refrigerant-cooled condenser 3, feed water pump 4 and generator 5 are shown in FIG. 1. The load on generator 5 can be sensed and the first refrigeration cycle 103 is used for direct cooling of the steam condenser 3 during part-loads when the excess power generated by the steam plant 101 is above a sufficient or greater for operating its compressor 6 and the load is below a first threshold value. The first refrigeration cycle 103 is made up of a compressor 6, driven by an electric motor 7, a condenser 8, a throttling valve 9 and an evaporator 3a within the refrigerant-cooled condenser 3, which acts at the same time as part of the steam condenser 3 of the steam plant 101. In this cycle 103, the cold refrigerant liquid exiting the throttle valve 9 evaporates as it passes through the tubes of the steam condenser (evaporator) 3 by absorbing vaporization heat of the turbine 2 exhaust steam. The water condensate and refrigerant vapor leaving the steam condenser (evaporator) 3 complete the steam cycle 101 and the first refrigeration cycle 103 respectively. The second refrigeration cycle 105 serves to produce cooling at low part-loads, below a second low threshold of loading, to be stored for later use at the peak-loads. It works simultaneously with the first refrigeration cycle 103 when the excess power is sufficient to drive the compressors 6, 10 of both cycles; otherwise the first refrigeration cycle 103 works alone. The second refrigeration cycle 105 consists of a compressor 10, operated by an electric motor 11, a refrigerant condenser 12, a throttling valve 13 and an evaporator 14. The cold refrigerant liquid leaving the throttle valve 13 evaporates as it flows through the evaporator 14 by absorbing heat from a heat sink such as cooling storage water container 15. In this way, media in the cooling storage container 15 gets colder, where the cooled media such as water is stored for later use during peak-loads. The cooling storage container 15 might use water for example as the storage media.

The two refrigeration cycles 103,105 have three different operating periods along the time of a working day: the period of direct cooling, the period of storing the cooling and the period of outage of both refrigeration cycles 103, 105. The period of direct cooling occurs at part-loads when the excess power of the steam plant 101 is adequate or greater for running the refrigerant compressor 6 of the first refrigeration cycle 103 for producing cooling that is used to directly condense the exhaust steam of the turbine 2. During this period, the valves 18 and 21 are opened and the valves 19 and 20 are closed. The cool refrigerant liquid getting out of the throttle valve 9 flows through the tubes of steam condenser (evaporator) 3, absorbs the heat of vaporization of the steam coming out of the steam turbine 2 and is vaporized. The refrigerant vapor exiting the steam condenser (evaporator) 3 is sent to the refrigerant compressor 6, where it then completes the first refrigeration cycle 103.

The period of storing the cooling takes place at low part-loads when the excess power of the steam plant 101 suffices to drive the compressors 6, 10 of both refrigeration cycles 103, 105. The cooling produced by the first refrigeration cycle 103 serves to directly condense the exhaust steam of the turbine 2 at this period, while the cooling produced by the second cycle 105 is stored in the cooling storage container 15. During this period the valves 19 and 20 are closed and the valves 18 and 21 are opened. The refrigerant vapor coming out of the steam condenser (evaporator) 3 and evaporator 14 are compressed in the compressors 6 and 10, respectively and complete the refrigeration cycles 103, 105 respectively. The period of outage of the refrigeration machines comes about over the period of the steam plant 101 peak-loads. During this period, the refrigeration compressors 6 and 10 are stopped, and the valves 18 and 21 are closed, while the valves 19 and 20 are opened. The cooling refrigerant of the steam condenser of cycle 101 changes its loop, in which it no longer flows through the first refrigeration cycle 103. Rather, the refrigerant vapor exiting the steam condenser (evaporator) 3 flows through the heat exchanger 16, where it rejects the heat absorbed in the steam condenser 3 to the cooling storage container 15 and is condensed. It is then pumped by the circulating pump 17 to the steam condenser (evaporator) 3 for condensing the exhaust steam of turbine 2. The refrigerant is vaporized in the steam condenser 3 and repeats this cooling loop until the demand of the end user gets enough low, so that the first refrigeration cycle 103 is re-activated.

FIG. 2 shows a simple control schematic 200 for the refrigerant cycles of the steam power plant and cooling thermal storage system 100. The power load on electrical line 50 is sensed 202 and the amount of load on line 50 determines the operation of the system 100. If peak loading 204 is sensed then cooling 206 from the storage tank 15 can supply the only source of cooling so long as the tank 15 had a temperature low enough to provide the required cooling. If the temperature of tank 15 was ever too high to provide required cooling then the cooling cycle 103 would turn on and this would result in some loss of efficiency. With proper system design tank 15 could always be able to control the cooling. If the load at line 50 is below peak load but above a low load a partial load 208 is sensed and single stage cooling 210 from cycle 103 is used. At a low load level 212, low enough to supply all the energy required at line 50 and still run both compressors 6 and 10, the system 100 will operate in dual stage cooling 214 with the second stage cooling the tank 15.

It will be obvious to those skilled in the art that modifications may be made to the embodiments described above without departing from the scope of the invention. Thus the scope of the invention should be determined by the claims in the formal application and their legal equivalents, rather than by the examples given.

Claims

1. A steam powered power plant includes;

a first boiler for providing steam to a turbine wherein said turbine drives a generator to produce power and wherein exhaust steam from said turbine is cooled in a condenser and returns to said boiler, and

a first refrigeration cycle wherein a first compressor compresses a first flow of refrigerant and wherein said compressed flow of refrigerant is cooled in an air cooled condenser, throttled and expanded in said condenser to cool said exhaust steam, and

a second refrigeration cycle wherein a second compressor compresses a second flow of refrigerant and said second flow of refrigerant rejects heat in an air cooled condenser, throttled and expanded to cool a thermal storage wherein said thermal storage can be used to cool said steam condenser.

2. The steam power plant of claim 1 wherein said generator generates electrical power to power a load and wherein said load is sensed to determine the cooling operation of said power plant, wherein during a low load condition said first refrigeration cycle provides cooling to said steam condenser and said second refrigeration cycle provides cooling to said thermal storage and during a peak load said first refrigeration cycle and said second refrigeration cycle are turned off and cooling of said condenser is provided from said thermal storage.

3. The steam power plant of claim 1 wherein said thermal storage is a tank of water.

4. The steam power plant of claim 1 wherein at a partial load condition, wherein said load is greater than said low load but less than said peak load said first refrigeration cycle provides cooling to said steam condenser and said second refrigeration cycle is turned off.

5. The steam power plant of claim 1 wherein said thermal storage includes a tank of water and a heat exchanger and wherein coolant from said condenser flows through said heat exchanger during said peak loading.

6. The steam power plant of claim 5 wherein the flow of coolant through said heat exchanger is controlled by valves that are opened during said peak loading.

7. The steam power plant of claim 5 wherein said first and second compressors are powered by said turbine.

8. A steam power plant includes;

a steam driven turbine wherein said turbine drives a generator to produce power and wherein exhaust steam from said turbine is cooled in a condenser, and

a first dry refrigeration cycle wherein a first compressor compresses refrigerant and wherein said compressed refrigerant is expanded in said condenser to cool said waste steam, and

a second dry refrigeration cycle wherein a second compressor compresses a second refrigerant and said second refrigerant is expanded to cool a thermal storage media wherein said thermal storage media can be used to cool said steam condenser.

9. The steam power plant of claim 8 wherein said generator generates electrical power to power a load and wherein said load determines the cooling operation of said power plant, wherein during a low load condition said first refrigeration cycle provides cooling to said condenser and said second refrigeration cycle provides cooling to said thermal storage media and during a peak load said first refrigeration cycle and said second refrigeration cycle are turned off and cooling of said condenser is provided from said thermal storage media.

10. The steam power plant of claim 9 wherein said thermal storage media is held in a tank and a heat exchanger is located in said tank in contact with said media and wherein refrigerant from said steam condenser flows through said heat exchanger during said peak loading to cool said exhaust steam.

11. The steam power plant of claim 9 wherein said thermal storage media is water.

12. The steam power plant of claim 9 wherein at a partial load condition, wherein said load is greater than said low load but less than said peak load said first refrigeration cycle provides cooling to said steam condenser and said second refrigeration cycle is turned off.

13. The steam power plant of claim 10 wherein the flow of coolant through said heat exchanger is controlled by valves that are opened during said peak loading.

14. The steam power plant of claim 10 wherein said first and second compressors are powered by said generator.

15. The method of operating a steam plant including the steps of;

boiling water to produce steam,

powering a turbine driven generator using said steam,

condensing exhaust steam from said turbine with a condenser,

sensing a load on said generator,

if said load is below a threshold,

driving a first compressor to provide refrigerant to said condenser to cool said exhaust steam,

if said loading is below a second threshold driving a second compressor to cool a heat sink.

16. The method of claim 15 wherein the step of driving a second compressor to cool a heat sink includes the step of providing a flow of refrigerant through said heat sink at a peak load of said steam power plant.

17. The method of claim 15 wherein the step of providing a flow of refrigerant through said heat sink is controlled by opening valves to a heat exchanger in said heat sink and wherein said heat sink is a water tank.

18. The method of claim 15 wherein if said load rises above said second threshold said second refrigeration cycle is turned off.

19. The method of claim 15 wherein the flow of refrigerant is controlled by opening valves to said condenser.

20. The method of claim 15 wherein the step of driving a first condenser and driving a second condenser includes drawing electrical power from said generator.