SYSTEM FOR PREHEATING BOILER FEEDWATER AND COOLING CONDENSER WATER

Abstract

A system for pre-heating boiler feedwater and cooling condenser water includes a boiler, a turbine, a turbine condenser, a heat pump, a first heat exchanger, a second heat exchanger, and an expansion valve. A water stream is heated by the boiler into a high pressure steam. The high pressure steam passes through the turbine and into the turbine condenser, converting the steam into condensate. The condensate is passed through a heat receiving side of the first heat exchanger. A refrigerant stream is pressurized by the heat pump and is thereby heated. The refrigerant stream passes through a heat dissipating side of the first heat exchanger, heating the condensate. The refrigerant stream is then depressurized and cooled, and passes through a heat receiving side of the second heat exchanger. A condenser water stream passes through a heat dissipating side of the second heat exchanger, cooling and entering the turbine condenser.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority of U.S. provisional application No. 62/016,500, filed Jun. 24, 2014, the contents of which are herein incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to power plants and, more particularly, to a system for preheating boiler feedwater and cooling condenser water.

A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. The pressurized steam passes through the turbine and exits at a lower pressure. A condenser lowers the temperature of the steam and condenses into condensate in order to maximize the energy extracted from the steam. The condensate provides feed water that must be preheated and returned to the boilers. The condensers are heat exchangers which convert steam from its gaseous state to its liquid state (condensate) at a pressure below atmospheric pressure by using cooling water.

Currently, the electric output from condensing steam turbine plants must be reduced (derated) when the weather is hot and humid because of the limitations of their waste heat dissipation (cooling) systems. If cooling towers are used, the amount of heat that can be dissipated through evaporation is limited by the wet bulb temperature of the ambient air which limits the amount of heat that can be dissipated by the cooling tower. In systems that use cooling water from nearby bodies of water, the amount of heat that can be dissipated is reduced in hot and humid weather because the temperature of the source water becomes too warm and/or because the thermal pollution of the warmer discharge water breaches an environmentally acceptable level.

As can be seen, there is a need for a system to optimize the efficiency of preheating boiler feedwater and minimizing the amount of cooling condenser water required.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a system for pre-heating condensate comprises: a boiler; a turbine; a turbine condenser; a heat pump; and a first heat exchanger, wherein a first fluid is heated by the boiler into a high pressure steam, wherein the high pressure steam passes through the turbine and into the turbine condenser and is converted into a condensate, wherein the condensate is passed through a heat receiving side of the first heat exchanger, and a second fluid is pressurized and thereby heated by the heat pump and passes through a heat dissipating side of the first heat exchanger, thereby heating the condensate.

In another aspect of the present invention, a system for pre-heating condensate comprises: a boiler; a turbine; a turbine condenser; a heat pump; a first heat exchanger; a second heat exchanger; and an expansion valve, wherein a water stream is heated by the boiler into a high pressure steam, wherein the high pressure steam passes through the turbine and into the turbine condenser and is converted into a condensate, wherein the condensate is passed through a heat receiving side of the first heat exchanger, a refrigerant stream is pressurized and thereby heated by the heat pump, passes through a heat dissipating side of the first heat exchanger heating the condensate, passes through the expansion valve, thereby depressurizing and cooling, and passes through a heat receiving side of the second heat exchanger, and a condenser water stream passes through a heat dissipating side of the second heat exchanger, cooling and entering the turbine condenser.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an embodiment of the present invention;

FIG. 2 is a schematic view of an embodiment of the present invention;

FIG. 3 is a schematic prior art view; and

FIG. 4 is a schematic prior art view.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

The present invention includes the use of an industrial heat pump for condensing steam turbines, which reduces cooling water requirements, fuel consumption, carbon emissions and derating losses. The industrial heat pump of the present invention preheats boiler feedwater five times more efficiently than a steam boiler. Therefore, fuel consumption is reduced because the fuel previously required to preheat the feedwater is no longer needed. By reducing fuel consumption, the industrial heat pump reduces carbon emissions.

Further, the industrial heat pump generates mechanical cooling as an intrinsic part of its normal operating cycle. The heat pump extracts waste heat from the condenser water thereby cooling the condenser water. By providing additional cooling while reducing fuel input, the industrial heat pump reduces the plant requirement for cooling water and thereby also reduces the thermal pollution of the environment caused by the operation of the plant. The present invention reduces the heat rate (BTUs per exported kWh) of a condensing turbine by approximately 2.5% and reducing the cooling water requirements by approximately 5%.

The condenser water that removes the latent heat from a condensing steam turbine provides an ideal low temperature heat source for an industrial heat pump. By extracting heat from this condenser water, the industrial heat pump lowers the condenser water temperature, thereby reducing the amount of cooling water that must be evaporated (or circulated once-through) to dissipate the condenser water heat. Because the industrial heat pump is a closed loop device, the cooling effect described above will remain the same regardless of ambient temperature and humidity conditions. Therefore, the frequency, depth and duration of derating events will be reduced and/or eliminated.

In certain embodiments, the present invention may use an industrial pump sized to satisfy the boiler feedwater preheat load, such that no excess heat is produced. Consequently there is no need for an external thermal load to absorb the excess heat as there would be if the heat pump were designed to cool the entire condenser water load. The present invention may utilize all of the heating and cooling output energy of the industrial heat pump within the turbine system. All of the heat may be used to preheat boiler feedwater, and all of the output cooling energy may be used to reduce the temperature of the cooling water, thereby reducing the flow requirements. Using the present invention, the parasitic load is only 3% of the plant's electric output, and the fuel energy saved by the enhanced heating efficiency is far greater than the electric energy lost by the reduced electric output.

Referring to FIGS. 1 through 4, the present invention includes a turbine system A, a condenser water cycle B, and a refrigerant cycle C. The turbine system A includes a boiler 10, a turbine 12 and a turbine condenser 14. Water and vapor run through the turbine system A. Feedwater is heated by the boiler 10 into a high pressure steam. The high pressure steam passes through the turbine 12 and exits as a lower pressure steam. The lower pressure steam enters the turbine condenser 14 and is condensed into a condensate liquid. The condensate liquid may be pumped through a heat receiving side of a preheat heat exchanger 20 by a pump 26. The preheated condensate liquid is now preheated boiler feedwater, which is delivered to the boner 10.

The turbine condenser 14 of the turbine system A receives cool water and discharges warm water via a condenser water cycle B. As illustrated in FIG. 2, cool water may be extracted from a body of water, such as a river. The cool water may be diverted into a first stream and a second stream. The first stream may run through a condenser water heat exchanger 18 on the heat dissipating side, thereby lowering the temperature of the water to a cold water. The cold water then meets with the second stream of cool river water and runs through the turbine condenser 14. The cold water lowers the temperature of the cool river water. In alternate embodiments, the present invention may include a single stream that runs through the heat dissipating side of the heat exchanger 18 and then into the turbine condenser. Warm water may be discharged from the turbine condenser into a body of water, such as a river, or may be directed to the condenser water heat exchanger 18 on the heat dissipating side.

As illustrated in FIG. 1, the condenser water cycle B may utilize a cooling tower 16. In such embodiments, warm water discharged from the turbine condenser 14 may run through a first stream and a second stream. The first stream of warm water may run through the cooling tower 16, thereby lowering the temperature of the water into a cooler water. The second stream of warm water may run through a condenser water heat exchanger 18 on the heat dissipating side, thereby lowering the temperature of the water into a cold water. The cold water then meets with the cooler water and runs through the turbine condenser 14. The cold water lowers the temperature of the cooler water. In certain embodiments, outside water, such as cool river water may mix with the warm water prior to entering the condenser water heat exchanger 18.

The refrigerant cycle C of the present invention may include a heat pump 22, and expansion valve 24. Refrigerant runs through the refrigerant cycle C. Refrigerant may include, but is not limited to, fluorocarbons, such as chlorofluorocarbons, ammonia, sulfur dioxide, and non-halogenated hydrocarbons, such as propane. A hot refrigerant vapor may be pumped by the heat pump 22 into the preheat heat exchanger 20. The hot refrigerant may run through the heat dissipating side of the preheat exchanger, thereby warming the condensate. The hot refrigerant vapor is thereby cooled and condenses into a liquid refrigerant. The liquid refrigerant runs from the preheat heat exchanger through the expansion valve 24, thereby transferring from high pressure to low pressure, and cooling. The cooled refrigerant liquid runs through the heat receiving side of the condenser water heat exchanger 18, thereby cooling the condenser water and turning into a refrigerant vapor. The refrigerant vapor is then pumped through the heat pump.

In certain embodiments, the refrigerant cycle C of the present invention may be used with an extraction steam turbine without a condensate return. An extraction turbine taps off steam from the turbine casing at intermediate pressures and uses this steam to satisfy other thermal loads. In some extraction turbine plants the steam condensate from the exported steam is not returned to the boiler, and in this case the lost condensate must be replaced with makeup water that is cooler than the turbine condensate. For example, if the temperature of the incoming makeup water is in the typical range of 60° F., the heat pump contributes a higher percentage of the heating load because it may raise the temperature of the incoming water by 120 ° F. (from 60° F. to 180° F.) in addition to raising the temperature of the steam condensate from the turbine from 100° F. to 180° F. In this case the fuel savings would be even greater because the more efficient industrial heat pump would be handling a larger percentage of the heating load.

When applied to an extraction steam turbine in which the condensate from the exported steam is not returned, the makeup water is cooler than the condensate. Therefore, the energy required to preheat a given mass of makeup water to 180 Deg. F is greater than the energy required to heat the same quantity of condenser water. Therefore, the size of the industrial heat pump is increased to enable it to preheat both the condensate and the makeup water. Therefore, the cooling capacity of the industrial heat pump is also increased. As the amount of exported steam increases, the amount of condensate decreases. Consequently the amount of condenser water cooling also decreases while the cooling capacity of the heat pump increases. This effect can be extended to the point where the cooling capacity of the industrial heat pump is sufficient to provide 100% of the cooling required to remove the heat from the condenser water. In this case we would have extraction condensing steam turbine that requires no cooling water. The condenser water loop would become a closed loop system with a cooling coil. This would be very significant in dry climates where the availability of cooling water is problematic.

In use, the feedwater is boiled by the boiler 10 and turned into high pressure steam. The high pressure steam drives the turbine 12 and passes through the turbine 12 losing pressure. The lower pressure steam is cooled and turned into a condensate via the turbine condenser 14. The condensate is pumped through a heat receiving side of the heat exchanger 20. The hot refrigerant vapor is pumped through the heat dissipating side of the heat exchanger 20, thereby heating the water condensate into a preheated boiler feedwater. The two fluid streams are separate and may run through the heat exchanger 20 in opposite directions (counterflow). The hot refrigerant vapor may raise the temperature of the condensate from about 100° F. to about 180° F. The preheated boiler feedwater may then return to the boiler 10. The refrigerant runs through the expansion valve from high pressure to low pressure, thereby significantly decreasing the temperature and the pressure. The cold refrigerant liquid passes through the condenser water heat exchanger 18 on a heat receiving side. Either water from an outside source or warm water from the turbine condenser 14 may pass through the heat dissipating side of the heat exchanger 18 and is thereby cooled off. The two fluid streams are separate and may run through the heat exchanger 18 in opposite directions (counterflow). The flow of water is enough to vaporize the entire refrigerant. Regardless of the weather, the condenser water in the heat exchanger is cooled which reduces the total amount of cooling water required by the plant. Further, the preheating of the boiler feedwater using the hot refrigerant vapor reduces the amount of fuel needed to run the turbine system.

A method of making the present invention may include the following. In order to construct this invention the flow rate of the boiler feedwater pump is determined, and then the amount of heat required to raise the temperature of the condensate to 180T is determined. One or more heat pump(s) with the total heating capacity determined above may be installed near the turbine condenser and boiler feedwater pump. A condensate heat exchanger is selected with the capacity to heat all of the pumped boiler feedwater to 180° F. This capacity may be approximately 470 BTUs per exportable kWh from the turbine. The amount of BTUs depends on the performance characteristics of the turbine/generator set (pounds of steam per kWh generated). The condensate heat exchanger may be installed in the boiler feedwater line, downstream from the boiler feedwater pump. A second heat exchanger, the condenser water heat exchanger, may be selected with the capacity to vaporize all liquid refrigerant produced by the condensate heat exchanger as it absorbs heat from the condenser water. The cooling capacity (BTUs per hour) of the condenser water heat exchanger may be approximately 400 BTUs per hour per exportable kWh from the turbine. The exact number may depend on the performance characteristics of the turbine/generator set (pounds of steam per kWh generated). The refrigeration cycle interfaces with the turbine system and the condenser water cycle via the condensate heat exchanger and the condenser water heat exchanger respectively.

The present invention may be installed in an existing condensing steam turbine power plant or may improve the design of a new condensing steam turbine power plant. The present invention reduces fuel consumption, the carbon footprint, cooling water requirements, reduce or eliminate derating events, and increase power plant profitability. Further, incorporating an industrial heat pump reduces the initial capital costs for new power plants because the size of the required cooling water systems could be reduced.

It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

1. A system for pre-heating condensate comprising:

a boiler;

a turbine;

a turbine condenser;

a heat pump; and

a first heat exchanger, wherein

a first fluid is heated by the boiler into a high pressure steam, wherein the high pressure steam passes through the turbine and into the turbine condenser and is converted into a condensate, wherein the condensate is passed through a heat receiving side of the first heat exchanger, and

a second fluid is pressurized and thereby heated by the heat pump and passes through a heat dissipating side of the first heat exchanger, thereby heating the condensate.

2. The system of claim 1, wherein the condensate is heated to about 180° F. while passing through the first heat exchanger, thereby becoming a preheated boiler feedwater.

3. The system of claim 1, further comprising a pump pumping the condensate from the turbine condenser to the first heat exchanger.

4. The system of claim 1, wherein the first fluid is water and the second fluid is a refrigerant.

5. The system of claim 1, further comprising:

a second heat exchanger; and

an expansion valve, wherein

the second fluid passes through the expansion valve, thereby depressurizing and cooling, and passes through a heat receiving side of the second heat exchanger, and

a third fluid passes through a heat dissipating side of the second heat exchanger, cooling and entering the turbine condenser.

6. The system of claim 5, wherein the third fluid is water.

7. The system of claim 6, wherein the third fluid is delivered from an outside water source.

8. The system of claim 7, wherein the outside water source diverts into a first stream and a second stream, wherein the first stream passes through the heat dissipating side of the second heat exchanger and meets with the second stream, cooling the second stream and entering the turbine condenser.

9. The system of claim 6, further comprising a cooling tower, wherein a warm water is discharged from the turbine condenser into a first stream and a second stream, wherein the first stream passes through the heat dissipating side of the second heat exchanger and the second stream passes through the cooling tower and meets with the first stream, cooling the second stream and entering the turbine condenser.

10. A system for pre-heating condensate comprising:

a boiler;

a turbine;

a turbine condenser;

a heat pump;

a first heat exchanger;

a second heat exchanger; and

an expansion valve, wherein

a water stream is heated by the boiler into a high pressure steam, wherein the high pressure steam passes through the turbine and into the turbine condenser and is converted into a condensate, wherein the condensate is passed through a heat receiving side of the first heat exchanger,

a refrigerant stream is pressurized and thereby heated by the heat pump, passes through a heat dissipating side of the first heat exchanger heating the condensate, passes through the expansion valve, thereby depressurizing and cooling, and passes through a heat receiving side of the second heat exchanger, and

a condenser water stream passes through a heat dissipating side of the second heat exchanger, cooling and entering the turbine condenser.

11. The system of claim 10, wherein the condensate is heated to about 180° F. while passing through the first heat exchanger, thereby becoming a preheated boiler feedwater.

12. The system of claim 10, further comprising a pump pumping the condensate from the turbine condenser to the first heat exchanger.

13. The system of claim 10, wherein the condenser water is delivered from an outside water source.

14. The system of claim 13, wherein the outside water source diverts into a first stream and a second stream, wherein the first stream passes through the heat dissipating side of the second heat exchanger and meets with the second stream, cooling the second stream and entering the turbine condenser.

15. The system of claim 10, further comprising a cooling tower, wherein the condenser water stream comprises a warm water discharged from the turbine condenser into a first stream and a second stream, wherein the first stream passes through the heat dissipating side of the second heat exchanger and the second stream passes through the cooling tower and meets with the first stream, cooling the second stream and entering the turbine condenser.