Title:
STEAM TURBINE CLOSED LOOP GEO-THERMAL COOLING
Kind Code:
A1


Abstract:
A power generation system for generating electricity using a steam turbine engine that yields high-pressure steam has been developed using a preferably non-toxic coolant circulating in a closed loop that passes through a rock and earth aquifer, for directly and/or indirectly condensing the low-pressure steam from the low-pressure side of the steam turbine into a liquid phase for re-circulation to the steam turbine, whereby the coolant acts to dissipate the heat from the low-pressure steam through the aquifer to the rock and earth encasing the aquifer. In one embodiment a containment shroud is employed to recycle condensing water utilized to condense the condensing vapor emitted from a steam condenser. In a second embodiment a sealed steam condenser is utilized through which the low-pressure steam passes, and water (or other suitable fluid) from an enclosed condensing water reservoir, through which the coolant is circulated, is employed to condense the low-pressure steam in the steam condenser. In yet another embodiment, the coolant is introduced directly into the steam condenser. In a further embodiment an intermediate refrigeration system pump is employed together with the coolant, for condensing the low-pressure steam.



Inventors:
Brown, Jeffrey J. (Haymarket, VA, US)
Application Number:
12/536573
Publication Date:
02/11/2010
Filing Date:
08/06/2009
Assignee:
HORIZON ENERGY ASSOCIATES, LLC (Gainesville, VA, US)
Primary Class:
Other Classes:
60/643, 62/260, 290/52
International Classes:
F01K13/00; F01K11/00; F25D23/12
View Patent Images:



Other References:
James, R.E. and McGurl, G.V., "IGCC System Analysis Utilizing Various Condenser Cooling Platforms Including CO2 Sequestration", Third Annual Conference on Carbon Capture & Sequestration, Alexandria, VA, May 3 - 6, 2004, pp. 1 - 25.
"aquifer" definition - Houghton Mifflin Dictionary of Geography: Places and Peoples of the World, 1997, p. 19.
Primary Examiner:
MEADE, LORNE EDWARD
Attorney, Agent or Firm:
Jeffrey J. Brown (Haymarket, VA, US)
Claims:
What is claimed is:

1. In a power generation system that includes a generator coupled with a fuel source where the generator interacts with a steam turbine for generating electricity, a steam condenser structure in which low pressure steam received from the steam turbine is condensed, and where the condensed steam is re-circulated to the steam turbine, the improvement comprising: a closed loop system in which a coolant circulates under pressure between an aquifer and the steam condenser structure to lower the temperature of the low pressure steam, whereby the coolant condenses the steam and dissipates heat received from the low pressure steam to the aquifer including its surrounding earth and rock encasement.

2. In a power generation system according to claim 1 where the steam condenser structure primarily includes an enclosed steam condenser containing a portion of the closed loop enabling the coolant to be routed through from the aquifer to condense the steam.

3. In a power generation system according to claim 1 where the steam condenser structure includes an enclosed steam condenser connected to a condensing water reservoir for feeding water cooled by the coolant through said enclosed steam condenser.

4. In a power generation system according to claim 1, including a pump for circulating said coolant under pressure.

5. In a power generation system according to claim 1, where the closed loop is a conduit designed to enable the coolant to flow through a sufficient area in the aquifer and in contact with the steam condenser structure to cool and condense the low pressure steam.

6. In a power generation system according to claim 1, where the coolant is ethylene glycol.

7. In a power generation system according to claim 4, where the conduit includes a relatively horizontal portion passing through the aquifer.

8. In a power generation system according to claim 1 where said aquifer is a surface aquifer.

9. In a power generation system that includes a generator coupled with a fuel source where the generator interacts with a steam turbine for generating electricity, a steam condenser in which low pressure steam is received from the power generation system for cooling low pressure steam and re-circulating the condensed steam to the steam turbine, whereby water from a condensing water reservoir flows through a conduit in contact with the steam condenser to lower the temperature of the low pressure steam, the improvement comprising: a closed looped system in which a coolant circulates under pressure between an aquifer and through a second conduit in contact with the condensing water reservoir to lower the temperature of the water in the condensing water reservoir, the coolant dissipating heat indirectly from the low pressure steam to the aquifer including its surrounding earth and rock encasement.

10. In a power generation system according to claim 9, where a portion of the closed loop system includes a relatively horizontal portion passing through the aquifer.

11. In a power generation system according to claim 9, including a pump for circulating said coolant under pressure.

12. In a system according to claim 11, where said pump interfaces with a refrigeration system lowering is inserted between the closed loop system through which the coolant flows and the steam condenser for further lowering the temperature of the low pressure steam.

13. In a power generation system according to claim 9, where the steam condenser is a pressure sealed chamber.

14. In a power generation system that includes a generator coupled with a fuel source and interacting with a steam turbine for generating electricity, a steam condenser in which low pressure steam is received from the power generation system, a water condensing reservoir for dispensing water to cool low pressure steam in the steam condenser and re-circulating the condensed steam to the steam turbine, the improvement comprising: enclosing the steam condenser and the condensing water reservoir in a containment shroud, placing within the containment shroud in the path of vapor from the steam condenser a cooling water condenser which is a portion of a closed loop system in which a coolant circulates under pressure from an aquifer to condense the vapor into the water condensing reservoir, the coolant dissipating heat from the vapor to the aquifer including its surrounding earth and rock encasement.

15. In a power generation system according to claim 14, including a coolant pump for circulating the coolant under pressure.

16. In a power generation system according to claim 12, including a condensing water feed from a water source for use, when needed, as an additional supply of water connected to the condensing water reservoir.

17. In a power generation system according to claim 14, where the closed loop is a conduit designed to enable the coolant to flow through the aquifer and through a sufficient area of the vapor emitted from the steam condenser to condense the water vapor.

18. In a power generation system according to claim 14, where a portion of the closed loop system includes a relatively horizontal portion passing through the aquifer.

19. In a process that employs a fuel source for generating electricity that includes a steam turbine, condensing the steam received from the low pressure side of the steam turbine for re-circulating the condensed steam to the steam turbine, the improvement comprising lowering the temperature of the low pressure steam during the condensing process by employing a coolant directed through a closed loop which coolant dissipates heat from the low pressure steam to a rock and earth encased aquifer.

20. In a process according to claim 19 including further lowering the temperature of the low pressure steam by employing a refrigeration process interconnected between the low pressure steam and the coolant flowing through the enclosed loop.

21. In a process according to claim 19, including inserting a geothermal pump between the closed loop through which the coolant flows and the steam condensing operation, for further lowering the temperature of the low pressure steam.

Description:

RELATED APPLICATIONS

Applicant claims priority with respect to the instant application to U.S. Provisional Patent Application No. 61/086,845 filed Aug. 8, 2008, and U.S. Provisional Application No. 61/148,808 filed Jan. 30, 2009. Each of the aforementioned priority applications is hereby incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of steam turbines, and, in particular, employing preferably a non-toxic coolant that is circulated through a closed loop system passing through a rock and earth aquifer for condensing low-pressure steam from the low-pressure side of a steam turbine employed for generating electricity.

2. The Prior Art/The Issues

Conventional commercial electrical power generation is often achieved using a heat engine such as a steam turbine in which high-pressure steam is expanded in a turbine driving a generator to produce electricity. Frequently, the output of the steam turbine is enhanced and made more fuel efficient using what is referred to in the power industry as the “Rankine Cycle”. In the Rankine Cycle, the spent steam exiting the low pressure side of the steam turbine is rapidly condensed to the liquid phase. The volume reduction is approximately 17,000 times. Increased output and greater fuel efficiency result from pressure reduction at the low pressure side of the steam turbine caused by this high and rapid volume reduction. The pressure reduction causes more steam to pass through and expand in the steam turbine, generating more power with no greater use of fuel. There are two generally accepted conventional methods for condensing steam: water and air cooling.

Air-cooling is not as effective as water in condensing steam, especially with high ambient air temperatures common during periods of high electric demand associated with hot weather. It is thus less reliable and results in de-rating of generation equipment at times when demand is at its highest.

With water cooling there are several variations: including the once-through and the re-circulating processes. In either case quite significant volumes of water are drawn into the condensing loop and either returned in part as liquid (once-through) or entirely vaporized (re-circulating). Even with once-through cooling between 10 and 30 percent of the water drawn into the system is lost to the atmosphere. Minimizing water lost to vapor and thermal degradation of returned water are major challenges facing the power generation industry.

Once-through water condensing is widely regarded as more effective, lower cost and more reliable. In this process, water is taken from a large body of water, such as a lake, river or an ocean and passed through and/or over internal coils in the steam condenser. The steam is cooled, condensing it to liquid and causing a rapid contraction. This contraction causes a vacuum to form on the low-pressure side of the steam turbine, pulling more steam through the turbine from the high to low pressure sides, resulting in greater power generation.

Re-circulating processes cool the condensing water in two main ways:

    • 1. by utilizing cooling towers in which some of the water is evaporated into the atmosphere, yet cooling the remaining water, which is returned to the condensing circuit.
    • 2. employing reservoirs in which the cooling water is returned to a pond, tank or other containment but where heat is dissipated or evaporated to the atmosphere. Again significant amounts of water are lost to evaporation.

In either case, valuable fresh water is lost, capital costs to build the cooling tower or reservoir are high, and added operating costs to treat the makeup water and run the pumps are incurred. Many residents within eye sight of power plants strongly object to the cooling towers and the visible plume of vapor.

Most large power stations are built near bodies of water for this purpose. Indeed, many nuclear stations were developed along with hydro reservoirs mainly to provide for their enormous cooling requirements. Inland power plant locations accessible to large bodies of water are becoming increasingly scarce and coastal locations becoming limited due to other demands for these sites, coastal zoning restrictions and coastal wetland protection measures.

Sources of potable fresh water are virtually off limits for power production. Aquifer depletion is becoming a major concern in the central plains and as far west as the Ogallala aquifer shows signs of reduced flow for agriculture. Even in situations where gray water is taken downstream of the potable sources, power plant cooling becomes a contributor to aquifer and river system depletion. Moreover, sources of non-potable water from which highly purified cooling water can be produced are increasingly polluted such that the cost of condensing water becomes ever more expensive, if at all feasible. The net result is to limit power production, increase the cost of electricity or both.

The economics of smaller generating stations such as gas fired combined cycle plants cannot tolerate the cost of building reservoirs and available sites for larger facilities are becoming more difficult to locate and develop.

Other sources of water need to be developed and currently, a common practice now is to take sewage flows, and treat the effluent sufficiently to extract the clean low mineral content condensing water required. InterGen's La Rosita station in Mexicali, Mexico processes water from the New River, arguably the most polluted river in the world. This is among the most sophisticated water treatment plants on earth due to the need to remove sewage as well as dissolved minerals, heavy metals agricultural run off and industrial chemicals.

For many gas-fired projects the limiting constraint is the availability of cooling water. A 600 MW 2-on-1 combined cycle plant will use between 5 and 11 million gallons per day. A 2-on-1 refers to two gas turbines feeding steam to one large steam turbine. This is generally regarded to be more energy efficient and optimizes capital costs. Thus it is the most common combined cycle configuration. Under standard practice, the entire amount of this expensive water resource is discharged.

Environmental Issues

In either case, the condensing water temperature is raised by 10° F. to 15° F. after which it is discharged, usually into the same body of surface water, but at a higher temperature. This is regarded by the EPA as thermal pollution and is regulated under the Clean Water Act. In 2007, due to a Federal Court ruling, the EPA is no longer permitting water intake structures for power plant cooling.

Where there is insufficient water of any quality, a project may not be economic or may require air cooling, jeopardizing the project's economics and/or its feasibility.

SUMMARY OF THE PRESENT INVENTION

The Geo-Cool inventive concept, as described in this paper, can be used with virtually any electric generation technology that uses the Rankine cycle (or its equivalent) of high-pressure steam through a steam turbine to drive a generator. This would include but not be limited to combustion turbine generators in combined cycle mode, oil, coal, lignite, bio-fuel or bio-mass fueled boilers and nuclear generators. It could also be used in solar thermal generators where steam is produced for power generation.

The principle behind Geo-Cool is to use available aquifers as a heat transfer mechanism to the surrounding rock, using the earth rather than the atmosphere or surface water as the heat sink. This is a well developed technology for geothermal heat pump applications. In simple terms, a closed loop system using a coolant medium such as ethylene glycol (or an equivalent), as the heat transfer fluid is inserted into an aquifer through a cased well bore. The glycol is circulated through cross linked polyethylene tubing (PEX) or another suitable tubing material that may be used as a heat transfer medium, where it is cooled (or warmed) by the aquifer.

Aquifers are found in a wide variety of sizes, geometry, physical characteristics, and most importantly their ability to transfer heat from the power plant to the rock and earth enclosing and surrounding the water in the aquifer. Aquifers also vary greatly as to their water characteristics. Some aquifers have very high dissolved mineral content and others contain very low concentrations. In many locations suitable for power generation, there may be several aquifers.

Many areas of the world are lying over the top of aquifers. Water from many of these aquifers is unsuitable for consumption or irrigation and could be used as for heat transfer to the rock encasing the aquifer.

One very important variable is the degree of water flow in the aquifer. Some aquifers have great water flows such as the source of the St. Johns River in northeast Florida. Others have very little flow and recharge at very slow rates. It is key to note that each site at which the Geo-Cool technology may be considered is unique and special design considerations may need to be employed to provide suitable cooling while protecting environmental resources.

The difference between Geo-Cool and conventional heat pump technology is the use of a low boiling point refrigerant (such as CFC-11 or ammonia). With a heat pump, the refrigerant is pressurized and cooled (i.e. heat extracted). The refrigerant is moved to the heat absorption zone (inside the building in the cooling cycle) and the pressure released causing the refrigerant to vaporize absorbing heat in the process. The cycle is repeated. In the heating cycle, the process is reversed, heat is extracted from the outside and absorbed in side the structure. A conventional heat pump uses the atmosphere to cool or warm the refrigerant whereas a geo-thermal heat pump uses the earth.

Geo-Cool technology uses a high boiling (BP) point heat transfer fluid to cool the steam quench water and condense it to the liquid phase where, as described in this document, it is reclaimed and recycled rather than allowing it to be vented to the atmosphere. A high BP heat transfer fluid is used because it will rise to a higher temperature without vaporizing. Vapor in the heat transfer system would result in blocked flow, similar to vapor lock in an automobile's fuel system. It also will absorb more heat and thereby increase the efficiency of the heat transfer process.

Recovering condensing water is technically feasible and in some cases may be economically attractive where cooling water is a limiting constraint to project development.

Some but not all of the objectives of the Geo-Cool System, which offer several cost and environmental benefits over conventional water cooling technologies, include:

1. a new and useful system and method for conservation of and substantially minimizing the amount of water that is drawn;

2. a new and useful system and method for allowing for construction of power plants that would otherwise not be built due to the lack of a source from which to draw water for either once through or re-circulating water condensation;

3. a new and useful system and method for allowing for the recovery and reuse, in the applicable embodiments, of the condensing water that would otherwise be vented to the atmosphere and lost;

4. a new and useful system and method for reducing operating costs for power plants that must treat surface water to produce steam condensing water;

5. a new and useful system and method for reducing anthropogenic (man-made) water vapor in the atmosphere, a known greenhouse gas;

6. a new and useful system and method for in some applications entirely eliminating the need for cooling water, and;

7. a new and useful system and method for minimizing the amount of water employed reducing the amount of potential pollution of water systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1—is a block diagram and schematic view in cross section representing a brief description of the prior art and, in particular, what is conventionally described as re-circulating cooling.

FIG. 1A—is a block diagram and schematic view in cross section representing a another brief description of an alternative version of the prior art and, in particular, what is conventionally called once through cooling.

FIG. 2—is a block diagram and schematic view in cross section of a preferred embodiment of the present invention that is an alternative to conventional re-circulating water-cooling.

FIG. 2A—is a block diagram and schematic view in cross section of a preferred embodiment of the present invention that is an alternative to once through water-cooling.

FIG. 2B—is a block diagram and schematic view in cross section of a preferred embodiment of the present invention that shows an implementation of an alternative enclosed conduit for directing the coolant passing through the aquifer.

FIG. 3—is a block diagram and schematic view in cross section of yet another preferred embodiment of the present invention that shows direct Geo-Thermal condensing with the coolant alone, eliminating the need for water.

FIG. 3A—is a block diagram and schematic view in cross section of yet another preferred embodiment of the present invention showing a variation of the concept in FIG. 3, where, in addition, a refrigeration system is additionally included.

DESCRIPTION OF THE PRIOR ART

The current state of the art process is shown in FIGS. 1 and 1A and described below for a combustion turbine in a one-on-one combined (Brayton+Rankine) cycle mode. From the point of steam generation the process would be identical for any form of steam generation electricity production technology.

As illustrated in FIG. 1, combustion air enters the compressor side of the gas turbine at 11 where it is compressed into the combustor and mixed with fuel, usually natural gas.

Then the fuel is burned in the combustor and exits through turbine and turbine blades at 12 causing the drive shaft to rotate. The drive shaft turns a generator, producing electricity. The hot exhaust gas exits the turbine and passes through the Heat Recovery Steam Generator (“HRSG”) at 13. The HRSG, similar to an automobile radiator, is a heat exchanger that contains water, flowing in a sealed closed loop 13a, that is flashed to steam at high-pressure. HRSGs are available in a variety of sizes and serve the same function as a boiler in a conventional steam plant: that is to turn water into high pressure steam.

The high-pressure steam enters the high-pressure side of a steam turbine 14 where its pressure is released allowing it to expand. As the steam expands it turns a series of fans driving a second generator as it passes to the low pressure side of the turbine. It is the second turbine generator set that distinguishes combined cycle generation from a simple or open cycle generation. Using the otherwise wasted heat from the gas turbine allows more power to be produced increasing fuel efficiency. That is, using the hot exhaust gas from the gas turbine to make steam allows this energy to be converted to electricity rather than vented to the atmosphere. The low-pressure steam contained in the sealed closed loop 13a is then diverted to and cooled in the steam condenser 15, enclosed within a cooling tower 15c, having an open receptacle 15a for receiving the condensing water over the condenser coils 15b.

The steam condenser takes one of two typical forms:

a. an open heat exchanger, as shown in FIG. 1, with coils 15b through which the low-pressure steam passes. The coils are cooled by water flowing over them changing the low-pressure steam into cooled water flowing back into the HRSG, or
b. a closed heat exchanger comprised of a sealed chamber through which the low-pressure steam flows shown as Alternative at 15d in FIG. 1A. Inside the sealed chamber is a continuous, closed coil containing relatively cool (˜85° F.) water. As the low-pressure steam contacts the coil it is condensed back to a liquid state contracting in volume and directed to flow back through the sealed closed loop 13a into the HRSG.

Regardless of the type of steam condenser, the process of condensing steam to water reduces its volume putting a vacuum on the low pressure side of the steam turbine 14 and pulling more steam through from the high pressure side, again producing more power from the same amount of fuel. The low-pressure steam can be used for process heat, referred to as co-generation.

As will be further elaborated on below, the condensing water feed 17, shown in FIG. 1, comes from the an available local water source as discussed earlier to which the condensing water is returned, however much of the condensing water is lost to the atmosphere as vapor. Where gray water is the local water source the condensing gray water is treated at 18 and after used for cooling discharged to a surface water body or returned to the source.

The source of condensing water is in two general forms:

a. re-circulating cooling is described in FIG. 1: Condensing water is drawn into a cooling tower 15c through a condensing water feed 17 from a local water source and passed over the condenser coils 15b. Much of the condensing water is turned to vapor and is lost to the atmosphere. The remainder is cooled by the vaporizing water and falls into receptacle 15a and then through the condensing water return to supplement the local water source and continues to be cycled over the condensing coils 15b until being lost to evaporation, or
b. once through cooling is described in FIG. 1A: Cooling water is usually drawn from a body of surface water (lake or river) and passed over the steam condensing coils in an open heat exchanger 15b. Alternatively the condensing water is passed through the coils in a closed heat exchanger. See section b above.

Regardless of the type of condenser, water for steam condensing comes from a variety of sources, more frequently treated waste or gray water. This is due to limitations on the use of surface water for cooling and the ever growing shortage of clean water. The gray water is processed through treatment plants (not shown) of varying complexity and sophistication based on the quality of the gray water feed. Evermore complex treatment plants are required to treat increasingly lower quality gray water.

DESCRIPTION OF EMBODIMENTS PREFERRED AT THE TIME OF FILING FOR THIS PATENT

In FIG. 2 there is shown a containment shroud 24 erected over the steam condenser 25b. In some cases, a cooling tower could be converted to serve as the containment shroud. In other cases, a simple structure similar to a storage tank would serve to contain the vapor within the containment shroud. The condensing water vapor elevates through another heat exchanger the cooling water condenser 25a where it is cooled by a cooling fluid flowing through the geo-thermal loop 26a, thereby condensing the condensing water vapor to liquid, where it is recovered and returned to a cooling water reservoir 25c for reuse, together with a feed of condensing water at 26, as and when necessary.

As required, additional condensing water is added to the condensing water reservoir 25c from the condensing water feed 26 although in much smaller quantities than with conventional re-circulating technology. Although it is shown that the primary source of condensing water will be from a gray water source, which would require treatment, it is possible that the primary source could be a non-gray water source. The coolant in the geo thermal loop 26a is sufficiently circulated via a coolant pump 26b through an aquifer 28 and cooled to the temperature of the aquifer and surrounding rock and earth encasement 28a and 28b. It is important to note that the heat is transferred to the rock and earth encasement where the heat is dissipated. The coolant and aquifer are the heat transfer mediums. The temperature of the rock and earth encasement is location specific, but likely is less than surface water and perhaps as cool as 60° F.

The advantage of Geo-Cool is that it greatly reduces or even eliminates for an extended period, the need to refine gray water or non-gray water into condensing water.

Most gas fired combined cycle power plants rely upon once-through cooling technology due to its simplicity and smaller footprint. Cooling towers are expensive and depending on the location may be offensive. The limited water supply however is a major constraint for developers. Geo-Cool offers several solutions as alternatives to once-through cooling. Illustrated in FIG. 2A and discussed below is one alternative.

Both open and closed heat exchangers can be used as steam condensers for once-through cooling. Regardless of the type of steam condenser, the Geo-Cool System reduces the amount of cooling water drawn. In practice, a Geo-Cool System could eliminate the open heat exchanger type of condenser. The reason is that open heat exchangers expose warmed cooling water to the atmosphere resulting in evaporation. An open heat exchanger could be covered with a containment shroud similar to the alternative to recirculating cooling illustrated in FIG. 2. However, it is likely that a closed heat exchanger may be more economic. This will certainly be the case for new power plants as there would be no need for the shroud and open condenser coils. In retrofits of older plants using open once through cooling with open heat exchangers, the decision to erect a shroud versus replacing the condenser will be specific to the site conditions of the plant.

A closed heat exchanger is depicted in FIG. 2A for a once-through system that is comprised of a pressure sealed chamber steam condenser 34 through which cooling coils 34a extend. Low pressure steam enters the condenser through the steam condensing loop 33 and is condensed upon contact with the cooling coils. Instead of water drawn from a surface body, the condensing water is circulated from a condensing water reservoir 35 through the coils 34a in the steam condenser. Water in the condensing water reservoir is in turn cooled by the coolant circulated by way of coolant pump 37a through the geo-thermal loop 37 into the aquifer 38 and back through cooling coils 35a in the condensing water reservoir. At no time does the steam, the condensing water, the coolant or the aquifer water, ever make direct contact. Only heat is exchanged between the steam and the three fluids. Again, the aquifer serves only as a heat transfer mechanism dissipating heat from the geo thermal loop to the encasing rock and earth strata 37b and 37c.

As may be required from time to time small incremental amounts of condensing water through a condensing water feed 36 from a local water source, may be added to the condensing water reservoir 35a. However, this is a practice that will likely occur only occasionally since this water, generally gray water, will need to be treated with corrosion and scale inhibitors, which is an expensive process. Alternately, potable water may be used.

In certain situations, greater heat transfer may be required than can be achieved by a single vertical well bore through the aquifer 38 as is shown in FIG. 2A. The thickness of the aquifer (e.g. its depth and width) and/or the directional flow of some particular aquifer could be an issue. In those cases horizontal and/or angular drilling, as illustrated in FIG. 2B may make sense to increase the exposure of the geothermal loop to the aquifer 38 and its encasing formation. This could serve to increase the thermal transfer capability of the geothermal loop beyond any single well bore. The increased heat transfer capacity could be achieved by increasing exposure to the aquifer by using one or more horizontal well bores 39 to position the geothermal loop as it passes through the aquifer.

As will be shown in FIGS. 3 and 3A, in certain situations, building, filling and maintaining a condensing water reservoir may be a needless expense. Provided the local conditions are appropriate, low pressure steam could be condensed directly by the geo-thermal coolant circulating in the steam condenser. The conditions might include one or more of the following:

    • a. very poor quality surface water,
    • b. the absence altogether of surface water,
    • c. a large and/or high flow aquifer, and/or
    • d. high heat absorption of the subsurface rock and earth. An example would be basalt or other high density rock adjacent to the aquifer.

FIG. 3 illustrates how this variation would work. A coolant pump 47 pumps the coolant through the geo-thermal closed loop 46 which includes passing the coolant through the steam condenser coils 44a forming a part of the closed loop, and then through the aquifer 45 via the geo-thermal loop, condensing the low pressure steam in the steam condenser 44 without the intervening step of condensing water cooling. The condensed steam is then routed back to the steam turbine.

FIG. 3A illustrates a variation using an intervening refrigeration system 47a acting as a method to lower the temperature even further. This technology would be useful under conditions where heat transfer must be accelerated by lowering the temperature of the condensing coils below the ambient temperature of the aquifer and its encasing rock.

The use of refrigeration technology has some similarities to a very large-scale ground source heat pump or geothermal system with a number of significant differences. First, the volume of heat being transferred is vastly larger than the air conditioning load of even the largest commercial buildings. Second, the purpose of air conditioning is to ensure air temperature and humidity are within a comfort zone for human occupation. Refrigeration for power generation serves a very different purpose: to optimize heat transfer from a relatively high temperature steam system to the sub-surface. Third, the refrigerant in the Geo-Cool system is expected to operate at much higher pressures than would a system designed for air conditioning. Fourth, ground source heat pumps or a geothermal system operate to both heat and cool occupied space. Geo-Cool, as its name implies is to be used only for cooling and thus will vary in many technical, but significant ways from heat pump applications. Finally, as stated several times, each location at which Geo-Cool may be used is unique and significant differences in local conditions and operating parameters will dictate site specific designs for effective heat transfer. Thus refrigeration as applied in power generation Rankine Cycle cooling is only partially similar to ground source heat pump technology.

Additional refrigeration is also applicable in recirculating systems where local conditions dictate that the steam condenser operate at a lower temperature than can be obtained solely through direct contact with the aquifer. In such circumstance, heat pump technology could be applied to lower the temperature of the condenser and increase or speed up condensing water recovery.

Application to Other Power Generation Technologies

The technology may have application for steam generation other than combined Brayton+Rankine cycle technology. It is conceivable that wherever cooling water is a constraint, whether economic or technical, and where an aquifer is accessible, Geo-Cool may enhance the project's economics. Thermal Solar generation is one such application.

In thermal solar generation, the sun'rays are concentrated to heat a transfer fluid to a very high temperature. Liquid sodium is the most commonly used heat transfer fluid. This hot liquid metal is then used to boil water to make high pressure steam which is then expanded in a steam turbine as it would be using any other source of heat. The low pressure steam is then condensed in a Rankine Cycle system as discussed herein. Thermal solar systems, while not now common, are expected to be located primarily in hot sunny areas where surface cooling water will be even more scarce. As such, using the geo-thermal cooling concept could enhance the viability of these systems.

The Geo-Cool concept may also be useful in a nuclear power generation application, again, condensing the steam in the Rankine Cycle.

In conclusion, wherever a Rankine Cycle steam system is used, Geo-Cool has the potential to reduce or eliminate the need to use precious surface water as a heat sink. Substituting the rock in the earth's crust as a heat sink could provide a more economic and environmentally sound solution to the cooling challenges of the Rankine Cycle.





 
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