US20100270002A1

US20100270002A1 - System and method of maximizing performance of a solid-state closed loop well heat exchanger

Info

Publication number: US20100270002A1
Application number: US12/462,661
Authority: US
Inventors: Michael J. Parrella
Original assignee: PARDEV LLC
Current assignee: PARDEV LLC
Priority date: 2008-08-05
Filing date: 2009-08-05
Publication date: 2010-10-28
Also published as: US20150101779A1; US20140000838A1

Abstract

A heat exchanger transfers heat from solid state heat conducting material to a fluid in a closed loop system. A heat harnessing component includes a closed-loop solid state heat extraction system having a heat exchanging element positioned within a heat nest in a well designed to optimize the transfer of heat from heat conductive material to a closed loop fluid flow. A piping system conveys contents heated by the heat exchanging element to a surface of the well.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of United States Non-Provisional patent application Ser. No. 12/456,434 filed on Jun. 15, 2009. This application also claims priority to 1) U.S. Provisional Application No. 61/137,956, filed on Aug. 5, 2008; 2) U.S. Provisional Application No. 61/137,974, filed on Aug. 5, 2008; 3) U.S. Provisional Application No. 61/137,955, filed on Aug. 5, 2008; and 4) U.S. Provisional Application No. 61/137,975, filed on Aug. 5, 2008, the contents of all of which are hereby incorporated in their entirety.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX

Not applicable.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of converting geothermal energy into electricity. More specifically, the present invention relates to capturing geothermal heat from deep within a drilled well and bringing this geothermal heat to the Earth's surface to generate electricity in an environmentally friendly process.
Wells that have been drilled for oil and gas exploration that are either depleted, or have never produced oil or gas, usually remain abandoned and/or unused and may eventually be filled. Such wells were created at a large cost and create an environmental issue when no longer needed for their initial use.
Wells may also be drilled specifically to produce heat. While there are known geothermal heat/electrical methods and systems for using the geothermal heat/energy from deep within a well (in order to produce a heated fluid (liquid or gas) and generate electricity therefrom), these methods have significant environmental drawbacks and are usually inefficient in oil and gas wells due to the depth of such wells.
More specifically, geothermal heat pump (GHP) systems and enhanced geothermal systems (EGS) are well known systems in the prior art for recovering energy from the Earth. In GHP systems, geothermal heat from the Earth is used to heat a fluid, such as water, which is then used for heating and cooling. The fluid, usually water, is actually heated to a point where it is converted into steam in a process called flash steam conversion, which is then used to generate electricity. These systems use existing or man made water reservoirs to carry the heat from deep wells to the surface. The water used for these systems is extremely harmful to the environment, as it is full of minerals, is caustic and can pollute water aquifers. Such deep-well implementations require that a brine reservoir exists or that a reservoir is built by injecting huge quantities of water into an injection well, effectively requiring the use of at least two wells. Both methods require that polluted dirty water is brought to the surface. In the case of EGS systems, water injected into a well permeates the Earth as it travels over rock and other material under the Earth's surface, becoming polluted, caustic, and dangerous.
A water-based system for generating heat from a well presents significant and specific issues. For example, extremely large quantities of water are often injected into a well. This water is heated and flows around the inside of the well to become heated and is then extracted from the well to generate electricity. This water becomes polluted with minerals and other harmful substances, often is very caustic, and causes problems such as seismic instability and disturbance of natural hydrothermal manifestations. Additionally, there is a high potential for pollution of surrounding aquifers. This polluted water causes additional problems, such as depositing minerals and severely scaling pipes.
Geothermal energy is present everywhere beneath the Earth's surface. In general, the temperature of the Earth increases with increasing depth, from 400°-1800° F. at the base of the Earth's crust to an estimated temperature of 6300°-8100° F. at the center of the Earth. However, in order to be useful as a source of energy, it must be accessible to drilled wells. This increases the cost of drilling associated with geothermal systems, and the cost increases with increasing depth.
In a conventional geothermal system, such as for example and enhanced geothermal system (EGS), water or a fluid (a liquid or gas), is pumped into a well using a pump and piping system. The water then travels over hot rock to a production well and the hot, dirty water or fluid is transferred to the surface to generate electricity.
As mentioned earlier herein, the fluid (water) may actually be heated to the point where it is converted into gas/steam. The heated fluid or gas/steam then travels to the surface up and out of the well. When it reaches the surface, the heated water and/or the gas/steam is used to power a thermal engine (electric turbine and generator) which converts the thermal energy from the heated water or gas/steam into electricity.
This type of conventional geothermal system is highly inefficient in very deep wells for several of reasons. First, in order to generate a heated fluid required to efficiently operate several thermal engines (electric turbines and generators), the fluid must be heated to degrees of anywhere between 190° F. and 1000° F. Therefore the fluid must obtain heat from the surrounding hot rock. As it picks up heat it also picks up minerals, salt, and acidity, causing it to very caustic. In order to reach such desired temperatures in areas that lack a shallow-depth geothermal heat source (i.e. in order to heat the fluid to this desired temperature), the well used must be very deep. In this type of prior art system, the geologies that can be used because of the need for large quantities of water are very limited.
The deeper the well, the more challenging it is to implement a water-based system. Moreover, as the well becomes deeper the gas or fluid must travel further to reach the surface, allowing more heat to dissipate. Therefore, using conventional geothermal electricity-generating systems can be highly inefficient because long lengths between the bottom of a well and the surface results in the loss of heat more quickly. This heat loss impacts the efficacy and economics of generating electricity from these types of systems. Even more water is required in such deep wells, making geothermal electricity-generating systems challenging in deep wells.
Accordingly, prior art geothermal systems include a pump, a piping system buried in the ground, an above ground heat transfer device and tremendous quantities of water that circulates through the Earth to pick up heat from the Earth's hot rock. The ground is used as a heat source to heat the circulating water. An important factor in determining the feasibility of such a prior art geothermal system is the depth of wellbore, which affects the drilling costs, the cost of the pipe and the size of the pump. If the wellbore has to be drilled to too great a depth, a water-based geothermal system may not be a practical alternative energy source. Furthermore, these water-based systems often fail due to a lack of permeability of hot rock within the Earth, as water injected into the well never reaches the production well that retrieves the water.

BRIEF SUMMARY OF THE INVENTION

Wells that have been drilled for oil and gas exploration that are either depleted, or have never produced oil or gas, can now be used to generate electricity. Wells can also be drilled specifically for the purpose of generating electricity. The only requirement is that the wells are deep enough to generate heat from the bottom of the well. The invention is a process for maximizing the performance of a heat exchanger that resides at the heat zone of a geothermic system in a well. The heat exchanging mechanism is a combination of a fluid heat exchanging element 3, heat conductive material and grout 6. The fluid heat exchanging mechanism maximizes the heat transfer from the bottom of the well to the surface. The invention uses a heat exchanger that has a fluid component and a sold state heat flow component where the solid state heat flow component transfers heat to the fluid.
There are pipe(s) carrying the heat conducting fluid into the fluid heat exchanging mechanism (fluid heat exchanging element plus heat conductive material and grout) at the bottom of the well from the surface and pipe(s) carrying the fluid, after being heated, back to the surface.
The heat exchanging mechanism needs to be able to enable the maximum amount of fluid flow while also maximizing the heat exchange to the fluid.
The pipe(s) need to minimize heat loss while transporting the fluid. The volume of fluid that flows through the fluid heat exchanging element needs to be as high a multiple as possible compared to the fluid flow of the pipe(s).
The rate of flow of the fluid in the fluid heat exchanging element will therefore be decreased by the volume differences between the pipe and the heat exchanger element. By slowing down the fluid flow in the fluid heat exchanging element you increase the time the fluid is exposed to the heat conductive material and grout in the heat zone and increase the heat that is transferred to the fluid. This allows the heat conductive material and grout part of the heat exchanging mechanism time to conduct and transfer the heat to the fluid. A standard heat exchanger transfers the heat from one fluid to another. The following embodiments transfer a solid state heat flow to a fluid.
Other embodiments, features and advantages of the present invention will become more apparent from the following description of the embodiments, taken together with the accompanying several views of the drawings, which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a conceptual view of a system according to one embodiment of the present invention showing a fluid heat exchanging element having a much larger diameter than the feeder pipes;

FIG. 2 is a conceptual view of a system according to another embodiment of the present invention showing a double helix design of the fluid heat exchanging element;

FIG. 3 is a conceptual view of a system according to another embodiment of the present invention showing the fluid heat exchanging element as a collection of smaller heat exchanger pipes where the sum of the volume capacity of the pipes is greater than the volume capacity of the feeder pipes;

FIG. 4 is a conceptual view of a system according to another embodiment of the present invention showing the fluid heat exchanging element built in modules having a total length that is the sum of the modules; and

FIG. 5 is a cross-sectional, conceptual view of pipes according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the present invention reference is made to the accompanying drawings which form a part thereof, and in which is shown, by way of illustration, exemplary embodiments illustrating the principles of the present invention and how it may be practiced. It is to be understood that other embodiments may be utilized to practice the present invention and structural and functional changes may be made thereto without departing from the scope of the present invention.
FIG. 1 illustrates a first preferred embodiment for the fluid heat exchanging element 3 where the element has a much larger diameter then the feeder pipes 2. The larger diameter slows the rate of flow of the fluid while it flows through the heat nest 10 portion of the system. The slower flow characteristics allow the fluid a longer time to pick up the heat from the heat conductive material and grout 6. The fluid travels down and up of the fluid heat exchanging element picking up heat;
FIG. 2 illustrates a second preferred embodiment for the fluid heat exchanging element 3 where the element is a double helix design. The double helix pipes have an equal or larger diameter than the feeder pipes and the twisted nature of the pipes increase the length of the travel path within the heat nest 10. The increased travel path (and the lager diameter if present) increase the time the fluid spends within the heat nest 10 portion of the system and the twisted pipe arrangement increases the heat transfer surface area increasing the transfer capability. The increased time allows the fluid a longer time to pick up the heat from the heat conductive material and grout 6 and the increased surface area increase the transfer capacity. The fluid travels down and up of the fluid heat exchanging element picking up heat;
FIG. 3 illustrates a third preferred embodiment for the fluid heat exchanging element 3 where the element is a collection of smaller heat exchanger pipes 4 where the sum of the volume capacity of the pipes is greater than the volume capacity of the feeder pipes 2. The increased volume of the heat exchanger pipes slows the fluid flow and the increased surface area of the pipes (versus a single pipe) increases the heat transfer capability. The smaller diameter of the pipes allows more of the fluid to be exposed to the heat thereby increasing the capability of the transfer of heat. The larger volume of the heat exchanger pipes increase the time the fluid spends within the heat nest 10 portion of the system and the increased surface area of he pipe surface increases and the smaller diameters increases the heat transfer capability. The increased time allows the fluid a longer time to pick up the heat from the heat conductive material and grout 6 and the increased surface area and smaller diameters improves the transfer capability per linear foot. The fluid travels down and up of the fluid heat exchanging element picking up heat;
FIG. 4 illustrates an embodiment of the fluid heat exchanging element where the element can be built in modules and the total length is the sum of the attached modules. The last module (FIG. 3) located at the bottom of the well has the downward flowing feeder pipe attached to the upward flowing feeder pipe creating a U-connection. As an example if the fluid heat exchanging element needed to be 500 feet long we can build it by connecting twenty five (25) twenty foot (20) modules. The module implementation can be accomplished regardless of the design of the heat exchanging element.
Each of the preferred embodiments is designed to maximize the exchange of heat from a solid state heat flow environment (heat conductive material and grout 6) to a fluid environment. This is accomplished by designing a fluid heat exchanging element that accomplishes one or more of the following functions:
1. Increases the fluid volume capacity of the heat exchanging element compared to the volume capacity of the feeder pipes. This increases the time the fluid spends in the heat nest thereby increasing the amount of heat that can be transferred;
2. Increase the surface area of the fluid heat exchanging element thereby increasing the linear capacity to exchange heat;
3. Modularize the design so the fluid heat exchanging element can be as long as required;
4. Decrease the diameter of the heat exchanging pipes allowing more of the fluid to touch the heat exchanging surface of the pipe;
5. Use heat conductive material and gout instead of a fluid to conduct heat from the hot rock to the heat exchanging element;
6. Use flexible connectors to attached the fluid heat exchanging modules together. These flexible connectors will provide a level of protection against earth movement, tremors and earth quakes;
7. The heat exchanger must fit into the bore hole of a well.
Referring now to FIG. 1, there is shown a preferred embodiment for the heat exchanging element 3 utilized in the present invention. Heat exchanging elements are devices built for efficient heat transfer which typically transfer heat from one fluid to another. They are widely used in many engineering processes. Some examples include intercoolers, pre-heaters, boilers and condensers in power plants. By applying the first law of thermodynamics to a heat exchanger working at steady-state condition, we obtain:
mi hi=0
where,
mi=mass flow of the i-th fluid
hi=change of specific enthalpy of the i-th fluid
In a preferred embodiment, the heat exchanging element utilized in the present invention is a high-temperature heat exchanger (“HTHE”) comprised of a recuperative type “cross flow” heat exchanger, in which a fluid exchanges heat with a solid state heat flow on either side of a dividing wall. Alternatively, the heat exchange element may be comprised of an HTHE which utilizes a regenerative and/or evaporative design. The embodiments of the invention replace one of the fluids with a solid state heat flow.
In a preferred embodiment FIG. 3, the heat exchanger will have a plurality of smaller capillaries (heat exchanger pipes 5). The fluid enters the heat exchanger from the downward flowing feeder pipe(s) 2, where it is then dispersed, flowing through each of the plurality of smaller capillaries. Preferably the capillaries are thinner (having a smaller diameter than the downward flowing pipe(s), thereby allowing the fluid to heat more quickly as it passes through the capillaries—increasing the overall efficacy of the heat exchanger. In a preferred embodiment, the combined flow of the capillaries of the heat exchanging element must be able to accommodate an equal or greater flow then the downward and upward flow pipe(s). This greater flow increases the time the fluid spends in the heat exchanger.
In a preferred embodiment, the heat exchanging element may be comprised from a titanium clad tube sheet, wherein the tube sheet may be formed from a high temperature nickel based alloy or ferritic steel. In this way, the heat exchanger is able to operate efficiently under high temperature/pressure conditions. Moreover, the thickness of the titantium may vary in accordance with specific temperature and/or pressure conditions under which the heat exchange element operates.
It is understood that there are other types of heat exchanging elements known the art which may also be used in the present invention such as parallel heat exchangers and/or reverse flow heat exchangers. In alternative embodiments, any of these types of exchangers may be utilized. A primary consideration in designing the heat exchanging element will be to ensure its efficient operation under high temperature/pressure conditions. Further, any such heat exchanger utilized in the present invention must be sized to fit within the bore hole of the well.
Still referring to FIG. 1, the upward flowing feeder pipe(s) 2 of the piping system are preferably coupled to the heat exchanging element 3 on an opposite side of the element. The upward flowing pipe(s) 2 draw the heated fluid from the heat exchanging element 3 and bring the heated fluid upward from the “heat point” in the well to the top surface.
In a preferred embodiment, the fluid that is used should be optimized to carry heat. An example of such a fluid is the antifreeze used in automobiles. Gas or water can also be used as a fluid. Further, the fluid cannot and should not have any corrosive properties and the piping material needs to be resistant to the fluid. Moreover, the fluid will be pressurized within the piping system so the system should be able to withstand the pressure generated by the depth of the well and the pumping mechanism, as the fluid is pumped through the system.
Referring still to FIG. 1, once the piping and heat exchanging element are fully installed in the well, the well is completely filled with a heat conductive material and grout 6. The heat conductive material and grout 6 must have heat conductive properties and preferably will bond and solidify within the well. In the preferred embodiment wherein the well is insulated, the heat exchanging element will be lowered into the well and then the heat conductive material and the grout will be inserted into the well before the insulation.
It is to be understood that other embodiments may be utilized and structural and functional changes me be made without departing from the scope of the present invention. The foregoing descriptions of the embodiments of the invention have been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Accordingly, many modifications and variations are possible in light of the above teachings. It is therefore intended that the scope of the invention not be limited by this detailed description.

Claims

1. A heat exchanger positioned at the bottom of a well that transfers heat from solid state heat conducting material to a fluid in a closed loop system comprising:

a heat harnessing component having a closed-loop solid state heat extraction system, the closed-loop solid state heat extraction system including a heat exchanging element positioned within a heat nest in a well designed to optimize the transfer of heat from heat conductive material to a closed loop fluid flow; and

a piping component including a set of downward-flowing pipes and a set of upward-flowing pipes, the upward-flowing pipes conveying contents of the piping component heated by the heat exchanging element to a surface of the well.

2. The system of claim 1, wherein the downward-flowing pipes couple to a first side of the heat exchanging element.

3. The system of claim 1, wherein the upward-flowing pipes couple to a second side of the heat exchanging element.

4. The system of claim 1, wherein the heat exchanging element is a pipe that has a larger diameter than the downward and upward piping components.

5. The system of claim 1, wherein the heat exchanging element comprises a double helix shape where the diameter of the pipe in the double helix is equal to or greater than the downward and upward pipe components in which the piping system within the heat exchanging element comprises at least one twisted pipe to increase the distance and slow the of the fluid flowing through the piping system of the heat exchanging element.

6. The system of claim 1, wherein the heat exchanging element includes a plurality of capillaries.

7. The system of claim 6, wherein the contents of the downward-flowing pipes are dispersed through the plurality of capillaries after entering the heat exchanging element.

8. The system of claim 7, wherein each capillary in the plurality of capillaries has a diameter smaller than a diameter of the downward-flowing pipes, thereby allowing the contents of the piping system to heat quickly as the contents pass through the plurality of capillaries.

9. The system of claim 8, wherein the sum of the volume of the capillaries attached to each of the downward and upward pipe components is greater than the volume of the pipe components thereby allowing the fluid to spend more time in the heat exchanging element.

10. The system wherein the heat exchanging element is built in modules that attach to one another with connecting pipes to form a heat exchanger of variable length. The heat exchanger element module at the bottom of the string of modules connects the downward flowing pipe to the upward flowing pipe creating a closed loop.