Patent Application
20170248345
Heat pipes are used to transport heat in a geothermal well to the surface. A heat pipe needs to survive in caustic environments. The Salton Sea is the worst environment discovered. The pH of the environment can be 5.5 and typical chemical composition concentration of produced fluids in parts per million (ppm) includes:
What is needed is a heat pipe that can withstand such harsh environments for an extended period of time without requiring replacement, and which can effectively transport heat in a geothermal well.
The present invention relates to heat pipes and heat pipe bundles. In accordance with the invention, heat pipes contain fluids that operate in a vacuum. Each heat pipe is self-contained. Many heat pipes are placed in a single well engineered geothermal system HeatNest™ system in order to increase the efficiency of the process of capturing the far rock heat. In a ColdNest™ system, the heat pipes transfer the heat to the air and ground. Examples of applicant's HeatNest™ and ColdNest™ systems can be found described in applicant's U.S. patent application Ser. Nos. 14/114,939 filed Jan. 28, 2015 (U.S. Patent Application Publication No. US2015/0163965) and 14/114,946 filed Jan. 28, 2015 (Publication No. US2015/0159918), which are hereby incorporated by reference in their entireties. As the temperature rises at one end of the heat pipe, the operating fluid turns to a vapor which absorbs the latent heat. The hot vapor within the heat pipe flows to the cooler end of the heat pipe where it then condenses and releases the latent heat. The condensed fluid then flows back to the hot side of the heat pipe and the process repeats itself. The heat pipes are slanted at a minimum angle of three degrees to facilitate the condensate returning to the bottom of the heat pipe. This transfer of heat takes place in only a few seconds. Conversely, when the heat source is removed, the heat pipes cool in only a few seconds.
According to embodiments of the invention, a heat pipe bundle can be provided composed of individual heat pipes that may carry seventeen kW of thermal power over a 120 feet length when operating at 190° C. at the cold end of the pipe, and have an outside diameter of 1¾ inches.
The heat pipe bundle will have a tip in the form of a nose cone specifically designed to facilitate insertion into the drilled appendage. The appendage hole diameter is to be at least ¾ inches larger than the diameter of the heat pipe bundle. The heat pipe bundle can be inserted into a curved appendage hole with a twenty-five foot bend radius without compromising structural integrity due to bending stresses and abrasion against granitic hardness and rough rock.
The heat pipe bundle will have a central “carrier tube”, “mud tube” or chamber with an internal diameter of at least one inch that will allow fluid circulation through the heat pipe bundle interior and attachment of an insertion and release device at the back end of the bundle during installation.
The heat pipes can withstand external fluid pressures of 450 bars. The heat pipes use materials and a design approach targeting a forty year life expectancy when exposed to corrosive fluids and temperatures corresponding to the Salton Sea, described above. If the brine content at a different site varies significantly from this specification, than either the life expectancy of the existing heat pipe design will be modified.
The heat pipes and heat pipe bundles may not have an external covering layer on the external metal surface, which can significantly retard heat transfer into or out of the external metal surfaces of the heat pipe bundle, with specific concern focused on open fluid exposure to maximize convective heat transfer mechanisms.
According to an aspect of the invention, an apparatus is provided for transporting geothermal heat from a geothermal well to a surface. The apparatus comprises at least one heat pipe comprising a wall surrounding a central tube or chamber, a fluid contained within the central tube or chamber, a first apparatus end that is closed and positioned at a first end of the heat pipe, and a second apparatus end that is closed and positioned at a second end of the heat pipe. The apparatus is configured to be in a vertical or inclined position in the geothermal well, and further, the fluid absorbs geothermal heat at the first apparatus end as it transitions to a vapor, rises to the second apparatus end, releases geothermal heat at the second apparatus end as it condenses back to a liquid state, and returns to the first apparatus end. The first apparatus end is configured for placement in the geothermal well and the second apparatus end is configured for placement near the surface. The fluid in the chamber can be water.
According to one embodiment of the apparatus, the wall of the at least one heat pipe includes a copper layer surrounding the central tube or chamber, a steel layer surrounding the copper layer; and a titanium layer surrounding the steel layer. At least the copper layer and the titanium layer are non-porous to water.
According to a further embodiment of the apparatus, the wall of the at least one heat pipe includes an internal coating layer surrounding the central tube or chamber, an iron layer surrounding the internal coating layer, which is configured to protect the iron layer from the fluid in the central tube or chamber, and an external coating layer of a caustic resistant material surrounding the iron layer. At least the internal and external coating layers are non-porous to water.
According to further embodiments of the invention, the at least one heat pipe can be made from titanium, copper or a copper-nickel alloy.
In accordance with one embodiment of the invention, the at least one heat pipe includes a plurality of pipes welded together vertically, a base section secured to a base of the plurality of pipes, a threaded plug configured to be secured to an uppermost pipe of the plurality of pipes, which comprises corresponding threading, and a port comprised in the uppermost pipe of the plurality of pipes and positioned so as to be covered by the threaded plug when the threaded plug is fully inserted into the uppermost pipe. During assembly of the at least one heat pipe, the threaded plug is partially inserted into the plurality of pipes, the fluid is injected into the at least one heat pipe through the port, and the threaded plug is then inserted further into the plurality of pipes to cover the port. In this embodiment, the plurality of pipes, the threaded plug and the base section can be made from titanium or another material.
According to a further embodiment of the apparatus of the present invention, the at least one heat pipe comprises a plurality of heat pipes arranged in a bundle surrounding a bundle central tube or chamber comprising the fluid. The bundle of heat pipes comprises at least six heat pipes surrounding the bundle central tube or chamber, each of the heat pipes comprising a wall surrounding a central tube or chamber. In an additional embodiment, the bundle of heat pipes comprises a plurality of bundles of heat pipes. The plurality of bundles of heat pipes comprises at least six bundles of heat pipes and comprises a total of at least seventy-two heat pipes. The plurality of bundles of heat pipes are arranged to surround a further central tube or chamber comprising the fluid.
The at least one heat pipe in accordance with the apparatus of the first aspect of the invention may also comprise appendages branching outwardly from a central heat pipe configured to insertion into horizontal or angled bore holes in the geothermal well.
The present invention will now be described with reference made to
A heat pipe 10 is shown in
Many heat pipes 10 can be used in a geothermal well 201. One or more geothermal well 201, as shown in
A boiler 212 can be used to augment the geothermal well 201 or replace the geothermal well 201 for the heat required. The boiler 212 can also burn fossil fuel, crude oil or gas that naturally comes from an oil well, such as flaring gas.
Additionally, if an additional heat source 213, such as waste heat or electrical resistant heat, is available, the other heat source 213 can be used to supply additional heat. For example, on an offshore oil platform where it would be more difficult to implement a geothermal well, waste heat or a combination of waste heat, electrical heat and/or a boiler can be used to supply the heat source for heating and/or flooding the oil reservoir. The other heat source 213 supplies heat to a manifold 218, such as a hot water manifold, for providing the hot water to applications requiring the thermal output.
In accordance with the invention, multiple constructions of the heat pipe can be provided According to a first embodiment shown in
According to a second embodiment, shown in
A third embodiment of a heat pipe 50 is shown in
An embodiment for converting titanium pipes into a heat pipe 60 is shown in
In contrast to the single tube designs of
The thermal capacity of the design is approximately 100 kW and may cost approximately $0.18/W.
In accordance with the present invention, there are several factors relevant to determining the appropriate construction of a heat pipe, including mechanical, thermal and environmental requirements.
A thermal evaluation of the potential effectiveness of the heat pipe includes examining the heat pipe power capacity limits of the fluid, or thermosiphon, used in the heat pipe. There are limiting factors for thermosiphons, including entrainment of flooding limits and boiling or evaporative limits. For example, water has a greater power capacity than methanol or other fluids when in the 100° C. to 200° C. range. The power limit of the thermosiphon depends on the gravity return of the condensate form of the fluid. The capillary limit does not apply and the viscosity limit is not an issue at higher temperatures. The sonic limit exceeds 2 kW at 100° C. and scales with the cross-sectional area of the heat pipe. The surface smoothness of the heat pipe also effects boiling of the thermosiphon. It is expected that entrainment is the main limiting factor where shear stress from the vapor flows up the heat pipe, which can prevent the counter flow of the condensate to the evaporator. This leads to “flooding” of the condenser.
A model can be used to estimate or project the entrainment or flooding limit of the thermosiphon. Suitable models found in the art include, for example: ESDU-81038 (1981) as reported in “Heat Pipes” by Dunn and Reay; Wallis (1969): Gas-liquid velocity criteria for flooding in counter-flow; Nguyen-Chi, H. and Groll, M.: Flooding Limit based on Wallis criteria with additional term for tube inclination; Taitel-Duckler (1976): Criteria for Kelvin-Helmholtz instability for finite waves in liquid films on inclined surfaces; and Weber number criteria with length scale based on the liquid film thickness. An example of an entrainment model estimating the liquid film thickness (t) in a tube 130 is shown in
The liquid velocity profile is integrated to get mass flow according to the following equation:
The shear stress balance can be determined according to the following equation:
The unity Weber number can be determined according to the following equation:
Table 2 shows predicted entrainment limited power:
With respect to the possibility of power capacity being limited by boiling, it is estimated that there would be heat flux levels of 3.4, 7.5 and 22 W/cm2 for tubes having inner diameters of 6, 28 and 84 millimeters, respectively. At 100 kW total power over a 15 meter length for the evaporator, the heat flux levels are 0.49, 1.26 and 2.53 W/cm2 for tubes having inner diameters of 6, 28 and 84 millimeters, respectively. As a result, it is not expected that boiling of the thermosiphon should be a limiting condition for the heat pipes according to the invention.
It is estimated that for a heat pipe having a sixty degree inclination from vertical and at 121° C., the power transport for a heat pipe including pipes having a ⅜ inch outer diameter and a seventy-two pipe bundle (
A vapor shear test can be conducted with the purpose of determining the entrainment or flooding limited power capacity of a thermosiphon and to provide a baseline for scaling to other tube sizes. The return of liquid condensate by gravity down a thermosiphon tube is opposed by the shear stress from the counter-flow in vapor. The same shear stress conditions can be created in an air-water analog in an open tube. Tests can be done at different tube inclinations and liquid and gas flow rates to determine the conditions where liquid is unable to flow down the tube. An apparatus for the test can include a glass tube having a length of eight feet and an inner diameter of eight millimeters, pure deionized water introduced at the top of the tube, which flows down by gravity, and clean nitrogen gas introduced at the bottom of the tube, which flows to the top and exits. Water wets the glass tube just as it wets the thermosiphon wall material and the normal liquid flow and flow reversal at higher gas velocities can be observed. The tests can be performed at room temperature and the tube can be inclined at 30, 45 and 60 degrees from horizontal.
An energy equation is used to calculate mass flow rate of vapor and liquid and velocity of vapor. The shear stress is calculated based on vapor velocity for the round tube using standard friction factor correlations. The equivalent velocity of N2 gas is calculated to match vapor shear stress. Table 3 below shows test conditions to simulate water liquid vapor counter-flow at 100° C. The flow becomes unsteady at the conditions labeled with an asterisk in Table 3.
24.276 *
A shear test shows that as the angle of inclination of the pipe or tube increases, the power carrying capacity also increases to a limit. From testing an eight feet section of eight millimeter (inner diameter) tubing, it is estimated a pipe can carry from 600 W at an angle of inclination from horizontal of 30 degrees up to 750 watts at an angle of inclination of 60 degrees. Increasing the angle from 30 to 45 improves the power capacity by approximately 10%, but increasing the 45 to 60 improves the power carrying capacity by only 1.3%. Further, a second tube shaped with helical swirls around a W″ mandrel was built and tested which produced similar results, indicating the heat pipe will function with a transposed tube winding.
As shown and described in reference to
As the number of heat pipes increases from a heat pipe 150 to the heat pipe bundle 170, the diameter of the individual heat pipes 150, 162, 172 decreases. Exemplary dimensions for the heat pipes 150, 160, 170 of
The material used for making the heat pipe wall may also vary based on compatibility with water as the working fluid, corrosion resistance to brine in the well bore, availability of tubes in the appropriate diameter and wall thickness material cost and ability to manufacture. One possible material is copper, which has a high thermal conductivity, compatibility with water as the working fluid, has well-known fabrication processes and is readily available at the lowest cost. A second material option is 70/30 cupro-nickel alloy, which is considered because of its excellent corrosion resistance and higher mechanical strength over copper. It is expected that it is compatible for making heat pipes having water, as a related material, Monel, is known to be acceptable. A third material for possible use is titanium KS50, which has superior mechanical strength, half of the weight of copper and excellent corrosion resistance. It is also known to be compatible with water for heat pipe use.
These three pipe materials are further compared in Table 5 below:
A stress analysis, as a result of bending of the material, can be performed for each of these materials. Because the metals being considered are ductile, the analysis compares the calculated stress values to the yield stress. Yield stress is usually measured as 0.2% yield or proof strength, which is the stress that produces a 0.2% strain without recovering. Stresses investigated in the analysis include bending around a large radius during installation and hoop stresses caused from internal tube pressures at 350° F. and 600° F. temperatures and external pressures at 6,000, 8,000 and 10,000 feet below ground level. The bending stresses are calculated using Hooke's Law, where the strain at the extreme fiber of the tube outer diameter, and E is the modulus of elasticity in 106 pounds per square inch (psi). Strain rate is determined from bending around the large radius, the appendage that must pass through during deployment into the hole. Strains can be determined for a forty feet and fifty feet bend radius. Hoop stresses can be determined using Lame's equation.
A summary of the bending stress analysis is shown in Table 6. The results labeled (*) indicate a possibility of the tube to yield during deployment, the results labeled (**) indicate an elastic tube, and the results with no asterisks indicate the tube will yield during deployment.
A sample analysis of the estimated cost for the three example raw materials is shown in Table 7:
A summary of the estimated raw material cost tradeoffs for the three example materials is shown in Table 8:
While there have been shown and described and pointed out fundamental novel features of the invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices and methods described may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice.
The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/061,444 filed Oct. 8, 2014, which is hereby incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2015/054662 | 10/8/2015 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62061444 | Oct 2014 | US |
