Over the years, efforts have been undertaken to obtain power through different thermodynamic cycles. For example, techniques for generating electrical power from equipment relying on the “Brayton”, “Stirling” or “Organic Rankine” cycle (ORC) have been developed. Unfortunately, these technologies have been generally ineffective and inefficient with lower heat sources, for example, below the boiling point of water.
By way of example, ORC equipment or engine manufacturers often provide a system that allows for practical operation with input heat temperatures as low as 170° F. However, as a result, this may only be rendered where a dramatically reduced output is also attained, thereby making the undertaking significantly less economical. In part, this is due to the fact that the method of operation uses two phase changes per cycle, from liquid to gas and back again, and uses turbine or turbine-like technology to convert the pneumatic forces of the gas to generate productive work.
Alternative technologies for converting very low grade heat into usable work also exist. Very low grade heat is defined herein as being below the boiling point of water at sea level. Regardless, these technologies are generally inefficient or unproductive as well. Again, most of these technologies are also based on the Organic Rankine thermodynamic cycle, which involves converting a liquid to a gas and back again. That is, two phase changes per cycle are exhibited. Therefore, these “thermal pneumatic heat engines” face a challenge in terms of efficiency.
ORC engines convert a liquid with a low boiling temperature, such as a refrigerant, to gas and then channels the gas, or a gas and liquid mixture, through a turbine-like device to produce rotary motion. Such engines operate at a “low” rotational speed of near 5,000 rpm. The gas mixture is then cooled back to a liquid state, changing phase again before reuse. Even setting aside these naturally occurring phase change inefficiencies, such speed and phase changes create significant noise, not unlike a jet engine.
Another technology that has been attempted is known as “thermal hydraulic heat engines”. These involve the use of heat applied to a liquid that may have a relatively high coefficient of expansion. As a practical matter, however, most liquids expand very little when heated and contract very little when cooled. Thus, in actual practice, such engines fail to attain successful commercialization due primarily to the difficulty of obtaining sufficient expansion, and sufficiently rapid expansion and contraction, in liquids, which in turn limits the economic viability of such engines. Further, even when utilized, such engines are only practical for use in a narrow set of specific circumstances given the general inflexibility in terms of available modifications for differing uses. In fact, extensive trial and error is generally required even for the circumstances in which the engines may be effectively utilized. This is due, in part, to the inherent limitation involved with relying on the expansion and contraction of a liquid by the introduction and removal of heat.
These types of engines generally include the use of a piston that is reciprocated by the alternating application of heated gas and cooled liquid, comparatively speaking. As a result, the piston is well suited for reciprocation in a linear manner. Thus, in theory, the added efficiencies of linear reciprocation may be available in generating work. However, as a practical matter, the ability to efficiently obtain work from such a linear reciprocating piston faces added challenges. That is, in addition to phase change and other engine inefficiencies that are commonplace with other thermal heat systems as noted above, as with any linearly reciprocating piston, a complete stop and reverse in direction is required with every stroke. However, due to the use of generally low input temperatures in facilitating stroking of the piston, the piston may face efficiency challenges with each stroke. This is because the piston reaching the end of a stroke must overcome forces from one direction for stroking in the opposite direction facilitated only by generally low input temperatures, generally below about 200° F.
A piston assembly is provided for a thermal cycle engine. The assembly includes a piston with a head defining an operating chamber for changing in volume. A floating head is also included which defines a compressible chamber and is in hydraulic communication with the operating chamber to enhance reciprocation of the piston. Additionally, the compressible chamber volume is dynamically dependent upon the operating chamber volume. In one embodiment, the operating chamber is defined by the piston head at one side whereas the floating head itself defines the other side of the chamber. In another embodiment, the operating chamber is actually a first operating chamber and the hydraulic communication with the floating head includes a tubular connection from the first operating chamber to a second operating chamber defined by the floating head at a location apart from the first operating chamber.
In the following description, numerous details are set forth to provide an understanding of the present disclosure. However, it will be understood by those skilled in the art that the embodiments described may be practiced without these particular details. Further, numerous variations or modifications may be employed which remain contemplated by the embodiments as specifically described. For example, embodiments herein are described with reference to illustrations depicting a certain floating dual-head piston assembly system or engine. However, a variety of layouts may be employed, with additional piston assemblies incorporated, a host of additional valving or timing controls, etc. However, these system/engine layouts are merely illustrative as a variety of different hydraulic or even mechanical layouts and other design options may be employed depending on system constraints and the intended application.
Embodiments detailed herein may use the controlled expansion and contraction of a compressible fluid, perhaps supercritical fluid, to move a piston in order to generate productive work. While it is not required that the operating fluid be a supercritical fluid, the system may govern a thermodynamic cycle similar to embodiments detailed in U.S. Provisional Patent Application 62/424,494 for a Thermal Cycle Engine and PCT/US17/60722 for a High Dynamic Density Range Thermal Cycle Engine, each of which is incorporated herein in its entirety. For example, the engine may display a “low” reciprocation speed of less than about 50 cycles per minute. Further, embodiments detailed herein may avoid changes in phase, and so are inherently more thermodynamically efficient, and with the appropriate operating fluid may operate effectively using input temperatures below 200° F. In fact, they can easily be tuned to operate with minor reductions in efficiency with input heat below 150° F. It also operates with greatly reduced noise.
As indicated, the embodiments detailed herein do not require the circulation of supercritical fluid. Additionally, a more complete circulation of the supercritical fluid may be utilized as detailed in U.S. Provisional Patent Application 62/618,689, for a Floating Head Opposing Piston Assembly, which is incorporated herein by reference in its entirety. In these embodiments, a unique floating head may be employed adjacent to a piston head to provide a sequentially timed, spring-like aid to filling the working fluid chamber and stroking of a piston for enhanced efficiency thereof
Referring specifically now to
As detailed further herein, the assembly 100 is constructed such that reciprocation of the working piston 110 is used to alternatingly change the volumes of intermediate chambers 125, 126. In this way, an incompressible working fluid such as hydraulic oil may be alternatingly circulated out of the chambers 125, 126 through working hydraulics 400 and directed toward a motor 430, flywheel 440, generator 450 or other suitable power retrieval device (e.g. see
Reciprocation of the piston 110 as described above is driven by the alternating introduction of operating fluid into adjacent chambers 150, 155 defined by working piston heads 114, 118. As detailed further below, the operating fluid may be a supercritical fluid such as CO2 or other appropriate fluid, generally one that is effectively circulated by way of efficient heating and cooling cycles. Regardless, as operating fluid is used to increase the volume of the upper adjacent chamber 150, the volume of the upper intermediate chamber 125 is reduced, forcing working fluid out of the intermediate chamber 125 as noted above and toward a power retrieval device. By the same token, as the piston 110 is reciprocated in the opposite direction, due to influx of operating fluid into the lower adjacent chamber 155, the volume of the lower intermediate chamber is compressibly reduced, again forcing working fluid out and toward a power retrieval device.
Continuing with reference to
In one embodiment, the floating chambers 140, 145 may be alternatively increased in volume, for example, by introduction of hydraulic oil or other suitable incompressible fluid from a nearby accumulator or other suitable location. Thus, a chamber 140 may be increased in volume with the head 142 forced along the distance (d) toward the upper adjacent chamber 150 to aid in smooth controlled stroking of the piston 110 (to the right as shown). In turn, working fluid may be circulated out of the upper intermediate chamber 125 as described above. Aid to circulating of the operating fluid out of the upper adjacent chamber 150 is also provided as a result of the movement of the floating head 142 in this manner. This embodiment of floating head actuation and circulation of operating and working fluids is detailed further below with specific reference to
In another embodiment, the movement of the floating heads 142, 147 may be a function of pressure where the floating head chambers 140, 145 are sealed off and isolated without hydraulic connection to any outside pressure source. For example, a chamber 140 may be filled with a compressible gas such as nitrogen, air or an inert gas of a predetermined pressure sufficient for holding the head 142 at the head stop 175, say about 1,500 psi. Thus, this feature may be referred to as a “gas” or an “air” spring as noted below. Regardless, as an adjacent chamber 150 is expanded by circulation of operating fluid thereinto, for example moving this chamber 150 from a starting psi of about 1,100 to over 1,500 psi, the corresponding floating head chamber 140 may decrease in volume and increase in pressure. However, once the pressure in this chamber 140 matches and/or exceeds pressure in the adjacent chamber 150, for example, with both reaching about 3,000 psi, the head 142 will be driven back toward the adjacent chamber 150, increasing pressure therein to provide an added kick for redirecting of the piston 110 in the opposite direction. Of course, these pressures are only meant to be illustrative as any suitable range of pressure options may be employed.
Recall now that the operating fluid which acts upon the piston 110 to drive reciprocation thereof may be a non-supercritical fluid, or a supercritical operating fluid such as CO2, helium or perhaps supercritical steam or other suitably efficient temperature effective fluid. That is, the fluid may be circulated through states of high temperature and pressure to states of low temperature and pressure, ultimately producing work. The addition of the described floating head concept provides an energy storage and recovery device, illustratively referred to as a “gas spring” or an “air spring”, to the system which enhances the efficiency of this circulation. This accumulator is initially kept at a set pressurization as indicated with a resulting temperature. However, the release of this spring upon pressurization and subsequent depressurization of the adjacent chamber helps regulate supercritical fluid circulation as indicated. In the embodiment where the floating head chamber 140 (or 145) is isolated, this action will maintain roughly a constant temperature condition in the gas of the chamber 140, improving the efficiency of the work produced by the cycle.
Referring now to
The more material distinctions of the segmented embodiment of the assembly 200 of
Another distinction for the embodiments of
Referring now to
As with the piston assembly 100 of
As illustrated, a heat flow 315, for example, heated water may be used to maintain heat of the heat exchanger 340. In one embodiment, maintaining the heat flow may be done by any of a number of low grade heat sources. For example, geothermal heat, solar heat or the waste heat from other unrelated system operations may be utilized to maintain the flow 315 at between about 100° F. and 200° F. This allows for an effective and economical utilization of a vast array of heat sources previously considered to be too cool and of no practical economic value. Of course, in other embodiments, higher temperatures may be utilized.
As shown in
Of course, in this same timeframe, the upper cold side valve 357 is opened with the lower cold side valve 355 remaining closed. Additionally, the upper floating head 142 may responsively begin to move upward as it slightly lags behind the upward movement of the piston 110 and upper head 114. Nevertheless, as noted above, this head 142 may also respond to a pressure buildup in the upper floating chamber 140, whether through pressurized air or the introduction of another working fluid, to initiate stroking of the piston 110 in the opposite direction following the depicted timeframe. In connection with this, the upper cold side valve 357 will be closed as the lower 355 is opened to accommodate the flow of operating fluid therethrough.
Continuing with reference to
The cooled operating fluid, perhaps supercritical CO2 that has been cooled from about 175° F. down to about 150° F., may then be pumped by an exchange pump 390 back through the recuperator 380 and eventually to the heat exchanger 340. Thus, the circulating of the operating fluid to the piston assembly 100 for stroking of the piston 110 may be continued as described above.
Referring now to
Continuing with reference to
Additionally, a portion of this working fluid may be directed from the location of the power retrieval devices 430, 440, 450 to a reservoir 470. For example, where the devices 430, 440, 450 are sufficiently provided for already, a portion of the working fluid may be directed to the reservoir 470 making it available to the accumulator 490 for pressurizing upper floating chamber 140 as described above (or the lower floating chamber 145 (as described below). In the embodiment shown, an accumulator pump 480 is provided to help facilitate drawing on the reservoir 470 in charging the accumulator 490. Note, the upward movement of the accumulator piston 495 as the accumulator 490 is charged (arrow 497).
Referring now to
Continuing with reference to
Referring now to
Referring now to
Referring now to
The preceding description has been presented with reference to presently preferred embodiments. Persons skilled in the art and technology to which these embodiments pertain will appreciate that alterations and changes in the described structures and methods of operation may be practiced without meaningfully departing from the principle, and scope of these embodiments. Furthermore, the foregoing description should not be read as pertaining only to the precise structures described and shown in the accompanying drawings, but rather should be read as consistent with and as support for the following claims, which are to have their fullest and fairest scope.
Filing Document | Filing Date | Country | Kind |
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PCT/US2019/013050 | 1/10/2019 | WO | 00 |
Number | Date | Country | |
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62618689 | Jan 2018 | US |