The present disclosure describes subject matter that relates to closed loop systems that circulate a working fluid, with particular discussion about embodiments of a system that can utilize working fluids to operate one or more components (e.g., a pump) to improve efficiency and/or reduce parasitic losses.
Systems that generate power include closed loop systems that operate under principles of a Rankine Thermodynamic Cycle. These systems use thermal energy from a thermal source fluid to evaporate a working fluid, e.g., a low temperature boiling organic fluid. This process generates high pressure vapor. In conventional designs, the system directs the vapor to a turbine, or like device, that can operate a generator to generate electric power. The system can also cool and condense the vapor to liquid form. During operation, the system circulates the working fluid, in liquid form, for use in the evaporation and power generating stages of the design.
For most closed loop designs, the system 100 is configured to continuously circulate the working fluid among the various stages (i.e. evaporation, power generation, and condensation). These configurations often employ a pump (e.g., pump component 102) that pressurizes the working fluid, in liquid form, prior to delivery to the evaporation and/or power generation stages. In many cases, the system will supply power to drive the pump from the generator. This feature, however, reduces the power from the system that would otherwise be available for use.
The present disclosure contemplates improvements that configure systems to harvest residual energy in the thermal source fluid to improve efficiency and to reduce power loss that can derive from the pump as well as other auxiliary loads (e.g., fans). The principles of operation of these systems can enjoy wide application, particularly with respect to closed loop (or hermetically sealed systems) that might, for example, utilize positive displacement machines instead of turbines. As noted herein, these systems can incorporate members that operate in response to the working fluid, often in vapor form and/or at higher pressure consistent with working fluid after evaporation and/or power generation stages. Examples of the working fluid can include refrigerants (e.g., R245fa), although this disclosure contemplates other fluids (and components) that can operate in closed-loop (and/or hermetically sealed) systems. The members can include mechanical elements, for example, that have motive action (e.g., reciprocate, rotate, etc.) that is useful to satisfy operating and power requirements of the auxiliary loads. For the pressurization stage, these mechanical elements may embody a piston-and-cylinder arrangement (or other positive displacement arrangement) that generates motion that can drive a pump.
Embodiments of the systems below enjoy a variety of operating advantages over conventional designs. For example, the improvements can eliminate the need to siphon power from the generator or to dedicate an external power source, both of which may be necessary in conventional systems to operate the pump to circulate the working fluid at appropriate pressures. In one implementation, assuming a nominal 10% efficiency for energy transformation, the electrical power to drive the pump in conventional designs may be ten (10) times more expensive than the thermal energy that the embodiments can be recouped by utilizing the working fluid as set forth herein. Moreover, because the system is configured so that the mechanical elements and the auxiliary load (e.g., the pump) utilize the same working fluid, the design of the embodiments below can tolerate internal leaks and enjoy wider, less stringent dimensional tolerances for these components. Any loss in volumetric efficiency is offset by the availability of “free” energy that the system recuperates, rather than discards as found in conventional designs. This feature can allow the system to incorporate mechanical elements that are favorably designed, e.g., with less attention to tight seals. The resulting designs can improve mechanical advantage, reduce friction, and, notably, further enhance the overall efficiency of the system.
Reference is now made briefly to the accompanying Appendix in which:
Where applicable like reference characters designate identical or corresponding components and units throughout the several views, which are not to scale unless otherwise indicated.
This discussion below describes embodiments of systems (e.g., closed loop systems) that are configured to utilize the working fluid F to operate one or more of the components and devices found therein. The components and devices may include fans and pumps that are necessary for the system to operate, e.g., to circulate the working fluid F at the appropriate working properties. In conventional designs, the devices represent parasitic losses that consume some amount of power, often power that the system generates during operation. Improvements to closed loop systems based on aspects of the present disclosure, on the other hand, can eliminate certain parasitic losses to maintain, and effectively improve, overall efficiency as compared to these conventional systems.
During operation, the system 200 leverages changes in the working properties and phases of the working fluid F to convert thermal energy to mechanical and/or electrical energy. Starting in the lower right corner of
Construction of the system 200 utilizes the working fluid F to drive the pump component 202. For example, the drive member 220 can embody one or more devices (e.g., a piston and cylinder, a diaphragm, an impeller, etc.) that move in response to flow of the working fluid F. This motive action can, in turn, drive the pump member 222 to elevate the pressure (e.g., from the first pressure to the second pressure) of the working fluid F. As shown in
As noted above, the design of the system 200 can accommodate different configurations for the drive member 220. These different configurations are useful to tailor one or more mechanical elements (e.g., a piston) in the drive member 220 and/or the pump member 222 to allow the pump component 202 to deliver the working fluid F at sufficient discharge pressure (e.g., the second pressure) and/or volume flow rate. This feature can compensate for variations in pressure of the working fluid F that is available to operate the drive member 220. At a high level, the drive member 220 and the pump member 222 can have, respectively, a first operative dimension and a second operative dimension. Examples of the operative dimensions can define dimensions (e.g., a diameter) of mechanical elements (e.g., a piston) and/or other parts of the member(s) that interface with the working fluid F or otherwise relate to operation of the pump component 202 to pressurize the working fluid. In one example, the first operative dimension can have a first value and the second operative dimension can have a second value, wherein the first value is proportional to the second value to configure the drive member to operate the pump member to pressurize the working fluid in liquid phase in response to the working fluid in vapor phase at a third pressure that is less than the second pressure. For implementations that use reciprocating piston-type elements, this feature can configure the drive piston to be made proportionately larger that the pump member to operate at lower pressures but still achieve sufficient mechanical advantage to move the pump member to pressurize the working fluid F, e.g., from the first pressure to the second pressure (discussed above). In one example, considering a working pressure of 20 bar, and a heat source of only 70° C. (corresponding to approximately 5 bar available pressure), the drive piston would need to be four (4) times the area of the pump piston. Any considerations for lowered system efficiency are not a concern because the source of thermal energy is effectively “free.” Moreover, embodiments of the system 200 can avoid inefficiencies inherent in the electric generator and, for example, an electric drive motor of the pump, by directly using the working fluid to drive the pump member 222.
The system 300 recovers thermal energy of a source fluid from the heat source 332. This source fluid is useful to evaporate the working fluid, e.g., in the evaporator component 304. Notably, the need for high efficiency in, e.g., Organic Rankine Cycle (ORC) systems, requires designers to operate vapor temperatures that are as high as possible. However, thermodynamic “pinch point” and like considerations in the evaporator component 304 can prevent use of all available heat in the source fluid. These limitations causes the source fluid to exit the evaporator component 304 at relatively high temperatures. In one example, the source fluid may enter the evaporator component 304 at a first source temperature (e.g., 150° C.) and exit the evaporator component 304 at a second source temperature (e.g., 120° C.) that is different (e.g., less than) the first source temperature.
The system 300 can recover the thermal energy at the second source temperature to provide working fluid F in vapor form to the drive member 322. For example, as shown in
Use of the second heat recovery unit 356 of
At start-up, the system 300 can utilize several of the peripheral components found in
The control system 347 can be configured to manage the process of the system 300. This configuration may require use of one or more processors, memory, and related circuitry that can allow the control system 347 to exchange signals, instructions, etc. with the various components of the system 300. In certain embodiments, the control system 347 may utilize executable instruction or machine readable instructions (e.g., software, firmware, etc.) that the one or more processors are configured to execute in order to perform, e.g., processing and generating of signals.
In light of the foregoing discussion, the embodiments contemplated herein use motive device(s) that can replace, for example, electric motors typical of conventional closed-loop ORC systems. These electric motors require electric power from the generator or from a power supply separate from the overall system. On the other hand, in lieu of using such external power, the embodiments can recycle and/or recuperate energy inherent in the overall design of the closed loop ORC design. This feature offers a net gain in efficiency of these embodiments by effectively removing losses related to use of electrical power to drive the pump or other electrical loads. Moreover, configurations of the embodiments that utilize the working fluid F to operate certain mechanical elements often do not require vapor-tight and/or hermetic seals. Because the working fluid is the same as the pumped fluid, small internal leaks are not critical and can be tolerated. These configurations can maintain appropriate volumetric efficiencies with looser tolerances that allow for small leaks and/or otherwise eliminate the need to seal the system from the surrounding environment. Designs and constructions with looser tolerances, in turn, reduce internal friction and improve mechanical efficiencies.
As used herein, an element or function recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or functions, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the claimed invention should not be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.
This written description uses examples to disclose embodiments of the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
This application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 61/837,989, filed on Jun. 21, 2013, and entitled “Systems and methods for Reducing Parasitic Losses in Closed Loop Systems.” The content of this provisional application is incorporated herein in its entirety.
Number | Date | Country | |
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61837989 | Jun 2013 | US |