Patent Application
20130327042
The present invention relates to externally heated engines. More particularly the invention relates to improvements in efficiency and performance of externally heated engines operating at low temperatures and pressures and a system including such an improved externally heated engine to enable the conversion of low temperature heat to useful power.
Externally heated engines especially those similar to the gas or liquid turbine type engines have always held great promise. This is because such engines are reasonably efficient, relatively simple in their operation, and flexible in the media they can employ as working fluids. At the same time however, they have been held back in many applications by certain serious limitations.
Turbine style engines that employ liquid fluid flows are the most limited. Unless one has access to a dam, with a large head of water behind it, or a particularly rapidly flowing stream with a large drop in elevation, one cannot produce significant amounts of power. Without a dam or a stream it is simply not feasible or efficient to heat the liquid sufficiently, or to pump it uphill far enough and cheaply enough, to obtain a useful net output. Similarly, a paddle wheel type structure such as found on certain steam ships for instance, require a separate source of motive power, such as a steam engine, to operate them.
Turbine type engines that employ flows of a gaseous fluid hold more promise. It is practical to employ fluids in the gas phase to power engines, as in steam locomotives for example. Other types of hot gas turbines are also well known in the prior art, and can operate effectively. In virtually all of these cases however, the required temperatures and pressures to which the gas must be raised are very high. It is not uncommon for such engines to reach temperatures of hundreds of degrees Fahrenheit, and at the same time to operate at pressures of hundreds of PSI. In general, this means that a source of combustion must be specifically provided and operated in conjunction with the engine, for the sole benefit of the engine, in order to reach the operating levels required.
Old style steam locomotives and stationary steam engines for instance ran on large coal fires, operating in conjunction with pressure-raising pumps, to produce the required levels. Such engines were well known for exploding at inopportune times.
Gas turbine engines, such as those used at electrical generation stations, also employ very high temperatures and pressures. Jet turbine engines, such as those employed on aircraft, also produce extremely high temperatures in their combustion chambers, and they further employ multiple stages of compression to reach the desired pressures and temperatures.
The present invention is directed to a heat engine in a thermodynamic power generating system that avoids high temperatures and pressure and relies instead on relatively low temperature heat sources and low pressure operating fluids to generate energy. The system functions without the need for its own dedicated source of combustion in order to operate and operates at a relatively high efficiency to produce significant amounts of power. The thermodynamic power generating system is designed to operate on low temperature waste heat left over from other processes, or to operate on low temperature solar, geothermal power, power plant waste heat, or waste heat available from air conditioning or refrigeration units or for instance.
The configuration of turbine power plants including in particular the turbine blades on a rotating member, the housing construction and the working fluid inlet and exhaust ports have been the subject of many prior art patents.
U.S. Pat. No. 3,501,249 to Scalzo, is directed to turbine rotors and particularly to structure for locking the turbine rotor blades in the periphery of the blade supporting disk.
U.S. Pat. No. 4,073,069 to Basmajian discloses an apparatus comprising a turbine rotor wheel made of a central circular disc with arc-bent plate turbine blades mounted on and bonded to the disc at close and regular intervals around the disc periphery and a stator-housing with a transparent cover for enclosing the turbine wheel, holding one or more feed nozzles and providing a stator reaction mount for the nozzles, the wheel and its housing being mounted from an instrument chassis containing parameter adjusting means and turbine output adjusting and measuring means to provide a compact, economical demonstrator of turbine operation.
U.S. Pat. No. 4,400,137 to Miller et al discloses a rotor assembly and methods for securing rotor blades within and removing rotor blades from rotor assemblies. The rotor assembly comprises a rotor disc defining a plurality of blade grooves, and including a plurality of tenons disposed between the blade grooves and defining a plurality of pin sockets radially extending inward from outside surfaces of the tenons; and a plurality of rotor blades, each blade including a root disposed within a blade groove to secure the blade against radial movement, and a blade platform overlaying a tenon and defining a radially extending pin aperture. The rotor assembly further comprises a plurality of locking pins radially extending through the pin apertures and into the pin sockets to secure the rotor blades against axial movement, each pin including a head and a base to limit radial movement of the pin.
U.S. Pat. No. 4,421,454 to Wosika discloses a full admission radial impulse turbine and turbines with full admission radial impulse stages. The turbines are of the single shaft, dual pressure type. Provision is made for utilizing working fluid exhausted from the high pressure section, in which the radial impulse stage(s) are located, in the low pressure section which contains axial flow turbine stages. The (or each) radial impulse stage in the dual pressure turbine has a rotor or wheel with buckets or pockets oriented transversely to the direction of wheel rotation and opening onto the periphery of the wheel. Working fluid is supplied to the buckets via nozzles formed in, or supported from, a nozzle ring surrounding the turbine wheel and aligned with the entrance ends of the buckets.
U.S. Pat. No. 4,502,838 to Miller et al discloses buckets of a turbine wheel that are formed as a series of equally spaced, overlapping U-shaped passages in the rim of a wheel blank. In the machining operation, an island is left as the inner segment of the curved portion of the U and this is used in combination with labyrinth seals to provide a fluid seal between the inlet and the outlet portion of each bucket.
U.S. Pat. No. 5,074,754 to Violette discloses a retention system for a rotor blade that utilizes the combination of a fixed retention flange and a removable retention plate with a closed-sided retention member. This system enables the rapid replacement or removal of the rotor blade for inspection, maintenance, or replacement purposes without requiring removal of surrounding major engine components or structural members. The rotor blade is installed in a retention member contained in a rotatable hub (not shown) by inserting an outwardly extending portion of a shaped blade root of the rotor blade below a radially-inwardly projecting shaped flange peripherally disposed within the interior of the retention member's structure. A removable shaped retention plate, which is releasably secured to, and adapted to mate with, the retention member, then captures and secures another outwardly extending portion of the shaped root of the rotor blade with a releasable fastener. The shaped root is secured within the retention member without a direct bolted connection. Preloading the fastener induces compressive loading among the system components, resulting in the attenuation or elimination of fretting and wear of their respective component surfaces.
The prior art includes many examples of power systems that attempt to capture waste heat from a primary heat source and reuse the energy in a secondary power system.
U.S. Pat. No. 3,822,554 to Kelly discloses a heat engine operating between temperatures T1 (low) and T2 (high) includes separate vapor closed-cycle motor and pump systems, in heat-exchange relation at T1 and T2, and heat-exchangers between the condensates of said systems.
U.S. Pat. No. 3,953,973 to Cheng et al discloses a heat engine, or a heat pump, in which the working medium is subjected alternatively to solidification and melting operations. A working medium is referred to as an S/L type working medium that is subjected to cyclic operations, each cycle comprises of a high temperature melting step conducted under a first pressure, and a low temperature solidification step conducted under a second pressure. Each heat pump cycle includes a high temperature solidification step conducted under a first pressure and a low temperature melting step conducted under a second pressure. When a non-aqueous medium is used, the first pressure and the second pressure are a relatively high pressure and a relatively low pressure, respectively. When an aqueous medium is used the two pressures are a relatively low pressure and a relatively high pressure, respectively. The operation of a heat pump is the reverse operation of a heat engine.
U.S. Pat. No. 4,292,809 to Björklund discloses a procedure for converting low-grade thermal energy into mechanical energy in a turbine for further utilization. The procedure is characterized in that a low-grade heating medium and a first cooling medium are evaporated in a heat exchanger. The steam is carried to a turbine for energy conversion and moist steam is carried from here to a heat exchanger for condensing. The condensate is pumped back to the heat exchanger. The heat exchanger is common to the steam turbine circuit and a heat pump circuit in such a manner that the heat exchanger comprises a condenser for the steam turbine circuit and an evaporator in the heat pump circuit. The heat removed in connection with condensing can be absorbed by a second evaporating cooling medium the steam of which is pumped via a heat pump to a heat exchanger which is cooled by cooled medium from the heat exchanger and where condensing takes place. The condensate is carried via an expansion valve back to the heat exchanger while outgoing cooled medium from the heat exchanger is either heated in its entirety to a lower level than the original temperature at the commencement of the process or else a partial flow is reheated to a level that is equal to or higher than the original temperature at the commencement of the process and returned to the heat exchanger. The hot gas of the heat pump is used for extra superheating of the ingoing first evaporated cooling medium supplied to the turbine.
U.S. Pat. No. 4,475,343 to Dibelius et al discloses a method for the generation of heat using a heat pump in which a heat carrier fluid is heated by a heat exchanger and compressed with temperature increase in a subsequent compressor, heat is delivered therefrom to a heat-admitting process; the fluid is then expanded in a gas turbine, producing work, and afterwards its residual heat is delivered to a thermal power process, the maximum temperature of the energy sources of which, that provide work for the compressor, lies below the temperature of heat delivery. The main heat source can consist of an exothermic chemical or nuclear reaction and the heat-admitting process can be a coal gasification process. The work in the compressor is furnished essentially by the gas turbine and the thermal power process.
U.S. Pat. No. 4,503,682 to Rosenblatt discloses an engine system that includes a synthetic low temperature sink which is developed in conjunction with an absorption-refrigeration subsystem having inputs from an external low-grade heat energy supply and from an external source of cooling fluid. A low temperature engine is included which has a high temperature end that is in heat exchange communication with the external heat energy source and a low temperature end in heat exchange communication with the synthetic sink provided by the absorption-refrigeration subsystem. It is possible to vary the sink temperature as desired, including temperatures that are lower than ambient temperatures such as that of the external cooling source. This feature enables the use of an external heat input source that is of a very low grade because an advantageously low heat sink temperature can be selected.
U.S. Pat. No. 5,421,157 to Rosenblatt discloses a low temperature engine system that has an elevated temperature recuperator in the form of a heat exchanger having a first inlet connected to an extraction point at an intermediate position between the high temperature inlet and low temperature outlet of a turbine heat engine and an outlet connected by a conduit to a second inlet to the turbine between the high and low temperature ends thereof and downstream of the extraction point. In the recuperator thermodynamic medium vapor from extraction point is in heat exchange relationship with thermodynamic medium conducted from the low temperature exhaust end of the turbine unit through a water cooled condenser and in heat exchange relationship in a refrigerant condenser with a refrigerant flowing in an absorption-refrigeration subsystem. The thermodynamic medium leaving the recuperator for return to the turbine is conducted through return conduit in further heat exchange relationship with the refrigerant of the absorbent-refrigerant subsystem and is heated in a heat exchanger by an external source of heat energy and is returned to the high temperature end of the turbine through conduit to complete the cycle. External coolant, such as water, is conducted through the thermodynamic-medium condenser in heat exchange relation with the thermodynamic medium passing there through from the low temperature exhaust end of the turbine.
U.S. Pat. No. 5,537,823 to Vogel, discloses a combined cycle thermodynamic heat flow process for the high efficiency conversion of heat energy into mechanical shaft power. This process is particularly useful as a high efficiency energy conversion system for the supply of electrical power (and in appropriate cases thermal services). The high efficiency energy conversion system is also disclosed. A preferred system comprises dual closed Brayton cycle systems, one functioning as a heat engine, the other as a heat pump, with their respective closed working fluid systems being joined at a common indirect heat exchanger. The heat engine preferably is a gas turbine, capable of operating at exceptionally high efficiencies by reason of the ability to reject heat from the expanded turbine working fluid in the common heat exchanger, which is maintained at cryogenic temperatures by the heat pump system. The heat pump system usefully employs gas turbine technology, but is driven by an electric motor deriving its energy from a portion of the output of the heat engine.
U.S. Pat. No. 6,052,997 to Rosenblatt discloses an improved combined cycle low temperature engine system having a circulating expanding turbine medium that is used to recover heat as it transverses it turbine path. The recovery of heat is accomplished by providing a series of heat exchangers and presenting the expanding turbine medium so that it is in heat exchange communication with the circulating refrigerant in the absorption refrigeration cycle. Previously recovery of heat from an absorption refrigeration subsystem was limited to cold condensate returning from the condenser of an ORC turbine on route to its boiler.
U.S. Pat. No. 7,010,920 to Saranchuk et al discloses a low temperature heat engine that circulates waste heat back through a heat exchanger to the prime mover inlet. The patent discloses a method for producing power to drive a load using a working fluid circulating through a system that includes a prime mover having an inlet and an accumulator containing discharge fluid exiting the prime mover. A stream of heated vaporized fluid is supplied at relatively high pressure to the prime mover inlet and is expanded through the prime mover to a lower pressure discharge side where discharge fluid enters an accumulator. The discharge fluid is vaporized by passing it through an expansion device across a pressure differential to a lower pressure than the pressure at the prime mover discharge side. Latent heat of condensation in the discharge fluid being discharged from the prime mover is transferred by a heat exchanger to discharge fluid that has passed through the expansion device. Vaporized discharge fluid, to which heat has been transferred from fluid discharged from the prime mover, can be returned through a compressor and vapor drum to the prime mover inlet. Vaporized discharge fluid can be removed directly from the accumulator by a compressor where it is pressurized slightly above the pressure in the vapor drum, to which it is delivered directly, or it can be passed through a heat exchanger where the heat from the compressed fluid is transferred to an external media after leaving the compressor in route to the vapor drum. Liquid discharge fluid from the accumulator is pumped to a boiler liquid drum, then to the vapor drum through a heat exchanger. The liquid discharge fluid may be expanded through an orifice to extract heat from an external source at heat exchanger and discharged into the vapor drum or the accumulator, depending on its temperature upon leaving heat exchanger.
U.S. Pat. No. 7,096,665 to Stinger et al discloses a Cascading Closed Loop Cycle (CCLC) and Super Cascading Closed Loop Cycle (Super-CCLC) systems are described for recovering power in the form of mechanical or electrical energy from the waste heat of a steam turbine system. The waste heat from the boiler and steam condenser is recovered by vaporizing propane or other light hydrocarbon fluids in multiple indirect heat exchangers; expanding the vaporized propane in multiple cascading expansion turbines to generate useful power; and condensing to a liquid using a cooling system. The liquid propane is then pressurized with pumps and returned to the indirect heat exchangers to repeat the vaporization, expansion, liquefaction and pressurization cycle in a closed, hermetic process. The system can be utilized to generate power from low temperature heat sources.
Although numerous attempts have been made to capture waste heat from a primary heat source and reuse the energy in a secondary power system all of these attempts have fallen short. Thus, what is needed is an efficient, reliable and cost effective power system and heat engine that utilizes low temperature waste heat and is capable of operation using a low temperature and pressure working fluid.
Briefly described, the present invention is comprised of three separate interacting thermodynamic loops including an external heat source loop, an externally heated heat engine loop and a heat reclaiming loop which consists of a plurality of subsidiary loops each operating at a different temperature. Depending on the embodiment the heat reclaiming loop is either the main source or sole heat source for the heat engine loop. The externally heated engine is contained within an enclosure. A rotating member is mounted within the enclosure on bearings, with a shaft that extends through a seal, to the outside of the engine. Mounted upon the rotating member are one or more blades. A flow of gasses is directed upon the surface of these blades by the action of one or more stationary nozzles. As a result of the action of the gasses upon the blades, force is exerted upon the blades. This causes the rotating member to revolve, and torque is exerted upon the shaft while it rotates.
A rotating shaft is able to perform work, and this is accomplished by coupling the shaft to an electrical generating device thereby producing electrical power. Very large volumes of useful, moderate pressure gas are produced easily in this invention, at low temperatures, by using a working fluid such as a refrigerant. For instance, refrigerant R134 is one possible type of working fluid. Many other standard refrigerant types are also suitable. This refrigerant, in its liquid form, will boil very readily at low temperatures and pressures, and produce voluminous amounts of hot gas after being heated. R134 gas is particularly suited for this purpose, and completely avoids the need for high pressures and temperatures.
The blades mounted on the rotating member of the instant invention are not of traditional design. Prior art blades tend to be made for either high pressure and temperature gas flows—like in a jet engine for instance—or for flows of liquids, especially water, as in a hydroelectric plant for instance. These blades do not function well for low pressure and temperature gasses. The instant invention overcomes the limits of the prior art by combining a unique blade design with a particular design, to thereby extract power effectively under the desired conditions.
As configured, the nozzle directs the flow almost straight on to the surface of the blade. This creates a higher pressure on the upstream side of the blade than on the downstream side, and due to this impact effect, the pressure differential, delta P, produces a net force on the blade in the desired direction. Even a few pounds of delta P can produce a large torque if the blade surface area is great enough, and the diameter of the rotating member is large.
In addition, the blade design additionally takes advantage of the change of momentum in a flow that is produced by the geometry of the blade and the flow of the hot gaseous working fluid. By reversing the flow of working fluid the resulting reaction force on the blade will be large, and in the desired direction. The momentum of a flow of gas is proportional to the square of its velocity, and so the nozzles are designed to greatly accelerate the velocity of the flow, prior to reaching the blade.
The force generated by the velocity of the gas flow is a vector quantity, and so a change in direction can be as effective as a change in speed. So, rather than have the flow crash to rest up against the blade surface, the blade surface is curved, and in turn the flow is also turned almost 180 degrees. This produces a momentum change almost double that than if the flow had been brought to rest against the blade. The combination of very high (even supersonic) velocities and radical change in direction result in a very large change in momentum. Thus a large reaction force is exerted on the blade.
The combination of both types of action and the multiplying effects of the carefully directed gasses produce force levels not otherwise available with gasses at these pressures and temperatures.
Additionally, to extract even greater performance from the whole system energy is recovered on both the input and exhaust of the heat engine_loop of the power system. On the input side of the engine, heat is brought from the external source to a heat exchanger serving the heat engine loop. This is done by circulating a heat transfer fluid from the external_heat source loop to the heat exchanger. Obviously not all of the available heat in the stream of heat transfer fluid will be absorbed into the engine in a single pass through. If the fluid were discarded at that point, the heat not absorbed would be lost. The system employs a pump and a loop to recirculate the fluid back to the source, and thence back around to the engine. In this way the heat is not wasted and is presented again and again to the engine and is ultimately nearly all used. Even the energy required to operate the pump is imparted to the flow, and thus captured and circulated around the process for eventual use.
On the exhaust side of the heat engine loop, a similar process is employed. The heat not converted in the heat engine loop to electricity is gathered up in a heat exchanger, and transferred into a heat reclaiming loop. This heat reclaiming loop includes a compressor which raises the temperature of and adds enthalpy to the working fluid and the working fluid_is then presented to another heat exchanger which is used to inject the heat back into the heat engine loop. Even the energy used to run the compressor in the heat reclaiming loop is captured in the working fluid, and is injected into the heat engine loop for use. The combination of recovery of heat, and reuse of heat, on both the input and the exhaust sides of the heat engine loop is extremely effective and makes far more power output available than would otherwise be the case, with a given heat source.
Alternatively, the external heat source loop can be directed to the heat reclaiming loop rather than to the heat engine loop. The introduction of heat from the external heat source to the heat reclamation loop by means of an additional subsidiary loop of the heat reclaiming loop enables the utilization of waste heat in temperature ranges lower than the arrangement wherein the external heat source is in direct communication with the heat engine loop. The utilization of relatively lower temperature waste heat greatly expands the areas of opportunity to recover waste heat that in practice is typically going unused.
Accordingly, it is an objective of the instant invention to operate a power system without a need for a dedicated source of combustion in order to operate.
It is a further objective of the instant invention to operate a power system on low temperature waste heat left over from power plant turbine condensers or air conditioning units.
It is a further objective of the instant invention to operate a power system on low temperature solar, or geothermal power.
It is yet another objective of the instant invention that is capable of efficiently utilizing low temperature heat sources and low pressure working fluids to generate substantial energy.
It is a still further objective of the invention to provide a highly efficient heat engine having one or more blades mounted on a rotating member that utilizes high velocity gas flow to apply force to the rotating member.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. Any drawings contained herein constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.
Beginning with the heat engine,
Mounted on the rotating member 1 are blades 2. It being understood that the numbers of blades and nozzles shown here are not the only quantities possible. For example these numbers could vary to increase the power output of the heat engine. Likewise, while bearings 5 are illustrated as ball bearings it should be understood that other types of bearings such as needle bearings, roller bearings, journal bearings, magnetic bearings and the like can be used as well. The rotating member 1 has a first planar surface 51 adjacent the left end bell 6 and a second planar surface 53 adjacent the right end bell 7. An outer peripheral surface 55 is contiguous with both the first and second planar surfaces. The blade 2 has a width approximately equal to the distance between the first and second planar surfaces and a height that extends outward from the outer peripheral surface 55.
In operation, the nozzles 8 direct high speed gasses at the concave surface 12 of each blade 2. The angle of the nozzles and the shape of the blades provide numerous advantages.
The large total flow (mass) in combination with a very high gas flow velocity exiting these nozzles results in a very large momentum for the mass flow. This flow is significantly superior as a result, when compared to prior art engines.
Since velocity, and thus momentum, are vector quantities, a momentum of “M” entering, becomes a momentum of almost “−M” coming out. This creates a momentum change of M−(−M)=2 M overall. The precise value of course depends on the exact blade angle. This is a great improvement over the momentum change that would have resulted from merely bringing the flow to rest against the blade, or by passing it across a slightly curved blade, both being done in the prior art. The total force on each blade is the combined result of both of the above significant forces.
The invention specifically provides a plurality of blades, and a plurality of nozzles, as shown in
It is understood that one of ordinary skill in the art could devise variations of these mounting features. The features shown illustrate the structures and are not limiting. It is also within the scope of this invention that a turbine having a larger diameter would produce more torque from the same pressure differential. Likewise a turbine having wider blades would result in increasing the reactive surface area thereby creating more force and torque than turbines having blades of smaller width. The heat exchangers utilized in the following systems can be of various types and numbers and it is contemplated that one skilled in the art would select the type and appropriate number of units to achieve the greatest operating efficiency.
We next examine the total thermodynamic system, as presented in
As shown in
The outside, or external heat source loop, begins with heat source 18. This source may be any source of low temperature heat, including waste heat from any number of waste heat sources or solar and geothermal heat sources as well. In this embodiment, the external heat source may supply temperatures as low as 250° F. In the operational mode of this loop, heat from the source 18 is conveyed by a first heat transfer fluid around to pump 21. The first heat transfer fluid may be Paratherm NF®, or one of many commercial equivalents. The speed of pump 21 is controlled by control unit 22, to achieve desired pressures and flow rates. A relief valve may be incorporated into the loop to avoid the buildup of damaging excess pressure. The hot heat transfer fluid is then conveyed to heat storage tank 23, where it is held using a phase change material. This material in storage tank 23 changes phase from solid to liquid when heated to the desired temperature. The heat of fusion of such material is very large and the material is_capable of holding very large quantities of heat in a small volume without increasing its temperature. This allows the heat to be supplied to the system at a steady temperature, while the temperature of the external heat source may vary widely at different times, for example as in the case of the waste heat from an air conditioning system at different times of day or season. The stored heat may be used at a later time when the external heat source may become temporarily unavailable. Nitrogen tank 20 is used to hold an inert gas such as nitrogen in the tops of the expansion tanks to prevent suction pressures from falling too low and causing pump cavitations, and to prevent corrosion.
Once the desired amount of heat is stored, and the desired temperatures are reached, then secondary pump 25 is started. This pump circulates a second heat transfer fluid from the storage tank 23 over to the main heat exchanger 24. Secondary speed controller 26 controls pump 25 and maintains the desired pressures and flow rates. Heat which has thus been supplied to the main heat exchanger 24 is now available for use. Also provided are bypass valves 47 which permit bypassing the heat source around the main heat exchanger 24 when desired, and also permit bypassing the heat into dump load 19, under conditions where excess heat is present and must be discarded to the environment.
The inside, or heat engine loop, functions in the following manner.
Heat from main heat exchanger 24 is conveyed by the heat engine loop heat transfer fluid, which is a refrigerant, to the heat engine 27. Heat engine 27 is constructed and operated in the manner disclosed in
After leaving the engine 27, the gaseous refrigerant passes into the heat exchanger 30, which serves to condense the gas back to a liquid. In the process, heat is released to the heat reclaiming loop, to be discussed presently. On leaving heat exchanger 30, the heat engine loop refrigerant, now a liquid, passes through pressure control valve 46, which prevents the pressure from dropping too low which would destabilize the loop function. Pressure control valve 46 is only needed in those cases where the system might be mounted in a cool climate. In such a case, the pressure of the condensed liquid coming out of the condensers could drop too low. Without enough pressure present, the refrigerant will not circulate in sufficient quantities, as pressure is needed to force circulation. The head pressure control valve prevents this loss of pressure by reducing temporarily and automatically the capacity of the condenser, keeping the pressure high. The refrigerant is then stored in the receiver 45, where it awaits further demand for circulation. Once further fluid is required, it departs the receiver 45 and makes its way through sub-cooler 38, where it is cooled just sufficiently to prevent premature formation of any gas bubbles in the liquid. The flow then continues on to pump 41. In addition to circulating the liquid around the loop, the pump acts to raise the pressure of the liquid to the level required for operation. Flow gauge 42 provides a measure of the rate of flow, which is controlled by the speed of the pump.
The high pressure liquid then proceeds to valve 40. This valve is normally on, but is closed when the engine is off, to prevent flooding of the downstream components.
On passing through valve 40 the flow reaches heat exchanger 39. Here it picks up reclaimed heat from the heat reclaiming loop to be discussed presently. This raises the temperature of the liquid and causes it to boil and to form a gas. From here, the flow travels back to heat exchanger 24, where it receives the balance of the required heat, and the cycle begins again. The system actually reclaims so much heat that the majority of the heat required to operate the engine comes from heat exchanger 39. In this embodiment the heat reclaiming loop is the primary heat source for the heat engine loop. Only a small amount of heat is added on each pass around the loop from the external heat source loop through heat_exchanger 24. This is central to the efficiency of the total system, and is totally unlike prior art engines.
We next describe the heat reclaiming loop.
Starting from receiver 36, liquid heat reclaiming transfer fluid, again a refrigerant, is supplied under pressure to expansion valve 31. Here the pressure is dropped sharply, in a controlled manner, and provided to heat exchanger 30. In this process, the refrigerant begins to boil, and becomes a very cold gas. This cold gas extracts heat from the inside loop, through heat exchanger 30, and carries away this heat to be reclaimed. The cold gas now travels to pressure control valve 32, where the drop in pressure is regulated. Pressure control valve 32 is considered to be optional and is intended to prevent the evaporators in the system from becoming too cold. In practice this seldom happens. The gas pressure is kept high enough that the gas temperature does not drop to a temperature lower than that which is desired. From there, the gas travels to accumulator 34 where any liquid drops inadvertently remaining are held temporarily, thus preventing them from reaching and damaging the compressor.
The flow, still a cold gas, then travels to compressor 35. While various types of compressors can be utilized it should be recognized that one skilled in the art would select the type and appropriate number of units to achieve the greatest operating efficiency. For example a multi unit scroll type compressor could be used. Here the gas is greatly compressed, reaching much higher levels of pressure and temperature. The flow then travels to heat exchanger 39, where the temperature is now high enough so that the heat may be efficiently re-injected into the heat engine loop process. Thus the waste heat from the heat engine loop has been reclaimed, along with the heat resulting from the compression work done by the compressor and the heat added by the electrical power used to run the compressor, all of which is injected into the heat engine loop by the heat reclaiming loop.
In the process of passing through heat exchanger 39, the heat reclaiming loop refrigerant gas cools sufficiently that it recondenses to a liquid once again. It then passes through sub-cooler 37 which condenses any remaining liquid and slightly sub-cools the liquid. It then passes through pressure control valve 33 which prevents the pressure from dropping too low and destabilizing the loop function, and then finally returns to receiver 36, where the heat reclaiming loop process begins again. A filter/dryer element is utilized to remove stray particles and also stray moisture from the loop thereby preventing all components from icing, damage and corrosion.
Additionally, system controller and display 43 is provided. This provides automatic control of the entire system, using software created for this purpose. It will be appreciated that a system of this complexity can only be operated in the field under automatic control.
As shown in
The system shown in
The external heat source loop, begins with heat source 18. This source may be any source of low temperature heat, including waste heat from any number of waste heat sources such as air conditioning units or power plant turbine condensers. The external heat source may supply temperatures as low as 50° F., but would preferably supply temperatures within the range of 90 to 150 degrees F. In the operational mode of this loop, heat from the source 18 is conveyed by a first heat transfer fluid around to pump 21. The first heat transfer fluid may be Paratherm NF®, or one of many commercial equivalents. The speed of pump 21 is controlled by control unit 22, to achieve desired pressures and flow rates. A relief valve may be incorporated into the loop to avoid the buildup of damaging excess pressure. The hot heat transfer fluid is then conveyed to heat storage tank 23, where it is held using a phase change material. This material in storage tank 23 changes phase from solid to liquid when heated to the desired temperature. The heat of fusion of such material is very large and the material is capable of holding very large quantities of heat in a small volume without increasing its temperature. This allows the heat to be supplied to the apparatus at a steady temperature, while the temperature of the external heat source may vary widely at different times, for example as in the case of the waste heat from an air conditioning system at different times of day or season. The stored heat may be used at a later time when the external heat source may become temporarily unavailable. Nitrogen tank 20 is used to hold an inert gas such as nitrogen in the tops of the expansion tanks to prevent suction pressures from falling too low and causing pump cavitations, and to prevent corrosion.
Once the desired amount of heat is stored, and the desired temperatures are reached, then secondary pump 25 is started. This pump circulates a second heat transfer fluid from the storage tank 23 over to the main heat exchanger 24. Secondary speed controller 26 controls pump 25 and maintains the desired pressures and flow rates. Heat which has thus been supplied to the main heat exchanger 24 is now available for use. Also provided are bypass valves 47 which permit bypassing the heat source around the main heat exchanger 24 when desired, and also permit bypassing the heat into dump load 19, under conditions where excess heat is present and must be discarded to the environment.
The heat engine loop functions in the following manner.
Heat engine 27 is constructed and operated in the manner disclosed in
After leaving the engine 27, the gaseous refrigerant passes into the heat exchanger 30, which serves to condense the gas back to a liquid. In the process, heat is released to the heat reclaiming loop, to be discussed presently. On leaving heat exchanger 30, the heat engine loop refrigerant, now a liquid, passes through pressure control valve 46, which prevents the pressure from dropping too low which would destabilize the loop function. Pressure control valve 46 is only needed in those cases where the system might be mounted in a cool climate. In such a case, the pressure of the condensed liquid coming out of the condensers could drop too low. Without enough pressure present, the refrigerant will not circulate in sufficient quantities, as pressure is needed to force circulation. The head pressure control valve prevents this loss of pressure by reducing temporarily and automatically, the capacity of the condenser, keeping the pressure high. The refrigerant is then stored in the receiver 45, where it awaits further demand for circulation. Once further fluid is required, it departs the receiver 45 and makes its way through sub-cooler 38, where it is cooled sufficiently to prevent premature formation of any gas bubbles in the liquid. The flow then continues on to pump 41. In addition to circulating the liquid around the loop, the pump acts to raise up the pressure of the liquid to the level required for operation. Flow gauge 42 provides a measure of the rate of flow, which is controlled by the speed of the pump.
The high pressure liquid then proceeds to valve 40. This valve is normally on, but is closed when the engine is off, to prevent flooding of the downstream components.
On passing through valve 40 the flow reaches heat exchanger 39. Here it picks up reclaimed heat from the heat reclaiming loop which in this embodiment includes the heat from the external heat source loop, as will be discussed. This raises the temperature of the heat engine loop's refrigerant liquid and causes it to boil and to form a gas. From here, the flow travels to the heat engine 27. Located immediately downstream of the heat engine 27 is a de-superheater 54. The function of de-superheater 54 is to dispose of excess heat present in the turbine exhaust. Inside the heat engine loop, enthalpy is converted to mechanical work. However, not all of the enthalpy can be effectively converted to work within the heat engine loop and therefore a considerable amount of enthalpy will be left in the exhaust. If all of this enthalpy were transferred to the heat pump loop for recycling it would overwhelm the capacity of the heat reclaiming loop's compressor. If the compressor were made powerful enough to avoid being overwhelmed, the compressor itself would then consume more energy than can be produced by the system, and by its compression would supply even more of a surplus of enthalpy to the heat engine loop. The de-superheater 54 can dump this excess enthalpy to the environment using an air cooled heat exchanger as shown in
We next describe the heat reclaiming-loop with its additional subsidiary loop in this embodiment, which operates at a different temperature.
Starting from receiver 36, liquid heat reclaiming transfer fluid, again a refrigerant, is supplied under pressure to expansion valve 31 in the first subsidiary loop of the heat reclaiming loop. Here the pressure is dropped sharply, in a controlled manner, and provided to heat exchanger 30. In this process, the refrigerant begins to boil, and becomes a very cold gas. This cold gas extracts waste heat from the exhaust of the heat engine loop, through heat exchanger 30, and carries away this heat to be reclaimed. The cold gas now travels to pressure control valve 32, where the drop in pressure is regulated. Pressure control valve 32 and other valves designated as EPR valve are considered to be optional and are intended to prevent the evaporators in the system from becoming too cold. In practice this seldom happens. The second subsidiary loop of the heat reclaiming loop starts at receiver 36 and supplies a separate flow of liquid heat reclaiming refrigerant to a separate expansion valve shown as Expansion Valve 2 in
The flow then travels to compressor 35. Here the gas is greatly compressed, reaching much higher levels of pressure and temperature. The flow then travels through the third subsidiary loop of the heat reclaiming loop to heat exchanger 39, where the temperature is now higher than that of the other subsidiary loops and hot enough so that the heat may be efficiently re-injected into the heat engine loop process. Thus the heat reclaiming loop re-injects into the heat engine loop the heat that has been reclaimed from the heat engine loop, the heat from the external heat source loop, the heat resulting from the compression work done by the compressor and even the heat from the power used to run the compressor itself. In this embodiment the heat reclaiming loop is the sole heat source for the heat engine loop.
In the process of passing through heat exchanger 39, the heat reclaiming loop refrigerant gas cools sufficiently that it re-condenses to a liquid once again. Optionally, located immediately downstream of the heat exchanger 39 is a water cooled condenser 56 that is used only during the start-up and adjustment phases of the operation of the system. The water cooled condenser 56 provides a condensing function for the hot gas in the heat reclaiming loop during such times (e.g. startup) when the main condenser has not yet ramped up to its intended capacity. Under certain conditions if the water cooled condenser 56 were not present, hot gas could fail to fully condense, resulting in a breakdown of the heat reclaiming loop function. The heat reclaiming— refrigerant then passes through sub-cooler 37 which condenses any remaining liquid and slightly sub-cools the liquid. It then passes through pressure control valve 33 which prevents the pressure from dropping too low and destabilizing the loop function, and then finally returns to receiver 36, where the heat reclaiming loop process begins again. A filter/dryer element is utilized to remove stray particles and also stray moisture from the loop thereby preventing all components from icing, damage and corrosion.
Additionally, system controller and display 43 is provided. This provides automatic control of the entire system, using software created for this purpose. It will be appreciated that a system of this complexity can only be operated in the field under automatic control.
The system embodiment shown in
The overall performance of the invention is determined by the relative efficiencies of the heat reclaiming loop and the heat engine loop.
In the heat reclaiming loop, efficiency is described by the ratio of heat output compared to the electrical energy input to run the compressor, commonly referred to as Coefficient of Performance (COP). For example, if 1 watt of power is consumed by the compressor and 12 watts of heat is transferred to the heat engine loop, the COP is 12. The greater the COP of the heat reclaiming loop, the less efficiency is required of the heat engine loop to produce net positive power output from the invention.
In the heat engine loop, efficiency is the percentage of heat input which is converted to power by the heat engine. For example, if the invention consumes 1 watt of electricity at a COP of 12, and the efficiency of the heat engine is 10% of 12, the resulting output of power is 1.2 watts.
Many factors contribute to the COP of the heat reclaiming loop, including temperatures and pressures of the refrigerant working fluid in various areas of the loop. In general, adding more enthalpy to the working fluid improves the COP. The colder the starting temperature of the liquid refrigerant, the more enthalpy it can carry before reaching a maximum practical temperature of the compressor's discharge gas. Further, a colder starting temperature of the liquid refrigerant results in a higher maximum temperature of the discharge gas.
In this invention, the heat reclaiming loop's output heat exchanger (condenser) transfers heat to the heat engine loop's heat input heat exchanger (evaporator). When the heat engine's working fluid is colder the heat reclaim loop's condensing occurs at a lower temperature and pressure, which increases the electrical efficiency of the compressor more than any other factor.
The benefits of a higher discharge gas temperature in the heat reclaiming loop are clear.
As to the efficiency of the heat engine loop, Carnot teaches that the maximum possible efficiency η of a heat engine is η=1−(Tc/Th) where Tc and Th are the hot and cold temperatures expressed in absolute degrees. Carnot further teaches that reducing the low temperature provides more benefit than increasing the high temperature. The maximum high temperature of the heat engine loop in this invention is determined by the temperature of the discharge gas from the heat reclaiming loop's compressor, which in turn is increased by lowering the temperature of the liquid refrigerant in the heat reclaiming loop. With the high temperature maximized as much as practical, to improve the efficiency of the heat engine we must lower the temperature of the cold side of the heat engine as much as possible.
The architecture of the invention provides a unique opportunity to reduce the cold side temperatures of both the heat reclaiming loop and the heat engine simultaneously, as follows.
In the heat reclaiming loop's heat output heat exchanger (condenser) which is also the heat engine's heat input heat exchanger (evaporator), the condensed liquid refrigerant in the heat reclaiming loop transfers heat to the incoming cold liquid refrigerant of the heat engine loop. Therefore, the colder the liquid refrigerant in the heat engine loop, the more heat can be transferred from the heat reclaiming loop and thus the colder the final temperature of the heat reclaiming loop's liquid refrigerant.
Colder liquid refrigerant in the heat reclaiming loop results in a lower evaporating temperature in the heat reclaiming loop's heat input heat exchanger (evaporator), which is also the heat engine loop's waste heat output heat exchanger (condenser). Thus more heat can be transferred from the heat engine loop to the heat reclaiming loop and the resulting temperature of the heat engine's liquid working fluid is colder.
To improve the low temperature heat transfer in both the heat reclaiming loop and the heat engine loop, a novel solution has been discovered whereby during operation a constant level of liquid refrigerant is maintained in the output ends of the heat reclaiming loop's heat output heat exchanger and the heat engine loop's waste heat output heat exchanger, both of which are condensers.
This solution maximizes liquid-to-liquid heat exchange in the low temperature areas where, compared to when either refrigerant is phase change conditions of condensing or evaporating, a much larger temperature change takes place by transferring relatively little heat.
For example, at 140 psia, the condensing temperature of R134A refrigerant is about 100° F. To reduce the temperature of 50% condensed gas from 100° F. to 95° F. requires heat transfer of 40 btu/lbm. To reduce liquid temperature from 95° F. to 65° F. requires only 10 btu/lbm.
It is common practice in a variety of refrigeration applications to maintain some desired level of liquid refrigerant in an evaporator by modulating the flow of liquid refrigerant.
However, maintaining a level of liquid refrigerant in a condenser is not known in the art and cannot be accomplished using conventional liquid receivers available in the market.
Conventional liquid receivers have the input port for incoming liquid refrigerant at or near the top of the receiver tank. The output port draws refrigerant from near the bottom of the receiver so as to permit flow when the receiver is nearly empty. When the receiver is not completely full, the empty space is filled with refrigerant gas. If the level of liquid refrigerant at the output end of the condenser rises to completely fill the pipeline from the condenser to the receiver, some of the liquid must be transferred to the receiver before any refrigerant will exit the receiver. The refrigerant cannot exit the receiver until the pressure in the receiver is equalized with that of the condenser, which is accomplished by purging enough refrigerant from the condenser that the pipe from the condenser to the receiver has some gas flowing through it which equalizes the pressures of the condenser and the receiver.
Thus a novel solution whereby a desired level of liquid refrigerant is maintained at the output end of each condenser was devised as shown in
Implementing this solution in the invention reduces the liquid temperature in the heat engine loop by 25° F. or more thereby increasing the efficiency of the heat engine loop by 20 percent or more. For example, converting all temperatures from ° F. to absolute and applying Carnot's Theorem n=1−(Tc/Th), a high temperature of 190° F. and a cold temperature of 83° F. shows n=16.46%. Reducing the low temperature to 58° F. shows n=20.31%, over 23% greater.
By maintaining a desired level of liquid refrigerant in the output end of the heat engine loop's waste heat output heat exchanger (condenser), the low temperature of the heat engine loop is reduced to only a few (e.g. 5) degrees higher than the evaporating temperature (e.g. 50° F.) of the heat reclaiming loop's heat input heat exchanger (evaporator) on the other side of the same heat exchanger.
Lowering the temperature of the heat engine loop's liquid refrigerant entering the heat engine loop's heat input heat exchanger (evaporator) also transfers more heat out of the heat reclaiming loop's heat output heat exchanger (condenser), improving sub-cooling by some 20° F. or more. The lower temperature liquid in the heat reclaiming loop evaporates at a lower temperature and pressure, and increases the amount of enthalpy the refrigerant can absorb at a given superheated temperature, thus improving the operating efficiency (COP) of the heat reclaiming loop. This also results in a higher discharge gas temperature from the heat reclaiming loop's compressor entering the heat reclaiming loop's heat output heat exchanger (condenser) and thus increases the high temperature of the heat engine loop by raising output temperature of the heat engine loop's heat input heat exchanger (evaporator) which is the other side of the same heat exchanger.
This higher temperature further improves the efficiency of the heat engine loop. For example, raising the high temperature from 190° F. to 200° F. with a low temperature in each case of 58° F. increases n'20.31% to n=21.52%. All together, implementing the solution described and shown in
In an additional embodiment, the first working fluid having transferred heat to the heat reclaiming loop through base heat exchanger 24 now reclaims heat from the heat reclaiming loop through subcooler 98 and from the heat engine loop through subcooler 99.
The heat reclaiming loop includes a second heat exchanger (subcooler) 98 positioned downstream of said base heat exchanger 39 whereby the first working fluid which has been cooled by transferring external waste heat to the heat reclaiming loop can reclaim heat from the third working fluid in an additional subsidiary loop of the heat reclaiming loop, thereby improving the efficiency of the system as a whole.
The heat engine loop includes a second heat exchanger (subcooler) 99 positioned downstream of the base heat exchanger 30 whereby the first working fluid which has been cooled by transferring external waste heat to the heat reclaiming loop can reclaim heat from the second working fluid in the heat engine loop, thereby increasing the efficiency of the system as a whole.
It will be appreciated that all of these components, including pressure gauges and service ports and other items not specifically discussed could be arranged in slightly different orders, and still lie within the intent of the system. The diagram presented is illustrative and not limiting.
All patents and publications mentioned in this specification are indicative of the levels of those skilled in the art to which the invention pertains. All patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference.
It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and any drawings/figures included herein.
One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments, methods, procedures and techniques described herein are presently representative of the preferred embodiments, are intended to be exemplary and are not intended as limitations on the scope. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims.
In accordance with 37 C.F.R. 1.76, a claim of priority is included in an Application Data Sheet filed concurrently herewith. Accordingly, the present invention claims priority as a continuation-in-part of U.S. patent application Ser. No. 12/858,265, entitled “Thermodynamic Power Generation System” filed on Aug. 17, 2010, which is a continuation-in-part of U.S. patent application Ser. No. 12/708,088, entitled Thermodynamic Power Generation System” filed on Feb. 18, 2010, now abandoned, which in turn claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/154,020, entitled “Efficient externally-heated low temperature heat engine” filed on Feb. 20, 2009, the entire contents of which are herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61154020 | Feb 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12858265 | Aug 2010 | US |
| Child | 13964560 | US | |
| Parent | 12708088 | Feb 2010 | US |
| Child | 12858265 | US |
