This invention relates to an organic Rankine cycle (ORC) system in which the turbine mechanical output is coupled to a common load with an engine mechanical energy output, the ORC utilizing the engine's waste thermal energy to evaporate the ORC fluid as it cools the engine. An electric generator or other load may be driven by the combined engine/ORC system of the invention.
Efficient power generation systems that provide low-cost energy with minimum environmental impact, and that can be readily and rapidly sited as stand-alone units for integration into the existing power grid, are appropriate for solving critical power needs in many areas. Reciprocating engines are the most common and most technically mature of these distributed energy resources, but turbines may also be used. These engines can generate electricity with efficiencies of 25% to 40% using commonly available fuels such as gasoline, natural gas and diesel fuel. However, atmospheric emissions such as nitrogen oxides, (NOx), carbon monoxide (CO) and particulates have always been an issue with these engines.
The efficiency of combustion engines can be improved without increasing the output of emissions by means of a bottoming cycle. One form of bottoming cycle is an organic (with fluid alternating phases) Rankine cycle system which is thermally coupled to a reciprocating engine and operates an electric generator.
Current practice provides separate loads driven by separate shafts for engines which integrate, via exhaust heat, with organic Rankine cycle devices, as illustrated in
The electrical output of the generators 21, 32 is applied to power combining and conditioning circuitry 43 so as to drive a common load 44, which may or may not be a power utility grid.
This approach requires separate, redundant generators, control equipment and power conversion components; the power combining circuitry is an additional burden to such a system.
The system described with respect to
Aspects of the invention include: utilizing substantially all the heat that must be eliminated from an engine driving a load in an associated ORC system which is thermally and mechanically coupled with the engine; utilizing an ORC system to eliminate substantially all of the heat which must be extracted from an engine driving a load; operating a single mechanical load directly with mechanical power provided by an engine and an ORC system which is mechanically and thermally coupled thereto; providing an engine sharing a mechanical load with an ORC system, without the need for redundant replicated equipment; driving a single generator with an engine and ORC system mechanically coupled thereto without the need for complicated load. sharing, power combining apparatus.
In accordance with the invention, the shaft of an engine is mechanically coupled with a shaft of a turbine of an organic Rankine cycle system, substantially all of engine waste heat being utilized to evaporate the organic Rankine cycle fluid, thereby maximizing the efficiency of the combined system. In further accord with the invention, condensed organic Rankine cycle fluid flows through various engine-related coolers, including one or more of: intake air (charge air) cooler; engine coolant; engine oil cooler; EGR cooler; as well as using engine exhaust in the evaporator.
According to the invention, coupling between the ORC turbine and the engine crank may be a shared shaft, or it could include coupling devices to limit application of torque, such as clutches; the coupling could include devices to directionally limit torque, such as sprag clutches or free-wheeling clutches. The coupling may also include speed modifying couplings such as gear sets, belt drives, fluid torque converters, or variable speed transmissions.
The utilization of the liquid-to-liquid heat exchangers 46-48 replaces large liquid-to-air heat exchangers and their associated fans, with considerable reduction in cost, and/or an in-coolant engine oil cooler.
Other features of the invention include: evaporator bypass (ORC fluid or exhaust) to maintain ORC vapor temperature, passively or in response to a controller; bypassing ORC fluid or engine fluid around heat exchangers to maintain engine fluid temperatures; combined heat exchangers; engine oil pump pressurizing turbine oil; ORC fluid in coolant passages within engine; refrigerating intake air, with coolant condenser heating ORC fluid; bypassing ORC turbine during turbine failure, with extra condenser cooling and/or evaporator bypass, or to control turbine pressure drop; controlling turbine pressure with mass flow, variable speed transmission; and adopting the evaporator to be a muffler and/or an emissions reducing device.
Other aspects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.
a illustrates gears.
The simplest embodiment of the present invention, illustrated in
A simplified illustrative representation of a reciprocating engine with an organic Rankine cycle subsystem utilizing substantially all of the waste engine heat is shown in
The exhaust in exhaust pipe 24 is fed to drive a turbocharger 51 that compresses ambient air in an inlet 52, and provides compressed air in a conduit 54 to the preheater 45. The compression heat is substantially removed from the charge air, by heat exchange with the ORC fluid in a conduit 26a, providing much cooler compressed air in a conduit 55. The cooler intake air provided in the conduit 55, being more dense, causes the engine efficiency to increase by several percent.
The ORC fluid leaving the preheater 45 in a conduit 26b is applied to the preheater 46 which receives in a conduit 57 coolant from the engine cooling jacket and/or labyrinth as the case may be. The coolant, passing through the heat exchanger 46 is driven by a pump 59 which may be coupled mechanically by a belt 60 to a pulley 61 driven by the combined engine/turbine shaft 20.
The ORC fluid then flows through a conduit 26c to the preheater 47, which also receives engine oil over a conduit 63. The oil is returned to the engine over a conduit 64 by means of a pump 65 which is indicated as being gear driven by means of a pair of intermeshed gears 67, 68.
The heat exchangers 46, 47 which will accomplish the preheating just described can be much smaller and therefore cheaper than the radiator (which is liquid-to-air) and the oil cooler (which is either oil to ambient air or oil to engine coolant). This is because there is forced liquid convection heat transfer on both sides of the heat exchanger, and the forced convection is provided by the ORC fluid pump 41, the coolant pump 59 and the oil pump 65, rather than using energy and space-consuming fans which would be required on a typical radiator or an ambient cooled oil cooler.
The ORC fluid then flows over a conduit 26d to the heat exchanger 48 where it is heated by the exhaust gas recycle (EGR) flow in an EGR conduit 24a. The cooled EGR gas is conducted to the air intake by a conduit 71.
The ORC fluid then flows through a conduit 26e to the evaporator 25, which comprises a bi-phase heat exchanger that receives exhaust from the turbo over a pipe 24b and applies it to the exhaust pipe 24c.
The ORC fluid, passing through the preheaters 45-48 and the evaporator 25 receives the highest possible enthalpy, while providing the cooling functions for the engine without use of fans. The ORC fluid flows through the conduit 27 to drive the turbine 28, the spent ORC fluid passing through the conduit 29 to the condenser 35. The fan 37 on the condenser is driven through a belt 38 by a pulley 39 on the common shaft 20. The ORC fluid then flows through conduit 40 and is driven by pump 41 to the preheater 45.
The generator 21 may be connected by a suitable electrical bus 73 to power conditioning circuitry 75 which in turn is interconnected with an electrical load 76, which may be a grid. A controller 79 may respond to load conditions, conditions in the turbine such as pressure ratio, speed and temperature, and engine conditions, so as to control various factors in the system, including turbine pressure relief, such as by means of bypass valves 81, 82.
Though not illustrated in
Although shown with four preheaters in
In a typical organic Rankine cycle system used with an internal combustion engine, such as for driving a generator, the main pump of the ORC is typically driven by an electric motor powered from the grid that the generator provides power to. Similarly, the fan providing cooling air to the condenser is also typically driven by an electric motor powered by the grid. In the event of failure of any ORC components, system control or grid power, the ORC system components should be protected, and cooling of the reciprocating engine must be assured.
Because most of the power being provided by the system is provided by the engine, rather than the ORC subsystem, the engine system should be able to operate in the event of an ORC subsystem failure, because it will supply substantial power, although with less efficiency.
In the event the ORC subsystem should fail, the free-wheeling clutch will isolate the shaft 20a from the shaft 20. The turbine is normally fed the heated ORC fluid through the valve 81, the valve 82 being blocked. But when there is an ORC subsystem failure, in order to prevent overheating of the engine, the bypass valve 82 is opened and the valve 81 is closed, so that the engine heat is passed from the conduit 27 through the conduit 29 to the condenser 35. Provisions can be made for additional fans or an increased fan speed at the condenser to remove additional heat from the ORC fluid, to compensate for the heat no longer being converted to work by the turbine.
The valves 81, 82 may be computer controlled, in response to characteristics of the system, such as engine temperature, turbine pressure ratio, and the like. On the other hand, the valves 81, 82 may simply comprise passively sprung vapor valves.
Various couplings may be used between the engine 19 and the turbine 28. For instance, they may be journaled on a common shaft 20 as described with respect to
The bypass valve 82 (
An alternative to the control of mass flow by the valve 89 is use of a variable speed transmission 84 referred to with respect to
For economy, a variable speed transmission may not seem suitable. In such a case, the coupling ratio of engine speed to turbine speed may be selected to be optimum at the maximum pressure drop across the turbine at the full load; this may result in less than optimum pressure ratios at reduced engine load. Alternatively, an intermediate pressure ratio could be chosen for optimization, and the pressure limiting bypass valve 82 or the mass flow controlling valve 89 utilized accordingly.
As illustrated in
For maximum engine efficiency, it is necessary to provide the charge air at the coolest possible temperature. However, if the ORC working fluid is heated too much in the heat exchanger 45, then it is possible that either the engine coolant or the engine oil might become too hot. In order to provide maximum cooling of the charge air, the heat exchanger 45 may be made excessively large, and the amount of ORC working fluid passing therethrough bypassed as necessary to permit proper cooling of the coolant and engine oil, as illustrated in
Similarly, if the engine coolant falls below a desirable temperature, such as on the order of 70° C. (160° F.), a remotely sensed temperature-controlled valve 94 will open proportionately to bypass some of the coolant around the heat exchanger 46 so that the coolant can maintain the minimal desired temperature. In the same way, a remotely sensed temperature-controlled valve 96 will bypass engine oil if necessary to maintain the minimum temperature, such as about 43° C. (110° F.). Alternatively, the valves 94, 96 may be placed between conduits 26b and 26c or 26c and 26d, respectively, to bypass ORC working fluid around the respective heat exchanger 46, 47.
In addition,
Less than half of the ORC heat load comes from the engine cooling jacket and/or labyrinth; the majority of the heat coming from the engine exhaust system. In order to ensure removal of engine heat, the evaporator is bypassed by the valve 99, as described hereinbefore.
In addition, the turbine must be bypassed by closing the valve 81 and opening the valve 82 to divert the ORC working fluid around the turbine. If these valves are not controlled by the computer, they may comprise passive spring vapor valves. When the ORC working fluid is used as the coolant for the engine, the condenser 35 may be provided with extra fans, or the fan 37 may preferably be driven by the shaft 20, as described with respect to
As an alternative to bypassing the exhaust around the evaporator from the pipe 24b to the pipe 24c, the ORC working fluid might be bypassed around the evaporator, as shown in
Referring to
A compressor 107 coupled to the shaft 20 provides compressed refrigerant over a conduit 108 to a condenser 109. The cooled liquid refrigerant is then applied over a conduit 112 through an expansion valve 113 and a conduit 114 to the inlet of the evaporator, which comprises the heat exchanger 45a, where it chills the engine's inlet air. This embodiment may be used with engines that do not use a turbocompressor at the air intake, as well as those that do. As seen in
As illustrated in
A large percentage of the engine's waste heat is carried in the exhaust stream, so successful bottoming cycles will generally incorporate a heat exchanger (such as the evaporator) on the engine exhaust. For further efficiency, one aspect of this invention consists of sharing the functions of a reciprocating engine exhaust muffler and catalyst for NOx and/or particulate removal, with that of a superheating heat exchanger for an organic Rankine bottoming cycle. Referring to
The benefit of U.S. provisional application No. 60/691,067 filed Jun. 16, 2005 is claimed.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2006/023301 | 6/16/2006 | WO | 00 | 12/14/2007 |
Number | Date | Country | |
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60691067 | Jun 2005 | US |