GB2501458A

GB2501458A - Exhaust energy recovery system with power turbine and organic Rankine cycle

Info

Publication number: GB2501458A
Application number: GB1203115.9A
Authority: GB
Inventors: Jonathan Mcguire
Original assignee: Bowman Power Group Ltd
Current assignee: Bowman Power Group Ltd
Priority date: 2012-02-22
Filing date: 2012-02-22
Publication date: 2013-10-30
Also published as: GB201203115D0

Abstract

A system for recovering exhaust energy of a reciprocating engine 100 comprises an Organic Rankine Cycle (ORC) 170 with a turbine 120 driving an electric generator 130 arranged between the engine 100 and the ORC heat exchanger 140. The power turbine 120 extracts energy and cools the exhaust gasses thereby limiting the maximum temperature of the ORC cycle to avoid overheating the ORC working fluid. There may further be a turbocharger 112 between the engine 100 and the power turbine 120, or the power turbine may be an electric turbocharger, i.e. a turbocharger which drives an electric generator (figure 3). Alternatively, the power turbine and ORC heat exchanger may be arranged in parallel with a turbocharger (figure 4)

Description

A System and Method for Recovering Exhaust Energy The present invention relates to a system and method for recovering exhaust energy from fluid in an exhaust conduit of a reciprocating engine. the exhaust gas from the exhaust conduit is utilised as an input into a heat exchanger of an Organic Rankine Cycle (ORC). An ORC is a well known form of energy production that is both clean, efficient and a reliable form of producing electricity. It is known in the art to use the exhaust flow of a reciprocating engine as a source of heat that can indirectly provide an input into the evaporator of an ORC, The working fluid of an ORC is usually a refrigerant having a low temperature boiling point and a decomposition temperature of around 160-170°C. It is imperative that the working fluid of the ORC does not decompose into its constituent elements as these include corrosive acids which can be both damaging and dangerous. For this reason, the temperature of the exhaust gas emanating from the engine must be reduced sufficiently that it passes through the evaporator at a temperature that will evaporate the refrigerant without it decomposing.

A commercially available prior art system achieves this with the use of an intermediate oil circuit in ordcr to stop the working fluid of the ORC overheating. The system is shown schematically in Figure 1. Exhaust flow from the engine 1 passes through the engine turbocharger 10 and then through the high temperature side of a heat exchanger 30 in the coil circuit 20 before flowing to an exhaust outlet 35. The working fluid of the intermediate circuit is oil, which is pumped through the low temperature side of the heat exchanger 30 where it is heated by the exhaust gas before being passed through the high temperature side of a further heat exchanger 40 forms part of the Organic Rankine Cycle. The oil temperature is low enough as it passes through the heat exchanger 40 that it evaporates the working fluid of the Organic Rankine Cycle without decomposition taking place. The working fluid is then expanded through turbine 50 and is finally recondensed at condenser 60 before it is pumped back through the heat exchanger/evaporator 40. This type of system has been used in industry by amongst others, Pratt & Whitney, Maxxtech and Free-Power. The system achieves the objective of ensuring that the working fluid of the Organic Rankine Cycle does not overheat. however, the solution of an additional oil circuit and accompanying additional heat exchanger is expensive and efficient as heat losses occur through two heat exchangers.

I

It is an aim of the present invention to redress at least to some extent the problems of

the prior art.

According to a first aspect of the invention, there is provided a system for recovering exhaust energy from fluid in an exhaust conduit of a reciprocating engine, the engine including an engine exhaust conduit and a turbocharger arranged in fluid communication with the engine exhaust conduit, the turbocharger comprising a compressor and a first turbine having a turbine exhaust conduit, the system comprising an organic rankine cycle having a heat exchanger arranged to evaporate a working fluid of the organic rankine cycle passing through a low temperature side of the heat exchanger, and a turbogenerator comprising a second turbine disposed downstream of the first turbine in the turbine exhaust conduit and arranged to extract heat from fluid in the turbine exhaust conduit, in which an outlet of the second turbine is arranged in fluid communication with an inlet of a high temperature side of the heat exchanger for heat exchange from the fluid in the turbine exhaust conduit downstream of the turbogenerator to the working fluid of the organic rankine cycle.

The use of a turbogenerator to extract heat from the engine exhaust fluid reduces the exhaust temperature sufficiently such that it can be used directly to heat the working fluid in the organic rankine cycle without the need for an intermediate oil circuit and additional heat exchanger, saving both cost and energy.

According to a second aspect of the invention, there is provided a system for recovering exhaust energy from fluid in an exhaust conduit of a reciprocating engine, the engine including an engine exhaust conduit and an electric turbocharger arranged in fluid communication with the engine exhaust conduit, the electric turbocharger comprising a compressor and a turbine having a turbine exhaust conduit, the system comprising an organic rankine cycle having a heat exchanger arranged to evaporate a working fluid of the organic rankine cycle passing through a low temperature side of the heat exchanger, and a generator comprising an alternator arranged to convert the turbocharger shaft power into electric power to extract heat from fluid in the turbine exhaust conduit, in which an outlet of the turbine is arranged in fluid communication with an inlet of a high temperature side of the heat exchanger for heat exchange from the fluid in the turbine exhaust conduit to the working fluid of the organic rankine cycle.

This embodiment again extracts sufficient heat from the exhaust fluid at the electric turbocharger that it can be used directly to heat the working fluid in the Organic Rankine Cycle without the need for an intermediate circuit and additional heat exchanger. In both embodiments, the maximum temperature of the working fluid in the heat exchanger is preferably no more than 170°C.

According to a third aspect of the invention, there is provided a method of operating a system for recovering exhaust energy from fluid in an exhaust conduit of a reciprocating engine, the engine comprising a turbocharger arranged in fluid communication with an exhaust conduit of the engine, the system comprising a turbogenerator including a turbine and an organic rankine cycle having a working fluid and a heat exchanger for evaporating the working fluid, the heat exchanger having a high temperature side and a low temperature side through which the working fluid flows, the method comprising passing exhaust flow from the turbocharger through the second turbine to extract heat therefrom and convert it to electrical power, and to pass the reduced heat exhaust flow into the high temperature side of the heat exchanger for heat exchange from the exhaust flow to the working fluid in the low temperature side thereof.

According to a fourth aspect of the invention, there is provided a method of operating a system for recovering exhaust energy from fluid in an exhaust conduit of a reciprocating engine, the engine comprising an electric turbocharger arranged in fluid communication with an exhaust conduit of the engine, the system comprising a generator comprising an alternator arranged to convert turbocharger shaft power into electric power to extract heat from fluid in the turbine exhaust conduit and an organic rankine cycle having a working fluid and a heat exchanger for evaporating the working fluid, the heat exchanger having a high temperature side and a low temperature side through which the working fluid flows, the method comprising passing exhaust flow through the turbocharger and alternator to extract heat therefrom and convert it to electrical power, and to pass the reduced heat exhaust flow into the high temperature side of the heat exchanger for heat exchange from the exhaust flow to the working fluid in the low temperature side thereof.

These and other aspects of the invention will be apparent to the skilled person upon reading the following non-limiting description of preferred embodiments with reference to the accompanying drawings, in which: Figure 1 is a schematic of a prior art system for recovering engine exhaust energy using an Organic Rankine Cycle; Figure 2 is a schematic of a first embodiment in accordance with the present invention in which a turbogenerator is used to reduce the exhaust temperature; Figure 3 is a schematic of a second embodiment in accordance with the present invention in which an electric turbocharger and alternator arc used to reduce the exhaust temperature; and Figure 4 is a schematic of a third embodiment in accordance with the present invention in which a turbogenerator is used to reduce the exhaust temperature.

Figure 2 shows a first embodiment of a system for recovering energy from the exhaust of a reciprocating engine 100. The engine 100 is a petrol or diesel engine having an exhaust conduit 105 in which a turbocharger 110 is arranged. The turbocharger 110 includes turbine 112 that exhausts into turbine exhaust conduit 115. The turbine exhaust conduit 115 is fluidly connected to a turbogenerator 120. The turbogenerator 120 consists of a turbine 125 and an alternator 130 arranged on an output shaft of the turbine 125 for the conversion of shaft power into electrical power. The turbine exhaust conduit 115 exhausts into an inlet 117 of the turbine 125. An outlet 118 of the turbine 125 is fluidly connected to a heat exchanger/evaporator of an Organic Ranicine Cycle 170. A turbogenerator exhaust conduit 122 fluidly communicates with the high temperature side of the heat exchanger/evaporator before exhausting to the atmosphere at exhaust 142.

The Organic Rankine Cycle 170 is standard and consists of the evaporator 140, a pump 145, a turbine 150 producing shaft power and a condenser 160. An alternator 155 arranged on the shaft of turbine 150 converts the shaft power into electricity. The working fluid of the Organic Rankine Cycle is a refrigerant such as Ethanol, Toluene or R245fa. The lower temperature side of the heat exchanger/evaporator 140 is fluidly connected to the inlet of the turbine 150. An outlet of the turbine 150 is fluidly connected to the condenser 160, which in turn is fluidly connected to the pump 145. The pump is fluidly connected to the low temperature side of the evaporator 140, completing the cycle.

The system is operated according to the following method. Exhaust gas from the reciprocating engine 100 passes via the engine exhaust conduit 105 to an inlet of the turbine 112 of the turbocharger 110. The temperature of the exhaust gas in the engine exhaust conduit 105 is approximately 600°C. The turbine 112 or the turbocharger 110 expands the exhaust gas in the exhaust conduit 105 and exhausts it via the turbine exhaust conduit 115 to the turbogenerator 120. The expansion reduces the temperature of the exhaust gas to approximately 450-550°C. The exhaust gas enters an inlet 117 of the turbine 125 and is expanded for a second time, producing shaft power to power the alternator 120. The alternator 130 converts the shaft power into electricity. A third expansion of the exhaust gas results in a further reduction of its temperature, which at the turbine outlet 118 is approximately 375-475°C. The exhaust gas is now cool enough for it to be passed through the high temperature side of the heat exchanger/evaporator 140 of the Organic Rankine Cycle 170. The working fluid of the Organic Rankine Cycle is pumped through the low temperature side of the heat exehangerlevaporator 140 where it is evaporated and subsequently expanded in the turbine 150. The expansion produces shaft power driving the alternator 155. The working fluid is then re-condensed in condenser 160 before returning to be pumped back to the evaporator. The temperature of the working fluid upon evaporation is less than 250 °C, and generally no more than 170°C. Upon expansion in turbine 150 its temperature is reduced to 125°C. Following re-condensation, the temperature of the working fluid is approximately 50°C until it is once more evaporated. The working fluid is thus never heated to a point at which it will decompose.

An alternative embodiment of the invention is shown in Figure 3 and is described as follows. Like reference numerals will be used to designate like components of the embodiment. The reciprocating engine 100 includes an exhaust conduit 105 in which an electric turbocharger 210 is arranged. The electric turbocharger outputs shaft power that is converted by a generator 220 into electrical power. The electric turbocharger includes a turbine 112 that exhausts into a turbine exhaust conduit 115. The turbine exhaust conduit 115 is fluidly connected to the high temperature side of the heat exchanger/evaporator 140 of the Organic Rankine Cycle 70. The remainder of the Organic Rankine Cycle is identical to that of the first embodiment and will not be described again here. In this embodiment of the system, although no extra turbine is required, the turbine 112 must be designed to extract more heat from the exhaust gas than is usually the case. This is achieved by altering the capacity or reduced flow characteristic of the turbine 112 in a standard manner.

Operation of the second embodiment of the system is identical to that of the first, other than that the exhaust gas exiting the turbine 112 is at temperature that is low enough for it to flow directly into the heat exchanger 140 without requiring passage through a turbogenerator 120.

Another embodiment of the invention is shown in Figure 4 and is described as follows. Like reference numerals will be used to designate like components of the embodiment. The 1 5 reciprocating engine 100 includes an exhaust conduit 105 in which a turbocharger 310 is arranged. The turbocharger 310 includes turbine 112 that exhausts into turbine exhaust conduit 115, which leads to an exhaust line 312 and exhausts to the atmosphere at exhaust 314. A branch line 316 leads off the exhaust conduit 105 and is fluidly connected to a turbogenerator 320. The turbogenerator 320 consists of a turbine 125 and an alternator 130 arranged on an output shaft of the turbine 125 for the conversion of shaft power into electrical power. The exhaust conduit 105 exhausts into an inlet 117 of the turbine 125. An outlet 118 of the turbine 125 is fluidly connected to the high temperature side of the heat exchanger/evaporator 140 of the Organic Rankine Cycle 170. A turbogenerator exhaust conduit 122 fluidly communicates with the high temperature side of the heat exchanger/evaporator 140 before exhausting to the atmosphere at exhaust 314.

The remainder of the Organic Rankine Cycle is identical to that of the first embodiment and will not be described again here. In this embodiment of the system, although no extra turbine is required, the turbine 125 must be designed to extract more heat from the exhaust gas than is usually the case. This is achieved by altering the capacity or reduced flow characteristic of the turbine 125 in a standard manner.

Operation of the third embodiment of the system is similar to that of the first, other than that the exhaust gas exiting the turbine 125 is at temperature that is low enough for it to flow directly into the heat exchanger 140 without requiring passage through any further heat reducing apparatus.

The system can be installed on a vehicle reciprocating engine or it can be used in a stationary power generation apparatus for providing electrical power at a stationary site.

Various modifications may be made to the described embodiments without departing from the scope of the invention as defined in the accompanying claims.

Claims

CLAIMS1. A system for recovering exhaust energy from fluid in an exhaust conduit of a reciprocating engine, the system comprising an organic rankine cycle having a heat exchanger arranged to evaporate a working fluid of the organic rankine cycle passing through a low temperature side of the heat exchanger, a turbine arranged in fluid communication with the engine exhaust conduit to extract heat from fluid in the engine exhaust conduit and having a turbine exhaust conduit, and a generator driven by the turbine to convert shaft power into electric power to extract heat from fluid in the engine exhaust conduit, in which the turbine exhaust conduit is arranged in fluid communication with an inlet of a high temperature side of the heat exchanger for heat exchange of the fluid in the turbine exhaust conduit downstream of the generator to the working fluid of the organic rankine cycle.
2. A system according to claim 1 comprising a turbocharger arranged in fluid communication with the engine exhaust conduit, the turbocharger comprising a compressor and a further turbine, wherein the further turbine is arranged in fluid communication with the engine exhaust conduit to extract heat from fluid in the engine exhaust conduit, and whcrcin the first turbine is disposed downstream of the further turbine and in an exhaust conduit of the further turbine to extract heat from fluid in the further turbine exhaust conduit.
3. A system according to claim 1 comprising an electric turbocharger arranged in fluid communication with the engine exhaust conduit, the electric turbocharger comprising a compressor and the turbine, and wherein the generator comprises an alternator arranged to convert turbocharger shaft power into electric power to extract heat from fluid in the turbine exhaust conduit.
4. A system according to claim 1 comprising a turbogenerator disposed directly downstream of the reciprocating engine and arranged in fluid communication with the engine exhaust conduit, and providing the turbine and the generator.
5. A system according to any preceding claim, in which the maximum temperature of the working fluid in the organic rankine cycle upon evaporation is less than 250 degrees Celsius.
6. A method of operating a system for recovering exhaust energy from fluid in an exhaust conduit of a reciprocating engine, the system comprising an organic rankine cycle having a heat exchanger arranged to evaporate a working fluid of the organic rankine cycle passing through a low temperature side of the heat exchanger, the method comprising passing exhaust flow from the engine through a turbine to extract heat therefrom and further extracting heat therefrom by means of a generator driven by the turbine to convert shaft power into electric power, and thereafter passing the reduced heat exhaust flow into an inlet of a high temperature side of the heat exchanger for heat exchange from the exhaust flow to the working fluid of the organic rankine cycle.
7. A method according to claim 6 further comprising passing the exhaust flow through a further turbine of a turbocharger arranged in fluid communication with the engine exhaust conduit to extract heat from fluid in the engine exhaust conduit, the first turbine being disposed downstream of the turbocharger in an exhaust conduit of the thither turbine to extract heat from fluid in the turbine exhaust conduit.
8. A method according to claim 6 further comprising employing an electric turbocharger comprising a compressor and the turbine, and wherein the generator comprises an alternator arranged to convert turbocharger shaft power into electric power to extract heat from fluid in the turbine exhaust conduit.
9. A method according to claim 6 further comprising passing the exhaust flow from the engine directly to the turbine.
10. A method according to any of claims 6 to 9 in which the maximum temperature of the working fluid in the in the organic rankine cycle upon evaporation is less than 250 degrees Celsius.
11. Apparatus including a reciprocating engine and a system as claimed in any of claims 1-5 arranged in fluid communication with the reciprocating engine for recovering exhaust energy emitted from the reciprocating engine.
12. A system, substantially as described herein and as shown in the accompanying drawings.
13. A method, substantially as described herein and as shown in the accompanying drawings.