SE540362C2 - An arrangement for recovering heat energy in exhaust gases from a combustion engine - Google Patents

An arrangement for recovering heat energy in exhaust gases from a combustion engine

Info

Publication number
SE540362C2
SE540362C2 SE1651010A SE1651010A SE540362C2 SE 540362 C2 SE540362 C2 SE 540362C2 SE 1651010 A SE1651010 A SE 1651010A SE 1651010 A SE1651010 A SE 1651010A SE 540362 C2 SE540362 C2 SE 540362C2
Authority
SE
Sweden
Prior art keywords
heat exchanger
working medium
valve
heat
combustion engine
Prior art date
Application number
SE1651010A
Other versions
SE1651010A1 (en
Inventor
Kardos Zoltan
Hall Ola
Original Assignee
Scania Cv Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Scania Cv Ab filed Critical Scania Cv Ab
Priority to SE1651010A priority Critical patent/SE540362C2/en
Priority to DE102017006171.8A priority patent/DE102017006171B4/en
Publication of SE1651010A1 publication Critical patent/SE1651010A1/en
Publication of SE540362C2 publication Critical patent/SE540362C2/en

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K23/00—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids
    • F01K23/02—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled
    • F01K23/06—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle
    • F01K23/10—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle with exhaust fluid of one cycle heating the fluid in another cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K13/00—General layout or general methods of operation of complete plants
    • F01K13/02—Controlling, e.g. stopping or starting
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K23/00—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids
    • F01K23/02—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled
    • F01K23/06—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle
    • F01K23/065—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle the combustion taking place in an internal combustion piston engine, e.g. a diesel engine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K23/00—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids
    • F01K23/02—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled
    • F01K23/06—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle
    • F01K23/08—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle with working fluid of one cycle heating the fluid in another cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N5/00—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy
    • F01N5/02—Exhaust or silencing apparatus combined or associated with devices profiting by exhaust energy the devices using heat
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02G—HOT GAS OR COMBUSTION-PRODUCT POSITIVE-DISPLACEMENT ENGINE PLANTS; USE OF WASTE HEAT OF COMBUSTION ENGINES; NOT OTHERWISE PROVIDED FOR
    • F02G5/00—Profiting from waste heat of combustion engines, not otherwise provided for
    • F02G5/02—Profiting from waste heat of exhaust gases
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B1/00—Methods of steam generation characterised by form of heating method
    • F22B1/02—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers
    • F22B1/028—Steam generation using heat accumulators
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D20/00—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00
    • F28D20/02—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00 using latent heat
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02G—HOT GAS OR COMBUSTION-PRODUCT POSITIVE-DISPLACEMENT ENGINE PLANTS; USE OF WASTE HEAT OF COMBUSTION ENGINES; NOT OTHERWISE PROVIDED FOR
    • F02G2254/00—Heat inputs
    • F02G2254/15—Heat inputs by exhaust gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F2260/00—Heat exchangers or heat exchange elements having special size, e.g. microstructures
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E20/00—Combustion technologies with mitigation potential
    • Y02E20/30—Technologies for a more efficient combustion or heat usage
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/14—Thermal energy storage

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Engine Equipment That Uses Special Cycles (AREA)

Abstract

The present invention relates an arrangement for recovering heat energy in exhaust gases from a combustion engine (2). The arrangement comprises a WHR system comprising a WHR circuit (18) with a circulating working medium, a first heat exchanger (20) in the form of an evaporator arranged at the high pressure side (18a) of the WHR circuit (18) in which the working medium is heated by exhaust gases from the combustion engine (2), and an expander (22) generating mechanical energy from the working medium. The WHR system comprises a second heat exchanger (21) arranged on the high pressure side (18a) of the WHR circuit (18) having at least twice the heat storage capacity as the first heat exchanger (20) and a valve device (24-27, 19) configured to direct exhaust gases and working medium to the heat exchangers (20, 21) in a manner such that the working medium is evaporated and superheated in at least one of said heat exchanger (20, 21) before it is directed to the expander (2).

Description

An arrangement for recovering heat energy in exhaust gases from a combustion engine BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates to an arrangement for recovering heat energy in exhaust gases from a combustion engine according to the preamble of claim 1.
A WHR system (Waste Heat Recovery System) can be used for recovering waste thermal energy and convert it to mechanical energy or electric energy. A WHR system includes a pump which pressurizes and circulates a working medium in a closed circuit. The circuit comprises an evaporator where the working medium is heated and evaporated by a heat source such as, for example, exhaust gases. The pressurized and heated gaseous working medium expands in an expander. The expander generates mechanical energy which can be used to support the engine and/or apparatuses in a vehicle. Alternatively, the expander is connected to a generator generating electric energy. The fuel consumption of a combustion engine can be reduced by means of a WHR-system. However, the waste heat energy can generally only be used at the time it is generated in case the WHR system does not comprise expensive equipment converting the heat energy to electrical energy. During certain operating conditions, there is more heat energy in the exhaust gases than can be utilized by the WHR system. During other operating conditions, there is substantially no heat energy in the exhaust gases that can be utilized by the WHR system.
WO 2014/096892 shows an engine arrangement comprising an internal combustion engine, a waste heat recovery system in which a working fluid is successively pumped by a pump, heated in a heat exchanger by means of a heat source produced by the engine operation, and expanded in an expander. The waste heat recovery system further comprises a heat storage device which is arranged outside from the heat exchanger, downstream from the pump and upstream from the expander, said heat storage device comprising a heat storage material which is in thermal contact with the working fluid through a partition wall and being arranged so as to be capable of storing heat from the heat source and of releasing previously stored heat in order to heat the working fluid.
SUMMARY OF THE INVENTION The object of the present invention is to provide an arrangement which is substantially always able to recover heat energy from exhaust gases to mechanical energy when there is a power demand.
The above mentioned object is achieved by the control system according to the characterizing part of claim 1. The arrangement comprises a WHR system designed with a first heat exchanger and a second heat exchanger having a considerably higher heat storage capacity than the first heat exchanger on its high pressure side. Preferably, the second heat exchanger have a heat storage capacity of at least five times or ten times the heat storing capacity of the first heat exchanger. The amount of heat energy in the exhaust gases is related to the load of the combustion engine. Advantageously, the WHR system is designed to make use of all heat energy in the exhaust gases at normal load of the combustion engine. In this case, the valve device directs the entire exhaust gas flow and the working medium to the first heat exchanger for evaporation and superheating of the working medium before it is directed to the expander.
At a high load of the combustion engine, the WHR system is not able to recover all heat energy in the exhaust gases to mechanical energy. In this case and when there is a power demand of the WHR system, the valve device directs exhaust gases and working medium to the first heat exchanger and the second heat exchanger in a manner such that the WHR system recovers a part of the heat energy in the exhaust gases to mechanical energy in accordance with its capacity at the same time as an exceeded part of the heat energy in the exhaust gases is used to heat the second heat exchanger. At a low load of the combustion engine, the valve device may directs the entire exhaust gas flow and the working medium to the second heat exchanger for evaporation and superheating of the working medium. At a load of the combustion engine when there is no power demand, the valve device may directs the entire exhaust gas flow to the second heat exchanger in order to heat it to a higher temperature.
Consequently, the above mentioned arrangement makes it possible to recover at least a part of the heat energy in the exhaust gases to mechanical energy and to store an exceeded part of the heat energy in the second heat exchanger. The heat energy stored in the second heat exchanger can be used when the load on the combustion engine is low at the same time as it is a power demand. Since the heat energy is stored in a heat exchanger, it is easy to utilize the stored heat energy. Furthermore, the WHR system can be given smaller dimensions than a corresponding conventional WHR system due to its ability to store heat energy in the second heat exchanger.
According to an embodiment of the invention, the second heat exchanger has a larger mass than the first heat exchanger. The capacity of a material body to store heat energy is related to the mass of the body. Thus, it is suitable that the second heat exchanger has a considerably larger mass than the first heat exchanger. The second heat exchanger may comprises a solid material heated by the exhaust gases. Such a solid material may, for example, be a ceramic material. Alternatively or in combination. The second heat exchanger comprises a phase changing material. A lot of heat energy can be transferred between the exhaust gases and such a material during a phase changing process. A second heat exchanger including a phase changing material does not need to be considerably heavier than the first heat exchanger. Furthermore, a second heat exchanger provided with a phase changing material has a substantially constant temperature during the phase changing process of the material. The phase changing material, for example, be tin or zinc. According to a further alternative, the second heat exchanger may comprises a mix of two phase changing materials. In this case, the second heat exchanger can be defined as a heat energy storage having two different temperature levels.
According to an embodiment of the invention, the first heat exchanger and the second heat exchanger are arranged in parallel in the WHR system and that the valve device comprises a valve directing the working medium flow to the first heat exchanger or the second heat exchanger. The valve may be configured to direct the working medium to the first heat exchanger at normal and high load of the combustion engine when there is a power demand of the WHR system. The valve may be configured to direct the working medium to the second heat exchanger at low load when there is a power demand of the WHR system.
According to an embodiment of the invention, the first heat exchanger and the second heat exchanger are arranged in series in WHR system and that the valve device comprises a valve arranged in a downstream position of the first heat exchanger and an upstream position of the second heat exchanger. In case the first heat exchanger and the second heat exchanger are arranged in an exhaust line of the combustion engine, the valve is configured to direct the working medium from the first heat exchanger past the second heat exchanger at normal and high load of the combustion engine when there is a power demand of the WHR system. The valve is configured to direct the working medium from the first heat exchanger to the second heat exchanger at low load when there is a power demand of the WHR system.
On the other hand, in case the first heat exchanger is arranged in an exhaust line of the combustion engine and the second heat exchanger are arranged outside the exhaust line of the combustion engine, the valve is configured to direct the working medium from the first heat exchanger past the second heat exchanger at normal load of the combustion engine when there is a power demand of the WHR system. The valve is configured to direct the working medium from the first heat exchanger to the second heat exchanger at low load and at high load when there is a power demand of the WHR system. When there is a high load on the combustion engine, the working medium is superheated to a too high temperature in the first heat exchanger. In this case, the working medium is de-superheated in the second heat exchanger. When there is a low load on the combustion engine, the working medium may be evaporated and superheated in the second heat exchanger.
According to an embodiment of the invention, the arrangement comprises first heat exchanger bypass line and the valve device comprises at least one valve controlling the exhaust gas flow through the first heat exchanger and the first heat exchanger bypass line. In this case, it is possible to provide a reduced exhaust gas flow to the first heat exchanger during operating conditions when there is a high load on the combustion engine in order to provide a too high superheating of the working medium in the first heat exchanger. The exhaust gases in the bypass line can be used to heat the second heat exchanger. Furthermore, it is possible to direct the entire exhaust gas flow via the first exchanger bypass line when there is no heat transfer in the first heat exchanger in order to reduce the flow resistance for the exhaust gases in the exhaust line.
According to an embodiment of the invention, the arrangement comprises a second heat exchanger bypass line and the valve device comprises at least one valve controlling the exhaust gas flow through the second heat exchanger and the second heat exchanger bypass line. The valve makes it possible to direct the exhaust gas flow to the second heat exchanger when it has a temperature high enough to heat the second heat exchanger and to the second exchanger bypass line when it has a too low temperature to heat the second heat exchanger.
According to an embodiment of the invention, it comprises a control unit configured to control the valve device by means of information from at least one operating parameter. Said operating parameter may be related to at least one of the following parameters the temperature of the exhaust gases, the temperature of the second heat exchanger, the load of the combustion engine and the power demand of the WHR system. The temperature difference between the exhaust gases and the second heat exchanger, can be used to determine if it is possible to heat the second heat exchanger by means of the exhaust gases. The load of the combustion engine is related to the exhaust gas flow and the temperature of the exhaust gases which define the heat energy in the exhaust gases.
BRIEF DESCRIPTION OF THE DRAWINGS In the following preferred embodiments of the invention are described, as examples, with reference to the attached drawings, in which: Fig. 1 shows an arrangement according to a first embodiment of the invention, Fig. 2 shows an arrangement according to a second embodiment of the invention and Fig. 3 shows an arrangement according to a third embodiment of the invention, DETAIFED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 shows a schematically disclosed vehicle 1 powered by a supercharged combustion engine 2. The combustion engine 2 may be a diesel engine. The vehicle 1 may be a heavy vehicle. The vehicle 1 comprises an exhaust line 3 receiving exhaust gases from the combustion engine 2. The exhaust line 3 comprises a turbine 4a of a turbo aggregate 4. The turbine 4a drives a compressor 4b of the turbo charger 4. The compressor 4b compresses air which is led, via a charged air line 5 to the combustion engine 2. The charged air line 5 comprises a charge air cooler 6 arranged at a front portion of the vehicle 1.
The vehicle 1 comprises a cooling system comprising an engine inlet line 7 directing coolant to the combustion engine 2. The engine inlet line 7 is provided with a pump 8 circulating a coolant in the cooling system. The coolant leaving the combustion engine 2 is received in an engine outlet line 9. A first valve member 10 in the form of a three way valve 10 is arranged at an end of the engine outlet line 9. The cooling system comprises a radiator bypass line 11 and a radiator 12. The first valve member 10 is able to receive coolant from the engine outlet line 9 and distribute a part of it to the radiator bypass line 11 and a remaining part of it to the radiator 12. The cooling system comprises a second valve member 14 in the form of a three way valve. The second valve member 14 may receive coolant from the radiator bypass line 1 land direct it to the engine inlet line 7 or to a condenser circuit 15 in which the coolant cools a working medium in a condenser 16 of a WHR system. In the latter case, coolant from the radiator bypass line 11 and possible coolant from the radiator 12 are mixed and directed to the condenser circuit 15. Alternatively, the second valve member 14 receives coolant from the radiator 12 and directs it to the engine inlet line 7. The condenser circuit 15 comprises a condenser inlet line 15a directing coolant to the condenser 16 and a condenser outlet line 15b directing coolant from the condenser 16 to the engine inlet line 7.
Consequently, the vehicle is provided with a WHR-system (Waste Heat Recovery system). The WHR system comprises a pump 17 which pressurizes and circulates a working medium in a WHR circuit 18. The working medium may be ethanol, R245fa or other kind of working medium. The working medium leaving the pump 17 enters a three way valve 19. The three way valve 19 can direct the working medium to a first heat exchanger 20 or a second heat exchanger 21. In this case, the first heat exchanger 20 and the second heat exchanger is arranged in parallel. The first heat exchanger 20 is configured to be used as evaporator and the second heat exchanger 21 is configured to be used as a heat storage and evaporator. The second heat exchanger 21 has a considerably higher heat storage capacity than the first heat exchanger 20. The second heat exchanger 21 may have a considerably higher mass than the first heat exchanger 20. The second heat exchanger 21 may comprise a solid material heated by the exhaust gases, for example a ceramic material. Alternatively or in combination, it can comprise a phase changing material, for example tin which melts at approximately 230°C or zinc which melts at approximately 430°C. A mix of two phase changing materials can also be used in the second heat exchanger 21.
The working medium is heated in at least one of the heat exchangers 20, 21 such that it is evaporated and superheated to a suitable temperature. The gaseous working mediums leaving the heat exchangers 20, 21 are received in a common line of the WHR circuit 18 directing the working medium to an expander 22. The working medium expands in the expander 22. The expander 22 generates a rotary motion which may be transmitted, via a suitable mechanical transmission, to a shaft of the drive train of the vehicle 1. After the working medium has passed through the expander 22, it is directed to the condenser 16. The working medium is cooled in the condenser 16 by the coolant in the condenser circuit 15 to a temperature at which it is condensed. The liquid working medium is directed from the condenser 16, to a receiver 23. Working medium is sucked from the receiver 23 to the pump 17. The part of the WHR circuit 18 located downstream of the pump 17 and upstream of the expander 22 comprises a high pressure side 18a of the WHR circuit 18. The part of the WHR circuit 18 located downstream of the expander 22 and upstream of the pump 17 comprises a low pressure side 18a of the WHR circuit 18.
The exhaust line 3 comprises a first heat exchanger bypass line 3a and a second heat exchanger bypass line 3b. The exhaust line 3 comprises a first valve 24 controlling the exhaust gas flow through the first heat exchanger 20, a second valve 25 controlling the exhaust gas flow through the first heat exchanger bypass line 3a, a third valve 26 controlling the exhaust gas flow through the second heat exchanger 21 and a fourth valve 27 controlling the exhaust gas flow through the second heat exchanger bypass line 3b. The valves 24-27 are adjustable in a stepless manner. The valve 24-27 may be butterfly valves. A control unit 28 controls the valves 24-27 and the three way valve 19. A first temperature sensor 29 sense the temperature of the exhaust gases in a position upstream of the second heat exchanger 21. A second temperature sensor 30 senses the temperature of the second heat exchanger 21. The control unit 28 also receives information about other operating parameters such as the load 31 of the combustion engine 2 and the power demand 32 of the WHR system. The load 31 of the combustion engine 2 is related to the amount of heat energy in the exhaust gases. In this case, the WHR system is designed to have capacity to recover all heat energy in the exhaust gases at a normal load of the combustion engine 2.
When there is a normal load on the combustion engine 2 and a power demand of the WHR system, the control unit 28 controls the valve device 19 such that it directs the entire working medium flow to the first heat exchanger 20. Furthermore, the control unit 28 opens the first valve 24 and closes the second valve 25 such that the entire exhaust gas flow is directed through the first heat exchanger 20. In this case, the working medium is heated by the exhaust gases in the first heat exchanger 20 such it is evaporated and superheated to a suitable temperature before it is directed to the expander 22. In order to avoid unnecessary pressure drops in the exhaust line 3, the control unit 28 closes the third valve 26 and opens the fourth valve 27 such that the exhaust gas flow is directed past the second heat exchanger 21.
When there is a very high load on the combustion engine 2, the WHR system has not capacity to utilize all heat energy in the exhaust gases. In this case, the control unit 28 controls the valve device 19 such that it directs the working medium flow to the first heat exchanger 20. The control unit 28 estimates the part of the exhaust gases to be directed to the first heat exchanger 20 without excessive superheating of the working medium in the first heat exchanger 20. The control unit 28 regulates the first valve 24 and the second valve 25 such that the estimated exhaust gas flow is directed through the first heat exchanger 21 and the remaining part of the exhaust gas flow is directed through the first valve bypass line 3a. The control unit 28 receives information about the temperature of the exhaust gases in a position upstream of the second heat exchanger 20 from the first temperature sensor 29 and about the temperature of the second heat exchanger 21 from the second temperature sensor 30. In view of this information, the control unit 28 estimates if it is possible to heat the second heat exchanger 21 and if it results in a larger gain than the penalty caused by added backpressure in the exhaust gas line 3. If this is the case, the control unit 28 opens the third valve 25 and closes the fourth valve 27 such that the exhaust gases flow through the second heat exchanger 2 land heat it to a higher temperature. If it is not the case, the control unit 28 closes the third valve 25 and opens the fourth valve 27 such that the exhaust gas flow is directed past the second heat exchanger 21. In this case, the e WHR system recovers a part of the heat energy in the exhaust gases and transform it to mechanical energy. An excess part of heat energy in the exhaust gases is stored in the second heat exchanger 21.
When there is no or a low load on the combustion engine 2 and a power demand of the WHR system, the control unit 28 determines if the temperature of the second heat exchanger 21 is necessary high to provide an efficient evaporation and superheating of the working medium in the second heat exchanger 21. If this is the case, the control unit 28 controls the valve device 19 such that it directs the working medium flow to the second heat exchanger 21. In order to avoid unnecessary pressure drops in the exhaust line 3, the control unit 28 closes the first valve 24 and opens the second valve 25 such that the entire exhaust gas flow is directed past the first heat exchanger 20. The control unit 28 opens the third valve 26 and closes the fourth valve 27 such that the entire exhaust gas flow is directed through the second heat exchanger 21. If it is not possible or suitable to heat the second heat exchanger 21, the control unit 28 shuts off the WHR system.
When there is a load on the combustion engine 2 and no power demand of the WHR system, the control unit 28 shuts off the pump 17 such that the circulation of the working medium in the WHR circuit 18 is ceased. In view of information about the load on the combustion engine 2, the temperature of the exhaust gases and the temperature of the second heat exchanger 21, the control unit 28 estimates if it is possible to heat the second heat exchanger by the exhaust gases and if it results in a larger gain than the penalty caused by added backpressure in the exhaust gas line 3. If this is the case, the control unit 28 closes the first valve 24 and opens the second valve 25 such that the entire exhaust gas flow is directed past the first heat exchanger 20. Furthermore, the control unit 28 opens the third valve 25 and closes the fourth valve 27 such that the entire exhaust gas flow is directed through the second heat exchanger 21. If it is not possible or suitable to store heat energy in the second heat exchanger 21, the control unit 28 closes the third valve 26 and opens the fourth valve 27 such that the entire exhaust gas flow is also directed past the second heat exchanger 21.
Figs 2 shows an alternative embodiment of the WHR system. In this case, the first heat exchanger 20 and the second heat exchanger 21 are arranged in series in the WHR circuit 18. The first heat exchanger 20 is arranged in a position upstream of the second heat exchanger 21. A three way valve 19 is arranged in a position downstream of the first heat exchanger 20 and upstream of the second heat exchanger 21. As a consequence, the working medium is always directed through the first heat exchanger 20. By means of the valve device 19, it is possible to direct the working medium leaving the first heat exchanger 20 to the second heat exchanger 2 lor past the second heat exchanger 21 before it enters the expander 22.
When there is a normal load on the combustion engine 2 and a power demand of the WHR system, the control unit 28 controls the valve device 19 such that the working medium flow from the first heat exchanger 20 is directed past the second heat exchanger 21 and to the expander 22. Furthermore, the control unit 28 opens the first valve 24 and closes the second valve 25 such that the entire exhaust gas flow is directed through the first heat exchanger 20. The working medium is heated by the exhaust gases in the first heat exchanger 20 such it is evaporated and superheated to a suitable temperature. In order to avoid pressure drops in the exhaust line 3, the control unit 28 closes the third valve 26 and opens the fourth valve 27 such that the entire exhaust gas flow is directed past the second heat exchanger 21.
When there is a very high load on the combustion engine, the WHR system has not capacity to utilize all heat energy in the exhaust gases. In this case, the control unit 28 controls the three way valve 19 such that the working medium flow from the first heat exchanger 20 is directed past the second heat exchanger 21 and to the expander 22. The control unit 28 estimates the part of the exhaust gas flow to be directed to the first heat exchanger 20 without excessive superheating of the working medium. The control unit 28 regulates the first valve 24 and the second valve 25 such that such that the estimated exhaust gases flow is directed to the first heat exchanger 21 and a remaining part of the exhaust gas flow is directed to the first valve bypass line 3a. As a consequence, the working medium is evaporated and superheated to a suitable temperature in the first heat exchanger 20 before it is directed to the expander 22. The control unit 28 receives information about the temperature of the exhaust gases in a position upstream of the second heat exchanger 20 from the first temperature sensor 29 and about the temperature of the second heat exchanger 21 from the second temperature sensor 30. In view of this information, the control unit 28 estimates if it is possible to heat the second heat exchanger 21 by the exhaust gases and if it results in a larger gain than the penalty caused by added backpressure in the exhaust gas line 3. If this is the case, the control unit 28 opens the third valve 25 and closes the fourth valve 27 such that the exhaust gas flow is directed through the second heat exchanger 21. If it is not possible to heat the second heat exchanger 21, the control unit 28 closes the third valve 25 and opens the fourth valve 27 such that the exhaust gas flow is directed past the second heat exchanger 21. In this case, the WHR system recovers a maximum amount of heat energy in the exhaust gases to mechanical energy. An excess part of the heat energy in the exhaust gases is stored in the second heat exchanger 21.
When there is no or a low load on the combustion engine and a power demand of the WHR system, the control unit 28 determines if the temperature of the second heat exchanger 21 is necessary high enough to provide an efficient evaporation and superheating of the working medium in the second heat exchanger 21. If this is the case, the control unit 28 controls the valve device 19 such that it directs the working medium flow from the first heat exchanger 20 to the second heat exchanger 21. In order to avoid pressure drops in the exhaust line 3, the control unit 28 closes the first valve 24 and opens the second valve 25 such that the entire exhaust gas flow is directed past the first heat exchanger 20. The control unit 28 opens the third valve 26 and closes the fourth valve 27 such that the entire exhaust gas flow is directed through the second heat exchanger 21. If it is not possible or suitable to heat the second heat exchanger 21, the WHR system is shut off.
When there is a load on combustion engine and no power demand of the WHR system, the control unit 28 shuts off the pump 17 such that the circulation of the working medium in the WHR circuit 18 is ceased. In view of information about the load on the combustion engine 2, the temperature of the exhaust gases and the temperature of the second heat exchanger 21, the control unit 28 estimates if it is possible to heat the second heat exchanger 21 by the exhaust gases and if it results in a larger gain than the penalty caused by added backpressure in the exhaust gas line 3. If this is the case, the control unit 28 closes the first valve 24 and opens the second valve 25 such that the entire exhaust gas flow is directed past the first heat exchanger 20. Furthermore, the control unit 28 opens the third valve 25 and closes the fourth valve 27 such that the entire exhaust gas flow is directed through the second heat exchanger. If it is not possible or suitable to store heat energy in the second heat exchanger 21, the control unit 28 closes the third valve 26 and opens the fourth valve 27 such that the exhaust gases flow also is directed past the second heat exchanger 21.
Figs 3 shows a further alternative embodiment of the WHR system. In this case, the first heat exchanger 20 and the second heat exchanger 21 is arranged in series in the WHR circuit 18 but the second heat exchanger 21 is not arranged in the exhaust line 3. A three way valve 19 is arranged in a position downstream of the first heat exchanger 20 and upstream of the second heat exchanger 21. Also in this case, the working medium is always directed through the first heat exchanger 20. By means of the valve device 19, it is possible to direct the working medium flow leaving the first heat exchanger 20 to the second heat exchanger 21 or past the second heat exchanger 21 before it is directed to the expander 22.
When there is a normal load on the combustion engine 2 and a power demand of the WHR system, the superheating of the working medium in the first heat exchanger 20 is usually within a suitable temperature range. The control unit 28 controls the three way valve 19 such that the working medium flow from the first heat exchanger 20 is directed past then second heat exchanger 21 and to the expander 22. Furthermore, the control unit 28 opens the first valve 24 and closes the second valve 25 such that the entire exhaust gas flow is directed through the first heat exchanger 20.
When there is a very high load on the combustion engine 2, the amount of heat energy in the exhaust gases is high. As a consequence, the working medium receives a too high superheating in the first heat exchanger 20. The control unit 28 receives information about the temperature of the second heat exchanger 21 and determine if it is possible to de-superheat the working medium in the second heat exchanger 21. If this is the case, the control unit 28 controls the first valve 24 and the second valve 25 such that the entire exhaust gas flow is directed through the first heat exchanger 20. Furthermore, the control unit 28 controls the three way valve 19 such that it directs the working medium flow leaving the first heat exchanger 20 to the second heat exchanger 21. The working medium is cooled in the second heat exchanger 21 such that it has a suitable superheating when it leaves the second heat exchanger 21 and enters the expander 22. At the same time the second heat exchanger 21 is heated by the superheated working medium. If it is not possible to de-superheat the working medium in the second heat exchanger 21, the control unit 28 controls the first valve 24 and the second valve 25 such that a part of the exhaust gas flow is directed through the first heat exchanger 21 such that the working medium receives a suitable superheating in the first heat exchanger 20.
When there is no or a low load on the combustion engine and a power demand of the WHR system, the control unit 28 determines if the temperature of the second heat exchanger 21 is necessary high to provide an efficient evaporation and superheating of the working medium. If this is the case, the control unit 28 controls the valve device 19 such that it directs the working medium from the first heat exchanger 20 to the second heat exchanger 21. In order to avoid pressure drops in the exhaust line 3, the control unit 28 closes the first valve 24 and opens the second valve 25 such that the entire exhaust gas flow is directed past the first heat exchanger 20. If it is not possible or suitable to heat the second heat exchanger 21, the WHR system is shut off.
When there is a load on combustion engine and no power demand of the WHR system, the circulation of the working medium in the WHR circuit 18 is to continue. In view of information about the load on the combustion engine 2, the temperature of the exhaust gases and the temperature of the second heat exchanger 21, the control unit 28 estimates if it is possible to evaporate and superheat the working medium in the second heat exchanger 21 If this is the case, the control unit 28 opens the first valve 24 and closes the second valve 25 such that the entire exhaust gas flow is directed through the first heat exchanger 20. Furthermore, the control unit 28 controls the valve device 19 such that it directs the working medium flow from the first heat exchanger 20 to the second heat exchanger 21. If it is not possible or suitable to heat the second heat exchanger 21, the WHR system is shut off.
The invention is not restricted to the described embodiment but may be varied freely within the scope of the claims.

Claims (10)

Claims
1. An arrangement for recovering heat energy in exhaust gases from a combustion engine (2), wherein the arrangement comprises a WHR system comprising a WHR circuit (18) with a circulating working medium, a first heat exchanger (20) in the form of an evaporator arranged at a high pressure side (18a) of the WHR circuit (18) in which the working medium is heated by exhaust gases from the combustion engine (2), a second heat exchanger (21) arranged on the high pressure side (18a) of the WHR circuit (18) having at least twice the heat storage capacity as the first heat exchanger (20) and an expander (22) generating mechanical energy from the working medium, characterized in that the arrangement comprises a valve device (24-27, 19) configured to direct exhaust gases and working medium to the heat exchangers (20, 21) in a manner such that the working medium is evaporated and superheated in at least one of said heat exchanger (20, 21) before it is directed to the expander (2) and that the second heat exchanger (21) comprises a mix of two phase changing materials to be heated by the exhaust gases which change phase at different temperatures.
2. An arrangement according to claim 1, characterized in that the second heat exchanger (21) has a larger mass than the first heat exchanger (20).
3. An arrangement according to claim 1 or 2, characterized in that the second heat exchanger (21) comprises a solid material to be heated by the exhaust gases.
4. An arrangement according to any one of the preceding claims, characterized in that the first heat exchanger (20) and the second heat exchanger (21) are arranged in parallel in the WHR circuit (18) and that the valve device comprises a valve (19) directing the working medium to the first heat exchanger (29) or the second heat exchanger (21).
5. An arrangement according to any one of the preceding claims 1 to 3, characterized in that the first heat exchanger (20) and the second heat exchanger (21) are arranged in series in the WHR circuit (18), and that the valve device comprises a valve (19) arranged in a position downstream of the first heat exchanger and upstream of the second heat exchanger between said heat exchangers (20, 21) directing the working medium leaving the first heat exchanger (20) to the second heat exchanger (21) or past the second heat exchanger (21).
6. An arrangement according to any one of the preceding claims, characterized in that the first heat exchanger (20) and the second heat exchanger (21) are arranged in an exhaust line (3) of the combustion engine (2).
7. An arrangement according to any one of the preceding claims 1 to 3 and 5, characterized in that the first heat exchanger (20) is arranged in an exhaust line (3) of the combustion engine (2) and the second heat exchanger (21) is arranged outside the exhaust line (3) of the combustion engine (2).
8. An arrangement according to any one of the preceding claims, characterized in that the it comprises a first heat exchanger bypass line (3 a) and that the valve device comprises at least one valve (24, 25) controlling the exhaust gas flow through the first heat exchanger (20) and the first heat exchanger bypass line (3a).
9. An arrangement according to any one of the preceding claims 1-6 and 8, characterized in that it comprises second heat exchanger bypass line (3b) and that the valve device comprises at least one valve (26, 27) controlling the exhaust gas flow through the second heat exchanger (21) and the second heat exchanger bypass line (3b).
10. An arrangement according to any one of the preceding claims, characterized in that it comprises a control unit (28) configured to control the valve device (19) by means of information from at least one operating parameter. 1 1. An arrangement according to claim 10, characterized in that said operating parameter is related to at least one of the following parameters the temperature of the exhaust gases, the temperature of the second heat exchanger, the load (31) of the combustion engine (2) and the power demand (32) of the WHR system.
SE1651010A 2016-07-07 2016-07-07 An arrangement for recovering heat energy in exhaust gases from a combustion engine SE540362C2 (en)

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