Patent Application
20190301311
The invention relates to a waste-heat recovery system.
Waste-heat recovery systems comprising a waste-heat recovery circuit can utilize for example the waste heat in an internal combustion engine in a motor vehicle. For this purpose, said waste heat is applied to a steam generator. The working fluid circulating in the steam circuit process is thereby heated, evaporated and overheated. The hot working fluid, which is under high pressure, is then expanded in an expansion machine and performs mechanical work, which can be used for instance as additional vehicle drive or to drive a generator or an air conditioning system.
The steam generator is typically formed by a heat exchanger, through which a working fluid can be guided to absorb heat.
In the expansion machine, for example an axial piston machine, the working fluid is expanded from the high first pressure level to a lower second pressure level by performing work. The pistons thereby drive a shaft, which serves for example to move a vehicle. The expanded fluid is cooled and liquefied in a condenser and is supplied to the fluid circuit again via a pump. The higher the pressure and temperature difference, the higher the efficiency of the unit.
Water can be used as working fluid, the steam of which is relaxed by outputting work. For example, organic working fluids or water comprising additives can be used as well, which may be valuable or harmful to the environment. An escape of the working fluid is then unwanted. A condenser arrangement located in the waste-heat recovery system downstream of the expansion machine serves to liquefy the expanded working fluid. Typical temperatures of the working fluid are several hundred ° C. for the energy-rich steam state and in the case of water 100° C. as condensation temperature. The condensed working fluid is supplied to a working fluid reservoir, typically in the form of a suitably realized container, which is present in the waste-heat recovery circuit, where it is available again for the waste-heat recovery circuit without losses.
In this context, DE 10226445 C1 as well as WO 2005/001248 A1 disclose conventional waste-heat recovery circuits. Feed water is used as working fluid. The water is evaporated in an evaporator. The steam is expanded by performing work in an expansion machine. After the expansion, the steam is condensed in a condenser and is supplied by means of an electrically or mechanically operated pump to a reservoir, from which it is available for the circuit again. The described working machine is used for example as auxiliary device in motor vehicles. To also use it in the winter, it is known to add antifreeze to the working fluid. It is further known to add lubricant, for instance oil, to the working fluid. Depending on the temperature in the steam generator, organic working fluids, comprising a lower boiling point and/or combustible working fluids are used as well.
The described arrangements can overheat, when for example too much heat is supplied to the steam circuit process. The components of the waste-heat recovery circuit may then be damaged.
It is thus an object of the present invention to create an improved embodiment for a waste-heat recovery system comprising a waste-heat recovery circuit, which has an improved protection against overheating and overpressure when the cooling circuit fails.
This object is solved according to the invention by means of the subject matter of the independent patent claim(s). Advantageous embodiments are the subject matter of the dependent patent claim(s).
It is thus the general idea of the invention to guide a coolant stored in a container via a fluid line into the condenser of the waste-heat recovery circuit. According to the invention, the container is thereby constructed in such a way that two sub-chambers, which are fluidically separated from one another, are provided in said container, wherein a first sub-chamber is fluidically connected to the actual waste-heat recovery circuit and can thus be filled with the working fluid of the waste-heat recovery circuit. The coolant is located in the second sub-chamber. The two sub-chambers are embodied in a volume-variable manner, namely in such a way that a volume decrease of the second sub-chamber is associated with a volume increase of the first sub-chamber, and vice versa. This can be realized for example in that the two sub-chambers are divided by means of a suitable divider made of a flexible material. A rising fluid pressure of the steam phase of the working fluid leads to an expansion of the first sub-chamber of the container, which is associated with a decrease of the volume of the second sub-chamber, such that the coolant is pushed out of said second sub-chamber and is guided via the fluid line into the condenser. The heat exchange with the working fluid taking place at that location has the result that the temperature thereof and thus also the fluid pressure thereof reduces again. However, it can at least be attained with such a feedback that the fluid pressure of the working fluid does not rise even further and takes on inadmissible values, which could lead to damages of individual components of the waste-heat recovery circuit.
In the case of the waste-heat recovery system according to the invention, a particularly effective cooling of the working fluid and thus an improved efficiency of the exhaust-heat recovery circuit is thus ensured on the one hand. However, it is simultaneously also ensured that damages to the condenser and thus to the entire waste-heat recovery circuit by overpressure or a temperature, which is too high, of the working fluid as well as of the coolant is avoided. As a result, a waste-heat recovery circuit with a high efficiency and also with a high operational safety can thus be created.
A waste-heat recovery system according to the invention comprises a waste-heat recovery circuit, in which a working fluid circulates and which is divided into a high pressure region and into a low pressure region. The waste-heat recovery system comprises a conveying device located in the waste-heat recovery circuit for driving the working fluid, a steam generator, which located in the high pressure region, for evaporating the working fluid, as well as an expansion machine for expanding the working fluid to the pressure of the low pressure region by performing work. At least one condenser for condensing the expanded working fluid is located in the low pressure region. According to the invention, a container is provided downstream of the condenser, in the container interior of which a divider is located, which divides the container interior into a first and a second sub-chamber of a variable volume. The first sub-chamber is thereby fluidically connected to the low pressure region of the waste-heat recovery circuit downstream of the condenser. The second sub-chamber of the container is filled or can be filled with a coolant. Said coolant can be introduced into the condenser, fluidically separately from the working fluid, via a fluid line of the waste-heat recovery system, such that the working fluid can be condensed by thermal interaction with the coolant in this way.
In the case of a preferred embodiment, the first sub-chamber is connected to the low pressure region of the waste-heat recovery system via a first pressure-relief valve. The first pressure-relief valve is thereby embodied in such a way that, in response to exceeding a predetermined first threshold pressure of the working fluid in the first pressure-relief valve, it releases a fluid connection between the first sub-chamber and the low pressure region for the flow-through with the working fluid. It is ensured in this way that the working fluid is introduced into the container only in the case of failure, thus at a fluid pressure, which is too high. The first pressure-relief valve can be embodied as non-return valve.
In the case of another preferred embodiment, the divider, for the embodiment as first pressure-relief valve, has a dividing membrane of a resilient material, which expands in response to exceeding the predetermined first threshold pressure of the working fluid, such that the working fluid can flow into the first sub-chamber and can be accommodated there. In the case of this alternative, the provision of a separate pressure-relief valve—for instance in the manner of a non-return valve—can be forgone, which reduces the production costs of the waste-heat recovery system.
In the case of a preferred embodiment, a second pressure-relief valve is further located in the fluid line. The second pressure-relief valve is embodied in such a way that, in response to exceeding a predetermined, second threshold pressure of the coolant in the second pressure-relief valve, it switches from a closed into an open state, thus opens, namely in such a way that the coolant can be discharged from the fluid line via a fluid outlet into the surroundings of the waste-heat recovery system. The second pressure-relief valve is designed in such a way that, in response to exceeding a second threshold pressure, the coolant can escape from the fluid line into the surroundings of the waste-heat recovery circuit. It is ensured in this way that in the case of a fluid pressure of the coolant, which is too high, in the fluid line or in the condenser, respectively, the latter is not damaged, but that a discharge of the coolant from the condenser can take place in order to reduce pressure.
In the case of a further preferred embodiment, the condenser is embodied as triple-flow condenser comprising three fluid paths. In the case of this alternative, a first fluid path is embodied for the flow-through with the working fluid. A second fluid path is embodied for the flow-through with the coolant, and a third fluid path is embodied for the flow-through with an additional coolant. The three fluid paths run fluidically separately from one another in the condenser and are thermally coupled to one another for the heat exchange between the working fluid and the two coolants. The working fluid can be cooled according to standard by means of the additional coolant in a nominal operating state of the waste-heat recovery system via the third fluid path. An additional cooling in the case of failure takes place by means of the coolant via the second fluid path. This alternative ensures an optimal cooling of the fluid both in the nominal operating state of the waste-heat recovery system and in the case of failure.
In the case of another preferred embodiment, the condenser is embodied as double-flow condenser comprising two fluid paths. In the case of this alternative, the first fluid path is embodied for the flow-through with the working fluid and the second fluid path for the flow-through with the coolant and, alternatively or additionally, for the flow-through with the additional coolant. The two fluid paths run fluidically separately from one another at least in the condenser and are thermally coupled to one another for the heat exchange between the working fluid and the coolant or the additional coolant, respectively.
In the case of an advantageous further development, the second fluid path is embodied for the simultaneous flow-through with the coolant and with the additional coolant. For this purpose, the fluid line outside of the condenser leads into the second fluid path, such that the coolant and the additional coolant can mix. The setup of the condenser can be kept simple in this way. In particular the provision of a technically more complex, triple-flow condenser or the provision of a separate additional condenser can be forgone. This has an advantageous effect on the production costs of the waste-heat recovery system.
In another advantageous further development, the second fluid path is embodied for the flow-through with the coolant. In the case of this alternative, a further, double-flow condenser comprising a first and a second fluid path is provided in the low pressure region. The first fluid path of this additional condenser is embodied for the flow-through with the working fluid and the second fluid path for the flow-through with the additional coolant. Due to the fact that the coolant and the additional coolant cannot mix even in the case of failure in the case of this alternative, maintenance of the waste-heat recovery system in the case of failure and a division of the two coolants associated therewith is not required.
The condenser can advantageously be located between the second pressure-relief valve and the container. In an alternative, the second pressure-relief valve can be located between the condenser and the container. Both alternatives require only very little installation space.
In the case of an advantageous further development, the divider is embodied as dividing membrane of a flexible, in particular of a resilient material. The variability of the two partial volumes, which is essential for the invention, can be realized in a technically simple and thus cost-efficient manner in this way.
In the case of a further advantageous further development, the divider has an expanded state, in which the first sub-chamber has a maximum volume and the second sub-chamber has a minimal volume. In the case of this alternative, the divider furthermore has a relaxed state, in which the first sub-chamber has a minimal volume and the second sub-chamber has a maximum volume. If the fluid pressure of the working fluid downstream of the condenser rises, the steam phase of the working fluid can flow into the first sub-chamber, whereby the divider is expanded, such that the first sub-chamber increases. The decrease of the second sub-chamber associated therewith has the result that the coolant is pushed out of the container into the fluid line and is guided via the latter into the condenser, where it can cool said working fluid by heat exchange therewith.
In the case of a further preferred embodiment, which can be combined with the above-described embodiments, a non-return valve is located fluidically parallel to the first pressure-relief valve, which non-return valve makes it possible for the working fluid to flow out of the container back into the waste-heat recovery circuit, when the coolant has escaped from the fluid line and when a predetermined third pressure of the working fluid has been exceeded in the container. Said non-return valve serves the purpose of making it possible to provide for the working fluid to flow out the container back into the waste-heat recovery circuit when coolant has escaped from the fluid line into the surroundings, thus in the case of “emptied” fluid line. In this scenario, it is thus not required to fill the waste-heat recovery circuit with further working fluid A.
Particularly preferably, the temperature difference between an evaporating temperature of the coolant and a condensation temperature of the working fluid is at least 30° C., preferably at least 80° C. A particularly high heat transfer between the working fluid and the coolant can be ensured in this way, which has an advantageous effect on the efficiency of the waste-heat recovery system.
The working fluid can advantageously be ethanol, acetone or cyclopentane and the first threshold pressure can be approximately 10 bar. In the case of a suitable determination of the first threshold pressure, it can be attained in this way that the working fluid condenses at approx. 150° C. The coolant advantageously comprises water and the second threshold pressure is between 1 bar and 1.5 bar. An evaporation of the cooling fluid, thus water, can take place at a temperature of between approx. 100° C. and 110° C. in this way.
Particularly advantageously, the coolant can contain glycol and/or salt. A particularly high antifreeze effect can be created by means of such an addition.
In the case of a further advantageous further development, a temporary storage of a variable volume for temporarily storing the working fluid is located in the waste-heat recovery circuit in the low pressure region.
Further important features and advantages of the invention follow from the subclaims, from the drawings, and from the corresponding figure description by means of the drawings.
It goes without saying that the above-mentioned features and the features, which will be described below, cannot only be used in the respective specified combination, but also in other combinations or alone, without leaving the scope of the present invention.
Preferred exemplary embodiments of the invention are illustrated in the drawings and will be described in more detail in the description below, whereby identical reference numerals refer to identical or similar or functionally identical components.
In each case schematically:
In schematic illustration,
A container 10, in the container interior 11 of which a divider 12 is provided, is located downstream of the condenser 9 in the low pressure region 4. Said divider 12 divides the container interior 11 in a fluid-tight manner into a first and a second sub-chamber 13a, 13b, each of a variable volume.
The already mentioned conveying device 6 is located downstream of the container 10, such that the waste-heat recovery circuit 2 is closed.
The divider 12 can be embodied as dividing membrane 19 of a flexible material. Preferably a resilient material. The divider 12, which is embodied as dividing membrane 19, can have an expanded state, which is shown in
The first sub-chamber 13a is connected to the low pressure region 4 of the waste-heat recovery circuit 2 downstream of the condenser 9 via a first pressure-relief valve 14a. The first pressure-relief valve 14a is embodied in such a way that, when a predetermined first threshold pressure p1 of the working fluid in the first pressure-relief valve 14a is exceeded, the latter switches from a closed state, in which a fluid connection for the working fluid A between the first sub-chamber and the low pressure region 4 is closed, into an open state. In the open state, the fluid connection between the first sub-chamber 13a and the low pressure region 4 is released for the flow-through with the working fluid A. If ethanol, acetone or cyclopentane is used as working fluid A, a value of approximately 10 bar can be selected as first threshold pressure p1.
The second sub-chamber 13b of the container interior 11 is filled with a coolant K, which can be guided into the condenser 9 via a fluid line 15 fluidically separately from the working fluid. The working fluid A can be condensed in the condenser 9 by thermal interaction with the coolant K. Water, which can contain glycol or a salt, can be used as coolant K. The coolant K is thereby ideally selected in such a way that as much heat as possible can be discharged in response to the evaporation of said coolant.
As can further be seen in
If water with glycol or a salt is used as coolant K, as already proposed above, between 1 bar and 1.5 bar turns out to be particularly advisable as value for the second threshold pressure p2.
In the example of
As can further be gathered from
In the case of this scenario, it is thus not required to fill the waste-heat recovery circuit 2 with further working fluid A. For this purpose, the non-return valve 18 opens in response to exceeding a predetermined, third pressure p3 of the working fluid A in the container 10 and thus also in the non-return valve 18, such that it is made possible for the working fluid A to flow back into the actual waste-heat recovery circuit 1. A temporary storage 20 of a variable volume for temporarily storing the working fluid A can be located in the low pressure region 4 of the waste-heat recovery circuit 2. An arrangement of the temporary storage 20 as shown in
The mode of the operation of the container 10 as well as of the two pressure-relief valves 14a, 14b in the waste-heat recovery system 2 is as follows:
If the fluid pressure of the working fluid A downstream of the condenser 9 rises beyond the first threshold pressure p1, the first pressure-relief valve 14a opens and the working fluid A can flow into the first part 13a of the container in the form of steam. The divider 12 in the form of the dividing membrane 19 is expanded in this way, such that the volume of the first sub-chamber 13a increases and the volume of the second sub-chamber 13b is accordingly reduced by the same amount. The coolant K located in the second sub-chamber 13b is thereby pushed via the fluid line 15 into the condenser 9, where a heat exchange with the working fluid A takes place as well. The working fluid A is cooled in this way. Due to the different threshold pressures p1, p2 of the two pressure-relief valves 141, 14b, working fluid A, which is now liquid, continues to flow into the first sub-chamber 13a and continues to displace the coolant K from the second sub-chamber 13b. The condensation of the working fluid A in the condenser 9 still ensured in this way. If the coolant K in the second pressure-relief valve 14b exceeds the second threshold pressure p2, the second pressure-relief valve 14b opens and the coolant K can escape into the surroundings 16 of the waste-heat recovery circuit 2. Damages to the waste-heat recovery circuit 2 and in particular to the condenser 9 is avoided in this way.
Due to the fact that the second pressure-relief valve 14b opens at a threshold pressure p2 in the pressure region between 1 bar and 1.5 bar, when the coolant is water, an evaporation of the water takes place at approximately 100° C. to 110° C. in the example scenario, an evaporation of the water takes place at approximately 100° C. to 110° C. when the coolant is water.
Due to the fact that evaporation enthalpy is required for evaporating the coolant, a small mass of coolant K can absorb a relative large amount of heat, so that relatively little coolant K has to be stored in the condenser 9 or in the container 10, respectively. Due to the fact that the first threshold pressure p1 of the first pressure-relief valve 14a is approximately 10 bar, it can be attained that, when using ethanol, acetone or cyclopentane as working fluid A, the latter condenses at 150° C., while, as already described, the coolant K evaporates at approximately 100° C. to 110° C. This driving temperature difference of an evaporation temperature of the coolant K and of a condensation temperature of the working fluid A leads to a better heat transfer between working fluid A and coolant K and thus to an improved efficiency of the condenser 9 and thus of the entire waste-heat recovery circuit 2.
The working fluid A and the coolant K are preferably selected in such a way and the two threshold pressures p1, p2 are determined in such a way that said temperature difference between an evaporation temperature of the coolant K and a condensation temperature of the working fluid A is at least 30° C., preferably at least 80° C. A particularly high heat transfer between the working fluid A and the coolant K can be ensured in this way, which has an advantageous effect on the efficiency of the waste-heat recovery system 1 and which in particular increases the operational safety, because an overpressure can be reduced largely without danger in the system in response to a malfunction.
The additional condenser 9b has a first fluid path 28a for the flow-through with the working fluid A, and a second fluid path 28b for the flow-through with the additional coolant. The two fluid paths 28a, 28b run fluidically separately from one another in the condenser 9b, but are thermally coupled to one another for the heat exchange between the working fluid A and the additional coolant K*. The first condenser 9a serves to cool the working fluid A in the case of failure, thus in the case of a fluid pressure of the working fluid A, which is too high, due to insufficient cooling. The additional condenser 9b also cools the working fluid A during the nominal operation of the waste-heat recovery system 1, thus when no failure is at hand.
The waste-heat recovery system 1 of
A mixing of the coolant K with the coolant K* is accepted in the case of the alternative of
In an alternative of
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2016 212 232.0 | Jul 2016 | DE | national |
This application claims priority to International Patent Application No. PCT/EP2017/066740 filed Jul. 5, 2017, and German Patent Application No. DE 10 2016 212 232.0, filed Jul. 5, 2016, the contents of both of which are hereby incorporated by reference in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/066740 | 7/5/2017 | WO | 00 |
