Waste heat recovery system of an internal combustion engine

Abstract

Waste heat recovery system of an internal combustion engine (5), wherein the waste heat recovery system comprises a working fluid circuit (1) with at least one heat exchanger (2a, 2b), an expansion machine (11), a condenser (12), a fluid pump (15) and a degassing device (21), characterized in that the degassing device (21) comprises a zeolitic and regenerable molecular sieve (22, 22a, 22b).

Description

[0001] The invention relates to a waste heat recovery system of an internal combustion engine, wherein the waste heat recovery system comprises a working fluid circuit with at least one heat exchanger, an expansion machine, a condenser, a fluid pump and a degassing device. State of the art

[0002] Such a waste heat recovery system is known from WO 2012 / 076132 A1. This waste heat recovery system is designed for an internal combustion engine and has a working fluid circuit that includes at least one heat exchanger, for example, integrated into an exhaust line of the internal combustion engine. Furthermore, the working fluid circuit includes an expansion machine, a condenser, a fluid pump, and a degassing device. The degassing device is designed as a diaphragm valve. The design of the diaphragm valve is not specified in detail.

[0003] The invention is based on the objective of providing a waste heat recovery system that is improved with regard to degassing of the working fluid. Disclosure of the invention

[0004] This problem is solved by the degassing device incorporating a zeolitic and regenerable molecular sieve. The grid structure of this molecular sieve is adjusted to match the molecular size of the media to be separated. Such a molecular sieve can be configured so that different media, depending on their molecular size, can either diffuse freely through the grid structure or be adsorbed by it. This property is utilized here by configuring the molecular sieve so that air can diffuse through its grid structure, while the working fluid from the working fluid circuit is adsorbed in the spaces between the grid cells.

[0005] In a further development of the invention, the molecular sieve is installed in a sieve housing which has at least one sieve housing inlet connected to the working fluid circuit. The working fluid is normally supplied to the sieve housing and thus to the molecular sieve through this sieve housing inlet.

[0006] In a further embodiment of the invention, the molecular sieve has a sieve housing outlet. Air that diffuses through the molecular sieve is normally discharged, for example into the environment, through this sieve housing outlet.

[0007] In a further embodiment of the invention, the molecular sieve is designed in a disc-shaped or cylindrical (pie-like) form and rotatably arranged in the sieve housing. This embodiment is suitable for the effective use of the molecular sieve because the rotational movement ensures that all circumferential areas of the molecular sieve come into successive contact with the sieve housing inlet (and preferably the opposite sieve housing outlet). Furthermore, this embodiment is suitable for simple and effective continuous regeneration of the molecular sieve by providing, for example, a regeneration inlet and a regeneration outlet, as further specified in the invention, at a distance from the sieve housing inlet and outlet. Hot steam is introduced into the molecular sieve through the regeneration inlet and discharged through the regeneration outlet.This superheated steam desorbs the molecules of the working fluid circulating in the working fluid circuit that are bound in the molecular sieve's lattice structure. A large amount of thermal energy is transferred via the molecular sieve to the adsorbed molecules, dissolving them from the lattice structure and thus regenerating the molecular sieve. Alternatively, the molecular sieve can also be regenerated using a cold process, in which regeneration occurs without requiring thermal energy for desorption.

[0008] In a further embodiment of the invention, the sieve housing has a cooling air inlet and a cooling air outlet through which cooling air is passed through the molecular sieve. The cooling of the molecular sieve thus described can take place downstream of the sieve housing inlet (and outlet) in the direction of rotation, or upstream of the sieve housing inlet (and outlet). With this rotatable arrangement of the molecular sieve in the sieve housing, the sieve housing must be sealed against the housing, for example, by one or more seals. These seals must be resistant to the various media, i.e., working fluid, superheated steam, and air, as well as to the different temperatures of the respective media.

[0009] In a further development of the invention, two molecular sieves are connected in parallel. This configuration makes it possible to use the first molecular sieve for adsorption and the second for regeneration, or vice versa. For this purpose, a switching valve is provided in a further embodiment, which is arranged in the regeneration lines connected to the regeneration inlets of both molecular sieves. Hot steam can be alternately supplied to the two molecular sieves for regeneration via this switching valve. In this embodiment, the volume of leakage between the switching valve and the environment is kept as small as possible to minimize overflow losses during the switchover between adsorption and regeneration.

[0010] In a further development of the invention, the molecular sieve is integrated into the working fluid circuit, and in a further embodiment, working fluid in a superheated vapor phase can be supplied to the working fluid circuit upstream of the molecular sieve. The supply of the working fluid in the superheated vapor phase can be controlled via a valve, in particular, it can be switched on and off. When the working fluid is supplied in the superheated vapor phase, a defined quantity of the working fluid is thus passed by the molecular sieve in the superheated vapor phase, and the molecular sieve is regenerated. When the supply of working fluid is switched off by the valve, the molecular sieve comes into contact again with cooler and more depressurized working fluid and is used for adsorption.

[0011] In a further development of the invention, the degassing device is arranged downstream of the expansion machine or the condenser. This arrangement is particularly advantageous for supplying a cooled and depressurized working fluid to the molecular sieve and thus utilizing the molecular sieve for adsorption.

[0012] In a further embodiment of the invention, the degassing device is electrically heated. With this embodiment, no regeneration agent needs to be supplied to the molecular sieve, and the regeneration of the molecular sieve is carried out exclusively by electrical heating.

[0013] Further advantageous embodiments of the invention can be found in the drawing description, in which exemplary embodiments shown in the figures are described in more detail.

[0014] They show: Fig. 1 a circuit diagram of a waste heat recovery system designed according to the invention with a working fluid circuit, Fig. 2 a detailed view of a disc-shaped molecular sieve installed in a corresponding sieve housing, Fig. 3 a detailed view in which two parallel molecular sieves are connected in the working fluid circuit and Fig. 4 a detailed view of a molecular sieve connected in a working fluid circuit, wherein working fluid can be supplied to the working fluid circuit upstream of the molecular sieve in a hot steam phase.

[0015] The in Fig. A schematically represented waste heat recovery system comprises a working fluid circuit 1 with a first heat exchanger 2a and a second heat exchanger 2b. The heat exchangers 2a and 2b are designed as evaporators and function as such, and are adapted to an internal combustion engine 5 for the recovery of waste heat generated during the operation of the internal combustion engine 5. The first heat exchanger 2a is fed by an exhaust gas stream 4 from the internal combustion engine 5, which is routed through an exhaust gas line 3 of the engine and forms a waste heat stream. In addition to the first heat exchanger 2a, the second heat exchanger 2b is installed in a line in the form of an exhaust gas recirculation line 6 or another heat transfer line. A portion of the exhaust gas is extracted from the exhaust gas stream 4 via the exhaust gas recirculation line 6 and fed, in a controlled manner via an exhaust gas recirculation valve 7, to an intake system 8 of the internal combustion engine 5.The intake system 8 can also be designed as a charge air duct system. The two heat exchangers 2a, 2b can optionally be bypassed via heat transfer bypass lines (not shown) under certain operating conditions of the internal combustion engine 5 of a vehicle in which the engine is installed. Furthermore, only a single heat exchanger can be provided, which is preferably carried by the exhaust gas flow 4.

[0016] During operation, the internal combustion engine 5 is supplied with fuel and combustion air, which combust in the combustion chambers of the engine 5, generating work and producing hot exhaust gas, which forms the exhaust gas stream 4. The exhaust gas stream 4 is ultimately discharged into the environment via the exhaust pipe 3, from which the exhaust gas recirculation pipe 6 also branches off. Exhaust silencers 10 and exhaust aftertreatment devices 9, such as a catalyst and / or a filter, can be installed in the exhaust pipe 3 upstream and / or downstream of the first heat exchanger 2a. The internal combustion engine 5 is, for example, a compression-ignition engine that runs on diesel fuel. The diesel fuel is injected into the combustion chambers, for example, by means of a common-rail injection system.The internal combustion engine can also be a spark-ignited, gasoline-powered internal combustion engine, which may also have a common-rail injection system.

[0017] The first heat exchanger 2a and the second heat exchanger 2b are, as previously explained, part of the working fluid circuit 1, which, in addition to the heat exchangers 2a and 2b, includes an expansion machine 11, a condenser 12, optionally a condensate pump 13, an expansion tank 14, a fluid pump 15, and a degassing device 21, which will be described below. The condensate pump 13 is not strictly necessary and can therefore be omitted. A distributor valve 16, for example a 3 / 2-way distributor valve, is arranged on the outlet side of the fluid pump 15, with its outlets opening into two fluid branches 20a and 20b of the working fluid circuit 1. The first working fluid branch 20a is connected to the first heat exchanger 2a, and the second fluid branch is connected to the second heat exchanger 2b. If only one heat exchanger is provided, the distribution valve 16 and the second fluid branch are of course omitted.

[0018] The total quantity of working fluid conveyed through the working fluid circuit 1 (total volume flow rate) Q = Q1 + Q2 can be adjusted, for example, by changing the speed of the electrically driven vane pump 16. The distribution valve 16 is adjustable so that, with a constant or adjustable total flow rate, the flow rate distribution to the first heat exchanger 2a (volume flow rate Q1) and to the second heat exchanger 2b (volume flow rate Q2) can be set to increase and decrease between 0% and 100%.

[0019] The fluid pump 15 and the distributor valve 16 can be designed as a single unit or as separate components. The distributor valve 16, designed as a 3 / 2-way distributor valve, can also be replaced by separate valves within the scope of the invention.

[0020] The expansion machine 11 can, for example, be a piston engine or a turbine. In the case of a turbine, a reduction gearbox is usually installed downstream to reduce the high turbine speeds and adapt them to the speeds of a downstream machine or other consumer.

[0021] During operation of the waste heat recovery system, a fluid suitable for a Rankine cycle is pressurized by the fluid pump 15 and fed to the heat exchangers 2a and 2b. The fluid is heated in the heat exchangers 2a and 2b and converted into a vaporous state under high pressure. The vapor thus generated is fed to the expansion machine 11 and drives it by expanding the working fluid. To allow the working fluid circuit 1 to bypass the expansion machine 11, a bypass line 17 with a bypass valve 18 can be provided, allowing the expansion machine 11 to be bypassed.

[0022] The working fluid supplied to the expansion machine 11 expands within it, performing mechanical shaft work that is carried away via an output shaft 19. The expanded, cooled vapor is then condensed in the condenser 12 and ultimately returned to the fluid pump 15. The expansion tank 14 is integrated into the connecting line between the condenser 12 and the fluid pump 15. Furthermore, a degassing device 21, comprising a molecular sieve, is installed in or connected to the working fluid circuit 1 between the expansion machine 11 and the condenser 12. The degassing device 21, described in detail and in various embodiments in the following figures, can also be installed elsewhere in the working fluid circuit 1, for example, downstream of the condenser 12.

[0023] In addition to the components described above, any number of other components, in particular sensors for determining temperatures and pressures in different sections of the working fluid circuit 1, may be present.

[0024] Fig. Figure 2 shows a first embodiment of the in Fig. 1. Degassing device 21, shown only schematically. The degassing device 21 comprises a zeolitic molecular sieve 22, which is installed in a sieve housing 23. In this embodiment, the molecular sieve 22 is disc-shaped, or more precisely, cylindrical, and rotatably arranged in the sieve housing 23, which is shown only schematically. The sieve housing 23 has a sieve housing inlet 24 and, on the opposite side of the molecular sieve 22, a sieve housing outlet 25. The sieve housing inlet 24 is, for example, as shown in Fig. 1 is connected to the working fluid circuit 1 via a branch line. The working fluid circulating in the working fluid circuit 1, along with any air it contains, is fed to the molecular sieve 22 through the sieve housing inlet 24. The air can diffuse through the grid structure of the molecular sieve 22 and is discharged into the environment on the opposite side through the sieve housing outlet 25. The working fluid, on the other hand, is adsorbed in the spaces of the grid structure of the molecular sieve 22.

[0025] For desorption, i.e., for the regeneration of the molecular sieve 22, thermal energy is required to desorb the molecules of the working fluid bound in the lattice structure of the zeolitic molecular sieve 22. For this purpose, hot steam, preferably taken from the working fluid circuit 1 downstream of the first heat exchanger 2a, is supplied via a regeneration inlet 26. The hot steam flows through the molecular sieve 22 and exits on the opposite side through a regeneration outlet 27, which, like the regeneration inlet 26, is embedded in the sieve housing 23. This releases the molecules of the working fluid adsorbed in the molecular sieve 22 from the lattice structure, thus regenerating the molecular sieve 22. The regeneration outlet 27 then returns to the working fluid circuit 1.

[0026] Additionally, cooling air is passed through the molecular sieve 22. Preferably, the cooling air is passed through the molecular sieve 22 before regeneration, but alternatively or additionally, it can also be passed through the molecular sieve 22 after regeneration. For introducing the cooling air, the sieve housing 23 has a cooling air inlet 28 and for discharging the cooling air, a cooling air outlet 29, wherein the cooling air inlet 28 is connected to any device for supplying the cooling air, and the cooling air outlet 29 can, for example, open into the sieve housing outlet 25.

[0027] All inlets and outlets are designed in conjunction with the sieve housing 23 such that the molecular sieve 22 is subjected to or flowed through by the different media in a pie-slice shape from a central axis of rotation to a circumferential section.

[0028] A seal is provided to seal the rotating molecular sieve 22 against the opposite sides of the sieve housing 23. This seal, operating continuously, seals the rotating disc in the form of the molecular sieve 22 against the sieve housing 23. This seal is designed to withstand both the different media and the different temperatures of the respective media.

[0029] In the embodiment according to Fig. The degassing device 21 comprises two molecular sieves 22a, 22b, each installed in a sieve housing 23a, 23b. The sieve housings 23a, 23b are preferably integrated directly into the working fluid circuit 1 or a channel wall 34 of the working fluid circuit 1, or alternatively, the sieve housings 23a, 23b can also be part of the channel wall 34. Within the fluid channel 35 bounded by the channel wall 34, the sieve housings 23a, 23b have sieve housing inlets 24a, 24b, which can, for example, extend over almost the entire length of the respective molecular sieve 22a, 22b. It is also possible to arrange a large number of individual sieve housing accesses 24a, 24b to the individual molecular sieves 22a, 22b side by side in the sieve housing 23a, 23b.Outside the fluid channel 35, a regeneration access point 26a, 26b is provided in the channel wall 34 or the sieve housings 23a, 23b for each of the two molecular sieves 22a, 22b. This access point is connected to a regeneration line 31a, 31b. The regeneration lines 31a, 31b are connected to a changeover valve 30, which is further connected to a superheated steam line 36 and a discharge line 37 to the environment. Depending on its switching position, the changeover valve 30 alternately supplies superheated steam to either molecular sieve 22a or 22b for regeneration of the respective molecular sieve 22a, 22b. In the switching state shown, superheated steam is supplied to molecular sieve 22b, and the molecular sieve 22b is regenerated by discharge of the superheated steam via the sieve housing access point 24b into the fluid channel 35. In the molecular sieve 22a, the air from the working fluid guided in the fluid channel 35 is adsorbed and then discharged via the sieve housing outlet 25 (according to . Fig. 2) The regeneration access 26a is discharged through the regeneration line 31a into the drainage line 37.

[0030] The in Fig. The embodiment shown in section 4 is fundamentally similar to that of the Fig. 3, where here only one molecular sieve 22a is installed in a sieve housing 23a. In this embodiment as well, the sieve housing 23a can be part of the channel wall 34. As in the embodiment according to Fig. 3. Here, too, a sieve housing inlet 24a is present, which opens into the fluid channel 35. Outside the fluid channel 35, a regeneration outlet 27a is present, which opens directly or via a discharge line 37 into the environment. During adsorption, the molecular sieve 22a functions as described in Figure 3. Fig. 3 and the regeneration outlet 27a corresponds to the sieve housing outlet 25 according to Fig. 2. For the regeneration of the molecular sieve 22a according to Fig. 4. Superheated steam from a superheated steam line 36 is introduced into the fluid channel 35 upstream of the molecular sieve 22a via a valve 32, the superheated steam being directed past the sieve housing inlet 24a by a guide device 33. This regenerates the molecular sieve 22a by means of superheated steam supplied via the sieve housing inlet 24a, which then functions as a regeneration inlet 26a, and discharged via the sieve housing outlet 25.

[0031] Another embodiment provides that an electric heating device is integrated into the sieve housing or directly into the molecular sieve. When the heating device is energized, the molecular sieve is regenerated. In this embodiment, the molecular sieve can be regenerated as in the exemplary embodiment shown. Fig. 4 be designed and arranged, but then the hot steam line 36, the valve 32 and the guide device 33 are omitted.

[0032] Finally, it should be noted that any previously described embodiments or partial features of the various embodiments can be combined with each other.

Claims

[1] Waste heat recovery system of an internal combustion engine (5), wherein the waste heat recovery system comprises a working fluid circuit (1) with at least one heat exchanger (2a, 2b), an expansion machine (11), a condenser (12), a fluid pump (15) and a degassing device (21), characterized by , that the degassing device (21) comprises a zeolitic and regenerable molecular sieve (22, 22a, 22b). [2] Waste heat recovery system according to claim 1, characterized by , that the molecular sieve (22, 22a, 22b) is installed in a sieve housing (23, 23a, 23b) which has at least one sieve housing access (24, 24a, 24b) connected to the working fluid circuit (1). [3] Waste heat recovery system according to claim 1 or 2, characterized by , that the molecular sieve (22, 22a, 22b) is installed in a sieve housing (23, 23a, 23b) which has at least one sieve housing outlet (25). [4] Waste heat recovery system according to one of the preceding claims 2 or 3, characterized by , that the molecular sieve (22) is disc-shaped or cylindrical and is rotatably arranged in the sieve housing (23). [5] Waste heat recovery system according to any one of the preceding claims 2 to 4, characterized by , that the sieve housing (23, 23a, 23b) has a regeneration access (26, 26a, 26b). [6] Waste heat recovery system according to any one of the preceding claims 2 to 5, characterized by , that the sieve housing (23, 23a, 23b) has a regeneration outlet (27, 27a). [7] Waste heat recovery system according to any one of the preceding claims 2 to 6, characterized by , that the sieve housing (23, 23a, 23b) has a cooling air inlet (28) and a cooling air outlet (29). [8] Waste heat recovery system according to one of the preceding claims, characterized by that two molecular sieves (22a, 22b) are connected in parallel. [9] Waste heat recovery system according to claim 8, characterized by , that a switching valve (30) is arranged in regeneration lines (31a, 31b) connected to regeneration inlets (26a, 26b). [10] Waste heat recovery system according to one of the preceding claims, characterized by , that the molecular sieve (22a, 22b) is integrated into the working fluid circuit (1). [11] Waste heat recovery system according to claim 10, characterized by , that working fluid is supplied in a hot steam phase to the working fluid circuit (1) upstream of the molecular sieve (22a, 22b). [12] Waste heat recovery system according to one of the preceding claims, characterized by that the degassing device (21) is electrically heated.

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