WO2018103909A1

WO2018103909A1 - Waste heat recovery system

Info

Publication number: WO2018103909A1
Application number: PCT/EP2017/075163
Authority: WO
Inventors: Bernhard ZICKGRAF
Original assignee: Robert Bosch Gmbh
Priority date: 2016-12-06
Filing date: 2017-10-04
Publication date: 2018-06-14
Also published as: DE102016224284A1

Abstract

The invention relates to a waste heat recovery system (100) comprising a circuit (100a) which conducts a working medium. In the flow direction of the working medium, the circuit (100a) comprises a fluid feed pump (102), an evaporator (103), an expansion machine (104), and a condenser (105). A bubble separator (90) is arranged in the circuit (100a) downstream of the condenser (105) for separating gas bubbles out of the working medium. A collector volume (91) is formed in the bubble separator (90). The bubble separator (90) has a separator housing (90a), and an inlet cross-section (3a) and an outlet cross-section (3b) for attaching to the circuit (100a) are formed in the separator housing (90a). The inlet cross-section (3a) and the outlet cross-section (3b) are arranged below the collector volume (91) with respect to the gravitational force (G).

Description

description

title

Waste heat recovery system

The present invention relates to a vent optimized

Waste heat recovery system for an internal combustion engine.

State of the art

Waste heat recovery systems for thermal energy recovery from the exhaust gases of an internal combustion engine are known from the prior art, for example from DE 2014 10 018 987 A1.

The known waste heat recovery system has a leading a working fluid circuit. The circuit includes in the flow direction of the

Working fluid a feed fluid pump, an evaporator, a

Expansion machine and a condenser. In the circuit is still a membrane expansion tank or a surge tank for

Volume compensation of the working medium arranged. By doing

Expansion tank is formed a fluid space for receiving the working medium.

Thereby, the total volume of the working medium can be adjusted within the cycle of different temperature levels. However, the volume change is minimized by the use of a membrane. Furthermore, the membrane is subject to high mechanical stresses, in particular to the stresses of the edges. Excretion of the gas bubbles from the circulation is not possible through the membrane.

Disclosure of the invention

The waste heat recovery system according to the invention used

in contrast, a bubble trap, so that large volume changes can be compensated by penetrated gas or air infiltration and the waste heat recovery system can be operated efficiently. The waste heat recovery system has a leading a working medium

Cycle up. The circuit comprises, in the direction of flow of the working medium, a feed fluid pump, an evaporator, an expansion machine and a condenser. In the circuit is a downstream of the capacitor

Bubble separator arranged for the separation of gas bubbles from the working medium. In the bubble trap, a header volume is formed. Of the

Bubble separator has a separator housing, wherein in the

Separator housing an inlet cross-section and an outlet cross-section are designed for connection to the circuit. The Einstrittsquerschnitt and the outlet cross-section are with respect to a gravitational force below the

Collector volume arranged.

The present invention thereby separates the entrained by the liquid phase of the working medium gaseous components - ie the gas bubbles - from the liquid stream. For this purpose, it is advantageous if the feed fluid pump conveys the working fluid with a sufficiently high mass flow. The

Separation or separation of the gas bubbles from the working medium takes place by taking advantage of the difference in density of the gas bubbles to the liquid working medium within the fluid-gas mixture. The gas bubbles thus rise in the bubble separator against the gravitational direction up to the collector volume.

Preferably, the rising of the bubbles is assisted by a local reduction of the flow velocity by increasing the flow cross section of the separator housing with respect to the inlet cross section.

Advantageously, the collecting region or the separation region of the gas bubbles is designed as a discharge labyrinth so that the renewed entrainment of the gas bubbles is prevented by the fluid flow of the working medium emerging from the outlet cross section of the bubble separator. The

Exit Labyrinth can be additional internals such as Abscheidegitter or Have perforated plates. As a result, the entrainment of the gas bubbles can be effectively suppressed even at very high flow velocities.

Deposited quantities of gas leave the bubble separator through a gas outlet opening in the separator housing. The separator housing can also be designed in several parts. Preferably, the gas outlet opening is thereby attached in the upper region of the bubble trap, in particular with respect to the gravitational force at the uppermost point of the bubble trap. The accumulator volume is arranged below the gas outlet opening.

Preferably, the accumulator volume is separated from the flow cross section of the separator housing. The existence of a separate

Receiver volume without direct contact with the flowing working medium effectively suppresses re-dissolution of already separated gas bubbles into the working medium flowing to the outlet cross-section because there is no direct contact of the working medium flow with the gas volume and no large flowing fluid surfaces on the gas volume. Thus, the separated gas volume no longer directly from the

Waste heat recovery system to be removed. Rather, it can wait for favorable system conditions and then the gas volume can be removed quickly and thoroughly.

For this purpose, in advantageous developments in the gas outlet opening or in a vent line connected thereto

Abwärm recovery system disposed a valve. Preferably that is

Switchable valve, so that the waste heat recovery system can be actively vented. Alternatively, however, the valve may be designed as a check valve that opens at a preset pressure. In advantageous embodiments, at least one is in the separator housing

Level sensor for measuring the level of a fluid level of the

Working medium arranged. Preferably, the at least one

Level sensor arranged in the collector volume. The level sensor indicates that there is a need for ventilation and preferably even controls the venting processes. Until the working medium enters the feed fluid pump, the

Gas bubbles are preferably deposited from the working fluid, so that the bubble preferably between the condenser and the

Feed fluid pump is arranged. This is the efficiency of

Feed fluid pump optimized.

For effective separation of gas bubbles on the density difference of the gas bubbles to the liquid working medium must be sufficiently condensed working fluid. The described bubble separator is therefore typically in the flow direction before the feed fluid pump and after

Condenser integrated in the circuit. To assist in the rising of the separated gas volume, the fluid flow of the working medium is preferably horizontal and the outlet direction of the gas volume from the gas separator is vertical.

The following developments of the invention relate to the positioning of the bubble trap within the waste heat recovery system, in particular with respect to the gravitational force. The trainings take advantage of the fact that the

Working medium in the circuit depending on the phase state with significantly

moved at different flow velocities. In the low-density vapor phase very high flow rates occur, rather low in the liquid phase. In part, these effects are influenced by adapted line cross sections of the circuit, but the differences are always considerable. An arrangement of those system components containing predominantly vaporous working medium, with respect to the gravitational force upper portion of the waste heat recovery system leads to an effective entrainment of existing air or existing gas due to the high vapor velocities, which at standstill

Waste heat recovery system has accumulated above. During operation of the waste heat recovery system, therefore, almost none can

gaseous components remain in certain positions in the circulation. Furthermore, the developments of the invention are based on the effect that the

Condenser in the normal operation of the waste heat recovery system always too Contains a certain part of condensed working fluid. The amount of liquid working fluid is operating point dependent and can by the

Control panel be influenced. To protect the arranged after the condenser feed fluid pump capacitors are structurally usually designed to prevent a passage of vaporous working fluid as possible, even at high thermal loads in the waste heat recovery system.

The area of the liquid working medium in the condenser - namely the fluid volume - is located in the rear area of the condenser near its outlet below the steam area of the condenser, as seen in the flow direction. The front condenser area is vaporous or filled with a vapor / liquid phase mixture. The retention of the vapor phase in the condenser by a certain liquid working medium volume in the

Condenser also applies to the air in the waste heat recovery system. During operation, the vapor drives

Working medium all gaseous impurities before it into the condenser. There the ingredients hit the barrier

Fluid volume. Depending on the amount of gas and amount of fluid volume, the gas is completely retained, or gaseous components dive with the

Flow of the working fluid against its buoyancy force down through the fluid barrier and leave the condenser in the direction of the feed fluid pump.

By a controlled change of the fluid volume can its

Locking effect influenced and the passage of existing air or existing

Gas controlled or even brought about. The passage can thus be actively controlled and placed in favorable operating phases, for example in the warm-up phase. On the other hand, the passage can also be effectively prevented.

The flushing of the steam-containing components and piping parts of the circuit during operation is supported by the fact that the capacitor in the

Abwärm recovery system is rather high and the gaseous components must not be promoted against their buoyancy down. The entrainment of the gas is also avoided by avoiding vertically downwardly oriented steam lines supported up to the condenser.

The removal of the gaseous components from the working medium is preferably carried out directly after the capacitor by the installation of the

Bubble trap. One of the main tasks of the bubble trap is to separate the separated components of the gas bubbles as possible from the fluid flow of the working medium to a return to the fluid flow

Effectively suppress, as already described above.

Typically, this is directly above the bubble trap the

Collector volume arranged, which receives the separated gas bubbles.

The level sensors in the collector volume detect separated air or separated gas and signal the system controller one

Ventilation requirements. Depending on the size of the collector volume

cached gas quantities are stored without having to be vented immediately. This can be waited for favorable for the system ventilation operating conditions of the waste heat recovery system.

In the presence of favorable operating conditions, the valve is opened and the gas contained in the collector volume escapes.

The prerequisite for the escape of the gas from the accumulator volume is a driving pressure difference from the accumulator volume in the environment or in the downstream tank volume, as well as a subsequent flow of working fluid from the circulation in the accumulator volume. This nachlaufendes working medium can come from both the liquid phase filled with the rear condenser area or from a collecting container, which is in the vicinity of the

Bubble trap connected to the waste heat recovery system, preferably upstream of the bubble trap is coupled to the circuit.

A deep arrangement of the bubble trap with respect to the condenser or with respect to the collecting container is advantageous for the

Waste heat recovery system and facilitates the venting

necessary fluid flow due to the additional hydrostatic pressure in the

Working medium. This is the collector volume with respect to the gravitational force arranged below the volume of fluid formed in the condenser. Preferably, the volume of the collector with respect to the gravitational force is also below the collecting tank or below the tank volume of the tank

Collecting container arranged.

An arranged in the waste heat recovery system sump offers the possibility of the deposited gaseous components in the

To direct collection container and thus to avoid a direct ventilation of the gas into the environment. A high arrangement of the collecting container in the system structure is therefore advantageous both in terms of flowing working medium from the tank volume in the circuit and with respect to gases to be received.

Accordingly, in advantageous developments, a vent line fluidly connects the bubble trap with the sump.

Furthermore, a connecting line preferably connects the collecting container fluidically to the circuit. Preferably, the connecting line opens back into the circuit downstream of the bubble trap.

Thus, in advantageous embodiments, a fluid path is arranged parallel to the circuit: the fluid path branches off at the bubble trap from the circuit and runs in the flow direction from the bubble trap via the vent line to the reservoir and on through the

Connecting line back to the circuit.

Brief description of the drawings

Hereinafter, embodiments of the invention below

With reference to the accompanying drawings described in more detail. It shows:

Fig. 1 shows schematically a waste heat recovery system a

Internal combustion engine, wherein only the essential areas are shown. Fig. 2 shows schematically a vent optimized

A waste heat recovery system with a bubble trap, wherein only the essential areas are shown. 3 shows a section through a bubble separator of a

Waste heat recovery system, with only the essential areas are shown.

Embodiments of the invention

Fig.l shows a waste heat recovery system 100 of an internal combustion engine 110. The internal combustion engine 110 is supplied with oxygen via an air supply 112; the exhaust gas discharged after the combustion process is discharged from the engine 110 through an exhaust pipe 111.

The waste heat recovery system 100 comprises a working medium leading circuit 100a, which includes a feed fluid pump 102, an evaporator 103, an expansion machine 104 and a condenser 105 in the flow direction of the working medium. The working medium can be fed as needed via a branch line from a sump 101 and a valve unit 101a in the circuit 100a. The collection container 101 may alternatively be incorporated in the circuit 100a, or even omitted, if a hermetically sealed waste heat recovery system 100 is present.

The evaporator 103 is connected to the exhaust pipe 111 of the internal combustion engine 110, thus uses the heat energy of the exhaust gas of the

Internal combustion engine 110. According to the invention, a bubble separator 90 is arranged in the circuit 100a or connected to the circuit 100a, in the embodiment of FIG. 1 between the feed fluid pump 102 and the

Evaporator 103. The bladder 90 is intended here with respect to the

Gravitational force can be arranged under the capacitor 105-

The operation of the waste heat recovery system 100 is as follows: Liquid working medium is conveyed by the feed fluid pump 102, possibly from the collecting container 101, into the evaporator 103 and vaporized there by the heat energy of the exhaust gas of the internal combustion engine 110. The vaporized working medium is then in the expansion machine 104 under release of mechanical energy, for example, to a non-illustrated

Generator or to a not shown gear, relaxed. Subsequently, the working medium in the condenser 105 is liquefied again and in the

Sump 101 returned or fed to the feed fluid pump 102. The volume ratios of the liquid and the gaseous phase of the

Working medium depend inter alia on the current heat supply in the exhaust pipe 111 and thus from the operating point of the internal combustion engine 110, which can change very dynamically depending on the driving profile. An increased

Heat input in waste heat recovery systems 100 of constant design volume results in a pressure increase of the working fluid. In so-called pressure-balanced systems, the volume increase of the working medium is compensated by the bubble separator 90. Of the

Bubble trap 90 receives working medium in its liquid or liquid-gas phase, thereby preventing a pressure increase in the system. As the heat input decreases, the system returns to the working medium and a drop in system pressure below ambient pressure is prevented.

The bubble trap 90 can take over the function of the collecting container 101 with a corresponding size. In this case, the

Bubble separator 90 mounted at the junction of the valve unit 101a, in different versions with or without valve unit 101a. Independently of this, the bubble separator 90 can also be arranged in further alternative embodiments on the low-pressure side of the waste heat recovery system 100, that is to say upstream of the feed fluid pump 102.

For a low-maintenance operation of the

Waste heat recovery system 100 over typical service intervals of mobile applications - for example, for commercial vehicles 1 year - the waste heat recovery system 100 via the bubble trap 90 no working fluid or only a negligible amount of working fluid is lost. 2 schematically shows the arrangement of the components of the waste heat recovery system 100 with respect to the gravitational force G. The working medium feed fluid pump 102 is typically placed deep. The subsequent evaporator 103 can also be arranged deep. The high-pressure steam line from the evaporator 103 as part of the circuit 100a leads to the highly positioned expansion machine 104. The condenser 105, which is arranged downstream in the flow direction FLOW, should be arranged similarly high as the expansion machine 104; a slightly deeper arrangement with a slight tube slope is also possible ,

An arrangement of the bubble trap 90 in the fluid line of the circuit 100a from the condenser 105 to the feed fluid pump 102 is as low as possible. An attached accumulator volume 91 of the bubble trap 90 must always be arranged below a fluid volume 105a of the condenser 105 so that the distance a from the fluid volume 105a to the accumulator volume 91 in the direction of the gravitational force G runs.

The accumulator volume 91 should preferably also be lower than that

Tank volume 101b of an optional existing collection container 101, so that the further distance b from the tank volume 101b to the accumulator volume 91 in the direction of the gravitational force G extends.

The necessary for the refilling of the working medium connecting line 106 from the collecting container 101 to the circuit 100 a is preferably disposed between the bubble trap 90 and the feed fluid pump 102.

Connecting line is preferably designed with a continuous slope as possible and with the shortest possible length. A vent line 92 from the accumulator volume 91 to the tank volume 101b is preferably likewise designed to be as short as possible and continuously ascending.

3 schematically shows the structure of the bubble trap 90 in a preferred embodiment.

In the typically with respect to the gravitational force G arranged horizontally Bubble trap 90 enters from right through inlet cross section 3a

Fluid flow with gas bubbles 2 from the pipeline of the circuit 100a. As a result of the cross-sectional enlargement of the separator housing 90a compared with the inlet cross-section 3a, the fluid flow of the working medium in the bubble trap 90 slows down and gas bubbles contained in the working medium can rise upwards as a result.

Preferably, a trained in the separator housing 90a difficult

Exit labyrinth 4 the separated gas bubbles re-entry into the outlet section 3b of the circuit 100a with high flow velocity. The outlet labyrinth 4 is arranged so that the gas bubbles rise against the gravitational force G in the separator housing 90a upwards and thereby kept away from the outlet section 3b, while the liquid working fluid continues to flow in the direction of the outlet section 3b. Gas located in the upper area of the bubble trap 90 passes through one

Connecting channel 5 directly into a separate air collector housing 6 with the accumulator volume 91 formed therein. The gas then collects in the upper portion of the accumulator volume 91 and a fluid level 7 decreases as the total volume below has decreased due to the deposition of the gas. In alternative embodiments, the

Separator housing 90a and the air collector housing 6 may also be integrally formed.

Arranged on the air collector housing 6 or in the collector volume 91

Level sensors 9 detect the fluid level - ie the level of

Fluid level 7 - and report a parent control unit

Ventilation requirements. The venting of the waste heat recovery system 100 can by a switchable valve 10 in a gas outlet opening 8 of the

Air collector housing 6 are controlled. Alternatively, the valve 10 may also be designed as a check valve, the starting from a certain pressure of the

Gas volume upstream of the valve 10 opens in the gas outlet opening.

Advantageously, the gas outlet opening 8 is formed with respect to the gravitational force G at the highest point of the air collector housing 6. Preferably, the gas outlet opening 8 opens into the vent line 92 to Collective container 101. Alternatively, however, the vent line 92, for example, also open into the environment or into the atmosphere.

Claims

claims

A waste heat recovery system (100) having a working medium carrying circuit (100a), the circuit (100a) comprising a feed fluid pump (102), an evaporator (103), an expansion engine (104), and a condenser (105) in the flow direction of the working fluid in which a bubble separator (90) for separating gas bubbles from the working medium is arranged in the circuit (100a) downstream of the condenser (105), an accumulator volume (91) being formed in the bubble separator (90),

characterized in that

the bubble separator (90) has a separator housing (90a), wherein in the separator housing (90a) has an inlet cross-section (3a) and a

Outlet cross-section (3b) for connection to the circuit (100a) are formed, wherein the Einstrittsquerschnitt (3a) and the

Outlet cross-section (3b) with respect to a gravitational force (G) below the collector volume (91) are arranged.

2. waste heat recovery system (100) according to claim 1

characterized in that

the flow cross section through the separator housing (90a) is greater than through the inlet cross section (3a).

3. waste heat recovery system (100) according to claim 1 or 2

characterized in that

in the bubble separator (90) an outlet labyrinth (4) for the separation of gas bubbles (2) from the circuit (100a) is arranged.

4. waste heat recovery system (100) according to one of claims 1 to 3, characterized in that

a gas outlet opening (8) is formed on the separator housing (90a), wherein preferably the gas outlet opening (8) with respect to the gravitational force (G) at the uppermost point of the separator housing

(90a) is arranged.

5. waste heat recovery system (100) according to claim 4

characterized in that

the gas outlet opening (8) in a vent line (92) of the

Abwärmückgewinnungssystems (100) opens.

6. waste heat recovery system (100) according to claim 4 or 5

characterized in that

in the gas outlet opening (8) or in the vent line (92), a valve (10) is arranged, wherein the valve (10) is preferably switchable.

7. waste heat recovery system (100) according to one of claims 1 to 6, characterized in that

in the separator housing (90a) at least one level sensor (9) for measuring the level of a fluid level (7) of the working medium is arranged.

8. waste heat recovery system (100) according to one of claims 1 to 7, characterized in that

the bubble trap (90) is disposed between the condenser (105) and the feed fluid pump (102).

9. waste heat recovery system (100) according to one of claims 1 to 8, characterized in that

the accumulator volume (91) is arranged with respect to the gravitational force (G) below a fluid volume (105a) formed in the condenser (105).

10. waste heat recovery system (100) according to one of claims 1 to 9, characterized in that

the waste heat recovery system (100) comprises a sump (101) for collecting the working medium.

11. A waste heat recovery system (100) according to claim 10

characterized in that the bubble trap (90) is disposed below the header tank (101) with respect to the gravitational force (G).

12. waste heat recovery system (100) according to any one of claims 10 or 11th

characterized in that

a vent line (92) fluidly connects the bubble trap (90) to the header tank (101).

13. A waste heat recovery system (100) according to claim 12

characterized in that

a connecting line (106) fluidly connects the collecting container (101) to the circuit (100a).

14. A waste heat recovery system (100) according to claim 13

characterized in that

a fluid path is arranged parallel to the circuit (100a), wherein the fluid path at the bubble separator (90) branches off from the circuit (100a), the fluid path in the flow direction of the

Bubble trap (90) via the vent line (92) to the

Sump (101) and further via the connecting line (106) back to the circuit (100a) extends.