DE102016220822A1 - Bubble-free low-pressure pump for liquefied gas - Google Patents

Abstract

Low-pressure pump (2) for providing bubble-free liquefied gas (1), comprising a compressor unit (4) connectable to a storage container (3) for the gas (1) for increasing the pressure of the gas (1), the compressor unit (4) having a pressure-tight outlet side Buffer container (5) is arranged, wherein the buffer container (5) in the region (52), in the liquid phase (la) of the gas (1) contained gas bubbles (1c) due to their buoyancy (53) in this liquid phase ( la), having a valve assembly (54) closable outlet (55), wherein the valve assembly (54) is adapted to close at least automatically when the level (1d) of the liquid phase (1a) of the gas (1 ) in the buffer tank (5) exceeds a predetermined height (56). An associated system (9) for supplying blister-free liquefied gas (1) at high pressure and injecting or injecting system (10) for liquefied natural gas (1) combustion engine (8).

Description

The present invention relates to a low-pressure pump for liquefied gas, in particular for liquefied natural gas (LNG) for use as a motor fuel.

State of the art

For commercial vehicles, diesel engines were converted to gasoline engine operation in the past. There was a removal of the complete diesel system, a reduction of the compression ratio and the installation of Otto engine components such as ignition system and throttle valve (monovalent concept) and the gas system.

Since the originally intended for diesel operation engines were not designed for the increased heat load of a stoichiometric gasoline engine operation, resorted to a lean or lean burn combustion. It was only with the aim of EURO VI that a major transition to stoichiometric operation took place, whereby the heat load was absorbed by design measures or by EGR.

Especially in long-distance traffic, concepts are now being sought to make up for the loss of efficiency as well as performance and torque disadvantages compared to diesel operation.

The most promising potential, however with a complex system environment, is assigned to diffusion combustion with gas valves for high-pressure direct injection. Expected benefits include high diesel engine efficiency, short dynamic response times and higher low end torque compared to other gas engines, and robustness to low methane ratings (low tendency to knock despite variance in natural gas quality), reduction of particulate emissions compared to diesel engines, and reduced CH ₄ emissions towards homogeneous mixture formation by reduced gas entry into the dead volume of the combustion chamber.

In the case of diffusion combustion, gas injection takes place directly in the combustion, as in the case of the diesel engine, within a small range of crank angles. The EP 1 546 548 Bl, the US 2004 011 323 A1 as well as the WO 2014 037 068 A1 give an overview of the relevant general state of the art.

For the diffusion combustion, gas pressures well above the combustion pressure are required, from which the term High Pressure Direct Injection (HP-DI) is derived. The combustion can be initiated, for example, by a preceding diesel injection.

To provide the high gas pressures reveal the US 2014 230 458 A1 , the US 2014 290 280 A1 as well as the WO 2016 112 462 A1 different concepts. In each case, the high pressure pump is preceded by a prefeed pump, which promotes the liquid phase of the gaseous fuel at a pressure of a few bar to several ten bar in the high-pressure pump.

Disclosure of the invention

In the context of the invention, a low-pressure pump has been developed for the provision of bubble-free liquefied gas. This low-pressure pump comprises a compressor unit which can be connected to a storage container for the gas for increasing the pressure of the gas. This compressor unit can advantageously have a variable working volume, wherein the liquid phase of the gas can be sucked into the working volume by increasing the working volume and can be expelled from the working volume by reducing the working volume. The compressor unit may for example be a piston pump, but also a rotating pump. Also suitable, for example, gear pumps.

According to the invention, a pressure-tight buffer container is arranged on the output side of the compressor unit. The buffer container has, in the region, the gas bubbles contained in the liquid phase of the gas, due to their buoyancy in this liquid phase, a closable with a valve assembly outlet. In this case, the valve arrangement is designed to close automatically at least when the level of the liquid phase of the gas in the buffer tank exceeds a predetermined level.

It has been found that the buffer container substantially completely compensates for gas bubble formation, to which a low pressure pump in principle tends. The liquid phase, which collects in the bottom of the buffer container in relation to the gravitational field of the earth, is free of bubbles and can therefore be further compressed, for example, by a high-pressure pump connected downstream of the buffer container with particularly high efficiency.

Specially liquefied natural gas used as motor fuel is typically stored in cryogenic reservoirs at a temperature and pressure which in combination are on the boiling curve. This means that a slight increase in temperature, a slight decrease in pressure, or a combination thereof, can lead to the formation of gas bubbles. The suction of the gas into the working space of the Low pressure pump is inevitably associated with a reduction in pressure. Regardless, a heat absorption of the liquid gas from the pump is possible, so that the temperature of the liquid gas increases. Although the compression of the liquid gas allows a greater distance from the boiling curve to be achieved, it is possible for localized gas bubbles to be temporarily retained. Thus, if a low-pressure pump according to the prior art is used as a prefeed pump to prevent gas bubble formation during suction of the gas by the high-pressure pump and to increase the efficiency of the high-pressure pump, this efficiency can be made worse by the bubble formation in the prefeed pump in the end.

The buffer tank ensures that the liquid phase and the gaseous phase of the gas are safely separated from each other. It is adjustable over the volume of the buffer tank, how much time is available for the delivery of the gas bubbles from the liquid phase of the gas. How much time is needed, depends among other things on gas type, mass flow, temperature and pressure. By allowing the buffer vessel to safely separate the gas bubbles from the liquid phase of the gas, the low pressure pump can ultimately perform its intended function of increasing the pressure of the gas sufficiently that the state of the gas is in the state space defined by pressure and temperature moved away from the boiling curve.

Related "reserves" have in the further compression of the gas in a downstream high pressure pump the effect that there no longer form bubbles due to suction and heat absorption. Bubble formation in the high pressure pump is a potentially self-reinforcing effect, because it degrades the efficiency, so that the high pressure pump produces correspondingly more heat loss, which in turn increases the temperature of the gas and further encourages bubble formation.

Considering the path of the gas from the reservoir to the high pressure injection in its entirety, it is inevitable that bubbles will be formed at some point in the aspiration of the liquid phase of the gas. It is energetically advantageous to shift this bubble formation into the compressor unit of the low-pressure pump. Although the blistering deteriorates the efficiency of the compressor unit, but since the compressor unit only has to produce a comparatively low pressure of a few bar, this comparatively little energy is lost. In the case of the high-pressure pump, which generates pressures of a few hundred bars, any loss of efficiency has a significantly greater effect.

Important for the separation of the gas phase from the liquid phase in the buffer tank is the valve arrangement at the outlet of the buffer tank. This valve assembly is, in a sense, the opposite of an overflow: if there is much liquid phase, it closes automatically so that no liquid is discharged through the outlet. When there is little liquid phase, the valve assembly opens to allow the gaseous phase of the gas to escape from the buffer container and clear space for the liquid phase. The valve arrangement thus ensures that only gas escapes from the outlet.

In applications where the liquified gas corresponds to a substantial component of the ambient atmosphere, such as oxygen or nitrogen, the outlet may deliver the gaseous phase formed from the separated gas bubbles to the atmosphere. For liquefied natural gas, this is not desirable because the methane contained therein has a 25 times greater greenhouse effect than CO ₂ and also can form an ignitable mixture with the atmospheric oxygen in closed spaces.

Therefore, in a particularly advantageous embodiment of the invention, the outlet is coupled to a return line, which is connectable to a region of the reservoir, which contains the gaseous phase of the gas. The return line contains a return valve, which is designed as a pressure relief valve or as a check valve and opens when exceeding a predetermined pressure p _R in the direction of the reservoir. In this case, a simple check valve opens as soon as an excess pressure with respect to the storage container forms at the outlet of the buffer container, ie, as soon as the pressure limit p _R = 0 is exceeded. On the other hand, a pressure relief valve can be flexibly adjusted so that it only opens when a pressure limit p _R different from zero is exceeded. The pressure limit p _R can also be preselected as an absolute value or as a relative value relative to the pressure in the reservoir.

In the reservoir, the recirculated gas can condense again. The pressure p _R is advantageously set slightly lower than the pressure generated by the compressor unit p _v in the interior of the buffer tank.

The start of the low-pressure pump varies depending on whether the return valve is designed as a check valve or as a pressure relief valve. If a check valve is used, during the filling of the buffer tank with the liquid phase of the gas, first of all the gaseous phase is first led via the return line into the storage tank until the liquid phase reaches the predetermined level and the valve arrangement closes. If, by contrast, a pressure relief valve is used, pressure is primarily built up in the buffer vessel and the gaseous phase is compressed there. Then, for example, a predetermined prefeed pressure is available faster, which a downstream high-pressure pump requires to work.

In a further particularly advantageous embodiment of the invention, the buffer container is coupled to a safety line, which is connectable to the reservoir. The safety line bypasses the valve assembly at the outlet and includes a safety valve, which is designed as a pressure relief valve and opens at a predetermined pressure p _s is exceeded in the direction of the reservoir. In this way, an impermissible pressure buildup in the buffer tank is avoided.

Advantageously, the safety line opens into the area of the buffer tank in which the liquid phase of the gas collects. Since the liquid phase has a significantly greater density than the gaseous phase, can be transported in this way, in the case of an impermissible pressure build quickly as large an amount of gas in the reservoir and the pressure can be reduced quickly.

Advantageously, a control and / or regulation for the compressor unit is provided, which is designed to keep the pressure p _v in the buffer tank below the pressure p _s . When gas is released through the safety line into the reservoir, the energy previously used for compression is lost. It is more efficient to regulate the compressor unit in good time beforehand and thus not spend the excess energy at all.

The valve arrangement can be designed in any way that is suitable for reacting to the level of the liquid phase in the buffer tank. For example, the level in the buffer tank can be measured electronically and, if required, a solenoid valve can be activated. In a particularly advantageous embodiment of the invention, the valve assembly comprises a float valve with an operable by the liquid phase of the gas float. This simple solution, which requires no auxiliary power, is particularly fail-safe.

For the relative structural arrangement of the compressor unit and the buffer container to each other there are two possible embodiments, each having specific advantages.

The compressor unit may be arranged outside the buffer container. This has the advantage that their waste heat is released to the environment and not to the gas. For more heat from the environment can be entered into the gas.

Alternatively, the compressor unit may be arranged inside the buffer tank. This minimizes the heat input from the environment at the price that the heat loss of the compressor unit is delivered directly to the gas.

Another possible combination involves the arrangement of the pump of the compressor unit in the buffer tank and the arrangement of the associated drive source outside the buffer tank. Then, that portion of the heat loss resulting from the drive source is no longer emitted directly to the gas. For example, the drive source may be a motor whose rotational energy is guided via a shaft in the compressor unit in the buffer tank.

In a further particularly advantageous embodiment of the invention, the buffer container, and / or the compressor unit, are adapted to be operated within the storage container. In this way, line paths can be saved, and the heat input into the gas can be minimized. The reservoir is thermally brought out of equilibrium only slightly. On the other hand, an arrangement of the compressor unit and the buffer tank outside the reservoir provides more degrees of freedom.

The compressor unit is advantageously designed to generate a pressure p _v of 5 bar or less, preferably 3 bar or less. This pressure value may be an absolute value or a relative value, for example based on the pressure in the reservoir. Then, in the state space of the gas which is spanned by temperature and pressure, a sufficient distance to the boiling characteristic curve is obtained without too much energy being expended because of the efficiency of the compressor unit, which is impaired by the formation of bubbles. Another possibility, advantageously using a control unit, is the generation of a constant differential pressure to the pressure in the reservoir. This ensures that the desired distance to the boiling curve is maintained.

The low-pressure pump according to the invention can be used in isolation and deliver bubble-free liquefied gas under the pressure p _v . However, the main application is the use as a feed pump for a high-pressure pump.

Therefore, according to the above, the invention also relates to a system for providing high-pressure, bubble-free liquefied gas p _H. This system comprises a high-pressure pump which is designed to generate the pressure p _H. According to the invention, the high-pressure pump is on the input side with the region of the buffer container connected, in which the liquid phase of the gas collects.

The high-pressure pump is advantageously designed to generate a pressure p _H of 300 bar or more, preferably of 500 bar or more. These pressures are sought in current HP-DI injection systems in which gaseous fuel is introduced directly into the combustion chamber of an engine cylinder.

Thus, the invention also relates to an injection or injection system for a liquefied natural gas powered internal combustion engine. This injection or injection system comprises at least one injector to the input side, the natural gas is supplied in the gaseous state at a high pressure p _H. According to the invention, the described system of high pressure pump and low pressure pump for generating the high pressure p _{H is} provided.

Further measures improving the invention will be described in more detail below together with the description of the preferred embodiments of the invention with reference to figures.

list of figures

• 1 Ausführungsbeispiel der Niederdruckpumpe 2 mit außerhalb des Pufferbehälters 5 angeordneter Verdichtereinheit 4;
• 2 Ausführungsbeispiel der Niederdruckpumpe 2 mit innerhalb des Pufferbehälters 5 angeordneter Verdichtereinheit 4;
• 3 Beispielhafte schematische Gesamtansicht des Systems 9 zur Hochdruckerzeugung und des Einspritz- oder Einblassystems 10.

It shows:

• 1 Embodiment of the low-pressure pump 2 with arranged outside the buffer tank 5 compressor unit 4;
• 2 Embodiment of the low-pressure pump 2 with arranged inside the buffer tank 5 compressor unit 4;
• 3 Exemplary schematic overall view of the system 9 for high-pressure generation and of the injection or injection system 10.

To 1 becomes the gas 1 in a storage container 3 stored. The liquid phase la of the gas 1 accumulates in the area 31 , The gaseous phase 1b of the gas 1 accumulates in the area above it 32 ,

The liquid phase la of the gas 1 is in the compressor unit 4 guided. The compressor unit 4 is designed as a piston pump and includes a pump housing 40 with a working volume 41 passing through one along the longitudinal axis of the pump housing 40 sliding piston 42 is enlargeable and reducible. The displacement of the piston 42 is powered by a rotary drive source 43 driven. Will the piston 42 moved to the right, the work volume becomes 41 enlarged and liquid gas la through the inlet valve 44 sucked, with bubbles 1c form. Will the piston 42 moved to the left, the working volume is reduced and the liquid gas la including the bubbles formed 1c through the outlet valve 45 pushed out. The mixture of liquid gas la and bubbles 1c is at the pressure p _v the buffer tank 5 fed. The pressure p _v is in the control unit 46 that the rotary drive source 43 controls, set.

In the buffer tank 5 collects the liquid phase la of the gas 1 in the area 51 , In this liquid phase la experienced the bubbles 1c a boost 53 and therefore rise in the area 52 to form a coherent gaseous phase 1b to build.

The gaseous phase 1b of the gas 1 gets out of the field 52 of the buffer tank 5 through an outlet 55 deducted, with a valve assembly 54 is provided. The valve arrangement 54 contains a float valve 54a with a float 54b that is with the level 1d the liquid phase la of the gas 1 in the buffer tank 5 emotional. Reached this level 1d the given height 56 , closes the float valve 54a ,

From the outlet 55 leads a return line 57 back to the area 32 of the storage container 3 in which there is the gaseous phase 1b of the gas 1 collects. The return line 57 is with a return valve 57a provided that when exceeding a predetermined pressure p _R in the direction of the reservoir 3 opens. The pressure p _R is set slightly smaller than p _v . The return valve 57a Primarily used to create a gas flow only from the area 52 of the buffer tank 5 in the area 32 of the storage container 3 but not in the opposite direction.

Out of the area 51 of the buffer tank 5 is the liquid phase la of the gas 1 under the pressure p _v through a bottom outlet 59 removable.

The buffer tank 5 is also to avoid an unacceptable pressure build-up via a safety line 58 with the reservoir 3 connected. This security line 58 contains a safety valve 58a which opens when a pressure p _{s is} exceeded. This pressure p _s is set greater than the pressure p _v from the compressor unit 4 is produced. The security line 58 flows into the area 51 of the buffer tank 5 in which there is the liquid phase la of the gas 1 collects, if necessary, quickly a large amount of gas 1 to be able to pay. On the side of the storage container 3 opens the security line 58 turn into the area 31 in which is the liquid phase la of the gas 1 collects. In this way, the reservoir 3 as little as possible unbalanced when gas la through the security line 58 is supplied.

The compressor unit 4 and the buffer tank 5 form together with the return line 57 and the security line 58 the low pressure pump 2 , To the low pressure pump 2 to start up, is the inlet port of the intake valve 44 the compressor unit 4 with the area 31 of the storage container 3 to connect, in which the liquid phase la of the gas 1 collects. With this area 31 is in the in 1 example shown also the security line 58 connected. The return line 57 is in the in 1 shown example with the area 32 of the storage container 3 connected, in which there is the gaseous phase 1b of the gas 1 collects.

The bottom outlet 59 of the buffer tank 5 is connected to any downstream device, the liquefied gas la under the pressure p _v needed connectable.

2 shows a further embodiment of the low-pressure pump 2 , In contrast to 1 is the compressor unit 4 here within the buffer tank 5 arranged. The feeder from the area 31 of the storage container 3 to the inlet port of the inlet valve 44 the compressor unit 4 So it is in the buffer tank 5 led into it. The outlet valve 45 the compressor unit 4 discharges the compressed to the pressure p _v mixture of liquid phase of the gas la 1 and gas bubbles 1c immediately in the area 51 the buffer container liquid phase la of the gas 1 , By the buoyancy 53 the gas bubbles move 1c in the area 52 of the buffer tank 5 where they form a coherent gaseous phase 1b , The control unit 46 for the rotary drive source 43 the compressor unit 4 is outside the buffer tank 5 arranged and via a cable with this drive source 43 connected.

3 illustrates the embedding of the low-pressure pump 2 in the system 9 , the liquefied natural gas la from the storage tank 3 takes and brings to the high pressure p _H. That from the bottom outlet 59 of the buffer tank 5 with the pressure p _v withdrawn liquid gas la is the high-pressure pump 6 fed and in the high pressure pump 6 brought to the high pressure p _H. In the evaporator 71 the liquid gas la is transferred to the gaseous state before it passes through the injector 7 in the cylinder 81 of the motor 8th is transferred. The system 9 forms together with the evaporator 71 and the injector 7 the injection or injection system 10 for the fuel supply of the engine 8th ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1546548 [0006]
• US 2004011323 A1 [0006]
• WO 2014037068 A1 [0006]
• US 2014230458 A1 [0008]
• US 2014290280 A1 [0008]
• WO 2016112462 A1 [0008]

Claims (15)

Low-pressure pump (2) for providing bubble-free liquefied gas (1), comprising a compressor unit (4) which can be connected to a supply container (3) for the gas (1) to increase the pressure of the gas (1), characterized in that the compressor unit (4) operates on the output side a pressure-tight buffer container (5) is arranged, wherein the buffer container (5) in the region (52), in the liquid phase (la) of the gas (1) contained gas bubbles (1c) due to their buoyancy (53) in this liquid phase (la), having a valve assembly (54) closable outlet (55), wherein the valve assembly (54) is adapted to close at least automatically when the level (1d) of the liquid phase (la) of Gas (1) in the buffer tank (5) exceeds a predetermined height (56). Low pressure pump (2) after Claim 1 , characterized in that the compressor unit has a variable working volume (41), wherein the liquid phase (la) of the gas (1) by enlargement of the working volume (41) in the working volume (41) sucked in and by reducing the working volume (41) the working volume (41) can be ejected. Low pressure pump (2) according to one of Claims 1 to 2 characterized in that the outlet (55) is coupled to a return line (57) connectable to a portion (32) of the reservoir (3) containing the gaseous phase (1b) of the gas (1) the return line (57) contains a return valve (57a) which is designed as a pressure relief valve or as a check valve and opens when a predetermined pressure p _R is exceeded in the direction of the reservoir (3). Low pressure pump (2) according to one of Claims 1 to 3 characterized in that the buffer container (5) is coupled to a safety line (58) connectable to the reservoir (3), the safety line (58) bypassing the valve assembly (54) at the outlet (55) and a safety valve (58). 58a), which is designed as a pressure relief valve and opens at a predetermined pressure p _s in the direction of the reservoir (3) is exceeded. Low pressure pump (2) after Claim 4 , characterized in that the safety line (58) in the region (51) of the buffer container (5) opens, in which the liquid phase (la) of the gas (1) collects. Low pressure pump (2) according to one of Claims 4 to 5 , characterized in that a control and / or regulation (46) for the compressor unit (4) is provided, which is adapted to keep the pressure p _v in the buffer tank (5) below the pressure p _s . Low pressure pump (2) according to one of Claims 1 to 6 characterized in that the valve assembly (54) comprises a float valve (54a) having a float (54b) operable by the liquid phase of the gas. Low pressure pump (2) according to one of Claims 1 to 7 , characterized in that the compressor unit (4) outside the buffer container (5) is arranged. Low pressure pump (2) according to one of Claims 1 to 7 , characterized in that the compressor unit (4) within the buffer container (5) is arranged. Low pressure pump (2) after Claim 9 , characterized in that a drive source (43) of the compressor unit (4) is arranged at least partially outside the buffer container (5). Low pressure pump (2) according to one of Claims 1 to 10 , characterized in that the buffer container (5), and / or the compressor unit (4), are adapted to be operated within the storage container (3). Low pressure pump (2) according to one of Claims 1 to 11 , characterized in that the compressor unit (4) for generating a pressure p _v of 5 bar or less, preferably 3 bar or less, is formed. System (9) for providing bubble-free liquefied gas (1) under high pressure p _H , comprising a high pressure pump (6) designed to generate the pressure p _H , characterized in that the high pressure pump (6) is a low pressure pump (2) one of the Claims 1 to 12 upstream, wherein the high-pressure pump (6) on the input side to the region (51) of the buffer tank (5) is connected, in which the liquid phase (la) of the gas (1) collects. System (9) after Claim 13 , characterized in that the high-pressure pump (6) for generating a pressure p _H of 300 bar or more, preferably of 500 bar or more, is formed. Injection or injection system (10) for an operating with liquefied natural gas (1) internal combustion engine (8), comprising at least one injector (7) to the input side, the natural gas is supplied in the gaseous state under a high pressure p _H , characterized in that a system (9) after one of the Claims 13 to 14 is provided for generating the high pressure p _H.

Images