EP3511569A1 - Method for compacting a fluid and compressor subassembly - Google Patents

Abstract

The invention relates to a method for compressing a fluid (F), wherein the fluid (F) is provided in a first compressor chamber (31) separated from a second compressor chamber (32) by means of a movable piston (30) of a compressor (3) is, wherein by means of a pump (11), a hydraulic fluid (H) is introduced into the second compressor chamber (32), so that the piston (30) moves and the fluid (F) in the first compressor chamber (31) is compressed a pump speed (n) of the pump (11) during the compression of the fluid (F) is controlled so that the product of the pump speed (n) and a pump torque (M) of the pump (11) remains constant, the pump torque (M ) depends on the pressure (p) prevailing in the first compressor chamber (31).

Furthermore, the invention relates to a compressor assembly (1), in particular for carrying out the method according to the invention.

Description

The invention relates to a method for compressing a fluid and a compressor assembly, in particular for carrying out the method according to the invention.

From the prior art, e.g. hydraulically driven compressors (also known as piston compressors) known. These have a movable piston in the compressor (also referred to as separator piston), which separates a first compressor chamber from a second compressor chamber. A fluid provided in the first compressor room may be compressed by introducing a hydraulic fluid into the second compressor room by means of a hydraulic fluid pump (for example, an axial piston machine, a radial piston machine or a gear pump) and moving the piston by the introduced hydraulic fluid.

Also known in the prior art are vehicles which are powered by gaseous fuels, e.g. Hydrogen, natural gas or methane, are drivable. Corresponding filling stations for these fuels are also known.

The infrastructure for such gas filling stations (such as hydrogen refueling stations) is currently not so strong in most regions that the transition would be without disadvantages for the majority of the population. Home gaseous fuel filling systems, such as prior art hydrogen, allow only low flow rates, which would prevent compliance with manufacturer-specific specifications under these circumstances.

Prior art fluid compression methods using hydraulic fluid pumps (which deliver hydraulic fluid through rotating or moving components) have the disadvantage that the maximum pumping capacity of the hydraulic fluid pump can not be exploited because too much back pressure occurs during the process by the compressed fluid ,

Therefore, it is the object of the present invention to provide a method which is improved with respect to the aforementioned disadvantages of the prior art.

This object is achieved by the method according to claim 1 and the compressor assembly according to claim 9. Advantageous embodiments of the method are specified in the subclaims 2 to 8. The invention will be described below.

A first aspect of the invention relates to a method for compressing a fluid, wherein the fluid is provided in a first compressor space, which is separated from a second compressor chamber by means of a movable piston of a compressor, wherein a hydraulic fluid is introduced into the second compressor chamber by means of a pump, so that the piston moves and the fluid in the first compressor space is compressed while reducing the volume of the first compressor space, wherein a pump speed of the pump during the compression of the fluid controlled so, in particular reduced, that the mathematical product of the pump speed and a Pump torque of the pump remains constant or substantially constant, the pump torque depends on the prevailing pressure in the first compressor chamber.

The pump torque is the moment which the compressor opposes to a motor driving the pump. This depends (in particular linear) on the back pressure of the hydraulic fluid in the second compressor chamber, wherein the back pressure of the hydraulic fluid in equilibrium corresponds to the pressure of the fluid in the first compressor chamber.

As a result of the method according to the invention, the pump torque, which is increased when the backpressure increases, is compensated for by a reduction in the pump speed, so that during the method the pump power or the delivery rate of the pump always remains constant. Thus, the compressor delivery rate during a compressor stroke (ie a movement of the piston in the compressor) are always kept at a maximum. In other words, the engine speed and thus the pump speed is always kept at a maximum (for the relevant backpressure), whereby the maximum power of the engine at the relevant speed point is kept at a maximum. Compared to prior art compaction processes, the compaction time can thus be shortened, in particular in hydraulically driven systems. This is possible with only a small additional cost compared to systems with constant speed.

In particular, the method according to the invention allows the pump to be operated at a maximum pump speed at the beginning of a compressor stroke with a relatively low backpressure. This allows for faster compression than in prior art processes where the pump speed is maintained at a constant lower level throughout the compressor stroke.

The fluid is in particular a gas. Furthermore, the fluid may also be formed by a liquid-gas mixture.

The pump has a pumping speed rotating or moving component or assembly for compressing the fluid. For example, The pump may be formed as axial piston machine, radial piston machine or gear pump.

In one embodiment, the pump speed is linearly reduced with time during the compression of the fluid. In this way, with an increase in the back pressure according to the adiabatic equation (assuming isentropic compression), at least approximately a constant product of pump speed and pump torque can always be achieved.

According to a further embodiment, the pump speed is kept constant in a precompression phase, the pump speed being reduced in a compression phase following the precompression phase, in particular linear with respect to time. In the first phase of compression, the pressure of the fluid increases only insignificantly according to isentropic compression. Therefore, it is possible at this stage to keep the pump speed constant in this phase. In the subsequent compression phase, a greater increase in the back pressure, which is compensated by the reduction of the pump speed.

According to a further embodiment, the pump speed in the precompression phase corresponds to a maximum pump speed of the pump.

The pump is configured during normal use to be operated at the maximum pump speed at most. That is, when the maximum pump speed is exceeded, the pump may e.g. may be damaged, it may be e.g. pose a safety risk to the user or the delivery rate of the pump may e.g. If the maximum speed is exceeded, this can not be increased by design.

According to another embodiment, the pump speed in the compression phase is reduced to a minimum pump speed.

The minimum pump speed corresponds in particular to that speed at which, at a maximum pressure (in particular compression end pressure) of the fluid in the first compressor chamber, the (constant) product results from pump torque and pump speed.

In this case, a freewheel valve is opened, in particular when reaching the minimum speed, so that the load is taken from the pump.

According to a further embodiment, the pump speed is maintained at the minimum pump speed in a stop phase subsequent to the compression phase.

According to a further embodiment, the pump speed is increased to the maximum pump speed before the precompression phase in a start phase, in particular linear with respect to the time.

According to a further embodiment, the pump speed in the starting phase is first increased to the minimum speed, wherein the pump speed is kept constant after reaching the minimum pump speed, and wherein the pump speed is then increased, in particular linear with respect to the time, to the maximum pump speed.

In accordance with a further embodiment, the pump speed is set on the basis of a predetermined speed curve over time.

According to a further embodiment, the pressure of the fluid in the first compressor space, in particular directly or indirectly, is determined or measured, the pump speed being set as a function of the determined or measured pressure. The determination of the pressure may e.g. by direct pressure measurement in the first compression chamber or alternatively by measuring the pressure of the hydraulic fluid in the second compression chamber or in a hydraulic fluid line downstream of the pump.

A second aspect of the invention relates to a compressor assembly, in particular for carrying out the method according to the first aspect, comprising a compressor having a piston movable in the compressor, which can be arranged in the compressor so that it separates a first compressor chamber from a second compressor chamber, a hydraulic fluid reservoir for receiving a hydraulic fluid communicable with the second compressor chamber, a pump configured to deliver the hydraulic fluid from the hydraulic fluid reservoir and introduce it into the second compressor chamber so that the piston moves and in the first compressor chamber compressed fluid, wherein the compressor assembly comprises a controller configured to control a pump speed of the pump during the compression of the fluid so that the mathematical product of the pump speed and a pump torque of the pump constant or remains substantially constant, wherein the pump torque depends on the pressure prevailing in the first compressor chamber.

The pump has a pumping speed rotating or moving component or assembly for compressing the fluid. For example, The pump may be formed as axial piston machine, radial piston machine or gear pump.

According to a further embodiment, the control device is configured to adjust the pump speed based on a predetermined time pump speed curve. This speed curve can be stored for example in a memory unit of the control device.

According to a further embodiment, the compressor assembly has at least one pressure sensor for determining or measuring the pressure of the fluid in the first compressor chamber, wherein the controller is configured to adjust the pump speed as a function of the determined or measured pressure.

Fig. 1

eine schematische Darstellung einer Verdichterbaugruppe mit einer Steuerungseinrichtung zur Durchführung des erfindungsgemäßen Verfahrens;

Fig. 2

ein Diagramm, das den zeitlichen Verlauf der Pumpendrehzahl und des Drucks des Fluids in dem ersten Verdichterraum während des erfindungsgemäßen Verfahrens darstellt.

Further embodiments of the invention are described below with reference to drawings. Show

Fig. 1

a schematic representation of a compressor assembly with a control device for carrying out the method according to the invention;

Fig. 2

a diagram illustrating the time course of the pump speed and the pressure of the fluid in the first compressor chamber during the process according to the invention.

Fig. 1 shows a schematic representation of a compressor assembly 1 according to the invention in longitudinal section. The compressor assembly 1 has a compressor 3 with a piston 30, which separates a first compressor chamber 31 of the compressor 3 for receiving a fluid F from a second compressor chamber 32 of the compressor 3 for receiving a hydraulic fluid H.

The compressor assembly 1 further comprises a hydraulic fluid H partially filled hydraulic fluid reservoir 9 and a pump 11 which is configured to convey the hydraulic fluid H from the hydraulic fluid reservoir 9 and to introduce via a hydraulic valve 6 in the second compressor chamber 32 of the compressor 3.

The piston 30 is movably arranged in the compressor 3, so that the piston 30 in the illustration of Fig. 1 can move to the right when the hydraulic fluid H is introduced into the second compressor chamber 32. As a result of the movement of the piston 30, the volume of the second compressor chamber 32 increases and the volume of the first compressor chamber 31 decreases correspondingly, so that fluid F in the first compressor chamber 31 is at such a movement of the piston 30 due to the reduction of the volume of the first Compressor space 31 is compressed.

As in Fig. 1 is shown, the second compressor chamber 32 is further connected via the hydraulic valve 6 and a hydraulic return valve 8 to the hydraulic fluid reservoir 9, so that upon movement of the piston 30 to the left as shown in FIG Fig. 1 (For example, when the first compressor chamber 31 is filled with the fluid F) the hydraulic fluid H displaced from the second compressor chamber 32 by means of the piston 30 can flow back into the hydraulic fluid container 9 via the hydraulic valve 6 and the hydraulic return valve 8.

A broken line represents an exemplary level of the hydraulic fluid H in the hydraulic fluid reservoir 9. Further, the arrows indicate the flow direction of the hydraulic fluid.

The pump 11 is designed in particular as an axial piston machine, radial piston machine or gear pump, thus has rotating components with a pump speed n (which can be given in the unit s ^-1 , for example), the delivery rate of the pump 11 is greater, the higher the pump speed n is.

In the Fig. 1 shown pump 11 (or its rotating components) are driven by a motor 10. The motor 10 thus sets the said rotating components of the pump 11 in rotary motion.

The motor 10 is connected to a control device 12, so that by means of the control device 12, the speed of the motor 10 and thus the pump speed n of the pump 11 is controllable.

In the method according to the invention hydraulic fluid H is introduced by means of the pump 11 from the hydraulic fluid reservoir 9 in the second compressor chamber 32 of the compressor 3, so that the piston 30 as shown in the Fig. 1 moved to the right, whereby the volume V of the first compressor chamber 31 is reduced and thus the fluid contained in the first compressor chamber 31 F is compressed.

The FIG. 2 shows a common time / pump speed and time / pressure diagram. In this case, the abscissa of the graph represents the time t and the ordinate of the graph represents the pump speed n of the pump 11 with respect to a pump speed curve n (M) and the pressure p of the fluid F with respect to a pressure curve p (V, κ) first compressor chamber 31 of the compressor 3 during the process according to the invention as a function of time t.

herleiten, wobei p den Druck des Fluids F in dem ersten Verdichterraum 31 bezeichnet, und wobei V das Volumen des ersten Verdichterraums 31 bezeichnet, und wobei κ den Adiabatenexponenten des Fluids F bezeichnet.It can be seen from the pressure curve p (V, κ) that the pressure p of the fluid F in the first compressor chamber 31 increases non-linearly with a reduction in the volume V of the first compressor chamber 31 to a maximum pressure p _max . In the Fig. 2 shown pressure curve p (V, κ) can be calculated assuming isentropic compression from the adiabatic equation $$p\cdot V^{\kappa }=\mathit{const}$$

where p denotes the pressure of the fluid F in the first compressor space 31, and V denotes the volume of the first compressor space 31, and where κ denotes the adiabatic exponent of the fluid F.

In the Fig. 2 shown speed curve n (M) shows that in the example of the method shown here, the pump speed n is controlled so that during a start phase t _start the pump speed n is first increased linearly from zero to a minimum pump speed n _min (minimum operating speed) ( wherein said linear increase is also referred to as a launch ramp or first ramp), then held constant for a period of time at the minimum pump speed n _min (also referred to as a first plateau) and subsequently linearly increased to the maximum pump speed n _max (also referred to as second ramp). During a precompression _phase t _predverd , the precompression of the fluid F follows, the pump speed n constantly corresponding to the maximum pump speed n _max (also referred to as the second plateau). It can be seen from the pressure curve p (V, κ) that the pressure p in the first compression _chamber 31 remains virtually constant during the precompression _phase t _predverd .

Subsequently, the pump speed n during a compression _phase t _Verd , in particular proportional to the pressure prevailing in the first compression chamber 31 back pressure p, is reduced, so that there is an at least approximately linear relationship between time and pump speed n for the compression _phase t _Verd . In the compression phase, the product of pump torque M and pump speed n remains constant according to the invention, so that in each case the maximum pump output at the current counter-pressure results.

As soon as the minimum pump speed n _min (the minimum pump speed also depends on manufacturer-specific information, these usually relate to a rotation-induced minimum lubrication), which occurs simultaneously with the achievement of the maximum back pressure p _max in the first compressor chamber 31 is, for example by opening a Freewheel valve, the load taken from the pump 11. Subsequently, the pump speed n is kept constant in a stop phase t _stop at the minimum pump speed n _min . After the end of the stop phase t _Stop , the pump speed n is reduced to 0 in a further ramp.

Dabei bezeichnet P die Pumpenleistung der Pumpe 11, M das vom Gegendruck (insbesondere linear) abhängige Pumpenmoment der Pumpe 11, ω die Winkelgeschwindigkeit der Pumpe 11 und η_Pumpe den Pumpenwirkungsgrad der Pumpe 11.By means of a power curve, for example, provided by the engine manufacturer of the engine 10 which drives the pump 11, the maximum pump speed n which can be generated by the engine 10 at a given present back pressure can be described by the following equation: $$P=M\cdot \omega \cdot {\eta }_{\mathit{pump}}$$

Where P is the pump power of the pump 11, the M by the counter-pressure (in particular linear) dependent pump torque of the pump 11, the angular velocity of pump 11 and _pump ω η pump efficiency of the pump. 11

The angular velocity ω can be converted into the pump speed n with the relationship ω = 2 π · n , so that the following equation results: $$P=M\cdot 2\pi \cdot n\cdot {\eta }_{\mathit{pump}}$$

This equation allows the pump speed n to be changed as follows: $$n=\frac{P}{2\pi \cdot M\cdot {\eta }_{\mathit{pump}}}$$

$$V_2=\left(V_1-N_{\mathit{Pumpe}}\cdot V_{\mathit{Pumpe}}\right)$$

The relationship between the isentropic compression and the number of pump revolutions can be described as follows as a function of the discharge pressure (maximum pressure p _max ). In the following, V ₁ denotes the maximum volume of the first compressor chamber 31 of the compressor 3 and V2 denotes the maximum volume of the first compressor chamber 31 minus the number of pump revolutions (N _pump ) multiplied by the volumetric displacement of the pump 11 (V _pump ). p ₁ denotes the back pressure of the fluid F in the first compression space 31 at the volume V ₁ and p ₂ denotes the back pressure of the fluid F in the first compression space 31 at the volume V2. $$p\cdot V^{\kappa }=\mathit{const}$$

$$V_2=\left(V_1-N_{\mathit{pump}}\cdot V_{\mathit{pump}}\right)$$

From equation (5): $$p_1\cdot {V_1}^{\kappa }=p_2\cdot {V_2}^{\kappa }$$

Substituting equation (6) into equation (7) gives: $$p_1\cdot {V_1}^{\kappa }=p_2\cdot {\left({\mathrm{\Omega }}_1-{\mathit{{\rm N}}}_{\mathit{pump}}\cdot V_{\mathit{pump}}\right)}^{\kappa }$$

$$N_{\mathit{Pumpe}}=\frac{V_1-V_1\cdot {\left(\frac{p_1}{p_2}\right)}^{\frac{1}{\kappa }}}{V_{\mathit{Pumpe}}}$$

Equation (8) can be changed as follows: $$V_1-{\left(\frac{p_1}{p_2}\right)}^{\frac{1}{\kappa }}\cdot V_1=N_{\mathit{pump}}\cdot V_{\mathit{pump}}$$

$$N_{\mathit{pump}}=\frac{V_1-V_1\cdot {\left(\frac{p_1}{p_2}\right)}^{\frac{1}{\kappa }}}{V_{\mathit{pump}}}$$

According to the speed _curve , the individual times or phases t _start , t _predverd , t _Verd and t _{stop can be} calculated.

The control of the pump speed n can, for example, based on a predetermined speed curve (such as in Fig. 2 shown). Alternatively, the back pressure of the hydraulic fluid H or the pressure of the fluid F in the first compressor chamber 31 may be measured during the process, with the pump speed n being set as a function of the measured pressure. <U> LIST OF REFERENCES </ u> 1 compressor assembly 3 compressor 6 hydraulic valve 8th Hydraulic return valve 9 Hydraulic fluid reservoir 10 engine 11 pump 12 control device 30 piston 31 First compressor room 32 Second compressor room F fluid H hydraulic fluid κ adiabatic N Pump speed n _min Minimum pump speed n _max Maximum pump speed M pump torque P print p _max Maximum pressure t Time t start start-up phase t _predverd Vorverdichtungsphase t _Verd compression phase t _stop stop phase V volume

Claims (9)

Method for compressing a fluid (F), wherein the fluid (F) is provided in a first compressor chamber (31) which is separated from a second compressor chamber (32) by means of a movable piston (30) of a compressor (3) a pump (11) a hydraulic fluid (H) is introduced into the second compressor chamber (32), so that the piston (30) moves and the fluid (F) in the first compressor chamber (31) is compressed, wherein a pump speed (n ) of the pump (11) during the compression of the fluid (F) is controlled so that the product of the pump speed (n) and a pumping torque (M) of the pump (11) remains constant, the pumping torque (M) of the in the first compressor chamber (31) prevailing pressure (p) depends. The method of claim 1, wherein the pump speed (n) is linearly reduced with respect to the time (t). Method according to claim 1 or 2, wherein the pump speed (n) is kept constant in a precompression _phase (t _predverd ), and wherein the pump speed (n) is reduced in a compression _phase (t _Verd ) following the precompression _phase (t _predverd ). The method of claim 3, wherein the pump speed (n) in the precompression _phase (t _predverd ) _{corresponds to} a maximum pump _speed (n _max ) of the pump (11). The method of claim 3 or 4, wherein the pump speed (n) in the compression phase (t _Verd ) is reduced to a minimum pump speed (n _min ). A method according to claim 5, wherein the pump speed (n) is maintained at the minimum pump speed (n _min ) in a stop phase (tstop) following the compression phase (t _Verd ). Method according to one of claims 3 to 6, wherein the pump speed (n) before the precompression phase (t _predverd ) in a starting phase (t _start ) to the maximum pump speed (n _max ) is increased. The method of claim 7, wherein the pump speed (n) in the starting phase (tstart) is first increased to the minimum pump speed (n _min ), and wherein the pump speed (n) after reaching the minimum pump speed (n _min ) is kept constant, and wherein the pump speed (n) is subsequently increased to the maximum pump speed (n _max ). Compressor assembly (1), in particular for carrying out the method according to one of claims 1 to 8, comprising a compressor (3) having a piston (30) movable in the compressor (3), which can be arranged in the compressor (3) so as to separate a first compressor chamber (31) from a second compressor chamber (32), - A hydraulic fluid reservoir (9) for receiving a hydraulic fluid (H), which is in fluid communication with the second compressor chamber (32), a pump (11) configured to deliver the hydraulic fluid (H) from the hydraulic fluid reservoir (9) and into the second compressor chamber (32) so that the piston (30) moves and in the first compressor chamber ( 31) provided fluid (F) is compressed, characterized,
that the compressor assembly (1) comprises a control device (12) is configured to a pump speed (n) of the pump (11) during the compression of the fluid (F) to control so that the product of the pump speed (n) and a pump torque (M) of the pump (11) remains constant, wherein the pump torque (M) of the in the first compressor chamber (31) prevailing pressure (p) depends.

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