METHOD FOR COMPRESSING A GAS, COMPUTING UNIT AND MULTI-STAGE PISTON COMPRESSOR

Abstract

A method for compressing a gas by means of a multi-stage piston compressor is disclosed, wherein, if an inlet pressure of a first compression stage exceeds a threshold value, the gas is at least partially, in particular completely, branched off before the first compression stage and fed to a second compression stage, which directly follows the first compression stage. A computing unit for performing the method to such a multi-stage piston compressor are further disclosed.

Claims

1. A method for compressing a gas by means of a multi-stage piston compressor, wherein the gas is diverted at least partially upstream of the first compression stage and fed to a second compression stage, which directly follows the first compression stage, if an inlet pressure of the first compression stage exceeds a threshold value.

2. The method according to claim 1, wherein the stroke (h.sub.1) of a piston of the piston compressor, which is assigned to the first compression stage, is furthermore reduced.

3. The method according to claim 2, wherein the stroke (h.sub.1) is reduced in dependence on a residual pressure after a reexpansion in the first compression stage and/or an inlet pressure of the second compression stage.

4. The method according to claim 3, wherein the reduction of the stroke (h.sub.1) is determined based on stored values for the residual pressure and/or the inlet pressure of the second compression stage.

5. The method according to claim 1, wherein the gas is diverted upstream of the first compression stage and fed to the second compression stage in that a first valve in a first flow path leading to the first compression stage is at least partially closed and a second valve in a second flow path leading from the first flow path to the second compression stage is at least partially opened.

6. The method according to claim 5, wherein an inlet valve of the second compression stage is used as the first valve.

7. The method according to claim 1, wherein at least one electric linear motor is used for moving pistons in the piston compressor.

8. A computing unit, for carrying out a method for compressing a gas by means of a multi-stage piston compressor, wherein the gas is diverted at least partially upstream of the first compression stage and fed to a second compression stage, which directly follows the first compression stage, if an inlet pressure of the first compression stage exceeds a threshold value.

9. A multi-stage reciprocating piston compressor with a gas inlet, a first compression stage and a second compression stage, wherein a first valve is arranged in a first flow path leading to a gas inlet of the first compression stage, wherein a second flow path branches off the first flow path upstream of the first valve and leads to a gas inlet of the second compression stage, and wherein a second valve is arranged in the second flow path.

10. The multi-stage reciprocating piston compressor according to claim 9, wherein the inlet valve of the first compression stage forms the first valve.

11. The multi-stage reciprocating piston compressor according to claim 9 with at least one electric linear motor for moving pistons of the reciprocating piston compressor.

12. The multi-stage reciprocating piston compressor according to claim 9 further comprising a computing unit for carrying out a method for compressing a gas by means of a multi-stage piston compressor, wherein the gas is diverted at least partially upstream of the first compression stage and fed to a second compression stage, which directly follows the first compression stage, if an inlet pressure of the first compression stage exceeds a threshold value.

13. The method according to claim 1 wherein the gas is diverted completely upstream of the first compression stage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 schematically shows an inventive multi-stage reciprocating compressor according to a preferred embodiment in the form of a flowchart.

[0038] FIG. 2 schematically shows stroke profiles of an inventive multi-stage reciprocating compressor according to a preferred embodiment in the form of a diagram.

EMBODIMENTS OF THE INVENTION

[0039] FIG. 1 schematically shows an inventive multi-stage piston compressor 100 according to a preferred embodiment in the form of a flowchart. In this case, the piston compressor 100 comprises a first compression stage 110 and a second compression stage 120. Both compression stages are respectively realized in the form of pistons that move in a cylinder. These pistons are driven by an electric linear motor 130. Additional compression stages may naturally be provided.

[0040] The first compression stage comprises an inlet valve ill and an outlet valve 112, which may be realized in the form of pressure-controlled check valves. The second compression stage 120 likewise comprises an inlet valve 121 and an outlet valve 122, which may also be realized in the form of pressure-controlled check valves.

[0041] In this case, the regular gas flow takes place along a first flow path 161 (illustrated on the left in FIG. 1) leading to the first compression stage 110 and then from the first compression stage 110 to the second compression stage 120. Subsequently, the gas can be fed to a desired application.

[0042] Pressure sensors 141, 142 and 143 are furthermore provided. An inlet pressure of the first compression stage can be measured with the pressure sensor 141, an outlet pressure of the first compression stage 110 or an inlet pressure of the second compression stage 120 can be respectively measured with the pressure sensor 142 and an outlet pressure of the second compression stage 120 can be measured with the pressure sensor 143. In this case, the pressure sensors 141, 142 and 143 are connected to a computing unit 170, which is realized in the form of a stored program control (SPC). The SPC 170 can therefore respectively acquire or read out the corresponding pressures.

[0043] A first valve 151 is furthermore provided in the first flow path 161. This first valve 151 can presently be activated, i.e. opened and closed, by means of the SPC 170. In this case, the first valve 151 is open during the normal operation.

[0044] A second flow path 162 in the sense of a bypass line is furthermore provided, wherein this second flow path branches off the first flow path 161, namely upstream of the first valve 151, and leads to the second compression stage 120. A second valve 152, which can likewise be activated, i.e. opened and closed, by the SPC 170, is provided in the second flow path 162. This second valve 152 is closed during the normal operation.

[0045] For example, the first valve 151 is completely closed if the SPC 170 respectively acquires or reads out an inlet pressure of the first compression stage 110, which lies above a threshold value, from the pressure sensor 141 during the operation of the piston compressor 100. The second valve 152 simultaneously is completely opened. The gas now flows directly to the inlet of the second compression stage 120 instead of to the first compression stage 110.

[0046] This threshold value can preferably be chosen in such a way that the output or the attainable power of the electric linear motor 130 for the first compression stage 110 just barely suffices for carrying out the required compression at inlet pressures below this threshold value. Inlet pressures, at which the required compression can no longer be carried out, are thereby prevented in the first compression stage 110.

[0047] The electric linear motor 130 is furthermore activated by the SPC 170 in such a way that the stroke of the piston assigned to the first compression stage 110 is reduced.

[0048] FIG. 2 schematically shows stroke profiles of an inventive multi-stage reciprocating piston compressor according to a preferred embodiment in the form of a diagram. In this diagram, the stroke h is plotted as a function of the time t.

[0049] In this diagram, h.sub.1 denotes the stroke profile of the piston assigned to the first compression stage and h.sub.2 denotes the stroke profile of the piston assigned to the second compression stage.

[0050] The stroke h.sub.1 of the piston of the first compression stage is now reduced by an amount h such that the piston of the first compression stage now has a stroke h.sub.1. The stroke of the piston of the second compression stage remains unchanded. As initially mentioned, a negative pressure in the second compression stage is thereby prevented.

[0051] The amount h, by which the stroke is reduced, can be calculated based on the following formula:

[00001]$.Math..Math.h\left(p_1\right)=\frac{\left[{\left(\frac{p_1}{p_2}\right)}^{\frac{1}{}}.Math.V_{\mathrm{stat}}-V_{\mathrm{stat}}\right]}{\frac{d^2}{4}.Math.}.$

[0052] In this formula, p1 denotes the residual pressure after the reexpansion in the first compression stage. The pressure p1 may be a freely definable pressure that should preclude an absolute pressure from falling short of 1 bar. In this context, p1>>1 bar absolute should preferably apply. For example, the pressure after the reexpansion may be determined computationally or ascertained indirectly if the pressure p1 drops below the pressure measured by the pressure sensor 141 in the reexpansion period. In this case, gas from the volume between the valves 151, 111 and the pressure sensor 141 would flow in such that the pressure measured by the pressure sensor 141 would drop. The reference symbol p2 denotes the inlet pressure of the second compression stage, which is measured by the pressure sensor 142.

[0053] The reference symbol denotes the ratio of specific heats of the adiabatic change and the reference symbol V.sub.stat denotes a static clearance volume of the first compression stage, which results from the dimensions of the piston and the cylinder. The reference symbol d ultimately denotes the diameter of the piston of the first compression stage. In other words, the clearance volume of the first compression stage is increased due to the stroke reduction.

[0054] If the pressure on the inlet side of the second compression stage increases, the value h decreases such that the effective stroke is extended. Consequently, a large clearance volume has to be accepted for lower pressures in order to prevent compromising the inlet pressure monitoring during the reexpansion.

[0055] In order to minimize the computing effort, it is very practical to record corresponding values in tables, e.g. in 0.5 bar increments, and to store these tables in the SPC. In practical applications, such an incremental shutdown is then only activated starting at the inlet pressure, at which the electric linear motor is no longer able to set the piston in motion.