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Apparatus and method for compressing a gas

Apparatus and method for compressing a gas description/claims

This application claims the priority of International Application No. PCT/EP2006/006520, filed Jul. 4, 2006, and German Patent Document No. 10 2005 034 907.2, filed Jul. 26, 2005, the disclosures of which are expressly incorporated by reference herein.

The invention relates to a compressor, in particular a piston compressor, for compressing a gaseous medium, having a low pressure stage for compressing the medium from an inlet pressure to an intermediate pressure, and having a high pressure stage for compressing the medium from the intermediate pressure to a high pressure.

In the case of compressors for gaseous media that are embodied as piston compressors, the stage pressure ratio is determined by the cylinder dimensions. In the case of a piston compressor with two compressor stages formed by a low pressure stage and a high pressure stage, and a stage pressure ratio in the range of 17, e.g., a medium with an inlet pressure of 1 bar, can be compressed in the low pressure stage, which has a stage pressure ratio of 17, to an intermediate pressure of 17 bar, and can be compressed in the high pressure stage, which has a stage pressure ratio of 17.6, to a high pressure of 300 bar.

These types of piston compressors are designed for a specific inlet pressure, whereby the inlet pressure of the medium may only be varied within narrow limits. If a generic piston compressor that is designed for an inlet 1 bar is operated with an inlet pressure of 5 bar instead of an inlet pressure of 1 bar, an intermediate pressure of 85 bar would take effect after the low pressure stage with the stage pressure ratio of 17, which would cause the low pressure stage to overheat.

A two-stage piston compressor is known from German Patent Document No. DE 199 33 989 A1, which is suitable for different inlet pressures. In this case, separate drives are provided for the piston compressor's low pressure stage and the high pressure stage. However, this type of two-stage piston compressor with a drive for the low pressure stage and a separate drive for the high pressure stage has a construction expense that is too high.

The present invention is based on the objective of making available a compressor of the kind cited at the outset, which, with low construction expense, is suitable for different inlet pressures.

This objective is attained in accordance with the invention in that a compensating volume with an adjustable dead volume is connected upstream of the high pressure stage. With this type of compensating volume that is connected upstream of the high pressure stage and thus on the high pressure stage, it is possible in a simple manner to provide an adjustable dead volume on the high pressure stage. During the compression stroke of the low pressure stage, gaseous medium is supplied partially to the compensating volume in the process. With the subsequent supplying of the medium from the compensating volume to the high pressure stage, during the following intake stroke of the high pressure stage, the gaseous medium expands adiabatically and cools down in the process to below the intake temperature of the low pressure stage. With this type of compensating volume, it is possible to change the intake volume of the high pressure stage in a simple manner and simultaneously achieve additional cooling of the compressor. As a result, it is possible in a simple way to operate the compressor with different inlet pressures, whereby overheating of the compressor continues to be avoided.

Particular advantages are produced according to one embodiment of the invention if the dead volume formed by the compensating volume can be adjusted as a function of the inlet pressure. In this connection, it is possible to use the compensating volume to control the dead space of the high pressure stage as a function of the inlet pressure with little effort.

Special advantages are produced if the compensating volume is set at a minimum dead volume with maximum inlet pressure and with decreasing inlet pressure can be adjusted in the direction of a maximum dead volume. Thus, it is possible for the additional cooling effect to increase in a simple way with falling inlet pressure due to the compensating volume. With decreasing inlet pressure, the stage pressure ratio of the high pressure stage increases, whereby at the same time the thermal load of the compressor increases. Because of a compensating volume that forms a dead volume for the high pressure stage and is allocated to the high pressure stage, and whose cooling effect increases with a falling inlet pressure because of the expansion of the dead volume, the compressor temperature of a compressor used at different inlet temperatures can be reduced in a simple manner as a result.

The compensating volume is expediently embodied as a compensating cylinder featuring a cylinder that is displaceable in a housing. This design of the compensating volume as an adjusting cylinder makes it possible to produce an adjustable dead volume in a simple way.

According to a preferred embodiment of the invention, the cylinder is expediently provided with a first control surface as a stepped piston, which is arranged in the compensating volume and is acted upon by the intermediate pressure, and features a second control surface, which is acted upon by the inlet pressure. With this type of cylinder that is embodied as a stepped piston, it is possible in a simple manner through a corresponding selection of the sizes of the first and second control surfaces to facilitate the pressurization of the cylinder in the direction of the minimum dead volume with a maximum inlet pressure and in the direction of the maximum dead volume with decreasing inlet pressure

According to a development of the invention, the compensating volume is provided with a cooling device, whereby the medium located in the compensating volume can be cooled in a simple manner and thus the cooling effect by the compensating volume can be increased further.

According to a preferred embodiment of the invention, the cooling device is formed by cooling fins arranged on the housing, whereby a cooling device of the compensating volume can be produced at a low construction expense.

According to a preferred embodiment of the invention, the compressor features a piston that is longitudinally displaceable in a housing, which can be driven hydraulically.

The low pressure stage expediently has a first pressure chamber and a second pressure chamber, whereby the piston actuates two pressure chambers of the low pressure stage.

As a result, pulsations in the pressurized lines can be reduced by two pressure chambers with a low requirement for construction space.

According to a development of the invention, the high pressure stage has a first pressure chamber and a second pressure chamber. As a result, the piston continues to actuate two pressure chambers of the high pressure stage, whereby low pulsations can be achieved with a low requirement for construction space for the compressor.

The compressor can be cooled in a simple manner in the area of the low pressure stage and the high pressure stage if external cooling is provided on the housing.

To improve cooling, internal cooling is expediently provided on the piston.

In this case, the piston is advantageously provided with at least one longitudinal borehole, which is connected to a drive pressure chamber. As a result, internal cooling of the piston can be accomplished in a simple manner by the hydraulic pressurizing means driving the compressor.

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