Abstract:
A multistage piston compressor for a gaseous or cryogenically liquefied medium with at least two compressor stages, which operatively interact with a shared drive train for purposes of joint powering, wherein each compressor stage exhibits a piston that is mechanically connected with the drive train, and arranged in a compressor cylinder so that it can longitudinally shift.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from German Patent Application Serial No. De 102010053091.3 filed Dec. 1, 2010. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a multistage piston compressor for a gaseous or cryogenically liquefied medium with at least two compressor stages, which operatively interact with a shared drive train for purposes of joint powering, wherein each compressor stage exhibits a piston that is mechanically connected with the drive train, and arranged in a compressor cylinder so that it can longitudinally shift. 
     A generic, multistage piston compressor is known from 10 2006 042 122 A1. 
     Such compressors are used to compress gaseous or liquid media, such as hydrogen, nitrogen or natural gas in a gaseous or liquid state. 
     In generic, multistage compressors where the pistons of the individual compressor stages are connected with a shared drive train, and the pistons of the individual compressor stages are mechanically joined with the drive train, the pistons of the compressor stages are jointly powered by the drive train, and with the drive train actuated each perform a piston motion with a constant piston stroke. Each piston of the corresponding compressor stage is exposed to the pressure of the medium built up in the corresponding compressor stage. If a compressor stage concurrently operates without compressor power, for example in a partial load range or no-load state, the built up pressure of the medium on the concurrently operating piston executing the piston stroke creates an additional energy demand, which must be applied by way of the drive train to power the piston. In addition, the built up pressure causes the concurrently operating piston to place a load on the drive train, as a result of which a non-uniform load is placed on the drive train, especially during the partial load operation or no-load operation of a compressor stage. Furthermore, loads and mechanical wear arise on allocated components in the piston of a compressor stage concurrently operating under a partial or no load, for example on the sealing devices for sealing the piston in the compressor cylinder, the mounts of the piston as well as the suction valve and pressure valve of the medium to be compressed. In addition, the piston stroke motion of the concurrently operating piston of a compressor stage produces wear on the corresponding surfaces between the piston and compressor cylinder. 
     If the compressor stages in a generic, multistage compressor are connected in series as stage compressors, and the output side of a compressor stage is connected with the input of a next compressor stage, the result in a generic compressor in which the pistons of the compressor stages are coupled with a shared drive train and synchronously powered is that the input pressure range and compression ratio of the respective compressor stage are confined to a narrow range by the fixed and constant piston stroke by the piston of the corresponding compressor stage. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a generic, multistage compressor in which the compressor stages can be operated independently of each other, and which is improved in terms of wear and energy efficiency. 
     This object is achieved according to the invention by virtue of the fact that the piston of the respective compressor stage is connected with a liquid column of an incompressible liquid situated in the compressor cylinder, which converts the piston stroke motion of the piston into a motion of a compressor piston arranged in the compressor cylinder so that it can longitudinally shift, wherein the liquid column for changing the compressor stroke of the compressor piston can be connected with an outlet. According to the invention, the piston of each compressor stage mechanically coupled with the drive train is hence connected by way of a liquid column of an incompressible liquid, for example a hydraulic fluid, with a compressor piston, which executes the corresponding compressor stroke for compressing the medium to be compressed. The liquid column of each compressor stage can be altered and varied in a manner according to the invention by connecting the liquid column with an outlet, so that given a constant piston stroke of the piston mechanically powered by the drive train, the compressor stroke of the compressor piston allocated to the piston can be controlled independently of the piston stroke. This makes it possible to partially or completely deactivate a compressor piston even though the piston is powered, and thereby shut down and immobilize the compressor piston or control it in the compressor stroke. In the multistage piston compressor according to the invention, independent and individually operable compressor stages can hence be achieved given a shared drive train. As a consequence, connecting the liquid column of hydraulic fluid powered by the piston according to the invention readily enables a partial load operation of a corresponding compressor stage. In addition, connecting the liquid column with an outlet makes it possible to deactivate one or more compressor stages, in which the corresponding compressor pistons have been immobilized and shut down, and do not perform any motions in the compressor cylinders. Shutting down or varying the compressor stroke of the corresponding compressor pistons leads to improved energy efficiency, since no drive power needs to be applied for the deactivated piston, or changing the corresponding compressor stroke of the compressor piston places a uniform load on the drive train in a partial load range. In addition, shutting down the compressor piston reduces or avoids mechanical wear on the surfaces between the pistons and compressor cylinders, the seals of the piston, and the inlet and outlet valve of the medium of a no-load compressor stage. 
     In a preferred embodiment of the invention, a valve arrangement is provided for connecting the liquid column with the outlet. A corresponding valve arrangement can be used to easily control the process of connecting the liquid column powered by the piston drivingly linked with the drive train with the outlet, so that the valve arrangement conveys the liquid column powered by the piston to the outlet, so as to partially or completely deactivate the compressor cylinder allocated to the piston. 
     In one embodiment of the invention, it is especially advantageous that the compressor cylinders be connected by means of a respective branching outlet line with a collecting outlet line, wherein the valve arrangement is situated in the branching outlet line. A collecting outlet line and a corresponding branching outlet line provided with a valve arrangement can be used on a multistage piston compressor at each compressor stage to easily control the process of individually connecting the liquid column of hydraulic fluid of each compressor stage with the outlet, so as to partially or completely deactivate the corresponding compressor piston of the compressor stage. 
     The valve arrangement is best designed as a control valve, in particular a slide valve or ball valve, with a locked position and a flow position. Through corresponding actuation, such a control valve can be used to easily connect the liquid column with the outlet in the direction of the flow position, with the goal of having the piston powered by the drive train convey the liquid column to the outlet, so as to control the motion and compressor stroke of the compressor piston. 
     The ability to actuate the valve arrangement with an electronic controller yields special advantages. By correspondingly actuating the valve arrangements, an electronic controller can be used to easily control the behavior of the compressor. 
     The collecting outlet line is best connected with a container, in particular a container exposed to a pretension pressure. A container exposed to a pretension pressure causes the liquid column to be conveyed from the powered piston to the container with the valve arrangement open under a certain counter-pressure. As an alternative, a specific pretension pressure in the collecting outlet line can be achieved by means of an overflow valve in the collecting outlet line. 
     A further development of the invention yields special advantages if at least one additional valve arrangement is situated in the collecting outlet line or branching outlet line. Additional valve arrangements make it easy to influence and/or control the behavior of the compressor. 
     In one embodiment of the invention, the additional valve arrangement can be designed as an overflow valve, in particular a pressure relief valve. A pressure relief valve in the corresponding branching outlet line makes it possible to secure the input pressure and/or output pressure of the corresponding compressor stage, so that the corresponding compressor stage can adjust to an altered input pressure and/or output pressure. 
     In another embodiment of the invention, the additional valve arrangement can be designed as a pressure control valve and/or flow limiting valve. Such an additional valve arrangement makes it easy to allow a partial load deactivation of the corresponding compressor stage. 
     In an advantageous embodiment of the invention, the drive train encompasses a crank or eccentric shaft powered by a drive motor, wherein the pistons are connected with the crank shaft by means of a respective connecting rod. The piston compressor can here be designed as a linear compressor, in which the pistons execute a pure linear motion in the compressor cylinder, and the connecting rod is arranged on the crank shaft by means of a mount. As an alternative, the compressor according to the invention can exhibit a swiveling piston configuration, in which the pistons carry out a pendulum movement in the compressor cylinder, and the connecting rod can be rigidly secured to a crank or eccentric shaft. 
     In a preferred further development of the invention, the liquid column can be linked with a supply source. A supply source can be used to easily refill the liquid column of the corresponding compressor stage, thereby making it possible to connect the compressor stage. A supply source also makes it possible to easily change out the hydraulic fluid and ventilate the liquid column. 
     The supply source best encompasses a supply pump linked with the container, which conveys by way of a supply line, wherein the compressor cylinders are connected by the respective branching supply line with a supply line, wherein the branching supply line incorporates a respective valve arrangement. A valve arrangement in corresponding branching supply lines makes it easy to refill the liquid column of the allocated compressor stage via the supply pump that feeds into the supply line. 
     In a possible embodiment of the invention, the compressor stages in a piston compressor according to the invention are connected in series. A stage compressor in which at least two compressor stages are connected in series, with the output of a compressor stage being connected with the input of another compressor stage, easily enables a partial load operation of a compressor stage via the connection of one or all compressor stages with the outlet as described in the invention. As a result, a uniform load is placed on the drive train. In addition, it allows the corresponding compressor stage to adapt to varying input or output pressures, so that the piston compressor according to the invention can be operated within a wide range of input and output pressures. 
     In another possible embodiment of the invention, the compressor stages are connected in parallel. In such a piston compressor, in which each compressor stage constitutes a separate compressor and provides a corresponding delivery capacity for the compressed medium, partially or completely deactivating the individual compressor stages as described in the invention makes it possible to easily provide a variable and adjustable delivery capacity. Connecting the corresponding liquid column of the allocated compressor stage according to the invention makes it easy to realize a multiple compressor solution for variable delivery capacity with a shared drive train. The partially or completely deactivated compressor stages here each comprise separate, stand-alone compressors. If such a multistage piston compressor requires a higher delivery capacity, additional compressor stages can be sequentially connected. In addition, the compressor according to the invention makes it possible to optimally utilize the installed engine output of the drive motor. If the counter-pressure of the compressed medium is low at the output, several compressor stages can be operated simultaneously. Given a higher counter-pressure at the output or during booster operation, the individual compressor stages can easily be disconnected to enable an adjustment to the engine output. 
     Connecting the liquid column of the corresponding compressor stage with the outlet as described in the invention further makes it possible to individually operate selected compressor stages in the case of a multistage compressor according to the invention. This enables the operation of selected compressor stages without the other compressor stages having to be operational, for example given a malfunction of a compressor stage. Given a failure or malfunction of one or more compressor stages in a multistage compressor according to the invention, the affected compressor stages can be switched off, and the compressor can continue to be operated with the functional compressor stages. 
     The piston compressor according to the invention can be designed in such a way that the compressor pistons operated by means of the liquid column are in direct contact with the medium to be compressed, and compress the medium. In a preferred further development of the invention, the compressor is designed as an ionic compressor, wherein the compressor piston of the corresponding compressor stage is in contact with a liquid column of an ionic operating liquid that is situated in the compressor cylinder, and used to compress the medium. Such ionic compressors displace the medium to be compressed from the ionic liquid column into the compressor cylinder, and are preferably used for compressing gaseous media, for example hydrogen. 
     A multistage piston compressor according to the invention makes it possible to connect the liquid column with the outlet so as to be able to partially or completely deactivate a compressor stage or several compressor stages as the drive train continues to run. The partial deactivation of individual compressor stages easily enables the partial load operation of selected compressor stages. The complete deactivation of individual compressor stages permits the adjustment of the compressor output to the installed engine output of the drive motor of the drive train and/or achievement of a variable compressor power. In addition, completely deactivating individual compressor stages allows the compressor to keep operating given a disrupted or inoperative compressor stage. 
     Furthermore, a multistage piston compressor according to the invention makes it possible to connect liquid columns of all compressor stages with the outlet so as to initiate an emergency shutdown of the compressor as the drive train continues to run. In the case of a multistage piston compressor according to the invention, all liquid columns of the compressor stages can be simultaneously connected with the outlet to realize an emergency load shedding, in which all compressor stages are deactivated without having to immediately bring the drive train to a standstill. 
     Additional advantages and details of the invention will be explained in greater detail based on the exemplary embodiments depicted on the schematic figures. Shown on: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a multistage piston compressor according to the invention, and on 
         FIG. 2  is a further development of the multistage piston compressor. 
     
    
    
       FIG. 1  shows a multistage piston compressor  1  according to the invention, which in the present exemplary embodiment encompasses four compressor stages A, B, C, D. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Each compressor stage A, B, C, D encompasses a piston  3 A,  3 B,  3 C,  3 D situated in a compressor cylinder  2 A,  2 B,  2 C,  2 D so that it can shift longitudinally. The pistons  3 A- 3 D are drivingly linked with a shared drive train  4  in order to jointly power the pistons  3 A- 3 D. 
     In the exemplary embodiment shown, the drive train  4  consists of a crank or eccentric shaft  6  powered by a drive motor  5 , for example an electric motor or combustion engine, wherein the pistons  3 A- 3 D are each mechanically connected with the crank shaft  6  by means of a connecting rod  7 A- 7 D. A mount  8 A- 8 D can be incorporated where the connecting rod  7 A- 7 D is hinged to the crank or eccentric shaft  6 . 
     According to the invention, each piston  3 A- 3 D is connected by means of a liquid column  9 A- 9 D consisting of an incompressible medium, for example a hydraulic fluid, in the compressor cylinder  2 A- 2 D with a compressor piston  10 A- 10 D, which can be longitudinally shifted in the compressor cylinder  2 A- 2 D and is used to compress the medium M to be compressed, for example gaseous or liquid hydrogen, either directly or with the insertion of a liquid column of ionic operating liquid  30 A- 30 D. Schematically depicted sealing arrangements are used to seal the piston  3 A- 3 D away from the corresponding compressor cylinders  2 A- 2 D. 
     Given a powered drive train  4 , the kinematics of the crank shaft  6  and connecting rod  7 A- 7 D lead to a predetermined, constant piston stroke KH between the upper lower dead point of the corresponding pistons  2 A- 2 D of the respective compressor stages A-D. 
     According to the invention, the receptive liquid column  9 A- 9 D of the allocated compressor stage A-D can further be connected with an outlet  15 . 
     Provided for this purpose is a collecting outlet line  21 , which is routed to a container  20 , and connected to the respective compressor cylinders  2 A- 2 D by a respective one corresponding branching outlet line  22 A- 22 D. Each branching outlet line  22 A- 22 D incorporates a an outlet line valve  23 A- 23 D in order to control the process of connecting the liquid column  9 A- 9 D with the collecting outlet line  21 , and hence to correspondingly drain hydraulic fluid of the allocated liquid column  9 A- 9 D. The container  20  can be exposed to a slight pretension.  22 B and  22 C represent branching outlet lines for compressor stages B and C and  28 B and  280  represent branching supply lines for compressor stages B and C.  23 B and  23 C and  29 B and  29 C represent valve arrangements for compression stages B and C. 
     The outlet line valve  23 A- 23 D can be designed as a slide valve or ball valve, which can be actuated between a flow position and locked position. 
     Provided for refilling hydraulic fluid from the container  20  into the corresponding liquid column  9 A- 9 D of compressor stages A-D is a supply source  25 , which exhibits a supply pump  26  that is connected with the container  20  on the suction side, and conveys into a supply line  27  on the pressure side. The compressor cylinders  2 A- 2 D are each connected by means of a branching supply line  28 A- 28 D with the supply line  27 . A respective supply line valve  29 A- 29 D is situated in the supply lines  28 A- 28 D for correspondingly filling hydraulic fluid in the allocated liquid column  9 A- 9 D. The valve arrangement  29 A- 29 D can be designed as a slide valve or ball valve, which can be actuated between a flow position and locked position. 
     Hydraulic fluid can be drained from the corresponding liquid column  9 A- 9 D by correspondingly actuating the outlet line valve  23 A- 23 D, so that given a predetermined and constant piston stroke KH of the allocated piston  3 A- 3 D toward the top on  FIG. 1 , the flowing pressure exerting means in the form of the hydraulic fluid of the liquid column  9 A- 9 D being conveyed in the compressor cylinder  2 A- 2 D is partially or completely conveyed to the outlet  15  with the outlet line valve  23 A- 23 D opened, and hence into the container  20 . When the outlet line valve  23 A- 23 D is opened, the hydraulic fluid conveyed by the mechanically powered piston  3 A- 3 D is prevented from not or only partially getting to the allocated compressor piston  10 A- 10 D, and a corresponding movement is imparted to the compressor piston  10 A- 10 D. This diversion of conveyed hydraulic fluid in the liquid column  9 A- 9 D into the collecting outlet line  21  makes it possible to switch the affected compressor stage A-D, and hence the compressor piston  10 A- 10 D, partially or completely to no load, and thereby render it motionless. The drive train  4  can here continue to run, and power the additional compressor stages. 
     As a consequence, connecting the liquid column  9 A- 9 D of the respective compressor stage A-D with the outlet  15  as described in the invention makes it possible to vary and change the compressor stroke VH of each compressor piston  10 A- 10 D independently of the constant piston stroke KH of the allocated piston  3 A- 3 D, wherein the compressor piston  10 A- 10 D can further be shut down completely with the compressor stroke VH at zero. Therefore, controlling the liquid column  9 A- 9 D with the outlet  15 , and hence the container  20 , enables the partial or complete deactivation of a compressor cylinder  10 A- 10 B. Individually activating the outlet line valve  23 A- 23 D further makes it possible to control and change the compressor stroke VH of each compressor piston  10 A- 10 D independently of the compressor stroke of the other compressor pistons of the other compressor stages. 
       FIG. 2  illustrates a further development of the invention based on a compressor stage A of the compressor  1  according to the invention. The other compressor stages B-D of the compressor  1  according to the invention can be correspondingly designed. 
     According to  FIG. 2 , the compressor  1  is designed as an ionic compressor  1 , wherein the compressor piston  10 A designed as a phase separator, which is moved by the hydraulic fluid and hence the liquid column  9 A- 9 D, is in contact with a liquid column of an ionic operating liquid  30 A that is situated in the compressor cylinder  2 A, and performs a compressor stroke at the fill level  31  corresponding to the compressor stroke VH of the compressor piston  10 A. The ionic operating liquid  30 A is used to compress the medium M, which is located in a displacement space created by the compressor cylinder  2 A and ionic operating liquid  30 A. An inlet valve  32 A and outlet valve  33 A at the compressor cylinder  2 A can be used to aspirate and eject the medium M. 
       FIG. 2  further shows an electrical activation device  40 A, for example a magnet or electric actuator, for the outlet line valve  23 A situated in the branching outlet line  22 A. The outlet line valve  23 A can be activated by means of an electronic controller  41 , which is connected with the activation device  40 A for this purpose. 
     According to  FIG. 2 , at least one additional valve  50 A or  55 A is arranged in the branching outlet line  22 A. In the present exemplary embodiment, an overflow valve  51 A, for example a pressure relief valve, and a control valve  52 A, for example a pressure control or pressure relief valve, are situated in the branching outlet line  22 A as an additional valve  50 A or  55 A. 
     There are a series of advantages associated with a multistage compressor  1  according to the invention. 
     In the multistage piston compressor  1  according to the invention, independent compressor stages A-D can be achieved given a shared drive train  4  with a single drive motor  5 . In the multistage piston compressor  1  according to the invention with a shared drive train  4 , individual compressor stages A-D can be partially or completely deactivated, and thereby operated under partial load or no load conditions, or individual compressor pistons can be rendered motionless. This yields improved energy efficiency and a reduced load for the drive with the compressor stage deactivated. In addition, a reduced load and less mechanical wear are achieved in an immobilized compressor piston of a compressor stage, for example on the seals of the compressor piston and the surfaces of the compressor piston as well as the compressor cylinder, and the valves of the compressor stage. 
     Partially or completely decoupling individual compressor stages from the drive train further results in an elevated energy efficiency during partial load operation. In addition, this makes it possible to maintain a uniform load on the drive train. 
     Furthermore, individually deactivating the separate compressor stages as described in the invention allows the compressor  1  to adjust to altered input and output pressures of the medium to be compressed. As a consequence, in a multistage piston compressor according to the invention designed as a stage compressor, this permits operation in an expanded input pressure range, and a variable compression ratio on the corresponding compressor stages. 
     Situating one or more additional outlet line valves in the branching outlet lines of the corresponding compressor stage makes it possible to easily influence and/or control the behavior of the compressor. One or more deactivation variants (partial load, pressure relief, complete shutdown) for the corresponding compressor stage can be readily enabled by arranging an overflow valve, for example a pressure relief valve, or and/or a control valve, for example a pressure control valve or flow control valve, in the corresponding branching outlet line of a compressor stage.