FR3118484A1 - Compression system with multiple compression stages mounted in series - Google Patents

Abstract

Compression system with several compression stages connected in series The invention relates to a gas compression system (2) comprising:- a gas inlet (10),- two compression stages (20) connected in series each comprising: - a rotary electric motor (60) configured to compress the gas, - an electric motor rotational speed control unit (27, 37), the control units each being configured to control the rotational speed of the corresponding electric motor (60) at least as a function of the gas pressure upstream of the corresponding compression stage or the control units each being configured to control the speed of rotation of the corresponding electric motor (60) at least as a function of the gas pressures downstream of the corresponding compression stage. Figure for abstract: Fig. 1

Description

Compression system with multiple compression stages mounted in series

The present invention relates to gas compression systems, in particular hydrogen, and gas compression methods using such compression systems.

From the emergence of hydrogen fuel cells, arises a need to compress a large quantity of gas in a small storage volume at low energy cost to power such systems.

Currently, there are different methods for compressing a gas. They consist in carrying out a volumetric compression of the gas in a compression chamber. The purpose of this compression is to reduce the volume of gas stored compared to the volume it would occupy at atmospheric pressure. The volumetric ratio of the compression system (or compression ratio) is the parameter which makes it possible to modify the pressure between the inlet (or intake pressure) and the outlet (or discharge pressure) of the compression system.

Each compressor has a possible operation for a pressure range upstream of the compressor and a gas pressure range downstream of the compressor that is very precise and is characterized by its compression ratio. In particular, it has an energy-optimized operation for a particular inlet pressure within the possible inlet pressure range. Outside these ranges, the compressor may not compress the gas, wear prematurely, or even deteriorate and has increased energy consumption.

In the case of the use of a single compressor, the compression is limited by the characteristics of the compressor itself and it is not possible to obtain significant pressure differentials between the pressure upstream and the pressure in downstream.

It may be advantageous to have several compression stages mounted in series. The operating characteristics of the compression stages, in particular their optimum admission pressures, are then different, in order to be adapted to the particular compression range to be achieved for each of them.

This configuration with several compression stages improves efficiency and therefore lower energy consumption compared to a single compressor solution. It also makes it possible to achieve significant compressions that are not achievable or difficult to achieve at low energy cost with a single compression stage.

State-of-the-art compression stages operate at a constant rotational speed of their electric motor. The gas flow at the outlet of each compression stage is therefore almost constant over time, except for variations linked to cyclic irregularities, to the closing and opening times of the valves and to the gas compressibility factor which can vary. depending on the pressure at the outlet of the compression system.

However, when variations in pressure at the inlet of the compression stage, for example linked to a variation in pressure generated by a system for producing said gas, or variations in the flow rate in the system, for example generated by a variation in consumption gas at the outlet, appear, they have repercussions on the various compression stages mounted in series. The inlet pressures of the various compression stages may no longer be optimized. This can lead to increased energy consumption, faster wear and even damage to the systems.

When variations in flow appear, it is known from patent EP 1 291 525 B1 to apply an “On/Off” operating strategy of a compression stage. In this patent, the compressors are stopped or restarted according to predetermined pressure thresholds. Such repeated stops and restarts generate premature aging of the compressors, in particular of the parts deforming in the compressors, such as the membranes in the membrane compressors.

In this case, the series compressors are generally controlled centrally by linking them to a central control unit remote from the compressors. This link can be interrupted for hardware or software problems, leading to malfunctions of the compressors. This risk increases with the distances between the compressors and the central control unit, which complicates the regulation of a chain of compressors far from each other, in particular in different places and can generate a degradation of the system.

It is also known from patent EP 0 431 287 B1 to regulate the gas flow of compressors by varying the geometry of compression vanes in centrifugal compressors.

There is a need for a compression system with optimized performance and therefore reduced energy consumption.

The invention meets this need with the aid of a gas compression system comprising:
- a gas inlet
- a first compression stage supplied with gas by the gas inlet and delivering a compressed gas,
- a second compression stage supplied with compressed gas by the first compression stage and delivering a compressed gas,
the first and the second compression stage each comprising
- a rotary electric motor configured to compress the gas, and
- a unit for controlling the rotational speed of the electric motor,
the first compression stage control unit being configured to control the speed of rotation of the corresponding electric motor at least as a function of the gas pressure at the inlet of the first compression stage and the second compression stage control unit being configured to control the speed of rotation of the corresponding electric motor at least as a function of the gas pressure at the inlet of the second compression stage
Or
the first compression stage control unit being configured to control the speed of rotation of the corresponding electric motor at least as a function of the gas pressure at the outlet of the first compression stage and the second compression stage control unit being configured to control the speed of rotation of the corresponding electric motor at least as a function of the gas pressure at the outlet of the second compression stage.

The fact that the inlet of the second compression stage is fed by the gas at the outlet of the first compression stage is characteristic of having two compression stages in series forming a chain of compression stages.

With such a system of compression stages in series, any variation in the gas flow rate of the first compression stage leads to a disagreement with the gas flow rate of the second compression stage and vice versa, which affects the pressure at the inlet of the second compression stage. This disagreement can prevent the proper functioning of the system, degrade its lifespan and its performance. The control units of the two compression stages make it possible to compensate for these variations and bring the system back to a predetermined optimum operating speed for each of the compression stages.

Such a device also makes it possible to optimize the system in the case where the flow rate varies during compression due to the variation of the compressibility factor of the gas and/or the temperature of the gas.

Finally, the fact that the regulation of engine speeds is done locally at the level of each compression stage with local data (pressure at the inlet and/or at the outlet of the corresponding compression stage) makes it possible to have efficient regulation even when the compression stages of the chain are far from each other, in particular in the case of a network of compressors of a certain scale or an environment making control communications difficult.

System

The system may comprise one or more additional compression stages mounted in series downstream of the second compression stage, the additional compression stage(s) each comprising:
- a rotary electric motor configured to compress the gas coming from the compression stage arranged upstream of said additional compression stage,
- a unit for controlling the speed of rotation of the electric motor as a function of the inlet gas pressure, when the control unit of the first and second compression stages controls the speed of the corresponding motor as a function at least of the pressure of gas at the inlet of the corresponding first or second compression stage, or
the gas pressure at the outlet, when the first and second compression stage control unit controls the speed of the corresponding engine as a function at least of the gas pressure at the outlet of the corresponding first or second compression stage.

Thus, the system comprises a chain of compression stages mounted in series with respect to each other, the compression stages all being regulated at least by the pressure upstream of each compression stage or all regulated at least by the pressure in downstream of each compression stage.

Preferably, the system comprises a gas reservoir at least between two consecutive compression stages, in particular between the first and the second compression stage. Such a gas reservoir makes it possible to absorb a variation in the flow rate of one of the two compression stages by preventing damage to the system.

Preferably, the system supplies gas to a closed gas storage tank or a gas consumption device which may be part of the system.

Preferably, the system comprises a gas source at the inlet, in particular an electrolyser supplying gas to the gas inlet or a finite volume gas reservoir.

When the gas source is an electrolyser, the second compression stage control unit can be configured to start the second compression stage when the pressure at the inlet or at the outlet of the second compression stage is greater than a pressure of predefined minimum setpoint of the second compression stage. The second stage compression may include a second stage compression gas bypass circuit between the first stage compression gas outlet and the second stage gas outlet when the second stage compression is off.

When the gas source is a finite volume compressed gas tank, the first stage compression control unit can be configured to turn on the first stage compression when the inlet or outlet pressure of the first stage compression is less than a pressure respectively at the inlet or at the outlet of the maximum setpoint of the first compression stage. The first stage compression may include a first stage compression gas bypass circuit between the gas inlet and the inlet of the second stage compression that is open when the first stage compression is off.

The device may comprise a pressure sensor at the gas inlet and a central control unit, configured to stop the system when the pressure at the gas inlet reaches a minimum inlet pressure, in particular a pressure less than or equal to a minimum allowable inlet pressure for the first compression stage. The minimum inlet pressure may be less than or equal to 30 bars, preferably less than or equal to 10 bars, better still less than or equal to 5 bars. Such a system shutdown is particularly useful when the gas source is a finite volume gas reservoir.

The device may comprise a pressure sensor at the outlet of the last compression stage and a central control unit, configured to stop the system when the outlet pressure is greater than or equal to a predefined final outlet pressure. The predefined final outlet pressure can be between 400 and 1000 bars, better between 600 and 850 bars, even better between 700 and 800 bars. Such a shutdown of the system is particularly useful when the system is used to fill a closed gas tank. This is particularly linked to automotive tank applications, where the typical hydrogen filling pressure is 350 bars or 700 bars according to current technologies. A hydrogen station tank at a pressure of around 750 bars is therefore suitable for this purpose.

The system may include a gas cooling device at the outlet of one or each compression stage. This makes it possible to increase the density of the gas and to limit the thermal stresses on the compression stages.

The system may include a measurement of the position of the flywheels and the control units may be high frequency drive units configured to vary the engine speed according to the position of the engine in real time. This makes it possible to reduce the rotational speed of the engines when passing the top and bottom dead centers of the piston corresponding to the openings and closings of the intake and discharge valves, which smooths out cyclic irregularities and increases the life of the compressors by reducing internal constraints.

Compression stages

The first and/or the second compression stage and/or the additional compression stage(s), if any, can be formed from a single compressor.

As a variant, the first and/or the second compression stage and/or the additional compression stage(s), if any, are formed by a plurality of compressors mounted in parallel. Each compressor may include a rotary electric motor. The control unit of the or each compression stage, having a plurality of compressors in parallel, can control the speed of all the electric motors of the compression stage. In this case, the compressors of the compression stage or stages having several compressors are preferably identical and the control unit generates the same speed setpoint for all the electric motors of the corresponding compression stage. As a variant, a different rotation speed setpoint can be applied to each of the compressors of the same stage.

Preferably, the or each compressor each comprises at least one compression chamber receiving a gas at an inlet pressure at the inlet, compressing it by reducing its volume and delivering at the outlet a so-called compressed gas at a discharge pressure greater than inlet pressure. The gas inlet and outlet in the compression chamber is preferably done via inlet and outlet valves.

Preferably, the compressor or compressors are membrane or slide compressors. For example, the electric motors of the compressor(s) compress the gas indirectly via a crankshaft driven in rotation by the electric motor and connected to a piston which it moves during its rotation in an alternating translational movement in a cylinder. The displacement of the piston generates the compression of the gas, in particular by an alternating variation of the volume of a compression chamber. The piston can compress a liquid, in particular a hydraulic oil, separated from the compression chamber by at least one deformable membrane. When moving the piston in the cylinder, the liquid is compressed and deforms the deformable membrane, which reduces the volume of the compression chamber and compresses the gas. The electric motor of the or each compressor can generate the compression of the gas in a plurality of compression chambers in parallel, in particular via several pistons mounted on the same crankshaft. Preferably, all the compression chambers have the same characteristics. They may or may not be out of phase with each other. For example, the electric motor can generate the compression of the gas in two compression chambers mounted in opposition, preferably having the same characteristics but being in compression phase inversion.

Control unit

Preferably, the control units regulate the speed of the corresponding electric motors in real time and continuously over time.

The first compression stage control unit can be configured to control the rotational speed of the corresponding electric motor only according to the gas pressure at the inlet of the first compression stage and the second compression stage control unit is configured to control the speed of rotation of the corresponding electric motor solely as a function of the gas pressure at the inlet of the second compression stage, where applicable the control unit of the or each additional compression stage is configured to control the speed of rotation of the corresponding electric motor solely as a function of the gas pressure at the inlet of said additional compression stage.

Alternatively, the first compression stage control unit is configured to control the rotational speed of the corresponding electric motor only as a function of the gas pressure at the outlet of the first compression stage and the second compression stage control unit compression is configured to control the speed of rotation of the corresponding electric motor only as a function of the gas pressure at the outlet of the second compression stage, where applicable the control unit of the or each additional compression stage is configured to control the speed of rotation of the corresponding electric motor only as a function of the gas pressure at the outlet of said additional compression stage.

Preferably, the first and second compression stages each comprise one or more variable speed drives controlled by the corresponding control unit and each supplying an electric motor.

Thus in the case where the first and/or the second compression stage comprise several compressors each comprising an electric motor as described above, a variable speed drive can supply all the electric motors simultaneously or the electric motors can be supplied by variable speed drives different.

The control units may each comprise a supervision device, in particular a supervision automaton controlling the electric motor(s), in particular via the variable speed drive(s), according to the pressure data at the input of the compression stage. or pressure data at the output of the corresponding compression stage.

The control unit of at least one of the compression stages may comprise at least one temperature sensor at the outlet and/or at the gas inlet of said compression stage. Preferably, the compression stage control unit having a temperature sensor is configured to slow down the speed of rotation of the electric motor or motors of the corresponding compression stage when the temperature measured by the corresponding temperature sensor is above a predetermined threshold temperature.

Such a reduction in speed depending on the temperature makes it possible to protect the system from overheating and therefore from degradation linked to an excessively high system temperature.

Preferably, the control units are configured so that the speed of rotation of the electric motor(s) can take at least one intermediate speed value between the maximum speed and the stopping of the electric motor. Preferably, the control units are configured to vary the rotational speed of the electric motor(s) continuously between at least two rotational speed values, in particular between a maximum value and a minimum rotational value of the electric motor, in plus the possibility of stopping the electric motor.

Preferably, the compression stage control units are independent of each other. By “ independent of each other ”, it is understood that the control units do not communicate directly with each other other than by means of the pressure variations detected at the inlet and at the outlet of the compression stage to which they belong. Thus, in operation, each control unit regulates the speed of the electric motor of the corresponding compression stage on the basis of local data measured at the level of said compression stage to maintain the pressure at the inlet or at the outlet, depending on the case, at a pressure of predefined setpoint. According to a variant, the compression stage control units are connected to a central control unit which provides each control unit with the pressure setpoint curve as a function in particular of the nature of the gas source and/or of the device in question. exit from the system.

According to another variant, the control units are totally independent and are not linked to any central control unit. They regulate the gas pressure downstream or upstream according to a predefined pressure curve.

Regulation by inlet pressure

When the control units of the first and second compression stages, and if necessary of the additional compression stages, are configured to control the speed of rotation of the corresponding electric motor as a function of the gas pressure at the inlet of the compression stage, corresponding compression, the system preferably comprises gas pressure sensors at the inlet of the corresponding compression stage.

In this case, the control units can be configured to maintain the inlet pressure of each compression stage at a predefined set inlet pressure. Preferably, the set inlet pressure is maintained substantially constant over time. Preferably, the set pressures at the inlet of the compression stages are substantially constant over time at optimum pressure values for the operation of the corresponding compression stage.

Thus, having a control unit for the first compression stage as a function of the pressure at the inlet of the first compression stage makes it possible to directly detect a variation in the pressure at the inlet and, by varying the gas flow at the outlet of the first compression stage, to keep the inlet pressure of the first compression stage according to a predetermined curve, in particular substantially constant at an optimum inlet pressure value for the first compression stage, or for the gas source, even in case of variation of the inlet pressure generated by the gas source. This optimization of the inlet pressure is reflected, via the variation in flow rate at the outlet of the first compression stage, on the second compression stage by a variation in the pressure at the latter's inlet. The control unit for the second compression stage as a function of the inlet pressure of the second compression stage makes it possible, by varying the flow rate of the second compression stage, to bring the pressure at the inlet of the second compression stage according to the predetermined curve , in particular at an optimum inlet pressure value in view of the characteristics specific to the second compression stage. If necessary, the control unit(s) of the additional compression stage(s) operate in the same way, so that the optimization of inlet pressure affects all of the compression stages. Thus, whatever the flow rate of the gas source at the inlet of the compression stages, the operation of the system can be optimized.

It is then possible to finely and locally regulate the pressure at the inlet of the first compression stage and/or the gas flow at the inlet of the first compression stage according to predetermined setpoint values and to pass on this regulation to all of the compression stages. compression downstream by regulations of the compression stages which each take place locally at the level of each compression stage without any communication between the various control units being necessary.

Preferably, the gas source is an electrolyser.

In this case, the second compression stage may comprise a gas bypass circuit between the outlet of the first compression stage and the gas outlet of the second compression stage as described previously.

The second stage compression control unit can be configured to start the second stage compression and close the bypass circuit when the inlet pressure of the second stage compression is higher than the set inlet pressure for the start of the second stage. compression stage. It can be the same for each of the additional compression stages, if necessary.

Alternatively, the gas source is a compressed gas reservoir of finite volume, the first compression stage may include a gas bypass circuit between its gas inlet and the inlet of the second compression stage as previously described and the the first stage compression control unit can be configured to start the first stage compression and close the bypass circuit when the inlet pressure of the first stage compression is less than the set maximum inlet pressure for the first stage compression . It can be the same for each of the additional compression stages, if necessary.

Outlet pressure regulation

Preferably, when the compression stage control units are configured to control the speed of rotation of the corresponding electric motor as a function of the gas pressure at the outlet of the corresponding compression stage, each compression stage comprises a pressure sensor of gas at the outlet of said compression stage.

The control unit of the second compression stage is preferably configured to maintain the pressure at the outlet of the second compression stage at a predefined outlet setpoint pressure, preferably substantially constant over time at an optimum pressure value for operation of second stage compression or gas consuming systems. Alternatively, the setpoint pressure at the outlet of the second compression stage can be variable. The output setpoint pressure can follow a predefined pressure curve over time.

The system can supply gas to an external system having a predetermined gas flow curve, the set point pressure at the outlet of the second compression stage can follow a curve adapted to the gas flow curve of the external system.

Thus, having a control system for the second compression stage as a function of the pressure at the outlet of the second compression stage makes it possible to detect in real time a variation in the pressure at the outlet and, by regulating the speed of rotation of the electric motor of the second compression stage, to keep the pressure at the outlet of the second compression stage according to the set pressure, in particular at an optimum outlet pressure value in view of the characteristics specific to the second compression stage, even in the event of variation outlet pressure. This optimization of the pressure at the outlet is reflected, via the variation in flow at the inlet of the second compression stage, on the first compression stage by a variation in the pressure at the outlet of the latter. The system for controlling the first compression stage as a function of the pressure at the outlet of the first compression stage makes it possible, by varying the flow rate of the first compression stage, to bring the pressure at the outlet of the first compression stage to a pressure value optimum output given the characteristics specific to the first stage of compression. If necessary, the control unit(s) of the additional compression stage(s) operate in the same way, so that the optimization of pressure at the outlet of the last compression stage of the chain affects all of the compression stages. upstream compression. Thus, regardless of the variation in the gas pressure at the outlet of the compression stages, the operation of the system can be optimized.

It is then possible to finely and locally regulate the pressure at the outlet of the last compression stage of the chain and/or the gas flow at the outlet of the last compression stage of the chain according to predetermined setpoint values and to pass on this regulation to all of the compression stages upstream by regulation of the compression stages which each take place locally at the level of each compression stage without any communication between the various control units being necessary.

Preferably, the gas outlet is connected to a reserve of gas of finite volume, to be brought to a certain setpoint pressure.

Preferably, the gas source is an electrolyser.

In this case, the second compression stage may comprise a gas bypass circuit between the outlet of the first compression stage and the gas outlet of the second compression stage as described previously.

The second stage compression control unit can be configured to start the second stage compression and close the bypass circuit when the inlet pressure of the second stage compression is higher than the set inlet pressure for the start of the second stage. compression stage.

Alternatively, the gas source is a compressed gas reservoir of finite volume, the first compression stage may include a gas bypass circuit between its gas inlet and the inlet of the second compression stage as previously described and the The first-stage compression control unit can be configured to start the first-stage compression and close the bypass circuit when the pressure at the outlet of the first-stage compression is less than the maximum setpoint pressure of the first-stage compression.

Gas

Preferably, the gas is hydrogen.

Process

The invention also meets this need using a gas compression method, in particular using a compression system as described above, comprising:
- the compression of a gas by a first compression stage comprising a rotary electric motor,
- the compression by a second compression stage of the compressed gas delivered by the first compression stage, the second compression stage comprising a rotary electric motor,
- the enslavement of the speed of rotation of the electric motor of the first stage of compression as a function at least of the gas pressure at the inlet of the first stage of compression and the enslavement of the speed of rotation of the electric motor of the second stage of compression as a function at least of the gas pressure at the inlet of the second compression stage, or the control of the speed of rotation of the electric motor of the first compression stage as a function at least of the gas pressure at the outlet of the first compression stage and the control of the speed of rotation of the electric motor of the second compression stage as a function at least of the gas pressure at the outlet of the second compression stage.

All of the characteristics described previously in the context of the compression system apply to the compression process independently of the device.

Preferably, the servo-control is in real time and continuous over time.

The servo-control of the rotational speed of the electric motor of the first compression stage can be performed as a function of the gas pressure at the outlet of the first compression stage and the servo-control of the rotational speed of the electric motor of the second compression stage can be performed as a function of the gas pressure at the outlet of the second compression stage so that the pressure at the gas outlet of the last compression stage of the chain is regulated at a set pressure, preferably substantially constant.

The servo-control of the rotational speed of the electric motor of the first compression stage can be carried out as a function of the gas pressure at the inlet of the first compression stage and the servo-control of the rotational speed of the electric motor of the second compression stage can be performed as a function of the gas pressure at the inlet of the second compression stage so that the pressure at the gas inlet is regulated at a set pressure, preferably substantially constant.

The method may comprise compression by one or more compression stages, downstream of the second compression stage, arranged in series, each compression stage comprising a rotary electric motor, and the control of the speed of rotation of the electric motor of the or of each additional compression stage as a function of the gas pressure at the inlet of said additional compression stage when the first and second compression stages are regulated by the corresponding upstream pressure, or as a function of the gas pressure at the outlet of said stage compression when the first and second compression stages are regulated by the corresponding downstream pressure.

Preferably, the speed of rotation of the electric motor(s) takes at least one intermediate speed value between the maximum speed and the stopping of the electric motor. Preferably, the rotational speed of the electric motor(s) can vary continuously between at least two rotational speed values, in particular between a maximum value and a minimum value, in addition to stopping the electric motor.

Preferably, the method comprises storing the gas compressed by the first compression stage in an intermediate gas reservoir between the two compression stages, said intermediate reservoir supplying gas to the second compression stage.

The method may comprise steps of compressing the gas by additional compression stages mounted in series and each comprising a rotary electric motor and the enslavement of each additional compression stage by a control unit for the rotational speed of the corresponding electric motor depending on the inlet gas pressure, when the control unit of the first and second compression stages controls the speed of the corresponding engine according to the inlet gas pressure of the corresponding first or second compression stage, or the outlet gas pressure, when the first and second compression stage control unit controls the speed of the corresponding engine as a function of the outlet gas pressure of the corresponding first or second compression stage.

The method may include storing the output compressed gas in a closed tank or feeding a gas consuming device.

Preferably, the compression of the gas by the two compression stages comprises an alternating variation of the volume of a compression chamber of each compression stage.

Preferably, the rotation of the electric motor of each compression stage directly or indirectly generates the alternating variation of the volume of the compression chamber of each compression stage. Preferably, the compression comprises the displacement in a cylinder of a piston connected to a crankshaft driven in rotation by the electric motor and the compression of the gas in the compression chamber by said piston. Preferably, the compression of the gas by said piston takes place by compression of a liquid, in particular a hydraulic oil, separated from a compression chamber containing the gas by a deformable membrane, the deformation of the membrane generating a variation of the volume of the compression chamber.

The method includes reducing the rotational speed of the electric motors when the pressure at the inlet of the compression stages decreases below a setpoint inlet pressure. This allows the inlet gas pressure to be increased to a set inlet pressure for each compression stage.

The method includes increasing the rotational speed of the electric motors when the inlet pressure of the compression stages increases beyond a set inlet pressure. This allows the inlet gas pressure to be reduced to a set inlet pressure for each compression stage.

The method includes increasing the rotational speed of the electric motors when the pressure at the output of the compression stages decreases below a set output pressure. This allows the outlet gas pressure to be increased to a set outlet pressure for each compression stage.

The method includes reducing the speed of rotation of the electric motors when the pressure at the output of the compression stages increases beyond a setpoint output pressure. This makes it possible to reduce the outlet gas pressure to a set outlet pressure for each compression stage.

The set point input or output pressures are predefined over time. They can be constant or follow a predefined curve.

The method includes measuring the temperature at the compression outlet and reducing the speed of the engines when this temperature exceeds a predetermined threshold temperature.

The process may include supplying gas to the first compression stage through an electrolyser or a finite size reservoir.

When the gas source is an electrolyser, the method may comprise starting up the second compression stage and closing a bypass circuit of the second compression stage when the pressure at the inlet of the second compression stage is greater than a input pressure set point for the start of the second compression stage.

When the source is a finite size reservoir, the method may include turning on the first stage compression and closing a first stage compression bypass circuit when the inlet pressure to the first stage compression is less than a setpoint input pressure for the first compression stage. It will be assumed here that, by design of the system, the second compression stage has been designed to withstand the pressures P2 experienced until the start of the first compression stage.

The invention may be better understood on reading the detailed description which follows, non-limiting examples of its implementation, and on examining the appended drawings, in which:

there schematically represents an example of a compression system,

there is a variant of compression system,

there is a variant of compression system,

there schematically represents an example of a compression stage,

there is an example of a compressor, and

there schematically represents a variant of a compression system.

detailed description

It has been illustrated at an example of a compression system 2. The compression system 2 comprises a gas inlet 10 supplying the input to a first compression stage 20, the compressed gas outlet of which supplies the input to a second compression stage 30. The second compression stage 30 delivers the compressed gas into a gas outlet 15.

The gas inlet is supplied with gas by a gas source 40. The gas source 40 is preferably a gas production unit such as an electrolyser. Alternatively, it may be a gas tank.

The gas outlet 15 can be connected to a compressed gas storage or consumption device 42, preferably a compressed gas storage device.

An intermediate gas reservoir 45 between the compression stages 20 and 30 facilitates the regulation of the pressure P2. The pressure P2 of the gas in the tank 45 depends on several parameters, in particular
- the gas pressure at the outlet of the first compression stage 20 which itself depends on the gas pressure P1 at the inlet of the first compression stage 20,
- the gas flow at the outlet of the first compression stage 20 and
- the gas flow at the inlet of the second compression stage 30.
In particular, if the gas flow rate of the first compression stage 20 is greater than the gas flow rate of the second compression stage 30, the pressure P2 will increase and vice versa if the gas flow rate of the first compression stage 20 is lower than the gas flow rate. gas from the second compression stage 30. If the two gas flow rates are identical, the pressure P2 will depend solely on the pressure of the gas at the outlet of the first compression stage 20 and therefore on the pressure of the gas P1 and the compression ratio.

The first and second compression stages 20 and 30 each comprise a compressor denoted respectively 25 and 35 having a rotary electric motor and a control unit for the rotational speed of the electric motor denoted respectively 27 and 37 which controls the rotational speed of the electric motor corresponding to a predetermined setpoint speed noted respectively V1c and V2c as a function of the pressures upstream P1 and P2 of the corresponding compression stage 20 or 30.

The regulation of the speed of the electric motors can be done by means of supervision PLCs, not shown, controlling speed variators, not shown, which supply current to the electric motors.

The first and second compression stages 20 and 30 are each configured to operate with a pressure upstream between a minimum pressure P1min and P2min respectively and a maximum pressure P1max and P2max respectively. Their operation is optimized in terms of energy consumption and wear for an optimal upstream pressure P1opt and P2opt respectively.

Preferably, as illustrated in the , the second compression stage 30 includes a gas bypass circuit 48 making it possible to bypass the second compression stage 30 and the first compression stage 20 includes a gas bypass circuit 50 making it possible to bypass the first compression stage compression 20. Such bypass circuits 48 and 50 make it possible not to go through the compressor or compressors of the compression stages 20 and 30 under certain conditions of use which we will detail below, in particular when starting up the system. The gas bypass circuit 48 connects the inlet of the second compression stage 30, in particular the reservoir 45, directly to the gas outlet. The gas bypass circuit 50 connects the inlet of the first compression stage 20 directly to the gas outlet of the first compression stage 20. Such bypass circuits 48 and 50 each comprise an inlet valve, not shown, allowing control their opening and closing.

In the example shown in the , the system comprises a reservoir 45 of gas between the two compression stages 20 and 30 which acts as a buffer between the latter. Such a tank 45 in particular allows the system to absorb the pulsations linked to the cyclic irregularities between the two compression stages 20 and 30 without damaging the latter. Reservoir 45 may be formed by a connecting conduit between the two compression stages. Its volume is defined according to the parameters specific to the installation, in particular the volumes of the compression chambers and/or the rotational speed ranges over which the electric motors can turn.

When using the system illustrated with a gas production unit, in particular an electrolyser, at the system inlet and a gas storage tank 42 at the outlet, the system will first of all operate according to a start-up regime at a predefined value. Gas source 40 and system 2 are turned on and bypass circuits 48 and 50 are open until pressure P1 equals first stage compression operating pressure P1min. The control unit 27 will then turn on the first compression stage 20 and the corresponding bypass circuit 50 is closed. The second stage compression bypass circuit 48 remains open and the second stage compression 30 is off. The control unit 27 then rotates the electric motor at low speed so that the output flow rate of the first compression stage is lower than the supply flow rate by the gas source 40. The pressure P1 will then increase to reach a constant setpoint pressure P1c, in particular the optimized pressure P1opt. Once this pressure P1c has been reached upstream of the first compression stage 20, the control unit will adapt the rotational speed of the engine to maintain this pressure P1c, that is to say so that the gas flow in the first compression stage is substantially equal to the gas flow rate of the gas source. In parallel, as long as the pressure P2 is lower than a predefined ignition pressure P2start of the second compression stage, in particular the pressure P2min or a pressure between P2min and P2max, the second compression stage 30 remains off and the bypass circuit 48 remains open. As soon as this pressure P2start is reached, the bypass circuit 48 is closed and the control unit 37 starts up the electric motor of the second compression stage 30 at a reduced setpoint speed V2c so that the pressure P2 increases to a constant setpoint pressure P2c, in particular the pressure P2opt. The reduced setpoint speed corresponds to a gas flow rate in the second compression stage 30 lower than the gas flow rate of the first compression stage 20. When the pressure P2c is reached, the control unit increases the speed of the electric motor of the second compression stage 30 so that the pressure P2 is substantially constant at the pressure P2c, that is to say that the gas flow rate of the second compression stage 30 is substantially equal to the gas flow rate of the first compression stage 20. When the two compression stages 20 and 30 are operating and the pressures P1c and P2c are reached, the system switches to a routine operating regime in which the compression stages 20 and 30 are slaved so that the pressures P1 and P2 upstream compression stages 20 and 30 are maintained at their predefined set point value continuously.

As a variant, the first compression stage does not have the bypass circuit 50 and as soon as the pressure P1min is reached, the control unit 27 starts up the electric motor of the first compression stage 20 at a reduced setpoint speed V1c so that the pressure P1 increases up to a constant set point pressure P1c, in particular the pressure P1opt.

As a further variant, the second compression stage does not have the bypass circuit 48 and as soon as the pressure P2start is reached, the control unit 37 starts the electric motor of the second compression stage 30 at a set speed V2c reduced so that the pressure P2 increases up to a constant setpoint pressure P2c, in particular the pressure P2opt.

When using the compression system in routine operating mode, the first compression stage control unit 27 measures the inlet pressure P1, in particular by means of an inlet pressure sensor not shown, and compares it to the predefined setpoint pressure P1c. It deduces therefrom a setpoint speed V1c to be applied to the electric motor in order to have the setpoint pressure P1c as input. Thus when the inlet pressure P1 is lower than the setpoint pressure P1c, the control unit reduces the speed of rotation of the electric motor of the compressor 25 and conversely, when it is higher than P1c, the control unit increases the rotational speed of the electric motor. The second compression stage control unit 37 measures the pressure P2 in the tank 45, in particular via a pressure sensor not shown, and compares it to the predetermined setpoint pressure P2c. It deduces therefrom a setpoint speed V2c to be applied to the electric motor of the second compression stage 30 in order to have the setpoint pressure P2c upstream of the latter. Thus when the inlet pressure P2 is lower than the setpoint pressure P2c, the control unit 37 reduces the speed of rotation of the electric motor of the compressor 35 and conversely, when it is higher than P2c, the control unit increases the speed of rotation of the electric motor of the compressor 35.

The pressures P1 and P2 are then regulated continuously to the setpoint pressures P1c and P2c respectively so that the system operates in an optimized manner and with low energy consumption. For example, the pressure P1c can be maintained at a pressure of 10 bars.

The setpoint pressures P1c and P2c may not be constant but vary according to a predefined curve, in particular over time, depending on the characteristics of the system, in particular the source of gas 40 and/or the technical characteristics of the compression stages 20 and 30, corresponding in particular to the most optimized operation of starting and/or stopping the system. This could, for example, correspond to a fixed speed of rotation of the compression motor(s) when the system is started, for a period ensuring its temperature rise, for example a few minutes, before switching to variable-speed operation at setpoint pressures P1c and P2c constants. System features can be pre-configured in the different control units. Alternatively, when turning on the system, the user can select the type of source on a user interface and the system then controls the compression stages according to a pre-recorded curve corresponding to the type of source chosen.

In the case where the gas source is a finished reservoir, the pressure at the inlet of the first compression stage will decrease over time. The pressure curve at the inlet of the first compression stage cannot therefore be maintained at the pressure P1opt. The setpoint pressures of the compression stages are therefore each slaved over time to an optimized predefined pressure curve in which in particular the energy consumption is reduced. The system can be configured to stop when the pressure at the P1 inlet reaches a threshold pressure, for example a pressure of 1 bar.

As illustrated in the , the system may include a temperature sensor T upstream or downstream of the second compression stage 30. The control unit 37 may reduce the rotational speed of the electric motor when the temperature upstream or downstream exceeds a predetermined threshold temperature , in particular a critical temperature beyond which the system risks being damaged.

The system may include a gas cooling system, not shown, downstream of one or each compression stage.

The system can also include a pressure sensor P3 downstream of the second compression stage 30 and the control unit 37 can be configured to stop the electric motor when the pressure P3 reaches a predetermined pressure P3 in particular, in the case of a finite volume reservoir at the outlet of the system, when the pressure in the reservoir 42 is at the maximum outlet pressure P3max that the second compression stage 30 or the outlet reservoir 42 can withstand without being damaged, or that one has reaches the desired final pressure value.

As illustrated in the , the control unit 27 can also regulate the speed of the electric motor of the first compression stage 20 as a function of the pressure P2 downstream of the first compression stage 20. This can in particular make it possible to stop the first compression stage 20 when the pressure P2 exceeds a maximum pressure P2max that the first compression stage 20 can withstand without being damaged, in particular after the second compression stage 30 has been stopped or in the event of failure of the second compression stage. This also makes it possible to avoid the continuous operation of the first compression stage without it succeeding in compressing the gas and therefore to avoid unnecessary energy consumption.

As a variant, the system comprises a central control unit which stops the entire system when the pressure in the reservoir 42 has reached the desired value or when the pressure in the reservoir is at the maximum outlet pressure P3max that the second compression stage 30 or the outlet tank 42 without being damaged.

The control units 27 and 37 can also each be configured to stop the corresponding electric motor when the corresponding input pressure P1 and P2 respectively is less than or equal to a predefined minimum pressure P1min and P2min.

In the variant illustrated in the , the control units 27 and 37 control the speed of rotation of the respective electric motors as a function of the gas pressure downstream P2 and P3 respectively of the first and second compression stages 20 and 30.

Such servo-control of the compression stages 20 and 30 downstream makes it possible in particular to adapt the behavior of the compression stages according to a variation in flow rate at the outlet of the system, or to a storage pressure target in a reservoir. 42.

When using the illustrated system with an inlet gas tank and an outlet gas consumption device, the control unit 37 controls the speed of the compressor motor 35 to have a downstream pressure P3 at a pressure of setpoint P3c and the control unit 27 controls the speed of the motor of the compressor 25 to have a pressure P2 at a setpoint pressure P2c. A variation in the output flow will cause a variation in the pressure P3. The control unit 37 will then adapt the speed of the electric motor of the compressor 35 to bring the pressure downstream to P3c. Consequently, the pressure P2 will also vary and the control unit 27 will bring the intermediate pressure back to P2c by adapting the speed of the compressor motor 25. Preferably, the starting regime is the same as previously described.

When using the system illustrated with a gas production unit, in particular an electrolyser, at the system inlet and a gas storage tank 42 at the outlet, the system then regulates the operating mode as a function of the outlet pressures P2 and P3, within the limits of the production capacities of the electrolyser, and of the desired pressure P3 at the outlet or of a maximum admissible pressure P3.

In addition, the system as a whole and/or each of the compression stages can also be controlled to stop when the pressure P1, or respectively the upstream pressure for a given compression stage, drops below a limit pressure bass for the source 40 or the compression stage considered. This limiting pressure can be linked to the technical characteristics of the source, or to the low limit of operating pressure at the inlet of a given compression stage.

For transient operating phases of the system, for example during an initial start-up, pressure rise slopes of P2 and P3 over time can be predefined. If P2 does not follow the expected pressure rise slope, the control unit 27 increases the speed of rotation of the motor of the compressor 25 within the limit of the gas flow that the electrolyser can provide. If P3 does not follow the expected pressure rise slope, the control unit 37 increases the speed of rotation of the compressor motor 35.

The system may comprise more than two compression stages each comprising an electric motor whose speed is slaved to a setpoint speed depending on the pressure upstream or on the pressure measured downstream. All compression stages are slaved at least upstream or all compression stages are slaved at least downstream.

Alternatively, as shown in , the first compression stage 20 comprises a plurality of compressors 21a to 21c mounted in parallel relative to each other, that is to say whose inputs and outputs are respectively connected to a same input 10 and a same output 45 The control unit 27 controls the speed of rotation of each of the electric motors according to the characteristics of each compressor 21a to 21c. Preferably, the compressors 21a to 21c are identical and the control unit 27 controls the various motors at the same setpoint rotation speed V1c. The fact of having a plurality of compressors in parallel makes it possible to increase the gas flow in the compression stage. It may be the same for the other compression stage(s) 30.

The compressors 25 and 35 are for example as illustrated in Figures 5.

On the , the compressor shown is a membrane compressor comprising a rotary electric motor 60 rotating a crankshaft 62 connected by a connecting rod/crank system 64 to a piston 66.

The piston 66 is driven by the crankshaft 62 in translation in a cylinder 68 forming the lower part of a reservoir 70. The reservoir 70 comprises two cavities 72 and 74 separated from each other in a sealed manner by a deformable membrane 76. The first cavity 72 contains a liquid, in particular a hydraulic oil, and the second cavity 74 forms a compression chamber intended to receive the gas to be compressed via the deformable membrane 76.

An inlet valve 78 allows gas to enter the cavity 74 and the compressed gas is evacuated via a discharge valve 80.

When the engine 60 rotates the crankshaft 62, the piston 66 is driven in translation in the cylinder between a delivery position and an intake position.

When the piston 66 moves from the position of top dead center to bottom dead center, the system is in the intake phase.

When the piston 66 moves from the bottom dead center position to the top dead center, the system is in the compression phase.

During the compression phase, the liquid in the first cavity 72 is compressed, which leads to a deformation of the membrane 76 towards the second cavity 74 so as to reduce the volume of the latter, which compresses the gas contained in the chamber. compression formed by the second cavity 74. When the system is in the compression phase, the pressure in the chamber is such that the discharge valve 80 opens and the compressed gas is expelled from the chamber by the latter. When the piston 66 descends from the top dead center to the bottom dead center, the membrane 76 deforms in the direction of the first cavity 72, which leads to an increase in the volume of the second cavity 74. The gas is then sucked into the chamber of compression by the inlet valve 78. When the piston is at bottom dead center, the volume of the second cavity 74 is maximum.

As a variant, the compressor(s) 25 and/or 35 may comprise a plurality of compression chambers as described previously, the compression of which is generated by the movement of several pistons 66. The corresponding pistons 66 are all connected to the same crankshaft 62. The pistons 66 can have displacements in the cylinders 66 out of phase with respect to each other.

Other compressor technologies can be used within the scope of the invention, for example drawer compressors.

Notably, the invention also covers the operation of chains of compression stages comprising more than two compression stages and all sharing a principle of regulation at least either by the pressure upstream of the compression stages or alternatively at least by the downstream pressure of the compression stages. These compression stages are not necessarily close to each other, or even not necessarily collocated on the same geographical site. This has the advantage of limiting and/or avoiding the need for a command link between them or with a central control unit, which may be subject to communication problems, or even simple distance for its establishment.

For example, as shown in the , the system may comprise at least one additional compression stage 100 downstream of the second compression stage 30 having the same characteristics as the first and the second compression stage 20 and 30, that is to say comprising a control unit 107 regulating the speed of the electric motor Vaddc of a compressor 105 by the pressure upstream Pamont to maintain the pressure upstream Pamont at a set value Pamontc when the first and the second stage of compression are also regulated by the pressure upstream, as shown, or regulated in rotational speed of the electric motor 105 by the pressure downstream Paval to maintain the pressure downstream Paval at a set value Pavalc when the first and the second stage of compression are also regulated by the pressure in downstream (not shown).

Such an additional compression stage may also include bypass circuit 110 operating like bypass circuits 50 and 48.

The invention is not limited to the examples of embodiments which have just been described. For example, the compressors may be different from those described. The compression stages can comprise a plurality of different compressors whose motors are slaved to different setpoint speeds, for example in connection with their differences in technical characteristics.

Claims (18)

Gas compression system (2) comprising:
- a gas inlet (10),
- at least one first compression stage (20) supplied by the gas inlet (10) with gas and delivering a compressed gas,
- at least one second compression stage (30) supplied by the first compression stage (20) with compressed gas and delivering a compressed gas into the gas outlet (15),
the first and the second compression stage (20, 30) each comprising
- a rotary electric motor (60) configured to compress the gas,
- a unit for controlling the rotational speed of the electric motor (27, 37),
the first compression stage control unit (27) being configured to control the rotational speed of the corresponding electric motor (60) at least as a function of the gas pressure P1 at the inlet of the first compression stage (20) and the the second compression stage control unit (37) being configured to control the speed of rotation of the corresponding electric motor (60) at least as a function of the gas pressure P2 at the inlet of the second compression stage (30),
Or
the first compression stage control unit (27) being configured to control the rotational speed of the corresponding electric motor (60) at least as a function of the gas pressure P2 at the outlet of the first compression stage (20) and the the second compression stage control unit (37) being configured to control the speed of rotation of the corresponding electric motor at least as a function of the gas pressure P3 at the outlet of the second compression stage (30). System according to claim 1, comprising one or more additional compression stages connected in series downstream of the second compression stage, the additional compression stage(s) each comprising:
- a rotary electric motor configured to compress the gas coming from the compression stage arranged upstream of said additional compression stage,
- a unit for controlling the speed of rotation of the electric motor as a function at least of the inlet gas pressure, when the control unit of the first and of the second compression stage controls the speed of the corresponding motor as a function of at least the gas pressure at the inlet of the corresponding first or second compression stage,
or as a function at least of the gas pressure at the outlet, when the first and second compression stage control unit controls the speed of the corresponding engine as a function at least of the gas pressure at the outlet of the first or second compression stage corresponding compression. System according to Claim 1 or 2, in which the first and/or second compression stages (20, 30) and/or the additional compression stage(s), if any, comprise one or more compressors connected in parallel (25, 35) . A system according to any preceding claim, wherein the control units (27, 37) regulate the speed of the corresponding electric motors (60) in real time and continuously over time. System according to any one of the preceding claims, in which the control units (27, 37) are configured so that the rotational speed of the electric motor (60) can take at least an intermediate speed value between the maximum speed and the stopping the electric motor, in particular to vary the rotational speed of the electric motor (60) continuously between at least two rotational speed values, in particular between a maximum value and a minimum value or stopping the electric motor. System according to any one of the preceding claims, in which the first compression stage control unit (27) is configured to control the rotational speed of the corresponding electric motor (60) only as a function of the gas pressure P1 in input of the first compression stage (20), the second compression stage control unit (37) is configured to control the rotational speed of the corresponding electric motor (60) only as a function of the gas pressure P2 at the input of the second compression stage (30), where applicable the control unit of the or each additional compression stage (100) is configured to control the speed of rotation of the corresponding electric motor (60) only as a function of the gas pressure P_upstreamat the input of said additional compression stage,
Or
the first compression stage control unit (27) is configured to control the rotational speed of the corresponding electric motor (60) only as a function of the gas pressure P2 at the outlet of the first compression stage (20) and the second compression stage control unit (37) is configured to control the speed of rotation of the corresponding electric motor only as a function of the gas pressure P3 at the outlet of the second compression stage (30), where applicable the control of the or each additional compression stage (100) is configured to control the speed of rotation of the corresponding electric motor (60) only as a function of the gas pressure P_downstream at the output of said additional compression stage. System according to any one of the preceding claims, in which the first and/or second compression stage control unit comprises a temperature sensor at the outlet of said first and/or second compression stage, the control unit said first and/or second compression stage being configured to slow down the speed of rotation of the electric motor of said first and/or second compression stage when the temperature measured by the corresponding temperature sensor is greater than a predetermined threshold temperature. System according to any one of the preceding claims, in which the control units of the first and of the second compression stage and, if applicable, of the additional compression stage(s) are independent of each other. System according to any one of the preceding claims, comprising a gas reservoir (45) at least between two consecutive compression stages, in particular between the first and the second compression stage (20, 30). System according to any one of the preceding claims, comprising at the outlet (42) a closed tank for storing the gas or a device for consuming the gas at the outlet. System according to claim 10, comprising a gas outlet pressure sensor and a central control unit configured to stop the system when the outlet pressure is greater than or equal to a predefined final outlet pressure. System according to any one of the preceding claims, comprising at the inlet a source of gas (40), in particular an electrolyser supplying gas to the gas inlet or a finite volume gas reservoir. System according to claim 12, comprising a gas inlet pressure sensor and a central control unit configured to shut down the system when the inlet pressure is less than or equal to a predefined minimum inlet pressure. System according to any one of the preceding claims, in which the first compression stage control unit (27) is configured to control the rotational speed of the corresponding electric motor (60) at least as a function of the gas pressure P1 at the inlet of the first compression stage (20) and the second compression stage control unit (37) is configured to control the rotational speed of the corresponding electric motor (60) at least as a function of the gas pressure P2 in inlet of the second compression stage (30), the control units (27, 37) each being configured to maintain the pressure at the inlet of the first and second compression stages (20, 30) corresponding to a variable corresponding predefined set point pressure or constant over time, preferably constant over time. System according to any one of the preceding claims, in which the first compression stage control unit (27) is configured to control the rotational speed of the corresponding electric motor (60) at least as a function of the gas pressure P2 at the output of the first compression stage (20) and the second compression stage control unit (37) is configured to control the speed of rotation of the corresponding electric motor at least as a function of the gas pressure P3 at the output of the second compression stage (30), the control units of the first and second compression stages (20, 30) each being configured to maintain the pressure at the outlet of the compression stage corresponding to a corresponding predefined setpoint pressure which is variable or constant over over time, preferably constant over time. Gas compression method using a compression system according to any one of the preceding claims comprising:
- the compression of a gas by a first compression stage (20) comprising a rotary electric motor (60),
- the compression by a second compression stage (30) of the compressed gas delivered by the first compression stage (20), the second compression stage (30) comprising a rotary electric motor (60),
- the enslavement of the speed of rotation of the electric motor of the first compression stage as a function of at least the gas pressure at the inlet P1 of the first compression stage (20) and the enslavement of the speed of rotation of the electric motor of the second compression stage (30) as a function at least of the gas pressure at the inlet P2 of the second compression stage, or the control of the speed of rotation of the electric motor of the first compression stage (20) as a function of at least the gas pressure P2 at the outlet of the first compression stage (20) and the control of the speed of rotation of the electric motor of the second compression stage (30) as a function at least of the gas pressure P3 at the outlet of the second stage compression (30). Method according to claim 16, in which the servo-control of the speed of rotation of the electric motor of the first compression stage is carried out as a function of the gas pressure at the outlet of the first compression stage and the servo-control of the speed of rotation of the electric motor of the second compression stage is carried out according to the gas pressure at the outlet of the second compression stage so that the pressure at the gas outlet is regulated at a set pressure, preferably substantially constant. Process according to Claim 16, in which the servo-control of the rotational speed of the electric motor of the first compression stage is carried out as a function of the gas pressure at the inlet of the first compression stage and the servo-control of the rotation speed of the electric motor of the second compression stage is carried out according to the gas pressure at the inlet of the second compression stage so that the pressure at the gas inlet is regulated at a set pressure, preferably substantially constant.