DEVICE AND METHOD FOR COMPRESSING A LOW-PRESSURE GAS

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a device and method for compressing low pressure gas. It applies, in particular, to the compression of biogas.

STATE OF THE ART

Collecting available low-pressure gas to compress it to a high pressure poses technical and economic difficulties. Various compressor technologies exist that perform this compression. These various technologies are very energy intensive.

To achieve the desired compression ratio, the compressor can include several compression stages with intermediate cooling, which makes the method more complex.

The compressors can be of different types with the configurations chosen from:

• • Positive displacement compressors (reciprocating or screw compressor), which provide an intermittent power flow. In these technologies, the gas is compressed into a small volume, thereby increasing its pressure.
  • Dynamic compressors (centrifugal or axial-flow compressor), which provide a continuous power flow. In centrifugal compressors, the kinetic energy is converted into potential energy, thereby increasing the pressure of the fluid.

Positive displacement compressors require frequent maintenance, only operate with low flow rates, have lower uptime, and are energy intensive.

Dynamic compressors are sensitive to the composition of the load and to flow rate variation, have a limited compression ratio, and are energy intensive.

SUBJECT OF THE INVENTION

The present invention aims to remedy all or part of these drawbacks.

To this end, according to a first aspect, the present invention envisages a device for compressing a low-pressure gas, which comprises:

• • at least one compression chamber comprising:
    • an inlet for low-pressure gas,
    • an outlet for high-pressure gas,
    • an inlet for fluid,
    • an outlet for fluid, and
    • a piston located between the gas inlet and outlet, on the one hand, and the fluid inlet and outlet, on the other hand;
  • a fluid movement means positioned on a fluid circuit connecting a fluid outlet and a fluid inlet of a compression chamber; and
  • a means for measuring the gas pressure inside the compression chamber and a circuit to recirculate gas to the inlet of a compression chamber when the measured pressure is less than a predefined limit value.

Thanks to these provisions, the energy cost of compressing the gas is reduced. Increasing the pressure of the fluid in the compression chamber results in the piston being moved and compressing the gas. And compressing a fluid uses less energy than compressing a gas.

In some embodiments, the device that is the subject of the present invention comprises a check valve configured to prevent a return of gas in a gas inlet.

These embodiments make it possible to prevent a return flow of gas towards the compression chamber inlet.

In some embodiments, the device that is the subject of the present invention comprises a fluid retention valve configured to hold the fluid in a compression chamber.

These embodiments make it possible to provide improved compression of the gas by restricting the exit of the fluid to a defined pressure.

In some embodiments, the movement means is configured such that the pressure of the exiting fluid is between 30 and 70 bar.

In some embodiments, the movement means is a pump.

In some embodiments, the device that is the subject of the present invention comprises a plurality of compression chambers in series for the fluid circuit, a fluid outlet of one compression chamber being connected to a fluid inlet of another compression chamber.

These embodiments make it possible to share the fluid circuit.

In some embodiments, the device that is the subject of the present invention comprises a plurality of compression chambers in parallel for the gas, each compression chamber comprising a gas inlet and outlet independent of any other compression chamber.

These embodiments make it possible to compress several quantities of gas simultaneously.

In some embodiments, the device that is the subject of the present invention comprises a means for measuring the gas pressure inside the compression chamber and a means for opening the gas outlet of the compression chamber as a function of the measured pressure.

According to a second aspect, the present invention envisages a method for compressing a low-pressure gas, which comprises:

• • a step of inputting low-pressure gas into a compression chamber;
  • a step of inputting fluid into the compression chamber;
  • a step of moving a piston located between the gas inlet and a gas outlet, on the one hand, and the fluid inlet and a fluid outlet, on the other hand, in the compression chamber;
  • a step of outputting high-pressure gas from the compression chamber;
  • a step of outputting fluid from the compression chamber;
  • a step of moving fluid over a fluid circuit connecting a fluid outlet and a fluid inlet of a compression chamber; and
  • a step of measuring the gas pressure inside the compression chamber and a step of recirculating gas to the inlet of a compression chamber when the measured pressure is less than a predefined limit value.

As the particular aims, advantages and features of the method that is the subject of the present invention are similar to those of the device that is the subject of the present invention, they are not repeated here.

BRIEF DESCRIPTION OF THE FIGURES

Other advantages, aims and particular features of the invention will become apparent from the non-limiting description that follows of at least one particular embodiment of the device and method that are the subjects of the present invention, with reference to drawings included in an appendix, wherein:

FIG. 1 represents schematically a first particular embodiment of the device that is the subject of the present invention;

FIG. 2 represents schematically a second particular embodiment of the device that is the subject of the present invention; and

FIG. 3 represents schematically, in the form of a logic diagram, a particular series of steps of the method that is the subject of the present invention.

DESCRIPTION OF EXAMPLES OF REALIZATION OF THE INVENTION

The present description is given in a non-limiting way, in which each characteristic of an embodiment can be combined with any other characteristic of any other embodiment in an advantageous way.

Note that the figures are not to scale.

Note that here, the term “gas” includes natural gas, biogas and synthesis gas.

Note that here, the term “fluid” refers to any fluid whatsoever. Preferably, use of an incompressible viscous fluid is envisaged.

FIG. 1, which is not to scale, shows a schematic view of an embodiment of the device 100 that is the subject of the present invention. This device 100 for compressing a low-pressure gas comprises:

• • at least one compression chamber 105 comprising:
    • an inlet 110 for low-pressure gas,
    • an outlet 115 for high-pressure gas,
    • an inlet 120 for fluid,
    • an outlet 125 for fluid, and
    • a piston 130 located between the gas inlet and outlet, on the one hand, and the fluid inlet and outlet, on the other hand; and
  • a fluid movement means 135 positioned on a fluid circuit connecting a fluid outlet and a fluid inlet of a compression chamber.

The compression chamber 105 is formed, for example, of an impermeable wall surrounding a given volume in which the piston 130 operates. Preferably, the only openings in the impermeable wall are:

• • an inlet 110 for low-pressure gas;
  • an outlet 115 for high-pressure gas;
  • an inlet 120 for fluid; and
  • an outlet 125 for fluid.

The compression chamber 105 can have a cylindrical interior volume, for example. The term “cylindrical” refers to a cylinder of revolution around an axis.

However, the interior volume of the compression chamber 105 can be of any type allowing a piston 130 to move. This generally implies a constant transverse cross-section relative to a movement axis of the piston 130.

This piston 130 constitutes an impermeable separation between fluid and gas. The compression chamber 105 is configured to allow the pressure of the gas to be increased to pressures over 50 bar, 100 bar or 200 bar, for example. Preferably, the pressure of the gas entering a compression chamber 105 is over 3 or 4 bar, and preferably over 7 bar.

Each element among the gas inlet 110 and outlet 115 and the fluid inlet 120 and outlet 125 is, for example, an opening in the compression chamber 105. Each of these elements, 110, 115, 120 and 125, is preferably associated to a line for transporting gas or fluid depending on the nature of the element.

In some preferred variants, at least one element among the gas inlet 110 and outlet 115 and the fluid inlet 120 and outlet 125 is equipped with a check valve 140. This check valve 140 can be mounted directly on an opening of the compression chamber 105 or downstream from this opening, at the location of a line associated to the element in question, for example.

Such a check valve 140 is configured, for example, to prevent a return of gas in a gas inlet 110.

In some variants, at least one check valve 140 is replaced by a valve or any other type of device that could block the passage of gas or fluid, depending on the associated element.

In some variants, the device 100 comprises a fluid retention valve 145 configured to retain the fluid in a compression chamber 105. This valve 145 can be any type known to the person skilled in the art and suitable for the operating pressure in the fluid circuit 150. This valve 145 can be mounted directly on the outlet from the compression chamber 105 or along the circuit 150.

Note that each element among the gas inlet 110 and outlet 115 and the fluid inlet 120 and outlet 125 can be formed of a multitude of sub-elements of the same type taking part in the same function. For example, the gas inlet 110 can be formed of a multitude of openings in the compression chamber 105, each opening being supplied by a separate line or by a line shared with other openings.

The piston 130 is, for example, an impermeable surface, or a membrane moving along an axis of the compression chamber 105. This piston 130 can be guided by a shaft fixed to one or other of the movement ends of said piston 130.

The movement means 135 can be any type allowing a fluid to move in a fluid circuit. The choice of the movement means 135 depends on the size of the circuit 150 and the total pressure drop of this circuit 150.

Preferably, the movement means 135 is configured such that the pressure of the exiting fluid is between 30 and 70 bar. However, the device 100 can produce compression at any pressure value, preferably below 300 bar.

Preferably, the movement means 135 is a pump.

In some preferred embodiments, the device 100 that is the subject of the present invention comprises a plurality of compression chambers 105 in series for the fluid circuit 150, a fluid outlet 125 of one compression chamber being connected to a fluid inlet 120 of another compression chamber.

In this variant, the chambers 105 are filled sequentially, starting from the chamber closest to the discharge of the fluid movement means 135. Once the operation has finished, the fluid is then sent to the second chamber 105, and so on.

In another variant, shown in FIG. 2, the chambers 105 are filled simultaneously. This filling is performed, for example, by a main circuit which supplies the various compression chambers 105.

In some preferred embodiments, the device 100 that is the subject of the present invention comprises a plurality of compression chambers 105 in parallel for the gas, each compression chamber comprising a gas inlet 110 and outlet 115 independent of any other compression chamber.

In some preferred embodiments, the device 100 that is the subject of the present invention comprises a means 165 for measuring the gas pressure inside the compression chamber 105 and a circuit 160 to recirculate gas to the inlet of a compression chamber when the measured pressure is less than a predefined limit value.

The pressure measurement means 165 is, for example, a pressure sensor positioned inside the compression chamber 105, on the gas side of the piston 130 or on the fluid side of the piston 130.

In some variants, the pressure measurement means 165 is mechanical or electrical, and operates by capturing the position of the piston 130 in the chamber. When this piston 130 reaches a predefined position on its movement axis, a gas pressure is deduced by the measurement means 165.

This predefined limit value can be set during the design of the device 100, or variable and recorded via a central control circuit connected to the device 100 by means of a wired or wireless control connection.

In some preferred embodiments, the device 100 that is the subject of the present invention comprises a means 165 for measuring the gas pressure inside the compression chamber 105 and a means 170 for opening the compression chamber gas outlet 115 as a function of the measured pressure.

The opening means 170 is, for example, a discharge device. In this example, the discharge device forms both the measuring means 165 and the opening means 170. This discharge device is calibrated to a setpoint pressure.

In some variants, a gas outlet valve is opened as soon as the target pressure is reached, this valve closing at a threshold pressure. These pressure levels will be chosen by the operator as a function of usage.

The operation of the device 100 as described with reference to FIG. 1 will be better understood with regard to the description, below, of the operating method 200 of said device 100.

FIG. 3 shows schematically a logic diagram of particular steps of the method 200 that is the subject of the present invention. This method 200 for compressing a low-pressure gas comprises:

• • a step 205 of inputting low-pressure gas into a compression chamber;
  • a step 210 of inputting fluid into the compression chamber;
  • a step 215 of moving a piston located between the gas inlet and a gas outlet, on the one hand, and the fluid inlet and a fluid outlet, on the other hand, in the compression chamber;
  • a step 220 of outputting high-pressure gas from the compression chamber;
  • a step 225 of outputting fluid from the compression chamber; and
  • a step 230 of moving fluid over a fluid circuit connecting a fluid outlet and a fluid inlet of a compression chamber.

Preferably the pressure in the compression chamber is initially lower than the pressure in a line transporting gas towards a gas inlet of said compression chamber. This can be achieved by pressurizing the gas upstream or by reducing the pressure in the fluid portion of the compression chamber.

To achieve such a pressure reduction, for example, a valve on the inlet side of the fluid inlet is closed while the movement means is in operation. This results in the piston moving towards the fluid outlet, which reduces the pressure inside the gas portion of the compression chamber whose gas outlet is also closed. Optionally, the gas inlet is also closed.

Where only the gas outlet is closed, a suction mechanism that aspirates the gas, through the gas inlet, is produced and gradually fills the gas portion of the combustion chamber. This means that a movement means specific to the gas supplied does not have to be used in the method 200 that is the subject of the present invention.

Regardless of the solution allowing the gas to enter the compression chamber, once entered the gas finds itself confined in the variable volume dedicated to gas of said compression chamber.

The movement means 135 is activated, such that the fluid portion of the compression chamber is filled with fluid, which gradually moves the piston towards the gas outlet, thereby compressing this gas.

Once the desired gas pressure has been reached, the gas is released towards the compression chamber gas outlet. To facilitate the outputting of said gas, the fluid can continue to circulate so that the piston continues to be moved until the gas is completely, or almost completely, evacuated towards the gas outlet.

To evacuate the fluid contained in the fluid portion of the compression chamber, the compression chamber fluid outlet is open.

Accordingly, it can be seen that a cycle of aspiration/compression/expulsion of the gas can be created by:

• • closing the gas outlet,
  • closing the fluid inlet,
  • opening the gas inlet,
  • opening the fluid outlet,
  • starting up the fluid movement means,
    resulting in the aspiration of the gas into the compression chamber, which is followed by:
  • closing the gas inlet,
  • opening the fluid inlet,
  • closing the fluid outlet,
  • starting up the fluid movement means,
    resulting in the compression of the gas, which is followed by:
  • opening the gas outlet,
  • starting up the fluid movement means,
    which results in the expulsion of the gas.

The method 200 that is the subject of the present invention is performed, for example, by utilizing one of the devices 100 or 300 that are the subjects of the present invention and described with reference to FIGS. 1 and 3.