FR3067099B1 - GAS MIXTURE SEPARATION DEVICE - Google Patents

Abstract

The separation device (1) comprises a compression unit (6) and a unit (7) for separation of the gas mixture (2, 8), intended to produce a permeate (3) and a retentate (4), and arranged in downstream of the compression unit (6). The compression unit (6) is shaped to achieve compression such that the temperature of the gas mixture remains substantially constant throughout this compression.

Description

Gaseous mixture separation device

The present invention relates to a gas mixture separation device and energy conversion.

Cryogenic separation is typically preferred in industry for producing large volumes of oxygen, nitrogen or the like, exploited in a variety of different energy conversion systems, for example for heating industrial furnaces or for gas-fired power plants. natural or charcoal.

However, the cryogenic separation has very high energy operating costs, in particular involves a compression phase particularly costly energy.

Already known in the state of the art, in particular according to US 2004/0016237, an integrated device for cryogenic air separation and energy conversion, comprising an air separation unit clean to produce the oxygen enriched air, anda compression unit for supplying compressed air to the air separation unit. The device further comprises a combustion unit powered by the oxygen-enriched air produced by the separation unit. The combustion unit is suitable for delivering a driving gas to a turbine.

Furthermore, according to US Pat. No. 6,382,958, a ceramic membrane separating device used in a heating method is known. In such a device, the air is heated to a very high temperature before separation. US 8,752,391 also discloses a high temperature ceramic membrane separation device in which the temperature of the gas mixture is raised above 540 ° C before separation. This type of membrane is particularly expensive and is not suitable for low temperature applications.

Also known from WO 2008/013843, a device for implementing an oxygen enriched combustion, wherein energy is produced by an independent Rankine cycle from a heat recovery. However, this device does not make a gas separation process more efficient.

It is also known from US Pat. No. 7,637,109 to use a refrigerant such as liquefied natural gas to cool oxygen prior to compression. This cooling device is arranged upstream of a compression system, and therefore does not allow isothermal compression.

Also known from US 2012 0324944 is a separation device operating at low pressures.

However, such devices are not entirely satisfactory.

In particular, the known separation processes are usually expensive in energy. The object of the invention is in particular to provide an integrated gas mixture separation and energy conversion device having a better efficiency. For this purpose, the invention particularly relates to a device for separating a gaseous mixture comprising: - a compression unit; a unit for separating the gaseous mixture, intended to produce a dermatate and a retentate, and arranged downstream of the compression unit; characterized in that the compression unit is shaped to achieve a compression such that the temperature of the gas mixture remains substantially constant throughout this compression. The compression unit thus performs a quasi-isothermal compression. Such quasi-isothermal radiation requires less energy to bring the gas mixture to a predetermined pressure. The invention is based on a gas separation process, using a cyclethermodynamics involving isothermal compression and providing for the use of heat generated by combustion to heat one of the separated gases. An example of application is oxycombustion.

The device according to the invention may furthermore comprise one or more of the following features, taken singly or in any combination that is technically possible. During compression, the difference between the temperature of the gaseous mixture at any time, and the initial temperature of the gaseous mixture, is less than 50 ° C. - The separation device comprises means for injecting a liquid into the compression unit, for adding a liquid to the gaseous mixture in the compression unit to form a two-phase fluid, the liquid being adapted to absorb the heat resulting from compression to maintain the temperature substantially constant during this compression. - The separation device comprises a heating unit, connected to the separation unit, and an expansion machine, arranged downstream of the heating unit. - The expansion machine is configured to perform a relaxation such that the temperature of the gaseous mixture remains substantially constant throughout the expansion, in particular the difference between the temperature of the gaseous mixture at any time, and the temperature of the gaseous mixture prior to expansion, is lower at 50 ° C. - The expansion machine is mechanically connected to an electric generator. - The heating unit has a heat exchanger. The separation unit comprises a membrane separation apparatus. - The gaseous mixture is formed of air, the permeate is air enriched in oxygen and the retentate is air depleted in oxygen. - The gas mixture is formed by combustion gas, the permeate is air enriched in CO2 and the retentate is air depleted in CO2. The invention also relates to an industrial installation, characterized in that it comprises a separation device as defined above. The installation according to the invention may furthermore comprise one or more of the following characteristics, taken singly or in any combination that is technically possible. - The industrial plant includes a combustion unit, connected to the separation unit so that the permeate or retentate feeds the combustion unit. - The industrial installation comprises a relaxation machine arranged downstream of the combustion unit (10). - The heating unit is connected to the combustion unit, so that the heating unit is fed with an exhaust gas from a combustion realized in the combustion unit. The invention also relates to a method for separating a gaseous mixture, characterized in that it is implemented by means of a separation device as defined above, and in that it comprises the following steps: step of compressing the gaseous mixture, during which the temperature of the gaseous mixture remains substantially constant during compression, to obtain a compressed gaseous mixture; a step of at least partial separation of the compressed gaseous mixture to obtain a permeate and a retentate; a step of heating the permeate or the retentate; a step of relaxing the permeate or the heated retentate. The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the appended figures, in which: FIG. 1 is a schematic view of an industrial installation comprising a device for gas mixture separation according to an exemplary embodiment of invention; and FIG. 2 is a diagram of a thermodynamic cycle representing the evolution of the gaseous mixture in the device of FIG.

It should be noted that in the present description, the terms "upstream" and "downstream" are defined with respect to a direction of flow of a gaseous mixture in a circuit.

There is shown in Figure 1, an industrial plant 20.

For example, the industrial plant 20 forms a steel plant, a glassware or an electric power plant. The industrial plant 20 comprises a separation device 1 and a combustion unit 10.

The separating device 1 comprises a main circuit 5 comprising a compression unit 6 and a separation unit 7. The compression unit 6 is supplied with a gas mixture 2 having a pressure PO and a temperature T0, and compresses this gaseous mixture 2 to obtaining a compressed gaseous mixture 8 having a pressure P1 greater than PO and a temperature T1.

The pressure P1 is for example greater than 7 bar, preferably greater than 24 bar.

For example, the gaseous mixture 2 is formed of air. This air can optionally be previously dehydrated. Alternatively, the gaseous mixture 2 is formed of combustion gas. The compression unit 6 is capable of delivering an almost isothermal compression. More particularly, the temperature of the gaseous mixture remains substantially constant throughout the compression.

Thus, by definition, the temperatures T0 and T1 are substantially equal.

Advantageously, the difference between the temperature T 0 of the gaseous mixture 2 and the temperature T1 of the compressed gaseous mixture 8 is less than 50 ° C.

Preferably, the difference between the temperature T0 of the gaseous mixture 2 and the temperature T1 of the compressed gaseous mixture 8 is less than 15 ° C.

Optionally, the gaseous mixture 2 is cooled beforehand under ambient temperature before the compression unit.

To perform such an isothermal or quasi-isothermal compression, a liquid may be added to the gaseous mixture 2 in the compression unit 6 to form a diphasic fluid. Thus, the liquid, in direct contact with the gas, absorbs the heat resulting from the compression of this gas, thereby obtaining an isothermal compression during which the temperature remains substantially constant throughout the compression. Said liquid may be able to undergo a phase change by evaporation during the absorption of the heat of compression. It should be noted that the temperature is considered substantially constant when the difference between this temperature and the initial temperature is in particular less than 50.degree. C., preferably less than 15.degree. By way of example, said liquid used may be water or an oil.

Another example of a quasi-isothermal compression unit is described in the paper "On The Strategies Towards Isothermal Gas Compression and Expansion", 2014, by Mahbod Heidari, Sylvain Lemofouet and Alfred Rufer.

Another example of a quasi-isothermal compression unit is described in US 4,027,993. This compression unit uses a mixture of gas and liquid, and has the advantage of keeping the temperature of the gas constant after compression. US 4,446,698 or WO 2010/037980 disclose isothermal compressors proposing a larger heat transfer surface in a heat exchanger. US 4,311,025, US 9,267,504 or US 7,401,475 disclose devices in which liquid is injected during the compression and expansion phases to guard the substantially isothermal system. The separation unit 7, arranged downstream of the compression unit 6, is intended to separate the compressed gaseous mixture 8 to obtain a permeate 3 and a retentate 4, respectively having temperatures T1a and T1b.

When the gas mixture 2, 8 is formed by combustion gas, the permeate 3 is CO2 enriched air and the retentate 4 is CO2 depleted air.

To achieve this separation, several embodiments are envisaged, and if necessary combined, according to the present invention.

According to a first variant, the separation unit 7 comprises a membrane separation apparatus 9 as visible in FIG.

In a manner known per se, the membrane separation apparatus 9 comprises a filter arranged transversely or radially to a flow of a compressed gaseous mixture. The filter then allows the selective passage of certain molecules and the stopping of others. The membrane separation apparatus 9 is able to operate at compressed gaseous mixture pressures 8 of between 7 bar and 80 bar.

Membrane separation processes usually exhibit high efficiency as well as ease of design and maintenance.

According to a second variant, the separation unit 7 comprises an adsorption separation apparatus.

In a manner known per se, the adsorptive separation apparatus, in particular by pressure reversal, removes a component from a compressed gaseous mixture by using its chemical affinity and its particular characteristics with respect to an adsorbent exposed to an oscillation of pressure strictly controlled.

According to a third variant, the separation unit 7 comprises a membrane separation apparatus and an adsorption separation apparatus in series, between which a compressor is arranged. This variant makes it possible in particular to improve the efficiency of the separation. The separation unit 7 does not exhibit any significant dissipation phenomena, the temperature T1a of the permeate 3 and the temperature T1b of the retentate 4 are therefore substantially equal to the temperature T1 of the compressed gas mixture 8.

Conventionally, the permeate 3 or the retentate 4 feeds a combustion unit 10. In the embodiment described, the permeate 3 feeds the combustion unit 10.

Advantageously, the combustion carried out in the combustion unit 10 forms part of the industrial process of the installation equipped with the device 1.

The separating device 1 comprises a secondary circuit 11 comprising a heating unit 12 and an expansion machine 13. The heating unit 12 is connected to the separation unit 7, which supplies it with cold entrluid 14. The cold fluid 14 is chosen from permeate 3 or retentate 4. More particularly, one of the permeate 3 or retentate 4 feeds the combustion unit 10, and the other feeds the heating unit 12. Thus, in the embodiment As described, the ether 4 forms the cold fluid 14. The heating unit 12 is intended to increase the temperature of the cold fluid 14 to obtain a heated fluid 15 at a predetermined temperature T2.

Advantageously, the heating unit 12 comprises a heat exchanger 16 designed to transfer heat energy from a hot fluid 17 to the cold fluid 14 to obtain the heated fluid 15.

As shown in FIG. 1, the hot fluid 17 is formed by exhaust gases resulting from the combustion carried out in the combustion unit 10.

As shown in particular in FIG. 2, the heating unit 12 preferably maintains the constant fluid pressure.

The expansion machine 13 is intended to use the energy of the heated fluid 15 to produce mechanical energy.

The expansion machine 13 and the compression unit 6 are advantageously mounted on the same axis. Thus, the energy required for compression is provided at least in part by the expansion machine 13. Preferably, the axis of the de-ducting machine 13 and the axis of the compression unit 6 are mechanically linked.

In the embodiment described, the expansion machine 13 is connected mechanically to an electric energy generator 18, which conventionally enables the mechanical energy of the expansion machine 13 to be converted into electrical energy.

The expansion machine 13 rejects a relaxed fluid 19.

The expansion machine 13 is preferably of the quasi-isothermal type, but the use of any other type of expansion machine, for example isentropic, is possible.

The expansion machine 13 may for example be an axial or radial turbine, a scroll turbine or screw or a piston expansion machine,

The operation of the separation device 1 according to the invention will now be described with reference to FIG.

FIG. 2 shows a diagram of a thermodynamic cycle of the operation of the separation device described above, according to one embodiment of the invention. The ordinate of this diagram shows the pressure P in the circuit and abscissemontre the volume V in the circuit. The state of the gas mixture circulating in the device can be represented by a polygonal curvature. Each intermediate line on the curve, located between two points of this curve, represents an energetic transformation in the separation device 1, that is to say that the different steps traveled during the conversion of electrical energy are represented by the different points. on the polygonal curve of Figure 2.

Thus, several parts of the polygonal curve can be described as follows.

A first part (shown in full lines) between a point A and a point B of the diagram represents the almost isothermal compression of the gaseous mixture 2 to obtain the compressed gaseous mixture 8.

A second portion between point B and a point C represents a separation step of the gaseous mixture. The gas mixture is separated into a retentate (shown in broken line in Figure 2) and a permeate (shown in dashed lines in Figure 2). It should be noted that this separation step has little impact on the retentate pressure.

A third part between the point C and a point D represents the cold fluid isobaredu heating 14 (retentate).

A fourth portion between the point D and a point E represents the isothermal expansion of the heated fluid (retentate).

On the other hand, a fifth part between the point C and a point F represents the evolution of the permeate following the separation.

Note that the invention is not limited to the previously described embodiment, but could have various variants.

In particular, it is possible that the separation device 1, in particular the heating unit 16, is supplied with heat by any heat source.

Furthermore, the device 1 is able to operate with various types of gas mixtures.

It is clear that the invention has a number of advantages.

The separating device according to the invention makes it possible to reduce the energy losses of the industrial installation while separating a gaseous mixture.

It should be noted that equipment in thermal contact with the compressed gas mixture 8 is less stressed if the compressed gas mixture 8 has a relatively low temperature T1. The requirements imposed on these equipments are therefore simplified.

This is particularly advantageous for the membrane separation apparatus 9 which does not usually operate at elevated temperatures.

In addition, by performing isothermal and non-adiabatic compression, the energy expenditure is decreased.

Claims (3)

1. Apparatus for separating (1) a gaseous mixture (2, 8) comprising: - a compression unit (6); a unit (7) for separating the gaseous mixture (2, 8), intended to produce a permeate (3) and a retentate (4), and arranged downstream of the compression unit (6): characterized in that compression unit (6) is shaped to effect a compression such that the temperature of the gas mixture remains substantially constant throughout this compression, and in that the gas mixture (2, 8) is formed of air, the permeate (3) is air enriched with oxygen and the retentate (4) is air depleted of oxygen. 2. Separation device (1) according to claim 1, wherein, during compression, the difference between the temperature of the gaseous mixture at any time, and the initial temperature of the gaseous mixture, is less than 50 ° C. 3. Separation device (1) according to claim 1 or 2, comprisingmeans for injecting a liquid into the compression unit (6), for adding liquid liquid to the gaseous mixture in the compression unit to form a two-phase fluid, the liquid being adapted to absorb the heat resulting from the compression to maintain the temperature substantially constant during this compression. 4. - Separating device (1) according to any one of claims 1 to 3, comprising a heating unit (12), connected to the separation unit (7), and a relaxation machine (13), arranged in downstream of the heating unit (12). 5. - Separating device (1) according to claim 4, characterized in that the pressure booster (13) is configured to perform such a relaxation that the temperature of the gaseous mixture remains substantially constant throughout the relaxation, especially the difference between the temperature of the gaseous mixture at any time, and the temperature of the gaseous mixture prior to expansion is less than 50 ° C. 6. -Dispositif separation (1) according to claim 4 or 5, wherein the booster machine (13) is mechanically connected to an electric generator (18). 7, - separating device (1) according to any one of claims 4 to 6, wherein the heating unit (12) comprises a heat exchanger (16). 8, -Dispositif separation (1) according to any preceding claim, wherein the separation unit (7) comprises a membrane separation apparatus (9). 9, - Industrial installation (20), characterized in that it comprises a deseparation device (1) according to any one of the preceding claims. 10, - Industrial plant (20) according to claim 9, comprising a combustion unit (10), connected to the separation unit (7) so that the permeate (3) or létentat (4) feeds the combustion unit (10). 11, Industrial plant (20) according to claim 10, comprisinga relaxation machine arranged downstream of the combustion unit (10). 12, - Industrial plant (20) according to claim 10 or 11, wherein the heating unit (12) is connected to the combustion unit (10), so that the heating unit (12) is fed by a exhaust gas from combustion produced in the combustion unit (10). 13, - Process for separating a gaseous mixture (2, 8), characterized in that it is implemented by means of a separation device (1) according to any one of claims 1 to 8, and in that it comprises the following steps: - a step of compressing the gaseous mixture (2), during which the temperature of the gaseous mixture remains substantially constant during compression, to obtain a compressed gaseous mixture (8); a step of at least partial separation of the compressed gaseous mixture (8) to obtain a permeate (3) and a retentate (4); a step of heating the permeate (3) or the retentate (4); a step of relaxing the heated permeate (3) or retentate (4).