WO2014147323A1

WO2014147323A1 - Method for dehumidifying the mixtures of industrial gases

Info

Publication number: WO2014147323A1
Application number: PCT/FR2014/050593
Authority: WO
Inventors: Joseph TOUBASSY; Denis Clodic; Camille MOUKARZEL
Original assignee: Ereie - Energy Research Innovation Engineering
Priority date: 2013-03-21
Filing date: 2014-03-14
Publication date: 2014-09-25
Also published as: FR3003476A1; FR3003476B1

Abstract

The invention relates to a method for dehumidifying a psychometric gas mixture at room temperature, including one step, said step including: a compression phase, in which the psychometric gas mixture is compressed to a given pressure; a cooling phase, in which the previously compressed psychometric gas is cooled to a given temperature; a separation phase, including a step of extraction of the condensates from the previous cooling step, in the psychometric gas; the previously described step being repeated consecutively and a plurality of times, such as to reduce the water vapor concentration in the psychometric gas to a predetermined threshold.

Description

METHOD FOR DEHUMIDIFYING MIXTURES OF INDUSTRIAL GASES

The present invention relates to a method and system for desiccating gas mixtures.

Gas mixtures can be of various origins. Thus these mixtures can be air or mixtures of industrial gases. The ambient temperature is defined as any current temperature between 0 and 40 ° C.

The gas mixtures in question are called psychometric mixtures, that is to say that the only chemical element capable of changing state is water. In other words, the other chemical elements that are generally found in gas mixtures, such as hydrogen, helium, nitrogen or oxygen remain in the gas phase. For various reasons, techniques have been developed for extracting a gas mixture, water or a chemical compound in particular. Thus, as reported in Patent No. FR 2 354 804 (BASF AKTIENGESELLSCHAFT), silica gels have been used for a long time for drying gases. Silica gels have an exceptional adsorption capacity.

Adsorption is the retention on the surface of a solid (the adsorbent), molecules of a gas or a substance in solution or in suspension. In other words, adsorption is the surface phenomenon by which atoms or molecules of gases or liquids attach to a solid surface.

Having proven themselves over the last decades, silica gels nevertheless have a major disadvantage. Their implementation requires special precautions, because of their enormous capacity for water absorption, any contact with the liquid water causes the bursting of the grains of gel by giving small particles. of the Special technological arrangements are therefore to be expected when it comes to using silica gels in the course of desiccation of a gas. The US patent application published under No. US 2012/0279394 (THYSSENKRUPP) discloses a method of desiccating gases. The desiccation of the gases is made in contact with them with a solvent in an absorbent column. This solvent belongs to the family of glycols. The device presented makes it possible to extract gaseous mixture, water and acid compounds. The gaseous mixture enters a first absorbing column where a first treatment allows a first separation. The solvent containing water and acidic compounds is recovered at the bottom of the absorbent column while the first treated gas is directed to the top of the column. The solvent containing the acidic compounds and water is treated to remove water and acidic compounds. The solvent is then returned to the absorbent column. Simultaneously, the gas obtained after the first treatment is treated a second time by the same method. The solvent containing the acidic compounds is recovered at the bottom of the second column, treated and the acidic compounds are extracted for use as an acid gas while the solvent is returned to the second column.

This desiccation process requires both an expensive installation and an important maintenance. The extraction of water and gaseous acids from the solvent used, which can not be optimal, the implementation of such a device requires replacing at least occasionally the solvent in question. In addition to the practical aspect, the glycol also has a high toxicity in case of ingestion. Special precautions for use are therefore to be provided by the staff.

The invention differs from the state of the art by its great simplicity. It does not require the use of any additive and allows effective desiccation of a gas.

A first object is to provide a method for desiccating a mixture of psychometric gas. A second object is to provide a method for obtaining a gas having a low water vapor content. A third object is to propose a method involving a simple and inexpensive device.

A fourth object is to provide a process that can be used both in industrial installations and also in mobile systems such as construction vehicles or compressed air hybrid vehicles, for example.

For this purpose, it is first proposed a dehumidification process of a psychometric gas mixture at room temperature comprising a step, this step including:

a compression phase, in which the psychometric gas mixture is compressed to a given pressure; a cooling phase, in which the previously compressed psychometric gas mixture is cooled down to a given temperature;

a separation phase, comprising a step of extracting the condensates from the previous cooling phase, in the psychometric gas; the step previously described, being repeated successively, a plurality of times, so as to reduce to a predetermined threshold, the concentration of water vapor in the psychometric gas.

This method is particularly advantageous when it comes to storing a gaseous mixture at high pressure typically between 10 and 60 MPa or when it is necessary to dehumidify a mixture of industrial gases so as to obtain very low moisture contents of the mixture. order of 100 ppm for dew points of the order of -40 ° C. Various additional characteristics may be provided, alone or in combination: the predetermined threshold corresponds to a water vapor content of less than about 20 parts per million (ppm) expressed in volume; the step is repeated successively four times, giving rise to a first, a second, a third and a fourth step; in the first step, the mixture of psychometric gases is compressed at a pressure of approximately 0.376 MPa; in the second step, the psychometric gas mixture is compressed to a pressure of about 1.41 MPa; in the third step, the psychometric gas mixture is compressed to a pressure of about 5.32 MPa. in the fourth step, the psychometric gas mixture is compressed at a pressure of about 20 MPa; after each compression phase, the psychometric gas mixture is cooled to a temperature of about 20 ° C; in each step, the compression ratio is substantially identical and is about 3.76; the psychometric gas mixture is composed of:

of dihydrogen in molar proportions ranging from 60 to 75%, of dinitrogen in molar proportions ranging from 25 to 40%,

- water vapor may vary from 50 to 10,000 ppm.

The set of three compositions for looping at 100%. Other characteristics and advantages of the invention will appear more clearly and concretely on reading the following description. embodiments, which is made with reference to the accompanying drawings in which:

FIG. 1 is a block diagram illustrating a device for desiccating a four-stage gas,

Fig. 2 is a block diagram illustrating a two-stage gas desiccator.

Figure 1 illustrates a block diagram of a desiccant device of a psychometric gas mixture. In the example described below, the gas in question is a psychometric mixture of dihydrogen, dinitrogen and steam, respectively in the following molar proportions: 39.756%, 59.633% and 0.611%. This corresponds to a volume concentration of 6110 parts per million of water vapor, ie a dew point of 0 ° C.

The extreme accuracy of these values is only one example. This is in no way limiting and in no way restricts the process that will be described later. Thus the molar proportions of the chemical species may be different as long as one remains in the conditions of a psychometric mixture as previously defined.

An example of a psychometric gas mixture is composed of:

dyhydrogen in molar proportions ranging from 60 to 75%,

of dinitrogen in molar proportions ranging from 25 to 40%, water vapor ranging from 50 to 10,000 ppm. All three compositions making 100%.

The fact that the mixture is psychometric is of particular importance. Chemical species other than water vapor are therefore far from their condensation conditions. The physical properties that count only then are the total pressure, the temperature of the mixture and the partial pressure of water vapor. It is shown in Figure 1 a block diagram of the dehumidification device. The latter is a four-stage device. Nevertheless the number of floors is variable and it could of course understand more or less. Each stage is composed of at least one compressor, a heat exchanger and a fluid separator.

In the embodiment described, the conditions of pressure and ambient temperature, that is to say at atmospheric pressure and for a temperature of 20 ° C.

With reference to FIG. 1, the psychometric gas mixture is sucked by the first compressor 1 and compressed to a pressure of 0.376 MPa. Compression causes a first rise in temperature of the order of 170 ° C.

At the outlet of the first compressor 1, the psychometric mixture being at a temperature of 170 ° C. and a pressure of 0.376 MPa passes through a first heat exchanger 2. At the outlet of the first heat exchanger 2, the psychometric gas mixture is cooled to a temperature of about 20 ° C by a heat transfer fluid whose temperature is about 15 ° C.

At the outlet of the first heat exchanger 2, the mixture of psychometric gas, thus cooled to a temperature of about 20 ° C., enters a first fluid separator 3. In the example chosen, with a volume concentration of 6110 ppm (v / v) of water vapor, no water vapor in the first heat exchanger 2 is condensed, so there is no water separated in the first fluidic separator 3.

At this point, the psychometric gas mixture has passed through the first stage. At the outlet of the first fluidic separator 3, the psychometric gas mixture enters the second stage at a temperature of about 20 ° C. The mixture is compressed by the second compressor 4 to a pressure of about 1.41 MPa and the temperature again reaches 170 ° C. At the outlet of the second compressor 4, the mixture is cooled in the same manner as before by a second heat exchanger 5, and this up to a temperature of 20 ° C.

At the outlet of the second heat exchanger, the mixture passes through a second fluid separator 6 where part of the condensed water vapor is extracted. At this stage, the volume concentration of the water vapor of the mixture goes from 6110 ppm (v / v) to about 1650 ppm (v / v). At this point, the mixture has passed through the second stage. At the outlet of the second fluid separator 6, the partially dehumidified mixture enters the third stage at a temperature of about 20 ° C.

The third compressor 7 compresses the mixture to a pressure of about 5.32 MPa and the temperature is raised to about 170 ° C. Again the gaseous mixture is cooled in a third heat exchanger to a temperature of about 20 ° C.

A third fluidic separator 9 extracts condensed water vapor in the third heat exchanger 8. The volume concentration of water vapor increases from 1650 ppm (v / v) to 440 ppm (v / v).

The gaseous mixture dehumidified a second time, leaves the third stage at a temperature of about 20 ° C and enters the fourth and last stage where it is first compressed by a fourth compressor 10 to a pressure of 20 MPa and the temperature reaches 170 ° C again. In a second step, the mixture is cooled by a fourth heat exchanger 11 to a temperature of about 20 ° C. After cooling, the mixture passes through a fourth fluid separator 12 where a third desiccation is carried out. The volume concentration of water vapor increases from 440 ppm (v / v) to about 117 ppm (v / v), which is the target concentration corresponding to a dew point of - 41 ° C.

At the outlet of the fourth fluid separator 12, the mixture consisting of dihydrogen, nitrogen and water vapor at 117 ppm (v / v) is stored in a tank 13, ready for use.

Each compressor 1, 4, 7, 10 is identical and has a compression ratio of about 3.76 and an isentropic efficiency of the order of 0.9. An identical compression ratio makes it possible in particular to minimize the energy consumption of all four compressors 1, 4, 7, 10.

The heat exchangers 2, 5, 8, 11 are countercurrent heat exchangers, that is to say that the heat transfer fluid circulates in a direction opposite to that of the fluid to be cooled. This is about heat exchangers plate or tubular. The geometric arrangement of the heat exchangers 2, 5, 8, 11 and fluid separators 3, 6, 9, 12 is such that the water condensate flows naturally from the heat exchangers 2, 5, 8, 11 to the heat exchangers. corresponding fluidic separators 3, 6, 9, 12.

The coolant enters each exchanger 2, 5, 8, 11 thermal at a temperature of about 15 ° C through an inlet 14 and out of an outlet 15.

In the fluidic separators 3, 6, 9, 12, the condensates fall to the bottom by simple effect of gravity while the gas stream is directed upwards of the separators 3, 6, 9, 12 fluidics.

Each fluid separator 3, 6, 9, 12 comprises a level controller 16 and a purge 17. Each level controller 16 controls the level of condensed water in the corresponding fluid separator 3, 6, 9, 12. When the high thresholds 18 are reached, the level controllers 16 send a signal to a control system so that the purges 17 open and release the liquid water at atmospheric pressure and maintain the upstream pressure prevailing in each separator 3, 6, 9, 12 fluidic, and the water is emptied of each separator 3, 6, 9, 12 fluidic until reaching the low threshold 19 where another signal is sent by the controller 16 corresponding level to close the purge 17.

The fluidic separators are in fluid communication with their heat exchanger 2, 5, 8, 11 via downward fluid lines. This arrangement makes it possible to use gravity to allow flow in a particular direction. In this case, the condensate flow must go in the exchanger to separator direction. The fluidic separators 3, 6, 9, 12 are therefore arranged in such a way that the corresponding heat exchangers 2, 5, 8, 11 are situated higher up. Each compressor 1, 4, 7, 10 except for the first compressor 1, is in fluid communication with a fluid separator 3, 6, 9, 12 via upward fluid lines 21. This arrangement makes it possible to use gravity to allow flow in a particular direction. In this case, the flow of the gas flow must here go in the separator to compressor direction. The separators 3, 6, 9, 12 fluidic are arranged so that the corresponding compressors are located higher.

Applications requiring the storage of compressed air are more and more numerous. This is particularly the case for certain mobile vehicles. It is advantageous to dehumidify the air before storing it at high pressure, for example 6 MPa. In fact, water causes both clogging and corrosion. Compressed air storage is used in hybrid compressed air and thermal engine vehicles or in construction machines and vehicles that require energy reserves in the form of compressed air at high pressure. Figure 2 illustrates a block diagram of a second embodiment of the invention. In this case, the number of compression stages is reduced. In this embodiment, a gas at the atmospheric pressure and a temperature of 20 ° C arrives in a first compressor 22 compact with a relative humidity of 50% or 11 697 ppm (v / v) volume concentration. In this example the gas is air. This is compressed to a pressure of 0.775 MPa and reaches a temperature of 200 ° C. At the outlet of the first compact compressor 22, the gas is cooled in a first heat exchanger 23 compact to a temperature of around 20 ° C. The cooled air is then directed to a first compact fluid separator 24 where part of the condensed water vapor is recovered at the bottom of the first compact fluid separator 24. At this stage, the air contains only 3020 ppm (v / v) of water vapor. The partially dehumidified air leaves the first compact fluid separator 24 and enters a second compact compressor. The gas stream is compressed to a pressure of 6 MPa. Compressed air at 6 MPa enters a second compact heat exchanger 26 where it is cooled to about 20 ° C. At the outlet of the second compact heat exchanger 26, the air cooled to 20 ° C enters a second compact fluid separator 27 where it loses some of the water vapor previously condensed in the second compact heat exchanger 26. At the outlet of the second compact fluid separator 27, the air contains only a residual moisture of about 390 ppm (v / v) corresponding to a dew point temperature of -30 ° C. The air is then stored in a storage tank 13 and is ready for use.

In the second embodiment, the compact compressors 22, 25 used comprise a wall cooling device such as water jackets in the case of piston compressors. These cooling devices make it possible to keep the compressor temperature below 200 ° C. Each compact compressor is identical and has a compression ratio of about 7.75. An identical compression ratio allows in particular to minimize the energy consumption of all two compressors 22, 25 compact.

This second embodiment illustrates the variety of possible applications for this method. It finds its application both in industrial environments or in mobile devices.

A first advantage of the invention is that it allows effective dehumidification in the image of the examples provided in the description.

A second advantage is its simplicity.

A third advantage is that it does not present a toxic risk, unlike other devices requiring the use of solvents including those belonging to the family of glycols.

A fourth advantage is that it does not require the use of silica gels conventionally used in industry to dehumidify gaseous mixtures through adsorption.

A fifth advantage is that it can be implemented in both industrial devices and mobile devices.

Claims

A method of dehumidifying a psychometric gas mixture at room temperature comprising a step, this step including:

a separation phase, comprising a step of extracting the condensates from the previous cooling phase, in the psychometric gas; the step previously described, being repeated successively, a plurality of times, so as to reduce to a predetermined threshold, the concentration of water vapor in the psychometric gas;

the psychometric gas mixture being composed of:

o dihydrogen in molar proportions ranging from 60 to 75%,

o dinitrogen in molar proportions ranging from 25 to

40%

o water vapor ranging from 50 to 10,000 ppm.

2. The method of claim 1 wherein the predetermined threshold corresponds to a water vapor content of less than about 20 parts per million (ppm) expressed in volume.

3. The method of claim 1 wherein the step is repeated successively four times, giving rise to a first, a second, a third and a fourth step.

4. The method of claim 3 wherein in the first step, the psychometric gas mixture is compressed to a pressure of about 0.376 MPa.

5. The method of claim 3 wherein in the second step, the psychometric gas mixture is compressed to a pressure of about 1.41 MPa.

The method of claim 3 wherein in the third step the psychometric gas mixture is compressed to a pressure of about 5.32 MPa.

The method of claim 3 wherein in the fourth step the psychometric gas mixture is compressed to a pressure of about 20 MPa.

The method of any of the preceding claims, wherein after each compression phase the psychometric gas mixture is cooled to a temperature of about 20 ° C.

The method of any one of claims 1 to 7 wherein in each step the compression ratio is substantially the same and is about 3.76.