FR2988623A1 - REDUCTION OF DEAD VOLUMES OF AN ADSORBER FOR ADSORPTION OF A GASEOUS FLOW - Google Patents

Abstract

Adsorber for adsorbing a gas stream, comprising a particulate adsorbent material (4) and at least one parallel passage contactor (7) located on the production side of the adsorber.

Description

The present invention relates to an adsorber wherein a particulate adsorbent bed is surmounted by a parallel passage contactor; and an adsorption process using such an adsorber, preferably a PSA process. The pressure swing adsorption separation processes are based on the physical adsorption phenomenon and make it possible to separate or purify gases by pressure cycling the gas to be treated through one or more adsorbent beds, such as a bed of zeolite, activated carbon, activated alumina, silica gel, molecular sieve or the like. In the context of the present invention, the term "PSA process" denotes any process for separating gas by pressure-swing adsorption, using a cyclic variation of the pressure between a high pressure, called the adsorption pressure, and a low pressure, called regeneration pressure. Therefore, the generic name PSA method is used indifferently to designate the following cyclic processes: VSA processes in which the adsorption is carried out substantially at atmospheric pressure, called "high pressure", that is to say between 1 bara and 1.6 bara (bara = absolute bar), preferably between 1.1 and 1.5 bara, and the desorption pressure, called "low pressure", is below atmospheric pressure, typically between 30 and 800 mbara, preferably between 100 and 600 mbara. the VPSA or MPSA processes in which the adsorption is carried out at a high pressure substantially greater than atmospheric pressure, generally between 1.6 and 8 bara, preferably between 2 and 6 bara, and the low pressure is below the pressure atmospheric, typically between 30 and 800 mbara, preferably between 100 and 600 mbara. the PSA processes in which the adsorption is carried out at a high pressure clearly above atmospheric pressure, typically between 1.6 and 50 bara, preferably between 2 and 35 bara, and the low pressure is greater than or substantially equal to the atmospheric pressure, therefore between 1 and 9 bara, preferably between 1.2 and 2.5 bara. We will also speak later of "RPSA process" to designate very fast cycle PSA processes, generally less than one minute. In general, a PSA process makes it possible to separate one or more gas molecules from a gaseous mixture containing them, by exploiting the difference in affinity of a given adsorbent or, where appropriate, of several adsorbents for these different molecules of gas.

The affinity of an adsorbent for a gaseous molecule depends on the structure and composition of the adsorbent, as well as the properties of the molecule, including its size, electronic structure and multipolar moments. An adsorbent may be, for example, a zeolite, an activated carbon, an activated alumina, a silica gel, a carbon molecular sieve, a metallo-organic structure, one or more oxides or hydroxides of alkali or alkaline-earth metals, or a porous structure containing a substance capable of reacting reversibly with one or more gas molecules, such as amines, physical solvents, metal complexing agents, metal oxides or hydroxides for example.

The adsorbent materials are used in containers (reactors) called "adsorbers". The most conventional adsorber geometries are cylindrical adsorbers with vertical axis, horizontal axis and radial adsorbers. The invention relates essentially to vertical axis adsorbers. It will be noted that the gas section reduction effect also exists in the upper part of a cylindrical adsorber with a horizontal axis, but this type of adsorber being used less for the PSA application, it is limited thereafter. to describe the case of the adsorber with vertical axis. Such an adsorber 1 is shown schematically in FIG. 1. It consists of a cylindrical shell 2 terminated in the upper part of an upper bottom 3. The adsorbent in particulate form arrives up to the line of tangency 5. The filling is made via the outlet pipe 6. The diameter of such an adsorber is generally set by the allowable pressure losses either in production or in regeneration and more generally by the concern not to move the adsorbent particles. Indeed, the friction of moving particles between them or with the wall of the adsorber causes an attrition phenomenon which creates dust and ends up destroying the particles. On the other hand, dead volumes such as that represented by reference 10 of Figure 1 are generally detrimental to the performance of PSA units. As a first approximation, the gas contained in the head of the adsorber is clean gas not recovered in the production and as such partially lost. Starting from there, a problem that arises is to reduce the dead volume at the top of the adsorbers while avoiding attrition and an increase in pressure drops.

A solution of the invention is an adsorber for adsorption of a gas stream, comprising a particulate adsorbent material 4 and at least one parallel passage contactor 7 located on the production side of the adsorber. By particulate adsorbent material is meant an adsorbent in the form of grain, beads, rod ... of millimeter size, generally of equivalent diameter in the range of 0.5 to 5mm. Parallel passage contactor means a device in which the fluid passes through channels whose walls contain adsorbent. The fluid circulates in essentially obstacle free channels, these channels allowing the fluid to flow from an input to an output of the contactor. These channels can be rectilinear connecting directly the input to the output of the contactor or present changes of direction. During its circulation, the fluid is in contact with at least one adsorbent present at said walls. Depending on the case, the adsorber may have one or more of the following characteristics: said adsorber comprises a cylindrical shell 2, a bottom bottom and an upper bottom 3; a particulate adsorbent material 4 contained in the cylindrical shell 2; and at least one contactor with parallel passages 7 contained at least partly in the upper bottom 3; the internal diameter of the cylindrical shell is greater than or equal to 0.5 m, preferably greater than or equal to 1 m; the upper bottom 3 is elliptical or hemispherical; the contactor with parallel passages 7 is fixed to the upper bottom 3; - The parallel passages contactor comprises a circular ring sealingly attached to its entire perimeter at the upper end; thus the incoming or outgoing gas flows completely crosses the contactor with parallel passages; the parallel-channel contactor 7 comprises housings 56 enclosing channels the walls of which contain adsorbent; it should be noted that the adsorber according to the invention may comprise in its upper bottom several contactors with parallel passages in series and having different geometries; the adsorbent is a zeolitic adsorbent of X or LSX type, and / or A; note that the zeolitic adsorbent can be exchanged or not; the adsorbent contained on or in the walls of the channels has a characteristic dimension of between 10 and 2,000 microns, preferably 40 to 500 microns, more preferably between 100 and 250 microns; "Characteristic dimension" means the average thickness of the adsorbent layer if it is deposited on a support, its half thickness if the gas flows on both sides of the adsorbent. In the case of contactor cylinder in the form of fibers, this will be the radius of the fiber. - The parallel passage switch 7 has a passage for filling and / or emptying the cylindrical shell; - The adsorber comprises an outlet pipe 6 and the parallel passage contactor 7 comprises a removable portion from the outlet pipe; the contactor with parallel passages 7 has a thickness of between 25 and 1000 mm, preferably between 50 and 600 mm; the contactor with parallel passages 7 is in the form of a truncated cone whose smallest diameter is between 95% and 30% of the internal diameter of the cylindrical shell of the adsorber, preferably between 80% and 50% of the diameter internal cylindrical shell of the adsorber. Figures 2.1 to 2.7 show schematically, but not limited to, different types of contactors. Indeed, the contactors may comprise channels of different shapes and sizes. We then distinguish: - rectangular channels of low thickness ep with respect to their width 1, that is to say with 1 greater than 10 ep (Figure 2.1); - the essentially square or rectangular channels but with ep in the same order of magnitude as the width 1 (Figure 2. 2); - the channels of intermediate form, with the large dimension in a ratio 1.5 to 10 with respect to the small dimension (ellipse, rectangle ...); - the channels arranged in circular rings (Figure 2.3); - channels arranged in a helix (Figure 2.4); - the circular channels (figure 2.5); The fluid can also circulate in the free space left by solid walls presented in the form of cylinders or fibers (Figure 2.6). The solid walls can also have the "packing" configuration as used in distillation (Figure 2.7). In the latter case, it is possible to use all the geometric possibilities relating to said packings by playing on the bending angles, the orientation of the passages relative to the vertical (supposed vertical contactor), the dimensions of the channels ... Many configurations are possible because the geometry of the channels is varied (triangle, trapeze, ellipse ...). In general, in all these types of contactors, which may be used in the context of the invention, the fluid, which is preferably a gas stream, circulates in channels presenting little (or no) obstacle. at the flow and the adsorbent is located -or constitutes the wall of said channels. When the adsorbent constitutes the majority of the wall, one generally speaks of monolith. (2.8) By way of example, the documents EP 1 413 348, EP 1 121 981 and WO 2005/094987 describe contactors with parallel passages. FIG. 3 represents an adsorber according to the invention. At least part of the parallel passage contactor 7 is located in an area whose gas passage section Sm (8) is smaller than the passage section of the adsorber S. By adsorber passage section, hear the normal section to the axis of the ferrule. The minimum section of the structured adsorbent bed Sm is generally between 0.95 and 0.5 S. FIG. 8 shows a system comprising two contactors 81 and 82 in series and of different geometry. The invention will now be described in more detail from the example of a PSA H2. More particularly, one takes the case of a PSA H2 treating a gas of SMIR to produce hydrogen containing less than 10 ppm mole of CO. It is a 12-3-4 cycle according to the usual nomenclature of PSA (12 adsorbers including 3 in production and 4 balancing). For a flow rate of 100,000 Nm 3 / h of hydrogen produced, the diameter of each adsorber is 3 m and the height of the shell is 5 m. By entering into the details of the calculations, one can realize that it is first of all the last balancing which is dimensioning with respect to the diameter. Note that by changing the step times, we can end up with other steps that would then become dimensioning. The adsorber head is a hemispherical bottom having an outlet tubing of approximately 600mm diameter. Note that this background represents a significant volume relative to the volume of adsorbent. In order to modify the R ratio of dead volume to adsorbent volume, a contactor with parallel passages is used in a part of the upper floor. Thus, the amount of useful adsorbent is increased and, above all, the dead volume is decreased. The ratio R evolves very favorably allowing an increase of the production at fixed feed rate. This bottom comprises a structure, preferably metal, fixed sealingly to the wall. This structure is likely to accommodate channels, whose walls contain adsorbent, which are housed in the spaces provided for this purpose. Many structural geometries and structured adsorbents are possible. Preferably, this structure makes it possible to perform filling and emptying of the adsorber either because it leaves enough free passage to perform these operations, or because it is partially removable from the outlet pipe. The parallel passage contactor is preferably implemented in full after filling the adsorbent with the particulate adsorbent material. This makes it possible to avoid any pollution of the contactor with parallel passages following prolonged contact with the atmosphere. Another possibility is to provide a protection for the contactor with parallel passages installed beforehand (sealed envelope for example or removable covers), protection removed after filling the adsorber. Figure 4 shows the upper part of an adsorber, the element 41 being the upper part of the shell 2, the element 3 the upper bottom, the element 6 the outlet pipe which also serves as an outlet for the gas. The particulate adsorbent 4, for example beads, reaches the tangent line 5 with the bottom. Element 7 corresponds to the contactor with parallel passages. In this figure, this contactor 7 is fixed on the upper bottom of the adsorber at 40. This fixation (continuous welding, suspension with tie rods and with seal ...) whatever it is is essentially gas-tight which must pass through the contactor with parallel passages 7.

The geometry of the support structure may be of varied shape, adapted to receive the structured adsorbent elements that will generally be implemented via the outlet pipe. The structure of the parallel-channel contactor shown in FIG. 5 comprises a circular ring 57 and spacers 58 creating housings 56 that fill the structured adsorbent elements. This structure is a radius structure intended to accommodate preferentially channels, whose walls contain the adsorbent manufactured in the form of a wheel. The size of the channels must allow them to pass and be put in place from the outlet pipe. These elements are based on the lower part of the structure on the outer 50 and inner 51 supports. Many types of support and more generally of maintaining the channels can be used. The gas tightness between the structure and the channels, whose walls contain the adsorbent, is achieved by any of the known means (seal, slightly conical elements maintained by a pressure ...). The channels can themselves be housed in an envelope, the seal between the channels and the wall of said envelope can be made permanently by an adhesive, a binder ..., the envelope being then fixed in a sealed manner in the structure for example by a seal at the periphery. Figure 6 shows the structure of the parallel passage contactor with the channels, the walls of which contain the adsorbent (62, 63 ..., 69) in place. The metal structure comprises 8 45 ° angle cells in which are inserted channels of channels cut on a wheel whose walls are covered with a layer of zeolite (LiLSX for example). Depending on the respective dimensions of the outlet pipe, the upper bottom, or the structure, each cell could receive one or more sets of channels maintained for example by a grid 4 placed under the structure. The various sets of channels are cut in a wheel whose dimensions have been defined to fit the structure. The assemblies may have their lateral faces (parallel to the flow of gas) as cut or covered by a material providing protection during handling.

The set of channels sets is done after filling the adsorber. A plastic film will advantageously protect the elements of the atmospheric moisture and more generally any pollution before placement. Note that the structure instead of being welded into the upper bottom during manufacture can also be held in place in the head of the adsorber being "pulled up" by one or more tie rods bearing on the flange higher. This can avoid any welding inside the adsorber. Figure 7.1, 7.2 and 7.3 show another type of structure suitable for various forms of parallel-passage contactors. FIG. 7.1 corresponds to a structured adsorbent 70 in the form of a stack of sheets. FIG. 7.2 corresponds to smaller elements, for example monoliths 71 with sides of 100 to 200 mm. Figure 7.3 shows schematically that the element can be of any shape (72,73), the structure easily adapting to receive them and hold them in place.

It will be noted that the non-central elements 75 may be put in place beforehand, the filling of the cylindrical shell then taking place through the central free section 74. The cost of a parallel-channel contactor being much greater than the cost of the same adsorbent under particulate form (for example a factor 10 based on the kg of adsorbent), it is understood that it is very interesting to limit the contactor with parallel passages to the upper part of the adsorber. The adsorber according to the invention can be used in various PSA processes such as H2 PSA to produce high purity hydrogen, PSA CO2, PSA 02, etc. It can also be used to dry, decarbonate or quench secondary impurities of a gas stream, especially from atmospheric air. By secondary impurities we mean the traces of hydrocarbons, NOx, SOx ...

Claims (15)

REVENDICATIONS1. Adsorber for adsorbing a gas stream, comprising a particulate adsorbent material (4) and at least one parallel passage contactor (7) located on the production side of the adsorber. 2. Adsorber according to claim 1, characterized in that said adsorber comprises: - a cylindrical shell (2), a bottom bottom and an upper bottom (3); a particulate adsorbent material (4) contained in the cylindrical shell (2); and - at least one contactor with parallel passages (7) contained at least partly in the upper bottom (3). 3. Adsorber according to claim 2, characterized in that the internal diameter of the cylindrical shell (2) is greater than or equal to 0.5 m, preferably greater than or equal to 1 m. 4. Adsorber according to one of claims 2 or 3, characterized in that the upper bottom (3) is elliptical or hemispherical. 5. Adsorber according to one of claims 2 to 4, characterized in that the contactor parallel passages (7) is fixed to the upper bottom (3). 6. Adsorber according to claim 5, characterized in that the contactor with parallel passages (7) comprises a circular ring sealingly attached to the whole of its perimeter at the upper end. 7. Adsorber according to one of claims 1 to 6, characterized in that the parallel passage contactor (7) comprises recesses (56) enclosing channels whose walls contain adsorbent. 8. Adsorber according to claim 7, characterized in that the adsorbent is a zeolitic adsorbent type X or LSX, and / or A. 9. Adsorber according to one of claims 7 or 8, characterized in that the adsorbent contained on or in the walls of the channels has a characteristic dimension between 10 and 2000 microns, preferably 40 to 500 microns, more preferably between 100 and 250 microns. 10. Adsorber according to one of claims 1 to 9, characterized in that the contactor parallel passages (7) has a passage for filling and / or emptying the cylindrical shell. 11. Adsorber according to one of claims 1 to 10, characterized in that the adsorber comprises an outlet pipe (6) and the parallel-channel contactor (7) comprises a removable part from the outlet pipe (6). ). 12. Adsorber according to one of claims 1 to 11, characterized in that the contactor parallel passages (7) has a thickness between 25 and 1000 mm, preferably between 50 and 600 mm. 13. Adsorber according to one of claims 1 to 12, characterized in that the parallel-channel contactor (7) has the shape of a truncated cone whose smallest diameter is between 95% and 30% of the internal diameter of the cylindrical shell of the adsorber, preferably between 90% and 50% of the internal diameter of the cylindrical shell of the adsorber. 14. Use of an adsorber according to one of claims 1 to 13 for drying, decarbonating or stopping secondary impurities of a gas stream. 15. Use of an adsorber according to one of claims 1 to 13, in a PSA cycle.