FACILITY AND METHOD FOR PURIFICATION BY ADSORPTION OF A GASEOUS FLOW COMPRISING A CORROSIVE IMPURITY

Abstract

The invention relates to a facility for purification by adsorption of gaseous flow comprising at least one impurity which has a corrosive effect on carbons steel, comprising a radial adsorber comprising a housing with an outer envelope made of carbon steel; a vertical perforated inner grating consisting of a corrosion-resistant material, a vertical perforated outer grating, an adsorbent which is held vertically by the outer grating and the inner grating, and allows at least partial blockage of the corrosive impurity, and a means for allowing a centrifugal circulation of the gaseous flow.

Claims

1-12. (canceled)

13. A TSA or PSA adsorption plant for purifying a gas stream comprising at least one impurity that is corrosive with respect to carbon steel, the plant comprising a radial adsorber comprising: a shell with an outer envelope made of carbon steel; a vertical and perforated internal grid made of corrosion-resistant material; a vertical and perforated external grid made of carbon steel; an adsorbent held vertically by the external grid and the internal grid, the adsorbent being resistant to the corrosive impurity, and configured to at least partially stop said corrosive impurity; a means configured to produce a centrifugal circulation of the gas stream; and a means configured to circulate the regeneration gas in a centripetal manner.

14. The plant of claim 13, wherein the plant comprises a TSA and the equipment of the plant in contact with the regeneration gas at the adsorber outlet is made of corrosion-resistant material.

15. The plant of claim 13, wherein the plant comprises a PSA and the equipment of the plant in contact with the waste gas is made of corrosion-resistant material.

16. The plant of claim 13, wherein the corrosion-resistant material is selected from the group consisting of stainless steels, noble metals, polymers, ceramics and carbon steel covered with an anti-corrosion material.

17. The plant of claim 13, wherein at least one end wall of the adsorber is made of carbon steel.

18. The plant of claim 13, wherein the vertically-held adsorbent rests on a support having a slope oriented toward the central axis of the adsorber.

19. The plant of claim 13, wherein said plant comprises at least one means of collecting and extracting liquids from the adsorber that originate from the gas stream to be purified and/or are formed during the regeneration.

20. The plant of claim 13, wherein the vertically-held adsorbent is selected from the group consisting of silica gel, porous glass, resins, silicalite, activated carbon and zeolite 3A.

21. A process for purifying a gas stream comprising at least one impurity that is corrosive with respect to carbon steel, using a plant of claim 1, and wherein the corrosive impurity is selected: from the group of acids: HCl, HNO.sub.3, HF and H.sub.2SO.sub.4; or from the group of gases: NOx, SOx and H.sub.2S in the presence of moisture.

22. The process of claim 21, wherein the gas stream is a gas stream resulting from combustion or resulting from metallurgy.

23. The process of claim 21, wherein the process is a drying or CO.sub.2 stripping process.

24. A process for purifying a gas stream comprising at least one impurity that is corrosive with respect to carbon steel, using a plant of claim 19, and wherein the corrosive impurity is selected: from the group of acids: HCl, HNO.sub.3, HF and H.sub.2SO.sub.4; or from the group of gases: NOx, SOx and H.sub.2S in the presence of moisture; and the liquids extracted from the adsorber are recycled in acid water washing processes or acid production processes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0074] For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

[0075] FIG. 1 illustrates a schematic representation of a radial adsorber indicating various flow regimes.

[0076] FIG. 2 illustrates a schematic representation of a radial adsorber.

[0077] FIG. 3 illustrates a schematic representation of a radial adsorber including two separate layers of adsorbents; and

[0078] FIG. 4 illustrates a schematic representation of one embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0079] According to one particular case, the invention relates to a process for purifying a gas stream comprising at least one impurity that is corrosive with respect to carbon steel, using a plant according to the invention comprising at least one means of collecting and extracting liquids from the adsorber that originate from the gas stream to be purified and/or are formed during the regeneration and wherein the corrosive impurity is selected: [0080] from the group of acids: HCl, HNO.sub.3, HF and H.sub.2SO.sub.4; or [0081] from the group of gases: NOx, SOx and H.sub.2S in the presence of moisture; and the liquids extracted from the absorber are recycled in acid water washing processes or acid production processes.

[0082] The invention will now be described in detail within the context of a CO.sub.2 capture process. It is recalled that in order to reduce emissions of CO.sub.2 of human origin in the atmosphere, it is a question of extracting the CO.sub.2 from a gas generated by an industrial process, optionally to purify it and finally, in general, to compress it in order to transport it in a pipeline. This treatment generally necessitates at least partially drying the CO.sub.2.

[0083] The gases resulting from processes of oxy-fuel combustion type are good candidates since they have a high content of CO.sub.2, the nitrogen having been eliminated from the air before combustion. These gases also contain a percentage of NOx (NO & NO.sub.2 predominantly) resulting from the combustion. These NOx will enter the adsorbers that aim to dry the CO.sub.2 in the form of NO, NO.sub.2 and also in the form of nitric acid (HNO.sub.3) resulting from the conversion of NO to give NO.sub.2 and of NO.sub.2 to give HNO.sub.3, in particular if the purification takes place after compression and cooling. HNO.sub.3 is retained by the adsorbent of the adsorbers and NO and NO.sub.2 are partially retained. In the adsorber, the reactions for converting NO to give NO.sub.2 and NO.sub.2 to give HNO.sub.3 are accelerated and the equilibria are shifted toward the formation of HNO.sub.3. At the time of the regeneration of the adsorbent, during the desorption of the previously adsorbed NOx, there is also a possibility of forming nitric acid in the presence of water trapped during the adsorption. The hot nitric acid formed and/or desorbed during the regeneration and also the water vapor desorbed will have a tendency to condense on the coldest zones located toward the outlet of the adsorber. The condensates formed will then contain a high concentration of nitric acid.

[0084] Reference is now made to FIG. 4, which represents a radial adsorber 10 according to the invention. The dimensions of this adsorber will depend on the flow rate of gas to be dried and on the operating conditions. Generally, the diameter of the shell varies from 2 meters to 6 meters and its height varies from 4 meters to more than 20 meters. The oxy-fuel combustion gas 1 to be dried is introduced in the upper portion, is distributed by means of the distributor 16 across the adsorbent mass 30, which here is a single bed of silica gel. This bed is held in place by the grids 14 and 15 to which the end wall 21 is attached. The dried gas 2 flows into the inter-wall space 17 then leaves through the lower portion of the adsorber. The regeneration gas 3 is introduced countercurrently firstly hot (heating step) then at ambient temperature (cooling step). It leaves the adsorber via the center and the upper end wall 4. Since the regeneration is carried out at 200 C., insulation by a simple gas-filled space 21 has been provided. The gas contained in this space is at equal pressure with respect to the gas circulating in the inter-wall space. The connection between the two gaseous volumes is provided here in the upper portion in order to limit the convection phenomena but other locations are possible according to the criteria adopted.

[0085] The liquids formed are collected by gravity in the volume 18 located at the bottom point of the support end wall 21. These liquids may originate from droplets present in the gas to be treated 1, the distributor 16 acting as gas/liquid separator or as already described from the condensation of vapor during the regeneration phase on the coldest portions located downstream. The shape of the support end wall 21 favors the entrainment of the liquids toward the central portion and the volume 18. These liquids are purged via the line 19 and the valve 20.

[0086] The volume 18 and the line 19 will advantageously be insulated in order to prevent a re-vaporization of the liquids 5. These highly concentrated liquids will advantageously be treated before the discharging thereof or optionally used for other applications. Among the latter, mention may be made of the most effective gas washing operations with waters having an acid pH, or for example the washing of coal or coal residues after combustion to extract therefrom the metals (iron, arsenic, mercury, vanadium, etc.) in order to recycle these constituents or to preventively remove them from the coal. These condensates may also act as raw material for the manufacture of acid.

[0087] The internal elements of the adsorber 10, such as the grids 14 and 15 and the line 19 for example, are designed so that their differential heat expansion between the steps of the TSA cycle (adsorption and regeneration) or between the various elements at a given moment of the cycle do not result in irreversible deformations that endanger the correct operation of the plant of the invention (loss of gas tightness, significantly heterogeneous thickness of the adsorbent mass, etc.). For example, the line 19 may have a coil shape (not represented in FIG. 4).

[0088] The upper flange, the distributor 16, the internal grid 15, the adjoining part between the flange and the internal grid, the reservoir 18, the support end wall 21, the line 19 and optionally the body of the valve 20 are made of stainless steel of NAG (Nitric Acid Grade) type. The shell 11 and the end walls 12 and 13, the external grid 14, the envelope of the insulating gas-filled space are made of carbon steel.

[0089] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.