Equipment for purifying a wet gas stream containing CO2 and NOx

Abstract

A plant for purifying a gas stream comprising at least 0.02% by volume of water, CO.sub.2 and NOx, comprising an adsorber characterized by: a cavity (1); an adsorbent (2) included in the cavity (1); an outer casing (3) made of carbon steel; an inner casing (4) made of stainless steel making a space having a width of between 10 and 100 mm between said inner casing and the outer casing, said space being at equal pressure with the cavity.

Claims

1. A process for purifying a gas stream comprising, CO.sub.2, NOx, and at least 0.02% by volume of water, comprising using an adsorber, wherein said adsorber comprises: a cavity; an adsorbent included within the cavity; an outer casing made of carbon steel; an inner casing made of stainless steel, wherein a space between 10 and 100 mm wide is between said inner casing and the outer casing, said space being at equal pressure with the cavity, the process comprising subjecting the adsorber to a purification cycle comprising an adsorption step and a regeneration step using a regeneration gas and wherein nitric acid and liquid water are present in the adsorber during the regeneration step.

2. The process as claimed in claim 1, wherein the adsorber further comprises a separator pot, and wherein the nitric acid and the liquid water are removed from the adsorber via the separator pot.

3. The process of claim 1, wherein the regeneration step is carried out at a temperature above 150° C.

4. An apparatus for purifying a gas stream comprising CO.sub.2, NOx, and at least 0.02% by volume of water, comprising an adsorber, wherein said adsorber comprises: a cavity; an adsorbent included within the cavity; an outer casing made of carbon steel; an inner casing made of stainless steel, wherein a space between 10 and 100 mm wide is between said inner casing and the outer casing, said space being at equal pressure with the cavity.

5. The apparatus in claim 4, wherein the space is at equal pressure with the cavity by means of a gas connection that opens into the cavity downstream of the adsorbent when considering the path of the gas stream.

6. The apparatus in claim 4, wherein the inner casing is divided into at least two inner casings that form a double casing.

7. The apparatus in claim 6, wherein, among the two inner casings, only the innermost inner casing of the adsorber is made of stainless steel.

8. The apparatus in claim 4, further comprising; the outer casing divided into a shell, a first base on the inlet side of the gas stream and a second base on the outlet side of the gas stream, and the inner casing is present level with the shell and continues over the first base.

9. The apparatus in claim 4, further comprising; the outer casing divided into a shell, a first base on the inlet side of the gas stream and a second base on the outlet side of the gas stream, the inner casing is present level with said shell, and a stainless steel plate is plated on the first base.

10. The apparatus of claim 8, further comprising: said adsorber comprises a separation pot integrated into or joined to the first base that makes it possible to separate acid condensates from a gas leaving on the inlet side of the gas stream to be purified and an outlet pipe for discharging said gas stripped of its condensates.

11. The apparatus of claim 4, wherein the adsorber comprises silica gel as adsorbent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1 illustrates one embodiment of the present invention

(3) FIG. 2 illustrates another embodiment of the present invention; and

(4) FIG. 3 illustrates another embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

(5) One solution to the present invention is a plant for purifying a gas stream comprising at least 0.02% by volume of water, CO.sub.2 and NOx, comprising an adsorber characterized by: a cavity 1; an adsorbent 2 included in the cavity 1; an outer casing 3 made of carbon steel; an inner casing 4 made of stainless steel making a space between 10 and 100 mm wide, preferably between 20 and 70 mm wide, between said inner casing and the outer casing, said space being at equal pressure with the cavity 1.

(6) Note that the double inner casing makes it possible to protect the adsorber from corrosion whilst the carbon steel outer casing makes it possible to withstand the pressure (1 to 60 bar).

(7) The inner casing may in practice consist of several casings around one another, separated by a few millimeters to a few tens of millimeters. The advantage of such a system is to create very good thermal insulation using the gas itself as insulator, which has low thermal conductivity relative to the solids.

(8) In practice, even though multilayer inner casings can be envisaged, the solution with two casings is recommended since with the space between the shell and the outer casing (of the inner part), this already constitutes very effective thermal insulation. This system (1 shell, 2 inner casings) is generally referred to as “double gas-filled space”.

(9) In this case, only the innermost casing may be made of stainless steel, the other or others being, for example, made of carbon steel like the shell of the adsorber.

(10) The space between the inner casing and the outer casing (shell), like that between the two inner casings in the “double gas-filled space” case (2 gas-filled spaces are generally sufficient to ensure a very good thermal insulation but it could be envisioned to use more thereof) is at any moment at the pressure reigning in the adsorber. This single or multiple inner shell does not therefore have a mechanical strength role other than holding the adsorbent and the thickness thereof is minimal.

(11) The various inter-wall spaces must therefore be in sufficient gas connection so that the variations of the operating pressure have an effect instantaneously on both sides both in the event of pressurization and depressurization. It is said that these gas volumes are at equal pressure, although there can be several tens of millibars difference depending on the operating phases and/or the height in the adsorber due to pressure losses through the adsorbent bed.

(12) This gas connection is made on the dry gas side so that there is no water capable of condensing on the sheets made of standard material (not of noncorrodible type).

(13) Depending on the case, the plant according to the invention may have one or more of the following characteristics: the space is at equal pressure with the cavity by means of a gas connection that opens into the cavity 1 downstream of the adsorbent 2 when considering the path of the gas stream; the inner casing is divided into at least two inner casings that form a double casing; among the two inner casings, only the innermost inner casing of the adsorber is made of stainless steel; the outer casing is divided into a shell 6, a first base 5 on the inlet side of the gas stream and a second base on the outlet side of the gas stream, and the inner casing 4 is present level with the shell 6 and continues over the first base 5 (cf. FIG. 1). the outer casing is divided into a shell 6, a first base 5 on the inlet side of the gas stream and a second base on the outlet side of the gas stream, the double inner casing is present level with the shell, and a stainless steel plate 7 is plated on the first base 5 (cf. FIG. 2). In this case, the stainless steel plate is welded to the lower base of the adsorber and will be used partly as support for the adsorbents. With this solution, the plating is limited to one portion of the equipment, therefore reducing the production cost thereof. said adsorber comprises a separation pot 8 integrated into or joined to the first base that makes it possible to separate acid condensates from a gas leaving on the inlet side of the gas stream to be purified and an outlet pipe for discharging said gas stripped of its condensates (cf. FIG. 3). the adsorber comprises silica gel as adsorbent. the pipes of the plant are corrodible.

(14) Note that in the case where the adsorber comprises a double inner casing level with the shell and a stainless steel plate covering the lower base, a stainless steel protective part ensures the continuity between the double casing and the lower base.

(15) Another subject of the present invention is a process for purifying a gas stream comprising at least 0.02% by volume of water, CO.sub.2 and NOx, using a plant according to the invention, wherein said adsorber is subjected to a purification cycle comprising an adsorption step and a regeneration step using a regeneration gas and characterized by the presence of nitric acid and liquid water in the adsorber during the regeneration step.

(16) Preferably, the nitric acid and the water are discharged from the plant via the separator pot. Specifically, the double casing and/or the stainless steel plate will enable the runoff of the water and of the acid to the outlet pipe and to the separator pot.

(17) The regeneration step is preferably carried out at a temperature above 150° C.