Antitelescoping device and clamp for spiral wound modules comprising a vent

Abstract

A gas separation module comprising: (a) a permeate collection tube; (b) a membrane envelope wound spirally around the tube to provide a wound membrane structure comprising two end faces; and (c) an anti-telescoping device (ATD) secured to the permeate collection tube, the ATD comprising: (i) an inner peripheral part, (ii) an outer peripheral part which surrounds the inner peripheral part, (iii) one or more connection parts which connect the inner peripheral part and the outer peripheral part and which contacts with one of said end faces; (iv) vents which allow gas to flow through the ATD; wherein the ATD satisfies Formula (1): (L CP?L contact)/(L VENT)=R Formula (1) wherein: R is from 1.47 to 1.88; L VENT is the cross sectional area of the vents which allow gas to flow through the ATD; L CP is the total area inside the outer peripheral part; and L contact is the contact area of the connection parts and the end face of the wound membrane envelope. Clamps are also claimed.

Claims

1. A gas separation module comprising: (a) a permeate collection tube; (b) a membrane envelope wound spirally around the tube to provide a wound membrane structure comprising two end faces; and (c) an anti-telescoping device (ATD) secured to the permeate collection tube, the ATD comprising: (i) an inner peripheral part, (ii) an outer peripheral part which surrounds the inner peripheral part, (iii) one or more connection parts which connect the inner peripheral part and the outer peripheral part and which contacts with one of said end faces; and (iv) vents which allow gas to flow through the ATD; wherein the ATD satisfies Formula (1):
(L.sub.CP?L.sub.contact)/(L.sub.VENT)=RFormula (1) wherein: R is from 1.47 to 1.88; L.sub.VENT is the cross sectional area of the vents which allow gas to flow through the ATD; L.sub.CP is the total area inside the outer peripheral part; and L.sub.contact is the contact area of the connection parts and the end face of the wound membrane envelope.

2. The gas separation module according to claim 1 wherein at least one of the one or more connection parts has a face nearest to the wound membrane structure and a face furthest away from the wound membrane structure, wherein the face nearest to the wound membrane structure is narrower than the face furthest away from the wound membrane structure.

3. The gas separation module according to claim 1 wherein the one or more connection parts have a trapezoidal cross section wherein the narrowest end of the trapezoid is nearer to the wound membrane structure than the widest end of the trapezoid.

4. The gas separation module according to claim 3 wherein the one or more connection parts has an isosceles trapezoidal cross section having a base angle of 70 to 89?.

5. The gas separation module according to claim 1 which further comprises a clamp for securing the ATD in contact with an end face of the wound membrane structure.

6. The gas separation module according to claim 5 wherein the clamp comprises vents through which gas may flow.

7. The gas separation module according to claim 1 wherein the permeate collection tube and the wound membrane structure have a circular cross section.

8. The gas separation module according to claim 1 wherein the ATD has the profile of a spoked-wheel, when viewed in a plane perpendicular to the permeate collection tube.

9. The gas separation module according to claim 6 wherein the clamp comprises at least two parts, which parts are secured together around the permeate collection tube.

10. The gas separation module according to claim 1 wherein the wound membrane structure further comprises a permeate carrier.

11. The gas separation module according to claim 1 wherein the wound membrane structure further comprises a permeate envelope comprising at least two permeate spacers and a gas-impermeable sheet, wherein the gas-impermeable sheet is located between the at least two permeate spacers.

12. The gas separation module according to claim 1 wherein the membrane envelope comprises a feed spacer and one or more membranes, wherein the feed spacer is sandwiched between the one or more membranes.

13. The gas separation module according to claim 1 which comprises two of said ATDs, one at each end of the wound membrane structure and in contact with the respective end face, thereby preventing the wound membrane structure from unwinding from the tube.

14. The gas separation module according to claim 10 which further comprises two clamps for securing the ATDs in contact with the respective end faces, wherein the clamps comprise vents through which gas may flow.

15. A gas separation device comprising two or more modules according to claim 1.

16. A process for separation of a feed gas containing a target gas into a gas stream rich in the target gas and a gas stream depleted in the target gas comprising passing the feed gas through a module according to claim 1.

17. A process for separation of a feed gas containing a target gas into a gas stream rich in the target gas and a gas stream depleted in the target gas comprising passing the feed gas through a module according to claim 6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an exploded, perspective view of part of a gas separation module;

(2) FIGS. 1(a) and 1(b) are perspective views of the two opposite sides of an ATD;

(3) FIG. 2(a) shows the vents which allow gas to flow through the ATD as the white spaces between the inner (15) and outer (14) peripheral parts and connection parts (9);

(4) FIG. 2(b) shows the contact area of the connection parts and the end face of the wound membrane structure (L.sub.contact) as the six black bars (L23?L22?6) inside the circle;

(5) FIG. 3 shows an alternative ATD profile;

(6) FIG. 4 shows an ATD and the isosceles trapezoidal cross section of one of its connection parts;

(7) FIG. 5 is a perspective view of a clamp comprising vents; and

(8) FIG. 6 is an exploded view of how membrane envelopes and spacer screens may be aligned for winding onto a permeate collection tube.

(9) FIG. 1 is an exploded, perspective view of part of a gas separation module comprising a perforated permeate collection tube (13) (perforations not shown), an optional clamp comprising two parts (3A) and (3B) secured together with bolts (2A) and (2B) (bolt (2B) is hidden behind the permeate collection tube (13)). The clamp (3) comprises six circular vents which allow gas to flow through the clamp. The ATD has connection parts (two of the connection parts indicated by numeral (9)), six vents (two of the vents indicated by numeral (4)) and the overall profile of a spoked-wheel. The module comprises a wound membrane structure comprising end face (12). In use, projections (not shown) on the connection parts (9) which extend in the axial direction are pressed firmly in contact with the end face (12) of the wound membrane structure. The circumference of the outer peripheral part has a rim, which is longer than the projections, fitting snugly over a part of the wound membrane structure to prevent the envelope from unwinding from the tube in radial direction.

(10) FIG. 1(a) shows the side of the ATD which does not contact with the end face of the wound membrane and FIG. 1(b) shows the side of the ATD which does contact with the end face of the wound membrane. FIG. 1(a) and FIG. 1(b) also show the inner peripheral part (15), the outer peripheral part (14) and the connection parts (9) which connect the inner and outer peripheral parts. Inner peripheral part (15) can slide onto a permeate collection tube.

(11) The vents which allow gas to flow through the ATD are shown in FIG. 2(a) as the white space between the inner peripheral part (15), the outer peripheral part (14) and the connection parts (9). Thus in the ATD of FIGS. 1(a), 1(b), 2(a) and 2(b), L.sub.VENT can be calculated approximately as follows, wherein L.sub.11, L.sub.12 and L.sub.13 are as shown in FIG. 2(a):
L.sub.VENT=?(L.sub.11/2).sup.2??(L.sub.12/2).sup.2?(6?L.sub.13?((L.sub.11?L.sub.12)/2))

(12) The contact area of the connection parts and the end face of the wound membrane structure (L.sub.contact) is shown in FIG. 2(b) as the six bars inside the circle. L.sub.contact can be calculated as follows, wherein L.sub.22 and L.sub.23 are as shown in FIG. 2(b):
L.sub.contact=6?L.sub.22?L.sub.23

(13) Thus in the ATD shown in FIGS. 1(a), 1(b), 2(a) and 2(b), L.sub.CP is total area inside the outer peripheral part shown in FIG. 2(b) (not FIG. 2(a)). Thus the value of L.sub.CP for the ATD shown in FIGS. 1(a), 1(b), 2(a) and 2(b) can be calculated as follows, wherein L.sub.21 is as shown in FIG. 2(b):
L.sub.CP=?(L.sub.21/2).sup.2

(14) FIG. 3 shows an alternative ATD having six circular vents. In this case, L.sub.CP=?(L.sub.FIG3/2).sup.2 wherein L.sub.FIG3 is the diameter of the outer circle shown in FIG. 3.

(15) FIG. 4 is an end view of an ATD with a cross-sectional view through one of the connection parts. The connection part has an isosceles trapezoidal cross section. The base angle ? (sometimes referred to as flap angle) is shown. The base angle (or flap angle) may be calculated as follows, wherein L.sub.3, L.sub.13 and L.sub.23 are as shown in FIG. 4:
?=Arctan[2?L.sub.3/(L.sub.13?L.sub.23)]

(16) The clamp in FIG. 5 comprises two semi-circular halves which may be bolted together to secure the clamp firmly on the permeate collection tube. The clamp has six identical, circular vents which allow gas to flow through the clamp. The area of the clamp vents which allow gas to flow through the clamp (i.e. the Clamp Porosity) may be calculated as follows:
Clamp Porosity=[CA?(6??.sub.r.sup.2)]/CA?100%
wherein CA is the cross-sectional area of the clamp and r is the radius of the vents shown in FIG. 5.

(17) FIG. 6 illustrates how a membrane structure may be prepared. A permeate carrier (24) is attached to permeate collection tube (21) having perforations (20). A stack of alternate membrane envelopes (27) and permeate carriers (24) are aligned on the permeate collection tube (21). The membrane envelopes (27) comprise a rectangular membrane sheet (23) folded around a feed spacer (25) and the folded edge of the membrane envelope abuts the permeate collection tube (21). The stack is then wound around the permeate collection tube (21) to provide a membrane structure comprising two parallel end faces and a third face of circular cross-section. In a preferred embodiment (not shown), in place of each permeate carriers (24) there is used a permeate envelope comprising two permeate spacers and a gas-impermeable sheet, wherein the gas-impermeable sheet is located between the at least two permeate spacers. Feed gas is prevented from entering the permeate carriers (24) without first passing through the membranes (23) by depositing adhesive along the edge of the permeate carrier to form a gas-tight seal.

(18) The modules according to the invention are particularly useful for separation of a feed gas containing a target gas into a gas stream rich in the target gas and a gas stream depleted in the target gas. For example, a feed gas comprising polar and non-polar gases may be separated into a gas stream rich in polar gases and a gas stream depleted in polar gases. In many cases the membranes have a high permeability to polar gases, e.g. CO.sub.2, H.sub.2S, NH.sub.3, SO.sub.x, and nitrogen oxides, especially NO.sub.R, relative to non-polar gases, e.g. alkanes, H.sub.2, N.sub.2, and water vapour.

(19) The target gas may be, for example, a gas which has value to the user of the membrane and which the user wishes to collect. Alternatively the target gas may be an undesirable gas, e.g. a pollutant or greenhouse gas, which the user wishes to separate from a gas stream in order to meet product specification or to protect the environment. The modules according to the invention are particularly useful for purifying natural gas (a mixture which predominantly comprises methane) by removing polar gases (CO.sub.2, H.sub.2S); for purifying synthesis gas; and for removing CO.sub.2 from hydrogen and from flue gases. Flue gases typically arise from fireplaces, ovens, furnaces, boilers, combustion engines and power plants. The composition of flue gases depend on what is being burned, but usually they contain mostly nitrogen (typically more than two-thirds) derived from air, carbon dioxide (CO.sub.2) derived from combustion and water vapour as well as oxygen. Flue gases also contain a small percentage of pollutants such as particulate matter, carbon monoxide, nitrogen oxides and sulphur oxides. Recently the separation and capture of CO.sub.2 has attracted attention in relation to environmental issues (global warming).

(20) The modules according to the invention are particularly useful for separating the following: a feed gas comprising O.sub.2 and N.sub.2 into a gas stream richer in O.sub.2 than the feed gas and a gas stream poorer in O.sub.2 than the feed gas; a feed gas comprising CO.sub.2 and N.sub.2 into a gas stream richer in CO.sub.2 than the feed gas and a gas stream poorer in CO.sub.2 than the feed gas; a feed gas comprising CO.sub.2 and CH.sub.4 into a gas stream richer in CO.sub.2 than the feed gas and a gas stream poorer in CO.sub.2 than the feed gas; a feed gas comprising CO.sub.2 and H.sub.2 into a gas stream richer in CO.sub.2 than the feed gas and a gas stream poorer in CO.sub.2 than the feed gas, a feed gas comprising H.sub.2S and CH.sub.4 into a gas stream richer in H.sub.2S than the feed gas and a gas stream poorer in H.sub.2S than the feed gas; and a feed gas comprising H.sub.2S and H.sub.2 into a gas stream richer in H.sub.2S than the feed gas and a gas stream poorer in H.sub.2S than the feed gas.

(21) The invention is further illustrated by the following Examples. Gas Flux and Selectivity were measured as follows:

(22) Gas Flux

(23) Flux of each gas was calculated based on the following equation:
Q.sub.i=(?.sub.Perm.Math.X.sub.Perm,i)/(A.Math.(P.sub.Feed.Math.X.sub.Feed,I?P.sub.Perm.Math.X.sub.Perm,i))
wherein: Q.sub.i=Flux of each gas (m.sup.3(STP)/m.sup.2.Math.kPa.Math.s) ?.sub.Perm=Permeate flow (m.sup.3(STP)/s) X.sub.Perm,i=Volume fraction of each gas in the permeate A=Membrane area (m.sup.2) P.sub.Feed=Feed gas pressure (kPa) X.sub.Feed,i=Volume fraction of each gas in the feed P.sub.Perm=Permeate gas pressure (kPa) STP is standard temperature and pressure, which is defined here as 25.0? C. and 1 atmosphere (101.325 kPa).
Selectivity

(24) Selectivity (?.sub.O2/N2) was calculated from Q.sub.O2 and Q.sub.N2 calculated above, based on following equation:
?.sub.O2/N2=Q.sub.O2/Q.sub.N2

EXAMPLE 1

(25) Part (a)Permeate Collection Tube

(26) A tube of internal diameter 47 mm and external diameter 50 mm, made from stainless steel Grade 316, was cut to a length of 1 m. Holes of diameter 4 mm were drilled through the tube wall to give an aperture ratio of 15% (i.e. the holes occupied 15% of the surface area of the permeate collection tube).

(27) Part (b)Wound Membrane Structure

(28) (b1) Permeate Envelopes

(29) A rectangular, gas-impermeable sheet made of PET (600 mm?600 mm) was sandwiched between two rectangular sheets of permeate carrier made of epoxy coated polyester (900 mm?900 mm). The gas impermeable sheet was positioned at the centre of the short edge of the permeate carrier sheets and fixed there using an adhesive to give a permeate envelope. This was repeated a further 20 times to give 21 permeate envelopes comprising permeate carrier-gas-impermeable sheet-permeate carrier.

(30) (b2) Membrane Envelopes

(31) A rectangular membrane sheet (900 mm?1,800 mm) was folded around a feed spacer sheet made of polypropylene (900 mm?900 mm). The feed spacer sheet was positioned at the centre of the short edge, inside the fold of the membrane sheets and fixed there using an adhesive to give a membrane envelope. This was repeated a further 21 times to give 22 membrane envelopes comprising membrane-feed spacer-membrane.

(32) (b3) Wound Membrane Structure

(33) The membrane fold of a membrane envelope prepared as described in (b2) above) was glued onto the permeate collection tube. The long sides of the collection were then glued to the long side of adjacent membrane envelopes to form a gas-tight seal, optionally with the permeate envelope (prepared as described in (b1) above) between each pair of membrane envelopes. This process was repeated until all to 22 membrane envelopes and 21 permeate envelopes were adhered to the permeate collection tube in an alternate manner. The envelopes were then wound spirally onto the permeate collection tube to give a cylindrical, wound membrane structure comprising alternate membrane envelopes and permeate envelopes having two parallel, essentially circular end faces. Plastic bands were applied to the resultant wound membrane structure to prevent unwinding.

(34) Part (c)Fitting the ATD and Clamp

(35) ATDs constructed as shown in FIGS. 1(a) and 1(b) were slid onto each end of the projecting tube and abutted firmly against the wound membrane structure, with the side shown in FIG. 1(b) contacting the end faces of the wound membrane structure. Two clamps constructed as shown in FIG. 5 (each being referred to as Clamp Type A for convenience) were then slid onto each end of the tube, pressed firmly against the relevant ATD and the clamp bolts were then tightened to ensure the ATDs remain in place.

(36) The plastic bands were removed and the resultant construct was placed in a pipe having an inlet for feed gas and separate outlets for permeate and retenate gases.

(37) The properties of the resultant module are shown in Table 1 below and the test results are shown in Table 2.

EXAMPLE 2

(38) Example 1 was repeated except that in place of the ATD shown in FIG. 1(a) and FIG. 1(b) there was used an alternative ATD having the properties shown in Table 1 below.

(39) The properties of the resultant module are shown in Table 1 below and the test results are shown in Table 2.

COMPARATIVE EXAMPLES 1 AND 2

(40) Comparative Examples 1 and 2 (CEx1 and CEx2) were prepared exactly as described for Example 1 except that L.sub.CP, L.sub.contact and L.sub.VENT were changed as shown in Table 1. The value of R for each ATD and the flap angles are also shown in Table 1.

(41) The properties of the resultant module are shown in Table 1 below and the test results are shown in Table 2.

(42) TABLE-US-00001 TABLE 1 ATD Properties L.sub.CP L.sub.contact L.sub.VENT Flap angle Example (mm.sup.2) (mm.sup.2) (mm.sup.2) R [?] 1 30,000 210 18,800 1.58 87.1 2 29,800 420 19,100 1.54 87.1 CEx1 27,400 960 18,800 1.41 90.0 CEx2 29,000 1,080 14,400 1.93 68.2
Test Results

(43) A feed gas (air comprising N.sub.2 and O.sub.2) was fed into the modules described in Table 1 above at a pressure of 6 bar. The gas flux and selectivity of the modules was measured using the methods described above and the results are shown in Table 2 below. In Table 2, the stated O.sub.2/N.sub.2 selectivity values are all relative to the O.sub.2/N.sub.2 selectivity of CEx1. For example, the O.sub.2/N.sub.2 selectivity of Example 1 was 1.070 times that of CEx1:

(44) TABLE-US-00002 TABLE 2 Test Results O.sub.2/N.sub.2 selectivity Flap angle (?O.sub.2/N.sub.2) Example R [?] relative to CEx1 Permeate flow 1 1.58 87.1 1.070 1.040 2 1.54 87.1 1.092 1.063 CEx1 1.41 90 1.000 1.000 CEx2 1.93 68.2 1.026 0.923

EXAMPLES 3 AND 4

Effect of Varying the Clamp

(45) Examples 3 and 4 were prepared by repeating Example 1, except that instead of using Clamp Type A shown in FIG. 5 at each end of the wound membrane structure, there was used Clamp Type B or Clamp Type C, wherein Clamp Types B and C have the properties shown in Table 3 below. For comparison purposes Table 3 also includes the results for Example 1 and CEx1 which used Clamp Type A at both ends of the wound membrane structure. In Table 3, the stated O.sub.2/N.sub.2 selectivity and permeate flow values are all relative to the corresponding values for CEx1:

(46) TABLE-US-00003 TABLE 3 Effect of Varying the Clamp on Selectivity and Permeate Flow O.sub.2/N.sub.2 selectivity Clamp (?O.sub.2/N.sub.2) Permeate Clamp Used at Porosity relative flow relative Example R each end (%) to CEx1 to CEx1 1 1.58 Clamp Type A 13 1.070 1.040 (6 holes) 3 1.54 Clamp Type B 0 1.03 1.00 (no holes) 4 1.54 Clamp Type C 21 1.072 1.042 (10 holes) CEx1 1.41 Clamp Type A 13 1.000 1.000 (6 holes)