ECN-RX-05-202

On the full-scale module design of anair separation unit using mixed ionicelectronic conducting membranes

J.F. Vente

W.G. Haije

R. IJpelaan

F.T. Rusting

Joumal of Membrane Science, In Press,Digital Object Identifier: doi 1 O. 1016/j.memsci. 2005. "10.0,~4

RevisionsA 10 October 2005; draft versionB 16 November 2005; final versionMade by: ..~

Appro~~_.ECN Energy Efficiency

in IndustryJ.F. Vente P.P.Ae. pexChecked by: Issued by:

Separation Technology..-í~, ~~I

H.M. van Veen

NOVEMBER 2005

Abstract The conceptual design for a full-scale air separation unit is discussed in terms of specific surface area and feasibility of manufacturing. The concept with highest specific surface area was found to be that using multi-channel monoliths, followed by that using tube-and-plate assemblies, and by that using single-hole tubes, and finally by that with hollow fibres. The basic unit size is, however, dependent on the maximum gas velocity allowed in the module (25 m/s). In this case, the number of modules required to house 5,000 m2 of membrane surface area follows a different order. A minimum of 32 modules is required when using single-hole tubes, followed by the concept with multi-channel monoliths (39 modules), and that with multiple tube-and-plate assemblies in one module (120 modules). The hollow fibre concept leads to about 1800 modules. A further discussion on the (dis)advantages of these concepts in relation with the manifolding, sealing, and the possibility of using a sweep/reactive gas is presented. We conclude that the concept using single-hole tubes is preferred for the production of oxygen with and without a sweep gas, and also for the partial oxidation of gaseous hydrocarbons using a reactive sweep gas. Keywords Single-hole tubes, hollow-fibres, multi-channel monoliths, tube-and-plate assemblies, oxygen conducting membrane, specific surface area.

2 ECN-RX--05-202

Contents

List of tables 4 List of figures 4 1. Introduction 5 2. Experimental 7 3. Results and discussion 10 4. Conclusion 16 5. Table of symbols 17 References 18

ECN-RX--05-202 3

List of tables

Table 2.1 Equations used to calculate the specific surface areas and the gas velocity on the permeate side for the three concepts studied 9

Table 3.1 Parameters used in the tube-and-plate module calculations 12 Table 3.2 The maximum support length of monoliths due to the maximum gas velocity of v

= 25 m/s 13 Table 3.3 Specifications and results for the number of basic units and specific surface

area for seven different cases, v = 25m/s 14

List of figures

Figure 2.1 View of the cross section of one quarter of a multi-channel monolith, high lighting the various parameters and the small channels near the edge 7

Figure 2.2 Full scale module for the tubular membrane concept, case 2, containing a membrane area of 157.3 m2. The tubes are fixed to the top of the module, and centred at the bottom, which allows for the different values of thermal expansion of the different materials used 8

Figure 3.1 The specific surface area of an infinitely large module (A∞) containing single-hole tubes as a function of the tube diameter (dt) for different distances (f) between hexagonally packed single-hole tubes 10

Figure 3.2 The specific surface area of an infinitely large module (A∞) containing multi-channel monoliths as a function of the tube diameter (dt) for different inner wall thicknesses (s), and channel size (g), with f = 40 mm 11

Figure 3.3 View of the tube-and-plate concept, featuring the various parameters 12 Figure 3.4 The specific surface area of an infinitely large module (A∞) containing tube-

and-plate assemblies as a function of the plate diameter (dp) for different plate thicknesses (t), and support tube diameter (dt), with f = 5 mm, values for zf and zp as given in Table 3.1 12

Figure 3.5 The maximum length of the support as a function of the diameter for the tube concept (top) or the plate diameter for the tube-and-plate concept (bottom), values for zf and zp as given in Table 3.1 13

4 ECN-RX--05-202

1. Introduction

Over the last decade, the interest in dense ceramic membranes for the transport of oxygen has grown considerably [1]. As a result, the knowledge of the intrinsic properties of the membrane materials is now overwhelming, and new publications are being published frequently [2]. The great majority of these papers deals with the materials properties or with membrane behaviour on a small scale. The shape is often a disc with a diameter of ~12 mm and a thickness of ~1 mm. Much less attention has been paid to the design of an actual full-scale module. To our best knowledge, this topic has only been addressed at conference series such as the "International Conference on Catalysis in Membrane Reactors" and "Gasification Technologies". These contributions are not widely available and do not provide detailed information. Mixed ionic electronic conducting (MIEC) membranes that can transport oxygen can be prepared from various oxides, have often the perovskite structure and operate typically at temperatures between 700 and 1000°C [3]. Two applications can be envisaged. The first is the production of oxygen from air. For this application, high temperature membrane technology has to compete with well-established techniques such as cryogenic distillation. The second is the production of syn-gas by partial oxidation of hydrocarbons in a membrane reactor. Three archetypes can be distinguished when the shape of the MIEC membrane is considered, namely: single-hole tube, plate, and multi-channel monolith. Praxair [4] has chosen for a 2 meter long single-hole tube [5]. These tubes can be prepared by extrusion. The demands on the fluxes and strength result in a concept consisting of a porous tubular support with a thin dense top layer on the outside. Praxair claims that the relatively simple preparation, sealing, and manifolding outweighs the low specific surface area of the tubular system. A pilot plant with a capacity of ~6 Nm3 O2/hr was in operation in 2002 [4]. Single-hole tubes with a diameter of 1 mm are also called hollow fibres. Bundles of hollow fibres have potentially a high membrane area per reactor volume [6,7]. A flat membrane can be prepared by tape-casting and an additional top layer can be deposited by screen-printing [8]. Sealing is expected to be difficult and the strength is most likely to be too low to accommodate the large pressure difference imposed by the process conditions. This can be overcome by the tube-and-plate concept as developed by Air Products [9-11]. Their concept can be explained as plates with an estimated size of 10 x 10 cm2 [10] connected with a central support tube for the transport of the pure oxygen. One stack consists of ~80 plates and has been designed to produce ~15 Nm3 O2/hr* [11]. The main apparent advantage of this system is the relatively large amount surface area per sealing location on the ceramic to metal interface. Air Products aims to have a pilot plant that can produce ~1000 Nm3 O2/hr by 2007 [10]. Finally, Hydro Oil & Energy [12] is developing the concept, which has intrinsically a very high specific surface area: the multi-channel monolith concept. Photographs [12] suggest that they are extruding square monoliths of ~30 x 30 mm2 with a channel size of ~5 x 5 mm2. The main disadvantage of such a system is the very complex manifolding. In this paper, numerical information will be presented on the expected specific surface areas of four different membrane configurations: single-hole tube, hollow fibre, tube-and-plate, and multi-channel monolith. The basis of these calculations is that the total oxygen flow (mol/s) through the membrane must be transported out of the permeate volume of the membrane. The calculation will be performed with realistic assumptions of the possible dimensions for the membranes, manifolding, flanges etc. The limitations on the reachable specific surface area of the membranes due to the maximum gas velocities allowed at the permeate side and the finite

* 1 Nm3 O2/hr 0.03 tonnes per day O2.

ECN-RX--05-202 5

size of the module will also be taken into account. The consequences of the utilisation of a condensable sweep gas for the production of oxygen, and of gaseous hydrocarbons for the production of syn-gas on the configuration will be discussed.

6 ECN-RX--05-202

2. Experimental

For the design of a full-scale air separation unit, a total capacity of 30,000 Nm3 O2/hr has been selected. This size is typical for a large-scale cryogenic air separation unit [13]. A techno-economical evaluation by Bredesen [14] has shown that an oxygen flux of at least 10 Nml·cm-2·min-1 is required for the profitable production of oxygen with this technology. Fluxes of this order of magnitude have been reported before [2,3,7,8]. Using this capacity and flux, a total required surface area of 5,000 m2 can be calculated. The feed pressure, air, of 16 bar and a permeate pressure, oxygen, of 0.3 bar were chosen, common to current pressures used in cryogenic installations. The calculations of the specific surface are started for infinitely large modules (A∞), where there are no effects due to the finite sizes of the modules. Table 2.1 provides on overview of all the equations used in the current calculations. Analytical methods were used for single-hole tubes, hollow fibres and tube-and-plate concepts, whereas numerical approximations were used in the case of multi-channel monoliths. The number of internal walls between the square channels was calculated by positioning first a wall through the centre of the tubular monolith. Subsequently, walls were positioned at a distance g up to the edge of the support tube. For each wall, the surface area was calculated with a correction for the overlap due to crossing walls. However, no corrections were performed for the presence of small channels near the edge of the tube. An example of one quarter of such a multi-channel monolith is given in Figure 2.1.

k = 0

k = 1

k = n

Flange Outer wall

Small Channels

g

½ f t

w g s k = 0

k = 1

k = n

Flange Outer wall

Small Channels

g

½ f

w g s

1/2 df Figure 2.1 View of the cross section of one quarter of a multi-channel monolith, high lighting

the various parameters and the small channels near the edge

The maximum support length calculations were based on a maximum gas velocity on the permeate side, at 850°C and 0.3 bar, of v = 25 m/s. At higher velocities, resonances may occur which are detrimental for the thin membrane layers applied on the supports especially when baffles are used. A constant oxygen flux of 10 Nml·cm-2·min-1 through the active membrane area was chosen. The pressure drop in the support was assumed to be negligible, as justified by preliminary estimates.

ECN-RX--05-202 7

In order to calculate the specific surface area of a real industrial module, an internal diameter of 1000 mm was selected for the basic unit size, being a standard industrial vessel size. The internal height depends on the concept, and relates to the maximum support length, which, for practical reasons, does not exceed 2500 mm. The internal module length was taken 50 mm longer than the support length to assure that the full support can be used effectively. All equations of Table 2.1 were evaluated using Igor Pro [15]. The number of holes that can be accommodated in the tube plate (see Figure 2.2) was calculated for large numbers with Tubepl from the Sugar Engineers Library [16] with a hexagonal alignment of holes. Small numbers (< 40) were calculated manually. The specific surface area calculated with the internal module dimensions Dint and Lint is Aint. When the external dimensions Dext and Lext of the module are used Aext is obtained. The external dimensions include also the space required for the module walls, tube plate manifolding heads, insulation, etc as is shown in Figure 2.2.

Tubes

Outer shell

Thermal insulation

Baffles

Inner shell

288

mm

Oxygen outlet

Air exhaust

Air inlet

Tube plate

Dint = 1000 mm

L int

= 2

550

mm

L ext =

450

0 m

m

Dext = 2060 mm

Figure 2.2 Full scale module for the tubular membrane concept, case 2, containing a

membrane area of 157.3 m2. The tubes are fixed to the top of the module, and centred at the bottom, which allows for the different values of thermal expansion of the different materials used

8 ECN-RX--05-202

Table 2.1 Equations used to calculate the specific surface areas and the gas velocity on the permeate side for the three concepts studied Tube

Hollow fibre Tube and plate Monolith

A∞

( )23

2

fd

d

t

t

+

π ( ) ( )

2pf

22

)(3

2

fd

zztdd

p

tp

+

++−π ( ) ( ) ( ) ( )

( )21

22

3

21122

18

fd

gkwdgswd

t

n

ktt

+

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛⋅−−−+− ∑

=

Aint

int2int

sup4L

lD

dn t ( )int

2int

22plsup2

LD

ddnn tpl − ( ) ( ) ( ) ( )

int2int

1

22sup 2

1122116

Ll

D

gkwdgswdnn

ktt

π

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛⋅−−−+− ∑

=

Aext

ext2ext

sup4L

lD

dn t ( )ext

2ext

22plsup2

LD

ddnn tpl − ( ) ( ) ( ) ( )

ext2ext

1

22sup 2

1122116

Ll

D

gkwdgswdnn

ktt

π

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛⋅−−−+− ∑

=

v

( ) PP

TTJ

wd

ldO

t

t 0

022

21 −

plate: ( )

PP

TTJ

zddd

Opt

tp 0

02

22

2−

support: ( )

( ) PP

TTJ

wd

ddnO

t

tppl 0

022

22

21

2

−

−

( ) PP

TTJ

sgl

O0

02

4−

ECN-RX--05-202 9

3. Results and discussion

Figure 3.1 presents the specific surface area, A∞ of an infinitely large module with hexagonally packed single-hole tubes as a function of the tube diameter dt, for different distances f between the tubes. Anticipated constraints on the size of the flange results in a minimum value of f = 10 mm. At this value for f, the optimal diameter of a single-hole tube is 10 mm, and the maximum value for A∞ is ~90 m2/m3. Assuming that each hollow fibre has to be sealed individually, the specific surface area decreases rapidly with decreasing diameter when dt < f.

250

200

150

100

50

0

A∞ (

m2 /m

3 )

200150100500dt (mm)

f = 0 mm

f = 10 mm

f = 6 mm

f = 20 mm

Figure 3.1 The specific surface area of an infinitely large module (A∞) containing single-hole

tubes as a function of the tube diameter (dt) for different distances (f) between hexagonally packed single-hole tubes

In the case of multi-channel monoliths, parameters to be chosen freely include the distance between inner-walls and the thicknesses of the inner and outer walls (see Figure 2.1). In all cases the outer-wall thickness (w) has been set at 2 mm. The flow pattern is another degree of freedom and relates to the manifolding. In a chessboard pattern each feed channel share four walls with permeate channels. In the plate-like flow pattern, as used by Hydro Oil & Energy [12], only two walls are being shared. As a result the specific surface area of the latter is 50% of the former [12]. Throughout the current study, the chessboard pattern has been used. The results obtained are depicted in Figure 3.2 and are in good agreement with those presented by Bruun [12]. From Figure 3.2, it is apparent that the channels of the monoliths should be smaller than ~2 x 2 mm2 while the diameter of the monolith should be at least 100 mm. Preparing inner walls that are thinner than ~10% of the channel size results in a limited increase in A∞. The resulting

10 ECN-RX--05-202

large and heavy monoliths require large flanges and manifolding heads: a value of f = 40 mm appears to be reasonable. Square monoliths, as presented by Bruun [12], leave less space unused and will thus result in a higher specific surface area. Simple geometric considerations lead, under identical conditions to an increase of ~10%.

1000

800

600

400

200

0

A∞ (

m2 /m

3 )

200150100500dt (mm)

g = 1 mm

sht (f = 10 mm)

g = 5 mm

g = 2 mm

s = 0.2 mm s = 0.5 mm

Figure 3.2 The specific surface area of an infinitely large module (A∞) containing multi-

channel monoliths as a function of the tube diameter (dt) for different inner wall thicknesses (s), and channel size (g), with f = 40 mm

The degree of freedom for the tube-and-plate concept is very high. Parameters to be chosen include diameter of the tube, diameter of the plates, thickness of the plates, spacing between the plates on both the feed and the permeate sides (see Figure 3.3), and the number of assemblies in the module. The influences of various parameters listed in Table 3.1 are presented in Figure 3.4. In this figure, the curves stop at a certain maximum value of the plate diameter. At these values and under given conditions, the gas velocities through the spacing between the plates on the permeate side reach the value of 25 m/s. These calculations show that it is more effective to use relatively small supports and small plates than it is to use relatively large support and plates. It is likely that this has been an important argument for Air Products in the dimensioning of their tube-and-plate assemblies.

ECN-RX--05-202 11

t zp ½ dt

½ dp

zf

w

t zp ½ dt

½ dp

zf

w

Figure 3.3 View of the tube-and-plate concept, featuring the various parameters

Table 3.1 Parameters used in the tube-and-plate module calculations dt (mm) t (mm) zf (mm) zp (mm)

70 2.0 and 4.0 1.0 0.5 115 4.0 and 6.0 2.0 1.0 250 6.0 and 8.0 3.0 1.5

300

250

200

150

100

50

0

A∞ (

m2 /m

3 )

10008006004002000dp (mm)

t = 2 mm

t = 4 mm

t = 6 mm

t = 8 mm

dt = 70 mm dt = 115 mm dt = 250 mm

Figure 3.4 The specific surface area of an infinitely large module (A∞) containing tube-and-

plate assemblies as a function of the plate diameter (dp) for different plate thicknesses (t), and support tube diameter (dt), with f = 5 mm, values for zf and zp as given in Table 3.1

12 ECN-RX--05-202

Up to now, the intrinsic specific surface area has been calculated, assuming units with an infinite number of supports of infinite length. Limitations in the support length can occur as a result of too high gas velocities, i.e. v > 25 m/s. In Figure 3.5, the maximum support length is depicted for several cases for the tube, hollow fibre, and the tube-and-plate concepts. The maximum support lengths for the monoliths are given in Table 3.2. From these data, it is clear that major restrictions exist on the maximum support length under the current conditions. This is especially true for all monoliths and hollow fibres, for small single-hole tubes with a relatively thick wall, and for tube-and-plate systems with a large plate diameter.

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Max

imum

sup

port

leng

th (

m)

302520151050

dt (mm)

w = 1 mm

w = 3 mm

w = 5 mm

w = 0.2 mm

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Max

imum

sup

port

leng

th (

m)

10008006004002000

dp (mm)

dt = 70 mm dt = 115 mm dt = 250 mm

t = 2 mmt = 4 mm

t = 8 mm

Figure 3.5 The maximum length of the support as a function of the diameter for the tube

concept (top) or the plate diameter for the tube-and-plate concept (bottom), values for zf and zp as given in Table 3.1

Table 3.2 The maximum support length of monoliths due to the maximum gas velocity of v = 25 m/s

g (mm) s (mm) maximum support length (m) 1 0.2 0.22 2 0.2 0.49 5 0.5 1.23 The effects of the finite dimensions were studied on an industrial sized module with an internal diameter of 1000 mm a maximum support length of 2500 mm. A shorter support leads to a smaller module. The additional length required to house the manifolding has been taken independent of the support length. Longer supports thus lead to a more efficient use of space.

ECN-RX--05-202 13

The module for the single-hole tube configuration is given in Figure 2.2 as an example. The full-scale module is equipped with a double steel shell. The inner-shell contains the feed gas in the module and functions at the membrane operation temperature. The function of the outer-shell is to withstand the pressure, at ambient temperature. The volume between the shells provides the insulation. Table 3.3 presents seven different cases that have been selected on the basis of feasibility and the influence of the support length on the number of basic units required. The high values for A∞ in the case of monoliths (cases 4 and 5) do not result in a smaller number of modules due to the short supports. The configuration using 19 mm single-hole tubes (case 2) requires only 32 modules to accommodate the 5,000 m2 of membrane surface area. This number increases to ~40 when 10 mm tubes or monoliths are used (cases 3, 4 and 5). The tube-and-plate concept results in up to 120 modules (cases 6 and 7). Finally, the hollow fibre concept gives a total of 1797 modules (case 1). The differences between the external and internal dimensions vary from concept to concept. In the case of monoliths, longer modules are anticipated due to the larger spatial requirements of the manifolding. These requirements were assumed to be independent of the support length. The module with a single tube-and-plate assembly requires a larger diameter to allow for an effective supply of air on the feed side. The results show that the specific surface area for the infinitely large case has a limited predictive value for the calculation of the specific surface area based on the external dimensions of the module.

Table 3.3 Specifications and results for the number of basic units and specific surface area for seven different cases, v = 25m/s

Case 1 2 3 4 5 6 7 Membrane geometry Hollow

Fibre single-hole tube multi-channel

monolith tube-and-plate

dt (mm) 1 19 10 100 100 250 70 Other dimensions (mm) w = 0.2 w = 3 w = 1 w = 2

g = 2 s = 0.2

w = 2 g = 5

s = 0.5

dp = 950 t = 8 zf = 3

zp = 1.5

dp = 240t = 2 zf = 1

zp = 0.5 f (mm) 10 10 10 40 40 5 npl 41 51 l (mm) 98 2500 1750 490 1230 840 280 nsup 9042 1038 2232 37 37 1 10 Surface area per module (m2)

2.8 154.8 122.6 127.8 126.5 54.1 42.2

Number of basic units 1797 32 41 39 39 93 119 Dint (mm) Lint (mm)

1000 148

1000 2550

1000 1800

1000 540

1000 1280

1000 890

1000 330

Dext (mm) Lext (mm)

2060 2148

2060 4500

2060 3750

2060 3060

2060 3800

2850 3220

2060 2660

A∞ (m2/m3) 30.0 81.9 90.7 543.7 232.4 74.0 273.1 Aint (m2/m3) 23.9 77.1 86.8 301.5 125.9 77.4 168.0 Aext (m2/m3) 0.4 10.5 9.8 12.5 10.0 2.6 4.8 The current calculations indicate that the more complicated membrane concepts of multi-channel monoliths and tube-and-plates do not have major advantages in terms of specific surface area over the simple single-hole tube concept. Examples of disadvantages of the former concepts are the more expensive and more complex manifolding and sealing compared with the tubular system. Sealing for the latter concept can be based on the patented ECN technology [17]. The fact that each hollow fibre requires to be sealed individually combined with the very short length leads to a very low specific surface area and renders the option unsuitable for the current application.

14 ECN-RX--05-202

The influence of the constraints imposed by the maximum gas velocity can be reduced when a higher permeate pressure is used. An additional benefit would be a reduced pump load and energy consumption on the permeate side. However, in order to keep the driving force constant the pressure on the feed side needs to be increased by the same factor. As a result, the overall energy consumption will increase. Further, the larger absolute pressure drop over the membrane may become larger than what the membrane can withstand mechanically. All the concepts discussed above can be used for the production of oxygen with a low pressure on the permeate side. A condensable sweep gas, e.g. steam, can be used easily in the case of single-hole tubes. The manifolding in the case of multi-channel monoliths is expected to be very complicated, especially for larger monoliths with small channels. The absolute pressure on the permeate side will be higher when a sweep gas is being used and the maximum allowable gas velocity increases. As a result, it is uncertain whether limitations due to the gas velocity will occur under these conditions. The use of sweep gas is not feasible in the case of the tube-and-plate module. The same arguments hold for a membrane reactor for the partial oxidation of gaseous hydrocarbons, where a reactive sweep gas is employed.

ECN-RX--05-202 15

4. Conclusion

We have shown that the presented calculations enable the choice of optimal dimensions and shapes of membrane entities. It is important to take the limiting effects of module dimensions and gas velocities into account when the specific surface area of a full-scale module is calculated. The results presented here show that a tubular system is the optimal choice for all conditions considered, i.e. low permeate pressure and sweep gas for the production of oxygen and the direct partial oxidation of gaseous hydrocarbons on the permeate side. Hollow fibre, Multi-channel monolith and tube-and-plate concepts result in a low specific surface area when a low permeate pressure is being used. The applicability of multi-channel monoliths is limited due to the complexity of the manifolding when a, reactive, sweep gas is used.

16 ECN-RX--05-202

5. Table of symbols

A∞ Intrinsic specific surface area Aext Specific surface area based on Dext and Lext.Aint Specific surface area based on Dint and Lint Dext External diameter of module Dint Internal diameter of module dp Diameter of plates dt Diameter of tubular support f Distance between membranes entities g Distance between inner walls JO2 Oxygen flux k Summation counter of inner walls, k = 0 is the central wall, l Length of supports Lext External length of module Lint Internal length of module n Number of walls in one direction in one quarter of the monolithnpl Number of plates nsup Number of tubular supports P Pressure P0 Pressure under standard conditions s Thickness of the inner walls t Thickness of single plates T Temperature T0 Temperature at standard conditions v Gas velocity w Thickness of the outer wall zf Space between the single plates on the feed side zp Space between the single plates on the permeate side See also Figure 2.1, Figure 2.2 and Figure 3.3 for graphical illustrations of the symbols.

ECN-RX--05-202 17

References

[1] Bouwmeester, H.J.M. (2003): Dense ceramic membranes for methane conversion. Catal. Today 82 (2003) 141.

[2] Kharton, V.V., F.M.B. Marques (2002): Mixed ionic-electronic conductors: effects of ceramic microstructure on transport properties. Curr. Opin. Solid State Mater. Sci. 6 (2002) 261.

[3] Teraoka, Y., H.M. Zhang, S. Furukawa, N. Yamazoe (1985): Oxygen permeation through perovskite-type oxides. Chem. Lett. (1985) 1743.

[4] Prasad, R., J. Chen, B.A. van Hassel, J. Sirman, J.H. White, E. Shreiber, J. Corpus, J. Harnanto (2002): OTM - An advanced oxygen technology for IGCC. Gasification Technologies 2002.

[5] Hassel, B.A. van, R. Prasad, J. Chen, J. Lane (2001): Ion-transport membrane assembly incorporating internal support. US 6,565,632 (2001).

[6] Liu, S., G.R. Gavalas (2005): Oxygen selective ceramic hollow fiber membranes. J. Membr. Sci. 246 (2005) 103.

[7] Schiestel, T., M. Kilgus, S. Peter, K.J. Caspary, H. Wang, J. Caro (2005): Hollow fibre perovskite membranes for oxygen separation. J. Membr. Sci. 258 (2005) 1.

[8] Vente, J.F., W.G. Haije, Z.S. Rak (2005): Performance of functional perovskite membranes for oxygen production. J. Membr. Sci. accepted for publication.

[9] Armstrong, P.A., D.L. Bennet, E.P.T. Foster, E.E. van Stein (2002): Ceramic membrane development for oxygen supply to gasification applications. Gasification Technologies 2002.

[10] Armstrong, P.A., J. Sorensen, E.P.T. Foster (2003): ITM oxygen: an enabler for IGCC. Gasification Technologies 2003.

[11] Armstrong, P.A., D.L. Bennet, E.P.T. Foster, E.E. van Stein (2004): ITM oxygen for gasification. Gasification Technologies 2004.

[12] Bruun, T. (2004): Design issues for high temperature ceramic membrane reactors. 6th International Conference on Catalysis in Membrane Reactors (2004).

[13] Ullmann's encyclopaedia of industrial chemistry; 6th edition, 1999 electronic release Wiley VCH (1999).

[14] Bredesen, R., J. Sogge (1996): A technical and economic assessment of membrane reactors for hydrogen and syngas production. Seminar on the Ecological Applications of Innovative Membrane Technology in the Chemical Industry.

[15] Wavemetrics Igor Pro [Computer Program] 2003.

[16] Tubepl: Tube plate layout, Sugar Engineers' Library, (2005), www.sugartech.co.za/software/tubeplate/index.php

[17] Rusting, F., G. de Jong, P.P.A.C. Pex, J.A.J. Peters (2001): Sealing socket and method for arranging a sealing socket to a tube. WO 01/63162 A1.

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