U.S. patent application number 13/503756 was filed with the patent office on 2012-08-23 for reactor with channels.
This patent application is currently assigned to CompactGTL plc. Invention is credited to David James West.
Application Number | 20120210995 13/503756 |
Document ID | / |
Family ID | 41426710 |
Filed Date | 2012-08-23 |
United States Patent
Application |
20120210995 |
Kind Code |
A1 |
West; David James |
August 23, 2012 |
Reactor with Channels
Abstract
A reactor defining first and second flow channels within the
reactor, wherein the first flow channels are for fluids that
undergo an exothermic reaction and contain a catalyst for the
exothermic reaction and wherein the second flow channels are for a
heat-removing fluid. Further wherein the channels at each end of
the reactor are such that no heat is generated within them, the
channels in which no heat is generated being non-flow channels
which are blocked off at one or both of their ends so no fluids
flow through those channels.
Inventors: |
West; David James;
(Ducklington, GB) |
Assignee: |
CompactGTL plc
Cleveland
GB
|
Family ID: |
41426710 |
Appl. No.: |
13/503756 |
Filed: |
October 12, 2010 |
PCT Filed: |
October 12, 2010 |
PCT NO: |
PCT/GB2010/051712 |
371 Date: |
April 24, 2012 |
Current U.S.
Class: |
126/263.01 |
Current CPC
Class: |
F28D 9/0062 20130101;
B01J 2219/2472 20130101; B01J 2219/2465 20130101; B01J 19/249
20130101; B01J 2219/2485 20130101; B01J 2219/2462 20130101; B01J
2219/2453 20130101; B01J 2219/2479 20130101; B01J 2219/2458
20130101; B01J 2219/2459 20130101; F28D 9/0068 20130101; B01J
2219/2497 20130101 |
Class at
Publication: |
126/263.01 |
International
Class: |
F24J 1/00 20060101
F24J001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 26, 2009 |
GB |
0918738.6 |
Claims
1-11. (canceled)
12. A reactor defining first and second flow channels within the
reactor, wherein the first flow channels are for fluids that
undergo an exothermic reaction and contain a catalyst for the
exothermic reaction, and the second flow channels are for a
heat-removing fluid, wherein the channels at each end of the
reactor are such that no heat is generated within them, the
channels in which no heat is generated being non-flow channels
which are blocked off at one or both of their ends so no fluids
flow through those channels.
13. A reactor as claimed in claim 12 wherein there are a plurality
of such non-flow channels at at least one end of the reactor.
14. A reactor as claimed in claim 12 wherein the flow channel
nearest to the non-flow channels is a second flow channel.
15. A reactor as claimed in claim 12 comprising a stack of reactor
blocks, each block defining a plurality of first and second flow
channels, wherein the first flow channels are for fluids that
undergo an exothermic reaction and contain a catalyst for the
exothermic reaction, and the second flow channels are for a
heat-removing fluid, wherein the channels at each end of the block
that are adjacent to another such block are second flow
channels.
16. A reactor as claimed in claim 15 wherein the channels at each
end of the block that are adjacent to another such block are of
smaller cross-sectional area than other second flow channels in the
block, by being less high in the direction of heat transfer.
17. A reactor as claimed in claim 12 comprising a stack of reactor
blocks, each block defining a plurality of first and second flow
channels, wherein the first flow channels are for fluids that
undergo an exothermic reaction and contain a catalyst for the
exothermic reaction, and the second flow channels are for a
heat-removing fluid, wherein the channels at each end of the block
that are adjacent to another such block are first flow channels and
are of smaller cross-sectional area than other first flow channels
in the block, by being less high in the direction of heat
transfer.
18. A reactor as claimed in claim 12 wherein the heat-removing
fluid is a fluid that undergoes an endothermic reaction, each
second flow channel containing a catalyst for the endothermic
reaction.
19. A reactor as claimed in claim 12 wherein the heat-removing
fluid is a coolant.
20. A reactor as claimed in claim 12 comprising a stack of metal
sheets that are arranged to define the first and second flow
channels, the first and second flow channels being arranged
alternately within the stack, and wherein removable
catalyst-carrying gas-permeable non-structural elements are
provided within each flow channel in which a reaction is to be
performed.
Description
[0001] The present invention relates to a reactor with channels for
performing chemical reactions at elevated temperatures, for example
Fischer-Tropsch synthesis, or steam methane reforming, and to a
reactor block that may be used to form the reactor.
[0002] The use of a catalytic reactor consisting of a stack of
metal sheets that define first and second flow channels, where
catalyst is provided on removable inserts such as corrugated foils
within the flow channels, is described for example in WO 03/006149,
which describes use of such a reactor for performing various
chemical reactions including steam methane reforming. In such
reactors the channels may be defined by flat plates spaced apart by
castellated plates, or flat plates space apart by spacer bars, or
by grooved plates. Another type of reactor utilises tubes. Steam
methane reforming is an endothermic reaction that requires an
elevated temperature, typically above 750.degree. C.; and the
requisite heat may be provided by a combustion reaction taking
place in the other set of channels within the catalytic reactor.
Although this approach is effective, it would be desirable to
reduce thermal gradients within the reactor, as these lead to
stresses in the material forming a reactor. Similar reactors may
also be used for Fischer-Tropsch synthesis. Fischer-Tropsch
synthesis is an exothermic reaction, so in this case the channels
adjacent to those for the synthesis reaction may carry a
coolant.
[0003] Not only do thermal gradients within a reactor tend to lead
to stresses within the material forming a reactor, but there is
also a further risk of thermal runaway. With some exothermic
catalytic reactions the rate of reaction may increase as the
temperature increases; and in such a case there is a positive
feedback between the reaction rate and the temperature within the
reactor. This can lead to a rapid increase of temperature, referred
to as a thermal runaway, and this can result in damage to the
catalyst or to the reactor, or both, and would reduce the useful
life of the reactor.
[0004] According to one aspect of the present invention there is
provided a reactor defining first and second flow channels within
the reactor, wherein the first flow channels are for fluids that
undergo an exothermic reaction and the second flow channels are for
a heat-removing fluid, wherein the channels at each end of the
reactor are such that no heat is generated within them.
[0005] Although mention has been made of there being first and
second flow channels for first and second fluids, it will be
appreciated that the reactor might define flow channels for more
than two different fluids.
[0006] Preferably the channels in which no heat is generated are
not flow channels, that is to say no fluids flow through those
channels, as they are blocked off at one or both of their ends
("non-flow channels"). Indeed there may be a plurality of such
non-flow channels at the end of the reactor, for example two or
three. Preferably the flow channel nearest to each end of the
reactor is a second flow channel, and may be of smaller
cross-sectional area than other second flow channels in the
reactor.
[0007] Such a reactor may be made of blocks, each block defining a
plurality of first and second flow channels, wherein the first flow
channels are for fluids that undergo an exothermic reaction and the
second flow channels are for a heat-removing fluid, wherein the
channels at each end of the block are second flow channels. In this
case these channels may be of smaller cross-sectional area than
other second flow channels in the block, by being less high (in the
direction of heat transfer). Since they are provided with heat on
only one side they are preferably no more than 50% as high as other
second flow channels within the block.
[0008] In an alternative, a reactor may be made of blocks, each
block defining a plurality of first and second flow channels,
wherein the first flow channels are for fluids that undergo an
exothermic reaction and the second flow channels are for a
heat-removing fluid, wherein the channels at each end of the block
are first flow channels and are of smaller cross-sectional area
than other first flow channels in the block, by being less high (in
the direction of heat transfer). They are preferably no more than
50% as high as other first flow channels within the block.
[0009] The heat-removing fluid may be a fluid that undergoes an
endothermic reaction. Alternatively the heat-removing fluid may be
a coolant.
[0010] When the reactor is constructed by combining the reactor
blocks end to end, there will be a small gap between successive
reactor blocks, which inhibits heat transfer. This gap is
preferably less than 5 mm wide.
[0011] Preferably each reactor block comprises a stack of metal
sheets that are arranged to define the first and second flow
channels, the first and second flow channels being arranged
alternately within the stack, and there are removable
catalyst-carrying gas-permeable non-structural elements within each
flow channel in which a reaction is to be performed.
[0012] Within each reactor block the first and second flow channels
may be defined by grooves in plates arranged as a stack, or by
spacing strips and plates in a stack, the stack then being bonded
together. Alternatively the flow channels may be defined by thin
metal sheets that are castellated and stacked alternately with flat
sheets; the edges of the flow channels may be defined by sealing
strips. The stack of plates forming the reactor is bonded together
for example by diffusion bonding, brazing, or hot isostatic
pressing.
[0013] To ensure the required good thermal contact both the first
and the second flow channels may be between 20 mm and 1 mm high (in
cross-section); and each channel may be of width between about 1.5
mm and 25 mm. By way of example the plates (in plan view) might be
of width in the range 0.05 m up to 1 m, and of length in the range
0.2 m up to 2 m, and the flow channels are preferably of height
between 2 mm and 10 mm (depending on the nature of the chemical
reaction). For example the plates might be 0.5 m wide and 1.0 m
long, or 0.6 m wide and 0.8 m long; and they may for example define
channels 7 mm high and 6 mm wide, or 3 mm high and 10 mm wide, or
10 mm high and 5 mm wide. Arranging the first and second flow
channels to alternate in the stack helps ensure good heat transfer
between fluids in those channels. For example the first flow
channels may be those for combustion (to generate heat) and the
second flow channels may be for steam/methane reforming (which
requires heat). The catalyst structures are inserted into the
channels, and can be removed for replacement, and do not provide
strength to the reactor, so the reactor itself must be sufficiently
strong to resist any pressure forces or thermal stresses during
operation.
[0014] Preferably each such catalyst structure is shaped so as to
subdivide the flow channel into a multiplicity of parallel flow
sub-channels. Preferably each catalyst structure includes a ceramic
support material on the metal substrate, which provides a support
for the catalyst. The metal substrate provides strength to the
catalyst structure and enhances thermal transfer by conduction.
Preferably the metal substrate is of a steel alloy that forms an
adherent surface coating of aluminium oxide when heated, for
example a ferritic steel alloy that incorporates aluminium (eg
Fecralloy.TM.), although the metal substrate may alternatively be
of a different material such as stainless steel or aluminium,
depending on the temperature and the chemical environment to which
it is to be exposed. The substrate may be a foil, a wire mesh or a
felt sheet, which may be corrugated, dimpled or pleated; the
preferred substrate is a thin metal foil for example of thickness
no more than 200 .mu.m, which is corrugated to define the
longitudinal sub-channels.
[0015] If the exothermic reaction is combustion, a flame arrestor
is preferably provided at the inlet to each flow channel for
combustion to ensure a flame cannot propagate back into the
combustible gas mixture being fed to the combustion channel. This
may be within an inlet part of each combustion channel, for example
in the form of a non-catalytic insert that subdivides a portion of
the combustion channel adjacent to the inlet into a multiplicity of
narrow flow paths which are no wider than the maximum gap size for
preventing flame propagation. For example such a non-catalytic
insert may be a longitudinally-corrugated foil or a plurality of
longitudinally-corrugated foils in a stack. Alternatively or
additionally, where the combustible gas is supplied through a
header, then such a flame arrestor may be provided within the
header.
[0016] The channels may be square in cross-section, or may be of
height either greater than or less than the width; the height
refers to the dimension in the direction of the stack, that is in
the direction for heat transfer. The catalyst element may for
example comprise a single shaped foil, for example a corrugated
foil; this is particularly suitable where the channel's minimum
cross-sectional dimension is no more than about 3 mm, although it
is also applicable in wider channels. Alternatively, and
particularly where the channel's minimum cross-sectional dimension
is greater than about 2 mm, the catalyst structure may comprise a
plurality of such shaped foils separated by substantially flat
foils. To ensure the required good heat transfer, for example in a
steam/methane reforming reactor, the combustion channels are
preferably less than 10 mm high. But the channels are preferably at
least 1 mm high, or it becomes difficult to insert the catalyst
structures, and engineering tolerances become more critical. As one
example, the channels might all be 7 mm high and 6 mm wide, and in
each case the catalyst element may comprise a single shaped foil,
or a plurality of shaped foils.
[0017] The invention will now be further and more particularly
described, by way of example only, and with reference to the
accompanying drawings, in which:
[0018] FIG. 1 shows a schematic perspective view, partly in
section, of part of a reactor block suitable for steam/methane
reforming (the section being on the line 1-1 of FIG. 2);
[0019] FIGS. 1a and 1b show modifications to the reactor of FIG.
1;
[0020] FIG. 2 shows a side view of the assembled reactor block of
FIG. 1 showing the flow paths;
[0021] FIGS. 3a, 3b and 3c show plan views of parts of the reactor
block of FIG. 1 during assembly; and
[0022] FIG. 4 shows a perspective view, partly exploded, of a
reactor that incorporates reactor blocks similar to that of FIG.
1.
[0023] The invention would be applicable to a process for making
synthesis gas, that is to say a mixture of carbon monoxide and
hydrogen, from natural gas by steam reforming. The synthesis gas
may, for example, subsequently be used to make longer-chain
hydrocarbons by a Fischer-Tropsch synthesis. The steam reforming
reaction is brought about by mixing steam and methane, and
contacting the mixture with a suitable catalyst at an elevated
temperature so the steam and methane react to form carbon monoxide
and hydrogen. The steam reforming reaction is endothermic, and the
heat may be provided by catalytic combustion, for example of
hydrocarbons and/or hydrogen mixed with air, so combustion takes
place over a combustion catalyst within adjacent flow channels
within the reforming reactor.
[0024] Referring now to FIG. 1 there is shown a reactor block 10
suitable for use as a steam reforming reactor, or for use in a
steam reforming reactor. The reactor block 10 defines channels for
a catalytic combustion process and channels for steam methane
reforming. The reactor 10 consists of a stack of plates that are
rectangular in plan view, each plate being of corrosion resistant
high-temperature alloy such as Inconel 625, Incoloy 800HT or Haynes
HR-120. Flat plates 12, typically of thickness in the range 0.5 to
4 mm, in this case 2.0 mm thick, are arranged alternately with
castellated plates 14 or 15, so the castellations define channels
16 or 17. The castellated plates 14 and 15 are arranged in the
stack alternately. The thickness of the castellated plates 14 and
15, typically in the range between 0.2 and 3.5 mm, is in each case
0.9 mm. The height of the castellations, typically in the range
2-10 mm, is 3.9 mm in each case, and solid bars 18 of the same
thickness are provided along the sides. The wavelengths of the
castellations in the castellated plates 14 and 15 may be different
from each other, but as shown in the figure in a preferred
embodiment the wavelengths are the same, so that in each case
successive fins or ligaments are 10 mm apart. The castellated
plates 14 and 15 may be referred to as fin structures.
[0025] At each end of the stack is a flat end plate 19, which in
this case is also of thickness 2.0 mm. As explained below in
relation to FIG. 3c, the channels defined in the last two
castellated plates 14a and 15a adjacent to the end plate 19 are
non-flow channels 20. In a modification the end plate may be of
different thickness, typically a greater thickness in the range 2.0
up to 10 mm. In this example the number of castellated plates 14,
14a, 15 and 15a in the reactor block 10 is thirteen, so that the
overall height of the reactor block 10 is 78.7 mm.
[0026] Although only five channels are shown as being defined by
each castellated sheet 14 or 15 in FIG. 1, in a practical reactor
there might be many more, for example over forty channels in a
reactor block 10 of overall width about 500 mm.
[0027] The stack of plates would be assembled and bonded together
typically by diffusion bonding, brazing, or hot isostatic pressing.
Into each of the channels 16 and 17 is then inserted a respective
catalytic insert 22 or 24 (only one of each are shown in FIG. 1),
carrying a catalyst for the respective reaction. These inserts 22
and 24 preferably have a metal substrate and a ceramic coating
acting as a support for the active catalytic material, and the
metal substrate may be a thin metal foil. For example the insert
22, 24 may comprise a stack of corrugated foils and flat foils, or
a single corrugated foil, occupying the respective flow channel 16
or 17, each foil being of thickness less than 0.1 mm, for example
50 microns. (There are no such catalytic inserts in the non-flow
channels 20.)
[0028] Referring now to FIGS. 1a and 1b there are shown some
modifications to the reactor block 10. Whereas the channels 16 and
17 of the reactor block 10 are wider than they are high, as
illustrated in FIGS. 1a and 1b they may instead be higher than they
are wide. The inserts 22 and 24 shown in FIG. 1 consist of a single
corrugated foil within each channel; in figure la the insert 22a is
again of a single corrugated foil, whereas in FIG. 1b the insert
22b comprises a stack of corrugated foils and flat foils.
[0029] Referring now to FIG. 2 there is shown a side view of the
assembled reactor block 10. The gas mixture undergoing combustion
enters a header 30 at one end of the reactor block 10 (top, as
shown) and after passing through a baffle plate flame arrestor 31
follows the flow channels 17 that extend straight along most of the
length of the reactor 10. Towards the other end of the reactor
block 10 the flow channels 17 change direction through 90.degree.
to connect to a header 32 at the side of the other end of the
reactor 10 (bottom right as shown), this flow path being shown as a
broken line C. The gas mixture that is to undergo the steam methane
reforming reaction enters a header 34 at the side of the one end of
the reactor block 10 (top left, as shown), passes through a baffle
plate 35 and then changes direction through 90.degree. to flow
through flow channels 16 that extend straight along most of the
length of the reactor block 10, to emerge through a header 36 at
the other end (bottom, as shown), this flow path being shown as a
chain dotted line S. The arrangement is therefore such that the
flows are co-current; and is such that each of the flow channels 16
and 17 is straight along most of it length, and communicates with a
header 30 or 36 at an end of the reactor block 10, so that the
catalyst inserts 22 and 24 can be readily inserted before the
headers 30 or 36 are attached. It may be preferable to provide
catalyst inserts 22 and 24 only along those parts of the straight
portions of the flow channel 16 and 17 that are adjacent to each
other.
[0030] Each of the flat plates 12 shown in FIG. 1 is, in this
example, of dimensions 500 mm wide and 1.0 m long, and that is
consequently the cross-sectional area of the reactor block 10.
Referring now to FIG. 3a there is shown a plan view of a portion of
the reactor block 10 during assembly, showing the castellated plate
15 (this view being in a plane parallel to that of the view of FIG.
2). The castellated plate 15 is of length 800 mm, and of width 460
mm, and the side bars 18 are of width 20 mm. The top end of the
castellated plate 15 is aligned with the top edge of the flat plate
12, so it is open (to communicate with the header 30). One of the
side bars 18 (the left one as shown) is 1.0 m long, and is joined
to an equivalent end bar 18a that extends across the end. There is
consequently a 180 mm wide gap at the bottom right-hand corner (to
communicate with the header 32). The rectangular region between the
bottom end of the castellated plate 15 and the end bar 18a is
occupied by two triangular portions 26 and 27 of castellated plate:
a first portion 26 has castellations parallel to the end bar 18a,
and extends to the edge of the stack (so as to communicate with the
header 32), whereas the second portion 27 has castellations
parallel to those in the castellated plate 15.
[0031] Referring to FIG. 3b there is shown a view, equivalent to
that of FIG. 3a, but showing a castellated plate 14. In this case
the castellated plate 14 is again of length 800 mm, and of width
460 mm, and the side bars 18 are of width 20 mm. The bottom end of
the castellated plate 14 is aligned with the bottom edge of the
flat plate 12, so it is open (to communicate with the header 36).
One of the side bars 18 (the right one as shown) is 1.0 m long, and
is joined to an equivalent end bar 18a that extends across the end.
There is consequently a 180 mm wide gap at the top left-hand corner
(to communicate with the header 34). In the rectangular region
between the top end of the castellated plate 14 and the end bar 18a
there are triangular portions 26 and 27 of castellated plate: a
first portion 26 has castellations parallel to the end bar 18a, and
extends to the edge of the stack (so as to communicate with the
header 34), while the other portion 27 has castellations parallel
to those in the castellated plate 14.
[0032] Referring to FIG. 3c there is shown a view, equivalent to
that of FIGS. 3a and 3b, but showing a castellated plate 14a
defining one of the non flow channels 20. In this case the
castellated plate 14a is of length 960 mm, and again of width 460
mm. In this case both the side bars 18 are 1.0 m long, and they
connect to end bars 18a at each end. Consequently there is no fluid
flow through the non-flow channels 20. However there are small
bleed holes 28, at the top right-hand corner and bottom left-hand
corner as shown, so that the non-flow channels 20 are at the
pressure of the surroundings.
[0033] It will be appreciated that many other arrangements of
portions of castellated plates may be used to achieve this change
of gas flow direction. For example the castellated plate 15 and the
portion of castellated plate 27 may be integral with each other, as
they have identical and parallel castellations; and similarly the
castellated plate 14 and the adjacent portion of castellated plate
27 may be integral with each other. Preferably the castellations on
the triangular portions 26 and 27 have the same shape as those on
the channel-defining portions 14 or 15.
[0034] As mentioned previously, after the stack of plates 12, 14,
15 has been assembled, catalyst inserts 22 and 24 are inserted into
the reaction channels 16 and 17. Preferably in the channels 17 for
the combustion gases C the catalyst inserts 24 are of length 600 mm
so as to occupy the bottom three-quarters of the straight channels
as shown in plan in FIG. 3a, this portion being indicated by the
arrow P, and the other 200 mm indicated by the arrow Q are occupied
by a non-catalytic spacer which may be in the form of a
loosely-fitting corrugated foil. Similarly in the channels 16 for
the steam reforming gas mixture S the catalyst inserts 22 are of
length 600 mm, and as indicated by the arrow R the catalyst inserts
22 occupy the upper three-quarters of the straight channels as
shown in plan in FIG. 3b; the other 200 mm as indicated by the
arrow Q are occupied by a non-catalytic spacer. After inserting the
catalyst inserts 22 and 24, a wire mesh (not shown) may be attached
across the bottom end of the reactor block 10 so that the spacers
and catalyst inserts 22 do not fall out of the flow channels 16
when the reactor block 10 is in its upright position (as shown in
FIG. 2). It will hence be appreciated that the catalytic inserts 22
and 24 are only present in those portions of the flow channels 16
and 17 which are immediately adjacent to each other.
[0035] It will be appreciated that headers 30, 32, 34 and 36 might
then be attached to the reactor block 10. However it may be more
convenient to provide a reactor of larger capacity, and this may be
achieved by combining several such reactor blocks together.
[0036] Referring now to FIG. 4 there is shown a reactor 40. This
consists of several reactor blocks 10a and 10b that are similar to
the reactor block 10 of FIG. 1. There are two reactor end blocks
10a that are at the ends of the reactor 40. These end blocks 10a
differ from the reactor block 10 in that they have non-flow
channels 20 at only one end of the stack, that being the end which
forms the end of the reactor 40; at the other end of the reactor
block 10a there are flow channels 16 for the steam methane
reforming gas flow S. Between these end blocks 10a are several
inner blocks 10b which differ from the end blocks 10a in having no
non-flow channels 20; at both ends of each inner block 10b are flow
channels 16 for the steam methane reforming gas flow S.
[0037] During assembly of the reactor 40, the reactor blocks 10a or
10b are welded to one another in such a way as to leave gaps 2.3 mm
wide between successive blocks, the welding filling in the gaps
around the edges in those positions where headers 30, 32, 34 and 36
(see also FIG. 2) are to be attached, but leaving an open gap 41
(only three shown) on those portions of the sides where no header
is to be attached. This may be achieved either by holding the
blocks at the desired spacing, and welding across the gap; or by
placing spacer bars 2.3 mm thick between the blocks along those
portions that are to be filled in, and welding the blocks and the
spacer bars together.
[0038] Headers 30, 32, 34 and 36 are then attached to the reactor
40. In this example each header extends over the entire length of
the reactor 40, which in this case is of total length 1.0 m, each
header 30, 32, 34 and 36 having a single fluid inlet or outlet duct
42, 43, 44 and 45 for the respective fluids C, S.
[0039] Hence in operation the reactor block 10 or the reactor 40
may be used as part of a plant for producing synthesis gas from a
mixture of methane and steam. A combustible gas mixture (see arrows
C) would be supplied to the header 30, so as to flow along the flow
paths 17 in which it undergoes catalytic combustion, the exhaust
gases emerging into the header 32. A mixture of methane and steam
(see arrows S) would be supplied to the header 34 so as to flow
along the flow paths 16 in which are the catalyst inserts 22,
typically being supplied at a temperature of about 600.degree. C.,
and the mixture is raised to a temperature of about 770.degree. C.
as it passes through the reactor 40. The resulting synthesis gas
emerges into the header 36, so as to emerge through the outlet duct
45.
[0040] The outermost flow channels in which gas flow occurs in the
reactor 40 are reforming channels 16. Heat transfer from these
outermost channels is restricted by the provision of the non-flow
channels 20. This reduces the thermal gradients within the reactor
40, and so decreases the thermal stresses to which it is
subjected.
[0041] In a modification, since the outermost reforming channels 16
experience heat in-flow on only one side, those outermost reforming
channels 16 may be of smaller height than the other reforming
channels 16 in the reactor block 10. For example they may be of
height between 30 and 70% that of the other reforming channels,
most preferably between 45 and 55% that of the other reforming
channels 16. The corresponding inserts 22 would therefore have also
to be of less height.
[0042] Since within each inner reactor block 10b the outermost flow
channels are reforming channels, the reactor design described above
ensures that combustion channels are not adjacent to combustion
channels, which is advantageous for reducing thermal gradients. The
air gap between successive blocks 10a, 10b may be open at the sides
to allow air circulation, as indicated above, or alternatively the
blocks may be welded together around their entire periphery so that
the air is enclosed. Such an air gap inhibits heat transfer.
[0043] It will be appreciated that the reactor block 10 and the
reactor 40 may be modified in various ways while remaining within
the scope of the present invention. As indicated above the channel
arrangements within the reactor block 10 is NNSCSCSCSCSNN (i.e.
thirteen layers of channels alternating between steam reforming
(S), and combustion (C), the outermost being steam reforming, but
with two non-flow layers (N) at the ends). In a less preferred
alternative the outermost layers are combustion, so that the layers
would be NNCSCSCSCSCNN. Similarly within each inner reactor block
10b the channel arrangements is SCSCSCSCSCSCS.
[0044] In an alternative and less preferred arrangement the
outermost layers are combustion: CSCSCSCSCSCSC; in this situation
the outermost channels are of smaller height than the other
combustion channels 17 in the block 10; they may for example be
between 40% and 70% of the cross-sectional area of the other
combustion channels, for example 50%. It will be appreciated that
the number of layers within a reactor block may differ from that
described. For example each inner reactor block might have only
three layers, and these might be arranged either SCS or CSC.
[0045] It will also be appreciated that although the flow
directions of the first flow channels and the second flow channels
are shown as being parallel, in co-flow, in the reactor described
above, the flow directions may be parallel in counter-flow, or
alternatively the flow directions may be in transverse directions,
or may be at an oblique angle.
* * * * *