U.S. patent application number 10/197886 was filed with the patent office on 2002-12-05 for reforming apparatus.
This patent application is currently assigned to AMMONIA CASALE S.A.. Invention is credited to Filippi, Ermanno, Rizzi, Enrico.
Application Number | 20020182129 10/197886 |
Document ID | / |
Family ID | 8223390 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020182129 |
Kind Code |
A1 |
Filippi, Ermanno ; et
al. |
December 5, 2002 |
Reforming apparatus
Abstract
A reforming apparatus of the type comprising an indirect heat
exchange zone (5) for the reforming reaction of a gaseous flow
comprising methane and steam into CO, CO.sub.2, and H.sub.2, is
distinguished by the fact that it comprises advantageously a
plurality of floating-head tubes (6) containing a reforming
catalyst, a chamber (9) for collection of the reaction products
positioned downstream of the tubes (6), and a duct (15) open in
said chamber (9) for extraction of the reaction products from the
apparatus.
Inventors: |
Filippi, Ermanno;
(Viganello, CH) ; Rizzi, Enrico; (Grandate,
IT) |
Correspondence
Address: |
SUGHRUE MION, PLLC
Suite 800
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3202
US
|
Assignee: |
AMMONIA CASALE S.A.
|
Family ID: |
8223390 |
Appl. No.: |
10/197886 |
Filed: |
July 19, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10197886 |
Jul 19, 2002 |
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08961237 |
Oct 30, 1997 |
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6426054 |
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Current U.S.
Class: |
422/600 ;
422/198; 48/61; 48/76 |
Current CPC
Class: |
B01J 2208/00221
20130101; F28D 7/1669 20130101; C01C 1/0405 20130101; B01J 8/067
20130101; C07C 29/152 20130101; Y02P 20/52 20151101; C01B 3/384
20130101; C01B 2203/0844 20130101; B01J 2208/00212 20130101; C01B
2203/0833 20130101; F28F 2265/26 20130101; B01J 8/008 20130101;
C07C 29/152 20130101; C07C 31/04 20130101 |
Class at
Publication: |
422/188 ;
422/198; 422/189; 422/196; 48/61; 48/76 |
International
Class: |
B01J 010/00; B01J
008/00; B01J 008/02; B01J 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 12, 1996 |
EP |
96118105.4 |
Claims
1. Reforming apparatus for the conversion of methane and steam into
CO, CO.sub.2, and H.sub.2, of the type comprising: a substantially
cylindrical external shell (2) in which are defined an indirect
heat exchange zone (5) and a zone (4) for feeding a gaseous flow
comprising methane and steam to the indirect heat exchange zone
(5); an opening (11) formed in said shell (2) for feeding in said
indirect heat exchange zone (5) a heating gas flow as heat source
for said conversion; characterized in that it also comprises: a
plurality of floating head tubes (6) containing a reforming
catalyst, extending longitudinally in said indirect heat exchange
zone (5) and in fluid communication with said feeding zone (4); a
chamber (9) for collecting a gaseous flow comprising CO, CO.sub.2,
and H.sub.2 obtained from said conversion and positioned downstream
of said tubes (6); a duct (15) open in said collection chamber (9)
for extracting from the shell (2) said gaseous flow comprising CO,
CO.sub.2, and H.sub.2.
2. Apparatus according to claim 1, characterized in that said
extraction duct (15) is arranged coaxially with said shell (2) and
extends parallel to said tubes (6) through said indirect heat
exchange zone (5) and said feeding zone (4), from said collection
chamber (9) to a gas outlet opening (14) from said shell (2).
3. Apparatus according to claim 2, characterized in that there are
provided suitable gas sealing means (16) between said duct (15) and
a tube plate (3) positioned between said feeding zone (4) and said
indirect heat exchange zone (5).
4. Apparatus according to claim 3, characterized in that there are
provided suitable gas sealing means (16) between said duct (15) and
said shell (2).
5. Apparatus according to claim 3, characterized in that there are
provided suitable gas sealing means (16) between said tube plate
(3) and said shell (2).
6. Apparatus according to claims 3 to 5, characterized in that said
gas sealing means (16) are arranged near said outlet opening
(14).
7. Apparatus according to claims 3 to 5, characterized in that said
gas sealing means (16) are of the compression ring type.
8. Use of a seal of the compression ring type in an apparatus for
carrying out endothermic or exothermic chemical reactions, in
particular reforming reactions, to ensure gas seal between
structurally distinct parts having different thermal expansion
rates.
Description
FIELD OF APPLICATION
[0001] The present invention relates to a reforming apparatus of
the type comprising an indirect heat exchange zone for the
reforming reaction of a gaseous flow comprising methane and steam
into CO, CO.sub.2 and H.sub.2.
[0002] In the description given below and in the following claims,
the term: "methane" is generally understood to mean a raw material
which is a source of hydrogen and carbon such as e.g. methane
itself or a mixture of liquid and/or gaseous hydrocarbons such as
natural gas and naphtha.
[0003] As known, in the field of methane reforming to obtain
hydrogen and carbon which are indispensable for the synthesis of
products such as ammonia and/or methanol, the requirement to make
available an apparatus which on the one hand allows obtaining a
reforming reaction of the methane as complete as possible and on
the other hand requires low energy consumption and investment and
maintenance costs and is easy to implement is ever more
pressing.
PRIOR ART
[0004] To satisfy the above mentioned requirement, an
exchanger-type reforming apparatus, i.e. having a heat exchange
zone for the methane reforming reaction, has been proposed in the
industry.
[0005] In this apparatus, the high quantity of heat necessary for
the endothermic reforming reaction is supplied by indirect heat
exchange with a flow of heating gas fed to such apparatus.
[0006] In particular, in ammonia plants where the methane reforming
reaction is performed in two distinct sections called primary and
secondary reforming with the latter operating at a higher
temperature than the former, it is possible to utilize the hot
reacted gas coming from the secondary reforming section as a heat
source for the primary reforming section.
[0007] The exchanger type reforming apparatus is generally used in
the state of the art in ammonia, methane or hydrogen synthesis
processes to replace the conventional primary reformer, as
described for example in EP-A-0 298 525.
[0008] Although advantageous in many ways the above described
apparatus displays a series of drawbacks the first of which is
being of very complex construction requiring high investment
costs.
[0009] Indeed, this apparatus comprises in it a plurality of
bayonet-type tubes, i.e. consisting of an external tubular element
with blind end for indirect heat exchange between the heating gas
flow and the gaseous reagents (methane and steam), and an internal
tube for extraction of the reaction products.
[0010] As may be readily imagined, a structure of this type is
complex and costly to construct, difficult to access for
maintenance operations, and involves large-diameter reforming
apparatus.
[0011] In addition, since the reforming reaction is of the
catalytic type, it is necessary that the annular space defined
between the external tubular element and the internal tube is
filled uniformly with catalyst and that the catalyst is replaced
periodically. These operations are clearly hindered or at least
made difficult by the presence of the internal tube.
[0012] Lastly, the use of bayonet-type tubes displays disadvantages
even from the energy viewpoint, because there is significant
undesired heat exchange between the reacted gas flow and the
reacting gas flow, with the added risk of occurrence of metal
dusting corrosion of the internal tube due to the reacted gas if
the latter is cooled excessively.
[0013] JP-A-4154601 describes a reforming apparatus of the
exchanger type comprising a plurality of individual tubes filled
with catalyst and outside which flows the heating gas.
[0014] The tubes are affixed at their ends to respective tube
plates which are also appropriately affixed to the reforming
apparatus.
[0015] Although simpler to construct and operate than the bayonet
tubes the heat exchange tubes described in JP-A-4154601 display the
serious disadvantage that they are not free to expand if subjected
to high temperatures--as in the case of the reforming
reaction--with the risk of cracking or even breakage thereof and
thus mixing of the reacting gas with the heating gas and damage to
the apparatus.
[0016] It follows that this type of apparatus not only entails high
maintenance costs for replacement of defective tubes, but is not
able to ensure optimal and reliable long term operation.
[0017] Because of these disadvantages, the exchange--type reforming
apparatus according to the prior art has heretofore found little
application despite the ever more urgently felt requirement in the
industry.
SUMMARY OF THE INVENTION
[0018] The problem underlying the present invention is to make
available a reforming apparatus which would be simple to implement,
reliable, and would provide a methane reforming reaction as
complete as possible with low investment, operating and maintenance
costs as well as low energy consumption.
[0019] The above mentioned problem is solved according to the
present invention by a reforming apparatus for the conversion of
methane and steam into CO, CO.sub.2 and H.sub.2 of the type
comprising:
[0020] a substantially cylindrical external shell in which are
defined an indirect heat exchange zone and a zone for feeding a
gaseous flow comprising methane and steam to the indirect heat
exchange zone;
[0021] an opening formed in said shell for feeding in said indirect
heat exchange zone a heating gas flow as heat source for said
conversion;
[0022] and which is characterized in that it also comprises:
[0023] a plurality of floating-head tubes containing a reforming
catalyst, extending longitudinally in said indirect heat exchange
zone and in fluid communication with said feeding zone;
[0024] a chamber for collecting a gaseous flow comprising CO,
CO.sub.2, and H.sub.2 obtained from said conversion and positioned
downstream of said tubes;
[0025] a duct open in said collection chamber for extracting from
the shell said gaseous flow comprising CO, CO.sub.2, and
H.sub.2.
[0026] In the description given below and in the following claims,
the term: "floating-head tubes" is understood to mean tubes having
at least one end (head) structurally free to move (floating) to
allow heat expansion of the tubes.
[0027] Advantageously, the reforming apparatus according to the
present invention calls for a collection chamber for the reacted
gas in fluid communication with a plurality of tubes containing
catalyst for indirect heat exchange, and a duct for extraction of
this gas from the shell.
[0028] In this manner, all the gas--once the reforming reaction has
taken place--is collected in the same chamber and extracted by
means of a single duct.
[0029] Thanks to this particular structure, it is possible to
obtain exchange-type reforming apparatus which is reliable,
extremely simple to construct and has low implementation costs and
which is at the same time effective as regards methane reforming
reaction, without the drawbacks typical of the prior art
apparatus.
[0030] In particular, maintenance operations and loading or
replacing the catalyst in the tubes are facilitated by the presence
of a plurality of individual floating-head tubes independent of one
another.
[0031] In addition, since the reacted gas is all collected in a
single chamber and extracted from the shell by means of a duct
which is thermally independent of the heat exchange tubes, the
undesired heat exchange between the reacted gas and the reacting
gas is advantageously eliminated to avoid the danger of metal
dusting corrosion of the extraction duct and to reduce operating
costs as compared with the prior art apparatus.
[0032] According to a preferred embodiment of the apparatus in
accordance with the present invention, the extraction duct is
advantageously arranged coaxially with said shell and extending
parallel to said tubes through the indirect heat exchange zone and
the feeding zone, from the collection chamber to a gas outlet
opening from the shell.
[0033] In this manner, there is obtained a very simple and compact
structure, permitting at the same time effective compensation for
the expansion of the different parts of the apparatus caused by the
different thermal stress to which these parts are subject and by
the use of different materials.
[0034] In particular, it is possible to appropriately and reliably
compensate the different expansion rates to which the heat exchange
tubes and the reacted gas extraction duct are subjected, without
thereby having to give up extremely simple apparatus from the
structural point of view.
[0035] Indeed, thanks to the special arrangement of the extraction
duct there is advantageously obtained a collection chamber which is
also of the floating type, with the heat exchange tubes and the
extraction duct free to expand in mutually opposite directions with
respect to the feeding zone.
[0036] In this manner, the different expansion rates of the
materials not only do not create mechanical problems for the
apparatus but can be mutually compensated in a certain manner.
[0037] Advantageously, according to this embodiment, between said
duct and a tube plate positioned between said feeding zone and said
heat exchange zone as between said duct and said shell, there are
provided suitable gas sealing means so as to avoid undesired
by-pass of the reaction gas or reacted gas and at the same time to
permit the different heat expansion rates of the apparatus.
[0038] Thanks to the present invention, the gas sealing means which
ensure correct operation of the apparatus are reduced to the
minimum and concentrated between the extraction duct, the tube
plate and the external shell only.
[0039] Preferably, the gas sealing means are arranged near said
outlet opening so as to facilitate access to the gas sealing means
and thus simplify and aid maintenance thereof.
[0040] The characteristics and advantages of the present invention
are set forth in the description of an embodiment thereof given
below by way of non-limiting example with reference to the annexed
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] In the drawings:
[0042] FIG. 1 shows a longitudinal cross section view of a
reforming apparatus according to the present invention;
[0043] FIG. 2 shows a longitudinal cross section view of a part of
the apparatus of FIG. 1, modified in accordance with a preferred
embodiment of the present invention;
[0044] FIG. 3 shows a longitudinal cross section view in enlarged
scale of a detail of the apparatus of FIG. 2.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0045] With reference to FIGS. 1-3, reference number 1 indicates as
a whole a reforming apparatus according to the present invention
for the reforming reaction of a gaseous flow comprising methane and
steam.
[0046] The apparatus 1 comprises a substantially cylindrical
external shell 2 in which extends over the entire cross section
thereof a tube plate 3 dividing the shell 2 in an indirect heat
exchange zone 5 and a zone 4 for feeding a gaseous flow comprising
methane and steam to the zone 5.
[0047] A plurality of floating heat tubes, all indicated by
reference number 6, extend longitudinally in the indirect heat
exchange zone 5 from the tube plate 3.
[0048] The tubes 6 define within them a zone (not shown) for
housing a reforming catalyst of known type. In addition, the tubes
6 have a first end 7 in fluid communication with the zone 4 and a
second end 8 in fluid communication with a chamber 9 for collecting
a gaseous flow comprising CO, CO.sub.2, and H.sub.2 obtained from
the reforming reaction.
[0049] Reference number 10 indicates a tube plate arranged between
the tubes 6 and the chamber 9, in the second end 8.
[0050] The shell 2 is also equipped--in the indirect heat exchange
zone 5--with openings 11 and 12 which are respectively for inlet
and outlet of a heating gas as heat source for the reforming
reaction.
[0051] Openings 13 and 14 are also defined in the shell 2 at zone
4, respectively for inlet of the reaction gas comprising methane
and steam and outlet of the reacted gas comprising CO, CO.sub.2,
and H.sub.2.
[0052] Advantageously, a duct 15 is provided in the shell 2 for
extracting from the apparatus 1 the reacted gas. The duct 15 is in
fluid communication with the chamber 9 and the gas outlet opening
14.
[0053] Thanks to the particular structure resulting from the
presence of a plurality of individual tubes 6 in combination with
the chamber 9 and the reacted gas extraction duct 15, it is
possible to secure an apparatus which is mechanically very simple
and easy to implement as regards construction and which is at the
same time extremely reliable and effective from the energy and
reforming reaction conversion yield viewpoint.
[0054] In the example of FIG. 1, the extraction duct 15 is arranged
coaxially with the shell 2 and extends parallel to the tubes 6
through the indirect heat exchange zone 5 and the feeding zone
4.
[0055] According to an alternative embodiment of the present
invention (not shown), the duct 15 extends from the chamber 9 to
the lower end of the apparatus 1, and the outlet 14 is defined
coaxially with and at the lower end of the shell 2.
[0056] With respect to the example of FIG. 1, it is possible in
this manner to increase in the zone 5 the useful space for
arrangement of the tubes 6 with resulting increase of the heat
exchange surface.
[0057] Reference number 16 indicates generally gas sealing means
for avoiding undesired by-pass of the reaction gas or reacted gas.
These means 16 also permit the different thermal expansions, in
particular of the tubes 6 and the duct 15, so as to ensure optimal
and reliable operation of the apparatus 1.
[0058] The gas sealing means 16 are arranged, with reference to
FIG. 1, between the duct 15 and the tube plate 3 and between the
duct 15 and the shell 2, while in the example of FIG. 2 they are
arranged between the duct 15 and the tube plate 3 and between the
tube plate 3 and the shell 2.
[0059] According to the embodiment of FIG. 1, the gas sealing means
16 are advantageously all arranged in relation to a single part of
the apparatus 1, i.e. the extraction duct 15, to simplify the
arrangement of these means inside the apparatus as much as
possible.
[0060] To facilitate maintenance operations of the gas sealing
means 16, the latter can be arranged near the reacted gas outlet
opening 14 as shown in FIG. 2.
[0061] According to this preferred embodiment of the present
invention, the gas sealing means 16 are arranged in relation to a
tubular appendage 17 of the tube plate 3 extending from the latter
towards the opening 14.
[0062] Advantageously, the gas sealing means 16 are of the
labyrinth type or of the compression ring type and preferably of
the compression ring type.
[0063] In the description given below, the term: "labyrinth sealing
means" is understood to mean a seal created by the coupling of two
parts of generally tubular shape, a male part and female part, with
the first having its external surface indented so that, once
coupled, there are created solid ridges and empty spaces
(labyrinth) between the coupled parts which prevent gas
passage.
[0064] In the description given below, the term: "compression ring
sealing means" is understood to mean a seal created by a
compression ring arranged between a coupled male part and female
part to prevent gas passage.
[0065] Thanks to this type of sealing means 16, it is possible to
ensure gas seal and permit reliable and lasting expansion
compensation even for continuous, large expansion rates as in the
case of reforming apparatus.
[0066] FIG. 3 shows in enlarged scale a detail of the reforming
apparatus 1 of FIG. 2 making clear the gas sealing means 16 of the
compression ring type between the extraction duct 15 and the
tubular appendage 17 of the tube plate 3.
[0067] The sealing means 16 comprise a plurality of compression
rings 18 (preferably at least two), housed in respective cavities
19 of a cylindrical element 20 affixed to the end 21 of the
extraction duct 15 preferably in a removable manner, e.g. by means
of bolts (not shown).
[0068] The presence of the compression rings 18 between the duct 15
(male) and the appendage 17 (female) prevents passage of reacted
gas into the heat exchange zone 5 and at the same time permits the
duct 15 to run along the appendage 17 to compensate expansion
thereof.
[0069] The gas sealing means 16 of the reforming apparatus 1 in the
examples of FIGS. 1 and 2 are preferably of the type shown in FIG.
3.
[0070] With respect to the labyrinth seal, use of compression rings
permits a series of advantages among which it is worthwhile
mentioning: a more effective gas seal (less gas by-pass through the
seal), greater structural flexibility (the gap between male and
female can be up to 10 times greater than with labyrinth seals),
and greater compactness of the sealing means (shorter for equal
seal).
[0071] This means that the piston-ring sealing means can ensure
good gas seal even in case of impairment and/or misalignment of the
male and female parts, as well as greater flexibility during
assembly and adjustment operations on the reforming apparatus 1,
less sensitivity to the entry of foreign bodies and less seizure
risk.
[0072] The use of piston-ring sealing means extends advantageously
to an apparatus for carrying out endothermic or exothermic chemical
reactions in general, e.g. even to ammonia or methanol synthesis
reactors, to ensure gas seal between structurally distinct parts
having different thermal expansion rates.
[0073] In FIGS. 1 and 2, the arrows F1 and F2 indicate the various
paths taken in the reforming apparatus 1 by the gaseous flow
comprising methane and steam (reaction gas) and by the hot gas flow
for indirect heat exchange respectively.
[0074] Operation of the reforming apparatus according to the
present invention is described herebelow.
[0075] The operating conditions of temperature indicated in the
present description are for a primary reforming apparatus.
[0076] With reference to FIG. 1, a gaseous flow F1 comprising
methane and steam (reaction gas), preheated to a temperature
between 300.degree. C. and 500.degree. C. is fed to the feeding
zone 4 of the apparatus 1 through the gas inlet opening 13 and made
to pass into the tubes 6 (tube side) for the reforming reaction at
a temperature between 500.degree. C. and 1000.degree. C. For this
purpose, the tubes 6 are appropriately filled with catalyst.
[0077] The reforming reaction is made possible thanks to the heat
transmitted by a hot gas flow F2 having a temperature between
900.degree. C. and 1100.degree. C. fed to the heat exchange zone 5
through the gas inlet opening 11. The hot gas flow F2 flows outside
the tubes 6 (shell side) and is discharged from the shell 2 through
the gas outlet opening 12 at a temperature between 300.degree. C.
and 600.degree. C.
[0078] In particular, the hot gas flow F2 transmits the reaction
heat by indirect heat exchange to the colder reaction gas flow
F1.
[0079] The gaseous flow F1 comprising CO, CO.sub.2, and H.sub.2
obtained from the reforming reaction is discharged from the tubes 6
through the end 8, is collected in the chamber 9 and extracted from
the apparatus 1 through the duct 15 and the gas outlet opening 14
at a temperature between 500.degree. C. and 1000.degree. C.
[0080] As set forth above, the gaseous flow F1, once collected and
fed into the duct 15, is no longer in thermal connection with the
reaction gas passing through the tubes 6 and thus there is
advantageously avoided undesired heat exchange between the reacted
gas and the reaction gas.
[0081] In addition, the expansion rates of the various parts of the
apparatus 1--especially of the tubes 6 and the duct 15
[0082] due to the different materials and thermal stress to which
they are subjected, are effectively compensated by the particular
structure of the chamber 9 and the duct 15 and by the arrangement
of the sealing means 16, which permit movement of the various parts
and at the same time prevent undesired gas leakage.
[0083] It is important to note that the use of these sealing means
does not negatively influence the construction simplicity of the
apparatus according to the present invention.
[0084] In the examples of FIGS. 1 and 2, the tubes 6 are
advantageously arranged in a tube bundle so as to optimize the
occupation rate of the heat exchange zone 5.
[0085] In addition, to increase the surface area available and thus
improve heat exchange, the tube bundle is preferably equipped with
appropriate diaphragms 22 and the tubes 6 have fins (not
shown).
[0086] For an ammonia synthesis process, the hot gas flow F2
comprises preferably the gaseous flow coming from the secondary
reforming section.
[0087] From the foregoing, the numerous advantages achieved by the
present invention are clear, in particular that of obtaining a
reliable reforming apparatus which is structurally simple and easy
to construct and which allows methane reforming with low energy
consumption and operating and maintenance costs.
* * * * *