U.S. patent application number 10/425168 was filed with the patent office on 2003-11-13 for method for preventing flashback in a mixture flowing into a reaction chamber.
This patent application is currently assigned to DaimlerChrysler AG. Invention is credited to Docter, Andreas, Gildein, Helmut, Kaupert, Andreas, Schoeffel, Stefan, Weger, Wolfgang, Wiesheu, Norbert.
Application Number | 20030211433 10/425168 |
Document ID | / |
Family ID | 7714479 |
Filed Date | 2003-11-13 |
United States Patent
Application |
20030211433 |
Kind Code |
A1 |
Docter, Andreas ; et
al. |
November 13, 2003 |
Method for preventing flashback in a mixture flowing into a
reaction chamber
Abstract
A method for preventing flashback in a reaction chamber that
includes providing a mixture of educts flowing through a mixture
distribution zone and into the reaction chamber. The mixture
distribution zone has an inlet opening and a variable flow
cross-section between the inlet opening and the reaction chamber.
The method also includes combusting the mixture in the reaction
chamber at a combustion rate, and varying the flow cross-section as
a function of a volume of the mixture so as to affect a flow rate
of the mixture into the reaction chamber such that the flow rate is
greater than the combustion rate. In addition, a reactor that
includes, an inlet opening for receiving a mixture of educts, a
mixture distribution zone disposed downstream of the inlet opening
and having a variable flow cross-section, a reaction chamber
disposed downstream of the mixture distribution zone, and a
regulation device disposed in the mixture distribution zone for
varying the flow cross section.
Inventors: |
Docter, Andreas; (Esslingen,
DE) ; Gildein, Helmut; (Winterbach, DE) ;
Kaupert, Andreas; (Ulm, DE) ; Schoeffel, Stefan;
(Korb, DE) ; Weger, Wolfgang; (Hochdorf, DE)
; Wiesheu, Norbert; (Guenzburg, DE) |
Correspondence
Address: |
DAVIDSON, DAVIDSON & KAPPEL, LLC
485 SEVENTH AVENUE, 14TH FLOOR
NEW YORK
NY
10018
US
|
Assignee: |
DaimlerChrysler AG
Stuttgart
DE
70567
|
Family ID: |
7714479 |
Appl. No.: |
10/425168 |
Filed: |
April 29, 2003 |
Current U.S.
Class: |
431/1 |
Current CPC
Class: |
C01B 2203/0244 20130101;
Y02E 60/50 20130101; F23D 14/82 20130101; B01J 19/002 20130101;
C01B 2203/12 20130101; B01J 2208/00309 20130101; C01B 2203/142
20130101; B01J 2219/00263 20130101; H01M 8/0618 20130101; B01J
8/0278 20130101; C01B 2203/82 20130101; C01B 2203/0844 20130101;
B01J 2208/00017 20130101; C01B 3/382 20130101; B01J 2208/0053
20130101 |
Class at
Publication: |
431/1 |
International
Class: |
F23C 011/04 |
Foreign Application Data
Date |
Code |
Application Number |
May 2, 2002 |
DE |
102 19 747.4 |
Claims
What is claimed is:
1. A method for preventing flashback in a reaction chamber, the
method comprising: providing a mixture of educts flowing through a
mixture distribution zone and into the reaction chamber, the
mixture distribution zone having an inlet opening and a variable
flow cross-section between the inlet opening and the reaction
chamber; combusting the mixture in the reaction chamber at a
combustion rate; and varying the flow cross-section as a function
of a volume of the mixture so as to affect a flow rate of the
mixture into the reaction chamber such that the flow rate is
greater than the combustion rate.
2. The method as recited in claim 1, wherein the mixture
distribution zone includes a plurality of flow segments and the
varying of the flow cross-section includes opening or closing at
least one of the plurality of flow segments.
3. The method as recited in claim 2, wherein the varying of the
flow cross-section includes increasing the flow cross-section by
opening at least one adjacent flow segment.
4. The method as recited in claim 2 wherein the varying of the flow
cross-section includes decreasing the flow cross-section by closing
at least one adjacent flow segment.
5. The method as recited in claim 1, wherein the mixture includes a
plurality of components and the varying of the flow cross section
is further performed as a function of a predefined value for
metering at least one component of the mixture.
6. The method as recited in claim 1, wherein the varying of the
flow cross-section includes increasing the flow cross-section from
a center region of the flow as the volume increases.
7. The method as recited in claim 2, wherein the varying includes
opening or closing each of the plurality of flow segments for a
predetermined time period such that each of the plurality of flow
segments is in contact with the mixture for approximately a same
length of time.
8. A reactor comprising: an inlet opening for receiving a mixture
of educts; a mixture distribution zone disposed downstream of the
inlet opening and having a variable flow cross-section; a reaction
chamber disposed downstream of the mixture distribution zone; and a
regulation device disposed in the mixture distribution zone for
varying the flow cross section.
9. The reactor as recited in claim 8, wherein the regulation device
includes dividers for dividing the mixture distribution zone into a
plurality of segments each having inflow openings, and wherein at
least one of the inflow openings is capable of being at least
partially closed.
10. The reactor as recited in claim 9, wherein the each of the
plurality of segments includes an annular duct.
11. The reactor as recited in claim 10, further comprising a first
annular covering element corresponding to a respective one of the
plurality of annular ducts.
12. The reactor as recited in claim 11, wherein the first annular
covering element is moveable to a closed position in a direction of
flow through the mixture distribution zone.
13. The reactor as recited in claim 11, further comprising a second
annular covering element fixedly connected to the first annular
covering element and moveable to a closed position together with
the first annular covering element.
14. The reactor as recited in claim 9, further comprising at least
one sheath for at least partially closing the at least one
segment.
15. The reactor as recited in claim 10, further comprising a needle
and a circular center duct disposed radially inward of the annular
ducts, the circular center duct being at least partially closeable
by the needle.
16. The reactor as recited in claim 9, further comprising a
plurality of needles, each of the plurality of needles moveable to
close one of the plurality of inflow openings.
17. The reactor as recited in claim 9, wherein at least one of the
plurality of segments includes a widening flow path along a length
of the segment in a direction of flow.
18. The reactor as recited in claim 9, wherein each of the segments
further includes an outlet and wherein a ratio of each inflow
cross-section to a sum of the plurality of inflow cross-sections
corresponds to a ratio of a respective outlet cross section to a
sum of the plurality of outlet cross sections.
19. The reactor as recited in claim 8, wherein the reaction chamber
includes a catalytically active material disposed on a carrier
structure.
20. The reactor as recited in claim 8, wherein the educts include
at least oxygen, water, and a hydrocarbon-containing compound for
generating a hydrogen containing gas.
21. The reactor as recited in claim 20, wherein the water is in the
form of steam.
22. The reactor as recited in claim 20, wherein the
hydrocarbon-containing compound includes at least one of diesel or
gasoline.
23. The reactor as recited in claim 20, further comprising a fuel
cell operated using the hydrogen containing gas
24. The reactor as recited in claim 23, wherein the fuel cell
includes a fuel cell of an auxiliary power unit.
Description
[0001] Priority is claimed to German Patent Application No. DE 102
19 747.4 filed on May 2, 2002, which is incorporated by reference
herein.
BACKGROUND
[0002] The present invention relates to a method for preventing
flashback in a mixture flowing into a reaction chamber, the flow
cross section being varied in a region between an inlet opening and
the reaction chamber. Furthermore, the present invention relates to
a reactor for carrying out the method specified above, and to the
use of the method together with the reactor.
[0003] From the general prior art, reactors are known which are
provided with a mixture of educts which are to be converted in a
reaction chamber of the reactors. In particular in the case of what
are referred to as autothermal reactors which generally have a
catalyst in the reaction chamber, the conversion of the educts then
takes place in such a way that exothermal and endothermal reactions
occur in the reaction chamber. After the start has taken place
and/or when the educts are appropriately conditioned there is thus
no need for a further supply of thermal energy. The autothermal
reformation of a mixture of educts composed of air, steam and a
hydrocarbon-containing compound, for example petrol, is an example
of such a reaction.
[0004] The educts which flow into the reactor through an inlet
opening typically first pass through a zone in which the educts are
thoroughly mixed with one another and, if appropriate, individual
educts are simultaneously vaporized before they penetrate the
actual reaction chamber and are correspondingly converted there. In
such reactors, a combustible mixture is then already present in
this mixture distribution zone. If there is a flashback from the
reaction chamber into the region of the mixture distribution zone
or if auto-ignition occurs in this region, the mixture located
there is at least partially converted. As a result, thermal energy
is released in a region at which it is not required and under
certain circumstances has disadvantageous effects, in the form of
thermal overloading, on the mixture distribution zone itself and on
its immediate surroundings. However, a generally more decisive
disadvantage is that the thermal energy released in the mixture
distribution zone is lost in the region of the reaction chamber.
The conversion of the mixture in the reaction chamber and/or the
composition and temperature of the mixture flowing out of the
reaction chamber are thus degraded or in the worst case do not
occur at all.
[0005] With the stipulation that a hydrogen-containing formate with
minimum carbon monoxide content is to be obtained in as far as
possible all operating states and load states which occur in the
reformation of methanol, German Patent Document DE 195 26 886 C1
proposes a method and a device which is suitable for carrying it
out, with which the entire length and/or the effective inlet cross
section of an input-end reaction chamber section which is
temperature-controlled to a high methanol conversion rate can be
set as a function of the throughput rate of mixture to be formed,
in such a way that an essentially constant resident time occurs of
the gas mixture to be reformed in the reaction chamber section
which is temperature-controlled to a high methanol conversion rate.
As a result, the methanol reformation can also be carried out with
significantly fluctuating throughput rates of gas mixture to be
reformed with a constantly high methanol conversion rate and a
constantly low formation of undesired carbon monoxide.
[0006] In view of an object of improving the dynamic response
behaviour of a reaction of a medium in a reaction chamber which has
a catalyst, German Patent Document DE 100 02 025 A1 also discloses
a method in which an effective cross section which is accessible to
the medium and has the required catalyst is influenced by the
pressure of the medium itself. A piston which is arranged in the
reactor or in the ducts to the reactor is pressed here against a
spring by the medium and, depending on the pressure in the medium
opens more or less of the effective cross section.
[0007] By means of the two methods described above or the
corresponding devices, the conversion of the methanol or the
medium, which according to the statements in the abovementioned
German Patent Document DE 100 02 025 A1 will generally be a
reformate, can be influenced with a greater or lesser degree of
outlay on control, regulation and actuator systems.
[0008] The problems described above relating to flashback, which
plays a role especially in autothermal processes, are not
recognized in the two abovementioned German patent documents.
SUMMARY OF THE INVENTION
[0009] An object of the present invention is to provide a method
for avoiding flashback in a mixture flowing into a reaction
chamber, and to specify a reactor which can be used to carry out
the method.
[0010] The present invention provides a method for preventing
flashback in a mixture flowing into a reaction chamber. The flow
cross section is varied in a region between an inlet opening and
the reaction chamber. The flow cross section is varied as a
function of the volume of the inflowing mixture (educts A), in such
a way that the flow rate (v) of the mixture (A) is greater for the
at least approximately greatest part of the occurring volumes of
the inflowing mixture (educts A) is higher than the combustion rate
(v.sub.br) of the mixture (educts A).
[0011] As a flashback can occur only if the combustion rate
v.sub.br of the mixture is greater than the flow rate v with which
the mixture flows onto the already reacting or burning component
which has previously flowed in, a flashback can be avoided by means
of a sufficiently high flow rate in the mixture distribution
zone.
[0012] The adaptation to a required load state is usually carried
out in such reactors by varying the volume flow of the fed-in
mixture. If the flow cross sections are configured in such a way
that a maximum flow rate v.sub.max occurs on the full load, the
combustion rate v.sub.br can usually be found to be of an order of
magnitude of 30 to 50% of the maximum rate as otherwise
unnecessarily high pressure losses would be generated in the higher
load range, which is important for the operation, as a result of
"excessively" small cross sections. However, this then also means
that only 50% to 70% of the possible load spread can be used for
the reactor as there would be the risk of a flashback with the
disadvantages described at the beginning in the remaining 30% to
50%.
[0013] With the method according to the present invention it is
then particularly advantageously possible, by varying the flow
cross section in the region upstream of the reaction chamber with a
predefined volume of flow in accordance with continuity law, to set
in each case a flow rate v, which is higher than the combustion
rate v.sub.br. In this way, it is possible to use a much larger
part of the load spread than before. By means of the entire range
of the load spread of the reactor which can thus be used it is also
possible to ensure that no flashback occurs. The release of the
thermal energy can thus take place precisely where it is desired,
specifically in the reaction chamber itself. The reaction chamber
can therefore be used under ideal operating conditions, enabling
the desired composition and the desired temperature level to be
achieved at the output of the reaction chamber in a reproducible
fashion.
[0014] In addition to the problems, already mentioned at the
beginning, of the release of thermal energy in an undesired region
as a result of the flashback, a disadvantageous formation of
byproduct may also occur during the conversion of the educts due to
the flashback. These byproducts, namely soot in the case of educts
containing carbon, may become deposited and adversely affect the
method of operation of the reactor. They accumulate, for example on
catalysts, sensors, parts which are to be moved mechanically or the
like and impair their functioning. However, preventing the
flashback can also avoid this formation of byproducts and the
associated disadvantageous consequences.
[0015] According to one very advantageous development of the method
according to the present invention, at least in the case of a cold
start of a reactor which has the reaction chamber, the flow cross
section is increased from the centre of the flow as the volume of
the inflowing mixture increases.
[0016] As a result of the fact that the cross section opened from
the centre of flow, a central flow into the reaction chamber can be
achieved even with a small volume flow. The heat, which is
generated centrally in the reaction chamber can be distributed over
the surrounding areas of the reaction chamber, in particular if the
reaction chamber is constructed, for example, with a catalyst which
is located on a carrier material and the heat in the carrier
material is conveyed away through thermal conduction. This
refinement in the present invention thus makes it possible, on the
one hand, to operate continuously in the case of load jumps and, on
the other hand, to improve the cold starting behaviour, in
particular the more rapid entry into the "normal" operating phase.
The reduction in the time necessary for cold starting can be
achieved by virtue of the fact that the heat which is conveyed away
to the outside by thermal conduction heats up the surrounding areas
of the reaction chamber and as a result no, or at least very
little, heat is lost, at least in all the load ranges below full
load.
[0017] If the reactor is instead in steady-state operating phase
without high dynamic requirements and/or in an operating phase in
which thermal losses can be accepted without large adverse effects
on the quality of generated products, it is possible, according to
one very favourable refinement of the present invention, also to
vary the flow cross section in such a way that, viewed over a
relatively long period of time, all the areas of the reactor are in
contact with the inflowing mixture at least for an approximately
equal length of time.
[0018] The loading of the reactor, in particular if it has, for
example, a catalyst, can thus be compensated over the long-term
average so that ageing processes are distributed uniformly over the
reactor. The service life of the reactor can thus be increased.
[0019] A reactor for carrying out the method according to the
present invention has, one following the other in the direction of
flow, an inlet opening for the educts, a mixture distribution zone
and a reaction zone, regulation devices for changing the flow cross
section being arranged in the mixture distribution zone.
[0020] The method according to the present invention can be
implemented in an ideal way with such an embodiment of the reactor.
Here, it is virtually insignificant how the regulation devices for
changing the cross section are embodied as long as they reliably
fulfil the required function under the conditions prevailing in the
mixture distribution zone, for example high temperature, aggressive
educts etc. The regulation devices could be embodied as
continuously acting regulation devices, for example, in the manner
of iris diaphragms such as are known, for example, from optics.
[0021] As an alternative to this, the regulation devices for
changing the cross section in the mixture distribution zone are
embodied, according to one very favourable element of the reactor,
in such a way that the mixture distribution zone is divided into a
plurality of segments, it being possible to at least partially
close off inflow openings in at least some of the segments.
[0022] This design which can be implemented in a very robust way
permits a good method of operation of the regulation device which
has a high degree of immunity to faults, even under unfavourable
conditions, for example in terms of the temperature and the
aggressiveness of the media. Furthermore, selective influencing of
the flow which is achieved in the mixture distribution zone by
means of corresponding built-in elements, diffusers or the like,
can be maintained, or achieved at all in the first place, even with
relatively low volume flows by means of the segmentation. If
desired, the effects mentioned above can also be adapted to the
respectively predefined volume flows by means of the refinement of
the geometry of the segments for said volume flows. The inflow can
thus be appropriately optimized not only in terms of the flow rate
but also in terms of the formation of the flow. In particular, it
is possible here to avoid dead zones in the flow in which there is
not a sufficiently high flow rate of the flow. As a result, on the
one hand, the undesired conversion of the educts and, on the other
hand, deposition of byproducts which are formed can be avoided in
these dead zones in a particularly advantageous way.
[0023] One particularly advantageous use of the method according to
the present invention and of the abovementioned reactor is the
autothermal reformation of an educt mixture, containing at least
oxygen, water, in particular steam, and a hydrocarbon-containing
compound, preferably petrol or diesel, in order to generate a
hydrogen-containing gas for operating a fuel cell, in particular
the fuel cell of an auxiliary power unit.
[0024] In particular for such a use in a gas generating system for
a fuel cell, the abovementioned advantages can be of particular
advantage in terms of achieving the largest possible load spread
and a robust and reliably operating design. If the fuel cell is
used in a mobile system, for example a vehicle or the like, the
advantages already mentioned are particularly advantageous with
respect to the basic requirements made of the vehicle components in
terms of robustness, complexity, weight and dynamic method of
operation.
[0025] The refinement of the method according to the present
invention in which, at least in the case of a cold start of a
reactor which has the reaction chamber, the flow cross section is
increased from the centre of the flow as the volume of the
inflowing mixture increases can also be used very favourably in
this specific case of application in mobile systems as, in such
systems, cold starts occur very frequently and accordingly an
improvement in the cold start behaviour constitutes a decisive
improvement in the entire system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Further advantageous refinements of the present invention
emerge from the claims and from the exemplary embodiment which is
illustrated below with reference to the drawing, in which:
[0027] FIG. 1 shows a reactor which is operated as an autothermal
reformer as well as possible temperature profiles T over its
overall length x;
[0028] FIG. 2 shows a diagram of a flow rate v in the region of the
inflow into a reactor chamber as a function of a load L;
[0029] FIG. 3 shows a possible refinement of the reactor with
regulation devices for changing the flow cross section;
[0030] FIG. 4 shows an alternative refinement of the reactor with
regulation devices for changing the flow cross section;
[0031] FIG. 5 shows a sectional view along the line V-V in the
embodiment in FIG. 4;
[0032] FIG. 6 shows a further alternative refinment of the reactor
with regulation devices for changing the flow cross section;
and
[0033] FIG. 7 shows a sectional view along the line VII-VII in the
embodiment in FIG. 6.
DETAILED DESCRIPTION
[0034] FIG. 1 illustrates a reactor 1 which is intended to be
operated here as an autothermal reformer, the present invention
being merely explained by means of this example and there is no
intention to restrict it to the specific application case of the
autothermal reformer.
[0035] According to its embodiment as an autothermal reformer for
generating a hydrogen-containing gas, the reactor 1 has a reaction
chamber 2 which contains, on a carrier structure 3, a catalytically
active material--which are referred to below as a catalystic
carrier 3. Educts A, for example air, hydrogen and petrol or
diesel, flowing into the reactor 1 pass through an inlet opening 4
into a mixture distribution zone 5 in which, if necessary, they are
thoroughly mixed and components which are still possibly present in
fluid form are vaporized and, if appropriate, are superheated.
Furthermore, the educts A are distributed by the mixture
distribution zone 5, for example by means of one or more diffusers,
in such a way that they flow into the reaction chamber 2 as
uniformly and homogeneously as possible.
[0036] The reaction chamber 2 which is provided with the catalyst
carrier 3 can be divided into two different zones: one exothermal
reaction zone 6 through which educts coming from the mixture
distribution zone 5 firstly flow, and an endothermal reaction zone
7 which follows the latter in the direction of flow. Furthermore,
the mixture distribution zone 5 has regulation devices 8 which are
indicated here in principle by a dot-dashed line and about which
more details will be given later.
[0037] In the view in FIG. 1, a number of temperature profiles T
are additionally plotted against an overall length x of the reactor
1. The constant temperature profile T.sub.min indicates the
temperature which the reformate obtained from the educts A must at
least have when it exits the reactor chamber 2. This temperature
T.sub.min is determined by the following components, for example
gas purification devices, shift stages or the like. The temperature
profile T.sub.1 would be ideal for reaching this temperature
T.sub.min at the outlet of the reactor chamber 2 with the best
possible level of efficiency and thus the lowest possible inlet
temperature T.sub.1. In the case of the temperature profile T.sub.1
leaving the inlet temperature T.sub.1, the educts A release the
thermal energy Q.sub.1 contained in them during the reaction in the
exothermal reaction zone 6. The volume flow, which then cools in
the region of the endothermal reaction zone 7, then reaches, at the
output of the endothermal reactor zone 7 and thus of the reacton
chamber 2, the temperature T.sub.1a which is higher than or equal
to the temperature T.sub.min.
[0038] However, as a combustible mixture of the educts A is then
already present in the mixture distribution zone 5, it is possible,
as already explained at the beginning, for a flashback which is
initiated by the hot catalyst carrier 3 to occur from the reaction
chamber 2 into the region of the mixture distribution zone 5, which
brings about an at least partial conversion of the educts A,
combined with a release of thermal energy. The temperature profile
T.sub.2 will then typically occur.
[0039] The temperature profile T.sub.2 starts at the same inlet
temperature T.sub.1. However, a release of the thermal energy
content Q.sub.2 which is contained in the educts A, and corresponds
in its absolute value to Q.sub.1, will then already occur in the
region of the mixture distribution zone 5. However, as a result of
this premature release of the energy Q.sub.2 said energy Q.sub.2 is
absent from the region of the reaction chamber 2. The resulting
outlet temperature T.sub.2a of the volume flow out of the reaction
chamber 2 is therefore lower than the required temperature
T.sub.min. In addition to this, there is generally also worsening
of the conversion of the educts A used so that in the following
components it is necessary to make greater expenditure in order to
purify the reformate.
[0040] So that, nevertheless, a sufficiently high outlet
temperature can then still be achieved, the temperature profile
T.sub.2 can be shifted upwards, towards the higher temperatures.
However, the resulting temperature profile T.sub.3 requires a
higher inlet temperature T.sub.1, and thus reduces the efficiency
of the reactor 1.
[0041] FIG. 2 is a diagram illustrating the dependence between a
flow rate v in the region of the inflow of the reaction chamber 2
and a load L which represents the required conversion of material
taking place or the volume flow of the educts A. Both the flow rate
v and the load L are standardized to the respectively occurring
values of the maximum flow rate v.sub.max and of the full load
L.sub.max and given in percentages.
[0042] The abovementioned undesired release of energy as a result
of the flashback or, under certain circumstances, also as a result
of auto-ignition of the educts A, will, as already mentioned at the
beginning, occur only if the flow rate v of the educts A is lower
than the combustion rate v.sub.br. In the diagram in FIG. 2, the
combustion rate v.sub.br is then set at 40% of the maximum flow
rate v.sub.max. The relationship between the flow rate v and load L
is given by the dashed curve 9. From its point of intersection 10
with the constant V.sub.br it is possible to read off that an
operating mode of the reactor 1 which is optimized and reliable in
terms of efficiency is possible only with a load spread between 40%
and 100% of the full load L.sub.max.
[0043] In order to reduce the problems of flashback and to be able
to use the greater part of the load spread accompanied by optimized
efficiency, that is to say with a temperature profile which is
analogous to T.sub.1, the regulation devices 8 are provided in the
mixture distribution zone 5 of the reactor 1. These regulation
devices 8 are used to vary the flow cross section in the region of
the mixture distribution zone 5 as a function of the volume flow of
the inflowing educts A so that variable flow rates v can be set in
accordance with the continuity law. As a result, the flow rate v in
the region before inlet into the reaction chamber 2, and here in
particular in the region between the inlet opening 4 and the
reaction chamber 2, can be set, as a function of the volume flow of
the educts A, which can either be measured or originate in an ideal
fashion from the predefined values for the metering of the educts
A, in such a way that said flow rate v is greater than the
combustion rate v.sub.br over the greatest possible area of the
load spread. Here, all of the predefined values which are as
characteristic as possible of the conversion, or only some of them,
can be used for the metering, for example the metered quantity of
fuel. The adaptation of the flow rate v is very important in
precisely this region of the mixture distribution zone 5 as here
usually a widening of the flow cross section is provided in order
to distribute the educts A, at least in the case of the full load,
over the entire cross section of the reaction chamber 2. The
problems relating to flashback are therefore concentrated
essentially in this region upstream of the reaction chamber 2.
[0044] FIG. 3 shows, in a sectional view of half the rotationally
symmetrical structure of a reactor 1, a possible refinement of the
regulation devices 8 in the region of the mixture distribution zone
5 of the reactor 1. The regulation devices 8 are composed here of a
plurality of annular walls which divide the mixture distribution
zone 5 into segments 11. The segments 11, which form annular ducts
111 here, can be closed by means of annular covering elements 13
which correspond to the inlet cross sections 12 of said segments
11. The flow cross section in the mixture distribution zone 5 can
thus be released or blocked in a plurality of stages. Of course, at
least two such segments 11 are necessary to ensure the desired
method of operation. The maximum number is determined by the
structural space and the cross section through which there is a
flow in the mixture distribution zone 5, as well as by the load
spread.
[0045] For the present application case of the exemplary
embodiment, a number of five annular ducts 11 with correspondingly
four of the annular coverings 13 have been selected. The resulting
profile of the flow rate v given successive opening of the
individual annular ducts 111 as the load L rises is illustrated by
means of the dot-dashed curve 14 in FIG. 2. After approximately 8%
of the full load L.sub.max has been reached, all the flow rates v
are above the combustion rate v.sub.br. The area of the load spread
which can be used under approximately ideal operating conditions is
therefore between 8% and 100%. This constitutes a significant
improvement over the design described by means of the curve 9.
[0046] The design of the regulation devices 8 in FIG. 3 shows that
here a distribution of the inflowing mixture of the educts A is to
be reached in the mixture distribution zone 5. For this purpose,
for the reasons already mentioned above, the flow cross section
widens in the direction of the catalyst carrier 3 in the manner of
a diffuser, by virtue of the use of a flow distributor 15. The
structure of the segments 11 is then selected which is such that
each of the inlet cross sections 12 has a specific portion of the
sum of the inlet cross sections 12, and thus of the available flow
cross section. Each of the segments 11 also has an outlet cross
section 16 which has the same proportion of the sum of the outlet
cross sections 16 as its inlet cross section 12 had of the sum of
the inlet cross sections 12. The fluidic effect generated by the
widening of the flow cross section that is to say the diffuser, is
thus transferred to each individual segment 11 so that a comparable
flow onto the catalyst carrier 3 is always achieved irrespective of
the volume flow of the educts A and the number of the closed or
opened segments 11.
[0047] According to the exemplary embodiment present here, the
annular covering elements 13 are arranged fixedly with respect to
one another on a common carrier 17. In this design which is very
robust and also has a high level of immunity to faults even under
the possibly aggressive conditions in the mixture distribution zone
5, the annular covering elements 13 are arranged on the carrier 17
in such a way that they can each be displaced together and in the
process successively open the individual annular ducts 111 in the
manner predefined by the arrangement, or successively enlarge the
flow cross section in the direction of the individual ducts 111.
Instead of the theoretically also conceivable displacement of all
the covering elements 13, in each case individually and independent
of one another, the common carrier 17 results in a very robust
design. The carrier 17 itself is displaced in the direction of the
main flow of the educts A. This is significantly more favourable in
terms of the soiling of sliding faces in comparison with a
displacement transversely with respect to said flow. Furthermore,
the parts which are to be displaced with respect to one another
cannot be pressed onto one another by the flow pressure, which
would strongly increase the friction and thus the force necessary
for activation. The driver of the carrier 17 can be displaced very
slightly towards the outside of the reactor 1 if the carrier 17 is
constructed to have corresponding length or if there is a suitable
transmission element, for example a push and pull rod. The
situation is comparable for guides and seals. The design can thus
be implemented independently of the conditions in terms of
temperature and aggressiveness of the educts A prevailing in the
region of the inlet opening 4 and in the region of the mixture
distribution zone 5, so that the control and/or regulation as well
as the sealing and guidance can be carried out with an
appropriately high level of reliability but yet easily and
cost-effectively.
[0048] The opening and the closing of the individual segments 11 is
carried out by means of the arrangements of the annular covering
elements 13 in such a way that segments 11 which are adjacent to
one another are opened or closed successively. This has the result
that the areas into which there is a new inflow in the region of
catalyst carrier 3 or the areas in which there is no longer an
inflow in each case lie directly next to one another. They can thus
interact and very easily exchange thermal energy with one another
so that the operation of the reactor 1 becomes more homogeneous and
is thus improved with respect to the desired conversion.
[0049] In particular in the case of a cold start of the reactor 1,
this can be used very favourably as there is firstly an inflow onto
the catalyst carrier 3 in a centrally located region 18 through
successive opening of the individual segments 11 from the inside to
the outside. As a result of the thermal conduction occuring in all
directions in the catalyst carrier 3, heat passes first from this
first-used central region 18 into all the surrounding regions. If
the inflow into the surrounding regions is then released through an
increasing volume flow of the educts A by opening the adjacent
segments 11, said regions are already pre-heated so that the
catalytically active material very quickly reaches its operating
temperature or has possibly already reached it. The conversion of
the educts A starts up very quickly, and the time required to cold
start the reactor 1 can be reduced. In addition, under all
conditions of partial load the conveying of heat out of the region
of the reactor chamber 2 into the surroundings, which always
constitutes a heat loss, is avoided or at least significantly
reduced, and the effectiveness of the reactor 1 thus increased.
[0050] FIG. 4 illustrates an alternative embodiment of the
regulation devices 8. Here too, the mixture distribution zone 5 is
divided into individual segments 11. These are embodied as
concentric annular ducts 11 1 about a central duct 112 which is
arranged in the central region. The segments 11 whose cross section
is illustrated once more at the junction between the inlet opening
4 and the mixture distribution zone 5 in FIG. 4, in the region of
the inlet opening 4, are also embodied here as regions which open
in the direction of the flow. The requirements which have already
been mentioned above and preferred refinements apply here
correspondingly with the exception of those of the annular covering
elements 13. The reference symbols in FIG. 4 and the following
figures of the exemplary embodiment are used analogously to those
in FIG. 3 when there is a comparable method of operation of the
components and/or cross sections.
[0051] Instead of the annular covering elements 13, the regulation
devices 8 according to the refinement according to FIG. 4 have
sheaths 19 and a needle 20. These are shown in FIG. 5, which is a
sectional view along the line V-V in FIG. 4 indicated in the
abovementioned cross section. The abovementioned functional
principle of the regulation devices does not change here. However,
as a result of the configuration with the sheaths 19 and the needle
20, each individual segment 11 or its inlet cross section 12 can be
selective if opened or closed. The needle 20 and the sheaths 19 are
moved for this purpose in the direction of flow of the educts A.
The drive can also be displaced very easily towards the outside of
the reactor 1 here if needles 20 and/or sheaths 19 are given a
corresponding length. The situation is comparable for guides and
seals. The design can also therefore be implemented here
independently of the conditions in terms of temperature and
aggressiveness of the educts A prevailing in the region of the
inlet opening 4 and in the region of the mixture distribution zone
5.
[0052] In order to ensure an exchange of the educts A over the
entire range of the inlet opening 4, and thus to provide the
possibility of being able to open and close the segments 11 in any
desired sequence, at least the sheaths 19, which are arranged
between the needle 20 and the sheath which is arranged furthest
away from the needle, should have openings 21. By means of these
openings 21, which may be embodied as drilled holes, windows or the
like and may, under certain circumstances, also constitute the
approximately largest part of the sheath 19, it is possible to
ensure the exchange of the educts A over the entire cross section
of the inlet opening 4. If the needle 20 is guided backwards out of
the structure, it may, under certain circumstances, also be
appropriate or necessary here, as illustrated, if the outermost of
the sheaths 19 also has openings 21 so that, for example, use is
made possible with a volume flow to the inlet opening 4 at a right
angle with respect to the needle 20.
[0053] The operating strategy during the opening and/or closing of
the individual segments 11 can thus be freely adapted to the
requirements of the reactor 1, and here in particular to those of
the reaction chamber 2 or of the catalyst carrier 3, without the
need to take into account mechanical specifications due to the
design of the regulation devices 8. The use of operation strategies
which have already been mentioned at the beginning for optimizing
the cold start behaviour, for optimizing the ageing processes etc.
thus becomes possible in a very easy and flexible way.
[0054] Furthermore, by means of a design such as described in FIGS.
4 and 5 it is possible to avoid dead zones of the flow of the
educts in the region of the mixture distribution zone 5 or at least
reduce them. The formation of byproducts, for example soot during
the autothermal reformation of petrol or in particular of diesel,
as already explained in the beginning, can thus be prevented in an
ideal way. Soiling of the mechanism, especially coating of the
catalytically active material with the soot, is thus prevented. It
is therefore possible to increase the operational reliability of
the reactor 1, as well as its service life and the quality of the
reformate.
[0055] FIG. 6 illustrates a further alternative embodiment of the
regulation devices 8. Here too, the mixture distribution zone 5 is
divided into individual segments 11. These segments 11 are formed
by dividing walls which segment the mixture distribution zone 5
which has a circular cross-sectional shape here into three line
regions 113 in the shape of a third of a circle. The segments 11
whose cross section is illustrated once more at a junction between
the inlet opening 4 and the mixture distribution zone 5 in FIG. 6
in the region of the inlet opening 4 are also embodied here as
regions which open in the direction of flow. In the region between
the inlet opening 4 and the mixture distribution zone 5, each of
the line regions 113 has an inlet opening 22. These inlet openings
22, which correspond in their function approximately to the
abovementioned inlet cross sections 12, can in turn be closed so
that the individual line regions 113 can be opened and closed
individually and independently of one another.
[0056] In theory, any desired method for opening or closing is
possible, but it is particularly favourable to adopt the solution
illustrated schematically in FIG. 7, in which the inflow openings
22 are each closed and/or opened by means of needles 23. The method
of operation and the bearing/guidance as well as the driving of the
needles 23 are the same as has already been described above with
respect to the needle 20 and the sheaths 19.
[0057] All the embodiments of the regulation devices cover, in the
reactor 1, the favourable possibilities mentioned above and in
particular discussed in general within the scope of FIG. 3.
Furthermore, all the conceivable and appropriate combinations of
individual features from the various exemplary embodiments to form
further regulation devices 8 are conceivable. These also
correspondingly permit favourable methods of functioning and
operating for the reactor 1, and fall within the scope of the
present invention.
* * * * *