U.S. patent application number 10/116038 was filed with the patent office on 2002-10-17 for method and apparatus for obtaining combustion pages of high calorific value.
Invention is credited to Steer, Thomas.
Application Number | 20020148597 10/116038 |
Document ID | / |
Family ID | 7924827 |
Filed Date | 2002-10-17 |
United States Patent
Application |
20020148597 |
Kind Code |
A1 |
Steer, Thomas |
October 17, 2002 |
Method and apparatus for obtaining combustion pages of high
calorific value
Abstract
The present invention relates to a method for obtaining
combustion gases of high calorific value, wherein carbonaceous
materials are allothermically gasified in a fluidized layer
containing solid particles, using a gaseous gasifying agent and by
supply of heat, and the gases thus produced are separated from the
solid particles and withdrawn. Said method is characterized in that
the solid particles are indirectly heated in a first descending bed
and supplied to a second ascending fluidized bed in which the
fluidized layer is formed and gasification takes place for the
greatest part. The method further relates to an apparatus for
performing said method.
Inventors: |
Steer, Thomas; (Freising,
DE) |
Correspondence
Address: |
Lawrence E. Laubscher, Sr
Suite 300
745 South 23rd Street
Arlington
VA
22202
US
|
Family ID: |
7924827 |
Appl. No.: |
10/116038 |
Filed: |
April 5, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10116038 |
Apr 5, 2002 |
|
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PCT/EP00/09767 |
Oct 5, 2000 |
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Current U.S.
Class: |
165/104.16 |
Current CPC
Class: |
C10J 2300/1261 20130101;
C10J 3/482 20130101; C10J 2300/0973 20130101; C10J 2200/09
20130101; C10J 2300/1246 20130101; C10J 3/56 20130101 |
Class at
Publication: |
165/104.16 |
International
Class: |
F28D 013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 7, 1999 |
DE |
199 48 332.9 |
Claims
1. A method for obtaining combustion gases of high calorific value,
wherein carbonaceous materials are allothermically gasified in a
fluidized layer containing solid particles, using a gaseous
gasifying agent and by supply of heat, and the gases thus produced
are separated from said solid particles and withdrawn, said solid
particles being indirectly heated in a first descending bed (1) and
supplied to a second ascending fluidized bed (2) in which said
fluidized layer is formed and gasification takes place for the
greatest part.
2. The method according to claim 1, characterized in that said
first descending bed (1) is loosened by injecting a gas.
3. The method according to claim 1, characterized in that said
first descending bed (1) is slightly fluidized.
4. The method according to at least one of the preceding claims,
characterized in that said first descending bed (1) is indirectly
heated with the help of a heat exchanger having a heating medium
flowing therethrough.
5. The method according to claim 4, characterized in that said
heating medium flows in pulsating fashion upon heat emission to
said first descending bed (1).
6. The method according to at least one of the preceding claims,
characterized in that said gasification process is carried out
under pressure.
7. The method according to at least one of claims 1 to 5,
characterized in that said gasification process takes place under
atmospheric conditions.
8. The method according to at least one of the preceding claims,
characterized in that said carbonaceous materials consist of
liquid, paste-like or solid materials in particular of coke, crude
oil, biomass or waste materials.
9. The method according to at least one of the preceding claims,
characterized in that said gasifying agent is steam.
10. An apparatus for performing the method according to claim 1,
comprising: a reaction zone (3) for gasifying said carbonaceous
materials, a means (4) for producing said ascending fluidized bed
(2) in said reaction zone (3), a means (5) for separating the gases
produced during gasification from said solid particles and for
discharging said gases, a heating zone (6) for heating said solid
particles in said descending bed (1), said heating zone (6) being
substantially separated from said reaction zone (3), a means (7)
for transferring the heated solid particles from said heating zone
(6) into said reaction zone (3), and an indirect heat supply means
(8) assigned to said heating zone (6).
11. The apparatus according to claim 10, characterized in that said
heating zone (6) and said reaction zone (3) are separated by
different fluidization of said fluidized bed, said different
fluidization effecting a circulation of the bed material about one
or several substantially horizontal axes.
12. The apparatus according to claim 11, characterized in that said
substantially horizontal axes are closed in the form of a ring.
13. The apparatus according to claim 10, characterized in that said
heating zone (6) and said reaction zone (3) are separated by a wall
(9).
14. The apparatus according to claim 10, characterized in that said
heating zone (6) and said reaction zone (3) are each formed in a
separate reactor.
15. The apparatus according to any one of claims 13 or 14,
characterized in that said means (7) for transferring said heated
solid particles is a wall opening (10) or a pipe.
16. The apparatus according to at least one of claims 13 to 15,
characterized in that said means (7) for transferring said heated
solid particles is provided in a lower portion of said heating zone
(6).
17. The apparatus according to at least one of claims 10 to 16,
characterized in that said means (7) for transferring said heated
solid particles comprises a nozzle bottom (11) for slightly
fluidizing said solid particles.
18. The apparatus according to at least one of claims 10 to 17,
characterized in that said indirect heat supply means (8) is at
least one heat exchanger (12) through which a heating medium can
flow and which is provided in or on said heating zone (6).
19. The apparatus according to claim 18, characterized in that said
heat exchanger (12) comprises at least one resonant tube (13) in
which said heating medium flows in pulsating fashion upon heat
emission to said heating zone (6).
20. The apparatus according to claim 19, characterized in that said
resonant tube (13) is connected to a combustion chamber for
generating resonance.
21. The apparatus according to claim 18, characterized in that an
acoustic resonator is provided for generating resonance, said
resonator being separated from a combustion chamber.
22. The apparatus according to at least one of claims 10 to 21,
characterized in that said means for producing said ascending
fluidized bed (2) is a nozzle bottom (15) provided in a lower
portion of said reaction zone (3).
23. The apparatus according to at least one of claims 10 to 22,
characterized in that said means for separating the gases produced
during gasification from said solid particles is a cyclone.
24. The apparatus according to at least one of claims 10 to 24,
characterized in that a vertical outflow of said gases produced in
said ascending bed is blocked by baffles (18, 19) which effect a
multiple deflection of the gas flow, and said multiple deflection
results in a substantial separation of said solid particles from
said gas flow.
25. The apparatus according to at least one of claims 10 to 24,
characterized in that for circulating said solid particles a means
(16) is provided for transferring said solid particles from said
reaction zone (3) into said heating zone (6).
26. The apparatus according to claim 25, characterized in that said
means (16) for transferring said solid particles from said reaction
zone (3) into said heating zone (6) is a wall opening (17) or a
pipe.
27. The apparatus according to at least one of claims 25 and 26,
characterized in that said means (16) for transferring said solid
particles is provided in an upper portion of said reaction zone
(3).
28. The apparatus according to at least one of claims 10 to 22,
characterized in that a feed means (21) for said carbonaceous
materials terminates in said heating zone (6).
29. The apparatus according to at least one of claims 10 to 28,
characterized in that a feed means for said carbonaceous materials
terminates in said reaction zone (3).
Description
[0001] The present invention relates to a method for obtaining
combustion gases of high calorific value and to an apparatus for
performing the method.
[0002] Careful use of resources becomes more and more the central
objective of society. Energy generation from waste materials and
regenerative substances such as biogenic fuels during first or
consecutive use is thus of special importance. Furthermore, towards
the end of the 20.sup.th century the generation of hydrogen becomes
more and more the center of interest, not least due to the
beginning exploitation of hydrogen in fuel cells.
[0003] The energetic exploitation of solid, paste-like or liquid
fuels is most of the time carried out by way of combustion with
subsequent use of the previously chemically bound heat released
during combustion.
[0004] Apart from this, there have been approaches for a long time
to establish gasification processes for generating combustion gases
of high calorific value from solid, paste-like or liquid fuels. The
combustible part of the crude gas during each gasification consists
for the greatest part of hydrogen and carbon monoxide; smaller
amounts are methane and higher hydrocarbons. Each type of
gasification thus generates hydrogen.
[0005] An essential advantage of gasification over combustion is
that the pollutants contained in the starting substance are
converted in a reducing atmosphere into constituents or into
relatively simple chemical compounds. The gas volumes are
considerably smaller in comparison with combustion, so that gas
purification in the case of gasification can be carried out more
easily and at lower costs as compared to combustion when the
objective is the same.
[0006] There are three basic types of gasification methods:
[0007] 1. Gasification of solid, paste-like or liquid fuels with
the gasification medium air is in technical terms the simplest
method and leads to partial oxidation. The calorific value of the
gas produced thereby is lower than that of the fuel used. The
gasification temperatures are typically within the range of
600.degree. C. to 900.degree. C. Tars are produced at said
temperatures to a considerable extent. A large-scale use of the
method has so far not been possible because so far the removal of
tars from the gas could not be sufficiently controlled technically
for small gasifiers.
[0008] 2. Like air gasification, the gasification of solid,
paste-like or liquid fuels with the gasification medium oxygen
results in partial oxidation with a decrease in the calorific
value. The gasification temperatures are typically at 1600.degree.
C. so that the formation of tar is ruled out. A large-scale use has
so far not been possible because the generation of the necessary
oxygen entails high costs and excessively burdens economic
calculations in industry. In comparison with air gasification,
oxygen gasification leads to smaller gas amounts because the
gasification medium does not introduce an inert nitrogen
amount.
[0009] 3. The gasification of solid, paste-like or liquid fuels
with the gasification medium steam leads to a gas of a higher
calorific value than the fuel used originally. Therefore, heat must
be supplied to the gasification reactor from the outside. The
gasification temperatures are typically between 600.degree. and
900.degree. C. Tar might be formed. However, its potential is lower
than in air gasification. A large-scale use has so far not been
possible because the problem of heat input into the reactor has, in
particular, not been solved in a satisfactory way. The gas amounts
of the steam gasification lie between those of air and oxygen
gasification. This is due to the fact that during steam
gasification the carbon of the fuel is oxidized by the oxygen of
the steam into carbon monoxide or carbon dioxide, whereby
additional hydrogen is formed. The potential of the steam
gasification to generate hydrogen is thus considerably higher than
that of air or oxygen gasification.
[0010] Gasification methods in which the reaction heat needed is
supplied by partial oxidation are called autothermic, whereas those
in which the reaction heat needed is supplied from the outside are
called allothermic.
[0011] The allothermic steam gasification of solid, paste-like or
liquid fuels normally takes place in a fluidized bed for ensuring
uniform reaction conditions. In this process, steam flows from
below to a bed of small solid particles. The inflow rate is here so
high that the solid particles are at least kept suspended. One
talks about a stationary fluidized bed when the solid particles
form a fixedly defined surface with ascending gas bubbles, whereas
in a circulating fluidized bed the main part of the solid particles
is discharged with the gas flow from the fluidized bed reactor and
is separated from the gas flow and then supplied again via a down
path to the lower part of the fluidized bed reactor proper. The
solid particles may be inert, consisting e.g. of quartz sand,
limestone, dolomite, corundium, or the like, but they may also
consist of the ash of the fuel. The solid particles can accelerate
the gasification reactions due to catalytic properties.
[0012] U.S. Pat. No. 4,154,581 describes a gas generator comprising
two reaction zones and having an exothermic reaction environment in
the heating portion, so that heat is directly provided. Heat
transportation is ensured by using bed material of different grain
sizes. A coarse-grained material remains in the exothermic bed,
whereas a fine-grained fraction travels from the exothermic into
the endothermic region and back. The fine-grained fraction assumes
the function of heat transfer.
[0013] Said method has the drawback that the transportation of the
solids between the beds must coincide with the heat balance of the
beds, which makes great demands on the control units at high
working temperatures and different load conditions Furthermore, as
far as the fuels are concerned, there is no separation between the
combustion region and the gasification region, so that possible
pollutants from the fuel may be found along both the gasification
path and the combustion path, which complicates the gas cleaning
system.
[0014] It is known from EP 0 329 673 and U.S. Pat. No. 5,059,404
that heat input is realized with the help of heat exchangers which
are provided in the fluidized bed, i.e. in the reaction zone. The
drawback of such a concept is that the arrangement of the heat
exchangers in the reaction zone predetermines the dimension of the
reaction zone and the fluidized bed, respectively, because of the
heat exchange surfaces required. Moreover, the heat exchange
surfaces are directly exposed to the corrosive effects of harmful
constituents of the fuel, which makes extreme demands on the
material at surface temperatures of from 600.degree. C. to more
than 900.degree. C.
[0015] Finally, a combination of autothermic and allothermic
methods is known from DE 197 36 867 A1. The necessary reaction heat
is here supplied via hot steam and flue gases from a partial
combustion of the product gas.
[0016] The combination of an autothermic and allothermic method has
the effect that the gas amount increases considerably due to the
nitrogen amount which is supplied with the air for partial
combustion. Thus the partial pressures of the industrial gases
decrease, which has a negative effect on the subsequent gas
cleaning and the aftertreatment of the gas.
[0017] A fluidized bed constitutes a technology which has been
tried and tested and often employed for many years. Applications
are e.g. the drying and burning of solid materials or of slurries.
The basis for each fluidized bed method is a reactor in which a
solids content is loosened by inflow from below to such an extent
that the individual particles start to float in air, with the
solids content being fluidized.
[0018] A distinction is made between two coarse types: When a solid
surface of the fluidized solids content is formed, one talks about
a stationary fluidized bed. When the particles are discharged with
the gas flow from the reactor, one talks about a circulating
fluidized bed. Further essential features of every circulating
fluidized bed are an apparatus for separating the discharged solid
particles from the gas flow and a further means for returning the
separated solid particles into the reactor.
[0019] In the course of time many constructional forms have been
used for both basic types in the attempt to avoid the drawbacks of
the one type and to exploit the benefits of the other.
[0020] The following documents should be mentioned by way of
example:
[0021] DE 28 36 531: A stationary fluidized bed method in which
regions of different fluidization are formed by installing a
partition so that bed material is circulated in a stationary
bed.
[0022] EP 0 302 849: A circulating fluidized bed which develops DE
28 36 531, but rather reminds of a stationary than a circulating
fluidized bed because of its constructional size.
[0023] DE 33 20 049: A stationary fluidized bed method in which bed
material is circulated due to different bed heights.
[0024] It is an object of the present invention to indicate a
method and an apparatus for obtaining combustion gases of high
calorific value for eliminating the above-mentioned problems at
least in part.
[0025] Said object is achieved by a method according to the
invention with the features of claim 1 and by an apparatus
according to the invention with the features of claim 10.
[0026] Advantageously, there is no heating means in the reaction
chamber in the method according to the invention and in the
apparatus according to the invention. Corrosion problems that have
so far existed are thereby avoided. Moreover, the inventive method
and the inventive apparatus are not limited to special heating
means, but permit the use of any desired heating means, in
particular tubular heat exchangers. Advantageously, no fuel
particles pass from the reducing zone into an oxidizing zone.
Moreover, the reaction chamber can be designed independently of the
geometrical dimensions predetermined for the heating means, so that
the constructional size of the apparatus according to the invention
can be optimized.
[0027] In a preferred embodiment of the method of the invention,
the first descending bed is loosened or slightly fluidized by
injecting a gas; advantageously, this prevents an undesired
agglomeration of the solid particles and is conducive to the
transportation of the bed material. In another embodiment, the
first descending bed is indirectly heated with the help of a heat
exchanger which has a heating medium flowing therethrough. The
heating medium may here flow in pulsating fashion in the heat
exchanger upon heat emission to the first descending bed. Heat
transfer from the heat exchanger to the first descending bed is
thereby improved.
[0028] Furthermore, gasification may take place under pressure or
under atmospheric conditions. The carbonaceous materials may
consist of liquid, paste-like or solid materials, in particular of
coke, crude oil, biomass or waste materials. Thus, the method
according to the invention advantageously permits the processing of
the most different carbonaceous materials. In a further preferred
embodiment of the method according to the invention, steam is used
as the gasifying agent.
[0029] In a preferred embodiment of the apparatus according to the
invention, the heating zone and the reaction zone may be separated
by way of different fluidization of the fluidized bed, the
different fluidization effecting a circulation of the bed material
about one or several substantially horizontal axes. The
substantially horizontal axes may be closed in the form of a ring.
Said embodiment of the apparatus according to the invention is
particularly characterized by a compact construction. In another
embodiment of the apparatus according to the invention, the heating
zone and the reaction zone are separated by a wall. Moreover, the
heating zone and the reaction zone may each be formed in a separate
reactor. Said two embodiments offer the advantage of a reliable
separation of the heating zone from the reaction zone by
constructional measures. The means for transferring the heated
solid particles may be a wall opening or a pipe. Furthermore, said
means for transferring the heated solid particles may be provided
in a lower region of the heating zone. In a preferred embodiment,
said means comprises a nozzle bottom with the help of which the
solid particles can be slightly fluidized in the heating zone.
[0030] In a preferred embodiment of the apparatus according to the
invention, the indirect heat supply means is at least one heat
exchanger through which a heating medium can flow and which is
provided in or at the heating zone. The use of heat exchangers as
heat supply means simplifies the construction of the reactor.
Moreover, the heat exchanger may comprise at least one resonant
tube in which the heating medium flows in pulsating fashion upon
heat emission to the heating zone. Advantageously, the heat
transfer from the heat exchanger to the heating zone is thereby
improved. The resonant tube may be connected to a combustion
chamber for resonance generation. The generation of the desired
resonance may also be achieved with the help of an acoustic
resonator which is arranged such that it is separated from the
combustion chamber.
[0031] In another embodiment, the means for producing the ascending
fluidized bed is a nozzle bottom provided in a lower portion of the
reaction zone. Such a nozzle bottom offers the advantage of a
uniform injection of the fluidizing medium into the reaction
zone.
[0032] The means for separating the gases produced during
gasification from the solid particles may be a cyclone. In another
preferred embodiment the separating means comprises baffles for
producing a sharp deflection of the gas flow, whereby the gas flow
and the solid particle flow are separated; the baffles are here
followed by a channel for gas discharge and by the heating zone.
Furthermore, a means for transferring the solid particles from the
reaction zone into the heating zone may be provided for circulating
the solid particles. Said means may be a wall opening or a pipe.
Preferably, said means is provided in an upper portion of the
reaction zone.
[0033] The supply region for carbonaceous materials may terminate
in the heating zone. Moreover, a supply means for the carbonaceous
materials may also terminate in the reaction zone.
[0034] The invention shall now be explained in more detail with
reference to embodiments taken in conjunction with the drawing, in
which:
[0035] FIG. 1 is a cross section through an embodiment of the
apparatus of the invention, where the means for separating the
gases from the solid particles comprises baffles; and
[0036] FIG. 2 is a cross section through another embodiment of the
apparatus of the invention, where the means for separating the
gases from the solid particles is a cyclone
[0037] The embodiment of the apparatus of the invention as shown in
FIG. 1 comprises a reaction zone 3 in which carbonaceous materials
are gasified. The carbonaceous materials are positioned in an
ascending fluidized bed 2 which is produced with the help of means
4 in the reaction zone 3. The means 4 provided in the lower area of
the reaction zone 3 may e.g. be an open or closed nozzle bottom
through which the fluidizing medium steam is blown into the zone.
The steam may be mixed with gases. The nozzle bottom 15 defines the
reaction zone 3 in which the fluidized bed 2 is formed. Next to or
below the nozzle bottom 15, there is provided an outlet (not shown
in FIG. 1) from which e.g. bed material, undesired materials
arising from the fuel, ash and non-reacted fuel components can be
withdrawn. Steam may be injected into the outlet, said steam
facilitating a withdrawal on the one hand and ensuring a
post-reaction of remaining constituents of the fuel on the other
hand. Furthermore, the illustrated embodiment comprises a heating
zone 6 which is separated from the reaction zone 3 by a device 9.
During operation of the reactor, a descending bed 1 of solid
particles is formed in the heating zone 6. The lower portion of the
heating zone 6 may have disposed therein a nozzle bottom 22 for the
inflow of steams the steam loosening or slightly fluidizing the bed
material of the heating zone for improving transportation of the
material.
[0038] As shown in FIG. 1, a means 8 for indirectly supplying heat
is arranged in the heating zone 6. Said heat supply means 8 may
e.g. be composed of one or several heat exchangers. It is clear
that the present invention is not limited to the special
arrangement of the heat exchanger 12 shown in FIG. 1, but other
arrangements are also possible, e.g. on the wall of the heating
zone 6. Moreover, instead of the illustrated tubular heat exchanger
12, a planar heat exchanger may be used that is e.g. integrated
into the wall of the heating zone 6.
[0039] The heat exchanger 12 provided in the heating zone may
partly consist of resonant tubes 13 in which the heating medium
flows in pulsating fashion into the heating zone 6 upon heat
emission. The resonant tubes 13 are connected to a combustion
chamber (not shown) or another resonance generator for generating
the resonant oscillation. The heating medium is directly heated by
combustion of a combustible substance with oxygen-containing
gas.
[0040] As can be seen in FIG. 1, the solid particles are thus
heated separately with respect to the gasification taking place in
the reaction chamber 3. Due to the weak fluidization of the heating
zone, a slowly descending bed 1 is formed in said zone, whereas due
to the strong fluidization of the reaction zone 3 a rapidly
ascending fluidized bed 2 is formed in said zone. The arrangement
of the heat exchanger 12 in the slowly descending bed 1 reduces the
great mechanical wear of the heat exchanger that has so far been
observed in the prior art. Moreover, the heat exchanger 12 in the
heating zone is subjected to less corrosive effects than in the
reaction zone 6. This means that the reactor has a longer service
life.
[0041] The heating zone 6 is connected to the reaction zone 3 via a
means 7 with the help of which the solid particles heated in the
heating zone 6 are transferred into the reaction zone 3. As shown
in FIG. 1, said means 7 is shaped as a wall opening 10. Said means
7, however, may e.g. also be designed as a pipe. For promoting the
transportation of the heated solid particles from the heating zone
6 into the reaction zone 3, the means 7 for transferring the heated
solid particles may comprise a nozzle bottom 11. With the help of
said nozzle bottom 11 it is possible to loosen or slightly fluidize
the solid particles. The nozzle bottom 15 used for producing the
ascending fluidized bed 2 may be used as the nozzle bottom 11.
Attention must here paid that the fluidizing action is more
pronounced in the reaction zone 3 than in the heating zone 6.
[0042] For circulating the solid particles, a means 16 is provided
in the upper area of the reaction zone 3 for returning the solid
particles from the reaction zone 3 into the heating zone 6. As
shown in FIG. 1, said means 16 may be a wall opening 17. It is also
possible to design said means 16 as a pipe. The means 6 for
separating the gases produced during gasification from the solid
particles and for discharging said gases are baffles 18 and 19 in
the embodiment shown in FIG. 1. The baffles 18 and 19 effect a
strong deflection of the flow which cannot be followed by the solid
particles. Gas flow and solid particle flow are thus separated at
the baffles. The gas flow is discharged via the gas path 20 by
which the baffles 18 and 19 are separated. The solid particle flow
showers into the heating zone 6 positioned below the baffles 18 and
19.
[0043] In the embodiment shown in FIG. 1, a feed means 21 for
carbonaceous materials terminates in the heating zone 6. The fuel
can either be pressed into said zone in the area of bed 1 or
discharged from above onto bed 1. Moreover, it is possible to
provide a further feed means which terminates in the reaction zone
3.
[0044] In the embodiment shown in FIG. 2, the bed material is
separated in a cyclone from the gas flow and fed again via the
descending bed 1 to the lower portion of the ascending bed 2. In
this instance the gas flow passes via pipe 23 in tangential fashion
into the separating chamber 5 which is designed as a cyclone.
* * * * *