U.S. patent application number 10/380421 was filed with the patent office on 2004-02-05 for alumina honeycomb structure, method for manufacture of the same, and heat-storing honeycomb structure using the same.
Invention is credited to Harada, Takashi, Kasai, Yoshiyuki, Mori, Isao, Nagoshi, Masayasu, Tada, Takeshi, Umehara, Kazuhiko.
Application Number | 20040023180 10/380421 |
Document ID | / |
Family ID | 26600710 |
Filed Date | 2004-02-05 |
United States Patent
Application |
20040023180 |
Kind Code |
A1 |
Kasai, Yoshiyuki ; et
al. |
February 5, 2004 |
Alumina honeycomb structure, method for manufacture of the same,
and heat-storing honeycomb structure using the same
Abstract
In an alumina honeycomb structural body according to a first
aspect of the invention and another invention relating it, the
alumina honeycomb structural body is constructed in such a manner
that alumina is a main ingredient and an amount of impurities is
limited to not greater than 2 weight %. Moreover, in an alumina
honeycomb structural body according to a second aspect of the
invention and another invention relating it, the alumina honeycomb
structural body is constructed in such a manner that an amount of
alumina as a main ingredient is limited to not less than 98 weight
%; an amount of Na containing compound is limited to 0.02 weight
%-1.0 weight % of Na.sub.2O when converting it into oxide; and
remainder is impurities.
Inventors: |
Kasai, Yoshiyuki; (Kasugai
City, JP) ; Harada, Takashi; (Nagoya City, JP)
; Umehara, Kazuhiko; (Nagoya City, JP) ; Mori,
Isao; (Tokyo, JP) ; Nagoshi, Masayasu; (Tokyo,
JP) ; Tada, Takeshi; (Yokohama-city, JP) |
Correspondence
Address: |
Oliff & Berridge
P O Box 19928
Alexandria
VA
22320
US
|
Family ID: |
26600710 |
Appl. No.: |
10/380421 |
Filed: |
June 18, 2003 |
PCT Filed: |
September 12, 2001 |
PCT NO: |
PCT/JP01/07910 |
Current U.S.
Class: |
431/215 |
Current CPC
Class: |
C04B 2235/72 20130101;
F23L 2900/15021 20130101; C04B 2235/9607 20130101; C04B 2235/3201
20130101; F27D 17/002 20130101; C04B 35/111 20130101; C04B
2111/00612 20130101; F28F 21/04 20130101; Y02E 60/142 20130101;
Y02E 60/14 20130101; C04B 2235/3217 20130101; F28D 20/0056
20130101; C04B 2235/3218 20130101; F23L 15/02 20130101; Y02E 20/348
20130101; C04B 38/0006 20130101; C04B 35/10 20130101; F27D 1/0006
20130101; Y02E 20/34 20130101; C04B 38/0006 20130101; C04B 35/10
20130101 |
Class at
Publication: |
431/215 |
International
Class: |
F23D 011/44 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 26, 2000 |
JP |
2000-291709 |
Sep 26, 2000 |
JP |
2000-291711 |
Claims
1. An alumina honeycomb structural body, comprising: alumina as a
main ingredient and not greater than 2 weight % of impurities.
2. The alumina honeycomb structural body according to claim 1,
wherein a porosity is not greater than 50%, preferably not greater
than 15%, a thermal expansion coefficient is not greater than
8.5.times.10.sup.-6/.de- gree. C., and a main crystal phase is
.alpha. alumina.
3. The alumina honeycomb structural body according to claim 1,
wherein an amount of impurities is not greater than 1 weight %.
4. A method of manufacturing an alumina honeycomb structural body,
comprising the step of: mixing 97 weight %-70 weight % of .alpha.
alumina, 3 weight %-30 weight % of aluminum hydroxide, forming
agents, and solvents to obtain a plastic substance; extruding the
plastic substance to obtain an extruded honeycomb body; and firing
the extruded honeycomb body to obtain an alumina honeycomb
structural body having .alpha. alumina as a main crystal phase.
5. An alumina honeycomb structural body, comprising: not less than
98 weight % of alumina as a main ingredient; a Na containing
compound having 0.02 weight %-1.0 weight % of Na.sub.2O when
converting it into oxide; and remainder of impurities.
6. The alumina honeycomb structural body according to claim 5,
wherein a porosity is not greater than 50%, preferably not greater
than 15%, a thermal expansion coefficient is not greater than
8.5.times.10.sup.-6/.de- gree. C., and a main crystal phase is
.alpha. alumina.
7. A method of manufacturing an alumina honeycomb structural body
containing Na, comprising the steps of: mixing 97 weight %-70
weight % of .alpha. alumina, 3 weight %-30 weight % of aluminum
hydroxide, necessary amount of sodium source, forming agents, and
solvents to obtain a plastic substance; extruding the plastic
substance to obtain an extruded honeycomb body; and firing the
extruded honeycomb body to obtain an alumina honeycomb structural
body having .alpha. alumina as a main crystal phase.
8. A honeycomb regenerator, comprising: at least one alumina
honeycomb structural body set forth in claim 1 or 5, wherein a
heating gas and a gas to be heated are alternately passed therein
so as to perform a heat-exchanging.
9. A switching regenerative burner, comprising: at least one pair
of honeycomb regenerators set forth in claim 8, wherein one
honeycomb regenerator stores heat while the other honeycomb
regenerator discharges heat, and a heat-exchanging operation is
performed by switching each other.
10. A heating furnace, comprising: the switching regenerative
burner set forth in claim 9.
11. A method of heating a substance to be heated, comprising the
step of: heating the substance by using the heating furnace set
forth in claim 10.
12. A steel heating furnace, comprising: the switching regenerative
burner set forth in claim 9.
13. A method of heating a steel, comprising the step of: heating
the steel by using the steel heating furnace set forth in claim 12.
Description
TECHNICAL FIELD
[0001] The present invention relates to an alumina honeycomb
structural body, wherein an exhaust gas and a gas to be heated are
alternately passed through flow passages defined by through holes
so as to recover a waste heat in the exhaust gas, a method of
manufacturing the alumina honeycomb structural body, and a
honeycomb regenerator utilizing the alumina honeycomb structural
body. The present invention further relates to various heating
furnace utilizing the honeycomb regenerator and a method of heating
the heating furnace.
BACKGROUND ART
[0002] Recently, as key energy-saving measures of a general
industrial heating furnace used for a melting and a heat processing
of steel, aluminum or glass and so, it is known a heating method
utilizing a regenerative burner, wherein a sensible heat of the
exhaust gas after combustion is recovered as a pre-heated air
having a high temperature.
[0003] In the heating method utilizing the regenerative burner
mentioned above, the use of cordierite material having a small
thermal expansion coefficient and an excellent thermal stability in
a low temperature region and alumina material having a high heat
resistance and a high corrosion resistance in a high temperature
region is disclosed. For example, as disclosed in Japanese Patent
Laid-Open Publication No. 11-30491, at least one pair of burners
each installing the honeycomb regenerator, and, a fuel burning step
and a combustion gas exhausting step are performed alternately. In
this case, a sensible heat in the combustion gas is stored in the
honeycomb regenerator when exhausting the combustion gas, and, an
air for firing is pre-heated to a high temperature by the stored
sensible heat when introducing the air for firing, thereby
obtaining a high waste heat recovering efficiency. Therefore, it is
possible to reduce a fuel cost and also reduce a discharging amount
of carbon dioxide.
[0004] As the regenerator, generally use is made of media such as
ball, pellet, and saddle. However, recently use is made of ceramic
honeycomb structures having large heat conduction per unit volume,
compact dimension and excellent heat performance.
[0005] The regenerative burner has a merit since an exhaust gas
having a higher temperature is heat-exchanged. Therefore, it is
more effective when it is used for an aluminum melting furnace or a
steel heating furnace. However, in a field using the aluminum
melting furnace or the steel heating furnace, that has an
environment having strong corrosion atmosphere, there is a drawback
that the alumina honeycomb having a normal composition is corroded.
That is, in the field mentioned above, corrosion substances such as
alkali metal elements, iron series elements and so on are existent
in the exhaust gas for heat-exchanging. Moreover, in the honeycomb
regenerator, when a temperature of the exhaust gas introduced
therein becomes over 1000.degree. C., deterioration and shortened
service life appear due to a reaction with the alumina honeycomb
structural body. The deterioration and the shortened service life
become remarkable in a temperature range over 1300.degree. C.
Particularly, in the steel heating furnace, a temperature in the
heating furnace is high, and a temperature of the exhaust gas used
for heat-exchanging is also high i.e. over 1300.degree. C. at a
portion showing highest temperature. Moreover, scale corrosion
substances from the heated steel are adhered to the alumina
honeycomb structural body. Further, in the case that alkali
components are included in the combustion gas, a deterioration of
the alumina honeycomb structural body due to the reaction is
promoted. As a means for preventing the deterioration of the
alumina honeycomb structural body, a method is thinkable such that
a cooling air is mixed in the exhaust gas introduced therein.
However, this method has a problem such that energy efficiency
becomes lower.
[0006] As an actual example, in by-product gasses generated at an
integrated iron foundry such as blast furnace gas (BFG), coke oven
gas (COG), LD converter gas (LDG) and so on, a small amount of
alkali components is included. Therefore, in the steel heating
furnace utilizing the by-product gasses as a fuel (generally
utilizing M-gas generated by mixing these by-product gasses), a
deterioration of the alumina honeycomb structural body appears
remarkably at a temperature range over 1000.degree. C.,
particularly at a high temperature range over 1300.degree. C. The
deterioration and damage of the alumina honeycomb structural body
cause a decrease of waste heat recovering efficiency due to a
decrease of heat performance of the honeycomb structure and
material, and also cause an increase of running cost caused by an
increase of honeycomb cost and exchanging operation cost.
DISCLOSURE OF INVENTION
[0007] An object of the present invention is to eliminate the
drawbacks mentioned above and to provide an alumina honeycomb
structural body which can perform a heat-exchanging effectively
under an atmosphere wherein metal dusts are flew in all direction
and also under a corrosion atmosphere, a method of manufacturing
the alumina honeycomb structural body, and a honeycomb regenerator
utilizing the alumina honeycomb structural body. Another object of
the present invention is to further provide various heating
furnaces utilizing the honeycomb regenerator and a heating method
of the honeycomb regenerator.
[0008] According to a first aspect of the invention of an alumina
honeycomb structural body, the alumina honeycomb structural body
comprises: alumina as a main ingredient and not greater than 2
weight % of impurities. Moreover, according to a first aspect of
the invention of a method of manufacturing the alumina honeycomb
structural body, the method comprises the step of: mixing 97 weight
%-70 weight % of .alpha. alumina, 3 weight %-30 weight % of
aluminum hydroxide, forming agents, and solvents to obtain a
plastic substance; extruding the plastic substance to obtain an
extruded honeycomb body; and firing the extruded honeycomb body to
obtain an alumina honeycomb structural body having .alpha. alumina
as a main crystal phase. Further, according to a first aspect of
the invention of a honeycomb regenerator, the honeycomb regenerator
comprises: at least one alumina honeycomb structural body mentioned
above, wherein a heating gas and a gas to be heated are alternately
passed therein so as to perform a heat-exchanging.
[0009] In the first aspect of the alumina honeycomb structural body
and the first aspect of the honeycomb regenerator, since an amount
of impurities is limited to not greater than 2 weight %, a scale of
steel does not react with the impurities in the alumina honeycomb
structural body so much and a life of the regenerator can be
prolonged, even if the regenerator is used in the steel heating
furnace. Moreover, in the first aspect of the method of
manufacturing the alumina honeycomb structural body, since use is
made of 97 weight %-70 weight % of .alpha. alumina and 3 weight
%-30 weight % of aluminum hydroxide as raw materials, it is
possible to obtain the alumina honeycomb structural body having an
excellent formability while maintaining high purity. Since
predetermined amount of aluminum hydroxide is used as raw
materials, it is possible to decrease porosity even under a low
temperature firing. Here, if an amount of .alpha. alumina exceeds
97 weight % and an amount of aluminum hydroxide is less than 3
weight %, it is difficult to obtain a formability increasing effect
due to the aluminum hydroxide. Moreover, if an amount of a alumina
is less than 70 weight % and an amount of aluminum hydroxide
exceeds 30 weight %, a shrinkage of the alumina honeycomb
structural body during the firing step becomes larger, and thus the
alumina honeycomb structural body is easily fractured during the
firing step. Further, an excess plasticity for the extrusion
operation is provided, and a shape retaining property for the
extrusion operation becomes worse. If the honeycomb structural body
having worse dimensional accuracy is used, a gap occurs between the
honeycomb structural bodies when they are stacked or combined, and
the heated exhaust gas and the air for firing are not used for
heat-exchanging and pass by a side wall of the honeycomb structural
body. Therefore, a thermal shock occurs and the honeycomb
structural body is easily fractured. Further, if a firing
temperature is set to not less than 1500.degree. C. preferably not
less than 1575.degree. C., it is possible to obtain preferable
porosity and crystal phase, and thus this firing temperature range
is preferable.
[0010] As a preferable embodiment of the first aspect of the
alumina honeycomb structural body, a porosity is not greater than
50%, preferably not greater than 15%, a thermal expansion
coefficient is not greater than 8.5.times.10.sup.-6/.degree. C.,
and a main crystal phase is .alpha. alumina, and, an amount of
impurities is not greater than 1 weight %. In both cases, it is
possible to increase effectively a corrosion resistance effect
according to the invention. As a means for densifying the alumina
honeycomb structural body, thereby increasing a corrosion
resistance performance, it is general to add yttrium oxide and
perform the firing under a non-oxidizing atmosphere at a high
temperature. However, yttrium oxide is expensive and a
manufacturing cost is also expensive since the firing under a
non-oxidizing atmosphere is performed. Therefore, the addition of
yttrium oxide is not adequate to the case wherein a large number of
the honeycomb structural bodies are used as the regenerator. This
invention is effective, because the alumina honeycomb structural
body is inexpensive and shows an excellent corrosion resistance
performance.
[0011] Moreover, as a preferable embodiment utilizing the first
aspect of the honeycomb regenerator, at least one pair of honeycomb
regenerators mentioned above, wherein one honeycomb regenerator
stores heat while the other honeycomb regenerator discharges heat,
and a heat-exchanging operation is performed by switching each
other. In this embodiment, it is possible to eliminate the problem
of short life due to a deterioration (hole plugging, fracture) of
the honeycomb regenerator originated from corrosion effectively,
particularly in the used at a temperature over 1000.degree. C., and
thus it is possible to reduce the running cost.
[0012] Further, it is preferable to construct the heating furnace
and the steel heating furnace by using the switching regenerative
burner mentioned above. In the case of constructing the heating
furnace, it is possible to prevent an increase of total cost due to
a deterioration of the honeycomb regenerator and also prevent an
increase of manufacturing cost of the substances to be heated,
effectively. In the case of constructing the steel heating furnace,
it is possible to eliminate the problem such that the honeycomb
regenerator is easily deteriorated since iron series elements are
unavoidably included in the exhaust gas of the steel heating
furnace, in addition to prevent the increase of total cost and the
increase of manufacturing cost as is the same as the heating
furnace. Moreover, since a life of the honeycomb regenerator can be
prolonged, it is possible to elongate a furnace stop cycle.
[0013] According to a second aspect of the invention of an alumina
honeycomb structural body, the alumina honeycomb structural body
comprises: not less than 98 weight % of alumina as a main
ingredient; a Na containing compound having 0.02 weight %-1.0
weight % of Na.sub.2O when converting it into oxide; and remainder
of impurities. Moreover, according to a second aspect of the
invention of a method of manufacturing the alumina honeycomb
structural body, the method comprises the step of: mixing 97 weight
%-70 weight % of .alpha. alumina, 3 weight %-30 weight % of
aluminum hydroxide, necessary amount of sodium source, forming
agents, and solvents to obtain a plastic substance; extruding the
plastic substance to obtain an extruded honeycomb body; and firing
the extruded honeycomb body to obtain an alumina honeycomb
structural body having .alpha. alumina as a main crystal phase.
Further, according to a second aspect of the invention of a
honeycomb regenerator, the honeycomb regenerator comprise: at least
one alumina honeycomb structural body including Na mentioned above,
wherein a heating gas and a gas to be heated are alternately passed
therein so as to perform a heat-exchanging.
[0014] In the second aspect of the alumina honeycomb structural
body and the second aspect of the honeycomb regenerator, since an
amount of Na containing compound is limited to 0.02-1.0 weight % of
Na2O when converting it into oxide, a part of Na, K and so on
contacted as incoming substances is caught up therein, and it shows
an effect for reducing a reaction with a scale and so on. Moreover,
since Na.sub.2O is included, it is possible to prevent a densifying
reaction easily even if the honeycomb structural body is
manufactured by a low temperature firing. If an amount of Na.sub.2O
is less than 0.02 weight %, the reaction reducing effect due to Na,
K and so on does not occur, and the densifying effect during the
manufacturing step does not appear. On the other hand, if an amount
of Na.sub.2O exceeds 1.0 weight %, an amount of caught up Na, K is
increased and a glass substance is generated, so that the reaction
to be reduced is adversely promoted. In addition, a thermal
expansion coefficient becomes larger, and thus the alumina
honeycomb structural body is easily fractured by a thermal shock.
Further, since an amount of Al.sub.2O.sub.3 as a main ingredient is
set to not less than 98 weight %, it is possible to promote a
chemical stability of alumina. If a large amount of impurities such
as SiO.sub.2, TiO.sub.2 and so on is included, the impurities are
reacted with substances such as Na.sub.2O, K and so on introduced
from the gas and a scale and so on, so that the honeycomb
structural body is fractured.
[0015] In the second aspect of the method of manufacturing the
alumina honeycomb structural body, since 97 weight %-70 weight % of
.alpha. alumina and 3 weight %-30 weight % of aluminum hydroxide
are used as raw materials, it is possible to obtain the alumina
honeycomb structural body having an excellent formability while
maintaining high purity. Here, if an amount of .alpha. alumina
exceeds 97 weight % and an amount of aluminum hydroxide is less
than 3 weight %, it is difficult to obtain a formability increasing
effect due to the aluminum hydroxide. Moreover, if an amount of
.alpha. alumina is less than 70 weight % and an amount of aluminum
hydroxide exceeds 30 weight %, a rapid shrinkage of the alumina
honeycomb structural body occurs during the firing step, and thus
the alumina honeycomb structural body is frequently fractured
during the firing step. Further, a plasticizing due to the aluminum
hydroxide becomes excess, and a complete formed body is not
obtained. Sodium source is not particularly limited, and it is
possible to use alumina and/or aluminum hydroxide containing high
Na.sub.2O. However, it is preferred to use sodium aluminate since
it is easy to use. If a firing temperature is set to not less than
1475.degree. C. preferably not less than 1550.degree. C., desired
porosity and crystal phase can be obtained.
[0016] Moreover, as a preferable embodiment utilizing the second
aspect of the honeycomb regenerator, a porosity is not greater than
50%, preferably not greater than 15%, a thermal expansion
coefficient is not greater than 8.5.times.10.sup.-6/.degree. C.,
and a main crystal phase is .alpha. alumina. In this case, an
effect for increasing corrosion resistance can be exerted
effectively.
[0017] Moreover, as a preferable embodiment utilizing the second
aspect of the honeycomb regenerator, at least one pair of honeycomb
regenerators mentioned above, wherein one honeycomb regenerator
stores heat while the other honeycomb regenerator discharges heat,
and a heat-exchanging operation is performed by switching each
other. In this embodiment, it is possible to eliminate the problem
of short life due to a deterioration (hole plugging, fracture) of
the honeycomb regenerator originated from corrosion effectively,
particularly in the used at a temperature over 1000.degree. C., and
thus it is possible to reduce the running cost.
[0018] Further, it is preferable to construct the heating furnace
and the steel heating furnace by using the switching regenerative
burner mentioned above. In the case of constructing the heating
furnace, it is possible to prevent an increase of total cost due to
a deterioration of the honeycomb regenerator and also prevent an
increase of manufacturing cost of the substances to be heated,
effectively. In the case of constructing the steel heating furnace,
it is possible to eliminate the problem such that the honeycomb
regenerator is easily deteriorated since iron series elements are
unavoidably included in the exhaust gas of the steel heating
furnace, in addition to prevent the increase of total cost and the
increase of manufacturing cost, as is the same as the heating
furnace. Moreover, since a life of the honeycomb regenerator can be
prolonged, it is possible to elongate a furnace stop cycle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic view showing one embodiment of an
alumina honeycomb structural body according to a first or a second
aspect of the invention;
[0020] FIG. 2 is a schematic view illustrating one embodiment of a
honeycomb regenerator utilizing the alumina honeycomb structural
body shown in FIG. 1; and
[0021] FIG. 3 is a schematic view depicting one embodiment of a
switching regenerative burner utilizing the honeycomb regenerator
according to the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0022] Hereinafter, an alumina honeycomb structural body according
to a first aspect and a second aspect of the invention, a method of
manufacturing the alumina honeycomb structural body, a honeycomb
regenerator, a switching regenerative burner, a heating furnace and
a method of heating the heating furnace will be explained.
[0023] FIG. 1 is a schematic view showing one embodiment of an
alumina honeycomb structural body according to a first or a second
aspect of the invention. In the embodiment shown in FIG. 1, an
alumina honeycomb structural body 1 is constructed in such a manner
that a plurality of through holes 3 arranged in parallel with each
other are formed in an outer wall 2 by means of cell walls 4. The
construction of the alumina honeycomb structural body 1 mentioned
above is the same as that of the known one.
[0024] An important feature of the first aspect of the alumina
honeycomb structural body 1 according to the invention is the use
of a ceramic consisting of not greater than 2 weight % preferably
not greater than 1 weight % of impurities and alumina as a main
ingredient. Moreover, as a preferable embodiment, a porosity of the
alumina honeycomb structural body 1 is not greater than 50%,
preferably not greater than 15%, a thermal expansion coefficient
thereof is not greater than 8.5.times.10.sup.-6/.degree. C., and a
main crystal phase thereof is .alpha. alumina.
[0025] The alumina honeycomb structural body of the first aspect of
the invention can be manufactured according to the following
manufacturing method. At first, 97 weight %-70 weight % of .alpha.
alumina, 3 weight %-30 weight % of aluminum hydroxide, and forming
agents are prepared. In this case, an amount of impurities of these
raw materials is low. Then, the thus prepared a alumina, aluminum
hydroxide and forming agents are mixed with a solvent and are
plasticized so as to obtain a batch. Then, the thus obtained batch
is extruded by using a die so as to obtain a honeycomb structural
formed body. Then, the thus obtained formed body is fired under an
oxidizing atmosphere at a temperature over 1500.degree. C.
preferably over 1575.degree. C. so as to obtain the alumina
honeycomb structural body 1 having a alumina as a main crystal
phase.
[0026] An important feature of the second aspect of the alumina
honeycomb structural body 1 according to the invention is the use
of a ceramic consisting of not less than 98 weight % of alumina as
a main ingredient, a compound including Na having 0.02 weight %-1.0
weight % of Na.sub.2O when converting it into oxide, and remainder
of impurities. Moreover, as a preferable embodiment, a porosity of
the alumina honeycomb structural body including Na is not greater
than 50%, preferably not greater than 15%, a thermal expansion
coefficient thereof is not greater than
8.5.times.10.sup.-6/.degree. C., and a main crystal phase thereof
is .alpha. alumina.
[0027] The alumina honeycomb structural body of the second aspect
of the invention can be manufactured according to the following
manufacturing method. At first, 97 weight %-70 weight % of .alpha.
alumina, 3 weight %-30 weight % of aluminum hydroxide, necessary
amount of sodium source, and forming agents are prepared. In this
case, an amount of impurities of these raw materials is low.
Moreover, sodium source is not particularly limited, but it is
preferred to use sodium aluminate since it is easy to use. Then,
the thus prepared .alpha. alumina, aluminum hydroxide, sodium
source and forming agents are mixed with a solvent and are
plasticized so as to obtain a batch. Then, the thus obtained batch
is extruded by using a die so as to obtain a honeycomb structural
formed body. Then, the thus obtained formed body is fired under an
oxidizing atmosphere at a temperature over 1475.degree. C.
preferably over 1550.degree. C. so as to obtain the alumina
honeycomb structural body 1 having .alpha. alumina as a main
crystal phase.
[0028] FIG. 2 is a schematic view showing one embodiment of a
honeycomb regenerator according to a first aspect or a second
aspect of the invention. In the embodiment shown in FIG. 2, a
honeycomb regenerator 11 is formed by stacking a plurality of
honeycomb structural bodies 1, 12 having a cuboid shape in such a
manner that flow passages thereof constructed by through holes 13
are aligned in one direction (in this case five honeycomb
structural bodies are stacked). In the embodiment shown in FIG. 2,
the alumina honeycomb structural bodies 1 according to the
invention mentioned above are arranged at an upper high temperature
portion to which an exhaust gas is contacted, and the honeycomb
structural bodies 12 made of cordierite, mullite, and so on having
the same construction as that of the embodiment show in FIG. 1 are
arranged at a lower low temperature portion other than the above
high temperature portion.
[0029] In the honeycomb regenerator 11 shown in FIG. 2, the alumina
honeycomb structural bodies 1 is used as the honeycomb structural
body at the high temperature portion to which a high temperature
exhaust gas is exposed. Therefore, it is possible to prevent a
deterioration of the honeycomb structural body at a high
temperature side even under a corrosion atmosphere, so that it is
possible to achieve a long life of the honeycomb regenerator
11.
[0030] FIG. 3 is a schematic view showing one embodiment of a
switching regenerative burner utilizing the honeycomb regenerator
11 according to the invention. In a switching regenerative burner
31 shown in FIG. 3, a numeral 21 is a combustion room, numerals
22-1 and 22-2 are a honeycomb regenerator having a construction
shown in FIG. 2, numerals 23-1 and 23-2 are a heat exchanging
apparatus constructed by the honeycomb regenerator 22-1 or 22-2,
and numerals 24-1 and 24-2 are a fuel supply inlet arranged at the
heat exchanging apparatus 23-1 or 23-2. In the embodiment shown in
FIG. 3, two heat exchanging apparatuses 23-1 and 23-2 are arranged
for the following reason. That is, when one of them stores heat by
flowing the high temperature exhaust gas, the other discharges heat
by flowing the gas to be heated, thereby performing the heat
exchanging operation effectively. Moreover, in the case such that
the switching regenerative burner is used for the heating furnace,
plural pairs of burners can be utilized. In this case, it is not
always necessary to apply the present invention to all the burner
pairs, and, it is effective even if the present invention is
applied to a part of the burner pairs to which a high temperature
gas is exposed.
[0031] As a combustion room of the heating furnace, it is possible
to utilize the combustion room 21 of the switching regenerative
burner 31 shown in FIG. 3. In this case, when the substances are
heated by using the heating furnace mentioned above, the honeycomb
regenerator 11 is not deteriorated. Therefore, it is possible to
reduce a total cost and a manufacturing cost of the substances to
be heated. Moreover, as a combustion room of the steel heating
furnace, it is possible to utilize the combustion room 21 of the
switching regenerative burner 31 shown in FIG. 3. In this case,
when the steel is heated by using the steel heating furnace
mentioned above, it is possible to prevent a deterioration of the
honeycomb regenerator 11 even under a condition such that the iron
series elements are unavoidably included in the exhaust gas, in
addition to the effects for reducing the total cost and the
manufacturing cost as is the same as the heating furnace mentioned
above.
[0032] Hereinafter, actual experiments of the alumina honeycomb
structural body according to the first aspect and the second aspect
of the invention will be explained.
[0033] Experiment 1 (Alumina Honeycomb Structural Body According to
the First Aspect of the Invention)
[0034] At first, as .alpha. alumina raw materials and aluminum
hydroxide raw materials, .alpha. alumina A, .alpha. alumina B,
.alpha. alumina C and .alpha. alumina D, each having a different
impurity amount as shown in the following Table 1, were prepared,
and aluminum hydroxide A, aluminum hydroxide B and aluminum
hydroxide C, each having a different impurity amount as shown in
the following Table 1, were also prepared. Here, the impurity
amount is indicated by a value obtained by converting it into
oxide, and it is calculated in such a manner that ignition loss
(Ig-Loss) and Al.sub.2O.sub.3 amount is subtracted from the total
amount.
1 TABLE 1 Name of raw materials Impurity amount (wt %) .alpha.
alumina A 1.0 .alpha. alumina B 1.5 .alpha. alumina C 2.3 .alpha.
alumina D 4.5 Aluminum hydroxide A 1.0 Aluminum hydroxide B 4.8
Aluminum hydroxide C 7.5
[0035] Then, the thus prepared various .alpha. alumina raw
materials and aluminum hydroxide raw materials were mixed at mixing
rates shown in the following Table 2 and were further mixed with
methyl cellulose and water for plasticizing so as to obtain various
batches. The thus obtained batches were extruded and then fired
under an oxidizing atmosphere so as to obtain honeycomb formed
bodies each having a condition such that a wall thickness is 0.43
mm and the number of cells is 15.5 cell/cm.sup.2. The thus obtained
honeycomb formed bodies were dried and then fired at firing
temperatures shown in the following Table 2 so as to obtain alumina
honeycomb structural bodies of sample Nos. T1-T16 according to the
examples of the invention and the comparative examples. Formability
during the manufacturing was examined, and alumina purity (impurity
density), porosity and thermal expansion coefficient (CTE) were
measured with respect to the thus obtained alumina honeycomb
structural bodies. Moreover, the regenerator for heat-exchanging
was manufactured by combining the alumina honeycomb structural
bodies, and an actual endurance test was performed in the steel
heating furnace. Then, an appearance and a dimension of the
regenerator after one year were measured, and a deterioration rate
was investigated. The results are shown in the following Table
2.
2TABLE 2 Aluminum .alpha. alumina hydroxide Firing blending .alpha.
blending Aluminum Alumina tem- Poro- CTE .times. Deterioration
status Sample amount alumina amount hydroxide purity perature Form-
sity 10.sup.-6 after one year use No. wt % brand wt % brand wt %
.degree. C. ability % .degree. C. (appearance) (dimension) Remarks
T-1 85 A 15 A 99 1600 good 10 8.0 no no deterioration shrinkage T-2
85 B 15 B 98 1600 good 8 8.2 little no deterioration shrinkage T-3
85 C 15 C 97 1600 good 7 8.6 powdering -- Comparative example T-4
85 D 15 C 95 1600 good 5 9.0 powdering -- Comparative example T-5
85 A 15 A 99 1590 good 15 8.0 no no deterioration shrinkage T-6 85
A 15 A 99 1580 good 20 8.0 no little deterioration shrinkage T-7 85
B 15 B 98 1580 good 17 8.3 little little deterioration shrinkage
T-8 85 A 15 A 99 1630 good 8 8.0 no no deterioration shrinkage T-9
85 A 15 A 99 1450 good 45 8.0 no large deterioration shrinkage T-10
85 A 15 A 99 1400 good 52 8.0 no shrinkage deterioration fracture
T-11 85 A 15 C 98 1600 good 3 9.1 little fracture deterioration
T-12 97 A 3 A 99 1600 good 18 8.0 no little deterioration shrinkage
T-13 70 A 30 A 99 1600 good 5 8.0 no no deterioration shrinkage
T-14 65 A 35 A 99 1600 bad 4 8.0 no no Comparative deterioration
shrinkage example T-15 60 A 40 A 99 -- not -- -- -- -- Comparative
formed example T-16 100 A 0 A 99 1600 bad 23 8.0 no no Comparative
deterioration shrinkage Example
[0036] From the results shown in Table 2, in the alumina honeycomb
structural body in which an amount of impurities is not greater
than 2 weight % i.e. an alumina purity exceeds 98 weight %, it is
understood that there is no fatal damage on the appearance and the
dimension. Moreover, among the examples according to the invention
in which an amount of impurities is not greater than 2 weight %, in
the examples shown by the sample Nos. T14-T16 in which a blending
amount of .alpha. alumina is not 97 weight %-70 weight % and a
blending amount of aluminum hydroxide is not 3 weight %-30 weight
%, it is understood that there is no deterioration but the
formability becomes worse. Further, if raw materials containing a
comparatively large amount of impurities as .alpha. alumina raw
material and/or aluminum hydroxide raw material are used, it is
understood that an alumina purity of the alumina honeycomb
structural body manufactured in the manner mentioned above cannot
be controlled in the range required by the present invention.
[0037] Experiment 2 (Alumina Honeycomb Structural Body According to
the Second Aspect of the Invention)
[0038] At first, as .alpha. alumina raw materials, aluminum
hydroxide raw materials and sodium source, .alpha. alumina A-E each
having Al.sub.2O.sub.3 amount and Na.sub.2O amount (as shown in the
following Table 3), aluminum hydroxide A-D each having
Al.sub.2O.sub.3 amount and Na.sub.2O amount (as shown in the
following Table 4) and sodium aluminate A having Al.sub.2O.sub.3
amount and Na.sub.2O amount (as shown in the following Table 5)
were prepared.
3TABLE 3 Alumina brand Al.sub.2O.sub.3 amount (weight %) Na.sub.2O
amount (weight %) .alpha. alumina A 99.1 0.02 .alpha. alumina B
99.3 0.20 .alpha. alumina C 98.3 0.02 .alpha. alumina D 98.9 0.20
.alpha. alumina E 99.3 <0.01
[0039]
4 TABLE 4 Al.sub.2O.sub.3 amount Na.sub.2O amount Aluminum
hydroxide brand (weight %) (weight %) Aluminum hydroxide A 99.1
0.02 Aluminum hydroxide B 99.4 0.20 Aluminum hydroxide C 97.2 0.02
Aluminum hydroxide D 98.5 0.20
[0040]
5 TABLE 5 Al.sub.2O.sub.3 amount Na.sub.2O amount Sodium source
(weight %) (weight %) Sodium aluminate A 69.2 29.5
[0041] Then, the thus prepared .alpha. alumina raw materials,
aluminum hydroxide raw materials and sodium source were mixed at
mixing rates shown in the following Table 6 for plasticizing so as
to obtain various batches. The thus obtained batches were extruded
so as to obtain honeycomb formed bodies each having a condition
such that a wall thickness is 0.43 mm and the number of cells is
15.5 cell/cm.sup.2. The thus obtained honeycomb formed bodies were
dried and then fired at firing temperatures shown in the following
Table 6 so as to obtain alumina honeycomb structural bodies
containing Na of sample Nos. 1-15 according to the examples of the
invention and the comparative examples. Formability during the
manufacturing was examined, and alumina purity (impurity density),
porosity and thermal expansion coefficient (CTE) were measured with
respect to the thus obtained alumina honeycomb structural bodies.
Moreover, the regenerator for heat-exchanging was manufactured by
combining the alumina honeycomb structural bodies, and an actual
endurance test was performed in the steel heating furnace. Then, an
appearance and a dimension of the regenerator after one year were
measured, and a deterioration rate was investigated. The results
are shown in the following Table 6. In Table 6, Al.sub.2O.sub.3
purity (amount) and Na.sub.2O amount as mixtures are also
shown.
6TABLE 6 Aluminum .alpha. alumina hydroxide Sodium blending .alpha.
blending Aluminum aluminate Sodium Al.sub.2O.sub.3 Na.sub.2O amount
alumina amount hydroxide amount aluminate purity amount No. wt %
brand wt % brand wt % brand wt % wt % 1 80 A 20 A 0 A 99.1 0.02 2
80 B 17.5 B 2.5 A 98.6 0.93 3 80 C 20 C 0 A 98.1 0.02 4 80 D 17.5 D
2.5 A 98.1 0.93 5 80 D 17.5 D 2.5 A 98.1 0.93 6 80 D 17.5 D 2.5 A
98.1 0.93 7 80 D 16.8 D 3.2 A 97.9 1.14 8 80 C 17.0 C 3.0 A 97.2
0.90 9 80 E 20.0 A 0 A 99.3 <0.01 10 80 E 20.0 A 0 A 99.3
<0.01 11 30 B 16.5 B 3.5 A 98.3 1.23 12 97 A 3.0 A 0 A 99.1 0.02
13 70 A 30.0 A 0 A 99.1 0.02 14 98 A 2.0 A 0 A 99.1 0.02 15 65 A
32.5 A 2.5 A 98.4 0.76 Firing tem- Poro- CTE .times. Deterioration
status perature Form- sity 10.sup.-6 after one year use No.
.degree. C. ability % .degree. C. (appearance) (dimension) Remarks
1 1600 good 10 8.0 no deterioration 2 1600 good 7 8.3 no
deterioration 3 1600 good 10 8.0 no deterioration 4 1600 good 5 8.4
no deterioration 5 1450 good 40 8.4 little deterioration 6 1400
good 50 8.4 little deterioration 7 1600 good 4 8.7 powdering
Comparative example 8 1600 good 5 8.4 powdering Comparative example
9 1600 good 15 8.0 large Comparative deterioration example 10 1400
good 60 8.0 powdering fracture Comparative example 11 1600 good 6
8.7 little fracture Comparative example 12 1600 good 18 8.0 no
deterioration 13 1600 good 5 8.0 no deterioration 14 1600 bad 20
8.0 no deterioration 15 1600 bad 4 8.4 no deterioration
[0042] From the results shown in Table 6, it is understood that, in
the examples in which an amount of Al.sub.2O.sub.3 is not less than
98 weight % and an amount of Na.sub.2O is 0.02-1.0 weight %, there
is no deterioration on the appearance and the dimension, and, even
if deteriorated, a deterioration rate is very small and it is no
problem. On the other hand, in the cases that an amount of
Al.sub.2O.sub.3 is less than 98 weight % or an amount of Na.sub.2O
is less than 0.02 weight % or exceeds 1.0 weight %, impurities such
as sodium and so on in the alumina honeycomb structural body is
reacted with the scale, and the alumina honeycomb structural body
is apparently deteriorated after one year endurance test.
[0043] Moreover, among the examples according to the invention, in
the examples shown by the sample Nos. 14-15 in which a blending
amount of .alpha. alumina is 97 weight %-70 weight % and a blending
amount of aluminum hydroxide is 3 weight %-30 weight %, it is
understood that there is no deterioration but the formability
becomes worse since the batch is plasticized excessively.
INDUSTRIAL APPLICABILITY
[0044] As is clearly understood from the above explanations,
according to the first aspect of the alumina honeycomb structural
body and the first aspect of the honeycomb regenerator, since an
amount of impurities is limited to not greater than 2 weight %, a
scale of steel does not react with the impurities in the alumina
honeycomb structural body so much and a life of the regenerator can
be prolonged, even if the regenerator is used in the steel heating
furnace. Moreover, in the first aspect of the method of
manufacturing the alumina honeycomb structural body, since use is
made of 97 weight %-70 weight % of .alpha. alumina and 3 weight
%-30 weight % of aluminum hydroxide as raw materials, it is
possible to obtain the alumina honeycomb structural body having an
excellent formability while maintaining high purity.
[0045] Moreover, according to the second aspect of the alumina
honeycomb structural body and the second aspect of the honeycomb
regenerator, since an amount of alumina as main ingredient is
limited to not less than 98 weight % and an amount of Na.sub.2O is
limited to 0.02-1.0 weight %, even in the regenerator used in the
steel heating furnace, a reaction of impurities in the alumina
honeycomb structural body due to the scale of steel is little, and
a life of the regenerator can be prolonged. Further, since an
amount of Na.sub.2O is limited to 0.02 weight %-1.0 weight %, Na, K
and so on in the gas are caught up and a reaction is reduced, so
that a life is prolonged. Furthermore, it is possible to make the
body dense even if a low temperature firing is performed during the
manufacturing step, make porosity small and improve a durability
against foreign substances.
* * * * *