U.S. patent application number 14/659686 was filed with the patent office on 2015-07-02 for methods and systems for recovery of co2 gas in cement-manufacturing facilities, and processes for manufacturing cement.
This patent application is currently assigned to Mitsubishi Materials Corporation. The applicant listed for this patent is Mitsubishi Materials Corporation. Invention is credited to Naohiro Higuchi, Takuya Komatsu, Hirokazu SHIMA, Yoshinori Takayama, Junzhu Wang.
Application Number | 20150183685 14/659686 |
Document ID | / |
Family ID | 43900015 |
Filed Date | 2015-07-02 |
United States Patent
Application |
20150183685 |
Kind Code |
A1 |
SHIMA; Hirokazu ; et
al. |
July 2, 2015 |
METHODS AND SYSTEMS FOR RECOVERY OF CO2 GAS IN CEMENT-MANUFACTURING
FACILITIES, AND PROCESSES FOR MANUFACTURING CEMENT
Abstract
An object of the present invention is to separate CO.sub.2 gas
generated in a cement-manufacturing facility in a high
concentration and recover the CO.sub.2 gas. The present invention
includes: feeding a cement material before calcination and a heat
medium which has a particle diameter larger than that of the cement
material and has been heated to the calcination temperature or
higher in a medium-heating furnace (14), to a mixing calciner (12);
and recovering the CO.sub.2 gas generated by the calcination of the
cement material. The heat medium circulates between the
medium-heating furnace and the mixing calciner. Another aspect of
the present invention includes: feeding a cement material before
calcination to a regenerative calciner (112) which has been heated
to the calcination temperature or higher and has stored heat
therein; and recovering the CO.sub.2 gas generated by the
calcination of the cement material.
Inventors: |
SHIMA; Hirokazu; (Ibaraki,
JP) ; Higuchi; Naohiro; (Ibaraki, JP) ;
Takayama; Yoshinori; (Ibaraki, JP) ; Komatsu;
Takuya; (Ibaraki, JP) ; Wang; Junzhu;
(Ibaraki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Materials Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Mitsubishi Materials
Corporation
Tokyo
JP
|
Family ID: |
43900015 |
Appl. No.: |
14/659686 |
Filed: |
March 17, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13389739 |
Feb 9, 2012 |
9028249 |
|
|
PCT/JP10/06047 |
Oct 12, 2010 |
|
|
|
14659686 |
|
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Current U.S.
Class: |
106/638 ;
422/164 |
Current CPC
Class: |
B01J 19/24 20130101;
C04B 7/00 20130101; F27D 17/002 20130101; C04B 7/365 20130101; Y02C
10/04 20130101; Y02P 40/18 20151101; B01J 2219/24 20130101; B01D
53/00 20130101; F27D 17/001 20130101 |
International
Class: |
C04B 7/00 20060101
C04B007/00; B01D 53/00 20060101 B01D053/00; B01J 19/24 20060101
B01J019/24 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 20, 2009 |
JP |
2009-241375 |
Nov 16, 2009 |
JP |
2009-261121 |
Claims
1. A process for manufacturing cement comprising preheating a
cement material with a first preheater, feeding the preheated
cement material to a cement kiln having an atmosphere in an inner
part held at high temperature and firing the fed cement material,
and further comprising recovering CO.sub.2 gas generated by
calcination of the cement material with a method for recovering
CO.sub.2 gas generated in a cement-manufacturing facility
comprising: feeding a non-calcined cement material, which has been
extracted from the first preheater, to a mixing calciner; heating a
heat medium, having a particle diameter larger than that of the
cement material, to a calcination temperature or higher in a
medium-heating furnace; feeding the heat medium to the mixing
calciner; calcining the non-calcined cement material with the heat
medium in the mixing calciner; separating a cement material which
has been calcined from the heat medium; feeding the cement material
which has been calcinedto a cement kiln; returning the heat medium
to the medium heating furnace and circulating the heat medium
between the medium-heating furnace and the mixing calciner; and
recovering CO.sub.2 gas generated by the calcining of the
non-calcined cement material in the mixing calciner.
2. A system for recovering CO.sub.2 gas generated in a
cement-manufacturing facility which is provided with a first
preheater for preheating a cement material and a cement kiln for
firing the cement material that has been preheated in the first
preheater, comprising: an extraction line for extracting a
non-calcined cement material from the first preheater; a mixing
calciner to which the non-calcined cement material that has been
extracted from the extraction line is introduced; a medium-heating
furnace for heating a heat medium having a particle diameter larger
than that of the non-calcined cement material, to a calcination
temperature of the non-calcined cement material or higher; a
circulation line for feeding the heat medium which has been heated
in the medium-heating furnace to the mixing calciner, and for
returning the heat medium to the medium-heating furnace from the
mixing calciner; a return line for returning one part of the cement
material which has been heated and calcined by the heat medium in
the mixing calciner, to the first preheater or to a cement kiln;
and a CO.sub.2 gas exhaust pipe for recovering CO.sub.2 gas
generated in the mixing calciner.
3. The system of claim 2, further comprising: a second preheater
which is provided independently from the first preheater and
preheats another non-calcined cement material; and a transfer pipe
for feeding the another non-calcined cement material before
calcination, which has been preheated in the second preheater, to
the mixing calciner, wherein the CO.sub.2 gas exhaust pipe
connected to the mixing calciner is a heating source of the second
preheater.
4. The system of claim 2, wherein the medium-heating furnace is a
moving bed having a heating source in a lower part.
5. A method for recovering CO.sub.2 gas generated in a
cement-manufacturing facility which preheats a cement material in a
first preheater, then feeds the preheated cement material to a
cement kiln having an atmosphere in an inner part held at high
temperature and fires the fed cement material, comprising: feeding
a non-calcined cement material, which has been extracted from a
first preheater, to a regenerative calciner which has been heated
to a calcination temperature or higher and has stored heat therein,
and calcining the fed non-calcined cement material; feeding the
cement material which has been calcined, to a cement kiln; and
recovering CO.sub.2 gas generated by the calcining of the
non-calcined cement material in a regenerative calciner.
6. The method of claim 5, further comprising: providing a plurality
of regenerative calciners; heating at least one of the regenerative
calciners to a calcination temperature or higher to store heat
therein, while at least one of the other regenerative calciners
calcines the cement material or alternately repeating the
calcination and heat storage in the plurality of regenerative
calciners; and recovering CO.sub.2 gas generated by the calcining
of the non-calcined cement material.
7. The method of claim 5, further comprising filling the
regenerative calciner with a heat medium having a particle diameter
larger than that of the non-calcined cement material.
8. The method of claim 7, wherein the heat medium is at least one
cement clinker obtained by firing the non-calcined cement material
in the cement kiln, silica stone or quicklime.
9. The method of claim 5, further comprising: feeding the
non-calcined cement material, which has been extracted from the
first preheater, and another non-calcined cement material, which
has been preheated in a second preheater independent from the first
preheater, to the regenerative calciner; using CO.sub.2 gas
generated in the regenerative calciner as a heating source of the
second preheater; and recovering resultant CO.sub.2 gas.
10. The method of claim 5, further comprising: fluidizing the
cement material with CO.sub.2 gas generated when the non-calcined
cement material is fed to the regenerative calciner and is calcined
therein, thereby making the cement material which has been calcined
overflow from the regenerative calciner; and feeding the
overflowing cement material to the cement kiln.
11. The method of claim 5, further comprising: entraining the
cement material with CO.sub.2 gas generated when the non-calcined
cement material is fed to the regenerative calciner and is
calcined; separating the cement material from the CO.sub.2 gas; and
feeding the cement material which has been calcined to the cement
kiln.
12. The method of claim 5, further comprising: returning one part
of the cement material which has been calcined in the regenerative
calciner to the first preheater.
13. The method of claim 12, further comprising: heat-exchanging one
part of the cement material with air; returning the cement material
which has cooled to the first preheater; and feeding heated air as
air for combustion in the regenerative calciner.
14. A system for recovering CO.sub.2 gas generated in a
cement-manufacturing facility which is provided with a first
preheater for preheating a cement material and a cement kiln for
firing the cement material that has been preheated in the first
preheater, comprising: an extraction line for extracting a
non-calcined cement material from the first preheater; a
regenerative calciner to which the cement material that has been
extracted from the extraction line is introduced and which heats
the cement material to a calcination temperature of the
non-calcined cement material or higher and stores heat therein; a
return line for returning one part of the cement material which has
been calcined in the regenerative calciner, to the first preheater
or a cement kiln; and a CO.sub.2-gas exhaust pipe for recovering
CO.sub.2 gas generated in the regenerative calciner
therethrough.
15. The system of claim 14, further comprising: a second preheater
which is provided independently from the first preheater and
preheats another non-calcined cement material; and a transfer pipe
for feeding the another non-calcined cement material, which has
been preheated in the second preheater, to the regenerative
calciner, wherein CO.sub.2 gas sent from the regenerative calciner
is a heating source of the second preheater.
16. The system of claim 14, wherein a plurality of the regenerative
calciners are provided.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of application Ser. No. 13/389,739,
filed Feb. 9, 2012, which is the National Stage of International
Application No. PCT/JP10/06047, filed Oct. 12, 2010, which claimed
priority to Japanese application no. 2009-241375, filed Oct. 20,
2009, and Japanese application no. 2009-261121, filed Nov. 16,
2009, of which all of the disclosures are incorporated herein by
reference in their entireties.
TECHNICAL FIELD
[0002] The present invention relates to methods and systems for
recovering CO.sub.2 gas in cement-manufacturing facilities, which
recover CO.sub.2 gas in a high concentration, which is generated
mainly when a cement material is calcined, and processes for
manufacturing the cement.
BACKGROUND ART
[0003] In recent years, attempts for reducing carbon dioxide
(CO.sub.2) gas which is the main cause of global warming are being
promoted around the world and in all industrial fields.
[0004] Incidentally, the cement industry, together with the
electric power industry, the steel industry and the like, is one of
the industries in which a large amount of CO.sub.2 gas is
discharged, and the amount occupies approximately 4% of the total
amount of CO.sub.2 gas discharged in Japan. For this reason,
reduction of the CO.sub.2 gas discharged in the cement industry
will result in largely contributing to the reduction of CO.sub.2
gas discharged in the whole of Japan.
[0005] FIG. 16 illustrates a general cement-manufacturing facility
in the above described cement industry. Reference numeral 1 in the
figure denotes a rotary kiln (cement kiln) for burning a cement
material.
[0006] In addition, in a kiln inlet part 2 in a left side of this
rotary kiln 1 in the figure, 2 sets of preheaters 3 for preheating
the cement material are provided in parallel, and also a main
burner 5 for heating the inner part is provided in a kiln outlet
part in a right side in the figure. In addition, reference numeral
6 in the figure denotes a clinker cooler for cooling a cement
clinker which has been burned.
[0007] Here, each of the preheater 3 is configured by a plurality
of stages of cyclones which are arranged in series in the vertical
direction. The cement material which has been fed to the cyclone in
the uppermost stage from a feed line 4 is preheated by a
high-temperature exhaust gas which is sent from the rotary kiln 1
and ascends from the lower part, as the cement material falls down
sequentially to the cyclones in the lower part, is extracted from
the cyclone in the second stage from the bottom, is sent to a
calciner 7, is heated and calcined by a burner 7a in the calciner
7, and is then introduced into the kiln inlet part 2 of the rotary
kiln 1 from the cyclone in the lowermost stage through a transfer
pipe 3a.
[0008] On the other hand, in the kiln inlet part 2, an exhaust gas
pipe 3b is provided for feeding a combustion exhaust gas which has
been discharged from the rotary kiln 1 to the cyclone in the
lowermost stage. The above described exhaust gas which has been
sent to the cyclone is sequentially sent to the cyclones in the
upper part, preheats the above described cement material, and
finally is exhausted by an exhaust fan 9 from the upper part of the
cyclone in the uppermost stage through an exhaust line 8.
[0009] In the cement-manufacturing facility having such a
structure, a cement clinker is manufactured by firstly preheating
limestone (CaCO.sub.3) contained as a main raw material of the
cement material with the preheater 3, then calcining the limestone
in the calciner 7 and the cyclone in the lowermost stage of the
preheater 3, burning the calcined limestone in the rotary kiln 1
under an atmosphere in a high temperature of approximately
1,450.degree. C.
[0010] In this calcination process, a chemical reaction occurs
which is expressed by CaCO.sub.3.fwdarw.CaO+CO.sub.2.uparw., and
CO.sub.2 gas is generated (generation of CO.sub.2 gas originating
in cement material). The concentration of the CO.sub.2 gas
originating in the cement material is theoretically 100%. In
addition, CO.sub.2 gas is generated also by the combustion of a
fossil fuel (generation of CO.sub.2 gas originating in fuel), as a
result of the combustion of the fossil fuel in the main burner 5 in
order to keep the atmosphere in the above described rotary kiln 1
at the above described high temperature. Here, the exhaust gas sent
from the main burner 5 contains much N.sub.2 gas in the air for
combustion, and accordingly the concentration of CO.sub.2 gas which
originates in the fuel and is contained in the exhaust gas is as
low as approximately 15%.
[0011] As a result, there coexist the above described CO.sub.2 gas
which has high concentration and originates in the cement material
and the above described CO.sub.2 which has low concentration and
originates in the fuel, in the exhaust gas to be discharged from
the above described cement kiln, and accordingly there has been a
problem that though a large amount of the CO.sub.2 is discharged,
the concentration of the CO.sub.2 is approximately 30 to 35% and
the CO.sub.2 gas is hard to be recovered.
[0012] On the other hand, though there are a liquid recovery
method, a membrane separation method and a solid adsorption method
in the methods for recovering CO.sub.2 gas, which are being
currently developed, any method has a problem that the recovering
cost is still extremely high.
[0013] In addition, a method of separating/recovering CO.sub.2
which has been discharged from a discharging source and is low
concentration, increasing the concentration to approximately 100%,
liquefying the CO.sub.2 and then storing the liquefied CO.sub.2 in
the ground and the like have been proposed as methods for
preventing global warming due to CO.sub.2 discharged from the above
described cement-manufacturing facilities, but have not been
realized similarly to the above recovery methods because the cost
for separating/recovering the CO.sub.2 is high.
[0014] On the other hand, an apparatus for producing and recovering
CO.sub.2 gas has been proposed in the following Patent Literature 1
as an apparatus for recovering CO.sub.2 gas generated in the step
of burning the limestone as CO.sub.2 gas having high utilization
value and a high purity. The apparatus includes a decomposition
reaction tower to which limestone is fed, a reheating tower to
which quicklime (CaO) is fed as a heat medium and which also heats
the quicklime to the calcination temperature of the limestone or
higher with a combustion gas, and a connecting pipe which connects
the decomposition reaction tower with the reheating tower.
[0015] In addition, the above described conventional recovering
apparatus has such a structure as to feed the quicklime which has
been heated in the reheating tower to the decomposition reaction
tower through the connecting pipe to form a fluidized bed, burn the
limestone thereby to produce CO.sub.2 gas in the decomposition
reaction tower, also discharge one part of thereby produced
quicklime, send another part of the quicklime to the reheating
tower through the connecting pipe again, and reheating the sent
quicklime therein.
[0016] Thus, the above described apparatus for producing and
recovering CO.sub.2 gas can prevent CO.sub.2 gas generated through
the decomposition reaction of the limestone and the combustion
exhaust gas generated due to heating of the heat medium from mixing
with each other, by separating the decomposition reaction tower
which is a place for conducting the decomposition reaction of the
limestone therein from the reheating tower which is a place for
generating heat quantity necessary for the decomposition reaction
therein, and accordingly is considered to be capable of recovering
CO.sub.2 gas having high concentration from the decomposition
reaction tower.
CITATION LIST
Patent Literature
[0017] Patent Literature 1: Japanese Patent Laid-Open No.
57-67013
SUMMARY OF INVENTION
[0018] If it is intended to manufacture cement by using CaO
produced in the apparatus for producing and recovering the CO.sub.2
gas disclosed in the above described Patent Literature 1, it is
necessary to burn limestone in the above described producing and
recovering apparatus, to further add another cement material such
as clay which includes SiO.sub.2, Al.sub.2O.sub.3 and
Fe.sub.2O.sub.3 to the burned limestone, and to burn the mixture in
a cement kiln. For this reason, it becomes necessary to mill the
raw material in two lines independently, which causes a problem of
requiring a large scale facility.
[0019] In addition, as is illustrated in FIG. 17, the temperature
of causing the calcination reaction of the limestone generally
rises rapidly as the concentration of the CO.sub.2 gas in the
atmosphere increases, and when the concentration of the CO.sub.2
gas approaches 100% (equivalent to partial pressure of 1 atm under
atmospheric pressure (1 atm)), the temperature reaches a
temperature exceeding 860.degree. C. For this reason, in order to
increase the recovery rate of the CO.sub.2 gas, it is necessary to
heat the limestone to excessively high temperature, which causes a
problem of causing a steep rise in a fuel cost.
[0020] In addition, the above described apparatus for producing and
recovering the CO.sub.2 gas uses the quicklime as a heat medium and
heats the limestone by this quicklime to calcine the limestone, and
accordingly needs to heat the above described quicklime to the
calcination temperature of the limestone or higher, specifically,
1,000.degree. C. or higher in the reheating tower. As a result, a
powder such as the quicklime flowing in the decomposition reaction
tower or in the reheating tower tends to be easily solidified,
which causes also a problem of deposition and blockage in the
connecting pipe or the like, and results in being unoperatable.
[0021] The present invention has been made in view of such
circumstances, and an object is to provide methods and systems for
recovering CO.sub.2 gas in cement-manufacturing facilities, which
can separate and recover CO.sub.2 gas generated in the
cement-manufacturing facilities in a high concentration by
effectively using a heating source in the cement-manufacturing
facilities, and processes for manufacturing the cement.
[0022] (1) First to Tenth Aspects of the Present Invention
[0023] In order to solve the above described objects, the first
aspect of the present invention is a method for recovering CO.sub.2
gas generated in a cement-manufacturing facility which preheats a
cement material in a first preheater, then feeds the preheated
cement material to a cement kiln having an atmosphere in an inner
part held at high temperature and burns the fed cement material,
includes: feeding the cement material before calcination, which has
been extracted from the first preheater, to a mixing calciner; also
heating a heat medium having a particle diameter larger than that
of the cement material, to the calcination temperature or higher in
a medium-heating furnace; then feeding the heat medium to the
mixing calciner; calcining the cement material before calcination
with the heat medium in the mixing calciner; then separating the
cement material which has been calcined, from the heat medium;
feeding the cement material which has been calcined, to the cement
kiln; also returning the heat medium to the medium-heating furnace
again and circulating the heat medium between the medium-heating
furnace and the mixing calciner; and recovering the CO.sub.2 gas
generated by the calcination of the cement material in the mixing
calciner.
[0024] For information, the above described calcination temperature
means a temperature at which a reaction of decomposing limestone,
in other words, CaCO.sub.3 (calcium carbonate) into CaO (calcium
oxide) and CO.sub.2 occurs.
[0025] The second aspect of the present invention is the method for
recovering the CO.sub.2 gas according to the first aspect, wherein
the heat medium is a cement clinker obtained by burning the cement
material in the cement kiln.
[0026] The third aspect of the present invention is the method for
recovering the CO.sub.2 gas according to any one of the first and
the second aspects, further including: feeding the cement material
before calcination, which has been extracted from the first
preheater, and another cement material before calcination, which
has been preheated in a second preheater independent from the first
preheater, to the mixing calciner; using the CO.sub.2 gas generated
in the mixing calciner as a heating source of the second preheater;
and then recovering the resultant CO.sub.2 gas.
[0027] The fourth aspect of the present invention is the method for
recovering the CO.sub.2 gas according to any one of the first to
third aspects, further including: extracting the heat medium from
the bottom part of the mixing calciner; returning the heat medium
to the upper part of the mixing calciner; thereby bringing the heat
medium into contact with the CO.sub.2 gas discharged from the
mixing calciner to separate the cement material which has deposited
on the heat medium, from the heat medium; and then returning the
resultant heat medium to the medium-heating furnace.
[0028] Furthermore, the fifth aspect of the present invention is
the method for recovering the CO.sub.2 gas according to any one of
the first to fourth aspects, further including returning one part
of the cement material which has been calcined in the mixing
calciner to the first preheater.
[0029] In addition, the sixth aspect of the present invention is
the method for recovering the CO.sub.2 gas according to the fifth
aspect, further including: heat-exchanging one part of the cement
material with air and returning the cement material which has
cooled to the first preheater; and also feeding the heated air as
air for combustion in the medium-heating furnace.
[0030] Furthermore, the seventh aspect of the present invention is
a process for manufacturing cement by preheating a cement material
with a first preheater, feeding the preheated cement material to a
cement kiln having the atmosphere in an inner part held at high
temperature and firing the fed cement material therein, including
recovering CO.sub.2 gas generated by the calcination of the cement
material, with the method for recovering CO.sub.2 gas in the
cement-manufacturing facility according to any one of the first to
sixth aspects.
[0031] Subsequently, the eighth aspect of the present invention is
a facility for recovering CO.sub.2 gas generated in a
cement-manufacturing facility which is provided with a first
preheater for preheating a cement material and a cement kiln for
burning the cement material that has been preheated in the first
preheater, including: an extraction line for extracting a cement
material before calcination from the first preheater; a mixing
calciner to which the cement material that has been extracted from
the extraction line is introduced; a medium-heating furnace for
heating a heat medium having a particle diameter larger than that
of the cement material, to the calcination temperature of the
cement material or higher; a circulation line for feeding the heat
medium which has been heated in the medium-heating furnace to the
mixing calciner, and also returning the heat medium to the
medium-heating furnace from the mixing calciner; a return line for
returning the cement material which has been heated and calcined by
the heat medium in the mixing calciner to the first preheater or
the cement kiln; and a CO.sub.2 gas exhaust pipe for recovering the
CO.sub.2 gas generated in the mixing calciner therethrough.
[0032] In addition, the ninth aspect of the present invention is
the facility for recovering the CO.sub.2 gas according to the
eighth aspect, further including: a second preheater which is
provided independently from the first preheater and preheats
another cement material; and a transfer pipe for feeding the
another cement material before calcination, which has been
preheated in the second preheater, to the mixing calciner, wherein
the CO.sub.2 gas exhaust pipe connected to the mixing calciner is
introduced as a heating source of the second preheater.
[0033] Furthermore, the tenth aspect of the present invention is
the facility for recovering the CO.sub.2 gas according to any one
of the eighth and the ninth aspects, wherein the medium-heating
furnace is a moving bed having a heating source in the lower part
thereof.
[0034] In the recovery methods according to the first to sixth
aspects, the process for manufacturing the cement according to the
seventh aspect, and the recovery systems according to the eighth to
tenth aspects of the present invention, the cement material before
calcination, which has been extracted from the first preheater, is
fed into the mixing calciner, and also the heat medium which has
been heated to the calcination temperature of the cement material
or higher in the medium-heating furnace is fed to the above
described mixing calciner. Thereby, the above described cement
material before calcination is calcined with the above described
heat medium, in the above described mixing calciner.
[0035] As a result, the inner part of the above described mixing
calciner is filled with CO.sub.2 gas generated by the calcination
of the cement material, and the concentration of the CO.sub.2 gas
becomes approximately 100%. Thus, the above described recovery
method or recovery system can recover CO.sub.2 gas which is
discharged from the above described mixing calciner and has the
concentration of approximately 100%, from the CO.sub.2 gas exhaust
pipe.
[0036] In addition, particularly in the above described third or
ninth aspect, the high-temperature CO.sub.2 gas which has been
generated in the above described mixing calciner, is sent to the
second preheater independent from the first preheater, is used for
preheating the cement material, and then can be recovered in the
as-is state from the exhaust gas pipe.
[0037] For information, the inner part of the above described
mixing calciner becomes an atmosphere containing such a high
concentration as nearly 100% of CO.sub.2 gas, and accordingly the
calcination temperature of the cement material becomes high.
However, the cement material contains clay, silica stone and a raw
material of iron oxide, in other words, SiO.sub.2, Al.sub.2O.sub.3
and Fe.sub.2O.sub.3 together with the limestone (CaCO.sub.3).
[0038] The above described cement material causes the reactions
expressed by the following formulae in an atmosphere at a
temperature of approximately 800 to900.degree. C.
[0039] reactions expressed by:
2CaCO.sub.3+SiO.sub.2.fwdarw.2CaO.SiO.sub.2+2CO.sub.2.uparw.
(1)
2CaCO.sub.3+Fe.sub.2O.sub.3.fwdarw.2CaO.Fe.sub.2O.sub.3+2CO.sub.2.uparw.
(2)
CaCO.sub.3+Al.sub.2O.sub.3.fwdarw.CaO.Al.sub.2O.sub.3+CO.sub.2.uparw.
(3)
[0040] The components are eventually converted to alite
(3CaO.SiO.sub.2) and belite (2CaO.SiO.sub.2) which are calcium
silicate compounds constituting the cement clinker, and an
aluminate phase (3CaO.Al.sub.2O.sub.3) and a ferrite phase
(4CaO.Al.sub.2O.sub.3.Fe.sub.2O.sub.3) which are interstitial
phases.
[0041] At this time, the above described reactions can be caused at
lower temperatures even when the partial pressure of the CO.sub.2
gas illustrated in a vertical axis becomes high, as is viewed in a
graph of a reaction temperature of the above described formula (1)
illustrated in FIG. 3, a graph of a reaction temperature of the
above described formula (2) illustrated in FIG. 4 and a graph of a
reaction temperature of the above described formula (3) illustrated
in FIG. 5.
[0042] Furthermore, in the above described cement material,
SiO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3 and other trace
components, which are brought from other raw materials than the
limestone such as the silica stone and the clay, not only cause the
reactions expressed by the above described formulae (1) to (3), but
also function as a mineralizer, and promote thermal decomposition
of calcium carbonate. Accordingly, both a start temperature and an
end temperature of the thermal decomposition reaction are lowered
in comparison with the case when calcium carbonate is solely
calcined, as is illustrated in FIG. 6. Incidentally, FIG. 6
illustrates a result of having confirmed the transition of the
above described thermal decomposition reaction from a change of
weight obtained when a sample of the above described cement
material (raw material) and a sample of the above described single
limestone (CaCO.sub.3) are heated respectively at a heating rate of
10 K/sec which is close to the heating rate in a general
cement-manufacturing facility.
[0043] Here, the following is considered as one of the reasons why
both the start temperature and the end temperature of the thermal
decomposition reaction are lowered by the presence of the above
described mineralizer, in comparison with the case in which the
single calcium carbonate is calcined.
[0044] Specifically, when activity is represented by "a" and an
equilibrium constant in a reaction formula of
CaCO.sub.3=CaO+CO.sub.2 is represented by K,
[0045] in the formula of P.sub.CO2=(a.sub.CaCO3/a.sub.CaO)K,
[0046] the value of a.sub.CaO becomes less than 1, because an
activity a of a solid is generally 1 regardless of the type of the
solid as long as the solid is a pure substance, but in the case of
calcium oxide (CaO), other source materials (in other words, the
above described mineralizer) dissolve into CaO formed after the
calcium carbonate (CaCO.sub.3) has been thermally decomposed. It is
considered that as a result, P.sub.CO2 in the above formula becomes
high, the temperature at which the P.sub.CO2 becomes 1 atm is
lowered, and the calcination is further promoted. For information,
the a.sub.caco3 is a value inherent to the type and producing
district of the limestone, and is not affected by the other
components in the raw material.
[0047] Because of the above description, the methods according to
the present invention can secure a desired recovery amount of
CO.sub.2 gas, even when an operation temperature in the mixing
calciner is lowered. Besides, the methods include heating and
calcining the cement material in the mixing calciner, by using a
heat medium which has a large particle diameter different from that
of the cement material and accordingly has an extremely small
specific surface area, accordingly suppress the sticking or
fusion-bonding among the above described heat media or between the
heat medium and a furnace wall or an inner wall of a chute even
when the above described heat medium is heated to 1,000.degree. C.
which is the calcination temperature or higher in the
medium-heating furnace, and can suppress the occurrence of a
coating trouble and the like.
[0048] In addition, the uncalcined cement material to be introduced
into the mixing calciner is preheated by the first preheater in the
cement-manufacturing facility, in a similar process to a normal
process of manufacturing a cement, and also the above described
another cement material in the above described third or ninth
aspect is preheated in the second preheater by the high-temperature
CO.sub.2 gas discharged from the mixing calciner.
[0049] Furthermore, the systems according to the present invention
use the heat medium while circulating the heat medium between the
mixing calciner and the medium-heating furnace, accordingly can
secure a large heat quantity in the mixing calciner, and can
selectively recover CO.sub.2 in high concentration, which is
generated during calcination and originates in the raw material,
without adding a new thermal energy to the existing
cement-manufacturing facility.
[0050] In addition, the systems include returning the
high-temperature cement material which has been sufficiently
calcined in the mixing calciner to the cement kiln, and accordingly
can reduce fuel necessary for burning a cement material in the
cement kiln. As a result, the systems can use a rotary kiln which
has shorter longitudinal dimensions than those of conventional
ones, a fluidized bed or a spouted bed as a cement kiln, and can
also further save the space, the facility cost or the energy.
[0051] Furthermore, in the third or the ninth aspect of the present
invention, the heat quantity generated when the CO.sub.2 gas is
generated is used for preheating the above described another cement
material, and accordingly the thermal efficiency of the whole
system can be further enhanced.
[0052] Here, the above described usable heat medium includes a
cement clinker other than a ceramic material such as quicklime
(CaO), silica stone (SiO.sub.2) and alumina (Al.sub.2O.sub.3) which
have heat resistance to heating temperature in the medium-heating
furnace and abrasion resistance when having been mixed with the
cement material, and a metallic material such as a heat-resistant
alloy. Incidentally, the quicklime has advantages of having such a
high melting point as 2,500.degree. C., and of resisting being
fusion-bonded. In addition, the quicklime does not cause a harmful
effect even when the fine powder generated by being gradually worn
out while being circulated as the heat medium is mixed into the raw
material, because the fine powder is one of the components of the
cement material. Furthermore, even when the limestone is charged
into the mixing calciner, a heat-medium feed pipe or a bucket
elevator in place of the quicklime, the limestone is decarbonized
to be formed into the quicklime, and can show a similar functional
effect to the case of the above described quicklime. At this time,
when the above described limestone is charged into the mixing
calciner or the heat-medium feed pipe, CO.sub.2 generated during
calcination can be recovered, which is preferable.
[0053] In addition, silica stone has advantages of having such a
high melting point as 1,700.degree. C. to resist being
fusion-bonded, having an extremely high hardness to resist being
worn out, and consequently requiring only a small amount of silica
stone to be supplemented as the heat medium. Furthermore, the
silica stone does not cause inconvenience even when the fine powder
which has been generated by being gradually worn out in the
circulation step is mixed into the raw material, because the fine
powder is similarly one of the components of the cement
material.
[0054] In addition, when a cement clinker which has been obtained
by burning the calcined material in the above described cement
kiln, is hard and has a particle diameter much larger than that of
the cement material is used as in the second aspect of the present
invention, the cost is economical, and the cement clinker also does
not give adverse effect on the operation of the cement kiln and the
quality of the cement as a product, even if having been brought
into contact with the cement material and having been worn out,
because the composition of the worn powder has been already
adjusted, and the worn powder having the same quality as that of
the cement material results in being sent to the cement kiln
again.
[0055] In addition, when the heat medium and the cement material
are mixed to each other in the mixing calciner and the heat is
exchanged with each other, the cement material deposits on the
surface of the heat medium having a particle diameter larger than
that of the cement material. Then, as in the fourth aspect of the
present invention, it is preferable to extract the above described
heat medium once from the bottom part of the mixing calciner,
return the heat medium to the upper part of the mixing calciner,
thereby bring the above described heat medium into contact with the
CO.sub.2 gas discharged from the mixing calciner to separate the
deposited cement material, and then return the heat medium to the
above described medium-heating furnace.
[0056] By the way, a combustion exhaust gas which is sent to the
first preheater from the cement kiln to preheat the cement material
contains N.sub.2 gas and also CO.sub.2 gas (generated CO.sub.2 gas
originating in fuel) which has been generated as a result of the
combustion of a fossil fuel.
[0057] Then, as in the fifth aspect of the present invention, if
one part of the cement material containing much CaO by being
calcined in the above described mixing calciner is returned to the
first preheater, the above described CaO comes in contact with the
combustion exhaust gas, causes a chemical reaction expressed by
CaO+CO.sub.2.fwdarw.CaCO.sub.3, and can adsorb the CO.sub.2 gas
originating in the fuel in the above described exhaust gas.
[0058] Thus produced CaCO.sub.3 is sent to the mixing calciner
again together with the cement material and is calcined there.
[0059] Because of this, it becomes possible to recover also the
CO.sub.2 gas originating in the fuel in addition to the CO.sub.2
gas which is generated when the cement material is calcined and
originates in the cement material.
[0060] Here, the calcined cement material which has been discharged
from the mixing calciner has high temperature, and the above
described reaction of CaO+CO.sub.2.fwdarw.CaCO.sub.3 is an
exothermic reaction. Because of this, it is preferable as in the
sixth aspect of the present invention to heat-exchange one part of
the above described cement material which has been discharged from
the mixing calciner with air once, lower the temperature of the
cement material, then return the cooled cement material to the
above described first preheater, and on the other hand, to feed the
above described heated air as air for combustion in the
medium-heating furnace, because thermal energy in the system can be
further effectively used.
[0061] Furthermore, in the tenth aspect of the present invention, a
movable tank having a heating source in the lower part thereof is
used as the above described medium-heating furnace. Because of
this, a heating gas such as a combustion gas flows towards the
upper part of the moving bed from the bottom part thereof, and
thereby the above described heat medium in the bottom part becomes
the highest temperature. Then, by feeding the heat medium from the
above described bottom part of the moving bed sequentially to the
mixing calciner, a thermal energy necessary for heating can be
reduced compared to the case in which the whole heat medium in the
medium-heating furnace is heated to a desired temperature. In
addition, because the heating gas is brought into contact with the
heat medium of approximately 900.degree. C. which has been
discharged from the mixing calciner in the upper part of the
furnace and is heat-exchanged with the heat medium, the gas
temperature to be discharged can be lowered to approximately
1,000.degree. C.
[0062] (2) Eleventh to Twenty Second Aspects of the Present
Invention
[0063] Furthermore, in order to solve the above described problems,
the eleventh aspect of the present invention is a method for
recovering CO.sub.2 gas generated in a cement-manufacturing
facility which preheats a cement material in a first preheater,
then feeds the preheated cement material to a cement kiln having an
atmosphere in an inner part held at high temperature and burns the
fed cement material, including: feeding the cement material before
calcination, which has been extracted from the first preheater, to
a regenerative calciner which has been heated to the calcination
temperature or higher and has stored heat therein, and calcining
the fed cement material therein; feeding the cement material which
has been calcined, to the cement kiln; and also recovering CO.sub.2
gas generated by the calcination of the cement material in the
regenerative calciner.
[0064] The above described calcination temperature means a
temperature at which a reaction occurs through which limestone, in
other words, CaCO.sub.3 (calcium carbonate) is decomposed into CaO
(calcium oxide) and CO.sub.2.
[0065] In addition, the twelfth aspect of the present invention is
the method for recovering CO.sub.2 gas according to the eleventh
aspect, further including: providing the plurality of the
regenerative calciners; heating at least one of the regenerative
calciners to the calcination temperature or higher to store heat
therein, while at least one of the other regenerative calciners
calcines the cement material; alternately repeating the calcination
and heat storage in the plurality of the regenerative calciners;
and thereby recovering the CO.sub.2 gas generated by the
calcination of the cement material.
[0066] The thirteenth aspect of the present invention is the method
for recovering CO.sub.2 gas according to any one of the eleventh
and the twelfth aspects, further including filling the regenerative
calciner with a heat medium having a larger particle diameter than
that of the cement material.
[0067] Furthermore, the fourteenth aspect of the present invention
is the method for recovering CO.sub.2 gas according to the
thirteenth aspect, wherein the heat medium is any one of a cement
clinker obtained by burning the raw material in the cement kiln,
silica stone or quicklime.
[0068] In addition, the fifteenth aspect of the present invention
is the method for recovering the CO.sub.2 gas according to any one
of the eleventh to fourteenth aspects, further including: feeding
the cement material before calcination, which has been extracted
from the first preheater, and another cement material before
calcination, which has been preheated in a second preheater
independent from the first preheater, to the regenerative calciner;
using CO.sub.2 gas generated in the regenerative calciner as a
heating source of the second preheater; and then recovering the
resultant CO.sub.2 gas.
[0069] The sixteenth aspect of the present invention is the method
for recovering the CO.sub.2 gas according to any one of the
eleventh to fifteenth aspects, further including: fluidizing the
cement material with CO.sub.2 gas generated when the cement
material is fed to the regenerative calciner and is calcined
therein; thereby making the cement material which has been calcined
overflow from the regenerative calciner; and feeding the
overflowing cement material to the cement kiln.
[0070] Furthermore, the seventeenth aspect of the present invention
is the method for recovering the CO.sub.2 gas according to any one
of the eleventh to fifteenth aspects, further including: making
CO.sub.2 gas generated when the cement material is fed to the
regenerative calciner and is calcined therein entrain the cement
material; separating the cement material from the CO.sub.2 gas with
particle-separating means; and feeding the cement material which
has been calcined, to the cement kiln.
[0071] In addition, the eighteenth aspect of the present invention
is the method for recovering the CO.sub.2 gas according to any one
of the eleventh to seventeenth aspects, further including:
returning one part of the cement material which has been calcined
in the regenerative calciner to the first preheater.
[0072] The nineteenth aspect of the present invention is the method
for recovering the CO.sub.2 gas according to the eighteenth aspect,
further including: heat-exchanging one part of the cement material
with air; returning the cement material which has cooled to the
first preheater; and feeding the heated air as air for combustion
in the regenerative calciner.
[0073] Furthermore, the twentieth aspect of the present invention
is a facility for recovering CO.sub.2 gas generated in a
cement-manufacturing facility provided with a first preheater for
preheating a cement material and a cement kiln for burning the
cement material which has been preheated in the first preheater,
including: an extraction line for extracting the cement material
before calcination from the first preheater; a regenerative
calciner to which the cement material that has been extracted from
the extraction line is introduced and which heats the cement
material to the calcination temperature of the cement material or
higher and stores heat therein; a return line for returning one
part of the cement material which has been calcined in the
regenerative calciner, to the first preheater or the cement kiln;
and a CO.sub.2 gas exhaust pipe through which the CO.sub.2 gas
generated in the regenerative calciner is recovered.
[0074] In addition, the twenty first aspect of the present
invention is the facility for recovering the CO.sub.2 gas according
to the twentieth aspect, further including: a second preheater
which is provided independently from the first preheater and
preheats another cement material; and a transfer pipe for feeding
the another cement material before calcination, which has been
preheated in the second preheater, to the regenerative calciner
therethrough, wherein the CO.sub.2 gas sent from the regenerative
calciner is introduced as a heating source of the second
preheater.
[0075] The twenty second aspect of the present invention is the
facility for recovering the CO.sub.2 gas according to the twentieth
aspect or the twenty first aspect, wherein the facility for
recovering the CO.sub.2 gas has the plurality of the regenerative
calciners provided therein.
[0076] In the above described recovery methods of the eleventh to
nineteenth aspects and the above described recovery systems of the
twentieth to the twenty second aspects of the present invention,
the cement material before calcination, which has been extracted
from the first preheater, is fed to the regenerative calciner which
heats the charged heat medium to the calcination temperature or
higher and stores heat therein. Thereby, in the above described
regenerative calciner, the above described cement material before
calcination is calcined by the above described heat medium.
[0077] As a result, the inner part of the above described
regenerative calciner is filled with CO.sub.2 gas generated by the
calcination of the cement material, and the concentration of the
CO.sub.2 gas becomes approximately 100%. Thus, the above described
recovery method or recovery system can recover the CO.sub.2 gas
which is discharged from the above described regenerative calciner
and has the concentration of approximately 100%, from the CO.sub.2
gas exhaust pipe.
[0078] Furthermore, in the twelfth aspect of the present invention,
the cement material before calcination, which has been extracted
from the first preheater, is calcined with the use of the plurality
of the regenerative calciners, and accordingly the calciner and the
medium-heating furnace can be integrated. For this reason, it
becomes unnecessary to take out the high-temperature heat medium
from the medium-heating furnace. As a result, it is possible to
reduce a cost for the facility because of having no need to provide
a facility such as a bucket elevator, and it is also possible to
suppress a problem of handling of a high-temperature substance as
much as possible and a heat loss because of not transferring the
heat medium. Furthermore, the twelfth aspect includes using the
above described plurality of the regenerative calciners,
accordingly can shorten a period of time for heating the medium and
a period of time for calcination, and can efficiently recover the
CO.sub.2 gas.
[0079] In addition, particularly in the fifteenth aspect or the
twenty first aspect of the present invention, the high-temperature
CO.sub.2 gas which has been generated in the above described
regenerative calciner is sent to the second preheater independent
from the first preheater, is used for preheating the cement
material, and then can be recovered entirely in the as-is state
from the exhaust gas pipe.
[0080] The inner part of the above described regenerative calciner
becomes an atmosphere containing such a high concentration as
nearly 100% of CO.sub.2 gas, and accordingly the calcination
temperature of the cement material becomes high. However, the
cement material contains clay, silica stone and a raw material of
iron oxide, in other words, SiO.sub.2, Al.sub.2O.sub.3 and
Fe.sub.2O.sub.3 together with the limestone (CaCo.sub.3).
[0081] Then, the above described cement material causes the
reactions expressed by the following formulae in an atmosphere at
approximately 800 to 900.degree. C.
2CaCO.sub.3+SiO.sub.2.fwdarw.2CaO.SiO.sub.2+2CO.sub.2.uparw.
(1)
2CaCO.sub.3+Fe.sub.2O.sub.3.fwdarw.2CaO.Fe.sub.2O.sub.3+2CO.sub.2.uparw.
(2)
CaCO.sub.3+Al.sub.2O.sub.3.fwdarw.CaO.Al.sub.2O.sub.3+CO.sub.2.uparw.
(3)
[0082] The components are eventually converted to alite
(3CaO.SiO.sub.2) and belite (2CaO.SiO.sub.2) which are calcium
silicate compounds constituting the cement clinker, and an
aluminate phase (3CaO.Al.sub.2O.sub.3) and a ferrite phase
(4CaO.Al.sub.2O.sub.3.Fe.sub.2O.sub.3) which are interstitial
phases.
[0083] At this time, the above described reactions can be caused at
lower temperatures even when the partial pressure of the CO.sub.2
gas viewed in a vertical axis becomes high, as illustrated in a
graph of a reaction temperature of the above described formula (1)
illustrated in FIG. 12, a graph of a reaction temperature of the
above described formula (2) illustrated in FIG. 13 and a graph of a
reaction temperature of the above described formula (3) illustrated
in FIG. 14.
[0084] Furthermore, in the above described cement material,
SiO.sub.2, Al.sub.2O.sub.3 and Fe.sub.2O.sub.3 which are brought
from other raw materials than the limestone such as the silica
stone and the clay, and other trace components not only cause the
reactions expressed by the above described formulae (1) to (3), but
also function as a mineralizer, and promote thermal decomposition
of calcium carbonate. Accordingly, both a start temperature and an
end temperature of the thermal decomposition reaction are lowered
in comparison with the case when calcium carbonate is solely
calcined, as is illustrated in FIG. 15. Incidentally, FIG. 15
illustrates a result of having confirmed the transition of the
above described thermal decomposition reaction, from a change of
weight obtained when a sample of the above described cement
material (raw material) and a sample of the above described single
limestone (CaCO.sub.3) are heated respectively at a heating rate of
10 K/sec close to the heating rate which is generally adopted in a
general cement-manufacturing facility.
[0085] Here, the following is considered as one of the reasons why
both the start temperature and the end temperature of the thermal
decomposition reaction are lowered by the presence of the above
described mineralizer, in comparison with the case in which the
single calcium carbonate is calcined.
[0086] Specifically, when activity is represented by "a" and an
equilibrium constant in a reaction formula of
CaCO.sub.3.fwdarw.CaO+CO.sub.2 is represented by K,
[0087] in the formula of P.sub.CO2=(a.sub.CaCO3/a.sub.CaO)/K
[0088] the value of a.sub.cao becomes less than 1, because an
activity a of a solid is generally 1 regardless of the type of the
solid as long as the solid is a pure substance, but in the case of
calcium oxide (CaO), other source materials (in other words, the
above described mineralizer) dissolve into CaO formed after the
calcium carbonate (CaCO.sub.3) has been thermally decomposed. It is
considered that as a result, P.sub.CO2 in the above formula becomes
high, the temperature at which the P.sub.CO2 becomes 1 atm is
lowered, and the calcination is further promoted. For information,
the a.sub.CaCO3 is a value inherent to the type and producing
district of the limestone, and is not affected by the other
components in the raw material.
[0089] Because of the above description, the methods according to
the present invention can secure a desired recovery amount of
CO.sub.2 gas, even when an operation temperature in the
regenerative calciner is lowered. Besides, the methods include
heating and calcining the cement material in the above described
regenerative calciner, by using a heat medium which has a large
particle diameter different from that of the cement material and
accordingly has an extremely small specific surface area,
accordingly suppress the sticking or fusion-bonding among the above
described heat media or between the heat medium and a furnace wall
even when the above described heat medium is heated to
1,000.degree. C. which is the calcination temperature or higher in
the regenerative calciner, and can suppress the occurrence of a
coating trouble and the like.
[0090] In addition, the cement material before calcination to be
introduced into the above described regenerative calciner is
preheated by the first preheater in the cement-manufacturing
facility, in a similar process to a normal process of manufacturing
a cement, and also the above described another cement material in
the fifteenth aspect or twenty first aspect of the present
invention is preheated in the second preheater by the
high-temperature CO.sub.2 gas discharged from the regenerative
calciner.
[0091] As in the thirteenth aspect of the present invention, the
method for recovering the CO.sub.2 gas includes filling the above
described regenerative calciner with a heat medium having a
particle diameter larger than that of the above described cement
material, accordingly can secure a large heat quantity in the above
described regenerative calciner, and can selectively recover
CO.sub.2 in a high concentration, which is generated during
calcination and originates in the cement material, without adding a
new thermal energy to the existing cement-manufacturing
facility.
[0092] In addition, the method for recovering the CO.sub.2 gas
includes returning the high-temperature cement material which has
been sufficiently calcined in the regenerative calciner to the
cement kiln, and accordingly can reduce the fuel necessary for
firing the cement material in the cement kiln. As a result, the
method can use a rotary kiln which is shorter than a conventional
one as a cement kiln, or alternatively can use a fluidized bed.
[0093] In addition, in the fifteenth aspect or the twenty first
aspect of the present invention, the heat quantity possessed by the
generated CO.sub.2 gas is used for preheating the above described
another cement material, and accordingly the thermal efficiency of
the whole system can be further enhanced.
[0094] Here, as in the fourteenth aspect, the above described
usable heat medium includes a cement clinker other than a ceramic
material such as quicklime (CaO), silica stone (SiO.sub.2) and
alumina (Al.sub.2O.sub.3) which have heat resistance to a heating
temperature in the above described regenerative calciner and
abrasion resistance when having been mixed with the cement
material, and a metallic material such as a heat-resistant alloy.
Incidentally, the quicklime has advantages of having such a high
melting point as 2,500.degree. C., and of resisting being
fusion-bonded. In addition, the quicklime does not cause a harmful
effect even when the fine powder is mixed into the raw material,
which has been generated by being gradually worn out while the
quicklime is repeatedly used for calcining the above described
cement material in the above described regenerative calciner as the
heat medium, because the fine powder is one of the components of
the cement material. Furthermore, even when the limestone is
charged into the above described regenerative calciner in place of
the quicklime, the limestone is decarbonized to be formed into the
quicklime, and can show a similar functional effect to the case of
the above described quicklime.
[0095] In addition, silica stone has advantages of having such a
high melting point as 1,700.degree. C. to resist being
fusion-bonded, having an extremely high hardness to resist being
worn out, and consequently requiring only a small amount of silica
stone to be supplemented as the heat medium. Furthermore, the
silica stone does not cause inconvenience even when the fine powder
which has been generated by being gradually worn out in the
calcination process is mixed into the raw material, because the
fine powder is one of the components of the cement material.
[0096] In addition, when a cement clinker which has been obtained
by burning the calcined material in the above described cement
kiln, is hard and has a particle diameter much larger than that of
the cement material is used as in the fourteenth aspect of the
present invention, the cost is economical, and the cement clinker
also does not give adverse effect on the operation and the quality
of the cement kiln as a product, even if having been brought into
contact with the cement material and having been worn out, because
the composition of the worn powder has been already adjusted, and
the worn powder having the same quality as that of the cement
material results in being sent to the cement kiln again.
[0097] Furthermore, when the heat medium and the cement material
are mixed to each other in the regenerative calciner and the heat
is exchanged with each other, the cement material deposits on the
surface of the heat medium having a particle diameter larger than
that of the cement material. Then, as in the sixteenth aspect, the
method for recovering the CO.sub.2 gas fluidizes the above
described cement material by CO.sub.2 gas generated when the above
described cement material is fed to the above described
regenerative calciner and is calcined, thereby makes the above
described cement material which has been calcined overflow from the
above described regenerative calciner, and accordingly can feed the
overflowing cement material to the above described cement kiln. As
a result, the above described cement material which has been
calcined can be simply taken out from the regenerative
calciner.
[0098] In addition, as in the seventeenth aspect of the present
invention, the method for recovering the CO.sub.2 gas makes
CO.sub.2 gas generated when the above described cement material is
fed to the above described regenerative calciner and is calcined
therein entrain the above described cement material, separates the
above described cement material from the CO.sub.2 gas with
particle-separating means, and can feed the above described cement
material which has been calcined to the above described cement
kiln. Thereby, the above described cement material which has been
calcined can be simply taken out from the regenerative
calciner.
[0099] By the way, a combustion gas which is sent to the first
preheater from the cement kiln to preheat the cement material
contains N.sub.2 gas and also CO.sub.2 gas (generated CO.sub.2 gas
originating in fuel) which has been generated as a result of the
combustion of a fossil fuel.
[0100] Then, as in the eighteenth aspect, if one part of the cement
material containing much CaO by being calcined in the above
described regenerative calciner is returned to the first preheater,
the above described CaO comes in contact with the combustion
exhaust gas, causes a chemical reaction expressed by
CaO+CO.sub.2.fwdarw.CaCO.sub.3, and can adsorb the CO.sub.2 gas
originating in the fuel in the above described exhaust gas.
[0101] Thus produced CaCO.sub.3 is sent to the regenerative
calciner again together with the cement material and is calcined
there.
[0102] Because of this, it becomes possible to recover the CO.sub.2
gas originating in the fuel in addition to the CO.sub.2 gas which
is generated when the cement material is calcined and originates in
the cement material.
[0103] Here, the calcined cement material which has been discharged
from the above described regenerative calciner has high
temperature, and the above described reaction of
CaO+CO.sub.2.fwdarw.CaCO.sub.3 is an exothermic reaction. Because
of this, it is preferable as in the nineteenth aspect to
heat-exchange one part of the above described cement material which
has been discharged from the above described regenerative calciner
with air once, lower the temperature of the cement material, then
return the cooled cement material to the above described first
preheater, and on the other hand, to feed the above described
heated air as air for combustion in the above described
regenerative calciner, because thermal energy in the system can be
further effectively used.
[0104] Furthermore, as in the twenty second aspect, the recovery
system for recovering the CO.sub.2 gas has the plurality of the
above described regenerative calciners provided therein,
accordingly can heat the above described heat medium to the
calcination temperature or higher and can store heat therein in at
least one regenerative calciner, when the above described cement
material before calcination is calcined in at least another
regenerative calciner, repeatedly heats and stores heat therein
alternately or according to a predetermined rotation, and thereby
can continuously calcine the above described cement material before
calcination.
BRIEF DESCRIPTION OF DRAWINGS
[0105] FIG. 1 is a schematic block diagram illustrating a first
embodiment of the systems for recovering the CO.sub.2 gas according
to the present invention.
[0106] FIG. 2 is a schematic block diagram illustrating a second
embodiment of the systems for recovering the CO.sub.2 gas according
to the present invention.
[0107] FIG. 3 is a graph illustrating a relationship between the
concentration of CO.sub.2 in an atmosphere and a reaction
temperature expressed by formula (1).
[0108] FIG. 4 is a graph illustrating a relationship between the
concentration of CO.sub.2 in an atmosphere and a reaction
temperature expressed by formula (2).
[0109] FIG. 5 is a graph illustrating a relationship between the
concentration of CO.sub.2 in an atmosphere and a reaction
temperature expressed by formula (3).
[0110] FIG. 6 is a graph illustrating a difference of starting
temperatures and ending temperatures of a calcination reaction
between the case when the cement material is calcined and the case
when limestone is solely calcined in CO.sub.2 atmosphere.
[0111] FIG. 7 is a schematic block diagram illustrating a third
embodiment of the systems for recovering the CO.sub.2 gas according
to the present invention.
[0112] FIG. 8 is an explanatory drawing for describing a
regenerative calciner of the third embodiment of the systems for
recovering the CO.sub.2 gas according to the present invention.
[0113] FIG. 9 is an explanatory drawing for describing a modified
example of the regenerative calciner of FIG. 8 which illustrates
the third embodiment of the systems for recovering the CO.sub.2 gas
according to the present invention.
[0114] FIG. 10 is an explanatory drawing for describing another
modified example of the regenerative calciner of the third
embodiment of the systems for recovering the CO.sub.2 gas according
to the present invention.
[0115] FIG. 11 is a schematic block diagram illustrating a fourth
embodiment of the systems for recovering the CO.sub.2 gas according
to the present invention.
[0116] FIG. 12 is a graph illustrating a relationship between the
concentration of CO.sub.2 in an atmosphere and a reaction
temperature expressed by formula (1).
[0117] FIG. 13 is a graph illustrating a relationship between the
concentration of CO.sub.2 in an atmosphere and a reaction
temperature expressed by formula (2).
[0118] FIG. 14 is a graph illustrating a relationship between
concentration of CO.sub.2 in an atmosphere and a reaction
temperature expressed by formula (3).
[0119] FIG. 15 is a graph illustrating a difference of starting
temperatures and ending temperatures of a calcination reaction
between the case when the cement material is calcined and the case
when limestone is solely calcined in CO.sub.2 atmosphere.
[0120] FIG. 16 is a schematic block diagram illustrating a general
cement-manufacturing facility.
[0121] FIG. 17 is a graph illustrating a relationship between the
concentration of CO.sub.2 in an atmosphere and a calcination
temperature of limestone.
DESCRIPTION OF EMBODIMENTS
First Embodiment
[0122] FIG. 1 illustrates a first embodiment of systems for
recovering CO.sub.2 gas in cement-manufacturing facilities
according to the present invention, and the first embodiment has
the same structure concerning the cement-manufacturing facility as
that in FIG. 16. Accordingly, the same portions are denoted by the
same reference numerals, and the description thereof will be
simplified.
[0123] In FIG. 1, reference numeral 10 denotes a second preheater
which is provided independently from the preheater (first
preheater) 3 in the cement-manufacturing facility.
[0124] This second preheater 10 is constituted by a plurality of
stages of cyclones which are serially arranged in a vertical
direction similarly to the above described preheater 3, and is
constituted so that the cement material is fed to the cyclone in
the uppermost stage from a feed line 11. The upper end of a
transfer pipe 10a is connected to the bottom part of the cyclone in
the lowermost stage of the second preheater 10, and the lower end
of this transfer pipe 10a is introduced to a mixing calciner 12.
This mixing calciner 12 is, for instance, a powder-mixing furnace
such as a fluidized-bed type, a rotary kiln type and a moving-bed
type.
[0125] On the other hand, the above described preheater 3 of the
cement-manufacturing facility has an extraction line 13 for
extracting a cement material before calcination from the cyclone in
the lowermost stage, and the head part of this extraction line 13
is connected to the transfer pipe 10a connected to the second
preheater 10. Thus, the cement material before calcination sent
from the second preheater 10 and the cement material before
calcination sent from the preheater 3 are introduced into the
mixing calciner 12.
[0126] Furthermore, this system for recovering the CO.sub.2 gas has
a medium-heating furnace 14 provided in parallel to the mixing
calciner 12 therein. This medium-heating furnace 14 is a moving bed
which is filled with a cement clinker that has been discharged from
the clinker cooler 6 and has a particle diameter larger than that
of the cement material, and has a burner 14a for heating the inner
part thereof provided on the side face in the lower part thereof.
In addition, an introduction pipe 14b for introducing a bleed gas
sent from the clinker cooler 6 as air for combustion is provided in
the bottom part. Furthermore, an exhaust gas pipe 14c for
exhausting a combustion exhaust gas in the inner part is provided
in the ceiling part of this medium-heating furnace 14, and this
exhaust gas pipe 14c is connected to the exhaust gas pipe 3b which
is connected to the rotary kiln 1. This medium-heating furnace 14
is not limited to a moving-bed type, and alternatively can employ,
for instance, a powder-heating furnace such as a fluidized-bed type
and a rotary kiln type.
[0127] A heat-medium feed pipe 15 for sending the cement clinker
which has been heated in the inner part to the mixing calciner 12
is connected to the lower part of this medium-heating furnace 14,
and a medium sedimentation device 16 which constitutes one part of
an exhaust duct from the mixing calciner 12 is connected to the
upper part of this mixing calciner 12. In addition, a discharge
pipe 17 for extracting the cement clinker is connected to the
bottom part of the mixing calciner 12, and the cement clinker which
has been extracted through this discharge pipe 17 is returned into
the above described medium sedimentation device 16 through a bucket
elevator 18.
[0128] Furthermore, a heat-medium return pipe 19 for returning the
above described cement clinker to the medium-heating furnace 14 is
connected to the bottom part of the medium sedimentation device 16.
The heat-medium feed pipe 15, the discharge pipe 17, the bucket
elevator 18 and the heat-medium return pipe 19 constitute a
circulation line of the heat medium, which feeds the cement clinker
that has been heated in the medium-heating furnace 14 to the mixing
calciner 12 and also returns the cement clinker to the
medium-heating furnace 14 from the mixing calciner 12. Reference
numeral 20 in the figure denotes a clinker tank for supplementing a
new cement clinker so as to compensate the worn quantity of the
cement clinker to be circulated through this circulation line.
[0129] On the other hand, a cyclone 21 is connected to the
discharge side of the medium sedimentation device 16, so as to
separate the CO.sub.2 gas discharged from the mixing calciner 12,
from the calcined cement material entrained by this CO.sub.2 gas
and the calcined cement material which has been separated from the
heat medium in the medium sedimentation device 16, and a return
line 22 for returning the calcined and separated cement material to
the kiln inlet part 2 of the rotary kiln 1 is connected to the
bottom part of this cyclone 21. In addition, a CO.sub.2 exhaust
pipe 23 for discharging the separated CO.sub.2 gas is connected to
the upper part of the cyclone 21, and this CO.sub.2 exhaust pipe 23
is also introduced as a heating medium in the second preheater 10.
Here, reference numeral 24 in the figure denotes an exhaust fan of
CO.sub.2 gas, and reference numeral 25 denotes an exhaust line of
CO.sub.2 gas.
[0130] Next, one embodiment of the methods for recovering the
CO.sub.2 gas and the processes for manufacturing the cement
according to the present invention using the above described system
for recovering of the CO.sub.2 gas shown in the first embodiment
will be described below.
[0131] Firstly, a cement material is fed to the cyclones in the
uppermost stages of the preheater 3 and the second preheater 10
from the feed pipes 4 and 11, respectively.
[0132] Then, the above described cement material is preheated by
the exhaust gas which is fed from the rotary kiln 1 through the
exhaust gas pipe 3b, in the process of being sequentially sent to
the cyclones in the lower part in the preheater 3, in a similar way
to that in a conventional process. Then, the above described cement
material which has been preheated up to a temperature (for
instance, approximately 810.degree. C.) just below the calcination
temperature is fed to the mixing calciner 12 from the extraction
line 13 through the transfer pipe 10a.
[0133] The cement material which has been fed to the second
preheater 10 is preheated by a high-concentration and
high-temperature CO.sub.2 gas which has been discharged from the
mixing calciner 12, is preheated up to a temperature (for instance,
approximately 760.degree. C.) before finally reaching the
calcination temperature, and is fed to the mixing calciner 12 from
the transfer pipe 10a.
[0134] On the other hand, in the medium-heating furnace 14, the
cement clinker (heat medium) in the inner part is heated to the
calcination temperature of the cement material or higher (for
instance, approximately 1,200.degree. C.) by the combustion of the
burner 14a. Then, the heated cement clinker is fed to the mixing
calciner 12 from the heat-medium feed pipe 15.
[0135] Thus, in the mixing calciner 12, the fed cement material is
mixed with the cement clinker and is heated to the calcination
temperature or higher (for instance, approximately 900.degree. C.)
and is calcined. At this time, CO.sub.2 gas is also generated.
Then, this CO.sub.2 gas and the calcined cement material are sent
to the cyclone 21 from the upper part of the mixing calciner 12
through the medium sedimentation device 16, and are separated from
each other in the cyclone 21. Then, the calcined and separated
cement material is returned to the kiln inlet part 2 of the rotary
kiln 1 from a return line 22, and is finally burned in the rotary
kiln 1.
[0136] On the other hand, the high-temperature CO.sub.2 which has
been separated by the cyclone 21 and has a concentration of
approximately 100% is introduced to the second preheater 10 from
the CO.sub.2 exhaust pipe 23 as a heating medium. As a result, the
CO.sub.2 gas which originates in the cement material and has the
concentration of approximately 100% can be recovered from the
exhaust line 25 of the CO.sub.2 gas.
[0137] In addition, at the same time, the cement clinker which has
lowered its temperature by calcining the cement material in the
mixing calciner 12 is sequentially extracted from the bottom part
of the mixing calciner 12 through the discharge pipe 17, is
transported to the upper part of the mixing calciner 12 by the
bucket elevator 18, and is charged into the medium sedimentation
device 16. Then, in this medium sedimentation device 16, the cement
clinker is separated from the cement material which has deposited
thereon, by CO.sub.2 gas that is sent from the mixing calciner 12,
and then the resultant cement clinker is returned to the
medium-heating furnace 14 through the heat-medium return pipe 19
again.
[0138] Thus, the above described method and system for recovering
the CO.sub.2 gas in the cement-manufacturing facility effectively
use a heating source in the cement-manufacturing facility, and can
recover CO.sub.2 gas which originates in the cement material and
occupies a half or more of the CO.sub.2 gas generated in the
cement-manufacturing facility, in a high concentration of nearly
100%.
[0139] At this time, because the cement material is heated and
calcined by using the cement clinker which has a large particle
diameter different from that of the cement material and accordingly
has an extremely small specific surface area as a heat medium in
the mixing calciner 12, the sticking or fusion-bonding among the
above described cement clinkers or between the cement clinker and a
furnace wall or an inner wall of a chute are suppressed even when
the above described cement clinker is heated to 1,000.degree. C.
which is the calcination temperature or higher in the
medium-heating furnace 14, and the occurrence of a coating trouble
and the like can be suppressed.
[0140] In addition, the method and system return the
high-temperature cement material which has been sufficiently
calcined in the mixing calciner 12 to the rotary kiln 1 from the
return line 22, and accordingly can reduce the fuel necessary for
burning a cement material in the rotary kiln 1. As a result, the
cement manufacturing facility can use a rotary kiln 1 which has a
shorter longitudinal dimension than that of a conventional one.
Second Embodiment
[0141] FIG. 2 illustrates a second embodiment of the systems for
recovering the CO.sub.2 gas according to the present invention. The
same components as those illustrated in FIG. 1 are denoted by the
same reference numerals, and the descriptions will be
simplified.
[0142] In this recovery system, a branch pipe 30 for branching one
part of the above described cement material is provided in a return
line 22 through which the calcined cement material is returned from
a cyclone 21 to a kiln inlet part 2 of a rotary kiln 1. This branch
pipe 30 is introduced to a heat exchanger 31.
[0143] This heat exchanger 31 is a device for heating an air which
is sent from a feed pipe 32 for air, with the above described
high-temperature (for instance, approximately 900.degree. C.)
cement material which is sent from the branch pipe 30, and a
transfer line 33 for returning the cement material having the
lowered temperature (for instance, approximately 300.degree. C.) to
the first preheater 3 is connected to the outlet side of the branch
pipe 30. On the other hand, a feed pipe 34 for feeding the air as
air for combustion in a medium-heating furnace 14 is connected to
the outlet side of the air which has been heated in the heat
exchanger 31.
[0144] The system for recovering the CO.sub.2 gas having the above
described structure according to the second embodiment returns one
part of the cement material containing much CaO by being calcined
in the mixing calciner 12 to the first preheater 3 through the
branch pipe 30, the heat exchanger 31 and the transfer line 33, and
accordingly the above described cement material absorbs the
CO.sub.2 gas in the combustion exhaust gas originating in the fuel,
as is expressed by CaO+CO.sub.2.fwdarw.CaCO.sub.3, by coming in
contact with a combustion exhaust gas for heating the cement
material in the first preheater 3.
[0145] Thus produced CaCO.sub.3 is sent to the mixing calciner
again together with the cement material, and is calcined
therein.
[0146] As a result, the CO.sub.2 gas which is generated by the
combustion in the main burner 5 of the rotary kiln 1 and in the
burner 14a of the medium-heating furnace 14 and originates in the
fuel can also be recovered, as well as the CO.sub.2 gas which is
generated when the cement material is calcined in the mixing
calciner 12 and originates in the cement material.
[0147] In addition, the system for recovering the CO.sub.2 gas
heat-exchanges one part of the cement material which has been
discharged from the mixing calciner 12 and has such a high
temperature as approximately 900.degree. C. with air in the heat
exchanger 31 to lower the temperature to approximately 300.degree.
C.; then returns the one part of the cement material to the first
preheater 3 from the transfer line 33; also feeds the above
described air which has been heated in the above described heat
exchanger 31 to the medium-heating furnace 14 from the feed pipe 34
as air for combustion; and accordingly can further effectively use
the thermal energy in the system.
[0148] At this time, the lower stage of the first preheater 3 forms
an atmosphere at a temperature of approximately 800.degree. C., but
in spite of this, a cement material having a temperature of
approximately 300.degree. C. which is lower than the
first-mentioned temperature results in being fed to the lower
stage. However, because the above described reaction expressed by
CaO+CO.sub.2.fwdarw.CaCO.sub.3 is an exothermic reaction, there is
no risk that a heat balance in the first preheater 3 comes
undone.
Third Embodiment
[0149] FIG. 7 illustrates a third embodiment of systems for
recovering the CO.sub.2 gas n in cement-manufacturing facilities
according to the present invention, and the third embodiment has
the same structure concerning the cement-manufacturing facility as
that in FIG. 16. Accordingly, the same portions are denoted by the
same reference numerals, and the description thereof will be
simplified.
[0150] In FIG. 7, reference numeral 10 denotes a second preheater
10 which is provided independently from the preheater (first
preheater) 3 in the cement manufacturing facility.
[0151] This second preheater 10 is constituted by a plurality of
stages of cyclones which are serially arranged in a vertical
direction similarly to the above described first preheater 3, and
is constituted so that a cement material before calcination
(uncalcined cement material) k is fed to the cyclone in the
uppermost stage from a feed line 111. The upper end of a transfer
pipe 10a is connected to the bottom part of the cyclone in the
lowermost stage of the second preheater 10, and the lower end of
this transfer pipe 10a is introduced to a regenerative calciner
112. This regenerative calciner 112 is constituted by a first
regenerative calciner 112a and a second regenerative calciner 112b,
and the lower end of the transfer pipe 10a is introduced to each of
the regenerative calciners.
[0152] On the other hand, the above described first preheater 3 of
the above described cement-manufacturing facility has an extraction
line 113 for extracting the uncalcined cement material k from the
cyclone in the lowermost stage, and the head part of this
extraction line 113 is connected to the transfer pipe 10a which is
connected to the second preheater 10. Thereby, the uncalcined
cement material k sent from the second preheater 10 and the
uncalcined cement material k sent from the above described first
preheater 3 are introduced into the regenerative calciner 112.
[0153] Furthermore, this system for recovering the CO.sub.2 gas n
has the first regenerative calciner 112a and the second
regenerative calciner 112b provided in parallel to each other
therein. As for these first regenerative calciner 112a and second
regenerative calciner 112b, the inner part of the horizontal
regenerative calciner 112 is filled with a heat medium t having a
particle diameter larger than that of the uncalcined cement
material k, as is illustrated in FIG. 8. This charged heat medium t
is any one of a cement clinker which has been discharged from a
clinker cooler 6, silica stone and quicklime. Burners 114 for
heating the inner parts are provided in the bottom parts,
respectively, and introduction pipes 115 for introducing a bleed
air sent from the clinker cooler 6 as air for combustion are also
provided in the bottom parts, respectively. Furthermore, transfer
pipes 10a for introducing the uncalcined cement material k are
provided in one side of the side faces, and return lines 118 for
returning the cement material (calcined cement material) k' which
has been calcined and separated from the CO.sub.2 gas n to a kiln
inlet part 2 of a rotary kiln 1 are provided in the other side of
the side faces, respectively. Moreover, these first regenerative
calciner 112a and second regenerative calciner 112b have exhaust
gas pipes 116 for exhausting a combustion exhaust gas or the
CO.sub.2 gas n in the inner parts provided in the ceiling parts
thereof.
[0154] The exhaust gas pipes 116 are connected to the exhaust gas
pipe 3b which is connected to the rotary kiln 1, and the first
preheater 3, and to the second preheater 10, and have switching
valves 117 respectively provided therein which switch between the
combustion exhaust gas and the CO.sub.2 gas n that are discharged
from the regenerative calciners 112 and introduce a switched gas to
the switched direction. This switching valve 117 is provided, for
instance, so as to send the combustion exhaust gas to be discharged
to the first preheater 3 when the regenerative calciner 112 stores
heat therein, and send the CO.sub.2 gas n to be discharged to the
second preheater 10 when the regenerative calciner 112 calcines the
cement material, thus to switch paths of the exhaust gas pipe
116.
[0155] Furthermore, the regenerative calciners 112 in FIG. 9, which
are a modified example of the horizontal regenerative calciners 112
illustrated in FIG. 8, have burners 114 for heating the inner
parts, and introduction pipes 115 for introducing the bleed air
sent from the clinker cooler 6 as air for combustion provided in
one side of the lower side faces of the first regenerative calciner
112a and the second regenerative calciner 112b, respectively. The
regenerative calciners 112 also have the discharge gas pipes 116a
for discharging the combustion exhaust gas generated when the
regenerative calciners 112 are heated and store heat therein
provided in the other side of the lower side faces. The discharge
pipe 116a discharges the combustion exhaust gas when the
regenerative calciner 112 stores heat therein.
[0156] In addition, in the modified example of the regenerative
calciner 112 illustrated in FIG. 10, the inner part of the vertical
regenerative calciner 112 is filled with a heat medium t having a
particle diameter larger than that of the uncalcined cement
material k. In addition, the regenerative calciners 112 have
burners 114 for heating the inner parts provided in the lower side
faces, respectively, and introduction pipes 115 for introducing the
bleed air sent from the clinker cooler 6 as air for combustion
provided in the bottom parts. Furthermore, the regenerative
calciners 112 have the transfer pipes 10a for introducing the
uncalcined cement material k provided in one side of the side
faces. In addition, these first regenerative calciner 112a and
second regenerative calciner 112b have discharge pipes 116b for
discharging the combustion exhaust gas or the CO.sub.2 gas n in the
inner part provided in the ceiling parts, and have cyclones 126
provided in the outlet side of these exhaust pipes 116b. In the
ceiling part of this cyclone 126, there is provided an exhaust gas
pipe 116 for exhausting the combustion exhaust gas or the CO.sub.2
gas n, and in the bottom part, there is provided a return line 118
for returning the calcined cement material k' which has been
separated from the CO.sub.2 gas n that has been generated during
the calcination to the kiln inlet part 2 of the rotary kiln 1.
[0157] In addition, the exhaust gas pipes 116 are connected to the
exhaust gas pipe 3b which is connected to the rotary kiln 1, and
the first preheater 3, and to the second preheater 10, and have
switching valves 117 respectively provided therein which switch
between the combustion exhaust gas and the CO.sub.2 gas n that are
discharged from the regenerative calciners 112 and introduce a
switched gas to the switched direction. This switching valve 117 is
provided, for instance, so as to send the combustion exhaust gas to
be discharged to the first preheater 3 when the regenerative
calciner 112 stores heat therein, and send the CO.sub.2 gas n to be
discharged to the second preheater 10 when the regenerative
calciner 112 calcines the cement material, thus to switch paths of
the exhaust gas pipe 116.
[0158] For information, reference numeral 119 in the figure denotes
an exhaust line of the CO.sub.2 gas n, and reference numeral 120
denotes an exhaust fan of the CO.sub.2 gas n.
[0159] Next, one embodiment of methods for recovering the CO.sub.2
gas n according to the present invention using the above described
system for recovering the CO.sub.2 gas n illustrated in the third
embodiment will be described below.
[0160] Firstly, the uncalcined cement material k is fed to the
above described cyclones in the uppermost stages of the first
preheater 3 and the second preheater 10 from the feed lines 4 and
111, respectively.
[0161] Then, the uncalcined cement material k is preheated by the
exhaust gas which is fed from the rotary kiln 1 through the exhaust
gas pipe 3b and by the combustion exhaust gas sent from the first
regenerative calciner 112a, in the process of being sequentially
sent to the cyclones in the lower parts, in a similar way to that
in a conventional process in the above described preheater 3. Then,
the uncalcined cement material k which has been preheated up to a
temperature (for instance, approximately 810.degree. C.) just below
the calcination temperature is fed to the second regenerative
calciner 112b from the extraction line 113 through the transfer
pipe 10a.
[0162] The uncalcined cement material k which has been fed to the
second preheater 10 is preheated by the CO.sub.2 gas n which has
been generated by the calcination of the cement material in the
regenerative calciner 112b, is preheated finally up to a
temperature (for instance, approximately 760.degree. C.) just below
the calcination temperature, and is fed to the second regenerative
calciner 112b from the transfer pipe 10a.
[0163] On the other hand, in the second regenerative calciner 112b,
as is illustrated in FIG. 8 and FIG. 9, the uncalcined cement
material k fed from a transfer pipe 10a is mixed with the cement
clinker (heat medium) t which has been charged into the inner part,
has been heated and has stored heat therein beforehand, is heated
to a calcination temperature or higher (for instance, 900.degree.
C.) and is calcined therein. At this time, CO.sub.2 gas n is also
generated.
[0164] Then, the CO.sub.2 gas n generated in the second
regenerative calciner 112b is introduced to the second preheater 10
from an exhaust gas pipe 116, as a heating medium. At this time, a
switching valve 117 provided in the exhaust gas pipe 116 opens a
path which leads to the second preheater 10, intercepts a path
which leads to the first preheater 3, and introduces the CO.sub.2
gas n to the second preheater 10. In addition, a calcined cement
material k' is fluidized by CO.sub.2 gas n generated during
calcination, overflows therefrom, is returned to a kiln inlet part
2 of the cement kiln 1 from a return line 118, and is finally fired
in the rotary kiln 1.
[0165] In addition, in a modified example illustrated in FIG. 10,
in the second regenerative calciner 112b, the uncalcined cement
material k fed from a transfer pipe 10a is mixed with a cement
clinker (heat medium) t which has been charged into the inner part,
has been heated and has stored heat therein beforehand, is heated
to a calcination temperature or higher (for instance, 900.degree.
C.) and is calcined. At this time, CO.sub.2 gas n is also
generated.
[0166] The CO.sub.2 gas n generated in the second regenerative
calciner 112b entrains the calcined cement material k', and is
introduced to the cyclone 126 from the exhaust pipe 116b. Then, the
CO.sub.2 gas n and the calcined cement material k' are separated
from each other in the cyclone 126. The calcined and separated
cement material k' is introduced to the kiln inlet part 2 of the
cement kiln 1 from the return line 118 which is provided in the
bottom part. In addition, the separated CO.sub.2 gas n is
introduced to the second preheater 10 from the exhaust gas pipe 116
in the ceiling part, as a heating medium. At this time, a switching
valve 117 provided in the exhaust gas pipe 116 opens the path which
leads to the second preheater 10, intercepts the path which leads
to the first preheater 3, and introduces the CO.sub.2 gas n to the
second preheater 10.
[0167] On the other hand, in the first regenerative calciner 112a,
the cement clinker (heat medium) t charged in the inner part of the
first regenerative calciner 112a is heated to the calcination
temperature of the uncalcined cement material k or higher (for
instance, 1,200.degree. C.) by a burner 114 and a bleed air which
has been introduced from a clinker cooler 6 through an introduction
pipe 115 and has stored heat therein, while the second regenerative
calciner 112b conducts calcination. A combustion exhaust gas
discharged at this time is introduced to the above described first
preheater 3 from the exhaust gas pipe 116, as the heating medium.
At this time, the switching valve 117 provided in the exhaust gas
pipe 116 opens the path which leads to the first preheater 3,
intercepts the path which leads to the second preheater 10, and
introduces the combustion exhaust gas to the first preheater 3. At
this time, in the regenerative calciner 112 illustrated in FIG. 9,
which is a modified example of the regenerative calciner 112
illustrated in FIG. 8, the combustion exhaust gas is discharged
from the discharge pipe 116a. Thereby, the cement clinker (heat
medium) t can be efficiently heated by the combustion exhaust gas.
In addition, in this case, the exhaust gas pipe 116 provided in the
ceiling part is closed.
[0168] Incidentally, though the cement clinker (heat medium) t
needs to be heated to the high temperature of approximately
1,200.degree. C. and store heat therein, the temperature of the
exhaust gas sent from the rotary kiln 1 is 1,100 to 1,200.degree.
C. Accordingly, the above described exhaust gas can be effectively
used by introducing the total amount or the fixed amount of the
exhaust gas sent from the rotary kiln 1 to the regenerative
calciner 112a and sending the exhaust gas again from the exhaust
gas pipe 116 to the above described first preheater 3.
[0169] Furthermore, as illustrated in FIG. 10, in the regenerative
calciner 112 of another modified example, the combustion exhaust
gas is introduced from the exhaust pipe 116b provided in the
ceiling part to the cyclone 126, and is introduced to the above
described first preheater 3 from the exhaust gas pipe 116, as the
heating medium.
[0170] In addition, the second regenerative calciner 112b heats the
cement clinker (heat medium) t which has been charged in the inner
part again by the burner 114 and the bleed air introduced from the
clinker cooler 6 through the introduction pipe 115 and makes the
cement clinker store heat therein, after having calcined the cement
material k. At this time, the switching valve 117 provided in the
exhaust gas pipe 116 opens the path which leads to the first
preheater 3, intercepts the path which leads to the second
preheater 10, and introduces the combustion exhaust gas to the
first preheater 3.
[0171] On the other hand, in the first regenerative calciner 112a
which has stored heat therein, the uncalcined cement material k fed
from the transfer pipe 10a is mixed with the cement clinker (heat
medium) t, is heated to the calcination temperature or higher (for
instance, 900.degree. C.) and is calcined, after the operation of
the burner 114 has been stopped. At this time, the CO.sub.2 gas n
is also generated.
[0172] Then, the CO.sub.2 gas n generated in the first regenerative
calciner 112a is introduced to the second preheater 10 from the
exhaust gas pipe 116, as a heating medium. At this time, the
switching valve 117 provided in the exhaust gas pipe 116 opens the
path which leads to the second preheater 10, intercepts the path
which leads to the first preheater 3, and introduces the CO.sub.2
gas n to the second preheater 10. In addition, the calcined cement
material k' is fluidized by CO.sub.2 gas n generated during
calcination, overflows therefrom, is returned to the kiln inlet
part 2 of the cement kiln 1 from a return line 118, and is finally
fired in the rotary kiln 1.
[0173] Thus, the above described method and system for recovering
the CO.sub.2 gas in the cement-manufacturing facility can
continuously recover the CO.sub.2 gas by repeating calcination,
heating and heat storage while using the first regenerative
calciner 112a and the second regenerative calciner 112b, and also
can simplify the facility. In addition, the method and system
effectively uses a heating source in the cement-manufacturing
facility, and can recover the CO.sub.2 gas n which originates in
the cement material and occupies a half or more of the CO.sub.2 gas
n generated in the cement-manufacturing facility, in a high
concentration of nearly 100%.
[0174] At this time, because the uncalcined cement material k is
heated and calcined by the cement clinker which has a large
particle diameter different from that of the uncalcined cement
material k and accordingly has an extremely small specific surface
area as a heat medium t in the regenerative calciner 112, the
sticking or fusion-bonding among the above described heat media or
between the heat medium and a furnace wall is suppressed even when
the above described cement clinker t is heated to 1,000.degree. C.
which is the calcination temperature or higher in the regenerative
calciner 112, and the occurrence of a coating trouble and the like
can be suppressed.
[0175] In addition, the method and system return the
high-temperature cement material k' which has been sufficiently
calcined in the regenerative calciner 112 to the rotary kiln 1 from
the return line 118 and accordingly can reduce the fuel necessary
for burning a cement material in the rotary kiln 1. As a result,
the cement manufacturing facility can use a rotary kiln 1 which has
a shorter longitudinal dimension than that of a conventional
one.
Fourth Embodiment
[0176] FIG. 11 illustrates a fourth embodiment of the systems for
recovering the CO.sub.2 gas n according to the present invention.
The same components as those illustrated in FIG. 16 are likewise
denoted by the same reference numerals, and the descriptions will
be simplified.
[0177] In this recovery system, a branch pipe 121 for branching one
part of the calcined cement material k' is provided in a return
line 118 through which the calcined cement material k' is returned
to a kiln inlet part 2 of a rotary kiln 1 from a regenerative
calciner 112. This branch pipe 121 is introduced to a heat
exchanger 122.
[0178] This heat exchanger 122 is a device for heating air which is
sent from a feed pipe 124 for air, with the high-temperature (for
instance, 900.degree. C.) calcined cement material k' which is sent
from the branch pipe 121, and a transfer line 123 for returning the
calcined cement material k' having the lowered temperature (for
instance, 300.degree. C.) to the first preheater 3 is connected to
the outlet side of the branch pipe 121. On the other hand, a feed
pipe 125 for feeding the air as air for combustion in the
regenerative calciner 112 is connected to the outlet side of the
air which has been heated in the heat exchanger 122.
[0179] The system for recovering the CO.sub.2 gas n having the
above described structure according to the fourth embodiment
returns one part of the cement material containing much CaO by
being calcined in the regenerative calciner 112 to the first
preheater 3 through the branch pipe 121, the heat exchanger 122 and
the transfer line 123, and accordingly the calcined cement material
k' absorbs the CO.sub.2 gas n in the combustion exhaust gas
originating in the fuel, as is expressed by
CaO+CO.sub.2.fwdarw.CaCO.sub.3, by coming in contact with a
combustion exhaust gas for heating the uncalcined cement material k
in the first preheater 3.
[0180] Thus produced CaCO.sub.3 is sent to the regenerative
calciner again together with the uncalcined cement material k and
is calcined there.
[0181] As a result, the CO.sub.2 gas n which is generated by the
combustion in the main burner 5 of the rotary kiln 1 and in the
burner 114 of the regenerative calciner 112 and originates in the
fuel can also be recovered, as well as the CO.sub.2 gas n which is
generated when the cement material is calcined in the regenerative
calciner 112 and originates in the uncalcined cement material
k.
[0182] In addition, the system for recovering the CO.sub.2 gas
heat-exchanges one part of the calcined cement material k' which
has been discharged from the regenerative calciner 112 and has such
a high temperature as approximately 900.degree. C. with air in the
heat exchanger 122 to lower the temperature to approximately
300.degree. C.; then returns the resultant cement material to the
first preheater 3 from the transfer line 123; also feeds the above
described air which has been heated in the heat exchanger 122 to
the regenerative calciner 112 from the feed pipe 125 as air for
combustion; and accordingly can further effectively use the thermal
energy in the system.
[0183] At this time, the lower stage of the first preheater 3 forms
an atmosphere at a temperature of approximately 800.degree. C., but
in spite of this, an uncalcined cement material k having a
temperature of approximately 300.degree. C. which is lower than the
temperature results in being fed to the lower stage. However,
because the above described reaction expressed by
CaO+CO.sub.2.fwdarw.CaCO.sub.3 is an exothermic reaction, there is
no risk that a heat balance in the first preheater 3 comes
undone.
INDUSTRIAL APPLICABILITY
[0184] According to the present invention, there are provided
methods and systems for recovering CO.sub.2 gas in
cement-manufacturing facilities, which can separate and recover
CO.sub.2 gas generated in the cement-manufacturing facilities in a
high concentration by effectively using a heating source in the
cement-manufacturing facilities, and processes for manufacturing
the cement.
REFERENCE SIGNS LIST
[0185] 1 Rotary kiln (Cement kiln) [0186] 3 Preheater (First
preheater) [0187] 10 Second preheater [0188] 10a Transfer pipe
[0189] 12 Mixing calciner [0190] 13 Extraction line [0191] 14
Medium-heating furnace [0192] 15 Heat-medium feed pipe [0193] 19
Heat-medium return pipe [0194] 21 Cyclone [0195] 22 Return line
[0196] 25 Exhaust line of CO.sub.2 gas [0197] 31 Heat exchanger
[0198] 33 Transfer line of cement material [0199] 34 Feed pipe of
combustion air [0200] 112 Regenerative calciner [0201] 113
Extraction line [0202] 116 Exhaust gas pipe [0203] 118 Return line
[0204] 122 Heat exchanger [0205] 125 Feed pipe of combustion air
[0206] k Uncalcined cement material (cement material before
calcination) [0207] k' Calcined cement material (cement material
which has been calcined)
* * * * *