JP2020070222A - Lime cake (high-water-content calcium carbonate) baking system - Google Patents

Abstract

To provide a lime cake baking system that reliably prevents re-carbonation of calcium oxide and improves the thermal efficiency by circumventing the re-carbonates from being stuck in a baking exhaust gas flow path to stop the operation as the lime cake (high-water-content calcium carbonate CaCO) is dried and baked to produce calcium oxide (CaO) and the calcium oxide in baked exhaust gas in the baking furnace is re-carbonated by carbon dioxide (CO) in the baked exhaust gas.SOLUTION: In order to prevent the re-carbonation of powdered calcium oxide contained in the baked exhaust gas which is discharged from lime cake baking, the baked exhaust gas discharged from the baking furnace is mixed with air, and the baking gas is rapidly cooled to a temperature of 550°C or lower. The partial pressure of carbon dioxide in the baking gas is reduced to 0.012 MPa or less to prevent re-carbonation. By bringing the mixed gas obtained by separating and collecting calcium oxide from the baked exhaust gas into direct contact with the lime cake, the efficiency of the dry heat transfer of the lime cake is improved.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a lime cake (highly water-containing calcium carbonate) baking system, and more particularly to a system for producing a powdery calcium oxide by baking a lime cake (highly water-containing calcium carbonate).

In recent years, electric vehicles have been showing rapid signs of widespread use due to environmental measures, and lithium battery cells are expected to be used as a vehicle-mounted storage battery for the power source. Lithium battery uses lithium hydroxide as the starting material for its electrode material, but since calcium hydroxide is used in the lithium hydroxide purification process, lime cake (high water content calcium carbonate) is generated as waste. To do.
The main components of the waste lime cake are powdery calcium carbonate and water. Recycling this lime cake by drying and baking it to calcium oxide, and then rehydrating it as calcium hydroxide through a hydration reaction contributes to the saving of limestone resources and the reduction of environmental load by the effective use of waste. It can be said that this is an urgent issue in connection with the expansion of production.

Conventionally, when calcining limestone to calcium carbonate (CaCO ₃ ) to produce quick lime (calcium oxide CaO), lumpy limestone having a particle size of 100 to 50 mm, or 25 to 10 mm is calcined in a vertical furnace. However, the firing of lumpy limestone requires a firing temperature of about 1200 ° C. and a firing time of 3 to 6 hours, and the fired calcium oxide (CaO) has a specific surface area (surface area per unit mass) of 10 to 15 m ^2. / g.
On the other hand, in calcination characteristics of limestone, the higher the temperature and the longer the time, the smaller the specific surface area and the lower the activity of calcium oxide (CaO). For this reason, in order to obtain highly active calcium oxide (CaO), the particle size of limestone should be made small (particle size is about 3 mmΦ or less) to shorten the baking time and to lower the baking temperature to about 900 ° C. The specific surface area is increased to about 40 to 50 m ² / g (about 3 times the JIS standard). Calcium oxide (CaO) is used as a flue gas purifying agent for desulfurization of sulfur oxides in flue gas such as incinerators and removal of hydrogen chloride by high-reactivity slaked lime obtained by hydration digestion.

Since the calcium carbonate in the lime cake is fine particles of 5 μm or less, it is a suitable raw material for producing highly active calcium oxide (CaO) if it is dried and calcined.
Conventionally, a fluidized bed firing furnace has been developed as a means for producing highly active calcium oxide (CaO), but the firing exhaust gas discharged from the fluidized bed firing furnace contains powdery calcium oxide (CaO). From this, as the temperature of the firing gas decreases, calcium oxide (CaO) recombines with carbon dioxide (CO ₂ ) in the firing gas to cause a recarbonation phenomenon to generate calcium carbonate (CaCO ₃ ). Calcium carbonate (CaCO ₃ ) generated by this recombination causes a sticking and hardening phenomenon in the flow path of the firing gas, which makes it difficult to operate the fluidized bed firing furnace for a long period of time. However, there is no record of operating a firing furnace using powdery (CaCO ₃ ).

From the above, in obtaining highly active calcium oxide (CaO) by firing lime cake, if high carbonation can be prevented during firing, production of highly active calcium oxide (CaO) by fluidized bed / jet bed firing is possible. On the other hand, on the other hand, in the case of firing in a fluidized bed firing furnace, the burning fuel consumption rate tends to increase as compared with the conventional firing method, and therefore it is desired to improve its thermal efficiency.

The following contents are described in the prior art documents shown below. The invention described in Document 1 (Japanese Patent Publication No. 58-11367) is production of calcined lime from lime cake (lime cake in the document), and the invention described in Document 2 (Japanese Patent No. 4474533) is carbonic acid having a particle size of 0.3 mm or less. The inventions relating to a method of baking quick lime to calcium oxide (CaO) using calcium, the inventions described in Document 3 (Japanese Patent No. 4825994) and Document 4 (Japanese Patent Laid-Open No. 2000-256047) relate to a method of baking a lime cake. It is a thing. These inventions, like the present invention, are aimed at producing highly active calcium oxide (CaO).

Japanese Patent Publication No. 58-11367 Japanese Patent No. 4474533 Japanese Patent No. 4825994 JP 2000-256047 A

Zement‐Kalk‐Gips, Vol 42, No 12, p621

However, the inventions related to the conventional production of quick lime to calcium oxide (CaO), and the inventions described in the above-mentioned patent documents have the following problems.

(Issue 1)
As a first problem, in recycling lime cake, in order to obtain highly active calcium oxide (CaO), it is necessary to set the firing temperature of the furnace to 1,000 ° C or lower. In that case, the calcium oxide (CaO) that accompanies the calcination exhaust gas discharged from the calcination furnace is oxidized with the carbon dioxide (CO ₂ ) contained in the exhaust gas during the temperature decrease process when it is discharged from the calcination furnace. There was a problem that recarbonation occurs due to recombining with calcium (CaO), and this recarbonate causes a sticking and hardening phenomenon in the calcination exhaust gas flow passage to block the flow passage. That is, it is necessary to prevent re-carbonation of calcium oxide (CaO) in the exhaust gas from the firing furnace as much as possible.

(Issue 2)
As the second problem, conventionally, limestone firing in a fluidized bed firing furnace has a lower thermal efficiency than a vertical furnace, and therefore, it was necessary to improve the thermal efficiency as a system in practical use. In particular, when the amount of heat retained by the exhaust gas from the firing furnace is used in the drying process of the high-water content lime cake, it is necessary to improve the heat transfer efficiency between the exhaust gas and the lime cake in the drying furnace.

(Problem 3)
The third problem is that the heat exchanger that recovers heat from the amount of heat of the exhaust gas has a structure in which recarbonite is not likely to stick to it. There is a problem that the structure must be able to

The invention according to claim 1 is a lime cake dryer for drying a high water content lime cake, and a high water content lime cake to a high water content powdery calcium carbonate (CaCO ₃ ) supplied from this lime cake dryer is calcined to obtain calcium oxide. (CaO), and a lime cake firing system comprising a firing furnace for thermally decomposing into carbon dioxide (CO ₂ ), wherein calcium oxide (CaO) and dioxide contained in the firing exhaust gas discharged from the firing furnace. In order to prevent recarbonation due to carbon (CO ₂ ), the firing exhaust gas is mixed with atmospheric normal temperature air and rapidly cooled at the exhaust gas discharge portion of the firing furnace, and the temperature of the mixed gas is set to 550 ° C. or lower. In addition, the carbon dioxide (CO ₂ ) partial pressure in the mixed gas is set to 0.012 MPa or less to suppress the re-carbonation reaction of calcium oxide (CaO).

That is, the invention according to claim 1 is, as a solution to the problem 1, the thermal decomposition temperature (CaCO ₃ = CaO + CO ₂ ) of calcium carbonate (CaCO ₃ ) in the firing furnace is the ratio of CaO produced by firing. In order to secure a surface area of 45 m ² / g or more, firing is performed at 1000 ° C or less.
In the coexistence of calcium oxide (CaO) and carbon dioxide (CO ₂ ) in the calcined exhaust gas discharged from the calciner, an equilibrium state exists due to the gas temperature and the CO ₂ partial pressure in the gas. In order to have a system configuration in which recarburized oxides due to bonding do not easily occur, atmospheric temperature air is mixed with the firing gas discharged from the firing furnace, and the temperature of the mixed gas is rapidly cooled to 550 ° C or lower. In addition, by reducing the partial pressure of CO ₂ in the mixed gas to 0.012 MPa or less, the binding rate of the both is reduced and recarbonation is suppressed.

The invention according to claim 2 is the above-mentioned item 1, in which a heat exchanger is provided in a stage subsequent to the exhaust gas discharge part in the firing furnace, and the mixed gas introduced into the high temperature side of the heat exchanger is used to heat the heat exchanger. The air supplied from the low temperature side of the is heated to combustion air for a firing furnace, and the combustion air is introduced into the firing furnace, and a dust collector for powdered calcium oxide (CaO) is further provided in the latter stage of the heat exchanger. Installed, the calcium oxide (CaO) is separated and collected from the mixed gas, the mixed gas after separation and repair is introduced into the lime cake dryer, and the dry heat transfer efficiency is achieved by direct contact between the mixed gas and the lime cake. The feature is to improve.
According to the invention of claim 2, since the mixed gas is brought into direct contact with the lime cake, the dry heat transfer efficiency is improved, and the water content of the lime cake can be efficiently reduced, and The cost of the lime cake dryer can be reduced.

According to a third aspect of the present invention, in the above-mentioned first and second aspects, when the heat exchanger is used, a mixed gas of firing exhaust gas and air is used as a hot fluid on the high temperature side of the heat exchanger, and a flow path thereof A thin tube group consisting of a straight tube section is used as a flow path to prevent re-carbonation and fixation of calcium oxide (CaO), and the air on the heated side divides the heat transfer tube case into multiple chambers to form a heat transfer tube. It is characterized by the application of a heat exchanger that has a low-temperature side flow path for heat recovery with the outer surface orthogonal to each other in multiple stages and has an inspection port for checking and removing recarbonated deposits in the straight pipe section. .

  In recent years, electric vehicles have been widely used to improve the global environment, and along with this, it is expected that lithium batteries will be used as on-vehicle batteries. In connection with the expansion of production of lithium storage batteries, the starting material of the electrode material is lithium hydroxide, but calcium hydroxide is required in the refining process, and high-water content lime cake is produced as waste. Drying and baking the lime cake to obtain highly active calcium oxide (CaO), and recycling it to calcium hydroxide through a hydration reaction contributes to saving limestone resources and reducing environmental load by reducing waste. It will be possible. The present invention makes it possible to obtain highly active calcium oxide and fulfills such a purpose.

And equilibrium temperature in the case of pyrolysis in a firing furnace calcium carbonate (CaCO _3), is a graph showing the relationship between the partial pressure of carbon dioxide (CO _2). FIG. 1 is a block diagram of a firing system used when firing lime cake to produce calcium oxide (CaO), in which a heat exchanger for heating air introduced into a firing furnace is a dust collector for collecting calcium oxide (CaO). It shows the case where it is installed in the previous stage. FIG. 1 is a block diagram of a firing system used when firing lime cake to produce calcium oxide (CaO), in which a heat exchanger for heating air introduced into a firing furnace is a dust collector for collecting calcium oxide (CaO). It shows the case where it is installed in the latter stage. It is an explanatory view showing an outline of a heat recovery heat exchanger used in an embodiment of a firing system of the present invention.

Hereinafter, a lime cake (high-hydrated calcium carbonate) baking system according to the present invention will be described in detail with reference to the accompanying drawings.
Figure 1 shows the partial pressure of carbon dioxide (CO ₂ ) contained in the firing gas and the equilibrium in the furnace during the thermal decomposition (CaCO ₃ → CaO + CO ₂ ) of calcium carbonate (CaCO ₃ ) which is the main component of lime cake. It is a graph which shows the relationship with temperature, a broken line is a curve described based on the formula described in Non-Patent Document 1 described above, and a solid line is a curve described based on the formula described in Patent Document 1.
As shown in FIG. 1, with these characteristic curves as boundaries, the upper part on the high temperature side is the thermal decomposition region of CaCO ₃ (CaO + CO ₂ ), and the lower part of the characteristic curve is the binding region (CaCO ₃ ). That is, when the firing temperature is lowered, when CO ₂ has a low partial pressure (low concentration), re-carbonation reaction (CaO + CO ₂ → CaCO ₃ ) occurs between CaO and CO ₂ . The present invention is intended to suppress such recarboxylation reaction and improve the yield of calcium oxide CaO when it is calcined.

FIG. 2 is a diagram showing an example of a schematic configuration of a system used when baking lime cake to produce CaO.
As shown in FIG. 2, the lime cake (high-hydrated calcium carbonate) baking system of the present embodiment includes a lime cake supply unit 1, a dryer 2 for drying the lime cake before baking, a baking furnace 3, and cold air. It comprises a mixing section (exhaust gas discharge section) 5, a heat exchanger 6, a dust collector 7 for collecting calcium oxide (CaO), and the like.
The water content of the lime cake supplied from the supply unit 1 is reduced to 10% or less by the dryer 2, and then the lime cake is supplied to the firing furnace 3 and fired at a firing temperature of 1000 ° C or less, and the thermal decomposition of calcium carbonate causes , Calcium oxide (CaO) and carbon dioxide (CO ₂ ) are generated, and the calcination exhaust gas is discharged from the calcination furnace 3. The calcination exhaust gas is accompanied by decomposed fine particles of calcium oxide (CaO). There is.

The calcined exhaust gas discharged from the calcining furnace 3 is mixed with cold air (normal temperature atmospheric air) through a cold air supply unit 50 and a cold air mixing unit (exhaust gas discharge unit) 5 to reduce the temperature to 550 ° C or lower. It is cooled rapidly. In addition, by introducing cold air, the partial pressure of CO ₂ in the calcination exhaust gas is reduced to 0.012 MPa or less to suppress the recarbonation reaction of the fine particles of calcium oxide (CaO) contained in the calcination exhaust gas, and to heat the combustion furnace 3 and heat. It is designed to prevent sticking and clogging in the pipe line connecting with the exchange 6.
Further, air is mixed in the calcination exhaust gas in the air mixing section 5, and the mixed gas is introduced into the heat exchanger (gas gas heater, GGH) 6 to become a high temperature side heat fluid, while the low temperature side air of the heat exchanger 6 Air is supplied from the air supply unit 55 to the inlet 63 as a low-temperature side heat fluid, and this air is heated by heat exchange and then supplied from the low-temperature side air outlet 64 to the firing furnace 3 as combustion air.

FIG. 3 is a configuration diagram of a firing system showing another embodiment of the firing system of the present invention, in which the heat exchanger 6 for heating air introduced into the firing furnace 3 in FIG. 2 is replaced with calcium oxide (CaO). This is the case where it is installed in the latter stage of the dust collector 7 for collection.
As shown in FIG. 3, when the heat exchanger 6 is installed in the latter stage of the dust collector 6, since the mixed gas introduced into the heat exchanger 6 is not accompanied by calcium oxide (CaO), the heat exchanger 6 6 does not require dust measures. Therefore, there is an advantage that other heat exchangers such as a plate type other than the straight tube heat exchanger can be applied, but since the high temperature mixed gas before heat exchange is introduced into the dust collector 7, it can be used. Dust collectors are limited to high temperatures. Further, since the mixed gas supplied to the dryer 2 is limited to the operating temperature of the dust collector or lower, the temperature of the combustion air in the firing furnace 3 is lowered, and the thermal efficiency of the lime cake firing system is lowered. It is desirable to adopt the system configuration of.

FIG. 4 is an explanatory view showing an outline of the basic structure of the heat exchanger 6 for heat recovery used in the firing system of this embodiment. As shown in the figure, since the heat fluid on the high temperature side of the heat exchanger 6 is accompanied by fine particles of calcium oxide (CaO), in order to avoid adhesion of fine powder in the pipe, The high temperature side gas flow path communicating with the gas inlet 61 and the high temperature side gas outlet 62 is constituted by the straight tube portion 60 to form a plurality of thin tube groups.
On the other hand, the air (low temperature side fluid) introduced from the low temperature side air inlet 63 crosses the surface of the straight pipe portion 60 which is the flow path of the high temperature side thermal fluid, and moves to the low temperature side air inlet 64 to recover heat. And becomes combustion air for the firing furnace 3.
That is, the high temperature side flow path of the heat exchanger 6 is a straight pipe part 60 for easy cleaning in order to prevent sticking due to recarbonation of powdery calcium oxide (CaO) accompanying the mixed gas, Further, a top plate 65 is installed on the upper part of the heat exchanger 6 and a bottom plate 66 is installed on the lower part of the heat exchanger 6 so as to be detachable, so that inspection and cleaning are easy.

The mixed gas, which is the high temperature side heat fluid that has been heat-exchanged in the heat exchanger 6, is introduced into the collecting dust collector 7 to collect the associated calcium oxide (CaO), and the mixed gas passes through the heat exchanger 6. As a result, the temperature decreases, and since the mixed gas does not contain dust, various dust collectors can be used, and the cost of the entire system can be reduced. The mixed gas discharged from the dust collector 7 for collection is blown into the lime cake drier 2 to be guided, and is brought into direct contact with the lime cake in the drier 2 to be heated and dried. As a result, the heat transfer efficiency of the lime cake is improved, so that the heat transfer area of the dryer 2 is reduced, which is effective in reducing the cost of the dryer. Further, in the mixed gas discharged from the dryer 2, the accompanying dust is collected by the cyclone dust collector 8 and separated, and then discharged from the exhaust pipe 9.

(Example)
Below, the Example in the case of manufacturing calcium oxide from a lime cake using the baking system of this embodiment is shown below.
Lime cake (1.5t / h): CaCO _3, 1,050kg / h, moisture 450kg / h
After drying lime cake: CaCO _3, 1,050 kg / h, water content 105 kg / h
Fuel consumption LNG 105m ³ / h
CaO yield 580kg / h

Although electric vehicles are becoming popular for improving the global environment, lithium batteries are expected to be used as batteries. In connection with the expansion of lithium battery production, the starting material for the electrode material is lithium hydroxide. Calcium hydroxide is required in the manufacturing process, and a high water content lime cake is produced as a waste product. The present invention can be used as an indispensable recycling system for the production of lithium storage batteries because it is possible to dry and bake a lime cake into calcium oxide, and the calcium oxide can be converted into calcium hydroxide by a hydration reaction. Is.
Calcium hydroxide (CaO) produced by low-temperature calcination of the present invention is obtained by hydrating, and calcium hydroxide is flue gas dry desulfurization (SOx removal) and desalination (HCl removal) as highly reactive slaked lime. As a purifying agent such as, the removal performance is higher than that of ordinary JIS standard slaked lime, and the usage amount can be reduced to about 1/2.
Further, the lime cake discharged in the process of refining sugar beet sugar and the like is used as a soil improver for agricultural land, but depending on the soil used, there is a case of excess alkali, so the present invention uses the lime cake. This will lead to the expansion of recycling and will be able to build an appropriate recycling business. As described above, the firing technique of powdery calcium oxide (CaO) can be used in various fields.

1 High Hydrous Calcium Carbonate (Lime Cake) Supply Unit 2 Fuel Storage Tank Lime Cake Dryer 3 Baking Furnace 4 Fuel Supply Unit 5 Cold Air Mixing Unit 50 Cold Air Supply Unit 55 Air Supply Unit 6 Heat Exchanger 60 Heat Exchanger High Temperature Side Small Tube 61 Heat Exchanger High Temperature Side Gas Inlet 62 Heat Exchanger High Temperature Side Gas Outlet 63 Heat Exchanger Low Temperature Side Air Inlet 64 Heat Exchanger Low Temperature Side Air Outlet 65 Heat Exchanger Top Plate 66 Heat Exchanger Bottom Plate 7 CaO Dust Collector 70 CaO collector 8 Cyclone dust collector 9 Exhaust stack

That is, the invention according to claim 1 is, as a solution to the problem 1, a lime cake dryer for drying a high water content lime cake, and a high water content lime cake supplied from the lime cake dryer (high water content powdery calcium carbonate CaCO ₃ ) Is calcined to calcinate calcium oxide (CaO) and carbon dioxide (CO ₂ ) to form a lime cake calcination system, which is contained in calcination exhaust gas discharged from the calcination furnace. In order to prevent re-carbonation due to calcium oxide (CaO) and carbon dioxide (CO ₂ ), air is mixed with the calcined exhaust gas at the exhaust gas discharge part of the calcining furnace to rapidly cool the temperature of the mixed gas. with a 550 ° C or less, the partial pressure of carbon dioxide (CO ₂₎ in the mixed gas as follows 0.012 MPa, to suppress re-carbonation reaction of calcium oxide (CaO), the exhaust gas discharge in the firing furnace A heat exchanger is provided in the latter part of the section, and the mixed gas introduced to the high temperature side of the heat exchanger heats air supplied from the low temperature side of the heat exchanger to form combustion air for a firing furnace, While introducing the combustion air into the firing furnace, a dust collector for powdered calcium oxide (CaO) is further installed in the latter stage of the heat exchanger to separate and collect calcium oxide (CaO) from the mixed gas. The repaired mixed gas is introduced into the lime cake drier, and the dry heat transfer efficiency is improved by direct contact between the mixed gas and the lime cake .

The invention according to claim 2 is a lime cake dryer for drying a high water content lime cake, and a high water content lime cake (high water content powdery calcium carbonate CaCO ₃ ) supplied from this lime cake dryer is calcined to obtain calcium oxide ( CaO) and a lime cake firing system having a firing furnace for thermally decomposing into carbon dioxide (CO ₂ ), wherein calcium oxide (CaO) and carbon dioxide contained in the firing exhaust gas discharged from the firing furnace. In order to prevent recarbonation due to (CO ₂ ), air is mixed with the calcined exhaust gas in the exhaust gas discharge part of the calcining furnace to rapidly cool it, and the temperature of the mixed gas is set to 550 ° C. or lower. The partial pressure of carbon dioxide (CO ₂ ) in the mixed gas is set to 0.012 MPa or less to suppress the recarbonation reaction of calcium oxide (CaO),
A dust collector for collecting powdery calcium oxide (CaO) is installed in the latter stage of the exhaust gas discharge section in the firing furnace, and a heat exchanger is further installed in the latter stage of the dust collector for collection, and introduced into the heat exchanger. The mixed gas as the high-temperature side hot fluid is not accompanied by powdery calcium oxide (CaO), the mixed gas is introduced into the lime cake dryer, and the mixed gas is directly contacted with the lime cake. The drying heat transfer efficiency is improved, and the air supplied from the low temperature side of the heat exchanger is heated by heat exchange and introduced into the firing furnace as combustion air for the firing furnace . ..

According to a third aspect of the present invention, in the above-mentioned first aspect, when the heat exchanger is used, a mixed gas of firing exhaust gas and air is used as a high temperature side heat fluid of the heat exchanger, and a flow path thereof is a straight pipe part. The thin tube group composed of is used as a flow path to prevent re-carbonation and fixation of calcium oxide (CaO), and for the heated air, the heat transfer tube case is divided into multiple chambers and the outer surface is orthogonal to the heat transfer tube. It is characterized by the application of a heat exchanger in which the flow path for heat recovery orthogonal to multiple stages is the low temperature side flow path, and an inspection port for the inspection and removal of recarbonated deposits on the straight pipe section is provided.

The calcined exhaust gas discharged from the calcining furnace 3 is mixed with cold air (normal temperature atmospheric air) through a cold air supply unit 50 and a cold air mixing unit (exhaust gas discharge unit) 5 to reduce the temperature to 550 ° C or lower. It is cooled rapidly. In addition, by introducing cold air, the partial pressure of CO ₂ in the calcination exhaust gas is reduced to 0.012 MPa or less to suppress the recarbonation reaction of the fine particles of calcium oxide (CaO) contained in the calcination exhaust gas, and to heat the combustion furnace 3 and heat. It is designed to prevent sticking and clogging in the pipe line connecting with the exchange 6.
Further, air is mixed with the calcination exhaust gas in the cold air mixing section 5 , and the mixed gas is introduced into the heat exchanger (gas gas heater, GGH) 6 to become a high temperature side heat fluid, while the low temperature side of the heat exchanger 6 Air is supplied to the air inlet 63 from the air supply unit 55 as a low temperature side heat fluid, and this air is heated by heat exchange, and then supplied from the low temperature side air outlet 64 to the firing furnace 3 as combustion air.

FIG. 3 is a configuration diagram of a firing system showing another embodiment of the firing system of the present invention, in which the heat exchanger 6 for heating air introduced into the firing furnace 3 in FIG. 2 is replaced with calcium oxide (CaO). This is the case where it is installed in the latter stage of the dust collector 7 for collection.
As shown in FIG. 3, when the heat exchanger 6 is installed in the latter stage of the collecting dust collector 7 , since the mixed gas introduced into the heat exchanger 6 is not accompanied by calcium oxide (CaO), The heat exchanger 6 does not require dust countermeasures. Therefore, there is an advantage that other heat exchangers such as a plate type other than the straight tube heat exchanger can be applied, but since the hot dust mixed gas before the heat exchange is introduced into the collecting dust collector 7. The dust collectors that can be used are limited to high temperatures. Further, since the mixed gas supplied to the dryer 2 is limited to the operating temperature of the dust collector or lower, the temperature of the combustion air in the firing furnace 3 is lowered, and the thermal efficiency of the lime cake firing system is lowered. It is desirable to adopt the system configuration of.

FIG. 4 is an explanatory view showing an outline of the basic structure of the heat exchanger 6 for heat recovery used in the firing system of this embodiment. As shown in the figure, since the heat fluid on the high temperature side of the heat exchanger 6 is accompanied by fine particles of calcium oxide (CaO), in order to avoid adhesion of fine powder in the pipe, The high temperature side gas flow path communicating with the gas inlet 61 and the high temperature side gas outlet 62 is constituted by the straight pipe portion 60 to form a plurality of thin tube groups .
On the other hand, the air (low temperature side fluid) introduced from the low temperature side air inlet 63 crosses the surface of the straight pipe portion 60 which is the flow path of the high temperature side thermal fluid, and moves to the low temperature side air inlet 64 to recover heat. And becomes combustion air for the firing furnace 3.
That is, the high temperature side flow path of the heat exchanger 6 is a straight pipe part 60 for easy cleaning in order to prevent sticking due to recarbonation of powdery calcium oxide (CaO) accompanying the mixed gas, Further, a top plate 65 is installed on the upper part of the heat exchanger 6 and a bottom plate 66 is installed on the lower part of the heat exchanger 6 so as to be detachable, so that inspection and cleaning are easy.

That is, the invention according to claim 1 is, as a solution to the problem 1, a lime cake dryer (2) for drying a high water content lime cake, and a high water content lime cake (high water content ) supplied from the lime cake dryer (2). powdery calcium CaCO ₃₎ calcined to calcium oxide carbonate (CaO), as well as a lime cake baking system comprising a carbon dioxide (CO ₂₎ thermally decomposing sintering furnace (3),
To prevent the firing furnace (3) calcium oxide contained in the firing exhaust gas discharged from the (CaO) and re-carbonation by carbon dioxide (CO _2), and exhaust gas discharge portion of the calcination furnace (3) (5 ) , The air is mixed with the calcined exhaust gas for rapid cooling, the temperature of the mixed gas is set to 550 ° C. or lower, and the partial pressure of carbon dioxide (CO ₂ ) in the mixed gas is set to 0.012 MPa or lower, Suppresses recarboxylation of calcium oxide (CaO),
Said heat exchanger downstream of the exhaust gas discharge portion of the sintering furnace (3) (5) (6) provided in the mixed gas to be introduced into the high temperature side of the heat exchanger (6), heat exchanger (6 ) , The air supplied from the low temperature side is heated to combustion air for the firing furnace (3) , and the combustion air is introduced into the firing furnace (3) , and further to the subsequent stage of the heat exchanger (6) . A powdery calcium oxide (CaO) dust collector (7) is installed to separate and collect calcium oxide (CaO) from the mixed gas, and the mixed gas after separation and collection is fed to the lime cake dryer (2) . It is characterized in that it is introduced and the dry heat transfer efficiency is improved by direct contact between the mixed gas and the lime cake.

The invention according to claim 2 provides a lime cake dryer (2) for drying a high water content lime cake, and a high water content lime cake (high water content powdery calcium carbonate CaCO ₃ ) supplied from the lime cake dryer (2). A lime cake baking system comprising a baking furnace (3) for baking calcium oxide (CaO) and carbon dioxide (CO ₂ ) to thermally decompose,
To prevent the firing furnace (3) calcium oxide contained in the firing exhaust gas discharged from the (CaO) and re-carbonation by carbon dioxide (CO _2), and exhaust gas discharge portion of the calcination furnace (3) (5 ) , The air is mixed with the calcined exhaust gas for rapid cooling, the temperature of the mixed gas is set to 550 ° C. or lower, and the partial pressure of carbon dioxide (CO ₂ ) in the mixed gas is set to 0.012 MPa or lower, Suppresses recarboxylation of calcium oxide (CaO),
A dust collector (7) for collecting powdery calcium oxide (CaO ) is installed after the exhaust gas discharge part (5 ) in the firing furnace (3), and heat is further provided after the dust collector (7) for collection. An exchanger (6) is installed, powdery calcium oxide (CaO) is recovered from the mixed gas before being introduced into the heat exchanger (6) by the dust collector (7) for collection, and the heat exchange is performed. after the mixed gas as a high-temperature side heat fluid introduced into a vessel (6) was prevented from being entrained powdered calcium oxide (CaO), and introducing the mixed gas into the lime cake drier (2), the The direct contact between the mixed gas and the lime cake improves the drying heat transfer efficiency.
Is characterized in that the air supplied from the low temperature side of the heat exchanger (6) so as to introduce into said sintering furnace (3) as combustion air for the firing furnace is heated by heat exchange (3).

Claims (3)

A lime cake dryer for drying a high water content lime cake, a high water content lime cake (high water content powdery calcium carbonate CaCO ₃ ) supplied from this lime cake dryer is baked to give calcium oxide (CaO), and carbon dioxide ( A lime cake baking system comprising a baking furnace for thermally decomposing to CO ₂ ),
In order to prevent recarbonation due to calcium oxide (CaO) and carbon dioxide (CO ₂ ) contained in the calcination exhaust gas discharged from the calcination furnace, air is added to the calcination exhaust gas at the flue gas discharge part of the calcination furnace. Are rapidly cooled, the temperature of the mixed gas is set to 550 ° C. or lower, and the partial pressure of carbon dioxide (CO ₂ ) in the mixed gas is set to 0.012 MPa or lower to re-carbonate calcium oxide (CaO). A lime cake baking system characterized by suppressing a reaction. A heat exchanger is provided in the latter stage of the exhaust gas discharge part in the firing furnace, and the air supplied from the low temperature side of the heat exchanger is heated by the mixed gas introduced into the high temperature side of the heat exchanger to perform the firing furnace. As combustion air for use, the combustion air is introduced into the firing furnace, and a dust collector for powdered calcium oxide (CaO) is further installed in the latter stage of the heat exchanger to remove calcium oxide (CaO) from the mixed gas. The mixed gas after being separated and collected and repaired is introduced into the lime cake dryer, and the dry heat transfer efficiency is improved by direct contact between the mixed gas and the lime cake. Lime cake baking system. When the heat exchanger is used, a mixed gas of calcined exhaust gas and air is used as a high-temperature side heat fluid of the heat exchanger, and the flow path is formed by a thin tube group composed of a straight tube portion, and calcium oxide ( To prevent re-carbonation and sticking of CaO),
For the heated air, the heat transfer tube case is divided into multiple chambers, and the flow path for heat recovery is orthogonal to the heat transfer tube and the outer surface is orthogonal to the multi-stage to be the low temperature side flow path. The lime cake baking system according to claim 1 or 2, wherein a heat exchanger provided with an inspection port for inspecting and removing chemical deposits is applied.

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