Chlorine bypass system and method for treating cement kiln extraction gas

Abstract

[Problem] To provide a chlorine bypass system or the like which is capable of suppressing device cost and operation cost while maintaining stable operation. [Solution] A chlorine bypass system 1 is provided with: a probe 3 for cooling some of combustion exhaust gas while extracting the gas from a kiln exhaust gas passage extending from a kiln end of a cement kiln 2 to a lowermost cyclone of a preheater; an admixture addition device (a tank 7 and a blower 8) for further cooling an exhaust gas G2 by adding a cement admixture M to an exhaust gas G1 that is extracted by the probe 3; and a bag filter 9 for collecting dust from an exhaust gas G5 to which the cement admixture M has been added. The chlorine bypass system 1 may comprise a cyclone 6 for collecting dust from an exhaust gas G3 that is extracted by the probe 3, wherein the cement admixture M may be added from the admixture addition device to an outlet gas G4 of the cyclone 6, and dust may be collected from the exhaust gas G5, to which the cement admixture M has been added, by the bag filter 9.

Description

Chlorine bypass system and method for treating extracted gas from cement kiln

[0001] The present invention relates to a chlorine bypass system that extracts a part of combustion exhaust gas from the kiln exhaust gas flow path extending from the kiln tail of a cement kiln to the lowermost cyclone of a preheater to remove chlorine, and a method for treating extracted gas from a cement kiln.

[0002] In recent years, with the increase in the amount of waste treated in cement production facilities, the amount of volatile components such as chlorine brought into cement kilns has also increased, and chlorine bypass systems for removing chlorine that causes problems such as clogging of preheaters in cement production facilities have been used.

[0003] As shown in FIG. 2, this chlorine bypass system includes a probe 23 that extracts a part G11 of combustion gas from the kiln exhaust gas flow path extending from the kiln tail of the cement kiln 22 to the lowermost cyclone (not shown), a cooling fan 24 that supplies cold air to the inside of the probe 23 to quench the extracted exhaust gas G11, a cyclone 25 as a classifier that separates coarse dust D21 of dust contained in the cooled exhaust gas G21, a heat exchanger 26 that cools the exhaust gas G22 containing fine powder D22 discharged from the cyclone 25, a cooling fan 27 that supplies cold air to the heat exchanger 26, a bag filter 28 that collects fine powder D24 in the exhaust gas G23 of the heat exchanger 26, a dust tank 29 that collects fine powder D23 discharged from the heat exchanger 26 and fine powder D24 (chlorine bypass dust D25) discharged from the bag filter 28, and a fan 32 for returning the exhaust gas G24 from the bag filter 28 to the cement kiln system, etc. (for example, Patent Document 1).

[0004] In the chlorine bypass system 21, the coarse powder D21 separated by the cyclone 25 has a low chlorine concentration and is therefore returned to the cement kiln system, and the recovered chlorine bypass dust D25 with a high chlorine concentration is transferred from the dust tank 29 through the dust tank 30 and the feeder 31 to the storage tank of the product mill by a tank truck, and is added to the product while performing quality control.

[0005] Japanese Unexamined Patent Publication No. 2017-52664

[0006] In the chlorine bypass system 21 described above, a bag filter 28 is used, so the exhaust gas G21 of the chlorine bypass needs to be cooled to the heat resistance temperature of the filter cloth (for example, 150°C). Although it is possible to cool the exhaust gas G21 by introducing cold air, since the exhaust gas G21 contains NOx and SOx, it needs to be returned to the cement kiln system after cooling, and the heat loss increases due to the introduction of cold air. For this reason, a highly efficient plate heat exchanger was used as the heat exchanger 26 for cooling the exhaust gas G21.

[0007] However, plate heat exchangers are expensive, and there is a risk of chloride buildup inside the heat exchanger causing blockage, making it difficult to maintain stable operation. In addition, although high concentrations of chlorine can be separated by classification using the cyclone 25, the recovered powder from the bag filter 28 becomes fine, high-concentration chloride, and when this is pumped into the product system, it adheres to the inside of the pumping pipe, posing a problem that prevents pumping.

[0008] This invention has been made in view of the problems of the above-mentioned conventional technology, and aims to provide a chlorine bypass system, etc., that can keep equipment costs and operating costs low while maintaining stable operation.

[0009] To achieve the above objective, the present invention provides a chlorine bypass system comprising: a probe that extracts and cools a portion of the combustion exhaust gas from the kiln exhaust gas flow path from the kiln tail to the lowest cyclone of the preheater; a cement mixture adding device that adds a cement mixture at a low temperature, preferably room temperature (-30°C to 100°C, preferably around -30°C to 50°C) to the exhaust gas extracted by the probe to further cool the exhaust gas; and a bag filter that collects dust from the exhaust gas to which the cement mixture has been added.

[0010] According to the present invention, since heat exchangers such as conventional plate heat exchangers are not installed, equipment costs can be reduced, and stable operation is possible as there is no need to consider blockages in the heat exchanger. Maintenance costs can also be reduced, keeping operating costs low. Furthermore, conventionally, the chlorine concentration of recovered chlorine bypass dust was high and it could not be pumped to the cement manufacturing process. However, according to the present invention, by mixing the chlorine bypass dust with a compound that can be added to cement, the chlorine concentration of the chlorine bypass dust can be reduced, resulting in better removal by the bag filter and enabling the chlorine bypass dust to be pumped to the cement mill.

[0011] In the chlorine bypass system described above, a cyclone may be provided to collect dust from the exhaust gas extracted by the probe, the cement mixture may be added to the outlet gas of the cyclone from the mixture addition device, and dust may be collected from the exhaust gas to which the mixture has been added by the bag filter.

[0012] Furthermore, by making the gas piping from the probe to the bag filter, or the gas piping from the cyclone to the bag filter, have an inverted V-shaped portion, dust accumulation inside the gas piping can be prevented.

[0013] Furthermore, by providing a spiral-shaped stationary mixer in the gas piping from the probe to the bag filter or from the cyclone to the bag filter, heat exchange between the exhaust gas and the cement mixture can be enhanced.

[0014] Furthermore, the present invention relates to a method for treating cement kiln extraction gas, characterized in that a portion of the combustion exhaust gas is extracted and cooled from the kiln exhaust gas flow path from the end of the cement kiln to the lowest cyclone of the preheater, a cement mixture is added to the extracted exhaust gas to further cool the exhaust gas, and dust is collected from the exhaust gas to which the cement mixture has been added.

[0015] According to the present invention, since it is not necessary to install heat exchangers such as conventional plate heat exchangers, equipment costs and operating costs are reduced, and stable operation is possible. Furthermore, by adding a compound that can be added to cement, the chlorine concentration of chlorine bypass dust can be reduced. In addition, the handling of the mixture of cement compound and high-concentration chlorine-containing dust (chlorine bypass dust) is improved, and stable extraction from the storage tank is possible.

[0016] Furthermore, by pumping high-chlorine-concentration dust obtained by collecting it from exhaust gas to which the cement mixture has been added to a cement mill or the like, operating costs can be further reduced.

[0017] This is an overall configuration diagram showing one embodiment of the chlorine bypass system according to the present invention. This is an overall configuration diagram showing an example of a conventional chlorine bypass system.

[0018] Next, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

[0019] Figure 1 shows one embodiment of the chlorine bypass system according to the present invention, which includes a probe 3 that extracts a portion of the combustion gas G1 from the kiln exhaust gas flow path from the kiln end to the lowest cyclone (not shown) of the cement kiln 2, a cooling fan 4 that rapidly cools the extracted exhaust gas G1 by supplying cold air inside the probe 3, a cooling fan 5 that further supplies cold air to the exhaust gas G2 to cool the exhaust gas G2, a cyclone 6 as a classifier that separates coarse dust D1 contained in the cooled exhaust gas G3, and exhaust from the cyclone 6 The system includes a tank 7 and a blower 8 that constitute a mixture supply machine for supplying cement mixture M as a coolant to exhaust gas G4 containing the emitted fine powder D2, a bag filter 9 for collecting dust from exhaust gas G5 after the cement mixture M has been added, a blower 11 for pumping the fine powder (chlorine bypass dust) D3 discharged from the bag filter 9 to the cement manufacturing process, and a fan 10 for returning the exhaust gas G6 from the bag filter 9 to the cement kiln system, and does not have a conventional heat exchanger 26 such as a high-efficiency plate heat exchanger (see Figure 2).

[0020] The probe 3, cooling fans 4 and 5, cyclone 6, and bag filter 9 can be the same as those commonly used in conventional chlorine bypass systems. The cement mixture M used as a coolant is, for example, room temperature calcium carbonate, slag, fly ash, pozzolan, calcined clay, clinker, or clinker dust, which is mixed with and cooled the exhaust gas G4. This cement mixture M may also contain moisture and can be used while drying in the gas piping.

[0021] Furthermore, if the gas piping from cyclone 6 to bag filter 9 were horizontal, dust accumulation inside the piping could hinder stable operation. Therefore, it is designed in an inverted V shape (lambda shape) to prevent dust accumulation.

[0022] Furthermore, in order to enhance the heat exchange between the exhaust gas G4 and the cement mixture M, a spiral-shaped stationary mixer may be incorporated into the piping between the cyclone 6 and the bag filter 9.

[0023] Next, a method for treating cement kiln extraction gas using the chlorine bypass system 1 having the above configuration will be explained with reference to Figure 1.

[0024] A portion of the combustion gas G1 is extracted by probe 3 from the kiln exhaust gas flow path from the kiln end to the lowest cyclone of cement kiln 2. At the same time, the exhaust gas G1, which is between 800°C and 1100°C, is first cooled to between 400°C and 600°C by cooling air A1 from cooling fan 4. As a result, chlorine compounds such as KCl in the exhaust gas G1 precipitate and adhere to the surface of fine powder in the exhaust gas G2.

[0025] Next, the exhaust gas G2 discharged from the probe 3 is secondarily cooled to approximately 250°C to 450°C by the cooling air A2 from the cooling fan 5.

[0026] Next, exhaust gas G3 is introduced into cyclone 6 and separated into exhaust gas G4 containing coarse powder D1 and fine powder D2. Since coarse powder D1 has a low chlorine concentration, it is returned to the cement kiln system. Meanwhile, room temperature cement mixture M is added to exhaust gas G4 from tank 7 and blower 8 as a coolant, and exhaust gas G4 is mixed and cooled. As a result, exhaust gas G5 is ultimately cooled to between 100°C and 200°C.

[0027] After adding cement admixture M, exhaust gas G5 is introduced into a bag filter 9 to recover fine particles (chlorine bypass dust) D3 with a high chlorine concentration. This is then pumped to the cement manufacturing process and added to the product while maintaining quality control.

[0028] In the above embodiment, the cement mixture M was pumped by the blower 8, but it can also be supplied by a mechanical transport device or the like.

[0029] Alternatively, without using the cyclone 6, the cement mixture M can be added to the exhaust gas G3 and then supplied directly to the bag filter 9. Furthermore, the cement mixture M may be added inside the probe 3 or to the outlet gas piping of the probe 3 to cool the exhaust gas G1, etc.

[0030] Using the chlorine bypass system 1 having the above configuration, the cement production rate is 6000 t / day, and the exhaust gas from the end of the cement kiln 2 is 2000 m³. ３ N / min, chlorine bypass rate 10% (extraction volume 200 m) ３ In case N), after introducing cold air with probe 3, the exhaust gas temperature at the outlet of cyclone 6 is 350°C and the exhaust gas volume is 710 m³. ３ By blowing in 1.8 t / h of fly ash (cement admixture M) at a rate of N / min, the temperature of the exhaust gas G5 at the inlet of the bag filter 9 could be reduced to below 150°C. The chlorine concentration of the fine powder (chlorine bypass dust) D3 recovered by the bag filter 9, which was previously 25%, could be reduced to 4.2%, making it possible to pump it to the storage tank in the cement mill room. In addition, the handling of the mixture of cement admixture and high-concentration chlorine-containing dust was improved, and it became possible to stably extract it from the storage tank.

[0031] The present invention is not limited to the embodiments described above, and can be implemented by partially modifying the configuration or partially adding other configurations within the scope of its gist. Furthermore, the illustrated embodiments are merely illustrative and are not intended to limit the technical scope of the present invention.

[0032] 1. Chlorine bypass system 2. Cement kiln 3. Probe 4, 5. Cooling fan 6. Cyclone 7. Tank 8. Blower 9. Bag filter 10. Fan 11. Blower

Claims

1. A chlorine bypass system characterized by comprising: a probe that extracts and cools a portion of the combustion exhaust gas from the kiln exhaust gas flow path from the kiln tail to the lowest cyclone of the preheater; a cement mixture addition device that adds a cement mixture to the exhaust gas extracted by the probe and further cools the exhaust gas; and a bag filter that collects dust from the exhaust gas to which the cement mixture has been added.

2. The chlorine bypass system according to claim 1, comprising a cyclone for collecting dust from exhaust gas extracted by the probe, the cement mixture being added from the mixture addition device to the outlet gas of the cyclone, and the bag filter collecting dust from the exhaust gas to which the mixture has been added.

3. The chlorine bypass system according to claim 1 or 2, characterized in that the gas piping from the probe to the bag filter or the gas piping from the cyclone to the bag filter has an inverted V-shaped portion.

4. The chlorine bypass system according to claim 1 or 2, characterized in that the gas piping from the probe to the bag filter or the gas piping from the cyclone to the bag filter has a spiral stationary mixer.

5. A method for treating extracted gas from a cement kiln, characterized by extracting and cooling a portion of the combustion exhaust gas from the kiln exhaust gas flow path from the kiln's tail end to the lowest cyclone of the preheater, adding a cement mixture to the extracted exhaust gas to further cool the exhaust gas, and collecting dust from the exhaust gas to which the cement mixture has been added.

6. The method for treating cement kiln extraction gas according to claim 5, characterized in that high-chlorine concentration dust obtained by collecting dust from exhaust gas to which the cement mixture has been added is pumped under pressure.

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