Cement clinker production facility and mercury recovery method

Abstract

To provide a production facility of cement clinker capable of efficiently removing and recovering mercury.SOLUTION: A cement clinker production facility 1 includes a raw material preparation device 2, a firing device 3, and a mercury removal and recovery device 4, wherein the mercury removal and recovery device 4 is equipped with: a dust collection device 41 that collects and recovers dust from the exhaust gas discharged from the raw material preparation device 2 or firing device 3; a mercury vaporization chamber 42 including an overheated steam introduction means 47, and heating the dust collected by the dust collection device 41 using overheated steam to vaporize the mercury attached to the dust; a pressure control means 49 that keeps the pressure less than atmospheric pressure inside the mercury vaporization chamber 42; and a mercury-containing water recovery device 43 that cools the mercury vaporized in the mercury vaporization chamber 42 together with the overheated steam to recover the resultant mercury-containing water.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cement clinker production facility that produces cement clinker while removing mercury, and also to a mercury removal and recovery method that removes and recovers mercury in the cement clinker production process. [Background technology]

[0002] When mercury (including mercury compounds) is contained in natural raw materials such as limestone, fuels such as coal and heavy oil, or waste materials such as sludge and incineration ash used in the cement clinker manufacturing process, the mercury vaporizes and becomes mercury gas in the high-temperature parts of cement clinker manufacturing equipment such as rotary kilns. The mercury gas-containing exhaust gas generated in the rotary kiln is sent to a raw material dryer or other raw material preparation equipment in order to use the residual heat for drying raw materials. The exhaust gas after passing through the raw material dryer or other raw material preparation equipment is sent to a dust collection device such as a bag filter or an electric dust collector, and the dust contained in the exhaust gas is collected. Mercury condenses and adheres to this dust as the temperature decreases, or even if it does not condense, it is adsorbed to the dust (both are simply referred to as "adhered" in the present invention), so that mercury is removed from the exhaust gas by collecting this dust. Meanwhile, the collected dust is reused as a cement clinker raw material.

[0003] However, as mentioned above, when the raw materials and fuel brought into the cement clinker production facility contain a large amount of mercury, there is a risk that the mercury gas sent to the dust collection device together with the flue gas will not completely adhere to the dust and will be released in that state into the atmosphere from the chimney together with the flue gas.

[0004] As an attempt to solve such problems, for example, Patent Document 1 discloses an invention titled "Method for Removing Mercury from Combustion Exhaust Gas" that relates to a method for easily and low-cost removing mercury contained in combustion exhaust gas generated in cement manufacturing facilities.

[0005] The invention disclosed in Patent Document 1 is characterized in that the flue gas discharged from the top cyclone of a suspension preheater in a cement manufacturing facility is introduced into a coal drying and crushing device, and mercury contained in the flue gas is adsorbed onto pulverized coal obtained by crushing coal in this coal drying and crushing device, and then the flue gas and the pulverized coal are introduced into a bag filter to capture only the pulverized coal, thereby purifying the flue gas.

[0006] According to this mercury removal method using a coal drying and crushing device, which is ancillary equipment of a cement production facility, there is no need to install a new device for mercury removal, so that purification of combustion exhaust gas can be performed easily and at low cost.

[0007] Furthermore, Patent Document 2 discloses an invention titled “Method for treating exhaust gas from a cement kiln,” which relates to a method for removing mercury, organic chlorine compounds, and dust from exhaust gas generated in a cement kiln in which various types of waste are used as raw materials or fuel.

[0008] The invention disclosed in Patent Document 2 is characterized in that exhaust gas is extracted from a dust collector and sent to an adsorption tower, in which mercury and organic chlorine compounds contained in the exhaust gas are adsorbed onto activated carbon or pulverized coal. The activated carbon or pulverized coal is then heated to 400°C or higher in a heating furnace to remove the mercury and organic chlorine compounds, and the activated carbon or pulverized coal obtained in this process is fed into a cement kiln.

[0009] According to such a method for treating exhaust gas from a cement kiln, it is possible to reduce the size of the heating furnace for removing mercury and organic chlorine compounds, and to reduce the energy required for heating. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2010-75784 A [Patent Document 2] JP 2006-96615 A Summary of the Invention [Problem to be solved by the invention]

[0011] As described above, various methods have been proposed for removing mercury from exhaust gases generated in cement manufacturing facilities, but new methods for more efficiently removing and recovering mercury are needed.

[0012] An object of the present invention is to provide a cement clinker production facility capable of efficiently removing and recovering mercury, and to provide a mercury removal and recovery method capable of efficiently removing and recovering mercury in the cement clinker production process. [Means for solving the problem]

[0013] As a result of intensive research aimed at solving the above-mentioned problems, the inventors have found that mercury can be efficiently removed and recovered from exhaust gas generated in cement manufacturing facilities by capturing and recovering dust in the exhaust gas and subjecting the dust to a specified treatment, and have completed the present invention.

[0014] That is, the present invention is as follows. [1] A cement clinker production facility equipped with a raw material preparation device, a calcination device, and a mercury removal and recovery device, The mercury removal and recovery apparatus comprises: a dust recovery device that captures and recovers dust in exhaust gas discharged from the raw material preparation device or the calcination device; a mercury vaporization chamber including a superheated steam introduction means for heating the dust collected by the dust collection device with the superheated steam to vaporize the mercury adhering to the dust; a pressure adjusting means for maintaining a pressure inside the mercury vaporization chamber at a pressure less than atmospheric pressure; a mercury-containing water recovery device that cools the mercury vaporized in the mercury vaporization chamber together with superheated steam to recover the mercury-containing water generated; A cement clinker production facility comprising:

[0015] [2] The cement clinker production facility according to [1] above, characterized in that the pressure adjustment means is a means for maintaining the pressure inside the mercury vaporization chamber at 20 kPa or less. [3] The cement clinker production facility described in [1] or [2] above, characterized in that the mercury removal and recovery device further includes a mercury separation and recovery device that separates and recovers mercury from the mercury-containing water obtained in the mercury-containing water recovery device.

[0016] [4] A method for removing and recovering mercury in exhaust gas generated during the production of cement clinker, comprising: a dust recovery step of collecting and recovering dust in the exhaust gas; a mercury vaporization step of heating the dust collected in the dust collection step under reduced pressure with superheated steam to vaporize mercury adhering to the dust; a mercury-containing water recovery step of cooling the mercury vaporized in the mercury vaporization step together with the superheated steam to recover the mercury-containing water produced; A method for removing and recovering mercury comprising the steps of:

[0017] [5] The mercury removal and recovery method according to [4] above, wherein the treatment pressure in the mercury vaporization step is 20 kPa or less. [6] The mercury removal and recovery method according to [4] or [5] above, further comprising a mercury separation and recovery process for separating and recovering mercury from the mercury-containing water recovered in the mercury-containing water recovery process. [7] The mercury removal and recovery method according to [6] above, wherein the treatment in the mercury separation and recovery step is a treatment in which mercury is precipitated and separated using a flocculant. Effect of the Invention

[0018] According to the cement clinker production facility of the present invention, mercury can be efficiently removed and recovered from exhaust gas generated in the cement production facility. Also, according to the mercury removal and recovery method of the present invention, mercury can be efficiently removed and recovered in the cement clinker production process. [Brief description of the drawings]

[0019] [Figure 1] 1 is a schematic diagram showing an entire cement clinker production facility according to an embodiment of the present invention. [Diagram 2] 1 is a schematic diagram of a mercury removal and recovery device for a cement clinker production facility according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The cement clinker manufacturing equipment of the present invention comprises a raw material preparation apparatus, a calcination apparatus, and a mercury removal and recovery apparatus. The mercury removal and recovery apparatus comprises a dust recovery apparatus that captures and recovers dust in the exhaust gas discharged from the raw material preparation apparatus or the calcination apparatus, a mercury vaporization chamber that is equipped with a superheated steam introduction means and heats the dust recovered in the dust recovery apparatus using superheated steam to vaporize mercury (including mercury compounds; the same applies below) attached to the dust, a pressure adjustment means that maintains a pressure within the mercury vaporization chamber at less than atmospheric pressure, and a mercury-containing water recovery apparatus that cools the mercury vaporized in the mercury vaporization chamber together with the superheated steam and recovers the mercury-containing water generated.

[0021] The raw material preparation equipment includes a raw material dryer, a raw material mill, etc. The calcination equipment includes a cyclone, a calcination furnace, etc., a preheater unit for calcining the cement clinker raw material, and a rotary kiln for main calcining the calcined cement clinker raw material.

[0022] In the present invention, the exhaust gas from which dust is recovered is not particularly limited as long as it is a gas before being discharged into the atmosphere from the raw material preparation apparatus or the calcination apparatus, and is preferably an exhaust gas discharged from the rotary kiln of the calcination apparatus, and more preferably an exhaust gas that is discharged from the rotary kiln and then introduced into the raw material dryer of the raw material preparation apparatus and discharged therefrom.

[0023] In the cement clinker production facility of the present invention, mercury can be efficiently removed and recovered from exhaust gas generated in the cement production facility by processing in a mercury removal and recovery device including a dust recovery device, a mercury vaporization chamber, and a mercury-containing water recovery device. In addition, because superheated steam is used as the carrier gas in the mercury removal and recovery device, carrier gas such as air that was previously introduced into the mercury removal and recovery device is no longer necessary, and the amount of exhaust gas can be reduced. Furthermore, because mercury is vaporized under reduced pressure, the amount of superheated steam supplied can be reduced, and the amount of mercury-containing water generated can be reduced. In the present invention, volatile heavy metals such as zinc, lead and cadmium can also be removed in addition to mercury.

[0024] A cement clinker production facility according to one embodiment of the present invention will be described below with reference to Fig. 1. Fig. 1 is a schematic diagram showing the entire cement clinker production facility. In the figure, solid arrows indicate the flow of raw materials moving through the cement clinker production facility, dotted arrows indicate the flow of exhaust gas, and dashed arrows indicate the flow of mercury in dust collected from the exhaust gas by a dust recovery device.

[0025] As shown in FIG. 1, the cement clinker production facility 1 includes a raw material preparation apparatus 2 that prepares raw materials for cement clinker, a calcination apparatus 3 that calcines the raw materials for cement clinker prepared in the raw material preparation apparatus 2, and a mercury removal and recovery apparatus 4 that removes and recovers mercury in exhaust gas.

[0026] The raw material preparation apparatus 2 includes a raw material dryer 21, a raw material mill 22, a raw material mixing silo 23, and a raw material storage silo 24. The raw material preparation apparatus 2 is used to prepare the cement clinker raw material (raw material preparation process).

[0027] In the raw material preparation process, limestone, clay, silica stone, iron oxide raw materials, etc. are mixed, and then sent to raw material dryer 21 where they are dried. In raw material dryer 21, the raw materials are dried using high-temperature exhaust gas sent from calciner 3. The raw materials are then sent to raw material mill 22 where they are pulverized. The raw materials pulverized in raw material mill 22 are sent to raw material mixing silo 23 where they are homogeneously blended, and then stored in raw material storage silo 24. Meanwhile, the exhaust gas discharged from raw material dryer 21 is sent to mercury removal and recovery device 4.

[0028] The calcination device 3 includes a plurality of cyclones 31 and a calcination furnace 32, a preheater section 33 for calcining the cement clinker raw materials, a rotary kiln 34 for calcining the calcined cement clinker raw materials, and a clinker cooler 35 for cooling the calcined cement clinker. The calcination device 3 is used to calcinate the cement clinker raw materials (calcination process).

[0029] In the firing process, the powdered raw materials that have been dried, crushed, etc. in the raw material preparation process are sent to the preheater section 33 and temporarily fired. The rotary kiln 34 has a gentle slope, and the powdered raw materials preheated in the preheater section 33 are fired at a high temperature (e.g., about 1450°C) while moving slowly inside the rotary kiln 34 due to this slope and rotational motion. The powdered raw materials fired in the rotary kiln 34 are quenched in the clinker cooler 35 and become a black, lumpy fired product called cement clinker.

[0030] Following the burning process, a finishing process is carried out in which gypsum and the like are added to the produced cement clinker to produce cement.

[0031] Next, the main flow of exhaust gas in the cement clinker manufacturing process will be described. The exhaust gas generated in the rotary kiln 34 rises inside the preheater section 33 in a direction opposite to the flow of the powder raw material, and is discharged from the uppermost cyclone 31, as indicated by the dotted arrow in Fig. 1. This exhaust gas is then sent to the raw material dryer 21 so that its residual heat can be used to dry the raw materials. The exhaust gas discharged from the raw material dryer 21 is sent to the mercury removal and recovery device 4, where the mercury (mercury-containing dust) is removed, and then the exhaust gas is released into the atmosphere from the chimney 5. Therefore, the exhaust gas released to the outside does not contain mercury.

[0032] Mercury vaporizes into mercury gas inside the preheater section 33 and the rotary kiln 34, and is not contained in the cement clinker sent to the finishing process.

[0033] Next, the mercury removal and recovery device 4 will be described with reference to Fig. 2. Fig. 2 is a schematic diagram of a mercury removal and recovery device for a cement clinker production facility according to one embodiment of the present invention.

[0034] As shown in FIG. 2, the mercury removal and recovery device 4 includes a dust recovery device 41, a mercury vaporization chamber 42, and a mercury-containing water recovery device 43.

[0035] (Dust collection device) The dust collection device 41 is equipped with a bag filter 44 (first bag filter), a cyclone 45 that classifies the dust collected from the bag filter 44, and a bag filter 46 (second bag filter) that collects fine dust particles obtained by classification in the cyclone 45.

[0036] First, dust is collected by a bag filter 44 from the exhaust gas discharged from the raw material dryer 21. A part of this collected dust is sent to a cyclone 45, and the remaining dust is returned to the system of the cement clinker production facility 1. In the cyclone 45, fine dust particles are separated, and the fine dust particles are collected in a bag filter 46. The relatively heavy dust particles are returned to the system of the cement clinker production facility 1. Since the fine dust particles have a high concentration of mercury, mercury can be removed efficiently by removing this fine dust.

[0037] The dust collection device is not particularly limited as long as it can collect dust from the exhaust gas, and an electric dust collector can be used in addition to a bag filter. In order to collect fine dust particles, it is preferable to combine a cyclone (powder separator) as necessary. When a multi-stage electric dust collector is used, it is preferable to collect dust from the latter stage in order to collect fine dust particles with a high mercury concentration.

[0038] (Mercury vaporization chamber) The mercury vaporization chamber 42 is equipped with a superheated steam introduction means 47, and is a means for heating the fine particles of dust with a high mercury concentration collected by the dust collection device 41 under reduced pressure using the introduced superheated steam, thereby vaporizing the mercury adhering to the dust. The mercury vaporization process is carried out in this mercury vaporization chamber 42.

[0039] The inside of the mercury vaporization chamber 42 is maintained at a pressure lower than atmospheric pressure by a vacuum pump 49 serving as a pressure adjusting means provided downstream of the mercury vaporization chamber 42 and the mercury-containing water recovery device 43. The vacuum pump 49 is a means for maintaining the pressure inside the mercury vaporization chamber 42 at preferably 20 kPa or less, more preferably 15 kPa or less, and even more preferably 10 kPa or less. The lower limit side may be appropriately determined, and is, for example, 1 kPa or more. The vacuum pump 49 reduces the pressure inside the mercury vaporization chamber 42 and the mercury-containing water recovery device 43, and guides the vaporized mercury and superheated steam downstream.

[0040] In the present invention, the mercury vaporization chamber 42 is kept under reduced pressure, and as a result, the amount of superheated steam introduced into the mercury vaporization chamber 42 is reduced, and the amount of mercury-containing water recovered by the mercury-containing water recovery device 43 is also reduced.

[0041] The temperature of the superheated steam introduced from the superheated steam introduction means 47 may be any temperature that can vaporize mercury at the reduced pressure, and is, for example, preferably 30° C. or more higher than the boiling point at that pressure, more preferably 50° C. or more higher, with the upper limit being, although not particularly limited, about 100° C. higher. Specifically, when the inside of the mercury vaporization chamber 42 is 10 kPa, the temperature is preferably 300° C. or more, more preferably 400° C. or more. This superheated steam not only serves to heat the mercury, but also serves as a carrier gas.

[0042] The mercury vaporization chamber 42 has a heat-retaining structure and is equipped with a heating means such as an external heater, and the inside of the chamber is preferably kept at a temperature approximately equal to the temperature of the superheated steam introduced. By keeping the temperature within this range, the mercury can be effectively vaporized and removed from the dust. In addition, by heating the chamber with the heating means, a sufficient amount of heat required to vaporize the mercury can be secured.

[0043] The mercury vaporization chamber 42 is equipped with a stirring means, and while stirring the dust introduced into the mercury vaporization chamber 42, it heats the dust using superheated steam under reduced pressure to vaporize the mercury attached to the dust into mercury gas. Dust is continuously or intermittently introduced into the mercury vaporization chamber 42 from the bag filter 46 of the dust recovery device 41, and the mercury gas vaporized in the mercury vaporization chamber 42 is sent together with the superheated steam to the downstream mercury-containing water recovery device 43. The dust from which mercury has been removed in the mercury vaporization chamber 42 is continuously or intermittently discharged and returned to the system of the cement clinker production facility 1.

[0044] (Mercury-containing water recovery device) The mercury-containing water recovery device 43 is a means for cooling the mercury vaporized in the mercury vaporization chamber 42 together with the superheated steam to recover the generated mercury-containing water. In the mercury-containing water recovery device 43, the mercury-containing water recovery process is carried out.

[0045] The mercury-containing water recovery device 43 is not particularly limited as long as it is a means capable of cooling the mercury vaporized in the mercury vaporization chamber 42 together with the superheated steam, and examples thereof include a heat exchange type and a scrubber type. Specifically, for example, as shown in Fig. 2, it is possible to use a device equipped with a cooler 48 (cooling means) that circulates cooling water for cooling. The cooler 48 may be a single stage or two or more stages.

[0046] The mercury-containing water recovery apparatus preferably uses a cooling means to cool the inside of the apparatus to a temperature below the boiling point of water at that pressure, and preferably to a temperature at least 10° C. lower, and more preferably at least 30° C. lower, than the boiling point at that pressure. By cooling to a temperature within this range, mercury and superheated water vapor can be effectively liquefied and recovered as mercury-containing water.

[0047] In the present invention, since the superheated steam serves as a carrier gas, no separate carrier gas is required, and since the superheated steam becomes liquid in the mercury-containing water recovery device 43, the generation of exhaust gas can be suppressed. Furthermore, in the mercury separation and recovery device described below, mercury can be recovered from mercury-containing water by simple water treatment. Furthermore, since mercury is recovered as mercury-containing water, adhesion of compounds such as mercury and other heavy metals within the device can be reduced. As described above, although superheated steam is used as a carrier gas in the present invention, the use of a carrier gas such as air is not excluded.

[0048] (Mercury separation and recovery equipment) The mercury-containing water recovered by the mercury-containing water recovery apparatus is separated into mercury and water in a mercury separation and recovery apparatus, and the mercury is recovered. A mercury separation and recovery process is carried out in this mercury separation and recovery apparatus. The treatment in the mercury separation and recovery process is not particularly limited as long as it is a treatment that can separate mercury from water, and an example of such a treatment is a treatment in which mercury is precipitated and separated using a flocculant. This makes it possible to recover high-concentration floc-like mercury. Note that in the present invention, volatile heavy metals such as zinc, lead, and cadmium can also be recovered simultaneously with mercury.

[0049] The mercury removal and recovery method of the present invention can be carried out using the cement clinker production facility of the present invention described above. That is, the mercury removal and recovery method of the present invention is a mercury removal and recovery method for removing mercury in exhaust gas generated in the production of cement clinker, and includes a dust recovery step of collecting and recovering dust in the exhaust gas, a mercury vaporization step of heating the dust recovered in the dust recovery step with superheated steam under reduced pressure to vaporize the mercury attached to the dust, and a mercury-containing water recovery step of cooling the mercury vaporized in the mercury vaporization step together with the superheated steam to recover the mercury-containing water generated. It is also preferable to include a mercury separation and recovery step of separating and recovering mercury from the mercury-containing water recovered in the mercury-containing water recovery step. Each step is the same as that described in the cement clinker production facility of the present invention, and therefore will not be described. EXAMPLES

[0050] 1450 g of the captured dust collected in the dust recovery device 41 was supplied to the mercury vaporization chamber 42, and the vacuum pump 49 was operated to maintain the inside of the system at a reduced pressure of 12 kPa. Next, the inside of the chamber was heated to about 400°C, and superheated steam at 400°C was introduced from the superheated steam introduction means 47 to gasify the mercury, and the steam containing the mercury gas was sent to the mercury-containing water recovery device 43 maintained at about 30°C, where the mercury gas and superheated steam were cooled and recovered as mercury-containing water. The time from heating the inside of the chamber to about 400°C and introducing superheated steam at 400°C from the superheated steam introduction means 47 to completion was 60 minutes.

[0051] The weight and mercury concentration of the captured dust were measured before and after treatment in the mercury chamber 42. The mercury concentration of the mercury-containing water recovered in the mercury-containing water recovery device 43 was also measured by reduction vaporization atomic absorption spectrometry. The results are shown in Table 1.

[0052] [Table 1]

[0053] As shown in Table 1, the mercury concentration in the captured dust before heating was 33.0 ppm, while the mercury concentration in the mercury-containing water after removal was 1071.8 ppm, which means that the concentration ratio was about 32 times. This shows that mercury was concentrated in the mercury-containing water obtained by heating and cooling the dust collected from the dust collection device 41, and that efficient separation and recovery processing is possible in the subsequent mercury separation and recovery process. [Industrial Applicability]

[0054] INDUSTRIAL APPLICABILITY The cement clinker production facility of the present invention is industrially useful since it can produce cement clinker while recovering mercury. [Explanation of symbols]

[0055] 1. Cement clinker manufacturing facility 2...Raw material preparation equipment 3…Baking equipment 4. Mercury removal and recovery equipment 5. Chimney 21...Raw material dryer 22...Raw material mill 23...Raw material mixing silo 24…Raw material storage silo 31...Cyclone 32... Temporary firing furnace 33…Preheater section 34…Rotary kiln 35…Clinker cooler 41...Dust collection device 42…Mercury vaporization chamber 43...Mercury-containing water recovery device 44...Bag filter (first bag filter) 45…Cyclone 46...Bag filter (second bag filter) 47...Superheated steam introduction means 48...Cooler (cooling means) 49...Vacuum pump (pressure adjustment means)

Claims

1. A cement clinker production facility including a raw material preparation device, a calcination device, and a mercury removal and recovery device, The mercury removal and recovery apparatus comprises: a dust recovery device that captures and recovers dust in exhaust gas discharged from the raw material preparation device or the calcination device; a mercury vaporization chamber including a superheated steam introduction means for heating the dust collected by the dust collection device with the superheated steam to vaporize the mercury adhering to the dust; a pressure adjusting means for maintaining a pressure inside the mercury vaporization chamber at a pressure less than atmospheric pressure; a mercury-containing water recovery device that cools the mercury vaporized in the mercury vaporization chamber together with superheated steam to recover the mercury-containing water generated; A cement clinker production facility comprising:

2. 2. The cement clinker production facility according to claim 1, wherein the pressure adjusting means is a means for maintaining the pressure inside the mercury vaporization chamber at 20 kPa or less.

3. 2. The cement clinker production facility according to claim 1, wherein the mercury removal and recovery device further comprises a mercury separation and recovery device that separates and recovers mercury from the mercury-containing water obtained in the mercury-containing water recovery device.

4. A method for removing and recovering mercury from exhaust gas generated in the production of cement clinker, comprising the steps of: a dust recovery step of collecting and recovering dust in the exhaust gas; a mercury vaporization step of heating the dust collected in the dust collection step under reduced pressure with superheated steam to vaporize mercury adhering to the dust; a mercury-containing water recovery step of cooling the mercury vaporized in the mercury vaporization step together with the superheated steam to recover the mercury-containing water produced; A method for removing and recovering mercury comprising the steps of:

5. 5. The method for removing and recovering mercury according to claim 4, wherein the treatment pressure in the mercury vaporization step is 20 kPa or less.

6. The mercury removal and recovery method according to claim 4, further comprising a mercury separation and recovery step of separating and recovering mercury from the mercury-containing water recovered in the mercury-containing water recovery step.

7. 7. The method for removing and recovering mercury according to claim 6, wherein the treatment in the mercury separation and recovery step is a treatment in which mercury is precipitated and separated using a flocculant.

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