JP2007015875A - Method for producing cement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing cement capable of efficiently removing mercury-containing materials from an exhaust gas exhausted from a cement firing facility. <P>SOLUTION: This invention is characterized by including an exhaust gas treatment process of using the exhaust gas exhausted from the cement firing facility 1 for drying raw materials of cement, discharging the exhaust gas into the atmosphere after separating collected dust from the cleaned exhaust gas in a dust collector 4 and returning the collected dust to the cement firing facility 1, where in the exhaust gas treatment process all of the exhaust gas exhausted from the cement firing facility 1 are passed through a humidity control tower 2 and a dryer 3 for the cement raw materials sequentially and transferred to the dust collector 4, where in the humidity control tower 2, the exhaust gas is cooled to or below a temperature at which mercury is deposited, and all or a part of dust collected in the humidity control tower 2 are/is extracted from the exhaust gas. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing cement, and more specifically, mercury-containing substances such as mercury and mercury compounds contained in cement raw materials are released into the atmosphere in a treatment process of exhaust gas discharged from cement firing equipment. The present invention relates to a method for producing cement for reducing the amount.

  In recent years, in order to promote the recycling of wastes, various types of wastes are increasingly used as raw materials for cement production. Some of the waste contains heavy metals such as municipal waste incineration ash, coal ash, and various sludges, and the amount of heavy metals brought into the cement manufacturing process is expected to increase in the future. Among heavy metals brought into the cement manufacturing process, heavy metals with high volatility such as mercury are volatilized in the cement burning equipment, which is the high temperature part of the cement manufacturing process, so they are hardly contained in cement clinker, and mercury Vaporized and contained in exhaust gas. Part of the mercury vapor in the exhaust gas is condensed on the way, deposited on the cement raw material particles as a mercury-containing material, collected as dust collection dust with an electric dust collector, etc., and then returned to the cement firing facility again. It circulates in the circulation path through the cement baking equipment and the dust collector, but the remainder is discharged from the dust collector together with the exhaust gas. Therefore, there is a concern that when the amount of mercury-containing substances from waste increases, the amount of mercury released into the atmosphere increases and adversely affects the environment.

  In order to reduce the amount of mercury-containing substances released into the atmosphere, for example, in Patent Document 1, the raw material used for cement production is led to a heating furnace, the mercury-containing substance contained in the raw material is gasified, and this high-temperature gas is adsorbed A method for producing a cement has been proposed in which the concentration of mercury-containing material in the raw material is reduced by introducing the material into a part and adsorbing the mercury-containing material, and the raw material is guided to a cement firing facility and the cement clinker is fired.

  Moreover, in patent document 2, the dust contained in the waste gas discharged | emitted from the cement baking equipment is collected with an electric dust collector etc., the dust collection dust is guide | induced to a heating furnace, The volatile metal component contained in dust collection dust of There has been proposed a method in which the volatile metal component is heated to a volatilization temperature or more to be gasified and removed, and dust collection dust from which the volatile component has been removed is used as a part of the cement raw material.

Furthermore, in Patent Document 3, a part of the exhaust gas at 350 ° C. or higher that circulates in the piping or equipment between the cement firing facility and the chimney is extracted, and after the dust is separated from the extracted exhaust gas by a cyclone, it is condensed. There has been proposed a method in which a gas is cooled to 100 ° C. or lower by an apparatus to condense vapors contained therein.
JP 2003-192407 A Japanese Patent Laid-Open No. 2002-355531 JP 2005-97005 A

  However, in Patent Documents 1 and 2, since the mercury content of the dust collection dust and the cement raw material is low, in order to reduce the amount of mercury circulating in the circulation path passing through the cement firing facility and the dust collector, the dust collection dust and the cement raw material are used. Therefore, it is necessary to treat a large amount of mercury, and the amount of mercury cannot be reduced efficiently.

  Further, in Patent Document 3, a part of the exhaust gas at 350 ° C. or higher that circulates in the piping or apparatus between the cement firing facility and the chimney is extracted, and the mercury-containing substance in the exhaust gas is condensed by cooling, The removal efficiency of mercury-containing substances is not always sufficient. In the method of Patent Document 3, a part of exhaust gas at 350 ° C. or higher is extracted and gas-solid separated by a cyclone, and then mercury-containing substances in the exhaust gas are condensed by cooling. It must be newly installed, and a large initial equipment cost is required.

  The present invention has been made in view of such problems, and a method for producing cement capable of effectively removing mercury-containing substances in exhaust gas discharged from cement firing equipment while sufficiently suppressing increase in equipment costs. The purpose is to provide.

  As a result of intensive studies to solve the above problems, the present inventors cooled at least a part of the exhaust gas discharged from the cement firing facility to a temperature equal to or lower than the temperature at which mercury is deposited in the humidity control tower, It has been found that the above problems can be solved, and the present invention has been completed.

  That is, the present invention transfers the exhaust gas discharged from the cement firing facility to a dust collector through a cement raw material drying apparatus, and separates the purified exhaust gas into the atmosphere after separating it into purified exhaust gas and dust collected by the dust collector. An exhaust gas treatment step of discharging and returning the dust collection dust to the cement firing facility, wherein in the exhaust gas treatment step, at least part of the exhaust gas discharged from the cement firing facility is dried in a humidity control tower and the cement raw material At least a part of the exhaust gas discharged from the cement baking equipment is cooled below the temperature at which mercury is deposited in the humidity control tower and collected by the humidity control tower. All or part of the dust is extracted from the exhaust gas.

  According to this method for producing cement, at least a part of the exhaust gas discharged from the cement firing facility is transferred to the cement raw material drying device and used for drying the cement raw material. At this time, the exhaust gas discharged from the cement firing facility is in a sufficiently high temperature until it reaches the cement raw material drying apparatus, and the mercury-containing substance is concentrated at a high concentration in the humidity control tower. In addition, dust is present in the exhaust gas. For this reason, when exhaust gas is cooled below the temperature at which mercury is deposited, precipitation of mercury is promoted by the presence of dust in the exhaust gas. That is, the precipitation of mercury effectively proceeds with dust as a nucleus. For this reason, mercury or the like can be more effectively removed as compared with a case where there is no dust in the exhaust gas or the dust is sufficiently small. Therefore, after separating the exhaust gas from which mercury-containing substances have been removed into purified exhaust gas and dust collection dust using a dust collector, the mercury-containing substances are not accumulated in the exhaust gas even if the dust collection dust is returned to the cement firing facility, and as a result The content of mercury-containing substances released into the atmosphere can be effectively reduced. In addition, since dust and mercury are collectively collected by the humidity control tower, there is no need to install a cyclone and a condenser for collecting dust and mercury, and only the humidity control tower needs to be installed. For this reason, the increase in equipment cost can fully be suppressed.

  The temperature at which mercury is deposited, that is, the temperature for depositing mercury and mercury compounds from the exhaust gas, is 357 ° C. or less because the boiling point of mercury (Hg) is 357 ° C. It is preferable that it is 300 degrees C or less.

  It is preferable to cool the exhaust gas introduced into the humidity control tower to a temperature equal to or lower than the temperature at which mercury is deposited by bringing the exhaust gas into direct contact with a liquid containing water. In this case, in addition to being able to deposit mercury more effectively on the surface of the dust, mercury vapor is quickly absorbed into the liquid containing water, and the mercury-containing material is deposited more effectively.

  It is preferable that the humidity control tower dust extracted from the humidity control tower is separately heat-treated in a heating furnace to volatilize and remove the mercury-containing material contained in the dust, and is used again as a cement raw material. Thereby, waste of a cement raw material can be prevented.

  According to the method for producing cement according to the present invention, before the exhaust gas discharged from the cement firing equipment is used for drying the cement raw material, it is cooled to a temperature lower than the temperature at which mercury is deposited in the humidity control tower and collected in the humidity control tower. By extracting all or part of the dust to be extracted from the exhaust gas, the mercury-containing substance can be effectively removed from the exhaust gas, and the circulation amount of the mercury-containing substance can be reduced in the circulation path passing through the cement burning facility and the dust collector, As a result, the amount of mercury-containing substances released into the atmosphere can be reduced. Moreover, since dust and mercury are collected in a batch in the humidity control tower, the increase in equipment cost can also be suppressed sufficiently.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
First, a first embodiment of the cement manufacturing method of the present invention will be described in detail with reference to FIG. FIG. 1 is a schematic view showing a cement production facility for carrying out a first embodiment of a cement production method according to the present invention. As shown in FIG. 1, in the cement manufacturing facility 100, a mixed raw material (cement raw material) composed of raw materials such as limestone, clay, silica, iron sources, and various other wastes is dried and pulverized by a raw material mill 3. The exhaust gas containing the prepared raw material pulverized in is introduced into the electrostatic precipitator 4 and separated into purified gas and electrostatic precipitating dust. The electric dust collection dust is transferred to the cement firing facility 1 as a feed material through a dust collection dust transfer line L1. In the cement firing facility 1, the feed material is preheated while being gas-solid separated by a plurality of cyclones 10, introduced into the rotary kiln 11 and fired, and then cooled and discharged. A cement clinker is thus obtained.

  On the other hand, the exhaust gas discharged from the cement firing facility 1 is introduced into the humidity control tower 2 via the exhaust gas transfer line L2 and cooled. In order to increase the dust collection efficiency of the dust collector 4, the humidity control tower 2 directly sprays a liquid containing water (for example, water) on the exhaust gas from the cement firing facility 1 to bring the exhaust gas and the liquid into direct contact with the humidity. It is equipment for adjusting or reducing exhaust gas temperature by reducing exhaust gas temperature.

  Here, the temperature at which the exhaust gas is cooled refers to the temperature at the outlet of the exhaust gas in the humidity control tower 2. Such temperature can be measured using a thermocouple or the like. The temperature at which the exhaust gas is cooled is not higher than the temperature at which mercury is deposited, specifically 357 ° C. or lower, preferably 300 ° C. or lower, more preferably 10 to 250 ° C.

  The exhaust gas thus cooled is introduced into the raw material mill 3 via the exhaust gas transfer line L2 and used as the dry gas of the raw material mill 3. Thereafter, the exhaust gas discharged from the raw material mill 3 is introduced into the electric dust collector 4 via the exhaust gas transfer line L2, and is separated into purified exhaust gas and dust collection dust by the electric dust collector 4, and passes through a chimney (not shown). Purified exhaust gas is released into the atmosphere.

  The exhaust gas discharged from the cement firing equipment 1 is used for drying the cement raw material in the raw material mill 3, but before the use, the exhaust gas is just exhausted from the cement firing equipment 1, so that the temperature is sufficiently high. The mercury-containing material is concentrated to a high concentration. In addition, dust is present in the exhaust gas. For this reason, when the exhaust gas is cooled to a temperature equal to or lower than the temperature at which mercury is deposited, precipitation of mercury is promoted by the presence of dust in the exhaust gas. That is, the precipitation of mercury effectively proceeds with dust as a nucleus. For this reason, mercury or the like can be more effectively removed as compared with a case where there is no dust in the exhaust gas or the dust is sufficiently small. Therefore, even if the exhaust gas from which the mercury-containing material has been removed is separated into purified gas and dust collection dust by the electric dust collector 4, the dust-containing material is accumulated in the exhaust gas even if the dust collection dust is returned to the cement firing facility 1. Therefore, the mercury-containing substance content released into the atmosphere can be sufficiently reduced.

  In addition, since dust and mercury are collected together in the humidity control tower 2, there is no need to install a cyclone and a condenser for collecting dust and mercury, respectively, and if only the humidity control tower 2 is installed. Good. For this reason, the increase in equipment cost can fully be suppressed.

  In some cases, the humidity control tower 2 is already present in the cement factory. In that case, the humidity control tower 2 is used, and the cement manufacturing facility 100 is manufactured by a relatively simple facility modification. That is, the increase in equipment cost can be suppressed more sufficiently.

  The humidity control tower dust extracted from the humidity control tower 2 as described above is heat-treated separately in the heating furnace 12 to volatilize and remove mercury and mercury compounds contained in the dust, and used again as a cement raw material. Is preferred. Thereby, waste of the cement raw material can be prevented.

  The heating furnace 12 is not particularly limited as long as it has a structure capable of heating to a temperature equal to or higher than the volatilization temperature of mercury and a mercury compound, that is, 400 to 600 ° C. For example, the heating furnace 12 may be a rotary kiln type heating furnace. In this case, the humidity control tower dust is introduced into the heating furnace 12 from the humidity control tower 2 via the humidity control tower dust transfer line L3, and the kiln exhaust gas discharged from the heating furnace 12 passes through the kiln exhaust gas transfer line L4. It is introduced into the bug filter 13 via. The heat-treated dust that has been heat-treated in the heating furnace 12 is returned to the cement firing facility 1 via the heat-treated dust transfer line L5 and the dust collection dust transfer line L1. The kiln exhaust gas transfer line L4 is preferably accompanied by a device 14 for blowing an adsorbent such as activated carbon. In this case, since the adsorbent is blown into the kiln exhaust gas transfer line L4 by the device 14, the mercury-containing substance in the kiln exhaust gas is adsorbed by the adsorbent and is collected by the bag filter 13, so that the mercury-containing substance is It can be prevented from being reintroduced and accumulated in the circulation path passing through the dust collector 4 and the cement firing facility 1.

(Second Embodiment)
Next, 2nd Embodiment of the cement manufacturing method of this invention is described with reference to FIG. FIG. 2 is a schematic view showing an example of a cement production facility used in the second embodiment of the cement production method of the present invention. In FIG. 2, the same or equivalent components as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 2, first, in a cement manufacturing facility 200, a mixed raw material made of raw materials such as limestone, clay, silica, iron sources, and various other wastes is dried and ground in a raw material mill 3. The exhaust gas used to dry the cement raw material in the raw material mill 3 is introduced into the electric dust collector 4 and separated into purified haiku gas and dust collection dust, and the purified exhaust gas is discharged into the atmosphere through a chimney (not shown). Then, the dust collection dust is introduced into the cement firing facility 1 as an input raw material via the dust collection dust transfer line L1. The blended raw material pulverized by the raw material mill 3 is introduced into the cement firing facility 1 together with dust collection dust. And in the cement baking equipment 1, after a feed raw material is preheated in a some cyclone, it is baked with the rotary kiln 11, cooled, and discharged | emitted. A cement clinker is thus obtained.

On the other hand, the exhaust gas discharged from the cement firing facility 1 passes through the exhaust gas transfer line L2, and then passes through the three routes of the exhaust gas transfer line L2, the first bypass line L6, and the third bypass line L8. The exhaust gas passed through the exhaust gas transfer line L2 is cooled by the humidity control tower 2. In the humidity control tower 2, water is sprayed on the introduced exhaust gas and collected together with dust. Here, in the humidity control tower 2, the exhaust gas is cooled to a temperature equal to or lower than the temperature at which mercury is deposited.
At this time, immediately after the exhaust gas is introduced into the humidity control tower 2, it is shortly after being discharged from the cement firing equipment 1, so that the temperature is sufficiently high, and the mercury-containing substance is concentrated to a high concentration. Yes. In addition, dust is present in the exhaust gas. For this reason, when the exhaust gas is cooled to a temperature equal to or lower than the temperature at which mercury is deposited, precipitation of mercury is promoted by the presence of dust in the exhaust gas. That is, the precipitation of mercury effectively proceeds with dust as a nucleus. For this reason, mercury or the like can be more effectively removed as compared with a case where there is no dust in the exhaust gas or the dust is sufficiently small.

  The exhaust gas cooled by the humidity control tower 2 as described above is introduced into the electric dust collector 4 via the exhaust gas transfer line L2.

  The exhaust gas passed through the first bypass line L6 is introduced into the dryer 15. In the dryer 15, for example, a high moisture content clay having a moisture content of 27.5% by mass and a poor handling property is introduced, and the high moisture content clay is dried by the exhaust gas. The exhaust gas that has passed through the dryer 15 is introduced into the electric dust collector 4 via the second bypass line L7 and the exhaust gas transfer line L2.

  The exhaust gas passed through the third bypass line L8 passes through the raw material mill 3, is used for drying the cement raw material, and then introduced into the electric dust collector 4 via the exhaust gas transfer line L2.

  As described above, even when a part of the exhaust gas discharged from the cement firing facility 1 is cooled to a temperature below the temperature at which mercury is deposited in the humidity control tower 2, the mercury-containing substance is effectively removed in the humidity control tower 2. Removed. For this reason, even if the exhaust gas from which the mercury-containing substance has been removed is separated into purified gas and dust collection dust by the electric dust collector 4, the mercury-containing substance accumulates in the exhaust gas even if the dust collection dust is returned to the cement firing facility 1. As a result, the mercury-containing substance content released into the atmosphere can be sufficiently reduced.

  In addition, since dust and mercury are collected together in the humidity control tower 2, there is no need to install a cyclone and a condenser for collecting dust and mercury, respectively, and if only the humidity control tower 2 is installed. Good. For this reason, the increase in equipment cost can fully be suppressed.

  In addition, when the humidity control tower 2 may already exist in a cement factory, it is the same as that of 1st Embodiment that an increase in equipment cost can be suppressed more fully.

  The present invention is not limited to the first and second embodiments. For example, in the first embodiment, the humidity control tower dust is processed by using the heating furnace 12, but the humidity control tower dust is not necessarily processed by the heating furnace 12, and is processed by, for example, landfill. May be.

  Hereinafter, the contents of the present invention will be described with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
As shown in FIG. 1, in a cement manufacturing facility 100, a blended raw material made of raw materials such as limestone, clay, silica, iron sources and various other wastes is dried and pulverized by a raw material mill 3 and pulverized by a raw material mill 3. The exhaust gas containing the raw material was introduced into the electrostatic precipitator 4 and separated into purified gas and electrostatic precipitating dust. The electric dust collection dust was transferred to the cement firing facility 1 as an input raw material via a dust collection dust transfer line L1. In the cement firing facility 1, the feed material was gas-solid separated by a plurality of cyclones 10, the feed material was preheated, introduced into the rotary kiln 11, fired, and then cooled and discharged. A cement clinker was thus obtained.

  On the other hand, all of the exhaust gas discharged from the cement baking equipment 1 was introduced into the humidity control tower 2 and cooled in the humidity control tower 2. In the humidity control tower 2, water was sprayed on the introduced exhaust gas and collected together with dust. The cooled exhaust gas was introduced into the raw material mill 3 via the exhaust gas transfer line L2, and used as the dry gas of the raw material mill 3. Thereafter, exhaust gas discharged from the raw material mill 3 is introduced into the electric dust collector 4 via the exhaust gas transfer line L2, and the exhaust gas is separated into purified exhaust gas and dust collection dust by the electric dust collector 4, and a chimney (not shown) After that, purified exhaust gas was released into the atmosphere.

  At this time, the inlet temperature of the humidity control tower 2 is 380 ° C., the outlet temperature is 250 ° C., the inlet temperature of the raw material mill 3 is 250 ° C., the outlet temperature is 100 ° C., the inlet temperature of the electrostatic precipitator 4 is 90 ° C., and the outlet temperature is 90 ° C. ° C.

  Table 1 shows the mercury content (mg / kg) of the mixed raw materials obtained by multiplying the mercury analysis values of various raw materials by the respective mixing ratios, the electrostatic precipitating dust, the humidity control tower dust, the incoming raw materials, and the clinker mercury. The content (mg / kg), the amount of raw materials and dust per unit time in the circulation path passing through the cement firing facility 1 and the electrostatic precipitator 4, and the amount of mercury (g / h) per unit time are shown.

  In addition, the analysis of mercury is based on the JG standard test method JCAS I-51 “Quantitative determination method of trace components in cement and cement raw material” 3.16 Hg determination method by atomic absorption photometry (reduction vaporization circulation method). went.

  As shown in Table 1, the clinker manufactured in the cement manufacturing process contains almost no mercury. From this, when mercury is evaporated and circulated in the cement manufacturing process, that is, in the circulation path passing through the cement firing equipment 1 and the electrostatic precipitator 4, it is condensed and deposited on the cement raw material particles in the low temperature part in the cement manufacturing process. Conceivable.

  In addition, the mercury content in the blended raw material is as small as 0.084 mg / kg, but the electric dust collection dust, humidity control tower dust and feed raw material collected in the cement manufacturing process have a content of several mg. It increased to the order of / kg. Among these, in the cement manufacturing process, it can be seen that the mercury content of the humidity control tower dust is the highest, and mercury and mercury compounds are most concentrated in the humidity control tower. In addition, the generation amount of humidity control tower dust is 15 t / h, which occupies about 4% of the blended raw material. Therefore, by extracting all or part of the humidity control tower dust outside the cement manufacturing process, It was confirmed that the circulation amount of mercury and mercury compounds in the cement manufacturing process can be reduced.

  The humidity control tower dust extracted in this example was heat-treated using an internal combustion rotary kiln as the heating furnace 12 shown in FIG. Specifically, the humidity control tower dust was fed into an internal combustion rotary kiln at a supply rate of 50 kg / h and heat-treated at 500 ° C. The rotary kiln had an inner diameter of 0.45 m, a length of 12 m, and a residence time in the kiln of 30 minutes. The kiln exhaust gas was exhausted after activated carbon was blown from the device 14 to remove the mercury in the exhaust gas, and the bag filter 13 was dedusted. The temperature inside the bag filter at this time was 120 ° C.

  Table 2 shows the chemical composition of the humidity control tower dust after heat treatment. The chemical analysis of dust after heat treatment is based on JIS5202 “Chemical analysis method of Portland cement”, and the mercury analysis is Cement Association standard test method JCAS I-51 “Quantitative determination method of trace components in cement and cement raw materials”. 3.16 It was performed according to the Hg determination method by atomic absorption photometry (reduction vaporization circulation method).

  As shown in Table 2, the amount of mercury in the dust after heat treatment was greatly reduced, and it was confirmed that the chemical components can be used as they are as cement preparation raw materials.

(Example 2)
As shown in FIG. 2, first, in the cement production facility 200, the raw material such as limestone, clay, silica, iron source and various other waste materials were dried and pulverized by the raw material mill 3. The exhaust gas used to dry the cement raw material in the raw material mill 3 is introduced into the electrostatic precipitator 4 and separated into purified haiku gas and dust collection dust, and the purified exhaust gas is discharged into the atmosphere through a chimney (not shown). Then, the dust collection dust was introduced into the cement firing facility 1 as an input raw material via the dust collection dust transfer line L1. The blended raw material pulverized by the raw material mill 3 was introduced into the cement firing facility 1 together with dust collection dust. And in the cement baking equipment 1, after the feed raw material was preheated in several cyclones, it was baked with the rotary kiln 11, cooled, and discharged | emitted. A cement clinker was thus obtained.

  On the other hand, the exhaust gas discharged from the cement firing facility 1 was passed through the exhaust gas transfer line L2, and then passed through three routes of the exhaust gas transfer line L2, the first bypass line L6, and the third bypass line L8. The exhaust gas passed through the exhaust gas transfer line L2 was cooled in the humidity control tower 2. In the humidity control tower 2, water was sprayed on the introduced exhaust gas and collected together with dust. The cooled exhaust gas was introduced into the electric dust collector 4 via the exhaust gas transfer line L2.

  The exhaust gas passed through the first bypass line L6 was introduced into the dryer 15. In the dryer 15, a high water content clay having a water content of 27.5% by mass and a poor handling property was introduced, and the high water content clay was dried by exhaust gas. The exhaust gas that passed through the dryer 15 was introduced into the electric dust collector 4 via the second bypass line L7 and the exhaust gas transfer line L2.

  The exhaust gas passed through the third bypass line L8 passed through the raw material mill 3, was used for drying the cement raw material, and then introduced into the electric dust collector via the exhaust gas transfer line L2.

  At this time, the inlet temperature of the humidity control tower 2 is 400 ° C., the outlet temperature is 250 ° C., the inlet temperature of the raw material mill 3 is 250 ° C., the outlet temperature is 100 ° C., the inlet temperature of the raw material dryer 15 is 400 ° C., and the outlet temperature is 100 ° C. The inlet temperature of the electrostatic precipitator 4 was 90 ° C., and the outlet temperature was 90 ° C.

  Table 3 shows the mercury content of the mixed raw materials obtained by multiplying the mercury analysis values of various raw materials by the respective mixing ratios, humidity control tower dust, pulverized raw materials, electrostatic precipitating dust, incoming raw materials, and mercury contents of clinker and their The amount in the cement manufacturing process is shown.

  As shown in Table 3, since the clinker contains almost no mercury, it evaporates and circulates in the cement manufacturing process, and condenses and precipitates on the cement raw material particles in the low temperature part of the cement manufacturing process. It is thought that.

  Further, as in Example 1, the mercury content contained in the blended raw material is as small as 0.061 mg / kg, but the humidity conditioning tower dust, the electrostatic dust collection dust and the feed raw material collected in the cement manufacturing process are , Its content increased to the order of several mg / kg. Among these, the mercury content of the humidity control tower dust is the highest, and it can be seen that mercury and mercury compounds are most concentrated in the humidity control tower. The amount of humidity control tower dust generated was 10 t / h, accounting for about 1.7% of the raw material.

  From the above, it was found that according to Example 1 and Example 2, mercury can be effectively removed.

  Therefore, at least a part of the exhaust gas discharged from the cement firing equipment is cooled below the temperature at which mercury is deposited in the humidity control tower, and the humidity control tower dust is placed outside the circulation path passing through the cement firing equipment and the electric dust collector. It was confirmed that the mercury-containing substance can be effectively removed from the exhaust gas by extracting.

It is the schematic which shows an example of the cement manufacturing equipment with which the manufacturing method of the cement by this invention is applied. It is the schematic which shows the cement manufacturing equipment for enforcing the manufacturing method of the cement concerning Example 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Cement baking equipment, 2 ... Humidity control tower, 3 ... Raw material mill, 4 ... Electric dust collector, 12 ... Rotary kiln, 13 ... Bag filter, 15 ... Dryer.

Claims (4)

The exhaust gas discharged from the cement firing facility is transferred to a dust collector through a cement raw material drying device and separated into purified exhaust gas and dust collected by the dust collector, and then the purified exhaust gas is discharged into the atmosphere, and the dust collector Including an exhaust gas treatment step for returning dust to the cement firing facility,
In the exhaust gas treatment process,
At least part of the exhaust gas discharged from the cement firing facility is sequentially transferred to a dust collector through a humidity control tower and a drying apparatus for the cement raw material,
At least a part of the exhaust gas discharged from the cement firing facility is cooled to a temperature below which the mercury is deposited in the humidity control tower, and all or part of the dust collected by the humidity control tower is contained in the exhaust gas. A method for producing cement, characterized in that it is extracted from the cement.   The method for producing cement according to claim 1, wherein a temperature at which the mercury is deposited is 357 ° C.   The method for producing a cement according to claim 1 or 2, wherein the exhaust gas introduced into the humidity control tower is cooled to a temperature equal to or lower than a temperature at which mercury is deposited by bringing the exhaust gas into direct contact with a liquid containing water. The dust according to any one of claims 1 to 3, wherein the dust is heat-treated in a heating furnace, the mercury-containing substance contained in the dust is volatilized and removed, and used again as a cement raw material. Production method.

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