JP5738882B2 - Method for producing cement clinker - Google Patents

Description

  The present invention relates to a method for manufacturing a cement clinker, and more particularly to a method for manufacturing a cement clinker in a cement clinker manufacturing facility such as a cement kiln facility with SP (suspension preheater) or a cement kiln facility with NSP (new suspension preheater).

  In general, dioxins that are harmful substances are likely to be generated from exhaust gas in incinerators and the like that process municipal waste and other general waste and industrial waste accompanying business activities. Dioxins are repeatedly decomposed and re-synthesized at 150 to 500 ° C. Dioxin suppression measures have been shown to sufficiently burn at a high temperature of 800 ° C or higher, not to make the incinerator into a reducing atmosphere, and to increase the exhaust gas cooling rate at 500 ° C or lower. ing.

  To avoid burning the incinerator sufficiently at a high temperature of 800 ° C or higher and not using a reducing atmosphere, the "Small and Medium Enterprises Corporation Manual for Chemical Safety Measures" Under the revised ministerial ordinance, enforced on December 1, 1997, Ministry of Health and Welfare Ordinance No. 65, etc., as a structural standard, it is necessary to install a combustion chamber that can stay for more than 2 seconds when the temperature of the combustion gas is 800 ° C or higher Install a cooling facility that can cool the temperature of the combustion gas to approximately 200 ° C or lower, maintain the temperature of the combustion gas to the combustion chamber at 800 ° C or higher as a maintenance standard, and set the combustion gas flowing into the dust collector. It has been shown that the temperature is generally cooled below 200 ° C.

  On the other hand, as an example of increasing the cooling rate of exhaust gas at 500 ° C. or lower, a case of a cement plant can be given. As shown in FIG. 1, in a cement plant, the kiln exhaust gas is decarbonated by a counter current from the bottom of the kiln kiln at about 1,000 ° C., decarboxylated by countercurrent, reaches about 400 ° C. in the upper stage of the cyclone, and water is supplied by a boiler. Because it is rapidly cooled by generating evaporation and heated steam, it is cooled to about 250 ° C at the boiler outlet, so the cooling rate from about 400 ° C to about 250 ° C is high. Compared with the incinerator to process, generation | occurrence | production of dioxins is suppressed.

  However, the amount of industrial waste used in cement plants has increased due to the recent popularization of the recycling-oriented society formation method, and even with SPs with exhaust heat power boilers and cement kiln facilities with NSP, they have chlorine and the like. The amount of dioxins generated from kiln exhaust gas is increasing due to an increase in the basic unit of industrial waste cement plants.

Further, CO ₂ emitted from raw fuel consumption and power consumption in a cement plant is formed from CO ₂ from thermal decomposition of limestone in raw materials, combustion of coal in fuel, power consumption due to energy. Since CO ₂ is a global warming gas, it is an important technique to reduce energy from consumption of these raw fuels and power consumption.

Hereinafter, the past technology will be described more clearly using actual examples.
Generally, a cement clinker manufacturing facility in a cement plant performs exhaust heat power generation by exchanging heat between a preheater 110 having a plurality of cyclones 103a, 103b, 103c, and 103d and a kiln exhaust gas from the preheater 110, as shown in FIG. The main part is a boiler 106 for waste heat power generation and a kiln 101 for firing the blended raw material into a cement clinker. The mixed raw material charged into the upper cyclone 103a forms counterflow with the exhaust gas from the kiln 101 by the preheater 110 at the upper stage of about 400 ° C., is heat-exchanged and decarboxylated, and enters the kiln 101 at about 1,000 ° C. Introduced and fired into cement clinker. The kiln exhaust gas is about 1,000 ° C. in the kiln kiln bottom 112, and while passing through the cyclones 103a to 103d, the mixed raw material is cooled while decarboxylating by countercurrent, and about 400 in the uppermost cyclone 103a. It is cooled by evaporating water in the exhaust heat power generation boiler 106 and generating heated steam, cooled to about 340 ° C. at the outlet of the boiler 106, sucked into a kiln IDF (Induced Draft Fan) 105, and dried by pulverizing the raw material The amount of heat for drying is consumed by the machine 107, the temperature is adjusted and humidified by the stabilizer 108, collected by the electric dust collector 109, and then exhausted from the chimney.

  On the other hand, in the cement clinker manufacturing facility, in the kiln kiln bottom portion 112, the rising duct portion 111, and the preheater 110, the organic chlorine compounds of dioxins are repeatedly decomposed and re-synthesized in the exhaust gas, and are contained in the kiln exhaust gas. ing.

  As a method for reducing organochlorine compounds of dioxins from these cement clinker production facilities, there is a method of changing the process on a large scale, such as industrially circulating exhaust gas.

  In JP 2004-244308 A (Patent Document 1), (A) exhaust gas from a cement manufacturing apparatus is treated using a dust collecting means to collect dust containing an organic chlorine compound, while the dust collecting means And a step of discharging the exhaust gas after the treatment by (B), and (B) introducing at least a part of the collected dust into a place of 800 ° C. or higher in the cement manufacturing apparatus. A method for treating exhaust gas from a manufacturing apparatus is described.

  Japanese Patent Application Laid-Open No. 2007-70173 (Patent Document 2) discloses a method for reducing organochlorine compounds in a cement manufacturing apparatus, in the middle of supplying exhaust gas from the top of a preheater to a raw material pulverization process section. A method is described in which a single exhaust gas branch pipe is used for separation, and this is put into the lower stage of the preheater that becomes 800 ° C. or higher during normal operation of the cement production facility. Thus, it is said that if organic chlorine compounds such as dioxins and PCBs contained in the exhaust gas are thermally decomposed, the amount of organic chlorine compounds discharged from the cement production facility can be reduced as compared with the prior art.

  Furthermore, Japanese Patent Application Laid-Open No. 2007-91547 (Patent Document 3) includes (A) a step of flowing exhaust gas generated in the cement manufacturing process into the preheater, and (B) heating provided in the preheater. And a step of enlarging a region of 800 ° C. or higher in the preheater by means. A method for treating an exhaust gas of a cement manufacturing apparatus is described.

  In JP 2009-184902 A (Patent Document 4), as a cement manufacturing method, exhaust gas discharged from the upper part of a suspension preheater of a cement firing facility is used for drying a cement raw material in the raw material grinding step. In the cement manufacturing process, after the exhaust gas discharged is separated into purified exhaust gas and dust collection dust with a dust collector, the purified exhaust gas is released into the atmosphere and the dust collection dust is sent to the upper part of the suspension preheater as part of the cement raw material. (A) A part of the dust collection dust is discharged from the circulation path of the cement clinker manufacturing process, and (B) the dust collection dust discharged by the process (A) is introduced into the heating device, The step of heat-treating in step (C), the step of rapidly cooling the dust-collected dust heat-treated in step (B), and the step (D) (C). Fast cooled collected dust is returned to the circulation path of the cement clinker manufacturing process, describes the preparation method of the cement, characterized in that a step of entering feed again as a cement raw material from suspension preheater upper.

  Furthermore, as a method for reducing dioxin organochlorine compounds from these cement plants, there is a method in which an additive is added to cause a chemical reaction.

In JP 2007-90261 A (Patent Document 5), (A) a process of generating exhaust gas containing hydrogen chloride in a cement manufacturing process using a cement raw material containing chlorine, and (B) process (A). At least one calcium compound selected from CaO and Ca (OH) ₂ is introduced into the exhaust gas containing hydrogen chloride generated in the above at a point upstream of the exhaust gas of the dryer or pulverizer, and the calcium compound and the exhaust gas And a process for producing calcium chloride, which is a neutralized product of hydrogen chloride therein, and a method for treating exhaust gas from a cement production apparatus. In this method, the amount of hydrogen chloride in the exhaust gas is reduced by neutralizing hydrogen chloride into calcium chloride, which is a solid component. As a result, in the region downstream of the exhaust gas from the calcium compound inlet, dioxin Generation of persistent organic pollutants such as It is also described that the input amount of CaO or Ca (OH) ₂ per equivalent of hydrogen chloride in the exhaust gas should be 1.0 to 10 equivalents.

JP 2004-244308 A JP 2007-70173 A JP 2007-91547 A JP 2009-184902 A JP 2007-90261 A

  In any of the methods of Patent Documents 1 to 4, a significant and expensive process change is required, and the effect of reducing the organic chlorine compounds of dioxins is not clear. According to the method described in Patent Document 5, such a large-scale process change is not required, and the calcium compound reduces the amount of hydrogen chloride in the exhaust gas, thereby generating residual organic pollutants such as dioxins. Although it is said to be suppressed, the reduction effect of dioxin organochlorine compounds is not clear, and there is still room for improvement.

Accordingly, an object of the present invention is to provide a method for producing a cement clinker capable of effectively suppressing the concentration of dioxins (DXN _S ) in exhaust gas without significantly changing the process. .

As a result of diligent research to solve the above problems, the present inventor has added dioxin in exhaust gas from a cement clinker manufacturing facility when slaked lime having a predetermined terminal sedimentation rate is added to a cyclone through which exhaust gas in a predetermined temperature range passes. We found that the concentration of the class (DXN _S ) was significantly reduced.

  Therefore, in one aspect, the present invention provides a cement clinker manufacturing method in a cement clinker manufacturing facility including a pre-heater having a plurality of cyclones and a rotary kiln, wherein slaked lime having a terminal sedimentation rate of 0.5 to 10 cm / sec is exhausted. It is a method including a step of introducing the gas into a cyclone having an exhaust gas temperature of 350 to 500 ° C. at the outlet.

  In one embodiment of the method for producing cement clinker according to the present invention, the slaked lime is added so that the amount of slaked lime is 20 to 200 kg per 1 ton of cement clinker.

  In another embodiment of the cement clinker manufacturing method according to the present invention, the slaked lime is charged into the uppermost cyclone.

  In yet another embodiment of the method for producing a cement clinker according to the present invention, the slaked lime is supplied to a raw material crushing and drying machine after being mixed with a cement preparation raw material or in parallel with the preparation raw material. It is fed into the uppermost cyclone through the supply line.

  In still another embodiment of the method for producing cement clinker according to the present invention, the ratio of the terminal settling speed of the slaked lime to the terminal settling speed of the cement clinker blending raw material is 0.5 to 1.5.

  In still another embodiment of the method for producing cement clinker according to the present invention, the slaked lime is slaked lime produced as a by-product when acetylene is generated from calcium carbide.

According to the present invention, in a cement clinker manufacturing facility, the concentration of dioxins (DXN _S ) in exhaust gas can be effectively suppressed without significant process changes. ADVANTAGE OF THE INVENTION According to this invention, the density | concentration of the dioxins in the waste gas of a cement clinker manufacturing facility can be suppressed to 20 ng / m < ³ > N or less, for example.

1 is a system diagram of a cement clinker manufacturing facility according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The cement clinker manufacturing facility according to the present embodiment is a cement kiln facility with an NSP (New Suspension Preheater), and as shown in FIG. 1, a rotary kiln 101, a preheater 110, a waste heat power generation boiler 106, a kiln IDF 105, a raw material pulverization It comprises a dryer 107, a stabilizer 108, and an electric dust collector 109.

  The pre-heater 110 connects four cyclones (first-stage cyclone 103a, second-stage cyclone 103b, third-stage cyclone 103c, fourth-stage cyclone 103d), calcining furnace 102, and these arranged in the vertical direction. Has a duct. The cement clinker blending raw material generally contains limestone, clay, silica stone, and iron base, and in addition, wastes such as main ash generated from incineration of municipal waste and foundry sand may be appropriately added. The raw material for cement clinker preparation is pulverized, mixed, and dried by the raw material pulverization dryer 107. Thereafter, when the cement clinker blended raw material is fed into the preheater 110 from the first-stage cyclone 103a through the blended raw material supply line 104, the high temperature discharged from the rotary kiln 101 in order along the solid line in FIG. The mixed raw material is preheated while exchanging heat with the exhaust gas. In the calcining furnace 102, the preheated cement clinker preparation material is calcined. The number of cyclones can be increased or decreased as appropriate. Although the calcining furnace 102 is installed to enhance the firing effect, it is not always necessary to install it.

The cement clinker blended raw material charged into the rotary kiln 101 at about 1000 ° C. gradually rises to about 1400-1500 ° C. while moving gradually in the rotary kiln 101 toward the outlet. The blended raw material is fired during this time to produce a cement clinker. From the rotary kiln 101, exhaust gas of about 1000 ° C. is discharged from the kiln kiln bottom 112. Dioxins (DXN _S ) are contained in the exhaust gas.

  The exhaust gas sequentially proceeds along the dotted line in FIG. 1 through the rising duct 111, the calcining furnace 102, and the cyclones 103 a to 103 d that extend right above the kiln kiln bottom 112, and then goes to the kiln IDF fan 105. During this time, the exhaust gas is cooled by heat exchange. In a typical embodiment, the exhaust gas outlet of the lowermost fourth cyclone 103d is 820 to 870 ° C, and the exhaust gas outlet of the third cyclone 103c is 730 to 790 ° C. It becomes 590-650 ° C. at the exhaust gas outlet of the stage cyclone 103b, 350-500 ° C. at the exhaust gas outlet of the uppermost first cyclone 103a, and is further cooled by the latent heat of evaporation when water is evaporated by the exhaust heat power boiler 106, It is cooled to about 340 ° C. at the outlet of the boiler 106. Further, the air is sucked into the kiln IDF 105, the amount of heat for drying is consumed by the raw material crushing and drying machine 107, the temperature is adjusted and humidified by the stabilizer 108, the dust is collected by the electric dust collector 109, and then exhausted from the chimney.

In the present invention, in order to reduce the concentration of dioxins (DXN _S ) in the exhaust gas, slaked lime having a terminal sedimentation rate of 0.5 to 10 cm / sec is used in a cyclone having an exhaust gas temperature of 350 to 500 ° C. at the exhaust gas outlet. One of the features is that

Although it is not intended that the present invention be limited by theory, an estimation mechanism for reducing the concentration of dioxins by adding slaked lime having such a specific terminal sedimentation rate will be described. Referring to FIG. 1, the inlet temperature of the first-stage cyclone 103a is about 590 to 650 ° C., and the outlet temperature is 350 to 500 ° C. Therefore, the exhaust gas passing through the first stage cyclone 103a is in a temperature range where dioxins are easily re-synthesized. On the other hand, slaked lime causes a dehydration reaction (endothermic reaction) by the following formula: Ca (OH) ₂ → CaO + H ₂ O at a temperature of 400 to 500 ° C., and the generated water loses latent heat by evaporation, thereby lowering the temperature. Therefore, when slaked lime is added to the first-stage cyclone 103a in which the outlet temperature of the exhaust gas is in the above range, the slaked lime is dehydrated in the cyclone, thereby producing a rapid cooling effect and suppressing resynthesis of dioxins. .

  The exhaust gas temperature at the exhaust gas outlet of the cyclone to which slaked lime is charged is preferably for the reason of ensuring the durability of the iron of the plant constituting the cyclone and the boilers after the cyclone, the kiln IDF, the stabilizer, the raw material crushing and drying machine, the electric dust collector, etc. It is 440 degrees C or less. In general, the cyclone at the lower stage of the kiln or preheater is protected by a refractory, but the material constituting the plant after the first stage cyclone is often iron, and the yield point of iron is 440 ° C. . On the other hand, regarding the lower limit of the exhaust gas temperature, consideration is given to the point of suppressing the generation of dioxins and the point of performing high-pressure steam recovery in the boiler. That is, as described above, it is better to increase the cooling rate at 400 to 250 ° C. in order to suppress the generation of dioxins. If exhaust gas is sent into the boiler at a very low temperature, the generation of dioxins is suppressed by rapid cooling in the boiler. The effect may not be obtained sufficiently. Further, it is known that the high-pressure steam recovery of the boiler can generate the power generation energy in the turbine as the temperature rises. Furthermore, as described above, the dehydration reaction of slaked lime is likely to proceed at 400 to 500 ° C. Accordingly, since it is not appropriate to set the exhaust gas outlet temperature of the cyclone to a temperature that is excessively lower than 400 ° C., the temperature is preferably 370 ° C. or higher, and more preferably 390 ° C. or higher.

  However, when the retention time of slaked lime is not secured sufficiently in the cyclone, the slaked lime flows out from the cyclone before the dehydration reaction is completed. According to the inventor's examination results, in order to obtain a sufficient holding time in the cyclone, the slaked lime needs to have a terminal sedimentation rate of 0.5 cm / sec or more, and preferably 1 cm / sec or more. More preferably, it is 2 cm / sec or more, and still more preferably 4 cm / sec or more. On the other hand, when the terminal settling velocity of slaked lime exceeds 10 cm / sec, a normal pre-heater does not form a sufficient swirling flow in the cyclone, and a short pass may occur due to falling in the cyclone, which may make operation difficult. is there. Therefore, the terminal sedimentation rate of slaked lime is preferably 10 cm / sec or less, and more preferably 7 cm / sec or less.

  The slaked lime charging point is not particularly limited as long as it can be charged into the cyclone. For example, a dedicated supply line can be provided, and the slaked lime charging point is charged into the mixed raw material supply line 104 between the raw material crushing dryer 107 and the first-stage cyclone 103a. Alternatively, after mixing with the mixed raw material or in parallel with the mixed raw material, the raw material crushing and drying machine 107 can be charged.

  The raw material analyzer that controls the mixing of raw materials to control the composition of the clinker performs the combined batch analysis of the mixed raw materials and controls the raw material feeder according to the result. Forms the lime component of the clinker. Therefore, it is included in the blended raw material value, analyzed, and the supply amount as the lime raw material is controlled so that the fluctuation of the clinker composition is controlled less. It is preferable to be fed into the raw material crusher / dryer 107 after being mixed with the raw material or in parallel with the prepared raw material.

  Next, the amount of slaked lime input will be described. As the amount of slaked lime having the predetermined terminal sedimentation rate decreases, the effect of reducing dioxins decreases.On the other hand, when the amount of slaked lime input increases too much, a large pressure loss occurs in the preheater. Driving may be difficult. Therefore, it is preferable to add the slaked lime to the blended raw material of the cement clinker so that the slaked lime is 20 to 200 kg (20 to 200 kg / tcl) per 1 ton of the cement clinker. More preferably, the slaked lime is added to the cement clinker preparation material so as to be 100 kg / tcl).

As slaked lime having a terminal sedimentation speed of 0.5 to 10 cm / sec, it is convenient to use by-product slaked lime generated in the process of producing acetylene gas by the carbide method, which is also useful for effective use of resources. A chemical reaction in which acetylene is generated from calcium carbide can be represented by the following formula: CaC ₂ + 2H ₂ O → C ₂ H ₂ + Ca (OH) ₂ .
The terminal sedimentation rate of slaked lime can be adjusted by methods such as sieving, granulation and pulverization.

  In addition, when the ratio of the terminal sedimentation rate of the slaked lime to be added is too large with respect to the terminal sedimentation rate of the cement clinker compounding raw material, the slaked lime does not form a sufficient swirl flow in the cyclone, and short pass and settle. In addition, heat exchange is not performed sufficiently, the fuel efficiency of the kiln deteriorates, and the clinker firing amount tends to decrease, whereas when the ratio is too small, the pressure difference in the cyclone tends to increase, Moreover, since the collection efficiency of the input slaked lime is also lowered, heat exchange is not sufficiently performed, the gas flow rate of the kiln IDF is lowered, the fuel efficiency of the kiln is deteriorated, and the clinker firing amount tends to be lowered. Therefore, the ratio of the terminal sedimentation rate of the added slaked lime to the terminal sedimentation rate of the cement clinker preparation raw material is preferably 0.5 to 1.5, and more preferably 0.7 to 1.3. The cement clinker blended raw material after passing through the raw material crushing and drying machine 107 is generally 0.2 to 15 cm / sec, typically 0.5 to 13 cm / sec, more typically 1 to 10 cm / sec. Having a terminal sedimentation rate of

  EXAMPLES Hereinafter, although this invention is demonstrated using an Example, this invention is not limited to these Examples.

<Example 1: Production of by-product slaked lime>
Water was added to calcium carbide having a particle size of 4.0 mm or less to generate acetylene gas, and slaked lime having a terminal sedimentation rate of 0.5 to 15 cm / sec was by-produced. The water content of by-product slaked lime was 7 to 10% by mass, and the terminal sedimentation rate was 5 cm / sec. Table 1 shows the quality of the calcium carbide and the specifications of the acetylene generator, and Table 2 shows the amount of components of the obtained byproduct slaked lime. The particle size of calcium carbide was measured using a JISZ8801 metallic steel sieve. The terminal sedimentation rate was measured by the Andreazen pipette sedimentation method specified in JIS Z8821. The component amount was measured according to JIS R5202. The amount of moisture was measured with an infrared moisture meter (Ket Science Laboratory model “FD-800”).

<Example 2: Effect of terminal sedimentation rate of by-product slaked lime on dioxin concentration in exhaust gas>
A cement blending raw material having the component composition shown in Table 3 and having a terminal sedimentation rate of 4 cm / sec was prepared. In addition, slaked lime with various terminal sedimentation rates produced by appropriately pulverizing the byproduct slaked lime with a terminal sedimentation rate of 5 cm / sec produced in Example 1 and commercially available slaked lime “Hishikar” (Ryoko Lime Industry) were prepared (Table). 4). Slaked lime “Hishikar” (Ryoko Lime Industry) used in the comparative example is used as a dioxin-suppressing adsorbent for general incinerators. The terminal sedimentation rate was measured by the Andreazen pipette sedimentation method specified in JIS Z8821.

  Next, the cement clinker manufacturing facility having the configuration shown in FIG. At this time, each of the slaked lime was supplied to the raw material crushing and drying machine 107 in parallel with the cement blending raw material, so that each unit of 50 kg / tcl was charged into the uppermost cyclone 103a. The inner diameter of each cyclone was 3 m.

In this case, the concentration of dioxins (DXN _S ) in the exhaust gas at the outlet of the electrostatic precipitator (EP), the kiln IDF outlet pressure, the first stage cyclone 103a outlet slaked lime collection efficiency, the pressure difference average value of each stage of the cyclone, one stage Table 5 shows the difference between the exhaust gas temperature at the exhaust gas inlet and the exhaust gas outlet of the first cyclone 103a, the IDF outlet gas flow rate, the IDF efficiency, and the power consumption rate.

The concentration of DXN _S is measured according to “JIS K 0311 Analysis of dioxins in exhaust gas”, and the concentration of organochlorine compounds (ng in PCDDs, PCDFs and DL-PCB) of dioxins per 1 m ³ N of kiln exhaust gas is measured. / M ³ N).

The first stage cyclone 103a exit slaked lime collection efficiency is the sizing method that matches the dust in the gas at the exhaust gas outlet of the first stage cyclone 103a to the sizing characteristics shown in JIS Z 8814 "Low volume air sampler", and JIS Amount of slaked lime collected by K 0901 “Shape, size and performance test method of filter medium for collecting dust sample in gas” and added to first stage cyclone 103a after quantifying slaked lime in dust by X-ray diffraction It was calculated by dividing by.
The average value of the pressure difference at each stage of the cyclone was obtained as cyclone outlet pressure-cyclone inlet pressure for each of the cyclones 103a to 103d, and the average value was used as a measured value.
The kiln IDF fan efficiency [%] was determined according to the following formula.
Kiln IDF fan efficiency [%] = air volume [m ³ / min] / 60 [sec / min] × pressure [MPa] / shaft power [kW] × 100
The IDF power unit is calculated based on the amount of heavy oil required to produce 1 ton of clinker. Expressed as the difference to 1.

By-product slaked lime (No. 1) has a terminal sedimentation rate of 5 cm / sec, and is close to the terminal sedimentation rate of 4 cm / sec of the blended raw material. Therefore, the average pressure difference at each stage of the cyclone is as small as -1.0 kPa, The IDF outlet pressure was as small as -7 kPa and was within the normal operating range. Moreover, the collection efficiency of input slaked lime in the first stage cyclone 103a exit as good as 99%, DXN _S concentration in EP outlet was suppressed with 14ng / m ³ N. If grinding a byproduct slaked lime in a mill (No.2 and 3), although the performance of the cement clinker production facility is lowered in accordance terminal settling velocity decreases progressed crushing degree is DXN _S concentration to target 20ng / M ³ N or less was achieved.

On the other hand, no. The slaked lime “Hishikar” produced by pulverization method No. 4 has a terminal sedimentation rate of 0.1 cm / sec, which is significantly smaller than the terminal sedimentation rate of 4 cm / sec of the prepared raw material. For this reason, the pressure difference average value of each stage of the cyclone was as large as -1.25 kPa. Also, kiln IDF outlet pressure is as large as -8KPa, outside the normal operating range, the first stage collection efficiency of input slaked lime in the cyclone outlet as small as 5%, DXN _S concentration in EP outlet 70 ng / m ³ N was high.

When by-product slaked lime with a terminal sedimentation rate of 5 cm / sec is used at a basic unit of 50 kg / tcl, when the kiln IDF outlet pressure is −7 kPa, the kiln IDF air volume is 6,000 m ³ / min. On the other hand, when fine slaked lime having a terminal sedimentation rate of 0.1 cm / sec is fed to the cement clinker manufacturing facility at a basic unit of 50 kg / tcl, the pressure loss at each stage of the cement SP = about −1.25 MPa, Since the IDF outlet pressure = −8 MPa and the negative pressure increased, the kiln IDF air flow rate decreased to 4,000 m ³ / min, and the heat exchange efficiency and the collection efficiency of the cement clinker production facility preheater decreased.

The cause of the terminal sedimentation rate of slaked lime affecting the concentration of dioxins in the exhaust gas will be discussed below. From the exhaust gas inlet temperature and outlet temperature of the first stage cyclone, it can be understood that 400 to 500 ° C., which is the temperature at which the dehydration reaction from slaked lime Ca (OH) ₂ to quick lime CaO occurs, is performed inside the first stage cyclone. .
At this time, no. In No. 1, since the terminal sedimentation rate of the slaked lime was appropriate, the slaked lime particles swirled sufficiently in the first-stage cyclone, and sufficient heat exchange retention time was ensured in the cyclone, so that a high cooling effect was obtained. In addition, it is thought that the dioxin suppression effect was high. Moreover, since slaked lime was collected with high collection efficiency, the amount of slaked lime flowing into the kiln IDF was reduced, a large IDF air volume was obtained, and the IDF efficiency was also considered high.
On the other hand, when the terminal sedimentation rate of slaked lime is reduced, the retention time of slaked lime particles in the first-stage cyclone is shortened, the cooling effect is reduced, and the dioxin suppression effect is gradually reduced. It is done. Moreover, it is thought that the collection efficiency of slaked lime fell and the pressure loss and IDF efficiency fell gradually. No. In No. 4, the degree of decrease was so great that the concentration of dioxins could not be reduced to 20 ng / m ³ N or less, which is a standard.

<Example 3: Effect of input amount of by-product slaked lime on dioxin concentration in exhaust gas>
The effect on the dioxin concentration in the exhaust gas when the input amount of the by-product slaked lime having a terminal sedimentation rate of 5 cm / sec obtained in Example 1 was changed was examined. Similarly to Example 2, in the cement clinker manufacturing facility having the configuration shown in FIG. 1, by-product slaked lime was charged into the upper cyclone 103a from the raw material crushing dryer 107 in various basic units, and the cement clinker manufacturing facility was operated.

In this case, the concentration of organochlorine compound (DXN _S ) of dioxins in the exhaust gas at the outlet of the electrostatic precipitator (EP) was measured. In addition to DXN _S , HCl in exhaust gas, which is generally related to the mechanism of DXN _S generation, was also measured. The results are shown in Table 6.

The concentration of DXN _S was measured according to “JIS K 0311 Analysis of dioxins in exhaust gas” and evaluated as the concentration of organic chlorine compounds (ng / m ³ N) of dioxins per 1 m ³ N of kiln exhaust gas.
HCl in the exhaust gas was determined by “JIS K 0107 Method for analyzing hydrogen chloride in exhaust gas”.

Byproduct hydrated lime DXN amount added by increasing the 0,2,5,10,20,50,200,300kg / tcl _S is reduced, in particular, if the byproduct slaked lime is 20 kg / tcl more intensity It can be seen that the concentration of dioxins organochlorine compounds in the exhaust gas is reduced to 20 ng / m ³ N or less. When the by-product slaked lime is a basic unit of 200 kg / tcl, the first-stage cyclone outlet temperature rises, and at 300 kg / tcl, the first-stage cyclone outlet temperature becomes 460 ° C. When the basic unit of by-product slaked lime was excessive, the outlet temperature of the first-stage cyclone tended to increase. Since the yield point of the iron material constituting the first-stage cyclone is in the region of about 440 ° C., the basic unit of by-product slaked lime is appropriately 200 kg / tcl or less.

In Japanese Patent Application Laid-Open No. 2007-90261 (Patent Document 5), CaO or Ca (OH) ₂ is introduced into exhaust gas containing hydrogen chloride, the amount of hydrogen chloride in the exhaust gas is reduced, and the neutralized product is chloride. It is said that calcium is produced and as a result, the production of persistent organic pollutants such as dioxins is suppressed. However, in the results of the present invention, even if the amount of slaked lime added increases, the amount of hydrogen chloride in the exhaust gas is not reduced, and the amount of hydrogen chloride in the exhaust gas does not depend on the amount of slaked lime added.
Although the present invention is not intended to be limited by theory, from these facts, the effect of reducing the concentration of organic chlorine compounds of dioxins in exhaust gas according to the present invention is disclosed in JP-A-2007-90261 (Patent Document 5). Rather than the neutralization mechanism described in 1), it is considered that the temperature drop in the first-stage cyclone 103a due to the dehydration reaction of slaked lime is affected.

101 Rotary kiln 102 Calciner 103a First stage cyclone 103b Second stage cyclone 103c Third stage cyclone 103d Fourth stage cyclone 104 Compound raw material supply line 105 Kiln IDF
106 Boiler for waste heat power generation 107 Raw material crushing and drying machine 108 Stabilizer 109 Electric dust collector 110 Preheater 111 Rising duct part 112 Kiln kiln bottom part

Claims (6)

  A cement clinker manufacturing method in a cement clinker manufacturing facility equipped with a preheater having a plurality of cyclones and a rotary kiln, wherein the exhaust gas temperature at the exhaust gas outlet is 350 to 500 ° C. with slaked lime having a terminal sedimentation rate of 0.5 to 10 cm / sec. A method comprising the step of introducing into a cyclone.   The method for producing cement clinker according to claim 1, wherein the slaked lime is added so that the amount of slaked lime is 20 to 200 kg per 1 ton of cement clinker.   The cement clinker manufacturing method according to claim 1 or 2, wherein the slaked lime is charged into a cyclone at the uppermost stage.   The slaked lime is supplied to a raw material crushing and drying machine after being mixed with a cement preparation raw material or in parallel with the preparation raw material, and is supplied to the uppermost cyclone through the preparation raw material supply line together with the cement preparation raw material. The cement clinker manufacturing method as described in any one of these.   The method for producing a cement clinker according to any one of claims 1 to 4, wherein a ratio of the terminal sedimentation rate of the slaked lime to the terminal sedimentation rate of the cement clinker preparation raw material is 0.5 to 1.5.   The method for producing a cement clinker according to any one of claims 1 to 5, wherein the slaked lime is slaked lime by-produced when acetylene is generated from calcium carbide.

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