JP2011084407A - Method for reducing lead in cement clinker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which can efficiently discharge lead which has volatilized in a cement kiln to the outside of cement kiln system, reduces lead content of cement clinker and increases the received amount of municipal refuse incineration ash or the like in a process for producing cement. <P>SOLUTION: When a part of combustion gas is extracted from a cement kiln exhaust gas flow path which extends from the end of kiln 2a of a cement kiln 2 to the lowest stage cyclone 4, lead chloride is blown near the extraction part, the dust contained in the extracted combustion gas G is classified, and fine powder dust F containing a lead compound separated by classification is removed to the outside of cement kiln system. In the presence of lead compound (PbO)<SB>2</SB>SiO<SB>2</SB>formed on the surface of a large-sized particle of SiO<SB>2</SB>which reacts with volatilized PbO and lead sulfate, a lead compound of a low viscosity is formed by reacting with lead chloride, and fine powder dust containing lead compound 3 [(PbO)<SB>2</SB>SiO<SB>2</SB>] 3PbSO<SB>4</SB>PbCl<SB>2</SB>which is exfoliated from the surface of a large-sized particle of SiO<SB>2</SB>and having a low viscosity is removed by classification to the outside of cement kiln system. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for reducing lead in cement clinker, and more particularly to a method for reducing lead in cement clinker while increasing the amount of waste such as municipal waste incineration ash.

  Wastes such as municipal waste incineration ash, construction waste soil, and slag are highly demanded for reuse as cement raw materials and detoxification treatment, and these reuse and detoxification treatments are actually being carried out. However, some of these wastes contain chlorine (Cl) and lead (Pb), which are the repellent components of cement, and are reused as cement raw materials, where the lead content in the cement is high May elute and lead to environmental pollution. For this reason, there is a limit to the amount of waste that can be received in the cement manufacturing process, and when it is attempted to accept the waste exceeding the allowable amount, the repellent component must be removed from the system by some method.

  With regard to chlorine as one of the repellent components, many studies have been made so far, and its acceptance tolerance has been greatly improved. On the other hand, a method has been proposed in which excess lead is volatilized in a cement kiln and then discharged from the cement process through a chlorine bypass system and treated separately (see Patent Document 1).

  Patent Document 2 discloses a technique of blowing a chlorine-containing substance from before the kiln of the cement kiln in order to promote the volatilization of lead in the cement kiln and reduce the lead concentration in the cement clinker. Here, as a chlorine-containing substance, waste containing a compound of chlorine and calcium or magnesium, for example, incineration fly ash, waste quick lime, etc. can be blown, and the chlorine-containing substance is 0.35 kg or less per ton of clinker. In the cement kiln, the raw material temperature is 1100 ° C. or higher, or L / D calculated from the kiln length (L) and inner diameter (D) of the cement kiln is 1 to 8 from the discharge end of the cement kiln. It is preferable to blow into the region.

JP 2006-347794 A JP 2007-238357 A

  However, in order to remove lead as a repellent component contained in municipal waste incineration ash and other waste, simply improving the volatilization rate of lead in the cement kiln causes sufficient discharge (recovery) of lead from the cement kiln. As a result, it was found that lead could be concentrated in the cement kiln and could not be increased as much as expected in the cement manufacturing process, such as municipal waste incineration ash containing lead.

  Accordingly, the present invention has been made in view of the above-described problems in the prior art, and reduces the amount of lead in a cement clinker, and produces a cement manufacturing process for waste such as municipal waste incineration ash containing lead. The purpose is to increase the amount of receipts.

  In order to achieve the above-mentioned object, the present inventors have conducted extensive research, and as a result, the behavior of lead in the cement kiln, that is, the mechanism from the volatilization of lead to the discharge from the cement kiln system, and the form of lead By taking measures based on the behavior of this lead, it is possible to efficiently discharge lead volatilized in the cement kiln out of the cement kiln system, and waste such as municipal waste incineration ash containing lead Has been found to be more acceptable in the cement manufacturing process.

The above investigation, Pb volatilizes at PbO, PbS, PbC1 ₂ forms in the cement kiln, PbS is, PbSO ₄ next part by reaction with O _2, some _{PbO [2PbS + 3O 2 → 2PbO} + 2SO 2] Thus, it has been found that there are relatively many volatile forms of PbO. PbO easily reacts with the SiO ₂ component-containing particles in the cement kiln exhaust gas stream. However, the cement kiln dust has few particles of 10 μm or less, and the ratio of coarse dust exceeding 10 μm is about 90%. For this reason, even if the volatilization rate of Pb in the cement kiln is improved, the amount of Pb recovered as chlorine bypass dust is as expected from the chlorine bypass system that removes only fine particles of 10 μm or less outside the cement kiln system. There was a case where the Pb recovery rate did not increase, but instead decreased.

Therefore, in the chlorine bypass system and the like, in the vicinity of the extraction points, such as kiln of the cement kiln blowing pBC1 _2, volatilized PbO of reacting with coarse particles greater than 10μm containing SiO ₂ component (hereinafter, the "SiO ₂ and lead compounds formed on the surface of coarse wherein the particles "), the presence of PbSO _4, and lower the viscosity by reacting pBC1 _2, a lead compound after reaction is stripped from the surface of the SiO ₂ of coarse particles Were discharged from the chlorine bypass system as fine particles.

  That is, the present invention is a method for reducing lead in a cement clinker, and when extracting a part of combustion gas from a cement kiln exhaust gas passage from the bottom of the cement kiln to the lowest cyclone, In this case, lead chloride is blown into the vicinity of the gas, dust contained in the extracted combustion gas is classified, and fine dust containing lead compounds separated by the classification is removed from the cement kiln system.

According to the present invention, a low-viscosity lead compound is produced by reacting lead compound formed on the surface of coarse particles of SiO ₂ by reacting with volatilized PbO and lead chloride in the presence of lead sulfate. In order to remove fine dust containing low-viscosity lead compounds generated and separated from the surface of coarse particles of SiO ₂ out of the cement kiln system by classification, coarse particles due to the reaction between PbO and SiO ₂ components as in the past The product does not return to the cement kiln, and the volatilized PbO can be efficiently removed out of the cement kiln system. As a result, the lead content of the cement clinker can be reduced, and the amount of waste containing lead in the cement manufacturing process can be increased.

In the lead reduction method in the cement clinker, the lead compound may be generated by a reaction between the lead chloride and dust in the cement kiln. The lead compound can contain SiO ₂ .

  In the method for reducing lead in cement clinker, the amount of lead chloride blown can be 2 g or more and 50 g or less per ton of clinker discharged from the cement kiln based on chlorine. A small amount of addition is sufficient as compared with the case where chlorine is added as a chlorine source.

  In the method for reducing lead in the cement clinker, the steps from the extraction of the combustion gas to the removal of fine dust containing lead from the cement kiln system can be performed using a chlorine bypass system attached to the cement kiln. it can. Thereby, the lead content rate of a cement clinker can be reduced using the chlorine bypass system normally attached to the cement kiln.

  As described above, according to the present invention, lead volatilized in the cement kiln can be efficiently discharged out of the kiln system, the lead content of the cement clinker is reduced, and a cement manufacturing process such as municipal waste incineration ash It is possible to increase the amount of receipts at.

It is the schematic for demonstrating the behavior of lead in the cement baking apparatus at the time of using the lead reduction method in the cement clinker concerning this invention. It is the schematic for demonstrating the behavior of the lead in the conventional cement baking apparatus.

  Next, a mode for carrying out the present invention will be described. Before that, the behavior of lead in a conventional cement baking apparatus will be described with reference to FIG.

  The cement baking apparatus 1 includes a cement kiln 2, a calcining furnace 3, a preheater (not shown) including a lowermost cyclone 4, a chlorine bypass system 11, and the like. The chlorine bypass system 11 is a kiln of the cement kiln 2. A probe 12 for extracting air while cooling a part of the combustion exhaust gas from the bottom 2a, a cyclone 13 for separating the extracted gas G into coarse powder C and fine powder (chlorine bypass dust) F, and the like are provided.

  In the cement firing apparatus 1, the cement raw material is preheated with a preheater including the lowermost cyclone 4, calcined in the calcining furnace 3, and main fuel such as pulverized coal is blown from a main burner (not shown) of the cement kiln 2. The cement raw material is fired, and the obtained cement clinker is cooled by a clinker cooler (not shown).

  Further, in the chlorine bypass system 11, the probe 12 is extracted while cooling a part of the combustion exhaust gas of the cement kiln 2 from the kiln bottom 2a, and the extracted gas G is separated into coarse powder C and fine powder F by the cyclone 13. The coarse powder C having a low chlorine content separated by the cyclone 13 is returned to the cement kiln 2 and the fine powder F having a high chlorine content is removed from the cement kiln 2.

In the above operation, the investigation of the present inventors, Pb contained in the cement raw material and fuel, volatilized in the cement kiln 2 PbO, in the form PbS, pBC1 _2, PbS is O in the cement kiln 2 _A part becomes PbSO ₄ by the reaction with _2, and a part becomes PbO [2PbS + 3O ₂ → 2PbO + 2SO ₂ ]. For this reason, there are relatively many volatile forms of PbO.

The volatilized PbO easily reacts with the SiO ₂ component-containing particles present in the combustion exhaust gas stream of the cement kiln 2. However, the dust in the cement kiln 2 has few particles of 10 μm or less, the ratio of coarse powder dust exceeding 10 μm is about 90%, and the ratio of fine powder dust is about 10%. Therefore, a part of (PbO) ₂ SiO ₂ generated by the reaction moves from the calcining furnace 3 to the lowermost cyclone 4 and is taken into the cement raw material in the lowermost cyclone 4 and again through the kiln bottom 2a. Returned to kiln 2. Further, (PbO) ₂ SiO ₂ contained in the combustion exhaust gas (extraction gas G) of the cement kiln 2 extracted by the probe 12 is separated to the coarse powder C side by the cyclone 13 and then cemented through the kiln bottom 2a. Returned to kiln 2.

As described above, since most of the PbO volatilized in the cement kiln 2 is returned to the cement kiln 2 as (PbO) ₂ SiO ₂ , even if the volatilization rate of Pb is improved in the cement kiln 2, fine powder Pb removed from the system of the cement kiln 2 as F is very small, and may lead to a decrease in the Pb recovery rate. PbO volatilized in the cement kiln 2 is efficiently discharged out of the cement kiln 2 system. I could not.

  Next, a method for reducing lead in a cement clinker according to the present invention will be described with reference to FIG. In the present invention, the basic structure and material flow of the cement baking apparatus 1 are the same as those of the conventional apparatus shown in FIG. 2, and therefore, the same reference numerals and symbols are used for the same apparatus and materials as those in FIG. The description is omitted.

In the present invention, lead chloride (PbCl ₂ ) is blown into the vicinity of the kiln bottom 2 a of the cement kiln 2. PbCl ₂ blown without decomposing by heat in the cement kiln 2, as it is suspended as PbCl _2, the presence of PbSO _4, formed on the surface of the SiO ₂ coarse particles (PbO) ₂ SiO ₂ react. As a result, low-viscosity 3 [(PbO) ₂ SiO ₂ ] .3PbSO ₄ .PbCl ₂ is generated and peeled from the surface of the coarse SiO ₂ particles. Since the dropped 3 [(PbO) ₂ SiO ₂ ] .3PbSO ₄ .PbCl ₂ is finer than at least the coarse particles of SiO ₂ , one of 3 [(PbO) ₂ SiO ₂ ] .3PbSO ₄ .PbCl ₂ The part moves from the calcining furnace 3 to the lowermost cyclone 4 and is taken into the cement raw material in the lowermost cyclone 4 and returned to the cement kiln 2 again. Most of it is separated to the fine powder F side by the cyclone 13 and then removed from the cement kiln 2 as chlorine bypass dust.

The amount of lead chloride blown into the kiln bottom 2a of the cement kiln 2 can be 2 g or more and 50 g or less per ton of clinker discharged from the cement kiln based on chlorine (in terms of chlorine). In the present invention, lead chloride is blown in, but lead does not cause chlorine volatilization. In conventional chlorination volatilization, an excess of chlorine equivalent to or more than Pb is added to volatilize lead in the clinker and remove it as PbCl _{2. In} the present invention, volatilization of lead from the clinker is reduced by volatilization. The blown PbCl ₂ plays a role in generating a low-viscosity compound. Therefore, a small amount of addition is sufficient as compared with about 350 g per ton of clinker when chlorine is added as a chlorine source for volatile chloride.

In order to promote the volatilization of PbO in the cement kiln 2, it is preferable to carry out the reduction volatilization in a reducing atmosphere, and the method for the reduction volatilization is not particularly limited. For example, combustible materials are mixed with the cement raw material. And supplying the cement kiln 2 to the cement kiln 2 or putting a combustible material in the temperature range of 1000 ° C. or higher. The region where the reduction volatilization is performed corresponds to a region where combustible material as a reducing agent is introduced and PbO is volatilized, and is considered to be a region around 1200 ° C. in the cement kiln 2. The presence of PbSO ₄ is also important for the reaction, and reduction volatilization is preferably performed in order to promote the volatilization of PbS in the cement kiln 2.

As described above, in this embodiment, generated by reaction with SiO ₂ of coarse particles (PbO) ₂ SiO _2, the presence of PbSO _4, is reacted with PbCl _2, 3 generated by the reaction [( A part of the combustion gas of the cement kiln 2 containing PbO) ₂ SiO ₂ ] · 3PbSO ₄ · PbCl ₂ is extracted by the probe 12 of the chlorine bypass system 11 and then separated to the fine powder F side by the cyclone 13 to obtain chlorine bypass dust. In order to remove the cement kiln 2 from the system, it is conventionally generated by reaction with coarse particles of SiO ₂ , separated to the coarse powder C side by the cyclone 13, and then returned to the cement kiln 2 through the kiln bottom 2a. In addition, (PbO) ₂ SiO ₂ can be removed out of the cement kiln 2, and the PbO removal efficiency can be increased accordingly.

  In the above embodiment, the lead content of the cement clinker is reduced by using the chlorine bypass system 11 attached to the cement kiln 2. However, in addition to the chlorine bypass system, from the kiln bottom 2a of the cement kiln. When a part of the combustion gas is extracted from the kiln exhaust gas flow path leading to the lowermost cyclone 4 and extracted, lead chloride is blown in the vicinity of the extracted part, and the lead content of the clinker is determined in the same manner as described above. Can also be reduced.

Finally, when the invention described in Patent Document 2 introduced in the background art section is compared with the present invention, the technique described in Patent Document 2 is based on chlorine-containing substances from the front of the kiln of the cement kiln when removing lead and the like. It is a technology that breathes in. However, this technology promotes the volatilization of lead in the cement kiln. In consideration of the reaction between the volatilized lead (mainly PbO) and the SiO ₂ component and the chlorine-containing substance, The present invention is essentially different from the present invention in which a chlorine-containing substance is blown in the vicinity of the extraction location of the kiln bottom of the cement kiln.

DESCRIPTION OF SYMBOLS 1 Cement baking apparatus 2 Cement kiln 2a Kiln bottom 3 Calcining furnace 4 Bottom cyclone 11 Chlorine bypass system 12 Probe 13 Cyclone

Claims (5)

When extracting a part of the combustion gas from the cement kiln exhaust gas flow path from the bottom of the kiln of the cement kiln to the lowermost cyclone, lead chloride is blown in the vicinity of the extraction location,
Classifying the dust contained in the extracted combustion gas;
A method for reducing lead in a cement clinker, wherein fine dust containing a lead compound separated by the classification is removed from the cement kiln system.   The method for reducing lead in a cement clinker according to claim 1, wherein the lead compound is produced by a reaction between the lead chloride and dust in the cement kiln. The method for reducing lead in a cement clinker according to claim 1, wherein the lead compound contains SiO ₂ .   4. The cement clinker according to claim 1, wherein the amount of lead chloride blown is 2 g or more and 50 g or less per ton of clinker discharged from the cement kiln based on chlorine. 5. Lead reduction method.   The process from the extraction of the combustion gas to the removal of fine dust containing lead out of the cement kiln system is performed using a chlorine bypass system attached to the cement kiln. A method for reducing lead in a cement clinker according to claim 1.

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