JP2011079716A - Method for reducing lead in cement clinker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for reducing lead in cement clinker which can efficiently exhaust lead volatized within a cement kiln to the outside of a cement kiln system, reduces the content of lead in a cement clinker, and increases the receiving amount in a cement production process in city waste incineration ash or the like. <P>SOLUTION: SiO<SB>2</SB>component-containing grains with a 50% grain size of ≤10 μm are sprayed into a cement kiln 2, a part of combustion gas is bled from a cement kiln exhaust gas flow passage ranging from the kiln inlet 2a to the lowermost stage cyclone 4, dust comprised in the bled combustion gas G is classified, and fine powder dust F comprising lead separated by the classification is removed to the outside of the system of the cement kiln. The SiO<SB>2</SB>component-containing grains are sprayed preferably to a PbO volatilization region in the cement kiln, and coal ash can be used as the SiO<SB>2</SB>component-containing grains. The process from the bleeding of the combustion gas to the removal of the fine powder dust comprising lead to the outside of the cement kiln system can be performed by using a chlorine bypass system fitted to the cement kiln. <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).

  By the way, in Patent Document 2, diatomaceous earth having a large specific surface area as a heavy metal adsorbent in order to reduce heavy metals such as lead in the exhaust gas of a waste incinerator efficiently and to reduce the amount of additives used for exhaust gas treatment as much as possible. A technique using an adsorbent using alumina, silica, activated carbon or the like as a carrier is disclosed.

  In addition, Patent Document 3 discloses a powder incineration composed of a specific substance in order to efficiently remove and stabilize harmful organic substances such as dioxin and heavy metals contained in exhaust gas generated in municipal waste incinerators. Furnace flue blowing agents and the like have been proposed.

  The techniques described in Patent Documents 2 and 3 utilize a physical adsorption mechanism for removing lead and the like, and supply an adsorbent into exhaust gas from a municipal waste incinerator or the like.

  In Patent Document 4, coal ash is directly blown into the cement kiln from the front of the kiln of the cement kiln, unburned carbon contained in the coal ash is burned, and the remaining ash is mixed into the cement clinker. A method of manufacturing cement to be fired is proposed.

  Furthermore, Patent Document 5 discloses that a silicon-containing substance is used in front of a cement kiln kiln in order to produce a low heat-generating cement for obtaining concrete that is difficult to neutralize using a general-purpose ordinary Portland cement production line. Is disclosed.

  The technologies described in Patent Documents 4 and 5 take coal ash and silicon-containing substances into a cement clinker and discharge them as part of the clinker fired product.

JP 2006-347794 A Japanese Patent Laid-Open No. 10-109016 Japanese Patent Laid-Open No. 11-9963 JP-A-6-329453 JP 2004-299954 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 dust 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, by blowing SiO ₂ component-containing particles having a particle size of 10 μm or less into a cement kiln and reacting with volatilized PbO, the product after the reaction is made fine and discharged from the chlorine bypass system as chlorine bypass dust. It becomes possible.

That is, the present invention is a method for reducing lead in a cement clinker, in which SiO ₂ component-containing particles having a 50% particle size of 10 μm or less are blown into a cement kiln, from the kiln bottom of the cement kiln to the bottom cyclone. A part of the combustion gas is extracted from the cement kiln exhaust gas flow path, the dust contained in the extracted combustion gas is classified, and the fine dust containing lead separated by the classification is removed from the cement kiln system. It is characterized by. Here, the 50% particle diameter is also called a median diameter, and is calculated based on a particle size distribution measured by a laser diffraction particle size distribution measuring device or the like.

According to the present invention, the lead obtained by classifying the dust contained in the extraction gas reacts with PbO in which the SiO ₂ component-containing particles having a 50% particle size of 10 μm or less injected into the cement kiln are volatilized. In order to remove fine dust dust containing cement from the cement kiln system, the product of the reaction between PbO and SiO ₂ component does not return to the cement kiln as in the past, and the volatilized PbO is efficiently removed from the cement kiln system. Can be removed. 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 SiO ₂ component-containing particles can be blown into the PbO volatilization region in the cement kiln. Thereby, the blown SiO ₂ component-containing particles can be efficiently reacted with Pb, and more Pb can be removed out of the system.

In the lead reduction method in the cement clinker, the SiO ₂ component-containing particles can be made of coal ash, and the amount of lead in the cement clinker can be reduced while effectively using the coal ash as waste.

  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, it turned out that there are many forms of PbO as a volatile form.

The volatilized PbO easily reacts with the SiO ₂ component-containing dust 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 The amount of Pb removed from the system of the cement kiln 2 together with F is very small. On the contrary, the Pb recovery rate may be reduced, and the 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, SiO ₂ component-containing particles having a 50% particle size of 10 μm or less are blown into the cement kiln 2 and reacted with PbO volatilized in the cement kiln 2. As a result, the generated (PbO) ₂ SiO ₂ is fine after the reaction, like the blown SiO ₂ component-containing particles. A part of (PbO) ₂ SiO ₂ as fine particles 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. However, the other (PbO) ₂ SiO ₂ is contained in the extraction gas G by the probe 12, separated to the fine powder F side by the cyclone 13, and then removed from the cement kiln 2 as chlorine bypass dust.

The SiO ₂ component-containing particles are preferably blown from before the kiln so as not to land on the cement kiln 2 of the cement kiln 2, and the SiO ₂ component-containing particles react with PbO in the gas and further ride on the gas flow to the probe 12. Need to reach. Therefore, it is required that the floatability is good, and SiO ₂ component-containing particles having a 50% particle diameter of 10 μm or less are used. Note that 10 μm or less is determined from the setting of the classification process, but according to the definition of what is subject to measurement in Japanese environmental standards, the definition of suspended particulate matter is that the particle size is 10 μm or less. Therefore, it is consistent with the floatable particle size.

Examples of the SiO ₂ component-containing particles to be blown include silica (silica) powder, feldspar powder, diatomaceous earth, coal ash, calcined clay, rice husk ash, and ground blast furnace slag. In the present invention, since the SiO ₂ component and PbO are reacted, it is desirable that the SiO ₂ component-containing particles to be blown have a higher SiO ₂ content. The SiO ₂ content is preferably 50% or more, more preferably 60% or more. On the other hand, among the SiO ₂ component-containing particles, coal ash can be effectively used from the viewpoint of utilization of recycled raw materials and cost. The SiO ₂ content of coal ash generated in Japan is said to be 50% to 70%, and can be sufficiently used in the present invention. The average particle diameter of the coal ash are the 5 to 10 [mu] m, which satisfies the condition regarding particle size of the SiO ₂ ingredient-containing particles blown.

  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. In addition, it is also possible to use this reduction volatilization together with the chlorination volatilization that volatilizes lead by adding a chlorine source such as calcium chloride.

As described above, in this embodiment, coal ash or the like is generated by blowing SiO ₂ component-containing particles having a 50% particle size of 10 μm or less into the cement kiln 2 and reacting with the PbO volatilized in the cement kiln 2. A part of the combustion gas of the cement kiln 2 containing (PbO) ₂ SiO ₂ as fine particles 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 be cement kiln as chlorine bypass dust In order to remove the PbO from the system 2, the PbO that has been generated by the reaction with coarse SiO ₂ and separated into the coarse powder C by the cyclone 13 and then returned to the cement kiln 2 through the kiln bottom 2a is removed. Since the cement kiln 2 can be removed from the system, 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, the kiln bottom 2a of the cement kiln 2 is also used. It is also possible to extract a part of the combustion gas from the kiln exhaust gas passage from the first to the lowest cyclone 4 and reduce the lead content of the clinker by the same method as described above.

Finally, when the inventions described in Patent Documents 2 to 5 introduced in the background art section are compared with the present invention, the techniques described in Patent Documents 2 and 3 are based on physical adsorption mechanisms for removing lead and the like However, unlike the present invention, it does not use a chemical reaction (chemical bond) between the Pb component (mainly PbO) and the SiO ₂ component. For this reason, in Patent Documents 2 and 3, the adsorbent is not supplied to the high-temperature firing furnace but is supplied to the exhaust gas to the last. The present invention is a lead removal technique using a chemical reaction between a Pb component and a SiO ₂ component in a high-temperature environment in the cement kiln 2, and even if particles containing the SiO ₂ component are supplied to a low-temperature exhaust gas. There is no effect of the invention.

Patent Document 4 discloses a technique in which coal ash is directly blown into the cement kiln from the front part of the cement kiln, and Patent Document 5 discloses a method of introducing a silicon-containing material into the cement kiln front. However, these technologies take coal ash and silicon-containing substances into cement clinker and discharge them as a part of the clinker fired product, and the SiO ₂ component contained in coal ash and the like is a PbO component. There is no suggestion that they are combined and discharged as dust in the exhaust gas, and there is no description regarding the setting of the particle size of the material to be blown in, which is essentially different from the present invention.

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 (4)

Injecting SiO ₂ component-containing particles having a 50% particle size of 10 μm or less into a cement kiln,
Extracting a part of the combustion gas from the cement kiln exhaust gas flow path from the bottom of the kiln to the bottom cyclone,
Classifying the dust contained in the extracted combustion gas;
A method for reducing lead in a cement clinker, wherein fine dust containing lead separated by the classification is removed from the cement kiln system. _{2. The} method for reducing lead in a cement clinker according to claim 1, wherein the SiO ₂ component-containing particles are blown into a PbO volatile region in the cement kiln. The method for reducing lead in a cement clinker according to claim 1 or 2, wherein the SiO ₂ component-containing particles are coal ash.   The process from the extraction of the combustion gas to the removal of the fine dust containing lead out of the cement kiln system is performed using a chlorine bypass system attached to the cement kiln. The method for reducing lead in cement clinker as described in 1.

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