Cement kiln firing device and method for denitrifying cement kiln exhaust gas

Abstract

[Problem] To efficiently reduce the NOx concentration in a cement kiln exhaust gas by using a reducing gas. [Solution] A cement calcination device 1 comprises: an extraction device 13 that extracts a preheated raw material from a preheater cyclone; a gasification device 14 that uses the preheated raw material R4 extracted by the extraction device as a heat source to gasify organic waste and generate a reducing gas RG; charging devices 15, 16 that charge the reducing gas generated by the gasification device and the preheated raw material R5 discharged from the gasification device into a kiln end 4 of the cement kiln or a combustion gas flow path from the kiln end to a calcination furnace 3; and a denitrification burner 9 that blows a fuel F3 and a portion A of air for combustion into the combustion gas flow path to induce the partial combustion of the fuel. The denitrification burner may be provided with a swirling means (swirling vane 9b) that causes the mixed flow of the fuel and the portion of the air for combustion to swirl. The reducing gas can be set to a temperature of 300°C to 600°C, inclusive.

Description

[Technical Field]

[0001] The present invention relates to a technique for reducing the concentration of nitrogen oxides (hereinafter referred to as "NOx") in combustion gas discharged from a cement kiln. [Background technology]

[0002] NOx is generated in the high-temperature region of the burning zone of a cement kiln. When the NOx concentration in cement kiln exhaust gas becomes high, the NOx concentration is reduced by adding denitrification agents such as urea or ammonia or by the reduction effect of combustion in the calciner. However, using urea as a denitrification agent increases operating costs due to its high price. Furthermore, adding urea alone does not achieve the desired denitrification efficiency, and there is a risk that excess ammonia that does not react with NOx will be emitted directly from the system.

[0003] Therefore, Patent Document 1 describes an invention in which organic waste such as waste plastics is gasified to generate reducing gas, and the reducing gas is introduced into a combustion gas flow path in a preheater from the raw material inlet end of a cement kiln to the calciner, into the calciner itself, or into a combustion gas flow path from the calciner to a cyclone two stages above, and used as a reducing agent for nitrogen oxides. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-18371 Summary of the Invention [Problem to be solved by the invention]

[0005] The invention described in Patent Document 1 is effective, but there is a problem in that even if the reducing gas obtained by gasifying organic waste is introduced into the bottom of a cement kiln, if the state of mixing with the cement kiln exhaust gas is poor, the desired NOx reduction effect cannot be achieved.

[0006] The present invention has been made in view of the above-mentioned problems in the prior art, and has as its object to efficiently reduce the NOx concentration in cement kiln exhaust gas by using a reducing gas. [Means for solving the problem]

[0007] In order to achieve the above object, the cement burning apparatus of the present invention comprises a separation device that separates preheated raw material from a preheater cyclone; a gasification device that uses the preheated raw material separated by the separation device as a heat source to gasify organic waste and produce a reducing gas; an introduction device that introduces the reducing gas produced by the gasification device and the preheated raw material discharged from the gasification device into a combustion gas flow path at the end of the cement kiln or from the end of the kiln to a calciner; and a denitration burner that injects fuel and a portion of the combustion air into the combustion gas flow path to partially combust the fuel, the denitration burner comprising a swirling means for swirling a mixed flow of the fuel and a portion of the combustion air, and the denitration burners comprise a pair of denitration burners that swirl in opposite directions and are located below a portion where the reducing gas produced by the gasification device and / or the preheated raw material discharged from the gasification device are introduced into the combustion gas flow path.

[0008] According to the cement firing apparatus of the present invention, by providing a denitration burner in the combustion gas flow path at the end of the cement kiln or from the end of the kiln to the calciner, mixing of the cement kiln exhaust gas with a reducing gas is promoted, and the synergistic effect of providing the denitration burner and introducing the reducing gas can efficiently reduce the NOx concentration in the cement kiln exhaust gas. Furthermore, the swirling means improves the mixing efficiency of the cement kiln exhaust gas with the reducing gas, further enhancing the NOx reduction effect. Furthermore, by providing a pair of denitration burners with different swirling directions below the introduction section into the combustion gas flow path of the reducing gas generated by the gasification system and / or the preheated raw material discharged from the gasification system, mixing of the cement kiln exhaust gas with the reducing gas can be further promoted, thereby increasing the denitration efficiency.

[0012] In the above-described method for denitrifying cement kiln exhaust gas, the reducing gas introduced into the combustion gas flow path at the end of the cement kiln or from the end of the kiln to the calciner can be set to a temperature of 300° C. to 600° C. Introducing a reducing gas with a relatively low temperature can suppress the formation of coating in the combustion gas flow path and increase the amount of fuel used in the calciner. [Effects of the Invention]

[0013] As described above, according to the present invention, the NOx concentration in cement kiln exhaust gas can be efficiently reduced by using a reducing gas. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing an embodiment of a cement kiln burning apparatus according to the present invention. [Figure 2] 1A and 1B are schematic diagrams showing an example of the arrangement of denitration burners in a cement kiln firing apparatus according to the present invention, in which (a) is a partially cutaway front view, (b) is a partially cutaway left side view, (c) is a partially cutaway right side view, and (d) is a top view. [Figure 3] 2A and 2B are diagrams showing the denitration burner of FIG. 1, in which (a) is a cross-sectional view, (b) is a side view, and (c) is a development view of the tip of the burner. DETAILED DESCRIPTION OF THE INVENTION

[0015] FIG. 1 shows one embodiment of a cement firing apparatus according to the present invention. This cement firing apparatus 1 includes a preheater 2 that preheats cement raw materials (hereinafter referred to as "raw materials") R, a calciner 3 that calcines raw materials R1 from a cyclone 2b that is second from the bottom of the preheater 2 using fuel F2 blown in from a calciner burner 11, a cement kiln 5 that burns raw materials R2 from a cyclone 2a at the bottom of the preheater 2 using fuel F1 blown in from a main burner 10, a clinker cooler 6 that cools cement clinker burned in the cement kiln 5, and a separator 11 that separates the preheated raw materials from the cyclone 2a at the bottom. The system is comprised of a preheater 13 for collecting preheated raw material R4, a gasifier 14 for gasifying organic waste using the preheated raw material R4 collected by the preheater 13 as a heat source to produce reducing gas, a feeder 15 for feeding the reducing gas RG produced by the gasifier 14 into the end 4 of the cement kiln or into the combustion gas flow path from the end 4 to the calciner 3, a chute (feeder) 16 for feeding the preheated raw material R5 discharged from the gasifier 14 into the combustion gas flow path from the end 4 to the calciner 3, and a denitration burner 9 for injecting fuel F3 and a portion A of the combustion air into the combustion gas flow path to partially combust the fuel F3 at a low air ratio. The preheater 2, calciner 3, cement kiln 5, and clinker cooler 6 are configured in the same manner as conventional systems.

[0016] The gasification device 14 gasifies organic waste such as waste plastic, wood chips, waste tires, and sludge to produce a reducing gas RG containing gases such as hydrogen, carbon monoxide, methane, and carbon dioxide, and can be a pyrolysis furnace. The introduction device 15 can be a pipe if the gas can be sucked in by the negative pressure inside the cement kiln 5, or a fan or the like if not. The reducing gas RG from the introduction device 15 can be introduced into the combustion gas flow path through a chute 16 that introduces the preheated raw material R5, or can be introduced through a pipe separate from the chute 16.

[0017] As shown in FIG. 2, a total of four denitration burners 9 (9A-9D) are provided, and fuel F3 and a portion of the combustion air A are blown in from each of the denitration burners 9 (9A-9D). Of the four denitration burners 9, two (9B, 9C) are arranged below a chute 16 into which reducing gas RG and preheating raw material R5 are introduced. As shown in FIG. 2(c), the swirling flow of denitration burner 9B is set to be clockwise, and the swirling flow of denitration burner 9C is set to be counterclockwise, thereby effectively promoting mixing of cement kiln exhaust gas G and reducing gas RG. Note that if the reducing gas RG and preheating raw material R5 are not introduced through the same chute 16, the two denitration burners (9B, 9C) are arranged below either the pipe into which reducing gas RG is introduced or the chute 16 into which preheating raw material R5 is introduced.

[0018] As shown in Figure 3, the denitration burner 9 comprises a cylindrical member 9h with six to ten swirl vanes (swirl means) 9b fixed to the tip of a cylindrical main body 9a at a swirl angle of 10 to 50 degrees, a rod-shaped member 9j located at the center of the cylindrical member 9h, and a ring-shaped member 9f located outside the tip of the cylindrical member 9h. The tip of the denitration burner 9 is covered with refractory material 9e, and a mounting member 9c at the rear end of the main body 9a is connected to the surface 4a of the kiln bottom 4 by a bracket 9d, and the denitration burner 9 is attached to the kiln bottom 4 or the like. The kiln bottom 4 or the like is also protected by refractory material 4b. The swirl angle is the angle θ between the axial direction 9m of the denitration burner 9 and the center line 9g of the swirl vanes 9b when the cylindrical member 9h is unfolded in a plane as shown in Figure 3(c). This angle corresponds to the swirl angle of the solid powdered fuel flow F at the tip 9k of the flow path. The number of swirl blades 9b and the swirl angle can be changed as appropriate.

[0019] Next, the method for denitrifying cement kiln exhaust gas according to the present invention will be described with reference to FIGS.

[0020] The preheater 2 of the cement firing apparatus 1 preheats the raw material R using exhaust gas G from the cement kiln 5, and the calciner 3 calcines the raw material R1 from the cyclone 2b of the preheater 2. During this, tertiary air G1 from the clinker cooler 6 is blown in together with fuel F2 from the calciner burner 11 to combust the fuel F2. Pulverized coal, heavy oil, combustible waste, combustible gas, etc. may be used as the fuel F2, and combustible waste may be used as part or all of the fuel F2.

[0021] Meanwhile, preheated raw material is collected by a collection device 13 from the raw material chute 12 of the lowest cyclone 2a, and the collected preheated raw material R4 is used as a heat source to gasify waste plastic as organic waste at approximately 10 t / h in a gasification device 14. The generated reducing gas RG, which is 300°C or higher and 600°C or lower, is injected by an injection device 15 through a chute 16 into the kiln end 4 or into the combustion gas flow path from the kiln end 4 to the calciner 3. Meanwhile, preheated raw material R5 discharged from the gasification device 14 is injected through a chute 16 into the kiln end 4 or into the combustion gas flow path from the kiln end 4 to the calciner 3.

[0022] If 50% or more of the fuel F2 supplied to the calciner 3 is introduced into the combustion gas flow path without using the reducing gas RG, coating will form and operation will not be possible. However, by introducing a reducing gas RG with a relatively low temperature of 300°C or higher and 600°C or lower and the preheated raw material R5 discharged from the gasification device 14, the deposition of coating can be suppressed and the amount of fuel F2 introduced into the calciner 3 can be increased.

[0023] Furthermore, fuel F3 is also injected from a denitration burner 9 installed at the kiln end 4 of the cement kiln 5, together with a portion of the combustion air A, to promote mixing of the cement kiln exhaust gas G and the reducing gas RG, and the synergistic effect of installing the denitration burner 9 and introducing the reducing gas RG can efficiently reduce the NOx concentration in the cement kiln exhaust gas G. As with fuel F2 for the calciner 3, pulverized coal, heavy oil, combustible waste, combustible gas, etc. can be used for fuel F3, and any one or more of these may be used simultaneously.

[0024] By injecting fuel F3 from the denitration burner 9, NOx contained in exhaust gas G from the cement kiln 5 can be reduced in the low-oxygen region in the kiln end. Furthermore, by partially combusting fuel F3 using part A of the combustion air and completely combusting the unburned portion using tertiary air G1 in the calciner 3, it is possible to decarbonate raw materials R2 and R3 and improve the decarbonation efficiency of the entire cement firing apparatus 1. In this case, the swirl blades 9b provided on the denitration burner 9 swirl the mixed flow of fuel F3 and part A of the combustion air and inject it between the kiln end 4 and the calciner 3, improving the combustion efficiency of fuel F3.

[0025] Next, fuel F1 such as pulverized coal is injected from the main burner 10 of the cement kiln 5 to burn the raw material R2 from the cyclone 2a of the preheater 2, and the resulting clinker is cooled in the clinker cooler 6 to obtain cement clinker CL.

[0026] Conventionally, when targeting cement kiln exhaust gas G, the introduction of reducing gas RG alone has been effective in reducing NOx by about 50 ppm, and the installation of denitration burners 9 (two-stage combustion) alone has been effective in reducing NOx by about 50 ppm. However, according to the present invention, the synergistic effect of the installation of denitration burners 9 and the introduction of reducing gas RG achieves a further NOx reduction effect of about 20 ppm or more.

[0027] In the above embodiment, the preheated raw material is taken from the lowest cyclone 2a and used as a heat source for the gasifier 14, but the preheater cyclone 2b above the lowest cyclone 2a may also be used. [Explanation of symbols]

[0028] 1. Cement baking equipment 2 Preheater 3. Calciner 4. Kiln end 5. Cement kiln 6 Clinker Cooler 9 (9A~9D) Denitrification burner 10 Main Burner 11 Calciner burner 12 Raw material chute 13 Preparation device 14 Gasifier 15 Dosing device 16 shots

Claims

[Claim 1] a fractionation device that fractionates the preheated raw material from the preheater cyclone; a gasification device that gasifies organic waste using the preheated raw material separated by the separation device as a heat source to generate reducing gas; an input device that inputs the reducing gas generated by the gasification device and the preheated raw material discharged from the gasification device into a combustion gas flow path at the end of the cement kiln or from the end of the kiln to a calciner; a denitration burner that blows fuel and a portion of combustion air into the combustion gas flow path to partially combust the fuel, the denitration burner is provided with a swirling means for swirling a mixed flow of the fuel and a portion of the combustion air, The cement burning apparatus is characterized in that the denitration burners are a pair of denitration burners having different rotation directions, and are provided below an input portion into the combustion gas flow path of the reducing gas generated by the gasification apparatus and / or the preheated raw material discharged from the gasification apparatus.

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