JPH0134941B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for reducing _NOx contained in exhaust gas from a cement raw material sintering device, and more specifically, the present invention relates to a method for reducing NOx contained in exhaust gas from a cement raw material sintering device. charcoal fuel origin
_{This NO _ _} This relates to a method for reducing _x . In general, modern cement firing equipment:
A calcining furnace having an independent heat source is usually provided between the raw material preheating device and the calcining furnace. However, due to the deterioration of the energy situation, the fuel for the calciner has been changed from heavy oil to nitrogen (e.g. pyrrole,
There is an urgent need to switch to pulverized coal, which contains a large amount of nitrogen-containing cyclic substances such as indole, and the use of this type of low-grade fuel increases the amount of NO _x in exhaust gas, causing air pollution. On the other hand, NO _x emission standards from cement factories tend to become stricter year by year.
Therefore, in order to keep up with the trends of the times, even when using low-grade fuels such as those mentioned above, it is necessary to reduce the amount of thermal NO _x in the combustion furnace exhaust gas and the fuel _NO It is necessary to establish technology to effectively suppress the outbreak. To be more specific, FIG. 1 is a systematic diagram showing the overall outline of the cement raw material firing apparatus, in which solid lines indicate the flow of gas and broken lines indicate the flow of raw materials. The cement raw material sintering apparatus mainly includes a suspension preheater 1 formed by vertically arranging C ₁ to C ₅ separation cyclones, a calcination furnace 2, a sintering furnace 3, and a clinker cooler 4. Then, the raw material powder descends while being sequentially preheated by C ₁ to C ₄ separation cyclones, is calcined in calciner 2, and then passes through the bottom separation cyclone.
C ₅ and then introduced into the kiln 3 via the connection housing 5 . High-temperature air is introduced into the firing furnace 3, and the clinker fired at high temperature enters a clinker cooler 4, is cooled, and is further conveyed out by a clinker conveyor 6. 7 is an exhaust gas induced ventilation fan, 8 is an excess air induced ventilation fan, and 9 is an exhaust gas induced ventilation fan.
10 represents a forced air blower, 10 represents a bleed air duct, 11 represents a calciner burner, and 12 represents a calciner burner. By the way, the raw material firing temperature in the firing furnace 3 is 1450
Since the gas temperature is extremely high at around 2000°C, and the gas temperature is over 2000°C, the thermal energy derived from the nitrogen content in the air is
A considerable amount of NO _x is generated, and the amount of NO _x in the firing furnace exhaust gas (converted to 10% oxygen concentration, the same applies below)
generally ranges from 400 to 1000 ppm. On the other hand, the temperature inside the calcining furnace 2 is 800 to 1000℃.
This is relatively low, and the amount of thermal _NO A large amount of so-called fuel NO _x is generated based on Therefore, the large amount of thermal generated in this way
Various _attempts have been _made to reduce NO _x and fuel _NO No satisfactory method has yet been proposed for simultaneously reducing fuel NO _x and thermal NO _x . For example, one method for reducing fuel NO _x is to use a mixture of pulverized coal fuel and low nitrogen-containing liquid fuel and simultaneously spray and supply it from the calciner burner 12. However, the NO _x in the suspension preheater exhaust gas is Since the reduction is only proportional to the fuel ratio (calorific value ratio), if you try to obtain a high NO _x reduction rate, the consumption ratio of liquid fuel will increase, which will significantly increase the fuel cost for calcination. be. Another method for reducing fuel NO _x is the so-called two-stage combustion method. That is, in this method, as a first step, the combustion air (primary air) from the extraction duct 10 is suppressed to about 0.7 to 1.0 times the theoretically required amount of air, and the thermal NO _x in the combustion furnace exhaust gas is reduced. After combustion is performed in the calciner while suppressing the generation of fuel _NO This is a method of additionally supplying air (secondary air) to the downstream side of the heat supply section. With this method, it is possible to reduce fuel _NO As the combustion efficiency is lower than that of fuel, etc., a large amount of free carbon and CO is generated, and these unreacted components flow out of the calciner without being completely combusted, resulting in blockage accidents in subsequent cyclones and exhaust gas treatment. This may lead to trouble with the equipment, and further damage to the fuel caused by secondary air.
It also causes the phenomenon of NO _x regeneration. The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a method that does not cause a decrease in combustion efficiency in a calciner even when pulverized coal fuel such as coal is used. , fuel in calciner
The object of the present invention is to provide a method that can reduce NO _x more than the two-stage combustion method and can also significantly reduce thermal NO _x in the combustion furnace exhaust gas. The configuration of the present invention that can effectively achieve the above object is a cement raw material sintering apparatus comprising a suspension preheater, a rotary kiln, a calcining furnace installed upright at the end of the kiln, and a clinker cooler. A pulverized coal fuel supply port, a burner, and a first combustion air inlet are provided adjacent to each other on the lower side wall of the calciner, and a pulverized coal fuel supply port, a burner, and a first combustion air inlet are provided in the side wall of the calciner at a position higher than the first inlet. and is configured by sequentially providing a second combustion air inlet and a third combustion air inlet at different positions in the height direction,
The air ratios m blown from the first, second, and third air inlets are m ₁ =0.5 to 0.85, m ₂ =0.15 in order from the bottom.
~0.5, m ₃ = 0.1 ~ 0.35 (1.1 < m ₁ + m ₂ + m ₃
<1.35, m ₁ + m ₂ ≦1. ), and form a primary reduction layer, a secondary reduction layer, and an oxidation layer corresponding to the first, second, and third inlets. That is, the calciner is formed into a first reduction layer, a second reduction layer, and an oxidation layer from the bottom to the top, and in the first reduction layer, the pulverized coal fuel combustion air is mixed with the pulverized coal fuel combustion air. Adding the amount of O ₂ is the air ratio m ₁ =
By supplying an air amount of 0.5 _to 0.85 and burning the pulverized coal fuel in an oxygen-deficient state, the generation of fuel NO _x is suppressed. is reduced and removed by free carbon generated from Furthermore, NH ₃ gas is generated around the so-called cone portion, which acts as a reducing component in the second reduction layer in the next step. Next, secondary air is supplied in the second reduction layer,
A reducing atmosphere containing a small amount of O ₂ is formed by supplying an amount of air with an air ratio m ₂ of 0.15 to 0.5. Here, the NH ₃ gas emitted in the primary reduction layer and the residual NO _x and fuel in the firing furnace exhaust gas are
Contact reaction occurs with NO _x , which remains in the first reduction layer.
NO _x is further reduced and removed. Furthermore, in the oxidation layer, as tertiary air, the air ratio m ₃ =
By supplying an air amount of 0.1 to 0.35, unburned components such as CO gas and free carbon generated by combustion in the primary reduction layer are completely combusted. In order to maintain a reducing atmosphere in both the first reduction layer and the second reduction layer, it is necessary that m ₁ +m ₂ ≦1, and in order to completely burn the unburned matter in the calciner as a whole, It is necessary that at least 1.1<m ₁ +m ₂ +m ₃ <1.35. Here, fuel NO _x can be significantly reduced, and thermal NO _x can also be effectively reduced. Next, the configuration and effects of the present invention will be explained based on drawings showing embodiments. FIG. 2 is a schematic explanatory diagram of a typical calciner used in the present invention, and the calciner 2 consists of three layers: a first reduced layer A, a second reduced layer B, and an oxidized layer C in order of the flow direction of the calciner exhaust gas. It is divided into stages. First, in the first reduction layer A, a pulverized coal fuel supply chute 13 is provided along the opening of the bleed air duct 10 (first combustion air inlet), and the pulverized coal fuel input from the chute 13 is supplied from the bleed air. Combustion air from the duct 10 and excess air in the exhaust gas sent from the firing furnace 3 are burned as primary air, and the preheated raw material introduced from the chute 14 is calcined. At this stage, as mentioned above, NH 3 gas is effectively generated by supplying an amount of air with an air ratio m ₁ -0.5 to 0.85 as primary air and burning the pulverized coal fuel, and at the same time, NH ₃ gas is effectively generated around the cone part a. Some free carbon is retained. When the exhaust gas from the firing furnace 3 comes into contact with this free carbon, the following denitrification reaction occurs, and a portion of NO _x in the exhaust gas is reduced and removed. 2NO+C→N ₂ +CO _2The pulverized coal fuel is mainly input through the 12 calciner burners, but if the O ₂ concentration in the calciner exhaust gas is high, the pulverized coal fuel is also input from the 12' auxiliary burner. By supplying a small amount of pulverized coal fuel, the combustion of the pulverized coal fuel can be made slower and the efficiency of reduction and removal of NO _x can be increased. Next, in the second reduction layer B, so-called secondary combustion air is led from branch pipes 10a and 10b branched from the bleed duct 10, and is introduced into the central part of the calciner 2 through a second combustion air inlet 16b. Supplied by At this stage, as mentioned above, a low concentration atmosphere of O ₂ is formed by supplying an air amount with an air ratio m ₂ =0.15 to 0.5 as secondary air, and the NH ₃ gas generated in the first reduction layer A is A part of the NO _{x is reduced and removed by causing a contact reaction with the remaining NO x in} the firing furnace exhaust gas and the fuel NO _x .
The denitrification reaction formula at this time is as follows. NO+NH ₃ +1/4O ₂ →N ₂ +3/2H ₂ O In the oxidation layer C, the so-called tertiary combustion air is supplied to a branch pipe 10a branched from the extraction duct 10,
Combustion air is introduced from the combustion air 10c and is supplied from the third inlet 16c at the upper part of the calcining furnace 2. At this stage, as mentioned above, air is used as tertiary air.
By supplying an air amount that satisfies m ₃ =0.1 to 0.35, unburned components such as CO gas and free carbon generated in the first reduction layer A are completely combusted. The combustion reaction formula at this time is as follows. C + O ₂ → CO ₂ CO + 1/2O ₂ → CO ₂ As a result, there will be no trouble in subsequent equipment due to a decrease in the combustion efficiency of the calciner 2, and no increase in the amount of pulverized coal fuel supplied to the calciner. Fuel NO _x in the calcination furnace and thermal NO _x in the exhaust gas of the calcination furnace
can be significantly reduced. In addition, the measurement results obtained by conducting a comparative experiment of the degree of reduction of _NO Shown in the table. As is clear from Table 1, the three-stage combustion method according to the present invention can achieve twice the effect of the two-stage combustion method, which has been considered to be relatively effective in the past.

[Table] The embodiment shown in Fig. 3 is intended to improve the mixing properties of the rising exhaust gas in the calciner and the secondary and tertiary air, and to further improve the reaction efficiency.
A is provided with twig pipes 10b and 10c, while a plurality of second inlet ports 16b, 16b, . . . There is. In the case of this embodiment, the blowing speed of the secondary and tertiary air can be made several times faster than the introduction speed of the secondary and tertiary air in the embodiment of FIG. As a result, in addition to the flows of the rising exhaust gas in the calciner and the secondary and tertiary air intersecting perpendicularly or oppositely, the relative speed difference becomes extremely large. It is possible to further improve the mixing properties of the oxidants and improve the reaction efficiency of combustion and denitrification. The pulverized coal fuel input from chute 13 is
Although it may be simply dropped by gravity as shown in FIGS. 2 and 3, it is also possible to directly blow and burn the material that has been accompanied by the transportation air from a burner. The present invention is generally configured and carried out as described above, but the point is that free carbon and NH ₃ gas reducing substances contained in the coal fuel supplied to the calciner are removed using the so-called three-stage combustion method. Because it is effectively generated and reacted using a new combustion technology, the combustion efficiency in the calciner does not decrease even when pulverized coal fuel is used, and it does not contain a large amount of nitrogen like pulverized coal fuel. Even if solid fuel is used, the generation of fuel NO _x in the calciner can be significantly suppressed, and thermal NO _x in the calciner exhaust gas can also be effectively reduced, which is required by the cement industry. This will make it possible to respond to the recent strict pollution regulations and the tense energy situation.

[Brief explanation of drawings]

FIG. 1 is a general explanatory diagram of a cement raw material firing apparatus, FIG. 2 is a schematic diagram of a calcining furnace used in the present invention, and FIG. 3 is an example of another calcining furnace. 2...Calcination furnace, 3...Calcination furnace, 10...Bleeding duct, 10a...Branch pipe, 10b, 10c...Twig pipe, 12...Calcination furnace burner, 12'...Auxiliary burner, 13... ...pulverized coal supply chute, 14... preheating raw material chute, 15b, 15c... annular pipe,
16b, 16c...Inlet.

Claims (1)

[Claims] 1. In a cement raw material firing device comprising a suspension preheater, a rotary kiln, a calciner installed upright at the bottom of the kiln, and a clinker cooler, a pulverized coal fuel supply port and a burner are provided in the lower side wall of the calciner. and combustion air first inlet ports are provided adjacent to each other, and combustion air inlet ports are sequentially provided on the side wall of the calciner at positions higher than the first inlet ports and different in height from each other. A second air inlet and a third combustion air inlet are provided, and the air ratio m from the first, second, and third air inlets is m ₁ =0.5 to 0.85 in order from the bottom. _m2 = 0.15~
0.5, m ₃ = 0.1 to 0.35 (1.1 < m ₁ + m ₂ + m ₃ <
1.35, m ₁ + m ₂ ≦1. ), and correspond to the first, second, and third inlet ports.
NOx of a cement raw material sintering device characterized by forming a secondary reduction layer, a secondary reduction layer and an oxidation layer
Reduction method.