JPS6065752A - Raw material powder calcining process - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for calcination of raw material powder such as cement raw material disposed between a raw material preheating device and a kiln, and particularly to a method for calcination of raw material powder such as a cement raw material disposed between a raw material preheating device and a kiln. At the same time, it promotes heat transfer from combustion gas to raw material powder and calcination reaction of raw material powder, thereby reducing fuel consumption or downsizing equipment.
Furthermore, the present invention provides a method for calcination of raw material powder, which is particularly suitable for use with solid fuels and low-grade fuels, and is capable of suppressing the generation of NoX (nitrogen oxides) in a calcination furnace.

A modern calcining apparatus is constructed by disposing a calcining furnace having an independent heat source between the raw material preheating device and the calcining furnace when viewed in the direction of flow of the raw material powder.

FIG. 1 is a diagrammatic system diagram showing the steps of preheating, calcining, firing, and cooling cement raw material powder, and the solid arrows in the figure indicate the flow of hot air, and the dashed arrows indicate the flow of the raw material powder. The outline of the apparatus is as follows: 11 a raw material preheating device consisting of a raw material powder separator Cl-03 such as Zylon, a duct 7, etc., a calcining furnace 2. It consists of a kiln i such as a rotary kiln and a clinker cooler 4, and the cement raw material powder supplied from the raw material input chute 5 descends sequentially through the first to third cyclones C and -wc3, and the other kiln 3 and clinker cooler 4. The high-temperature exhaust gas from the calcining furnace 2 is sucked by the induced draft fan 8 and rises inside the raw material preheating device 1, so that the raw material powder and the high-temperature gas are mixed and heat exchanged in the duct 7 and the cyclones C and -C3.・Separation is repeated. The preheated raw material powder is introduced from the raw material preheating device 1 into the calciner 2 through the preheated raw material chute 14. On the other hand, combustion is carried out in the calciner 2 by the high temperature secondary combustion air introduced from the clinker cooler 4 into the calciner 2 through the bleed air duct 13 and the fuel supplied from the burner 6a together with the primary combustion air. The raw material powder is calcined by receiving the combustion heat and the heat of the firing furnace exhaust gas.

The calcined raw material powder enters the separation cyclone C4 as a separation means from the calciner 2 together with the combustion gas and is separated from the combustion gas, and then enters the calciner 3 from the calciner raw material chute 15 through the calciner port 12. After being subjected to necessary heat treatment in the firing furnace 3 by the combustion heat of fuel supplied from the burner 6b installed at the lower end of the firing furnace 3 to become clinker, it is cooled by cooling fi4. Note that the air for clinker cooling is supplied by forced air blowing talo, and a part of the air that has been heated by exchanging heat with the clinker is distributed and introduced into the calcining furnace 2 and the calcining furnace 3 as described above. The air is exhausted by the induced draft fan 9. The clinker discharged from the clinker cooler 4 is transported to the next process by a conhair 11.

FIG. 2 is a conceptual diagram showing in more detail the structure around the calcining furnace shown in FIG. 1, and the structure and function of the calcining furnace will be explained with reference to these figures as follows.

That is, in this configuration example, the calcining furnace 2 has a cylindrical vertical shape, and the constricted part 2
The upstream side (
The downstream side (upper side) forming a mixing zone with the combustion chamber 2a (lower side)
The lower end of the combustion chamber 2a has an inverted conical shape with its cross section gradually reduced downward, and an opening 2Δ
It is connected to the firing furnace 3 via the inlet end ff112. Further, a bleed air duct 13 that guides high-temperature bleed air from the clinker cooling 1illI4 as secondary air for combustion is connected to the lower side wall of the combustion chamber 2& in the radial or tangential direction through an opening 2e, and the ceiling wall of the bleed air duct 13 is combustion chamber 2@
A burner 6, which blows fuel together with primary air toward the high-temperature bleed air flowing into the combustion chamber 2a, is located near the side wall.
and a preheated raw material input chute from the cyclone C3 of the raw material preheating bag W1, which is located above the burner 6a and is directed toward the combustion zone formed in the two combustion chambers by the fuel supplied from the burner 6a. 14 is connected, while mixing chamber 2I.

The combustion gas outlet 2f of is connected to the separation cyclone C4.

When using these devices, the preheated raw material from the raw material preheating device 1 is supplied through the chute 14 into the combustion chamber 2 □ that forms the combustion zone of the calciner 2, and is passed through the opening 2a through the entrance end cover 12 and downwardly. The exhaust gases from the firing furnace 3 flowing upward are mixed and stirred in the combustion chamber 28 to form a spouted bed. The high-temperature bleed air from the clinker cooler 4 is introduced into the jet tL layer through the bleed air duct 13 as secondary air for combustion, and through the burner 6fi installed above the inlet 2e of the bleed air duct 13 into the combustion chamber 2a. Fuel is supplied together with primary air for combustion, and combustion occurs within the spouted bed. The combustion chamber 2 through the preheated feed chute 14.
The raw material powder supplied into the chamber absorbs the combustion heat of the fuel and the heat of the firing furnace exhaust gas to advance the calcination reaction, and passes through the throttle part 2C together with the combustion gas to the mixing chamber 2b forming a mixing zone. However, the agitation and mixing is promoted by the diffusion effect due to acceleration and deceleration when passing through the constriction part 2C and the turbulent flow generated in the mixing chamber 2, and the combustion gas is mixed inside the mixing chamber 2. After complete combustion of the combustible components contained in the fuel, the fuel is discharged from the opening 2f to the separation cyclone C+ that constitutes the separation means.

Combustion chamber 2 of such a spouted bed type calciner or air flow type calciner
In a, the entire amount of the preheated raw material to be calcined from the raw material preheating device is directly supplied to the combustion chamber or passes through the combustion chamber, and the heat generated by the combustion of the fuel in the combustion chamber is immediately absorbed. Because the temperature is transmitted to the raw material powder, the temperature inside the calciner combustion chamber is close to the equilibrium temperature determined from the heat balance in the combustion chamber.
It is maintained at a relatively low temperature around ℃.

Maintaining the inside of the calciner combustion chamber at a low temperature in this way is effective in sufficiently safely protecting the furnace wall of the combustion chamber 2a, but it also inhibits the combustibility of the fuel within the combustion chamber 2a. Although the calciner 2 as a whole is equipped with an intermediate throttle mechanism 2c and a mixing chamber 2c following it to improve fuel combustibility, it is theoretically necessary to ensure sufficient combustion. It is necessary to introduce a considerable amount of combustion air into the calciner in excess of the amount of combustion air required, leading to an increase in fuel consumption in the calciner. In particular, when solid fuel such as pulverized coal or low-grade fuel is used as the calcining fuel, the combustion time is longer than that of liquid fuel such as heavy oil, so the residence time of the fuel in the combustion chamber is In order to extend the combustion chamber, it is necessary to increase the capacity of the combustion chamber, leading to an increase in equipment costs.

In addition, the degree of progress of the calcination reaction of the raw material powder in the calcination furnace is related to the partial pressure of carbon dioxide in the atmospheric gas, but it is mainly controlled by the temperature of the atmospheric gas, so if the inside of the combustion chamber is maintained at a low temperature. Since the calcination reaction cannot sufficiently proceed to the center of the raw material powder particles, the calcination rate of the raw material powder discharged from the calcination furnace to the calcination furnace has not been sufficiently satisfied. Furthermore, since combustion in a calciner is carried out in the temperature range where so-called fuel No In this case, a large amount of NO is generated in the calcining furnace, which is discharged from the raw material preheating device, causing atmospheric pollution.

The present invention solves the above-mentioned problems of the prior art, improves the combustibility of fuel, and reduces the amount of excess air for combustion by adjusting and maintaining the atmospheric temperature inside the calciner combustion chamber at an appropriately high temperature. Fuel consumption is reduced by promoting the calcining reaction of raw material powder! ! The object of the present invention is to provide a method for calcining raw material powder that can reduce the amount of raw material powder or downsize the equipment, and at the same time can effectively suppress the generation of NOx in the calciner.

The present invention will be described in detail below based on the drawings, but the drawings show specific examples of implementation, and the present invention is not limited to these illustrated examples. Alternatively, the same implementation can be performed by changing some of the columns.

FIG. 3 is a conceptual diagram showing one embodiment of the present invention, showing the basic structure of the main body of the calciner 2, the method of introducing exhaust gas from the calciner 3 into the calciner 2, and the method for high-temperature combustion from the extraction duct 13. Regarding the method of introducing secondary air, the flow of combustion gas in the calciner 2, the method of discharging the combustion gas from the calciner 2, etc., please refer to the above-mentioned Section 2.
This is the same as the case of the conventional device shown in the figure.

Therefore, based on FIG. 3, the configuration of the present invention will be explained in detail as a difference from FIG. The branching member 14J branches the preheated material into two chutes 14a and 14b, one separation chute 148 is connected to the combustion chamber 2a forming the combustion zone of the calciner 2, and the other branch chute 14I is connected to the combustion chamber 2a forming the combustion zone of the calciner 2. 2 mixing chambers 21. connected to. These branching chutes14. The connection point W between the combustion chamber 2a and the mixing chamber 2 and the combustion chamber 2a and the mixing chamber 2 is not particularly limited; The preheated raw material powder introduced into the combustion chamber 2a by the burner 6a is directed to the combustion zone formed in the combustion chamber 2□ to prevent the formation of localized high temperature areas in the combustion chamber, or Lower end opening 2a of calcining furnace 2
(The first jet stream is directed toward the exhaust gas from the firing furnace 3 that rises and flows into the combustion chamber 2a, making it more dense inside the combustion chamber 2a)
The preheated raw material which assists in forming the bow and is fed into the mixing chamber 2t by the branch shoe l141°) is the combustion chamber 2a which rises and flows into the mixing chamber 2b from the intermediate constriction part 2c of the calciner 2. A connection arrangement is recommended that helps direct the combustion gases from the mixing chamber 2I to form a second spouted bed.

With such a configuration, only a part of the preheated raw material to be calcined from the raw material preheating device is supplied to the combustion chamber 2a,
Since the preheated raw material supplied to the mixing chamber 2b is introduced into the separation cyclone C1 without substantially passing through the combustion chamber 28 by 1 ffl, the temperature inside the combustion chamber 21 can be increased compared to the case of the conventional structure. This combustion chamber 2. The temperature inside depends on the distribution ratio of the preheated raw material to the combustion chamber 2a and the mixing chamber 2b (8)! a, and the combustibility of the fuel, which will be described next, occurs.

It is selected by comprehensively considering the formation of raw material coating on the furnace wall and the thermal protection of the furnace wall, but generally 950 to 11
It is appropriate to create a high-temperature atmosphere of 00°C, preferably 1000-1050°C, and for this purpose, 90-50% of the preheated raw material from the raw material preheating device is sent to the combustion chamber 21, and the remaining 10-50% is Distribute and feed 50% to mixing chamber 2. Here, we will explain the effect of combustion temperature in combustion chamber 2□.
First, the combustion rate of the fuel increases exponentially with the absolute temperature inside the combustion chamber 28, so sufficient combustion can be achieved with a small amount of excess air, and the large temperature difference between the combustion gas and the feed material Based on this, the combustion heat of the fuel can be effectively and quickly transferred to the raw material powder, so that the fuel droplets η'ffl in the calciner can be reduced. Furthermore, even when solid fuel such as pulverized coal or low-grade fuel is used, the required combustion time is shortened due to the increase in combustion temperature, so the capacity of the calciner can be selected to be small. Furthermore, since the temperature inside the combustion chamber 2a is much higher than the calcination reaction temperature of the raw material 1 powder, which is determined by the partial pressure of carbon dioxide in the combustion gas in the same chamber, the combustion chamber 2 ．．
The raw material 15) powder supplied to the combustion chamber 2a quickly completes the calcination reaction.

On the other hand, the raw powder supplied to the mixing chamber 2 through the branch shoe 114b can undergo a calcination reaction to the same extent as in the prior art, and the amount of raw powder supplied to the mixing chamber 2b is
Since the amount is smaller than the raw material powder supplied to a and where the calcination reaction has significantly progressed, the temperature of the calcination raw material powder discharged from the separation cyclone C to the firing furnace 3 as a mixed raw material is about the same as that of the conventional technology. Despite this, the calcination reaction has progressed further, and the thermal efficiency of the calcination apparatus as a whole can be improved. Next, NOx inside the combustion chamber 2a
To explain the generation of NOx, as is known (in general, there are two types of NOx: fuel NOx, which is caused by the nitrogen content in the fuel, and thermal NOx, which is caused by the nitrogen content in the combustion air). , -= :f-JL/N Ox is approximately 900
In the temperature range above ℃, the amount generated decreases as the temperature increases, and thermal NOx gradually increases when the combustion zone temperature exceeds about 1100 to 1200℃, and the amount generated increases as the combustion zone oxygen concentration increases. . According to the device of the present invention, the temperature of the combustion zone is in a temperature range in which both fuel NOx and thermal NO8 are difficult to generate, and as described above, the oxygen concentration can be maintained low by reducing excess air in the combustion zone. Therefore, the generation of NOx can be significantly suppressed. At this time, if the temperature in the combustion chamber exceeds about 1100°C, coating of raw material powder is likely to occur on the wall surface of the combustion chamber 2a, and from the standpoint of thermal protection of the furnace wall, the temperature in the combustion chamber should be kept to this level. Further, if the temperature inside the combustion chamber is lower than about 950° C., there is little improvement effect in terms of suppressing the combustion of the fuel and the retardation of the combustion history. To easily control the amount of NOx generated in consideration of combustibility by measuring the combustion gas temperature and NOx content near the intermediate throttle cap 2c of the calciner 2 and adjusting the distribution valve 14c accordingly. This makes it possible to always maintain a stable low level even when operating conditions fluctuate.

In this way, the temperature inside the combustion chamber 2a is high; based on the surrounding air temperature,
In a state where both the MAR of the fuel and the calcining reaction of the raw material powder are highly advanced while suppressing the generation of NOx, the combustion gas and the raw material powder pass through the throttle part 2c and are introduced into the mixing chamber 2I, where they are branched. It is stirred and mixed with a part of the preheated raw material t4) supplied through the shoe 14b, and a second jet is formed here to stagnate the raw material powder, and the newly supplied raw material powder As the calcination reaction progresses, a low-temperature atmosphere is created in which the temperature drops to around 900°C, and the mixture is discharged from Sekiguchi 2 of mixing chamber 2I to separation cyclone C. At this time, since the "secondary gas" passing through the intermediate constriction part 2c is accelerated, a substantial portion of the raw material powder supplied to the mixing chamber 2I through the branch chute 14b falls into the combustion chamber 2n. This is prevented, and the inside of the combustion chamber 2□ can be maintained at a high temperature.

In these calciner structures, the shape of the °C1 calciner cross section, the introduction form of fuel and combustion air, and whether or not calciner exhaust gas is introduced into the calciner can be freely selected depending on the purpose. For example, when solid fuel is used, a fuel supply chute may be provided in place of the burner 6□, and the powdered solid fuel may fall and be introduced into the combustion chamber 2a by gravity. or,
At this time, the preheated raw material powder is supplied to the calciner together with the solid fuel through the supply chute to prevent the formation of a localized high temperature area near the fuel supply part in the combustion chamber, and the preheated raw material powder is supplied from the separation cyclone C4 to the calciner. Circulate part of the fuel into the combustion chamber,
Alternatively, it may be combined with other means for suppressing NOx generation or denitration, such as installing a separate burner in the inverted cone-shaped portion of the combustion chamber 2a. Furthermore, there are no restrictions at all regarding the type of raw material preheating device (cyclone type, base type, etc.), the number of five-stage series, the number of powder separators constituting each stage, etc.

The present invention is constructed as described above, and when supplying the preheated raw material from the raw material preheating device to the calciner, the calciner is configured with a combustion zone on the upstream side and a mixing zone on the downstream side. ,
By dividing the preheated raw material into the combustion zone and the mixing zone and supplying it in an adjusted manner, the atmospheric temperature in the combustion zone is appropriately raised, thereby improving the combustibility of the fuel, and reducing heat transfer from the combustion gas to the raw material powder. It promotes the transmission and calcination reaction of the raw material powder, reduces fuel consumption and downsizes the equipment, and can significantly suppress the generation of NOx in the calcination furnace.

[Brief explanation of the drawing]

Figure 1 is a diagrammatic system diagram showing the conventional 7-mentoring force production process, Figure 2 is a conceptual diagram of the vicinity of the calcining furnace in Figure 1,
FIG. 3 is a conceptual diagram showing an embodiment of the present invention. (Explanation of symbols) ■... Raw material preheating device W 2... Calcination furnace 2a... Combustion chamber 2... Mixing chamber 2,... Throttle section 3... Calcining furnace 4... Tallinn power cooler 6...Fuel supply device 12.
...Inlet end cover 13...Bleed air duct 14...Preheated raw material chute 14m, 14b...Branch chute 14c...Distribution valve 14. l... Branch member 15...
- Calcined raw material chute c, -C3... Raw material powder separator C4... Separation cyclone. Applicant Kobe M Steel Co., Ltd. Agent Patent Attorney Takeo Honjo Figure 1 τ 1 Figure 2

Claims (2)

[Claims] (1) The calciner, which is disposed between the preheating device and the calcining furnace when viewed in the direction of flow of the raw powder, and is equipped with a means for separating the raw powder, separates the combustion zone on the upstream side and the mixing zone on the downstream side. configured,
In a method for calcining raw material powder, the preheated raw material powder supplied to the combustion zone is calcined while being discharged from the separation means via the mixing zone by introducing fuel and combustion air into the combustion zone. 50 to 90% of the raw material powder to the combustion zone,
In addition, 10 to 50% of the raw material powder is supplied to the mixing zone, and a substantial part of the raw material powder supplied to the mixing zone is introduced into the separation means without passing through the combustion zone, thereby reducing the combustion in the calciner. A method for calcination of raw material powder, characterized in that the zone is placed in a high temperature atmosphere of 950 to 1100C, and the mixing zone is placed in a low temperature atmosphere of around 900C. (2) The method for calcining raw material powder as set forth in claim 1, characterized in that the combustion zone is set to a high temperature atmosphere of 1000 to 1050°C.