JPH0657315B2 - Method and apparatus for firing raw material powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and apparatus for firing raw material powder, and more particularly to a method and apparatus for firing cement raw material, alumina raw material or limestone powder.

“Prior Art” Conventionally, for example, as a device for firing a cement powder raw material to obtain a clinker, (A) a so-called suspension type raw material preheating device, a calcination device having an independent heat source, a rotary kiln for firing, and Those equipped with a clinker cooling device and the like, for example, those disclosed in Japanese Patent Application Laid-Open No. 60-65752, (B) From a fluidized bed firing furnace having an independent heat source, an air preheater and a raw material preheater (C) Vertical raw material preheating device for introducing cement raw material granulated into pellets of small diameter in advance, hot air supply device as secondary air for fluidization or combustion, independent heat source Including a two-stage fluidized-bed calciner having a heat exchanger and a packed bed clinker cooling device, and (D) a calcining furnace having an independent heat source Combined raw material preheating device, high temperature separator, unsintered raw material separator, firing furnace with independent heat source, clinker cooling device, etc. are configured so that unsintered raw materials etc. can be fed into the clinker cooling device. Until it reaches the high temperature separator, the unbaked raw material separator, and the closed furnace formed by the connection of the firing furnace, make sure that it is circulated and retained in a high temperature state and discharged from the outlet of the firing furnace. The high temperature exhaust gas is introduced into the raw material preheating device through the high temperature separator, the unsintered raw material separator, and the calcination furnace, which is disclosed in, for example, Japanese Patent Publication No. 60-13737. The four types can be listed as typical examples.

Particularly, for the convenience of the following description, a typical example of the above-mentioned (A) method will be described with reference to FIG.

Incidentally, this FIG. 6 corresponds to FIG. 1 in the above-mentioned JP-A-60-65752.

FIG. 6 is a diagrammatic system diagram showing the steps of preheating, calcination, firing, and cooling the cement raw material powder. In the figure, the solid line arrows show the flow of hot air exhaust gas, and the broken line arrows show the flow of raw material powder. Shows.

In this device, a preheating device 1 mainly composed of powder separators C _{1 to} C ₃ such as a cyclone for preheating raw material powders in a vertical direction and a dust discharge port were connected to an inlet end cover 12 of a firing furnace 3 described later. It is composed of a separation cyclone C ₄ , a firing furnace 3 such as a rotary kiln for clinker firing, and a clinker cooling device 4.

In such a cement raw material firing device, the charging chute 5
The supplied raw material powders are cyclones C _{1 to} C for preheating.
_It descends in sequence while going through ₃ . On the other hand, the high-temperature exhaust gas supplied from the calcining furnace 3 and the calcining furnace 2 provided in communication with the inlet end cover 12 of the calcining furnace 3 is sucked by the induction ventilator 8 and the raw material preheating device. Rise within 1. Therefore, in the duct 7 and in the cyclones C _{1 to} C ₃ , the mixing, heat exchange and separation of the raw material powder and the high temperature exhaust gas are repeated.

In this way, the preheated raw material powder is introduced into the calcination furnace 2 from the raw material preheating device 1 through the preheating raw material chute 14.

In addition, the bleeder duct 13 extending from the clinker cooling device 4 is connected to the calcination furnace 2 and the high temperature secondary air for firing generated in the clinker cooling device 4 is supplied to the calcination furnace 2. Has been introduced. Therefore, in the calciner 2, and the combustion secondary air of high temperature, occur combustion by the fuel supplied together with the combustion primary air from the burner 6 _a to uniquely occupied, with its combustion heat of the combustion furnace exhaust gas The raw material powder is calcined by receiving heat.

The calcined raw material powder enters the separation cyclone C ₄ as a powder separator connected to the combustion gas outlet 2f side of the calcining furnace 2 together with the combustion gas to be separated, and thereafter, through the calcining raw material chute 15. It is sent to the inlet end cover 12 of the firing furnace 3 and put in the firing furnace 3. Then, the raw material powder is to feed stream of sintering furnace 3 by the heat of combustion of the fuel supplied from the burner 6 _b installed at the downstream lower end, is subjected a heat treatment required in the sintering furnace 3, become clinker After that, it is cooled by the cooling device 4.

The air for cooling the clinker is supplied by the forced air blower 10, and a part of the air heated by exchanging heat with the clinker is distributed and introduced into the calcination furnace 2 and the firing furnace 3 as described above. The air is discharged by the induction fan 9.
Then, the clinker discharged from the clinker cooling device 4 is carried out to the next step by the conveyor 11.

[Problems to be Solved by the Invention] However, among the above, in the method (A) that is mainly put into practical use at present, since it is necessary to form a high temperature flame for firing the calcination raw material, Inconveniences such as severe burnout of the kiln lined refractory and short service life due to frequent occurrence of toxic gases such as NO _X and excessive heat load in the firing zone in the kiln are recognized.

Furthermore, focusing on the clinker produced during the treatment process, its particle size composition is widely distributed from fine particles of 1 mm or less to large particles of several tens mm, and the clinker is segregated in the cooling device to cool the clinker. Efficiency is reduced. Also,
Clinker movement (circulation) in a rolling rotary kiln
As a result, the coarse particles move on the outside and the fine particles move on the inside, so when trying to obtain the desired clinker quality, the coarse particles are over-burned and the fine particles are insufficiently baked. As a result, the quality of the clinker varies, and the crushability in the subsequent cement mill deteriorates.

Next, in the method (B), which is considered to be still in the stage of pilot plant, the sensible heat possessed by the clinker has not been recovered and utilized, and moreover, the clinker particle generation in the fluidized bed of the firing furnace has not been performed. Since the fine clinker after cooling is circulated as the core, reduction in heat consumption cannot be expected.

On the other hand, it seems that the (C) method has not been put to practical use so far. This is because a considerable amount of heat is required to dry the pelletized cement raw material that is fed into the raw material preheating device, and the progress of decarboxylation reaction and firing reaction inside and outside of these pellets is inevitably uneven. Therefore, the characteristics of the clinker are likely to vary, and the suspension-type raw material preheating device with a calcination furnace cannot be applied, so the required fluidized bed firing furnace becomes large, resulting in a reduction in heat consumption. It is considered that there are disadvantages and disadvantages such as an increase in the total equipment cost because the pellet granulation equipment is required.

Further, in the (D) method, the inconveniences observed in the above methods (A), (B), and (C), when viewed in the publication,
Disadvantages, drawbacks, etc. are eliminated, and it is possible to reduce the equipment area of the entire device, reduce heat consumption, prevent the generation of harmful gases such as NO _X , extend the life of refractory linings, and moreover, use the rotary kiln system. By comparison, a clinker with smaller particles can be obtained, so the crushing power of the cement mill can be reduced. However, in such a scheme,
In order to entrain the granulated clinker in the firing furnace with the ascending gas without depositing it in the firing furnace, the gas velocity in the fluidized bed needs to be high (above the terminal velocity). In that case, the residence time of the raw material in the firing furnace becomes extremely short, and a large amount of high-temperature raw material circulates in the separator and the firing furnace, resulting in variations in particle size, which is extremely high in thermal efficiency. In addition, when the liquid phase component is inferior, the risk of fusion of the raw materials in the duct part and the separator part is high, and therefore a special mechanism must be provided separately. In this case, the above-mentioned effects cannot always be obtained in actual use, and it is extremely difficult from the viewpoint of practical use.

"Object of the invention" Therefore, the main object of the present invention is to eliminate the above-mentioned problems in the prior art such as prevention of generation of toxic gas such as NO _X and extension of life of refractory linings, and in particular, A clinker that excels in heat exchange, reduces heat consumption and downsizes the entire device, has a uniform and small particle size, improves cooling efficiency, and improves crushing efficiency in a cement mill, for example. The object of the present invention is to provide a method of firing a raw material powder that can be manufactured, and to provide an apparatus suitable for the firing method.

"Means for Solving the Problems" In order to achieve the above object, the main means adopted by the present invention is, in the method, a calcination zone of a raw material powder using a calcination zone having an independent combustion means. A raw material preheating step for performing treatment, a firing step in which an independent combustion means for firing the preheated and partially calcined raw material powder is provided following the preheating step, and cooling of the firing raw material following the firing step In the firing method of the raw material powder carried out through the steps, in the high temperature exhaust gas introduced from the cooling step to the firing step, the position is downstream in the flow direction and above the discharge portion of the firing raw material. From the upstream side to the downstream side, the raw material powder sent from the raw material preheating step is charged, and the passing speed of the high-temperature exhaust gas introduced during the firing step is seen in the flow direction in each of a plurality of stages. As it goes, the speed gradually increases from the high speed to the low speed, and in each stage, at the upstream inlet side of each stage, the passage speed at the upstream side of the downstream side is slower than that at the downstream side. The step speed is changed stepwise from the high speed to the low speed as it goes from the upstream side to the downstream side when viewed in the flow direction, and the raw material powder conveyed to this high temperature exhaust gas is calcined, and by the calcining, Only the coarse powder raw material granulated to a predetermined size,
It is a point to be supplied to the subsequent cooling step, and in an apparatus for suitably performing the method, a raw material preheating device equipped with a calcination furnace having an independent combustion means, and the preheated raw material powder In a calcining device for raw material powder, which comprises a calcining furnace having an independent combustion means for calcining and a cooling device for cooling the calcined calcining raw material, as seen in the flow direction of the high temperature exhaust gas introduced. A downstream side of the firing furnace and above the discharging portion of the firing raw material, an inlet for introducing raw material powder supplied from the raw material preheating device is provided, and the cooling port is provided on the upstream side. An opening for introducing the high-temperature exhaust gas supplied from the apparatus is formed, and in addition, the inner wall of the firing furnace is formed in a plurality of steps in a stepwise manner, and in each of the steps, it gradually increases as it goes to the upstream side. Specifically, and Among the trays, the firing furnace is stepwise expanded toward the upstream side at each upstream inlet side of each tray while enlarging the outlet side of the upstream tray from the inlet side of the downstream tray. The point is that the cross-sectional area of is reduced.

[Advantages of the Invention] According to the present invention, prevention of generation of toxic gas such as NO _X ,
It is possible to extend the life of the refractory lining and to improve the heat exchange efficiency, thereby making various devices such as firing furnaces compact and reducing fuel consumption and NO _X in exhaust gas. .

Further, since the calcined raw material powder has a uniform and small particle diameter, for example, it is possible to manufacture a clinker having a good cooling property in a cooling device and a good pulverizability in a cement mill.

The above-mentioned objects, other objects, features and advantages of the present invention will be more apparent from the detailed invention of the following embodiments with reference to the drawings.

[Embodiment] FIG. 1 is a schematic system diagram showing a main part of a firing apparatus according to an embodiment of the present invention, and FIG. 2 is a line showing a main section of a firing apparatus according to another embodiment of the present invention. FIG. 3 is a schematic system diagram, FIG. 3 is a graph showing the relationship between the clinker particle diameter and the terminal velocity, and FIGS. 4 and 5 are explanatory views showing modified examples of different types of firing furnaces.

The following embodiments are merely specific examples of the present invention, and the technical scope of the present invention is not limited to these embodiments.

Further, elements common to those of the conventional apparatus for firing raw material powder shown in FIG.

In FIG. 1, the raw material powder firing apparatus is equipped with the calcination furnace 2 shown in FIG. 6, and the firing furnace 30 located downstream and the subsequent cooling with respect to the flow of the raw material powder (broken line in the figure). The apparatus 4 is provided.

The preheating device in this embodiment has the same structure and function as those of the conventional device shown in FIG.

The upper end of the firing furnace 30 is the lower throat 2 of the calcination furnace 2.
_It is connected to the calcination furnace 2 via _b , and the lower end thereof is connected to the cooling device 4 via the lower nozzle 31 of the baking furnace 30. Therefore, the high temperature exhaust gas of the cooling device 4 is introduced from the lower nozzle 31 and the firing raw material (clinker) granulated in the firing furnace 30 is discharged toward the cooling device 4.

The upper portion of the firing furnace 30 is a cylindrical portion provided with an inlet (not shown) for introducing the raw material powder supplied from the raw material preheating device 1 (FIG. 6) through the separation cyclone C ₄ and the calcination raw material chute 15. 30 _e and a conical portion 30 _{a that} opens upward (small chamber)
The lower portion is composed of small chambers 30 _b , 30 _c and 30 _{d each} having a conical shape of a lower throttle whose diameter decreases in the following order.

In this case, the conical portion _30a and the small chambers _30b , _30c ,
The opening area of the connecting portions of 30 _{d which} are vertically arranged is set so that, for example, when viewed in the flow direction of the exhaust gas, the upstream side becomes larger, and each connecting portion is arranged with respect to the firing furnace 30.
In other words, it is a shelf-like portion in which the diameter is gradually reduced toward the upstream side. As a result, in the firing furnace 30, the gas flow velocity of the high-temperature exhaust gas is higher toward the upstream side of each small chamber, the gas flow velocity of the high-temperature exhaust gas is lower toward the downstream side thereof, and between the small chambers, the downstream side is higher. The velocity of the gas flow at the outlet of the small chamber on the upstream side of the inlet of the small chamber becomes slow.

The lower nozzle 31 of the firing furnace 30 and each small chamber 3
0 _b, the flow rate of the hot exhaust gas passing through the 30 _c, the opening between 30 _d is illustrated such clinker particle size and terminal velocity relationship and the furnace temperature in Figure 3, considering the amount of gas or the like, It is decided as appropriate.

Therefore, the raw material preheater 1 end calcination in almost (Figure 6), the raw material powder coming thrown into the top of the chamber 30 _a firing furnace 30 through the calcining raw material chute 15, first the chamber 30 _a Fell along the inner wall of the room, followed by small room 3
At the lower opening of 0 _a, the hot exhaust gas is blown up at a relatively high speed from the small chamber 30 _b connected immediately below it, while in the upper part, it is separated from the exhaust gas at a relatively low speed. And fall again.

In this way, the raw material powder, first in small chamber 30 _a
Repeated steps of lifting and lowering, at this time,
Heat exchange with exhaust gas, firing and granulation are performed. In addition,
Unless the raw material powder is discharged from the lower opening of the small chamber 30 _a, the raw material powder is normally continuously fed from the calcination raw material chute 15 so that the raw material powder in a high-concentration state is obtained. Will be retained. Thereby, the heat exchange of the raw material powder with the high temperature exhaust gas and the coarsening (granulation) of the raw material particles can be efficiently performed.

Then, subsequent chamber from the lower opening of the chamber 30 _a 30
_The raw material particles that have grown to a size that can fall into _b are
Against the gas flow rate blown up by coming exhaust gas from the chamber 30 _b, it falls into small chamber 30 _b, followed the chamber by 30 _a
Perform the same exercise as described in 1.
0 even within _b, blown up by a relatively blown up by coming hot flue gas at high velocity from driving chamber 30 _c immediately below.

At this time, the small chamber 30 _b, the second phase of the lifting movement of the material particles are repeated, heat exchange with the exhaust gas, coarsening of progression and the particles of the baked reaction (granulation) is performed. Then, the raw material particles, against the gas flow rate blown up by coming exhaust gas from the chamber 30 _c, Komuro by gravity when coarse enough may fall into small chamber 30 _b subsequent chamber 30 _c from the lower opening of the It falls into 30 _c .

Thereafter, in the small chambers _30c and _30d , the same particle raising / lowering motion, heat exchange, calcination and granulation are repeated, and the raw material calcined to a predetermined particle size is discharged from the lower nozzle 31 to the cooling device 4. It

As described above, since the gas flow velocity of the exhaust gas blown up from each of the lower chambers is set to gradually decrease as it rises to the upper stage, each of the small chambers 30 _a to 30 _d in the firing furnace 30.
Then, only particles of a certain fixed size exist. Therefore, the elephant grain composition is mainly formed by pair formation (union type granulation) rather than the rare ring (snowman type granulation) found in general rolling granulation such as rotary kiln. Therefore, as the final raw material particles, the clinker has many voids and the apparent density of the particles is lower than that of the clinker of the rotary kiln, and the particle size of the clinker is much more uniform than that of the clinker of the rotary kiln. .

In the case of the conventional method as illustrated in FIG. 6, segregation of the clinker in the cooling device 4 causes a blow-through or a fine high-temperature clinker flow (red river) which is difficult to be cooled, which lowers the cooling efficiency and, in some cases, the cooler. Was burned out,
Here, in combination with the prevention of them and the high cooling performance of the produced clinker, high cooling efficiency and a significant extension of the device life can be achieved. Further, the clinker produced by the pair formation has excellent pulverizability in the subsequent cement mill, and can significantly reduce the mill power and improve the capacity.

Incidentally, the burner 6 _b supplies heat for calcination is usually more at least one is placed in the chamber 30 _c on one of the lowermost chamber 30 _d or the bottom, all the chambers other 30 _a
It is also possible to install at least one burner on each of the 30 _d .

On the other hand, looking at the amount of NO _X generated, it has been found that in the case of the rotary kiln type, the maximum temperature in the kiln exceeds 2000 ° C., and therefore the amount of generation is extremely high. Therefore, there is an advantage that the maximum temperature in the furnace does not become so high as exceeding the clinker firing temperature of 1450 ° C. and the amount of NO _X generated can be suppressed to an extremely low value.

Next, referring to FIG. 2, another embodiment of the apparatus according to the present invention will be described. This example is different from the apparatus of the embodiment shown in FIG. 1 in that a firing furnace exhaust gas conduit 34 and a fine powder raw material separator 32 are provided between the firing furnace 30 and the calcination furnace 2. It is intended to be compact.

In the case of the apparatus of this embodiment, the gas flow velocity in the upper cross section of the uppermost chamber of the firing furnace 30 can be set to a relatively high value without being restricted by the properties of the raw material from the calcination raw material chute 15. The cross-sectional area can be reduced and the number of small chambers can be reduced, which has the advantage that the volume, height, etc. of the firing furnace 30 can be reduced.

Since the set temperatures of the exhaust gas passing through the firing furnace exhaust gas conduit 34 and the raw material can be kept below the liquid phase generation start temperature (about 1250 ° C.), the conduit 34 and the fine powder raw material separator 3
No fusion of the raw material to the respective inner walls of No. 2 occurs.

Further, in the apparatus of this embodiment, part or all of the calcined raw material powder sent from the separation cyclone C ₄ is branched from the calcined raw material chute 15 to obtain the calcined raw material chute 1.
It is introduced into the sintering furnace exhaust gas conduit 34 through 5 _b. Therefore, in this apparatus, the above-mentioned calcination raw material is added to the sudden temperature rise in the conduit 34, and a trouble in temperature can be promptly dealt with.

In addition, the fine powder raw material separator 32 is provided with a chute 33 _a and _a chute 33 _a and a raw material powder which is collected in the firing furnace 30 in the same manner as the raw material powder collected in the separation cyclone C ₄ to one or more places. Forked shoot 33 _b
Through the.

As described above, in the embodiment apparatus shown in FIGS. 1 and 2, the center line of the firing furnace is almost the same as the gravity direction, and the structure thereof is
It has line symmetry in the longitudinal section. However,
In addition to this, as illustrated in FIG. 4, a structure in which the center l ₁ of the baking furnace 30 ′ is inclined at an angle with the gravity direction, or, as illustrated in FIG. 5, a vertical cross section of the baking furnace 30 ″ In the above, a structure in which one surface 30 _a ″ is vertical and _a shelf is provided on the opposite surface side is also in line with the gist of the present invention. It should be noted that there are at least two small chambers that are divided into trays in the firing furnace.
As long as there is one, the number is not limited.

[Brief description of drawings]

FIG. 1 is a schematic system diagram showing a main portion of a firing apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic system diagram showing a main portion of a firing apparatus according to another embodiment of the present invention. FIG. 3 is a graph showing the relationship between clinker particle diameter and terminal velocity, FIGS. 4 and 5 are explanatory views showing different types of modification of the firing furnace, and FIG. 6 is a background of the present invention. It is a diagrammatic systematic diagram showing a conventional firing apparatus for raw material powder. (Reference Numerals) 2 ...... calciner, 4 ...... cooling device 30 ...... sintering furnace, 30 _a ...... conical portion (chamber) ₃₀ b to 30 _d ...... chamber 31 ...... bottom nozzle, 32 ...... fines Raw material separator 34 ... Exhaust gas conduit for firing furnace.

Claims (2)

[Claims] 1. A raw material preheating step in which a raw material powder is subjected to a calcination process using a calcination zone having an independent combustion means, and following the preheating step, the preheated and partially calcined raw material powder is fired. In the firing method of the raw material powder performed through the firing step in which an independent combustion means is provided for performing the firing step and the firing step cooling step following the firing step, in the high temperature exhaust gas introduced from the cooling step to the firing step In addition, the raw material powder sent from the raw material preheating step is introduced from a position downstream of the firing material discharge portion in the flow direction, and the high temperature introduced during the firing step is introduced. The passing speed of the exhaust gas is gradually increased from a high speed to a low speed as it goes from the upstream side to the downstream side when viewed in the flow direction in each of a plurality of stages, and upstream of the inlet side of the downstream side of each stage. Side stage While slowing the passage speed at the outlet side of the, the passage speed at each upstream inlet side of each stage is changed stepwise from high speed to low speed as it goes from the upstream side to the downstream side as viewed in the flow direction, A method for firing a raw material powder, wherein the raw material powder conveyed to the high temperature exhaust gas is fired, and only the coarse powder raw material granulated into a predetermined size by the firing is supplied to the subsequent cooling step. 2. A raw material preheating device equipped with a calcination furnace having independent combustion means, a firing furnace having independent combustion means for firing the preheated raw material powder, and the fired firing raw material. In a calcining device for a raw material powder, which is provided with a cooling device for cooling, in a position downstream of the calcining furnace and above the discharging part of the calcining raw material as viewed in the flow direction of the high temperature exhaust gas introduced. , Providing an inlet for introducing the raw material powder supplied from the raw material preheating device, and forming an opening on the upstream side for introducing the high temperature exhaust gas supplied from the cooling device, in addition, The inner wall of the firing furnace is formed into a plurality of steps in a stepwise manner, and in each of the steps, gradually toward the upstream side, and in each of the steps, upstream of the inlet side of the downstream side shelf. The exit side of the side shelf Calciner the raw material powder such as the cross-sectional area of the respective stepwise the firing furnace is made smaller in accordance toward the upstream side in the upstream inlet side of the trays.