JPH0541579B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the fuel supplied to each calcining zone in an apparatus for calcining cement raw material powder using two stages of calcining zones provided with individual fuel supply means. It is.

The firing reaction of cement raw materials mainly includes the calcining (decomposition) reaction of limestone, which is an endothermic reaction, and the cement clinker production reaction, which is an exothermic reaction. A calcination device equipped with an independent fuel supply means is arranged between the two, and before supplying the cement raw material powder to the calcination furnace, it is preheated in a floating state within the preheating device using the exhaust gas from the calcination device and the calcination furnace. The post-calciner is introduced into a post-calciner, where most of the calcination reaction is completed by the heat of combustion of the fuel supplied to the calcifier, and then this calcined raw material is similarly provided with an independent fuel supply means. The remaining calcination reaction and clinker production reaction are carried out here by supplying it to a calcination device.

In such a firing method with a calcination device, the combustion of the supplied fuel is shared between the calcination device and the firing furnace, with the calcination device mainly performing the calcination reaction, and the calcination device mainly performing the cement clinker production reaction. By doing so, we are able to eliminate problems associated with larger firing equipment, such as the shortened lifespan of refractories due to increased heat load in the firing furnace, and at the same time dramatically increase the production volume per internal volume of the firing equipment. It is well known that this firing method is more effective than other firing methods in that it enables stable operation over a long period of time.

In particular, by configuring the calcination process in multiple stages with two stages of calcination zones each equipped with an individual fuel supply means, and passing the raw material powder through these two stages of calcination zones in sequence, cement A method of promoting the calcination reaction of raw material powder more effectively at a relatively low temperature can further increase the productivity of the calcination equipment, and furthermore, it is possible to further increase the productivity of the calcination equipment, and furthermore, it is possible to further increase the productivity of the calcination equipment, and furthermore, it is possible to further increase the productivity of the calcination equipment. When applied to a firing method in which the gas is bypassed and discharged to the outside of the system without being used in the gas, it has features such as being able to minimize heat loss due to the bypass gas.

Figure 1 is a diagrammatic system diagram illustrating a cement clinker production facility using such a conventional multi-stage calciner. is indicated by a dashed arrow. As shown in the figure, the apparatus consists of a preheating device 1, a calcination device 2, a sintering furnace 3 such as a rotary kiln that controls the sintering process, and a clinker cooling device 4.

The preheating device 1 is a powder separator C ₁ such as a cyclone.
C ₃ and a duct 6, and the calcination device 2 is of a series arrangement type in this example, with a calcination zone 21 on the downstream side and a calcination zone 22 on the upstream side as seen in the flow direction of hot gas. It is constructed by arranging two stages of calcination zones in series, and each calcination zone 21, 22 is connected to the calcination furnace 7, 8, which is individually equipped with a fuel supply device 7a, 8a, and the calcination furnace. Consists of attached powder separators _C4 , _C5 , etc.

The raw material powder supplied from the raw material input chute 5 is sent to each powder separator C ₁ to _{C 3} that constitute the preheating device 1.
On the other hand, high-temperature exhaust gas from the calcination furnace 3 and the calcination device 2 is sucked by the induced draft fan 13 and rises inside the preheating device 1, so that it flows into the duct 6 and the powder separators _C1 to _C3. Heat exchange and separation between the raw material powder and the high-temperature gas is repeated. The preheated raw material powder is introduced from the lowermost powder separator C ₃ of the preheating device 1 to the downstream primary calcination furnace 7 constituting the calcination device 2, and then passes through the powder separator C ₄ to the upstream 2 It is introduced into the next calcining furnace 8.

On the other hand, inside the secondary calciner 8, high-temperature combustion air introduced from the cooling device 4 through the high-temperature air conduit 10 and exhaust gas still containing oxygen from the calciner 3 are supplied, and from the fuel supply device 8a. Combustion occurs due to the supplied fuel, and exhaust gas still containing sufficient oxygen is supplied from the secondary calciner 8 through the powder separator _C5 in the primary calciner 7, and is supplied from the fuel supply device 7a. The raw material powder receives the combustion heat of the fuel and the heat possessed by the exhaust gas, and then burns in the primary calcining zones 21 and 2.
It is calcined while successively passing through the next calcining zone 22.

The calcined raw material powder enters the calcining furnace 3 from the powder separator C ₅ through the calcining furnace inlet cover 9, and enters the calcining furnace 3.
The combustion heat of the fuel supplied together with the primary air for combustion from the fuel supply device 3a installed at the outlet end cover 19 of the fuel is subjected to necessary heat treatment in the kiln 3 to form clinker, and then the clinker is produced in the clinker cooling device 4. cooled down.

Note that air for cooling the clinker is supplied by a forced air blower 16, and a part of the high-temperature air heated by exchanging heat with the clinker is distributed and introduced into the calcining device 2 and the calcining furnace 3. A part of the high-temperature air to the apparatus 2 may be short-circuited to the downstream calcining zone 21 through the high-temperature air branch conduit 10a as shown in the first figure, if necessary. Further, surplus air in the cooling device 4 is discharged by an induced air fan 17, while clinker discharged from the cooling device 4 is carried out to the next process by a conveyor 18.

According to the multi-stage calcination method as shown in FIG.
1, the carbon dioxide gas generated from the fuel and raw material powder does not flow into the upstream calcining zone 22, and approximately the same amount of gas passes through the upstream calcining zone 22 as in the downstream calcining zone 21. Therefore, the upstream calcining zone 22
The partial pressure of carbon dioxide gas in the hot gas can be reduced as much as possible, and the calcination reaction of the raw material powder can be efficiently promoted at a relatively low temperature.

At this time, the larger the amount of fuel supplied from the fuel supply device 7a to the primary calciner 7, the more highly calcined the raw material powder is supplied to the secondary calciner 8. At the same time, the amount of carbon dioxide generated from the raw material powder in the calcining zone 22 is reduced, and at the same time, the amount of fuel supplied from the fuel supply device 8a to the secondary calciner 8 is reduced, so that the amount of carbon dioxide generated by combustion of the fuel is reduced. The amount of gas also decreases, and as a result, the partial pressure of carbon dioxide gas in the hot gas can be significantly reduced in the upstream calcining zone 22 compared to the downstream calcining zone 21, which reduces the calcining reaction of the raw material powder. A favorable reaction atmosphere can be created to further accelerate the reaction.

However, as a result of supplying a large amount of fuel from the fuel supply device 7a to the primary calciner 7, the amount of fuel supplied from the fuel supply device 8a to the secondary calciner 8 decreases as described above. The disadvantage is that the temperature of the exhaust gas discharged by the induced draft fan 13 after passing through the preheating device 1 rises, and a large amount of heat is discharged, resulting in an overall increase in the amount of fuel consumed by the calcination device 2. accompanied by.

SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned drawbacks and provide a calcining method that can perform a comprehensively efficient fuel distribution when supplying fuel to a plurality of calcining zones. The gist of this is that after preheating cement raw material powder in a dispersed state by suspending it in a gas, and calcining it using a two-stage calcining zone each equipped with an individual fuel supply means, In a multi-stage calcination method for cement raw powder, in which the exhaust gas is discharged to the firing process where the exhaust gas is led to one of the calcination zones, the concentration of carbon dioxide in the exhaust gas in the final stage of the calcination zones is determined. The carbon dioxide concentration in the exhaust gas of this final stage calcining zone is calculated from the detected oxygen concentration by detecting the oxygen concentration in the exhaust gas of the firing furnace that constitutes the firing process. The present invention provides a multistage calcination method for cement raw material powder in which the amount of fuel supplied to each calcination zone is controlled so that the carbon dioxide concentration does not become lower than the carbon dioxide concentration.

Next, embodiments embodying the present invention will be described with reference to the accompanying drawings starting from FIG. 2 to provide an understanding of the present invention.

2 to 4 are diagrammatic system diagrams of cement clinker manufacturing equipment according to first to third embodiments to which the present invention is applied, respectively.

Note that the same reference numerals are used for elements common to those used in the conventional example shown in FIG. 1, and detailed explanation thereof will be omitted.

As shown in FIG. 2, a gas analyzer 14 is connected to the gas conduit 6' connecting the powder separator _C5 constituting the secondary calcining zone 22 and the calcining furnace 7 constituting the primary calcining zone 21.
A gas analyzer 15 is attached to the inlet cover 9 of the firing furnace 3 to detect the carbon dioxide concentration contained in the exhaust gas from the final stage calcining zone 22, and a gas analyzer 15 is also attached to the inlet cover 9 of the firing furnace 3 to detect the concentration of carbon dioxide gas contained in the exhaust gas from the final stage calcining zone 22. The concentration of oxygen contained in the exhaust gas supplied to the burning zone 22 is detected. Furthermore, the carbon dioxide concentration in the exhaust gas from the secondary calcining zone 22 detected by the gas analyzer 14 is equal to the carbon dioxide concentration in the exhaust gas from the calcining furnace 3 calculated from the oxygen concentration value detected by the gas analyzer 15. Of the fuel supplied to the calcination device 2, the fuel supplied from the fuel supply device 7a to the primary calcination furnace 7 and the fuel supplied from the fuel supply device 8a to the secondary calcination furnace 8 so as not to become lower than the gas concentration. control the fuel distribution.

In this way, making the carbon dioxide concentration in the exhaust gas from the firing process lower than the carbon dioxide concentration in the exhaust gas from the final stage calcination zone 22 suppresses the recarbonation reaction of the raw material powder at the inlet end of the firing furnace 3. This is effective in that the temperature of the exhaust gas from the calcination device 2 is lowered and the amount of fuel consumed by the calcination device 2 is not increased unnecessarily.

To explain the above point more specifically, from the powder separator C ₅ of the final stage calcining zone 22 to the inlet end cover 9
When the raw material powder is supplied to the firing furnace 3 through the rotary kiln 3, it comes into contact with the atmosphere leaking from the seal between the rotating part of the rotary kiln 3b that constitutes the firing furnace 3 and the inlet end cover 9, which is a fixed part. The temperature of the raw material powder decreases slightly, but in this state, the raw material powder is subjected to rotational action due to the high speed rotation of the rotary kiln 3b, and is transferred to the final stage calcining zone at the inlet end 3c of the firing furnace 3. When it comes into contact with a hot gas having a higher carbon dioxide concentration than the hot gas in the 22, a part of the calcined calcium oxide in the raw material powder and the carbon dioxide component contained in the hot gas undergo a recarbonation reaction. and
In the final stage calcination zone 22, a part of the raw material powder that has been calcined to a high degree is recarbonated and returned to calcium carbonate. The calcination reaction must be carried out, thus requiring a calcining furnace of extra size. That is, even if the partial pressure of carbon dioxide gas in the exhaust gas in the final stage calcination zone 22 is excessively reduced and the calcination reaction proceeds too much, the effect will be poor. This can be avoided by keeping the partial pressure of carbon dioxide in the exhaust gas from the firing furnace 3 within a range that does not become lower than the partial pressure of carbon dioxide in the exhaust gas from the firing furnace 3. In order to achieve this kind of operating condition,
If the amount of fuel supplied from the fuel supply device 7a to the primary calcination furnace 7 is reduced, the degree of calcination of the raw material powder discharged from the primary calcination zone 21 to the secondary calcination zone 22 will be reduced. In response to this, it becomes necessary to increase the amount of fuel supplied from the fuel supply device 8a to the secondary calcination furnace 8, so the amount of carbon dioxide gas generated from the fuel and raw material powder in the calcination zone 22 increases, causing the Calcining zone 2
The carbon dioxide partial pressure at 2 increases. Note that a part of the high-temperature air supplied from the cooling device 4 to the calcining device 2 through the high-temperature air conduit 10 is transferred to the high-temperature air branch conduit 1.
When the air is short-circuited and introduced into the primary calcining zone 21 by 0a, the secondary calcining zone 22 is
The concentration of carbon dioxide gas contained in the hot gas inside increases.

Therefore, the concentration of carbon dioxide gas contained in the exhaust gas of the final stage calcination zone 22 is detected, and the amount of fuel supplied to each calcination zone 21, 22 is adjusted so that the detected value does not become lower than the concentration of carbon dioxide gas in the combustion furnace exhaust gas. By controlling the distribution, the inlet end 3c of the firing furnace 3 as described above
It is possible to prevent the recarbonation reaction in the firing process, and the firing furnace 3 can be effectively utilized over its entire length. At the same time, by reducing the amount of fuel distributed to the primary calcining zone 21, the temperature of the hot gas introduced from the powder separator _C4 of the primary calcining zone 21 to the preheating device 1 decreases, and as a result, the exhaust gas from the preheating device 1 decreases. Since the temperature is lowered, the amount of fuel consumed by the calcination device 2 is reduced, and the thermal economy of the cement raw material sintering device can be improved.

According to such a multi-stage calcination method, the residence time of the raw material powder in the calcination device 2 as a whole becomes longer, and at the same time, the raw material powder sequentially passes through the calcination zones 21 and 22 where the partial pressure of carbon dioxide gas is lowered. Therefore, the calcination reaction of the raw material powder in the calcination device 2 is promoted, and the raw material powder whose calcination reaction has been substantially completed can be discharged to the firing process.

Next, to explain the case of the cement clinker manufacturing equipment shown in FIG. 2 applied to the above embodiment based on specific numbers, when heavy oil is used as fuel, the carbon dioxide concentration in the exhaust gas of the kiln 3 is generally It is about 10 to 20% (however, the value varies depending on the air ratio in the kiln), and the fuel supplied to the kiln 3 is about 20 to 30% of the fuel supplied to the entire cement clinker manufacturing equipment. The remaining 70 to 80% of the fuel supplied to the calcination device 2 is supplied to the primary calcination zone 21 and the secondary calcination zone 22 (40 to 70): 10 to 30) (however, this ratio varies somewhat depending on the amount of air short-circuited and supplied through the high-temperature air branch pipe 10a to the primary calcining zone), from the secondary calcining zone 22. The carbon dioxide concentration in the exhaust gas from the firing furnace 3 can be controlled to be the same as or slightly higher than the carbon dioxide concentration in the exhaust gas from the firing furnace 3.

3 and 4 are diagrammatic system diagrams of second and third embodiments of cement clinker production equipment to which the present invention is applied; Parts having similar functions will be described with the same reference numerals.

In FIG. 3, the calcination device 2 is composed of two stages of calcination zones: a primary calcination zone 23 on the downstream side and a secondary calcination zone 24 on the upstream side when viewed in the flow direction of hot gas. The calcining zones 23 and 24 are provided with fuel supply devices 33a and 3, respectively.
Calciner 33, 34 equipped with 4a and the calciner 3
Powder separators C ₄ and C ₅ attached to 3 and 34 are arranged. In the calcination device 2 having such a configuration, high-temperature air from the cooling device 4 is introduced into the secondary calcination zone 24, and the fuel supplied from the fuel supply device 34a to the secondary calcination furnace 34 is fed into the secondary calcination zone 24. 34 , while the exhaust gas from the calciner 3 is passed through the gas conduit 20 from the inlet end cover 9 to the calciner 33 .
It is now being introduced directly into

Then, the raw material powder from the powder separator C ₃ of the preheating device 1 is introduced into the primary calcination furnace 33 via the gas pipe 20 or directly as required, and is subsequently transferred to the powder separator C ₄ and the secondary calcination furnace 33 . The furnace 34 and the powder separator _C5 are descended in order, and the final stage calcination zone is the secondary calcination zone 2.
A gas analyzer 14 is attached to the gas conduit 6' that connects the powder separator C ₅ and the primary calcination furnace 33, which constitutes the powder separator C 4, and detects the concentration of carbon dioxide contained in the exhaust gas of the final stage calcination zone 24. At the same time, a gas analyzer 15 is also attached to the gas conduit 20 to detect the concentration of oxygen contained in the exhaust gas from the firing process, calculate the carbon dioxide concentration from this, and calculate the carbon dioxide concentration in the exhaust gas from the final stage calcining zone. The distribution of fuel supplied to the primary calcination zone 23 and the secondary calcination zone 24 is controlled in the same manner as in the case of FIG. 2 so that the concentration does not become lower than the concentration of carbon dioxide in the exhaust gas from the calcination process. It is. However, according to this embodiment, the exhaust gas from the firing process is transferred to the final stage calcining zone.
4 is not allowed to pass through, the amount of hot gas processed in the final stage calcining zone 24 is reduced, and the equipment cost of the equipment constituting the calcining zone 24 can be reduced.

Next, a description will be given of a third embodiment of the cement clinker to which the present invention is applied, shown in FIG. 4. As shown in the figure, an exhaust gas system primary calcining zone 25 that uses exhaust gas from the kiln 3; The combustion gas system primary calcination zone 26 that uses combustion gas produced by high-temperature air from the cooling device 4 is arranged in parallel when viewed in the flow direction of hot gas, and the combustion gas system primary calcination zone 2
A secondary calcining zone 27 is disposed on the upstream side of the gas of No. 6, and each calcining zone 25, 26, 27 is a calcining furnace 35, 36 equipped with an individual fuel supply device 35a, 36a, 37a. , 37 and powder separators C ₁₄ , C ₂₄ , C ₂₅ attached to the calcining furnace, and each primary calcining zone 25 and 26 has a separator, respectively.
Preheating device 1 composed of C ₁₁ to C ₁₃ , C ₂₁ to C ₂₃ , etc.
1 and 12 are connected.

The preheating devices 11 and 1 are heated by using the high temperature gas discharged from each of the primary calcining zones 25 and 26.
The raw material powder preheated in step 2 is transferred to a preheating device 11,
A calcining furnace 35 constituting the exhaust gas system primary calcining zone 25 and a calcining furnace 36 constituting the combustion gas system primary calcining zone 26 from the 12 lowermost powder separators C ₁₃ and C ₂₃ respectively.
powder separators C ₁₄ and C ₂₄ attached to each calciner 35 and 36.
After being supplied to the secondary calcination zone 27 arranged in the combustion gas system and subjected to secondary calcination, the powder separator
It is supplied to the firing furnace 3 through the C ₂₅ and the inlet end cover 9.

At this time, the secondary calcination zone 27 as the final stage calcination zone
Gas analyzer 1 measures the concentration of carbon dioxide contained in the exhaust gas.
4, and in order to prevent this detected value from becoming lower than the carbon dioxide concentration of the exhaust gas from the firing process similarly detected by the gas analyzer
Controlling the distribution of fuel supplied to 5, 26 and the secondary calcining zone 27 is the same as described above.
According to this embodiment, since the combustion air in the exhaust gas system primary calcination zone 25 is introduced from the cooling device 4 through the firing furnace 3, the carbon dioxide concentration in the exhaust gas from the firing furnace 3 is 10 The amount of fuel distributed to the primary calcination zones 25 and 26 is increased, and conversely, the amount of fuel distributed to the secondary calcination zone 27 is reduced. Even when operating with a low carbon dioxide gas partial pressure in the firing zone 27, the recarbonation reaction of the raw material powder at the inlet end of the calcining furnace 3 does not occur, so the secondary calcining zone 2
In step 7, the calcination reaction can be promoted more efficiently in an atmospheric gas with a low partial pressure of carbon dioxide gas.

In the above explanation, instead of the carbon dioxide concentration contained in the exhaust gas from the final stage calcination zone, the carbon dioxide concentration in the exhaust gas inside or at the outlet of the final stage calcination furnace is detected, or the exhaust gas from the final stage calcination zone is detected. It is within the spirit of the present invention to make the carbon dioxide concentration in the carbon dioxide gas slightly lower than the carbon dioxide concentration in the exhaust gas from the firing process to an extent that does not cause any practical problems. Further, the technical scope of the present invention is not limited only to the above explanation, and is not limited to, for example, the structure of the preheating device (cyclone type, tower type), the number of series, the number of stages, etc. structure (spouted bed type, swirling flow type, etc.), arrangement (built-in type, separate type, etc.), type of fuel used in each calcining zone (liquid, solid, or gas), type and format of fuel supply means, The mounting position etc. can be changed freely.

Furthermore, it is also possible to provide appropriate means for circulating raw material powder in the calcining zone, or to combine means for denitrating the exhaust gas discharged from the calcining apparatus.

As described above, the present invention involves preheating cement raw material powder in a dispersed state by suspending it in a gas, and calcining it using a two-stage calcining zone each equipped with an individual fuel supply means. In a multi-stage calcination method for cement raw powder, in which the exhaust gas is discharged to a firing process where the exhaust gas is led to a calcination zone, the concentration of carbon dioxide in the exhaust gas of the final stage of the calcination zones is detected. The carbon dioxide concentration in the exhaust gas of this final stage calcining zone is calculated from the detected oxygen concentration by detecting the oxygen concentration in the exhaust gas of the firing furnace that constitutes the firing process. This is a multi-stage calcination method for cement raw material powder, which is characterized by controlling the amount of fuel supplied to each calcination zone so that the concentration does not become lower than the carbon dioxide concentration, so that the recarbonation reaction of the raw material powder occurs in the firing process. In addition, the fuel consumption in the calcination process can be reduced and the raw material can be calcined efficiently.

[Brief explanation of drawings]

FIG. 1 is a diagrammatic system diagram of cement clinker manufacturing equipment according to a conventional example, and FIGS. 2 to 4 are diagrammatic diagrams of cement clinker manufacturing equipment according to first to third embodiments to which the present invention is applied. It is a system diagram. (Explanation of symbols) 2...Calcination device, 3...Calcination furnace (firing process), 7, 8, 33-37...Calcination furnace, 7
a, 8a, 33a to 37a...Fuel supply device, 1
4, 15...Gas analyzer, 21, 23, 25, 26
...Primary calcining zone, 22, 24, 27...Secondary calcining zone.

Claims (1)

[Claims] 1 Cement raw material powder is suspended in a gas and dispersed, preheated and calcined using two stages of calcining zones each equipped with a fuel supply means, and then the exhaust gas is transferred to one of the calcining zones. In a multi-stage calcination method for cement raw material powder that is discharged to a calcination process in which the The concentration of carbon dioxide in the exhaust gas of the firing furnace is not lower than the concentration of carbon dioxide in the exhaust gas of the firing furnace, which is calculated from the detected oxygen concentration by detecting the oxygen concentration in the exhaust gas of the firing furnace that constitutes the firing process. A multi-stage calcination method for cement raw material powder, characterized in that the amount of fuel supplied to each calcination zone is controlled.