JPS5839786B2 - How to fire granular limestone or dolomite - Google Patents

Description

Detailed Description of the Invention The present invention involves forming an improved spouted bed of granular limestone or dolomite (hereinafter also referred to as granular material) in order to calcine and decarboxylate limestone or dolomite. This method involves injecting fuel into a layer and burning it to burn limestone or dolomite.

It has been known in the past to form a fluidized bed, spouted bed or modified spouted bed of inorganic solid particles and to sinter the inorganic solid material.

However, in conventionally known calcination methods, the thermal efficiency, which is the ratio of heat effectively used for decarboxylation of limestone or dolomite to the heat generated by combustion of fuel, is not sufficiently high. Another drawback was that the processing capacity, which is the ratio of the amount of calcined limestone or dolomite per unit cross-sectional area of the calcining furnace, was low.

The present invention provides a method for sintering limestone or dolomite that achieves the above-mentioned thermal efficiency and high throughput of a sintering furnace when granular limestone or dolomite is formed into an improved spouted bed and sintered.

That is, the present invention provides: (4) As a kiln for fluidizing and firing powdery limestone or dolomite, (a) the bottom has a funnel-like structure, and the funnel-like bottom (hereinafter referred to as The fuel burner protrudes upward from the center of the funnel (also referred to as the funnel-shaped section), and the inverted conical section of the funnel-shaped section is formed of a perforated plate, and further downward from the center of the funnel-shaped section. The extending legs serve as a nozzle for ejecting a gas jet stream, and (b) the body at the bottom and the top is formed of a hollow cylindrical body, and the lower side wall of the body has a It has an extraction port for extracting the fired powder and granules, and has a supply port for supplying the powder and granules in the upper wall of the body, and (c) the top part allows the powder to flow. (B) (A) A first multi-stage preheater is installed in the kiln using a kiln having a waste gas outlet for discharging the waste gas of the kiln produced by burning. The powder body, which has been preheated by contacting with a part of the waste gas, is supplied from the supply port, and (b) the powder immediately after firing is extracted from the outlet of the firing furnace in the second multistage preheater. Air that has been preheated in contact with the granules is
The fluidizing gas is supplied to the firing furnace through a perforated plate in the funnel-shaped part of the firing furnace. From the nozzle, a gas jet stream is ejected into the firing furnace to form an improved spouted bed of powdered material in the firing furnace, (C) toward the spouted part of the improved spouted bed of this powdered granular material,
The present invention relates to a method for firing granular limestone or dolomite, which comprises firing and decarboxylating limestone or dolomite by ejecting and burning fuel from a fuel burner.

The present invention provides for exhaust gas exhaust at the top of the kiln when granular limestone or dolomite is fired using a kiln whose bottom part is shaped like a funnel consisting of a perforated plate and a spout nozzle as described above. A part of the waste gas discharged from the outlet is brought into contact with the granular material supplied to the kiln to preheat the granular material, and another part of the waste gas is brought into contact with the air and heat used for the gas jet flow. The air is exchanged and preheated, and the powder body immediately after firing, which is extracted from the outlet of the firing furnace, is brought into contact with the air used as fluidizing gas to preheat the air, so that high-temperature waste gas and This is a firing method with excellent thermal efficiency, in which the heat of the powder immediately after firing is effectively used to preheat the powder and the air for fluidization or jet flow supplied to the firing furnace.

Further, in the method of the present invention, in the above-mentioned firing furnace, the part corresponding to the moving bed part of the normal spouted bed is made close to a fluidized bed with a low particle density by the fluidizing gas supplied through the perforated plate of the funnel-shaped part. An improved spouted bed that is fluidized in a state of , the calcination of limestone or dolomite takes place very quickly and uniformly.

Therefore, according to the method of the present invention, the throughput of the firing furnace has been dramatically increased due to the above-mentioned high thermal efficiency and quick and uniform firing.

Hereinafter, the method of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a flow sheet showing an outline of the flow for carrying out the method of the present invention.

FIG. 2 is a sectional view schematically showing a firing furnace used in the method of the present invention.

FIG. 3 is a sectional view schematically showing an example of the first or second multistage preheater.

In the method of the present invention, as shown in FIG. 1 or 2, the firing furnace 1 for fluidizing and firing powder and granules has the following features: (a) the bottom has a funnel-like structure; Moreover, a fuel burner 3 protrudes upward from the center of the funnel-shaped part 2, an inverted conical part of the funnel-shaped part 2 is formed of a perforated plate 4, and a fuel burner 3 protrudes upward from the center of the funnel-shaped part 2. (b) The body 6 between the bottom and the top is formed of a hollow cylindrical body; The lower side wall of the section 6 has an extraction lower for extracting the fired powder, and the upper side wall of the body 6 has a supply port 8 for supplying the powder. c) A firing furnace is used, the top of which has a waste gas outlet 9 for discharging the waste gas of the firing furnace 1 produced by fluidizing and firing the granular material.

The funnel-shaped part 2 of the firing furnace 10 has a perforated plate 4 as described above.
It consists of an inverted conical part formed by a gas jet flow and a leg part which becomes a jet nozzle 5 of the gas jet flow.

The upward expansion angle of the perforated plate 4 of the inverted conical portion is 60
-135° is preferable; below 60°, it becomes difficult to form an improved spouted bed, and above 135°, the powder body forms the perforated plate 4.
It becomes difficult to move smoothly toward the center of the funnel-shaped part 2 along the upper surface of the funnel-shaped part 2.

Further, the perforated plate 4 has a large number of pores in order to rectify the fluidizing gas when it is supplied to the inside of the firing furnace 1, and the diameter and arrangement of the pores are particularly limited. It is not something that will be done.

Furthermore, the spout nozzle 5 has an inner diameter Di that has a ratio (Di/Dc) of 0 to the inner diameter Dc near the bottom of the firing furnace 1.
．． Preferably, it is set to 1 to 0.5.

If the inner diameter Di becomes smaller, it becomes difficult to form a suitable improved spouted bed inside the firing furnace 1, and if a large amount of gas for gas jet flow is supplied from a jet nozzle with a small inner diameter Di, so-called jet pulverization may occur. causing a phenomenon,
This is not preferable because it increases the abrasion of the powder and the amount of dust.

If the inner diameter Di becomes too large, only gas that does not act as a gas jet flow can be supplied to the firing furnace 1,
Again, it becomes difficult to form a suitable improved spouted bed.

A cover 19 having a fluidizing gas supply port 20 for supplying fluidizing gas is provided below the funnel-shaped part 2 of the firing furnace 10, and the funnel-shaped part 2 and the cover 19 retain the fluidizing gas. It is preferable to form a space A where

The fuel burner 3 provided at the bottom of the kiln 1 can eject fuel along the ejecting direction of gas for gas jet flow from the ejecting nozzle 5 at the center of the funnel-shaped part 2. It may be of a formal type like this.

The shape of the body 6 of the firing furnace 1 may be any shape as long as it is a cylindrical body with a hollow interior, for example, it is cylindrical or the upper part of the body 6 has an inner diameter Dc of the lower part of the body 6. From 1.1
It may also be a cylindrical body having an inner diameter that is about twice as large.

In the method of the present invention, (A) the above-described firing furnace 1 is used as a firing furnace for fluidizing and firing the powder, and (B) (a) the firing furnace 1 is provided with a first multi-stage preheating process. The granular material preheated by direct contact with a part of the waste gas in the vessel 10 is supplied from the supply port 8 of the firing furnace 1, and (b) the second multistage preheater 11 is used to extract the powder from the firing furnace 1. Air that has been preheated by direct contact with the granular material just after firing extracted from the lower is supplied to the firing furnace 1 as a fluidizing gas through the perforated plate 4 of the funnel-shaped part 2 of the firing furnace 10, ()→ Further, in the heat exchanger 12, the air preheated by a part of the waste gas is ejected from the ejection nozzle 5 of the funnel-shaped part 2 of the kiln 10 into the kiln 1 as a gas jet stream, and the inside of the kiln 1 is heated. forming an improved spouted bed of powder and granules.

In the method of the present invention, the improved powder layer of the powder and granules formed inside the firing furnace 1 is formed by a jet section in which the powder and granules are raised at high speed through the center of the firing furnace 1 by the gas used by the gas jet. , around the return flow section, the powder and granules as a whole are gradually descended because they are not fluidized by the fluidizing gas and are drawn into the jet flow section.

A normal spouted bed is one in which a central spouted part and a moving bed part around it are formed only by gas jet flow, whereas the improved spouted bed in this invention is characterized by the movement of the spouted bed described above. It does not have a part corresponding to a layer part, but has a fluidized part that is fluidized by a fluidizing gas.

Compared to a normal spouted bed, this improved spouted bed has a much larger circulating amount of powder and granules per unit time, and like the moving bed section of a normal spouted bed, the powder is layered with each other during circulation. The powder and granules are always suspended by the fluidizing gas and the gas for the gas jet, so when fuel is burned in this improved spouted bed, the generation of Heat quickly spreads throughout the improved spouted bed,
Uniform firing of powder particles is possible.

In the method of the present invention, the empty tower conversion velocity (Vo) at the lower part of the firing furnace 1 due to the total gas amount of the fluidizing gas supplied to the firing furnace 1 and the gas for gas jet flow is determined by the average particle size of the powder and granular material. so that Q is 5 to 4 times, preferably 0.6 to 3 times, the fluidization start speed (Umf) at
Preferably, the supply of gas for the fluidizing gas and the gas jet flow is adjusted.

The above-mentioned superficial column conversion velocity (Vo) is the total gas supply amount obtained by converting the supply amount of fluidizing gas and gas jet flow gas supplied to the firing furnace 1 by the average temperature and average pressure inside the firing furnace 1, respectively. It is the value obtained by dividing (Vo fn″/see) by the horizontal cross-sectional area (m) of the lower part of the body 6 of the firing furnace 1, and is expressed in the unit of rrL/sec.

In addition, the fluidization start speed (Umf
) is the minimum fluidizing gas velocity required to form a fluidized bed by supplying fluidizing gas from the bottom of the packed bed of powder and granules, and is also called the minimum fluidizing velocity, Shown in units.

If the total gas supply amount of the fluidizing gas and the gas for gas jet flow is such that Vo/Umf is less than 0.5, it is not appropriate because the movement of the fluidized bed around the improved spouted bed will deteriorate; If the above-mentioned total gas supply amount is such that /Umf is larger than 4, the improved spouted bed itself may not be formed, or the rising speed of the powder at the central spout section of the improved spouted bed will become too high. Not suitable for firing granules.

The gas for the gas jet flow is determined by the ratio (uj/U
It is preferable to eject from the ejection nozzle 5 so that t) is 1.8 to 1.5, particularly 1 to 12.

The ejection velocity (Uj) of the gas jet flow is defined as the supply amount (m''/see) of gas for the gas jet flow at the temperature and pressure at the ejection port of the ejection nozzle 5, by the cross-sectional area of the ejection port of the ejection nozzle 5. It is the value divided by rrL/sec
It is expressed in units of.

The particle terminal velocity (Ut) is calculated by a formula derived from the drag laws of Stokes, Allen, and Newton, and is the velocity when a particle moves uniformly in a fluid, m
It is expressed in units of /see.

If the ratio (Uj/Ut) is less than 0.8, it is undesirable because the amount of powder and granules that rises upwards of the jet nozzle 5 at high speed will be reduced. If it is too large, the rate at which the powder and granules rise through the spouted portion of the improved spouted bed becomes too high, which is not preferable.

Furthermore, the supply amount (Vj) of gas for gas jet flow ejected from the ejection nozzle 5 of the funnel-shaped part 2 to the firing furnace 1
The ratio (■
f/■j) is 0.05 to 0.6, especially 0.1 to 0.4
It is preferable that

If the above ratio (■f/Vj) is smaller than 0.05, the movement of the powder particles in the fluidized bed section of the improved spouted bed will deteriorate and become close to the moving bed section of a normal spouted bed, which is undesirable. (Vf/
If Vj) is larger than 0.6, the spouted part of the improved spouted bed becomes unstable or disappears, making it impossible to uniformly sinter the granular material, which is not preferable.

In the method of this invention, granular limestone or dolomite is transported from the raw material hopper 13 to the first multistage preheater 10.
It passes through and is supplied to the firing furnace 1.

This limestone or dolomite has an average particle size of 0.1 to
It is preferable that the particle size is 5 mm, particularly 0.2 to 4 mm, and the maximum particle diameter is 7 mm or less, particularly 6 mm or less.

The heat source of the multi-stage preheater 10 is sensible heat contained in a part of the waste gas discharged from the waste gas outlet 9 of the firing furnace 1,
When the limestone or dolomite descends inside the multi-stage preheater 10, it comes into direct contact with a portion of the waste gas and is preheated to about 500-1000C, particularly about 600-900C.

In the method of this invention, air for fluidizing gas supplied from the perforated plate 4 of the funnel-shaped part 2 of the firing furnace 10 is supplied to the piping 25.
It passes through the second multi-stage preheater 11, and if necessary, the entrained powder and granules are separated by the cyclone 16, and then it passes from the pipe 26 through the fluidizing gas supply port 20 of the cover 19, and is fed to the funnel-shaped part 2. The flow is rectified by the perforated plate 4 and supplied to the inside of the firing furnace 1.

In the second multistage preheater 11, the air for fluidizing gas is heated to approximately 500 to 1000°C, particularly 600 to
Approximately 30 degrees Celsius
It is cooled to below 0°C, especially below 270°C.

In the method of this invention, the air for the gas jet flow ejected from the ejection nozzle 5 of the load-shaped part 2 of the firing furnace 1 is
It passes through the heat exchanger 12 from the piping 32 and is ejected from the ejection nozzle 5 through the piping 33 to the center of the bottom of the firing furnace 1 .

In the heat exchanger 12, the air for the gas jet is heated to approximately 500 to 1000°C, particularly 600 to
Preheated to 900°C.

Note that the first multistage preheater 10 and the second multistage preheater 1
1, as shown in FIG. 3, a gas supply port 35 for waste gas or air, a gas discharge port 36, and a powder supply port 3.
7 and a powder outlet 38, a dispersion plate 40 is provided above the gas supply port 35, and a plurality of perforated plates 39 are further provided.

In particular, the first multistage preheater 10 for preheating powder and granular materials is
It is preferable that 2 to 10 stages of perforated plates 39, more preferably 3 to 6 stages of perforated plates 39 are provided. 6
Perforated plate 39 in stages, more preferably perforated plate 3 in 2 to 4 stages
9 is preferably provided.

Generally, when using a multi-stage preheater as described above, if the number of stages of perforated plates 390 is small, the heat exchange rate will decrease, and if the number of stages is too large, the pressure loss will increase, which is not preferable.

In the method of this invention, (4) the aforementioned firing furnace 1 is used as a firing furnace for fluidizing and firing the powder, and (B) the above-mentioned (a) −+→ is carried out. , firing furnace 1
(C) Fuel is ejected from the fuel burner 3 toward the central spout part of the improved spouted bed of the powder and granules to burn it, and limestone or dolomite is burned. is calcined and decarboxylated.

The above-mentioned fuel may be a gaseous fuel at normal temperature, a liquid fuel at normal temperature, a granular fuel, or a mixture thereof.For example, as a gaseous fuel, a methane gun,
Ethane gas, propane gas, natural gas, etc. can be mentioned, and liquid fuels can include those obtained by petroleum refining such as heavy oil, light oil, and dissolved oil, or mixed fuels of petroleum crude oil, petroleum, and coal, etc. Further, examples of the granular fuel include pulverized coal and petroleum coke.

The fuel is preferably ejected from the lower part of the central spout section of the improved spouted bed, along the jet section, that is, along the gas jet stream.

If a liquid fuel or a granular fuel is used in supplying the fuel, it may be transported, ejected or atomized with a suitable auxiliary gas, such as air, nitrogen or the gaseous fuel.

In this invention, the amount of fuel supplied is close to the maximum amount of fuel that can be theoretically combusted by the total amount of air, which is the sum of air for fluidizing gas, air for gas jet flow, air for the auxiliary gas, etc. In particular, the value of the excess air coefficient, which is the ratio (At/Ao) between the total air amount (At) and the theoretical air amount (Ao) necessary for combustion of the supplied fuel, is 1. .01-1.5, especially 1.02-1.
It is preferred to supply fuel in an amount such that 2.

In the method of the present invention, the average temperature inside the firing furnace 1 for firing and decarboxylating limestone or dolomite powder is preferably 700 to 1500°C, particularly for limestone or dolomite. In the case of firing, the temperature is 800 to 1400°C, more preferably 850 to 1200°C.
°C, and in the case of dolomite firing, 700 to 1400 °C, more preferably 750 to 1400 °C.
Preferably, the temperature is 1000°C.

In the method of this invention, the powder and granules, which have been fired and decarboxylated by the combustion heat of the fuel while forming an improved spouted bed and circulating inside the firing furnace 1, are continuously transported from the extraction lower of the firing furnace 1. It is extracted from the pipe 23 and sent to the second multistage preheater 11, where it is cooled while preheating the air for fluidizing gas, and then passed through the pipe 24.
The powder is collected in the powder receiver 15, and further cooled to room temperature using an appropriate cooling method.

The powder thus obtained is called quicklime or calcined dolomite.

Further, in the method of the present invention, the waste gas used and generated inside the firing furnace 1 is discharged from the waste gas outlet 9 of the firing furnace 1, and if necessary, is supplied to the cyclone 17 through the piping 27 and entrained. The dust is separated, and a part of the waste gas is supplied to the heat exchanger 12 through the pipe 29, where it is cooled while preheating the air for the fluidizing gas, and then discharged to the atmosphere, and also into the cyclone 17. The remainder of the waste gas that has exited is passed through the pipe 28 to the first multistage preheater 1.
The raw material powder is cooled while being preheated in this first multi-stage preheater 10, and then, if necessary, entrained dust is separated in a cyclone 18, and then it is released into the atmosphere.

Therefore, in the method of the present invention, the high-temperature waste gas discharged from the firing furnace 1 and the high-temperature powder and granules extracted from the firing furnace 1 immediately after firing are combined with air for fluidizing gas and air for gas jet flow. and for preheating raw material powder and granules.

As a result, the thermal efficiency of the combustion heat of fuel in the calcination and decarboxylation of limestone or dolomite powder has been dramatically increased.

Examples and reference examples are shown below.

In the examples, thermal efficiency, fuel ratio, and processing capacity of the firing furnace were calculated using the following formulas.

However, Ql is the amount of heat required to decompose limestone to produce 1 kg of quicklime, and in this example, Ql was set to 759 Kcal, 7 kg.

※※ Q2 is the combustion heat of 1 kg of fuel, and in this example, Q2 is 10000 K cal
7 kg of heavy oil was used.

Example 1 Limestone was calcined using a kiln as shown in FIG. 2 and a flow apparatus as shown in FIG. 1.

The firing furnace has an inner diameter of 300 mm at the lower part of the body, an inner diameter of 500 mm at the upper part of the body, an inner diameter of the gas jet nozzle of 80 mm, and a perforated plate in the funnel-shaped part. The spread angle was 900.

The first multistage preheater and the second multistage preheater have a structure as shown in FIG. 3, the first multistage preheater has an inner diameter of 200 mm, and the number of stages of the perforated plate is 5. The second multi-stage preheater had an inner diameter of 150mm, and the number of stages of perforated plates was three.

165 kg/hr of powdered limestone with a grain size of 1 to 5 mm was preheated to about 840°C in the first multi-stage preheater to the above-mentioned kiln.
and a second multi-stage preheater with a feed rate of approximately 720 m
Air preheated to 78 °C, I N rrl/hr
The fluidizing gas was supplied to the firing furnace through the perforated plate of the funnel at a supply rate of 22.3 Nm3/hr, and air, which had been preheated to about 800°C by a heat exchanger, was ejected from the funnel at a supply rate of 22.3 Nm3/hr. The gas is ejected from the nozzle into the firing furnace as a jet stream, and as a result, inside the firing furnace,
While forming an improved spouted bed of the powder body, 9.58 kg/h of heavy oil is pumped from the fuel burner toward the spouted part of the improved spouted bed.
r and air as auxiliary gas 11.2 N m3/
The limestone was calcined and decarboxylated at approximately 950° C., producing 94.5 kg/hr of quicklime.

The average decarboxylation rate of this quicklime was 98% or more.

In firing this limestone, the thermal efficiency was 72.4%, and the fuel ratio was 10.1 x 10-2 kg/kg.
The processing capacity of the firing furnace was 1340 kg/hr-m.

The value obtained by dividing the total air (112Nr11''/hr) by the amount of air required for combustion of the fuel (excess air ratio) was 1.05.

Example 2 An apparatus with the same flow as Example 1, except that the number of stages of the perforated plate of the first multistage preheater was changed to three stages, and the number of stages of the perforated plate of the second multistage preheater was changed to one stage. Using the same air and fuel supply amounts as in Example 1, limestone was calcined at 950°C to produce quicklime with an average decarboxylation rate of 98% or more at a rate of 91.1 kg/hr. produced.

In firing this limestone, the thermal efficiency was 68.9%, the fuel ratio was 10.6 x 10'' kg/kg, and the processing capacity of the firing furnace was 1290 kq/hr-m2.

Reference Example A firing furnace shown in Figure 2 in which the bottom part is not funnel-shaped but consists only of a flat perforated plate for a normal fluidized bed is used. The first multi-stage preheater has an inner diameter of 250 mm and three stages of perforated plates, and the second multi-stage preheater has an inner diameter of 2001 mm and one perforated plate. Using a device with the same flow as in Figure 1, except for using
Air 165 as a fluidizing gas is supplied from the perforated plate to the firing furnace.
．． A normal fluidized bed of limestone was formed by supplying 8 Nm3/hr (Uo /Umf = 3.6), 12.5 kg/hr of fuel from the fuel burner and 14.6 N m'/hr of air as auxiliary gas. The limestone was blown out and burned, and the limestone was calcined at about 950°C and decarboxylated, producing 84.3 kq/hr of quicklime.

In firing this limestone, the thermal efficiency was 49.5%, the fuel ratio was 14.8 x 10-2 kg/kg, and the throughput of the firing furnace was 1190 ky/hr-m''.

Here, the ratio of the total supplied air to the air required for fuel combustion (air excess ratio) was 1.30.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing an outline of the flow for carrying out the method of the present invention. FIG. 2 is a sectional view schematically showing a firing furnace used in the present invention. FIG. 3 is a sectional view schematically showing an example of the first or second multistage preheater. 1 is a firing furnace, 2 is a funnel-shaped part, 3 is a burner 4 is a perforated plate, 5 is a jet nozzle for gas jet flow, 7 is a powder outlet, 8 is a supply port for powder and granules, and 9 is a waste gas Outlet, 10 is a first multi-stage preheater, 11 is a second multi-stage preheater, 12 is a heat exchanger (gas-gas), 16, 17 and 18 are cyclones.

Claims (1)

[Scope of Claims] 1. A firing furnace for fluidizing and firing granular limestone or dolomite (hereinafter also referred to as granular material): (a) The bottom has a funnel-like structure; Moreover, a fuel burner protrudes upward from the center of the funnel-shaped bottom (hereinafter also referred to as the funnel-shaped part), and the inverted conical part of the funnel-shaped part is formed of a perforated plate.
Furthermore, the legs extending downward from the center of the funnel-shaped part serve as jet nozzles for ejecting the gas jet flow, and (b) the body between the bottom and the top is formed by a hollow cylindrical body. The lower side wall of the body has an extraction port for extracting the fired granular material, and the upper side wall of the body has a supply port for supplying the powder and granular material. , (C) Using a firing furnace whose top part has an exhaust gas outlet for discharging the waste gas of the firing furnace generated by fluidizing and firing the powder and granules, (B) (a) The granular material that has been preheated by direct contact with a portion of the waste gas in the first multistage preheater is supplied to the firing furnace from the supply port, and Air that has been preheated by direct contact with the powder and granules extracted from the outlet of the sintering furnace is supplied as a fluidizing gas to the sintering furnace through the perforated plate of the funnel-shaped part of the sintering furnace. Air preheated by a portion of the waste gas in the heat exchanger is ejected into the kiln as a gas jet stream from the ejection nozzle in the funnel-shaped part of the kiln, creating an improved spouted bed of powder and granules in the kiln. While forming (q), fuel is ejected from a fuel burner toward the jet part of the improved spouted bed of the powder and granules to burn it, thereby calcining and decarboxylating limestone or dolomite. Method of firing limestone or dolomite.