KR20060023806A - Manufacturing method of burnt lime from limestone sludge and fine limestone - Google Patents

Abstract

Basically, the present invention is a raw material for limestone sludge containing 3% to 10% of magnesium oxide (MgO) and 15% or less of fine limestone. After drying in a rotary dryer of the invention to reduce the moisture to 10% or less, after a baking process at a temperature of 830 ~ 1150 ℃ in a specially designed rotary kiln (rotary kiln) after cooling and pulverized through a conventional exhaust gas process The present invention relates to a method for producing conidia, which can produce conidia.

Description

Manufacturing method of burnt lime using limestone sludge and fine grain limestone {Manufacturing method of burnt lime from limestone sludge and fine limestone}             

1 is a process chart of the present invention.

2 is a schematic explanatory diagram of a rotary drying furnace of the present invention.

3 is a schematic explanatory diagram of a firing furnace according to the present invention.

<Code Description of Main Parts of Drawing>

1. Drying furnace 2. Classifier 3. Heating stand

4. Drying Furnace Lifter 5. Firing Furnace

6. Preheating space 7. Firing furnace lifter 8. Cooling space

The present invention relates to a method for producing powdered quicklime using limestone sludge and fine grain limestone.

Usually, the steel mill uses a large amount of limestone in the manufacturing process. However, wastes such as limestone sludge have not been recycled because they have no use, and have caused enormous environmental pollution.In addition, some intermediate process by-products (also known as "fine-grain limestone") are inevitably used without appropriate additional process application or process improvement. As a result, improper use of raw materials has resulted in many problems such as product quality deterioration, productivity degradation and process failures.

In order to solve the above problems, the present invention has been newly invented a process for manufacturing powdered lime, which can generate high value by allowing the limestone intermediate process by-product and sludge to be properly processed to make powdered lime and re-introduced into the steelmaking process.

In general, condensed lime is produced by calcining ingot limestone at 825 ° C. or higher to produce ingot lime and then pulverizing with a grinder. Therefore, the limestone manufacturing technology has been used mainly in the size of the limestone particle size of 25m / m to 85m / m because the breathability in the limestone firing process should be good in any type of kiln.

Therefore, in order to meet such a good raw material condition, steel mills are left with or discarded as industrial waste the fine limestone containing less than 15m / m of intermediate process by-products naturally occurring during raw material pretreatment and 30% of moisture. Waste, of course, has caused enormous environmental problems.                         

In addition, these fine limestones have not only impeded breathability in the preparation of quicklime, but also have been a major obstacle in the manufacturing process due to the generation of a large amount of dust during the manufacturing process.

Therefore, in the present invention, as described above, the intensive study on the production method of powdered lime from fine limestone using limestone sludge and fine-grained limestone can simultaneously satisfy three effects of resource recycling, prevention of environmental problems, and cost reduction. It is an object of the present invention to be able to provide at the end of the experiment.

Basically, the present invention has a limestone sludge having a particle size of 1 mm or less and a fine limestone of 15 mm or less, which generally have a water content of 32% or less and a magnesium oxide (MgO) component of 3-10%. The raw material for this purpose is dried in a rotary dryer of the present invention to reduce moisture to 10% or less, and then cooled and pulverized after a calcination process at a temperature of 830 to 1150 ° C. in a specially designed rotary kiln. The present invention relates to a method for producing powdered lime, which can be produced by the conventional flue gas process.

In the present invention, when the fine limestone raw material having a moisture content of 10% or less is put into a firing furnace, the raw material receives heat and can be pelletized by itself as an impact light during rotation and movement of the firing furnace. By designing the length of the kiln to longer than usual, it also serves as a preheater to achieve efficient and uniform firing.

It is a feature of the present invention to make pellets by putting the limestone sludge in the dryer mentioned above. Limestone sludge remains at 10% or less even when dried in a rotary dryer, so the preliminary heating function is provided to increase thermal efficiency from the entrance of the kiln, such as a rotary kiln, which is the next process, and the length of the kiln is 20-30% longer than before. It was designed and manufactured.

In general, quick lime is prepared by dissociating carbon dioxide bound in limestone by applying heat of 825 ° C. or more in a rotary kiln or a vertical furnace.

The reaction formula at this time

As a general rule, a very simple reaction path is used, but there are many gaps in the quality of quicklime in the firing process depending on the passage speed of the sublimation process, the sublimation temperature, and the structural conditions of the furnace.

By-products having a particle size of about 15 mm or less generated during the raw material pretreatment process have poor defects and weak durability, so that powder and dust are easily generated during firing. On the other hand, the fine grain by-product has the advantage that the thermal permeation due to the generation of CO ₂ gas is easy because fine powder forms a large amount of pores.

That is, since the basic raw material conditions in the present invention is a fine-grained limestone of fully fine limestone sludge or fine particles of 15 m / m or less, it is difficult to expect good quality with a conventional limestone firing method. In the case of the limestone sludge, as the aggregate of fine powder forms a large amount of pores therein, the heat penetration is easier and thus the dissociation reaction proceeds easily. However, since there is no cohesion, it is easily crushed during the firing process, so that dust is generated in the kiln.

It undergoes heat exchange and dissociation at the surface, reaction diffusion into the inside, and topochemical reaction, so the reaction speed is slow and the firing time takes a lot. However, limestone agglomerated with limestone of fine powder has a large amount of pores (sponge structure) in itself, so it has a characteristic that the reaction time is very short due to the rapid thermal penetration and the smooth reaction.

Therefore, the present invention focuses on this point, and by the method of the present invention, it becomes possible to be fired at the firing temperature range of 830 to 1150 ° C, which is the firing temperature range of the present invention, and the passing time of the firing table is shortened to 30 minutes to 60 minutes, compared to the usual 4 hours. Firing time was reduced to the level of 1/8 to 1/4, and it was confirmed that the heat source unit was smaller.

Table 1 is a limestone composition comparison table for each shape. Here it can be seen that the physical properties of the fine-grain limestone, lime sludge as the raw material of the present invention is poor.

Then with reference to the accompanying drawings and Tables 1 to 2 will be described with reference to the embodiment of the present invention mainly on the firing furnace and firing working conditions.

Table 1. Comparative composition of limestone composition by shape

As described above, in the present invention, intermediate process by-products having a particle size of 15 m / m or less, which are usually generated in the preliminary processing of raw materials, are directly charged into the kiln 5 without undergoing a drying process when moisture is 10% or less. However, the limestone sludge has an excessively high water content of about 30%, so that it is dried within 10% of moisture in a rotary dryer (1) in advance, and the size of the pellet (P) discharged from the rotary kiln is In order to favor the firing of the resin, it is preferably limited to 30 m / m or less, particularly 25 mm or less. Because the particle size of the limestone sludge used is small, the particle size uniformity is reduced when the particle size difference is reduced to 30 mm or less, especially 25 mm or less.

In the present invention, for this purpose, a fractionation port is installed in the inlet area of the drying furnace so as to split the fine limestone mass in the cake state to a size of 25 mm or less as high as possible.

Particularly, in the case of using fine limestone having a particle size of 15 m / m or less as a main raw material as in the present invention, in order to improve the uniformity of the particle size, experiments and work results show that the size of the discharge pellet is uniform to the particle size of 10 to 22 mm. Was found to be the most efficient at firing. If the particle size is less than 10mm breathability is worse, if it exceeds 22mm it is difficult to penetrate the calcined heat. This was especially true when exceeding 30 mm.

The heat source used in the drying furnace is usually used to recover the waste heat generated in the kiln. The structure of the dryer according to the present invention, as shown in Fig. 1, is provided with a classifier 2 such as a chain at a raw material inlet of a rotary dryer to obtain a water-containing sludge mass 1. In addition, the lifter 4 is attached to the heating table 3 from the inlet of the dryer 1, for example, to a depth of 6 m out of a total of 15 m, for the second grinding, so that the fine raw material passes through the dryer. While spontaneously falling by the lifter 4 with water evaporation while being slid by rotation of the kiln, round pellets P are formed.

If the sludge strength is maintained during the drying process, the sludge is not broken and is discharged through the outlet of the dryer. At this time, the pellet size adjustment is performed at the optimum speed of the rotary dryer and the lifter. It is adjusted according to the depth and the degree of water content of the sludge.

The strength of the pellets and the degree of dust generation vary depending on the installation conditions. Therefore, the pellets should be adjusted to suit the firing conditions in order to optimize them.

On the other hand, in order to improve the raw material input conditions in the rotary kiln and to enhance the pellet strength, a strength enhancer (for example, cement, molasses, water treatment, etc.) may be added as a caking agent to the inlet of the dryer.

However, this is only possible if there is no burden on manufacturing costs without affecting the purity of the product.

The rotary kiln has a structure as shown in FIG.

Usually, the calcining process in the rotary kiln 5 is designed to be drawn out from the raw material input through the preheating zone, the baking zone, and the cooling zone.

By the way, the raw material used in the present invention is a low-strength limestone particles, fine powder or fine particles, etc., the heat penetration is faster than the particles of calcite (usually 25m / m ~ 85m / m) for each individual, but the total volume (volume) In consideration of the low permeability, the heat penetration is difficult, so the overall plasticity is lowered. In addition, because the fine limestone slides while the furnace rotates, it is only spread underneath, so it is hard to expect a good result with the calcination which is almost dependent on radiant heat.

Accordingly, in the present invention, since the firing is almost performed by the interfacial chemical reaction, all raw materials such as fine lime are separated in the rotation process by attaching a lifter 7 fixed or movable on the bottom of the rotary kiln to the firing table. Forced fall. The lifter 7 is installed in parallel with the firing direction of the raw material. The shape of the lifter 7 may be a long rod, semi-circle, or triangular iron.

As a result of using the lifter (7), both calcite and unanalyzed lime proceed in the spiral movement by the rotation of the kiln, making it difficult to stick to the furnace bottom plate and easily exposed to the direct heat from the burner, thereby achieving complete lime burning. In addition, it showed complete calcination rate even at the temperature of 80 ℃ lower than the previous furnace temperature. In particular, while the pellet is preheated and rotated in the preheating space 6, the pellet is cured and hardened before reaching the firing table while the moisture gradually decreases.

The firing temperature of the conventional limestone kiln is carried out in the range of about 1200 ~ 1300 ℃, in the case of the present invention, the firing temperature by the above-described elements such as preliminary drying, pelletization, composition of the preheating table of the kiln, installation of the lifter, etc. The present invention is innovative in that it can be carried out in the range of 830 ~ 1150 ℃, and it is also innovative that the limestone sludge can be naturally pelletized in a rotary dryer without additives.

The calcination temperature is higher than 830 ℃ because limestone can be chemically reacted with limestone when it is chemically higher than 825 ℃. If the calcination temperature exceeds 1150 ℃ and the furnace temperature is too high, coating of lime sludge will occur. Since the operation is difficult, in the present invention, the firing temperature is set to 830 ~ 1150 ℃. The preliminary drying of the present invention, the installation of a pelletized lifter, and the like make it possible to perform the firing process sufficiently in this temperature range.

Processed raw materials passed through the kiln (5), such as rotary kiln, are cooled through the cooling space (8) and transported and pulverized (adjusted to the requirements of steel mill sintering plant, preferably to the particle size (m / m or less)) After shipment, it is shipped as congener. This process is shown in FIG.

The rotary dryer process of FIG. 1 is a system which has not existed conventionally, and the rotary kiln process also differs significantly from the conventional one in that it is a process process different from the conventional one.

On the other hand, in the past, many cases of operation interruption occurred due to severe adhesion of limestone raw material to the furnace wall by firing at high temperature, that is, furnace wall coating. However, the present invention has a preliminary drying, pelletization and preheating zone extension, and the bottom of the firing table. By attaching and installing the lifter, the raw material is placed on the lifter as the kiln rotates and the surface of the raw material is inverted. Therefore, radiant heat is spread evenly over the entire surface of the raw material. In addition, in the present invention, although a large amount of magnesium oxide (MgO) component is contained in the raw material, no coating phenomenon occurs.

Example

end. The present invention will be described below with reference to one embodiment. However, the present invention is not limited only to the following examples, and a technique having a similar meaning will also belong to the scope of the present invention.

First, the rotary furnace and working conditions used in this example are described below.

I. Main equipment specifications

1. Furnace type: Rotary kiln with rotary lifter

2. Furnace size: 2300mmØ × 45,000mmℓ

3. Fuel used: COG gas

4. Rotating speed: 1 RPM

5. Furnace tilt angle: 2 °

The raw materials, working conditions and results of this example are shown in Table 2.

TABLE 2

As can be seen in Table 2 above, in the present embodiment, the limestone raw material is classified by particle size, so that sample A is fine particles having a particle size of 3 to 10 mm, sample B is fine grain of 15 mm or less, and sample C is used as limestone sludge. (Normally 15 mm or less, but the size of the revolving particle size in consideration of the firing efficiency was measured to be about 1 mm, so it was set to -1 mm, that is, 1 mm or less).

As can be seen from Table 2, Sample C had the best results, and it was found that the high quality condensed lime product was obtained by a short passage through the present invention even at a low firing temperature according to the present invention.

In the present embodiment, because of the large amount of dust in the furnace due to the processing of the fine raw material, the capacity of the dust collecting equipment in the post process was increased by 30% than that of the preparation of quicklime.

① preheat

By recycling the waste heat generated during firing, the rotary dryer (rotary dryer) of FIG. 2 is installed and operated prior to firing to increase the fluidity of the raw material to facilitate thermal penetration.

In addition, the length of the body of the rotary kiln 20% longer than usual to serve as a preheater from the raw material inlet.

② filling rate

In general, the raw material filling rate in the rotary kiln during the production of quicklime is usually 6-11%, but in the present invention, the productivity can be increased in comparison with the facility capacity by increasing it to 15%.

Since the input raw material was mainly fine particles of about 13m / m, the heat penetration and diffusion speed proceeded rapidly.

③ Furnace temperature and passing time

On the other hand, when the temperature inside the furnace was less than 828 ° C., even if the passage time was 4 hours or more, the CO ₂ decomposition was not good and the baking was not performed. In addition, the firing time was adjusted to 830-1000 ° C., and the firing time was 4-12 hours. Therefore, the firing temperature in the furnace was performed at 1030 to 1069 ° C, far exceeding 830 ° C, which is a possible firing temperature, in consideration of the conventional firing time. In addition, the firing temperature was further increased and the temperature at the firing table was passed at 1150 ° C. for 60 minutes. As a result, the firing itself was 100% complete, but some non-uniformly fired lime was found. On the other hand, when passed for 60 minutes at a temperature of 1300 ℃, the undercalcination occurs, CaO is hydrated reaction, such as the role as a conservative lime is insufficient.

It was confirmed in the above examples, the samples A, B, C was calcined without the furnace wall coating adhesion phenomenon, even if the sample D and sample E is the performance value of the genuine limestone genuine Ig.-loss, particle size It was found that the firing efficiency was significantly reduced due to the heterogeneity of the distribution. Although it was not shown in the table, it was confirmed that in the case of Sample E, the coating phenomenon on the calciner wall of limestone was severe.

Samples A, B, and C according to the present invention were found to be more than 30% reduced in total calorie consumption as well as perfect firing even though the passage time in the furnace was 65% compared to sample D.

Therefore, there is no groundbreaking method that has ever been able to produce powdery lime by particle size uniformity, lifter attachment installation, etc., using limestone raw material of fine or fine grains, which has been difficult to use conventionally, using lime sludge having a particle size of 15 mm or less. As a result of the present invention, there is a feature of the present invention.

Claims (4)

In order to produce condensed lime from raw material limestone sludge containing 32% or less moisture and fine limestone with a particle size of 15mm or less, The raw material is manufactured by a rotary dryer into pellets having a water content of 10% or less, and then the rotary kiln is formed by installing a lifter at the bottom of the baking table. Firing at 830 ~ 1150 ℃ and then cooled and pulverized to prepare the powdered lime through a conventional flue gas process According to claim 1, wherein the rotary dryer is attached to the raw material inlet by a plurality of chains (classifier) is installed to split the water-containing sludge lumps, and a lifter (lifter) is attached to the heating table of the drying furnace The water-containing raw material passes through the dryer and evaporates the water, and by this lifter, it naturally falls and slides, so that round pellets are formed and dried. The method of claim 1, wherein the pellets have a particle size of 10 to 22 mm when discharged from the drying furnace. The preheating stand according to claim 1, wherein the rotary kiln firing furnace is provided with a lifter provided at the bottom of the firing table in the width (lateral) direction of the rotary kiln, and is 20 to 30% longer than a conventional rotary kiln length. Method for producing conidia lime from fine limestone, characterized in that to install

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