JPS62230616A - Production of granulated quick lime - Google Patents

Abstract

PURPOSE:To obtain granulated quick lime having high reactivity and uniform particle diameters efficiently, stably and inexpensively, by attaching dry mud of lime slurry to a nucleus substance for granulation to form pellets, thermally decomposing the pellets and calcining. CONSTITUTION:Lime slurry discharged from a caustification process in a kraft pulp manufacturing process is blended with green liquor, dehydrated by a mud filter 1 to give mud cake, which is sent to a paddle mixer 3, ground by a cage mill 4, dried under heating at about 450 deg.C and then dried by cyclones 5 and 6 to give dry mud of lime slurry. The dry mud is continuously fed through a dried lime slurry feed bin 7 to a fluidized calcining furnace 11 kept at 750-800 deg.C by combustion of heave oil and attached to a nucleus substance for granulation, which is successively supplied from the top of the furnace 11 and has 0.5-4mm particle diameters under 1,500-2,300mm H2O pressure condition to form pellets. Then, the pellets are thermally decomposed at <=830 deg.C at an upper fluidized bed 15 in the furnace 11 exhausted to 0--100mm H2O by an exhaust fan to granulate quick lime particles having 1.2-3mm particle diameters, which are discharged through a lower fluidized bed 16 from a pellet outlet pipe 19 to give granulated quick lime having >=90% purity.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to an improvement in a method for producing quicklime by burning lime mud discharged from the causticizing step of the kraft pulp production process using a fluidized roasting method. It is.

"Prior Art" The main components of the chemicals used in the kraft pulp (hereinafter simply referred to as rKP) cooking method are caustic soda and sodium sulfide, and small amounts of caustic potash, potassium sulfide, etc. are also used. An aqueous solution containing these chemicals is usually called "white liquor", and the white liquor is used to digest lignocellulosic material and separate it into so-called "black liquor" containing lignocellulose fibers and chemicals.

As described above, in the KP cooking method, since expensive soda chemicals are used as cooking chemicals, recovery of the soda chemicals is an essential requirement, and the chemical recovery process is an extremely important part of the KP cooking method. In the recovery process, the black liquor discharged from the cooking and washing process is concentrated and burned, and the resulting smelt (molten material) is dissolved in weak liquor (a dilute solution of white liquor) to produce green liquor.
Quicklime is added to make it caustic, and the white liquor is regenerated and used again in the cooking process. Furthermore, since most of the lime mud discharged from the green liquor causticizing process is calcium carbonate, this is burned to make quicklime and is reused in the recovery process.

There are various methods for firing lime mud, but the so-called "fluidized roasting method" in which a dry mat of lime mud is introduced into a fluidized roasting furnace and fired is well known.

This fluidized roasting method involves introducing a dry mat of lime mud into a fluidized roasting furnace (calciner) as shown in Figure 1, and firing it.
This is a method of producing quicklime by thermally decomposing lime mud.

``Problems to be solved by the invention'' However, in the conventional fluidized roasting method, the temperature of the fluidized roasting furnace is maintained at a high temperature of 870 to 900°C to burn the dry mat of lime mud. Crystallization of quicklime tends to proceed, and quicklime with satisfactory reactivity cannot necessarily be obtained. Moreover, dry mat attached to the inside of the calciner may grow as a scale as the quicklime crystallizes, making stable operation difficult. Furthermore, in the conventional fluidized roasting method, the particle size of the regenerated quicklime is insufficiently controlled, resulting in the problem that the particle size becomes too large or too small.

In view of this current situation, as a result of intensive research into solving the above-mentioned problems, we added a granulation core material and changed the firing temperature and pressure conditions when calcining lime mud dry mat using the fluidized roasting method. By adjusting within a certain range, the crystallization of quicklime can be effectively prevented, resulting in increased reactivity,
Moreover, they discovered that quicklime of uniform particle size could be obtained extremely efficiently, leading to the completion of the present invention.

"Means for Solving the Problems" The present invention provides a method for producing quicklime by burning lime mud dry mat discharged from the causticizing process in the kraft pulp production process using a fluidized roasting method. This method of producing granulated quicklime is characterized by adhering matte to a granulating core material under pressure at a temperature of 830°C or lower, and thermally decomposing it under reduced pressure at a temperature of 830°C or lower.

"Operation" In the method of the present invention, as a first step, a dry mat of lime mud is attached to the core material for granulation under pressure, and it is preferable to use quicklime as the core material. It is. Although the quicklime may be new, a portion of the quicklime granulated and discharged by the method of the present invention may be separated and reused.

In addition, when the particle size of the nuclear material becomes smaller than 0.51-, the particle size of the quicklime granulated in the furnace becomes too fine.
There is a risk that it may be mixed with the combustion gas and discharged (carryover), or it may adhere to the inner wall of the circulation pipe and impair the flow of the pipe. On the other hand, in the case of large particles exceeding 4 dragons, the granulated quicklime becomes too large to be discharged and accumulates in the furnace, reducing the function of the fluidized roasting furnace. The particle diameter of the core material for granules is desirably adjusted to about 0.5 to 4 mm, more preferably about 1 to 3 cm.

In order to attach a dry mat of lime mud to the core material, it is desirable to mix in an inorganic binder that melts under the firing temperature conditions but does not decompose, especially sodium carbonate, sodium hydroxide, sodium sulfate, Alkaline substances such as sodium sulfide, potassium carbonate, potassium hydroxide, potassium sulfide, and potassium periosulfate are preferably used.

The amount of binder added is not necessarily limited, but it is 0.5% by weight or more, more preferably 0.5% by weight or more based on the dry mat.
It is desirable to add 8% by weight or more. Note that the alkaline substances attached to the lime mud also act as a binder, but since the amount attached is small, it is desirable to add additional binder to the dry mat.

In the method of the present invention, a dry mat of lime mud is first attached to the core material for granulation as described above, and the temperature and pressure conditions at that time are extremely important. That is, the dry mat is under pressure, more preferably 1500 to 2
300 Yoiho H20, most preferably 2000-2300
It is necessary to adhere to the nuclear material under pressure conditions of weight 1 + 20, and high temperature conditions such as those in conventional methods exceeding 870°C must be avoided, and 830°C or less, more preferably 815°C. It is set as below. Incidentally, 8
If the treatment is carried out under temperature conditions exceeding 30° C., the formation of crystalline quicklime will be promoted, making it impossible to achieve the intended purpose of the present invention.

The dry mat of lime mud thus adhered to the nuclear material is sequentially modified into the desired quicklime particles by firing under reduced pressure in the second stage, but the temperature and pressure conditions are also changed during the second stage of firing. is extremely important.

That is, the dry mat of lime mud adhered to the nuclear material is heated to 830°C or lower, more preferably 750°C to 800°C under reduced pressure, more preferably 0 to -100°C.
It is thermally decomposed at a low temperature of 15°C and sequentially modified into quicklime particles.

Note that the above-mentioned depressurization conditions can be easily adjusted by adjusting the damper opening of the exhaust fan, etc., but the temperature inside the fluidized flow roasting furnace can be controlled by, for example, temperature measurement using the electromotive force of a temperature sensor in a thermocouple. It is preferable to accurately adjust the equipment, the injection amount of heavy oil as fuel, the feed amount of lime mud dry mat, the rotational speed of the air blower, etc., using a computer control or the like that corresponds appropriately. Further, the time during which the dry mat is fired in the fluidized roasting furnace is appropriately adjusted depending on the bed level formed by the dry mat introduced into the furnace, the amount of discharged quicklime produced, and the like.

"Example" The present invention will be described in more detail with reference to Examples below, but the present invention is of course not limited to these.

Concentration of 45% discharged from the causticizing process during the KP cooking process
Green liquor corresponding to 5% solid content was added to and mixed with the lime mud, and then dehydrated with a mud filter to obtain a mud cake. This was ground in a cage mill, heated and dried at 450°C, and then dried in a cyclone at 300°C to form a dry mat of lime mud.

This dry mat was then continuously introduced into a fluidized torrefaction furnace. In addition, the fluidized roasting furnace uses heavy oil combustion to produce a
The temperature is controlled at 800℃, and the introduced dry mat is continuously introduced from the top of the furnace with a particle size of 1.0.
~2000-2300 am for granulation core material of 2.5 dragons
It adhered under a pressurized condition of If□0 to form a pellet.

The pellets are flowed through the furnace by blowing with an air blower, and are heated from 0 to -100 s 1 Iz by an exhaust fan.
It was thermally decomposed at a temperature of 815° C. or lower in the upper part of the furnace where the pressure was reduced to 0.000 C, and it was granulated into quicklime particles having a particle size of 1.2 to 3 mm.

The granulated quicklime is sequentially discharged from the bottom of the fluidized roasting furnace, and the obtained quicklime has a purity of over 90%, and when it was reused in the causticizing process, it showed an extremely excellent reaction. showed his sexuality. Incidentally, when using quicklime obtained by the conventional method, about 0.3% of causticized unreacted quicklime was observed, but in the case of quicklime obtained by the method of the present invention,
No causticized unreacted quicklime was observed.

Moreover, even after four months of continuous operation, there was no accumulation of quicklime grains in the furnace or interruption of the carryover operation. Furthermore, in the conventional method, about 300 to 800 scales were deposited inside the furnace, but in the method of the present invention, only about 2 to 5 scales were deposited, and extremely excellent continuous operability was exhibited.

Furthermore, because the firing temperature is low, fuel consumption is low.
In the conventional method, 210 to 2401 parts of heavy oil were consumed per ton of quicklime, whereas only 1901 parts of heavy oil was consumed.

"Effects" As is clear from the above examples, according to the method of the present invention, quicklime with high reactivity and uniform particle size can be produced extremely efficiently (and stably).

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a fluidized roasting furnace and its series. 1... Filter 2... Conveyor 3... Paddle mixer 4... Cage mill 5... Cyclone 6... Cyclone 7... Dry lime mud supply bin 8... Feeder 9... Gas Cooling tower 10...
・Blower 1)...Fluidized roasting furnace 12...Baking chamber 13...Pipe 14...Pipe
15... Upper fluidized bed 16... Lower fluidized bed
17... Hole 18... Heat recovery chamber 19...
Bullet discharge pipe 20...valve 21...elevator 22...branch 23...seed feeder 24,
25...Crusher 26...Storage bin 27...
blower

Claims (4)

[Claims] (1) In a method for producing quicklime by burning lime mud dry mat discharged from the causticizing process in the kraft pulp production process using a fluidized roasting method, the dry mat is heated under pressure at a temperature of 830°C or less. A method for producing granulated quicklime, which comprises adhering it to a core material for granulation and thermally decomposing it under reduced pressure and at a temperature of 830° C. or lower. (2) The manufacturing method according to claim (1), wherein the particle diameter of the granulation core material is 0.5 to 4 mm. (3) Dry mat at 1500-2300mmH_2O
It is attached to the core material for granulation under pressurized conditions of 0 to -10.
The manufacturing method according to claim (1), wherein the thermal decomposition is carried out under reduced pressure conditions of 0 mmH_2O. (4) The manufacturing method according to claim (1), wherein the dry mat is adhered to the granulation core material at a temperature of 815°C or lower, and is thermally decomposed at a temperature of 750 to 815°C.