KR790001442B1 - Method for calcining pellet-shaped calcium hydroxide - Google Patents

Abstract

Spherical or elipsoidal Ca(OH)2 was heated in a down draft of gasses from a series of burners while moving on a travelling grate to produce a product suitable for the manuf. of CaC2. The Ca (OH)2 was fed onto the grate from a hopper and subsequently covered by a layer of granular calsite with particle size of 10-30mm whose thickness, less than 50% of the whole, should be increased with an increase of the size(10-40cm3) of the Ca(OH)2. The temp. of the top layer was 1,000-1,100≰C, and that of the gas leaving below 300-400≰C.

Description

Firing method of particulate calcium hydroxide

1 is a process chart for explaining the method of the present invention.

The present invention relates to a method for calcining particulate calcium hydroxide which forms part of a flux and an ore mixture (hereinafter simply abbreviated as a charge) in an electrothermal calcium carbide furnace. It is made by granulating or shaping moist calcium hydroxide, and is transported to a sintered grate over a grater maintained by the combustion of the gas at the top of the grate, where it is discharged below the grate. Calcium hydroxide produced by the reaction of calcium carbide with water is preferably used.

Calcination of calcium hydroxide to recycle the calcined material to the carbide production stage has already been reported in the literature (RH Hall, The Engineering Journal, December 1951, pages 1,176-1,182). Calcium hydroxide should be granulated or shaped (Germany Patent 913,534).

Calcium hydroxide formed in this form usually contains 10-25% moisture, which is not chemically bound. It is also known that impurities such as SiO ₂ and Al ₂ O ₃ present in the carbide raw material are concentrated in the molded calcium hydroxide.

Calcium hydroxide particles are usually fired in a rotary kiln, and a method of using suction draught sintering grate has also been proposed (German Patent Application A3125V / 80C).

It is also possible to fire using solids such as coke or gaseous fuels such as carbide furnace gas, where the absorption of CO ₂ by particulate matter is controlled or limited.

However, the above conventional processes are not completely satisfactory in various respects. For example, to prevent calcium hydroxide particles from agglomerating during firing and adversely affect the permeability of the particles to the gas and the reactivity of the resulting lime, calcium hydroxide must be purified. In addition, it is necessary to carefully dry the moist particles before firing to prevent them from rupturing during firing, which are detrimental to the efficiency of the prior art process.

The inventors found that in the firing of particulate calcium hydroxide, it is possible to calcinate the particulate calcium hydroxide in an improved yield in terms of space and time by a process of temporarily carbonizing the particulate calcium hydroxide, in contrast to the prior art which attempted to avoid carbonization of granular calcium hydroxide. Found.

For this purpose, in the present invention particulate calcium hydroxide is placed on the grate and covered with a pulverized limestone layer and the undried particles are transported directly through a heating table.

The particles covered with the crushed limestone are preferably passed through the heating zone at a rate at which the decarbonized limestone and dehydrated calcium hydroxide can be obtained at the end of the heating zone.

Another advantage is that the lime-covered layer of calcium hydroxide and granular material used in spherical or ellipsoidal form is fired on the grate to have a height selected according to the size of the particles.

In particular, layers having a height in the range of 0.3-0.4 m, 0.4-0.5 m and 0.5-0.6 m, respectively, should be used when the volume of the particles is in the range of 10-2 Occ, 20-3 Occ and 30-4 Occ. Grinded limestone is advantageously used in the form of particles having a diameter of 10-3Omm, but the particle size should be matched to the size of the calcium hydroxide particles.

The pulverized limestone layer is convenient to have a height in contact with 50% of the total phase formed of calcium hydroxide and limestone. Limestone containing at least 95% calcium carbonate is most conveniently used. It is also advantageous to ensure that the temperature of the upper heating zone of the material to be fired is in the range of 1,000-1,200 ° C. The temperature in the first three parts of the heating zone shall be maintained at least 90% of the temperature in the three parts of the heating end.

It is convenient to divide the heating table into two separate heating zones, where the head is heated in an atmosphere that contains more carbon dioxide than the atmosphere at the end. The atmosphere at the end is usually produced by the combustion of hydrogen or hydrogenated gas. Fuels burning in the head are preferably selected from carbonaceous gas, solid carbonaceous fuels or liquid fuels, which are either dispensed or sprayed onto the calcining material. The rate of travel and oxygen supply, the amount and particle size of the solid fuel or the amount of liquid fuel, on the other hand, should be controlled to burn in the zone where the solid or liquid fuel is heated with carbonized gas. Carbide furnace gas is preferable as the carbonaceous gas, and coal, coke or petroleum coke having a size of 1-6 mm is preferable as the solid fuel, and fuel oil is preferable as the liquid fuel. It is preferable to combust hydrogen, natural gas, light hydrocarbons or a mixture of hydrogen and carbide at the end of the heating zone.

Another advantage of this process is that a temperature in the range of 1,000-1,200 ° C. is maintained in the heating charge section above the pulverized limestone layer to balance the followings.

(a) the bed height of particulate calcium hydroxide and pulverized limestone, (b) the amount of gas exhausted under the grate, (c) the gas emitted under the grate is 300-400 ° C,

Great travel speed to have an average temperature in the range.

The hot gas discharged under the grate can be used to dry the moist coke forming part of the charge.

An apparatus for carrying out the process of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, the apparatus constitutes a movable intake venting grate 1 where the chute 2 is located above the grate 1 and carries particulate calcium hydroxide over the grate. The burner 3 is located downstream of the chute 2 when viewed in the direction of motion of the grate, above the grate 1 and below the grate a gas exhauster 4 is installed in the category of the burner 3. It is. Another chute 5 carries the pulverized limestone phase to the grate 1 and is placed between the chute 2 and the burner 3.

The two chutes are arranged such that the height of the granular calcium hydroxide phase and the limestone phase can be varied independently on the grate 1. It is advantageous to install slides 6 and 7 in chutes 2 and 5, respectively, which are spaced apart so that the spaces between the grate and the two slides on the sintered grate 1 can be changed independently of each other. Are located a couple of times.

It is also advantageous to divide the burner 3 into two independent burner systems 3a and 3b, each having a separate fuel inlet.

According to another embodiment of the invention, a conduit 8 for supplying particulate fuel to the pulverized limestone layer is installed between the chute 5 and the burner 3, the conduit transversely with respect to the grate 1. It is installed to move forward and backward and is connected to the granular fuel storage 10 through a bendable hose 11 and a bucket wheel 9.

In addition, it has been found that the present invention has a stabilizing effect to prevent the damp material from rupturing during firing, thereby deteriorating gas permeability and thereby making it difficult to supply heat required for material firing.

In other words, there is no need to dry the material beforehand. As a result, a high gas temperature at the top of the grate can be maintained even at the beginning of the heating table.

Higher temperatures are formed at the end of the heating zone where carbonized material is brought into contact with the combustion gases and carbon is removed, especially in the atmosphere of this area. As a result, the permeability of the particulate matter to the gas is improved, the heat is distributed therein, such that there is no phenomenon such as superheat or aggregation of the particulate matter. The fired material from the grates has a temperature of 150 ° C. because the present invention also allows sufficient cooling air to enter the downstream of the cooling zone.

There is another reason why the ground limestone bed covering calcium hydroxide acts as a protective layer. This is because overheating is actually prevented by the endothermic reaction that occurs while releasing carbon dioxide within the temperature range of 750-850 ° C. as long as calcium carbonate is decarbonized.

The released carbon dioxide penetrates into the particulate calcium hydroxide, causing a semithermal reaction and removing the chemically bound water. This is a heat distribution mechanism where the layer of material heats up quickly at the head of the heating table and combines with the surface stabilization carbonization of particulate matter. In other words, even when the particulate matter is heated at a high temperature, it does not rupture, decompose or agglomerate. Particulate matter remains a loosely aggregated material with good gas permeability.

The present invention provides optimum gas production, optimal heat supply, and optimum space and time yields at temperatures in the range of 1,000-1,100 ° C., where the temperature of electricity is in contact with the material to be fired in order to avoid aggregation of particulate matter on the grate. This is the maximum permissible temperature of the gas (the gas permeability is lowered by the electric flocculation) and the sintering of the calcined material (thereby impairing the reactivity of the material) is prevented.

If the material is easily penetrated by gas, it is possible to use a thicker layer. This means longer residence times and improves the use of energy. Desirable reversible carbonization effects can be further enhanced and fuel gas energy can be replaced by solid fuel energy, for example by depositing coke or petroleum coke with a particle size of 1-6 mm on crushed limestone. Do. Coke is conveniently used in the amount and particle size needed to burn in the head of a heating zone heated by carbonaceous gas.

In this way up to 5% of coke particles can be used with respect to the amount of calcined material produced and a solid fuel can be used to generate 50% of the required heating energy.

The benefit of dividing the burner into two separate systems is well expressed as the performance gains resulting from the resulting benefits. It has been found that when the entire heating zone is heated with hydrogen, particulate matter carried in the heating zone in the form of a relatively thin layer is agglomerated. In other words, at low gas temperatures above the grate, almost no gas can be transported through the bed, so the production of calcined material is limited to 3.0 tonnes per hour. In this case, the partially burned fired material is also transported to the cooling stand. It is possible to produce 7.4 tonnes per hour of material fired by the same heating zone, except that the heating zone is divided into a head zone heated by gas with carbide and a terminal end heated by hydrogen.

Similar results are obtained when the gas is partially replaced by coke particles with carbides used in the head of the heater. The following examples illustrate the beneficial effects of the present invention.

Example 1

The suction draft sintered grate is 1.5 m wide. The heating stage is 8.0 m long, the cooling stage is 3.5 m long, and the calcium hydroxide particles are generally oval and have an average volume of 28 cc. Grinded limestone had a diameter in the range 8-25 mm.

Claims (1)

In the calcining process of granular calcium hydroxide forming part of flux and ore mixture in electrothermal calcium carbide furnace, the temperature of grate, which is heating zone, is formed at 1,000-1,200 ℃ by the gas which is burned at the top of the grate and discharged to the bottom of the grate. The temperature at the inlet three-minute zone of the heating zone is maintained at least 90% of the terminal three-minute zone temperature and is sintered to a particle size of 10-30 mm to fire spherical or ellipsoidal calcium hydroxide particles with a water content of 10-25%. Limestone containing% calcium carbonate covers the calcium hydroxide layer, and the calcium hydroxide particle layer covered with lime layer has a height of 0.3-0.4m, 0.4-0.5m, when the calcium hydroxide particles are 10-20cc, 20-30cc, 30-40cc, respectively. A calcining method of particulate calcium hydroxide, characterized in that 0.5-0.6m, the maximum height of the limestone layer is 50% of the total layer.

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