CA1220323A

CA1220323A - Process and apparatus for fluidized calcination of diamide lime, and desulfurizing agent

Info

Publication number: CA1220323A
Application number: CA000399484A
Authority: CA
Inventors: Hiroyuki Ishizaka; Atsushi Takahashi; Yoshihara Muratsubaki
Original assignee: Nippon Carbide Industries Co Inc
Current assignee: Nippon Carbide Industries Co Inc
Priority date: 1981-04-09
Filing date: 1982-03-26
Publication date: 1987-04-14
Also published as: NO164832B; JPS57170823A; NO821190L; JPH0118014B2; NO164832C; DE3212210A1; DE3212210C2

Abstract

A B S T R A C T
In a process for calcining diamide lime in a fluidized bed using a heat medium in a calcination furnace, the improvement wherein the heat medium has a particle diameter of 0.1 to 2.5 mm, the amount of the diamide lime fed into the calcination furnace is 0.1 to 5 times the weight of the heat medium per hour, the burnt gas is allowed to flow at a space velocity of 0.8 to 3.0 meters/sec., and the resultant lime powder is recovered by a carry-over method; an apparatus for calcining diamide lime in a fluidized bed using a heat medium, which comprises a furnace, at least two pneumatic injecting means opened toward the center of the furnace for injecting the starting diamide lime together with a carrier gas into the furnace, and means for drying the starting diamide lime; and a desulfur-izing agent for molten iron, which comprises quick lime powder obtained by calcining diamide lime in an oxidizing atmosphere.

Description

BACKGROUND OF THE INVENTION
.
1. Field of the Invention This invention. relates to an economical and easily operable process for continuously producing large quantities of lime powder having excellent gas transport-ability and an excellent ability to desulfurize molten iron, which comprises calcining doomed lime under certain specified conditions; a simple apparatus for use in carry-in out this process; and a desulfurizing agent comprising lime powder obtained by calcining doomed lime in an ox dozing atmosphere.
. Description of the Prior Art In recent years, there has been an increasing demand for lime powder having excellent gas transport-ability. Despite their low cost, conventional types of lime powder have been much limited in industrial use because they have poor gas transportability. Conventional lime powders have the serious defect that when a lime powder is finely pulverized so as to increase its specific surface area and thereby its chemical reactivity, its gas transportability decreases with increasing specific surface areas. One application which requires lime powder of increased specific surface areas is the desulfurization of molten iron by blowing of lime powder, which has recently been investigated actively see, for example, Japanese Laid-Open Patent Publication No. 110712/1980).
In this use, lime powder is blown by means of a carrier gas, if required together with desulfurization aids, into molten iron to react sulfur therein with the lime powder and transfer it as calcium sulfide to the slag, and the gas transportability of lime powder has a very important bearing on its efficiency of desulfurization, Attempts were therefore made to improve the gas transportability of lime powder. For example, the above-cited Japanese Laid-Open Patent Publication No. 110712/1980 proposed the addition of about 0.5% of a silicone oil which is much higher in cost than lime powder. Previously, we found that as means for improving the gas transportability of lime powder without the need to add such an expensive silicone oil, the addition of doomed lime to Buick lime powder is very effective (Japanese Patent Application No. 61,261/1980). As a result of a series of further investigations, we found that quick lime powder obtained by the fluidized calcination of doomed lime under specie fled conditions, preferably in an oxidizing atmosphere, has the best desulfurizing ability as quick lime powder to which doomed lime is to be added.
An attempt to obtain a desulfurizing agent comprising a quick lime produced from doomed lime is disclosed in Japanese Laid-Open Patent Publication No. 50414/1969. This patent document discloses that the desulfurizing ability of quick lime is improved when doomed lime is calcined in a non-oxidizing atmosphere together with an additional carbonaceous substance in an external h cling furnace (stationary type), and only states that the presence of an oxidizing atmosphere is undesirable because it reduces the activity of Buick lime.
SUMMARY OF THE INVENTION
. _ _ _ _ It is an object of this invention to improve a process and an apparatus for fluidized calcination of doomed lime to give quick lime powder having excellent gas transport-ability and excellent desulfurizing ability for use as a raw material for a desulfurizer composition for molten iron.
According to an aspect of this invention, there is provided a process for producing finely divided quick lime powder in a fluidized bed, which process comprises:
maintaining a fluidized bed of a heat medium having a particle diameter of 0.1 to 2.5 mm in a calcination furnace;
feeding doomed lime into the fluidized bed, the amount of the doomed lime being 0.1 to 5 times the weight of the heat medium per hour;
burning a fuel thereby calcining the fed doomed lime without substantially nodulizing in the fluidized bed such that the burnt gas flows in the furnace at a space velocity of 0.8 to 3.0 meters/sec; and recovering the resultant calcined lime powder carried over together with the hot burnt gas.
The term "carried-over" is used in contrast to overflowing, and denotes the carrying of quick lime powder obtained by fluidized calcination from the calcination furnace . Jo .,~, together with hot burnt gas.
In another aspect, the present invention provides an apparatus for calcining doomed lime in a fluidized bed to produce finely divided quick lime, which comprises:
a. a furnace, at least the fluidized bed calcination section of which is of a cylindrical configuration, and which is adapted to form therein when in use a fluidized bed consisting of a heat medium with a particle diameter of 0.1 to 2.5 mm which is a non-combustible infusible solid medium incapable of acting as a binder in order to calcite in the fluidized bed doomed lime about 90% by weight of which has a particle diameter off to a quick lime about 90% by weight of which has a particle diameter of 10-60~ in a fluidized state;
b. a plurality of means disposed at the side of said fluidized bed section for feeding said doomed lime into said fluidized bed toward the center of said bed pneumatically so that the amount of the doomed lime is 0.1 -to 5 times the weight of the heat medium in said bed per hours;
c. a means for supplying an oxidative fluidized gas to the lower part of said fluidized bed such that the space velocity of a burnt gas may be maintained at 0.8 3.0 m/sec;
d. a fuel supplying means disposed at the side of said fluidized bed section for causing the burning with said oxidative fluidized gas in said fluidized bed; and 3~3 pa -e. a means for withdrawing said quick lime brought to the upper part of said fluidized bed by means of the burnt gas by carrying-over from the top of the fluidized calcination furnace.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figures 1 and 2 are schematic views showing the principle of the apparatus used in the fluidized calcining process of this invention; and Figure 3 is a cross sectional view of the furnace shown in Figures 1 and 2, indicating a plurality of injection openings for injecting the starting material into -the furnace.
DETAILED DESCRIPTION OF THE INVENTION
In -the desulfurization of molten iron, it is desired to minimize the amount of a carrier gas for preventing the lowering of the temperature of the molten iron and the splashing of the molten iron and -to blow a desulfurizer into molten iron while maintaining a relatively high solids concentration with seduced fluctuations. Such a blowing method is specifically disclosed, for example, in Japanese Laid Open Patent Publication No. 31518/1974. The Buick lime powder produced by the calcining process of this invention exhibits excellent gas transportability even when the concentration of the carrier gas is not more than 20 NQ/kg of the desulfurizing agent.
The term "doomed lime", as used in the present application, denotes a mixture of fine calcium carbonate and carbon precipitated by a chemical reaction from .

~L~2~;32~

an aqueous solution or suspension. For example, it is a mixture of calcium carbonate and carbon occurring as a by-product in the production of dicyandiamide from calcium cyanamide or Thor from calcium cyanamide.-The mixture of calcium carbonate and carbon obtained in the production of dicyandiamide from calcium cyanamide is preferred. Dicyandiamide is produced by reacting an aqueous suspension of calcium cyanamide with carbon dioxide gas. The by-product doomed lime, a filtration residue, generally contains 70 to 90% of calcium carbonate, 5 to 15% of carbon and impurities such as iron oxide, aluminum oxide and silicon oxide. It is a very fine mixture of calcium carbonate and carbon. The particle size distribution of such doomed lime is as shown in Examples l and 2 given hereinafter. Prior to the present invention, no process has been known to obtain quick lime powder having excellent gas transportability and an excel-lent ability to desulfurize molten iron by calcining such a finely divided mixture of calcium carbonate and carbon.
Thus, the present invention also provides a desulfurizing agent comprising quick lime powder which is obtained by calcining doomed lime and has excellent gas transportability and a desirable chemical composition, and exhibits very much reduced variations in quality within a given lot. According to this invention quick lime powder having an excellent ability to desulfurize molten iron can be produced in quantities at low cost on an industrial scale.

, ~2~2~3;~

The process and apparatus for fluidized calcina-lion and the desulfurizing agent of this invention will now be described in detail.
The heat medium used in the fluidized calcination of doomed lime in accordance with this invention is a non-combustible infusible solid medium incapable of acting as a binder. Examples include quick lime, silica sand, alumina-silica sand, clinker, gypsum particles, feldspar, pottery stone, agalmatolite, zircon, petalite, commute, Malta, cordierite, solemnity, keynote, andalusite, luminous shale, calcium silicate compounds, refractory bricks, metal powders, metal oxide powders and glass powder.
Quick lime is especially preferred.
The heat medium forms a fluidized layer, and provides the introduced doomed lime with an amount of heat required for the reaction. It also serves to prevent the starting doomed lime from flying away from the fluid-iced bed before its calcination is completed. In order to ensure its actions mentioned and calcite the starting doomed lime well and in consideration of the possible bumping phenomenon of the fluidized layer, the heat medium should have such a particle size distribution that the proportion of particles having a particle diameter of 0.1 mm to 2.5 mm is at least 70% by weight, preferably at least By% by weight, based on the total weight of the medium. Desirably, particles having a particle diameter of 0.2 to I mm, preferably 0.25 mm to 0.5 mm, occupy at least 70% by weight preferably at least 80%

3~3 by weight, of the entire heat medium If the particle diameter of the heat medium exceeds 2.5 mm, it is frequent-lye impossible to obtain quick lime powder which is uniform-lye calcined. If it is smaller than Al mm, the particles of the medium will be scattered.
Good results tend to be obtained when the start-in doomed lime is fed into the fluidized layer formed of the heat medium in an amount 0.1 to 5 times, preferably 0.3 to 2.5 times the weight of the heat medium per hour.
If the amount of the starting Damon lime exceeds 5 times the weight of the heat medium, it tends to be non-uniformly calcined. If it is less than 0.1 times the weight of the heat medium, hard calcination occurs. As a result the reactivity of the resulting quick lime is reduced, and the productivity is reduced. The suitable height of the fluidized layer is at least 0.5 m, preferably 1.0 m to 3.0 m.
Depending upon the type of the heat medium, the type of a fuel used, the operating conditions, etc.
the heat medium may be agglomerated with time and increase in size and density. As a result, the height of the fluid iced layer gradually decreases, and the quality of the calcined quick lime is reduced (for example, the content of Cook increases. When the agglomeration ox the heat medium and the decrease of the height of the fluidized layer occur, it it preferred to remove a part of the heat medium into an air separator from the bottom of the fluid-iced bed through a withdrawing pipe either intermittently or continuously, classify it, return fine particles to the calcination furnace, discard the coarser particles, and feed a fresh supply of the heat medium in an amount core-sponging to the discarded coarser particles either inter-mittently or continuously.
By limiting the particle diameter of the heat medium to the above-specified range and the amount of the starting doomed lime to be introduced to the above-specified range with respect to the amount of the heat medium, it has become possible to effectively calcite the doomed lime, which is an assembly of ultra fine particles, to quick lime powder on a fluidized bed of the heat medium. As a result, while the calcination time required in the technique disclosed in the above-cited Japanese Laid-Open Patent Publication No. 50414/1979, it can be shortened in accordance with the present invention to only less than about 1 minute, and thus, a surprisingly marked increase in productivity has been achieved by the present invention.
The space velocity of the burnt gas should be within the range of 0.8 to 3.0 m/sec, preferably 1.5 to

2.5 m/sec., in order to obtain quick lime powder of good quality.
The "space velocity of a burnt gas", as used in this application, is obtained by dividing the total amount ~m3~hr) of gases (ego, air and carbon monoxide) fed to the calcination furnace and expanded as a result of being heated to a given furnace temperature (e.g., 1000C) by the cross sectional area (my) of the fluidized bed in the furnace and converting the quotient mar into an m/sec unit.
If the empty column velocity is less than 0.8 m/sec., the quick lime powder obtained tends to become hard as a result of over-burning and decrease in desulfur-icing ability. If it is higher than 3.0 m/sec., the starting material becomes incompletely calcined and the uncalcined portion increases. Thus, the space velocity should be within the aforesaid range.
In order to produce an especially good calcining effect and to obtain quick lime powder having good gas transportability and good desulfurizability, the residence time of the starting material in the fluidized layer is preferably 20 to 60 seconds, especially 30 to 50 seconds.
If the residence time is longer than 60 seconds, hard calcination cover-burning increases and the desulfurizing ability of the lime powder decreases. If it is less than 20 seconds, calcium carbonate remains in the resulting lime powder to reduce its desulfurizing ability.
Heat sources for calcination include gaseous fuels such as carbon monoxide, natural gas, propane and city gas, liquid fuels such as heavy oils and solid fuels such as coke powder. Solid carbon contained in an amount of 5 to 15% in the starting doomed lime can also be effectively utilized as a solid fuel. Diamlde lime collected by a bag filter (shown at 23 in Figure 2) in the drying step of the starting doomed lime is , . . .

I

especially suitable for use as a heat source in the present invention because it contains 20 to 45% of carbon.
Generally, in a fluidized calcination process, oxygen required for complete burning of such a fuel is secured by the supplying of air. In the present invention, it is preferred to carry out calcination in an oxidizing atmosphere. For this purpose, the amount of oxygen in the air is desirably 1.05 to 1.5 times, preferably 1.15 to 1.25 times, the amount of oxygen required for complete burning of the fuel. It has been found that when doomed lime is calcined in the presence of an excessive amount of oxygen as specified above, a significant increase in desulfurizability is observed (see, for example, Japanese Patent Application No. 61,261~1980). No reason has been able to be assigned to this phenomenon, but one possibility is that it is due to the difference in the micro structure of Coo crystals.
The calcining temperature may generally be above the temperature at which calcium carbonate is decomposed to quick lime. Good results are obtained when the calcining temperature is in the vicinity of 900C to 1100C.
Another feature of the fluidized calcining pro-cuss of this invention is that by changing the calcination conditions, particularly the residence time and the space velocity, calcium carbonate can be included, as required, in the quick lime powder. Such quick lime powder has a Cook content of O to 30%, preferably 2 to 30%, especially preferably 7 to 25%, an exhibits excellent gas ~22~3~

transportability and good desulfurizability particularly in a torpedo ladle. It has not been entirely clear, however, why the CaC03-containing quick lime powder obtained my the present invention has both good gas trays-portability and a good desulfurizing ability in a torpedo.
In an especially preferred embodiment of this invention, the starting wet doomed lime is dried by hot air issued from a cyclone. Doomed lime as a by-product of the production of dicyandiamide is generally obtained after filtration as a cake having a water content of 20 to 40%. The product withdrawn from the fluidized calcination furnace in accordance with this invention together with hot air is collected by a cyclone to an extent of about 90%. By using the hot air containing the remainder of the product for the drying of the starting doomed lime, the heat energy can be effectively utilized, and the particulate product carried by the hot air can be very effectively collected in a doomed lime recovery step, particularly by a bag filter. It is recycled together with the starting material for effective reuse.
One specific embodiment of the process of this invention is described below with reference to the accompanying drawings.
With reverence to Figures 1 and 2, the starting doomed lime and a heat medium are fed prom a hopper 2 or a hopper 2' into a calciantion furnace 1 by such a method as a pneumatic transporting method or a mechanical trays-porting method using a screw feeder, etch A fuel sent

3~3 from a fuel tank 3 is burnt at a burner opening 4. Air comes from a filter 6 and flows from the bottom to the top of the furnace 1 through a porous plate 5 or a plate 5 having a plurality of nozzles provided therein. Quick lime obtained by calcination in the furnace 1 comes out from the top of the furnace and passes through a hot air pipe 7 and is mostly collected by a cyclone 8. The collected quick lime is sent to a product hopper 10. Hot air from the cyclone 8 while carrying some fine particulate product is conducted to a flash dryer 21 for the starting wet doomed lime through a hot air pipe 9. The starting undried doomed lime is fed into the hot air pipe 9 from a hopper 20. The dried doomed lime is passed through a duct 22 and mostly collected by a cyclone 8'. The remaining fine doomed lime and the aforesaid particulate product (Coo) are collected by a bag filter 23 and stored in the hopper 2.
When the heat medium becomes agglomerated with time and increases in particle diameter and density, it is desirable to withdraw a part of the heat medium intermittently or continuously from a withdrawing pipe 24 and sent to an air separator 25 from the bottom of the fluidized bed. The withdrawn heat medium is classified by the air separator, and finely divided particles of the heat medium are returned to the calcination furnace 1 through a recycle pipe 27. Coarser particles are disk charged from a. withdrawing pipe 26. A fresh supply of the heat medium in an amount corresponding to the weight ~2~3~3 of the coarser particles of the heat medium is intermittent-lye or continuously fed into the calcination furnace 1 from a hopper 2'. In this way, the particle size distribution of the heat medium and the height of the fluidized bed of the heat medium can be very easily controlled to prude-termined ranges. Consequently, a product (Coo) having a fixed level of quality (e.g., the content of Cook) with much reduced variations can be obtained.
Figures 1 and 2 show examples of a basic apparatus used to carry out the process of this invention.
In practice, it is possible to use various heat exchangers for an increased heat efficiency, or a plurality of fluidized layers, or to construct the apparatus in a multiplicity of units.
Figure 3 shows an example in which a plurality of jet openings 11 directed toward the center of the furnace 1 are provided in the furnace 1 in order to perform a pneumatic injecting supplying method for preventing localization of the starting doomed lime within the furnace.
The provision of two or more material injecting openings is preferred in the fluidized calcination of doomed lime which is an aggregate of very fine particles.
It is especially preferable in the case of supplying a mixture of doomed lime and a solid fuel such as coke powder to the furnace because a more uniform calcining effect can be achieved.
The desulfurizing effect of the desulfurizing ~2~2~

agent of this invention can be improved by incorporating various conventional desulfurizers and desulfurization aids, examples of which include calcium carbide, calcium cyanamide, fluorspar, cruelty, the oxides, hydroxides and carbonates of sodium, magnesium and aluminum, calcium hydroxide and carbonate, carbonaceous materials (e.g., graphite, lime, coke, petroleum coke and charcoal), powders of synthetic resins, compounds of a component capable of liberating water or hydrogen in the desulfuriza-lion system, and doomed lime.
The following Examples illustrate the present invention Gore specifically.
Examples 1 and 2 _ Calcination of doomed lime:-A fluidized calcination furnace of the type shown in Figure 1 having an inside diameter of 500 mm and a height of 3000 mm was used. Quick lime (85% by weight) having a particle diameter of 0.25 to 0.5 mm was used as a heat medium. While maintaining the temperature of the inside of the furnace at 1000C, doomed lime was calcined under the conditions shown in Table 2, and the resultant lime powder was obtained by means of a cyclone.
Table 1 summarizes the chemical composition and particle size distribution of the doomed lime used.

31 ~2~323 Table 1 . . . . . . .__. ..
Chemical composition (wt.%) Particle size distribution (it.%) F assay 85 above 61 2 C 10 61 - 46 0.5 Sue 1.8 it - 35 30 23 1.3 35 - 23 u 34 Foe 0.8 23 - 10 27 Moo 0.7 below 10 6.5 Others 0.4 .~.. , . . . _ . _ . . .

Table ?
.__ . Calcining conditions Example example 2 ___ __ . , __ _ --- ----- I
1) Amount of Coo as a heat medium (kg) 100 100 2) Amount of doomed lime fed (kg/hr) 100 100 3) Amount of air fed (N m3/hr) 201 241

4) Amount of oxygen in the air (tummies*) 1.21.25

5) Amount of CO gas fed (N m3/hr) 30 40

6) Space velocity (mmJsec) 1520 1850

7) Residence time (sea ) _____________ 30 (*): Times the amount of oxygen required for complete burning of the fuel.

~32~
_ 16 -The chemical composition and particle size disk tribution of the quick lime powder obtained in each of these examples are shown in Table 3.

Table 3 Example 1 Example 2 Jo __ _ I..._ Coo 88.9 70.6 Cook 2.5 22.0 c Sue 3.5 3.1 03 I 2.2 o Moo 1.3 1.1 c o Others 1.4 1.0 . _ , .. .. _ ., ___ above 61 1.5 2 o 46 - 35 24 23 _ below 10 2.5 _ _ . . .
5 Examples 3 and 4 and Coy Example 1 , _ The desulfurizing ability and gas transport-ability of the quick lime powders obtained in Examples 1 and 2 and quick lime for comparison were examined.

By using the blowing device described in Japanese Laid Open Patent Publication No. 31518/1974, each of the quick lime powders shown below was blown through a lance with dry nitrogen gas as a carrier gas at a blowing speed of 80 to 150 kg/min. into a torpedo 3L~2~32~

ladle having a capacity of 350 tons and containing 300 to 350 tons of molten iron having a sulfur content of 0.035 to 0.039% to desulfurize the molten iron.
The results are shown in Table 4.
The quick lime powders used were as follows:
1) Quick lime Dull: the quick lime powder obtained in Example 1 2) Quick lime DL2: the quick lime powder obtained in Example 2 3) Quick lime * : Obtained by calcining doomed lime at 950C for 60 second using nitrogen gas (85% by weight of particles having a particle diameter of less than 100 and described in Calcination No. 4, Example, Table 1 of the specification of Japanese Laid-Open Patent Publication No. 86417/1979.
The various terms used in Table 4 have the following meanings.
(a) Unit consumption The quotient obtained by dividing the weight (kg) of the quick lime powder blown into the molten iron by the weight (tons) of the molten iron.
by Carrier gas/quick lime powder The ratio of the flow rate (NQ/min.) of the 32~

carrier gas to the blowing speed (kg/min.) of the quick lime powder.
(c) Blowing pressure The pressure (kg/cm2) of the carrier gas connected to the discharging portion when the quick lime powder was carried by the carrier gas and blown into the molten iron (corresponding to the lower pressure Pi connected to the discharge opening in Figure 2 of the specification of Japanese Laid-Open Patent Publication No. 31518/1974).
(c) Desulfurizing ability Sluice ( was ) Unit consumption Sloth sulfur content (%) of the molten iron before desulfurization S2=the sulfur content (%) of the molten iron after desulfurization arative En 2 . . .
Desulfurizing agent:-Molten iron was desulfuriæed under the same conditions as in Examples 3 and 4 and Comparative Example except that quick lime having a Coo content of 95% by : weight of Coo and containing 50% by weight of particles with a particle diameter of 100 I, a raw material for industrial carbide, was used. Blowing of the quick lime was impossible even when the carrier 6as/quick lime powder ratio was set at more than 70 NQ/kg.

~2~3~3 Table 4 demonstrates that the desulfurizing agents comprising the quick lime powders obtained in Examples 1 and 2 showed excellent desulfurizing ability and gas transportability.

_ . _ __ S I q O o ox - ._ __ _ I N
ED Lo ox C 3 3 3 o o TV g O O O

3 U 0 CO o m I
31 Lowe Eye I 3 I, d I CO

owe o ___ .. . _ - _ _ ^
Jo I . Jo l ---

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for producing finely divided quick lime powder in a fluidized bed, which process comprises:
maintaining a fluidized bed of a heat medium having a particle diameter of 0.1 to 2.5 mm in a calcination furnace;
feeding diamide lime into the fluidized bed, the amount of the diamide lime being 0.1 to 5 times the weight of the heat medium per hour;
burning a fuel thereby calcining the fed diamide lime with-out substantially nodulizing in the fluidized bed such that the burnt gas flows in the furnace at a space velocity of 0.8 to 3.0 meters/sec; and recovering the resultant calcined lime powder carried over together with the hot burnt gas.

2. The process according to claim 1, wherein the resi-dence time of the diamide lime in the fluidized bed is 20 to 60 seconds.

3. The process according to claim 1, wherein the calci-nation is carried out in an oxidizing atmosphere.

4. The process according to claim 1, 2 or 3, wherein the heat medium is quick lime.

5. The process according to claim 1, 2 or 3, wherein the starting diamide lime is dried with hot air from a cyclone prior to being fed into the calcination furnace.

6. The process according to claim 1, 2 or 3, wherein a portion of the heat medium is withdrawn from the bottom of the fluidized bed, and a fresh supply of the heat medium in an amount corresponding to that withdrawn is fed into the flui-dized bed to control the particle size disribution of the heat medium and/or the height of the fluidized bed of the heat medium.

7. The process according to claim 1, 2 or 3, wherein the diamide lime is fed together with a carrier gas into the calcination furnace through at least two pneumatic injection openings provided in the furnace so as to be directed toward the center of the furnace.

8. A process for producing finely divided quick lime powder, which process comprises:
maintaining a fluidized bed of a heat medium in a calci-nation furnace adapted for a fluidized bed calcination, wherein the heat medium is a non-combustible infusible solid medium incapable of acting as a binder and at least 70% by weight of the heat medium has a particle diameter of 0.2 to 2.0 mm;
continuously feeding diamide lime into the fluidized bed wherein the diamide lime is in the fine powdery mixture form containing 70 to 90% by weight of calcium carbonate and 5 to 15%
by weight of carbon and the amount of the diamide lime is 0.3 to 2.5 times the weight of the heat medium per hour;
continuously burning a fuel thereby calcining the fed di-amide lime in a fluidized bed without substantially nodulizing it such that the burnt gas flows in the furnace at a space velocity of 0.8 to 3.0 meters/sec; the residence time of the diamide lime in the fluidized bed is 20 to 60 seconds; and the calcined lime is entrained from the top of the furnace into an outlet with the burnt gas; and recovering the resultant calcined lime powder, at least about 90% by weight of which has a particle diameter of 10 to 60µ and which is carried over from the top of the furnace to-gether with the burnt gas.

9. A process according to claim 8, wherein at least about 90% by weight of the fed diamide lime has a particle diameter of 10 to 60µ.

10. A process according to claim 9, wherein oxygen and a gaseous fuel are fed into the furnace in such an amount that oxygen is 1.05 to 1.5 times of the amount required for complete burning of the fuel whereby the calcination is carried out in an oxidizing atmosphere.

11. A process according to claim 10, wherein oxygen is supplied in the form of air.

12. A process according to claim 10 or 11, wherein car-bon monoxide is used as the gaseous fuel.

13. A process according to claim 11, wherein quick lime is used as the heat medium.

14. A process according to claim 10, 11 or 13, wherein the calcination conditions are selected such that the calcined lime powder contains up to 30% by weight of calcium carbonate.

15. A process according to claim 10, wherein the calcination conditions are selected such that the calcined lime powder contains 2 to 30% by weight of calcium carbonate.

16. A process according to claim 1, 2 or 3, wherein at least about 90% by weight of the fed diamide lime has a particle diameter of 10 to 60µ.

17. An apparatus for calcining diamide lime in a fluidized bed to produce finely divided quick lime, which comprises:
a. a furnace, at least the fluidized bed calcination section of which is of a cylindrical configuration, and which is adapted to form therein when in use a fluidized bed consisting of a heat medium with a particle diameter of 0.1 to 2.5 mm which is a non-combustible infusible solid medium incapable of acting as a binder in order to calcine in the fluidized bed diamide lime about 90% by weight of which has a particle diameter of 10-60µ to a quick lime about 90% by weight of which has a particle diameter of 10-60µ in a fluidized state;
b. a plurality of means disposed at the side of said fluidized bed section for feeding said diamide lime into said fluidized bed toward the center of said bed pneumatically so that the amount of the diamide lime is 0.1 to 5 times the weight of the heat medium in said bed per hours;
c. a means for supplying an oxidative fluidized gas to the lower part of said fluidized bed such that the space velocity of a burnt gas may be maintained at 0.8 - 3.0 m/sec;
d. a fuel supplying means disposed at the side of said fluidized bed section for causing the burning with said oxidative fluidized gas in said fluidized bed; and e. a means for withdrawing said quick lime brought to the upper part of said fluidized bed by means of the burnt gas by carrying-over from the top of the fluidized calcination furnace.

18. The apparatus according to claim 17 wherein the fuel supplying means is a gas burner situated in said fluidized bed.

19. The apparatus according to claim 17 or 18, which is further provided a means for withdrawing the heat medium at the bottom side of the fluidized bed and a means for supplying a new heat medium in an amount corresponding to said amount withdrawn to control the particle diameter of the heat medium and the height of the fluidized bed.