JPH0118014B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention produces quicklime powder with excellent gas transportability, and furthermore, quicklime powder with excellent hot metal desulfurization properties, by fluidized roasting diamide lime, which can be produced continuously at low cost and in large quantities with easy operation and simple equipment. This article relates to a method of roasting diamide lime that can be produced. More specifically, in the fluidized roasting method for diamide lime, a heating medium with a particle size of 0.1 to 2.5 mm is used, and the raw material, precipitated calcium carbonate, is heated to
Supply 0.1 to 5 times the amount, and the superficial velocity of combustion gas is 0.8 to 5 times.
The present invention relates to a method for roasting precipitated calcium carbonate, which is 3.0 m/sec and is characterized in that calcined quicklime powder is taken out by a carry-over method. Demand for quicklime powder with excellent gas transportability has increased rapidly in recent years. However, conventional quicklime powder has poor gas transportability, and therefore, despite its low cost, its industrial use has been severely restricted. This gas transportability gives quicklime powder a fatal drawback in that it decreases in inverse proportion to the increase in specific surface area when trying to improve chemical reactivity by increasing the specific surface area by pulverizing quicklime powder. Ta. An example of an application that requires an increase in the specific surface area of lime powder is the quicklime powder injection desulfurization method for hot metal, which has been rapidly developed in recent years (e.g., JP-A-Sho).
55-110712). In this case, the quicklime powder is blown into the molten hot metal using a carrier gas, together with an auxiliary agent if necessary, and the sulfur content in the hot metal is reacted with the quicklime powder and transferred to the slag as calcium sulfide and removed. In such applications, the gas transportability of quicklime powder has an extremely important effect on desulfurization efficiency. For this reason, an attempt to improve the gas transportability of quicklime powder has been proposed, for example in the above-mentioned Japanese Patent Application Laid-Open No. 110712/1982, in which the addition of approximately 0.5% silicone oil, which is extremely expensive compared to quicklime powder, has been proposed. This is a situation. The inventor of the present application has discovered that adding diamide lime to quicklime powder has an extremely significant effect as a means of improving the gas transportability of quicklime powder without the need for the addition of such expensive silicone oil ( Japanese Patent Publication No. 55-61261). Subsequently, as a result of a series of studies, we found that quicklime powder containing diamide lime and fluidized roasting of diamide lime under specific conditions, preferably fluidized roasting in an oxidizing atmosphere, achieved the best desulfurization properties. This discovery led to the present invention. On the other hand, an attempt was made to obtain a desulfurizing agent made from quicklime made from diamide lime.
No. 50414, which discloses that the desulfurization properties of quicklime are improved when diamide lime is calcined in an external heat treatment furnace (static type) in a non-oxidizing atmosphere together with an additional carbon substance. There is only a statement that an oxidizing atmosphere is undesirable because it reduces the activity of quicklime. The present invention provides a fluidized roasting method for obtaining quicklime powder from diamide lime, which has excellent gas transport properties and extremely excellent desulfurization properties as a raw material for a hot metal desulfurization agent composition. When desulfurizing hot metal, it is desirable to inject the desulfurizing agent into the hot metal with a relatively high solids concentration and small fluctuations in concentration, in order to lower the hot metal temperature and prevent splashing. It will be done. Such a blowing method is specifically disclosed, for example, in JP-A-49-31518, and the quicklime powder produced by the roasting method of the present invention has a high solid content of 20Nl/Kg desulfurization agent or less. It shows excellent gas transport properties even at different concentrations. In the present specification, "diamide lime" is used to mean a mixture of fine calcium carbonate and carbon that is precipitated from an aqueous solution or aqueous suspension by a chemical reaction. For example, when producing dicyandiamide from lime nitrogen, It refers to a mixture of calcium carbonate and carbon that is produced as a by-product when producing thiourea, etc. from lime nitrogen, etc., but preferably a mixture of calcium carbonate and carbon obtained when producing dicyandiamide from lime nitrogen is optimally used. . Dicyandiamide is produced by reacting carbon dioxide gas with a lime nitrogen aqueous suspension, and the by-product diamide lime, which is the excess residue at that time, is generally calcium carbonate 70 to 90%
%, carbon 5 to 15%, and other impurities such as iron oxide, aluminum oxide, and silicon oxide, and is a mixture whose main components are extremely fine calcium carbonate and carbon. The particle size distribution of such diamide lime is, for example, as described in detail in Examples 1 and 2 below. In this way, diamide lime is a fine powder mixture whose main components are extremely finely divided calcium carbonate and carbon, and this is calcined into quicklime powder that has excellent gas transport properties and also has excellent hot metal desulfurization properties. A firing method aimed at obtaining this was not yet known. Thus, the present invention provides quicklime powder by roasting diamide lime, which has excellent gas transport properties, has a desirable chemical composition, and has very little variation in quality within a lot, thereby making it possible to desulfurize hot metal. It has become possible to industrially produce quicklime powder, which has excellent desulfurization properties as a chemical agent, at low cost and in large quantities. Details of the fluidized roasting method of the present invention will be explained below. As the heat medium used in the fluidized roasting method of diamide lime of the present invention, a non-binder, non-combustible, infusible solid medium is used, such as quicklime, silica sand, alumina silica sand, clinker, gypsum granules, feldspar, Pottery stone, Rouseki, Ball stone, Zhang stone, Zircon,
Examples include betalite, siyamoto, mullite, cordierite, sillimanite, kyanite, andalyusite, shale, calcium silicate compounds, refractory bricks, metal powders, metal oxide powders, glass powders, etc., but preferred are Quicklime is preferably used. The heat transfer medium forms a fluidized bed and provides the introduced raw material diamide lime with the amount of heat necessary for the reaction, and at the same time, the raw material diamide lime jumps out of the fluidized bed before it has been sufficiently roasted. It acts to prevent such things. In order to fully achieve these effects and perform good roasting of the raw material diamide lime, the particle size of the heating medium must be entirely within the range of 0.1 mm to 2.5 mm, taking into account the air boiling phenomenon in the fluidized bed. at least 70 of the medium
It is necessary to account for at least 80% by weight, preferably at least 70% by weight, preferably at least 80% by weight, preferably 0.2 mm to 2.0 mm, particularly preferably 0.25 mm to 0.5 mm. . When the heating medium is too large (more than 2.5 mm), it often happens that uniformly fired quicklime powder cannot be obtained, and
If it is too small (less than 0.1 mm), it is not preferable because media particles will scatter. The feed of the raw diamide lime into the fluidized bed formed by the heating medium is preferably 0.1% of the weight of the heating medium.
Good results tend to be obtained when the amount is applied 5 times to 5 times/hour, more preferably 0.3 times to 2.5 times/hour. If the amount is too high (more than 5 times/hour), there is a strong tendency for uneven roasting, and if it is less than 0.1 times/hour, the reactivity of the quicklime will decrease, and productivity will also decrease. Undesirable. The height of the fluidized bed is 0.5m
It is preferably 1.0 m to 2.0 m. In this way, as mentioned above, by setting the particle size of the heating medium within a specific range and by limiting the amount of raw diamide lime introduced to a specific range relative to the amount of heating medium, it is possible to form an aggregate of extremely fine particles for the first time. It has become possible to effectively fluidize and roast certain diamide lime into quicklime powder. As a result, the above-mentioned Japanese Patent Application Laid-open No.
The roasting time of 30 to 120 minutes in No. 50414 can be shortened to only about 1 minute in the present invention, and the remarkable improvement in productivity is surprising. Further advantages of the invention will become apparent from the description below. In addition, the superficial velocity of the hot air combustion gas needs to be within the range of 0.8 to 3.0 m/sec, preferably 1.5 to 2.5 m/sec, in order to obtain good quicklime powder.
A sky velocity of seconds is desired. In this specification, the superficial velocity of combustion gas means that the gas (e.g., air, carbon monoxide, etc.) supplied to the fluidized column furnace is heated to a predetermined furnace temperature (e.g., 1000°C) and expanded. The quotient (m/hr) obtained by dividing the total supply amount (m ³ /hr) by the cross-sectional area of the fluidized bed (m ² ) is converted into units of m/sec. If the speed is too slow (less than 0.8 m/sec), the quicklime powder will often tend to harden and the desulfurization performance will decrease, which is undesirable. On the other hand, if the speed is too slow (more than 3.0 m/sec), it may cause insufficient roasting (contamination of unfired products). ), and since calcium carbonate is likely to remain in the interior in the candy-like form of a manju, the above range of the superficial velocity of the hot air combustion gas is recommended. In order to achieve a particularly good roasting effect and to obtain good desulfurization properties as well as gas transport properties, the residence time in the fluidized bed is preferably 20 to 60 seconds, especially 30 seconds. Residence times in the range of ~50 seconds are desirable. If the residence time is too long (more than 60 seconds), it is undesirable because sintering will become stronger and the desulfurization performance will be lowered, and if the residence time is too short (less than 20 seconds), calcium carbonate will remain and the desulfurization performance will be lowered, which is undesirable. . Gaseous fuels such as carbon monoxide, natural gas, propane, and city gas, liquid combustion such as heavy oil, and solid fuels such as coke powder are also well used as the roasting heat source. 5～15
% of solid carbon can be effectively used as a solid fuel, and a combination of two or more of the above fuels can also be effectively used. In the fluidized torrefaction method, the oxygen necessary for complete combustion of the fuel is generally secured by supplying air, but in the present invention, it is preferable to perform the torrefaction in an oxidizing atmosphere. For this purpose,
It is desirable that the amount of oxygen in the air is 1.05 to 1.5 times, preferably 1.15 to 1.25 times, the amount of oxygen required for complete combustion of the fuel. It has been found that when diamide lime is roasted in this range of oxygen content, that is, with a specific excess of oxygen, there is a clear improvement in desulfurization properties, although the reason is unknown. (For example, the patent application filed in 1983-
No. 61261 (see Japanese Patent Application Laid-open No. 158827/1983). CaO
It is also possible that this is due to differences in the microstructure of the crystals. The temperature of fluidized roasting generally needs to be kept above the temperature at which calcium carbonate decomposes into quicklime.
Temperatures around 900°C to 1100°C are associated with good results. Another feature of the fluidized roasting method for diamide lime of the present invention is that calcium carbonate can be added to quicklime powder as needed by changing the above-mentioned roasting conditions, especially the residence time and superficial velocity. can contain. Such quicklime powder, for example, has a _CaCO3 content of 5 to 30%, preferably 7 to 25%, and has good desulfurization properties, especially desulfurization properties in a torpedo ladle, while maintaining excellent gas transport properties. shows.
The reason why the CaCO ₃ -containing quicklime powder according to the present invention has good gas transport properties and torpedo desulfurization properties at the same time is not entirely clear, but at least the candy-like CaCO ₃ of a bun (for example, JP Showa 52
-111812), and it is presumed that this is because CaCO ₃ is mainly present on the surface of quicklime. Next, one embodiment of the method of the present invention will be explained using the accompanying drawings. In FIG. 1, raw material diamide lime and heat medium are both supplied from a hopper 2 to a furnace body 1. As the supply method, a pneumatic transportation method, a mechanical transportation method such as a screw feeder, etc. are appropriately adopted. fuel tank 3
The fuel oil sent from the fuel oil is burned at the burner port 4. Air flows from the filter 6 through a perforated plate or a plate 5 provided with a large number of nozzles, and flows from the bottom of the furnace to the top of the furnace. Most of the quicklime roasted in the furnace body 1 is collected by a cyclone 8 from the top of the furnace through an exhaust pipe 7 and enters a product hopper 10. Exhaust wind is cyclone 8
It is led to a bag filter (not shown) through an exhaust pipe 9, and some of the accompanying quicklime powder is collected. Figure 1 shows the basic equipment in which the present invention is implemented; in reality, various heat exchangers may be used to increase thermal efficiency, several fluidized beds may be used, or a multi-stage system may be used. You can also do it. FIG. 2 shows an example in which a plurality of injection ports 11 are provided in the furnace body 1 toward the center of the furnace body 1 in a pneumatic injection supply system in order to prevent uneven distribution of the raw material diamide lime in the furnace. Furthermore, if necessary, a plurality of injection ports 11' may be provided tilted in the circumferential direction of the furnace body as shown in FIG. It is also suitable to provide multiple injection ports in two stages. Providing two or more raw material supply ports in this way
It is preferable for fluidized roasting of diamide lime, which is an aggregate of fine particles, because a more uniform roasting effect can be achieved especially when a solid fuel such as coke powder is mixed with diamide lime and fed to the furnace body. preferable. The present invention will be specifically explained below using Examples. Examples 1 to 2 Using a fluidized roasting furnace with an inner diameter of 500 mm and a height of 3000 mm shown in FIG. 1 and having a raw material injection port shown in FIG. 2,
Using quicklime with a particle size of 85% by weight from 0.25 to 0.5 mm as a heating medium, diamide lime was roasted at a furnace temperature of 1000° C. under the conditions shown in Table 2, and calcined lime powder was obtained using a cyclone. The chemical composition and particle size distribution of the diamide lime used are those in Table 1.

【table】

【table】

Table 3 shows the chemical composition and particle size distribution of calcined quicklime powder obtained under the fluidized roasting conditions shown in Table 2 above.

[Table] The results of testing the desulfurization performance and gas transportability of the calcined lime powder obtained in Examples 1 and 2 are shown in Reference Examples. Reference Examples 1 to 3 A 350T capacity torpedo ladle filled with 300 to 350T of hot metal with a sulfur content of 0.035 to 0.039% was filled with dry nitrogen gas as a carrier gas using the blowing device described in JP-A-49-31518 as shown in Table 4. Desulfurization was carried out using a lance at a blowing rate of 80 to 150 kg/min. The results are shown in Table 4. The quicklime powder used in Reference Examples 1 to 3 in Table 4 is as follows. (1) (Quicklime) DL1: Calcined quicklime powder obtained in the above Example 1 (2) (Quicklime) DL2: Calcined quicklime powder obtained in the above Example 2 (3) (Quicklime) *: JP-A-54-86417 No. specification,
The diamide lime described in Table 1, Examples, Sintering No. 4 was used as the sintering raw material, and was obtained under sintering conditions of nitrogen gas, 950°C, and 60 seconds. Particle size below 100μ accounts for 85% by weight. The meanings of the terms used in Table 4 are as follows. (a) Basic unit: Weight of quicklime powder injected into hot metal (
Kg)/Weight of hot metal (T) (b) Carrier gas/quicklime powder: Flow rate of carrier gas used (Nl/min)/Blowing speed of quicklime powder (Kg/min)
(c) Blow pressure: Pressure (Kg/cm 2 ) of the carrier gas connected to the discharge part when the quicklime powder is entrained in the carrier gas and blown into the hot metal (Kg/cm ² ) (JP-A-49-
This corresponds to the relatively low pressure P ₃ connected to the discharge hole 4 in FIG. 2 of the specification of No. 31518. (d) Desulfurization performance: S ₁ = Sulfur content in hot metal before desulfurization (%) S ₂ = Sulfur content in hot metal after desulfurization (%) S ₁ −S ₂ (=△S) / Basic unit reference Example 4 The chemical composition of quicklime, the raw material for industrial carbide, is
Desulfurization was carried out under the same conditions as in Reference Examples 1 to 3 above, except that 95% by weight of CaO and 50% by weight of quicklime with a particle size of 100μ or less were used, but carrier gas/quicklime powder was used.
Even if the amount exceeded 70Nl/Kg, it was impossible to inject. As shown in Table 4, the calcined quicklime powders of Examples 1 and 2 obtained by the fluidized roasting method of the present invention exhibited excellent desulfurization performance and gas transportability.

【table】 [Brief explanation of drawings]

FIG. 1 is a principle diagram of the apparatus used in the fluidized roasting method of the present invention, in which 1 is the furnace body, 2 is the raw material hopper,
5 is a perforated plate, and 10 is a product hopper. 2nd~
FIG. 4 is a cross-sectional view of the furnace body, in which numeral 11 indicates a pneumatic material injection port facing toward the center, and 11' indicates a material injection port inclined in the circumferential direction. Figure 4 is the third
The injection port shown in the figure is further provided with two injection ports in opposite directions.

Claims (1)

[Claims] 1. In the fluidized roasting method of diamide lime, 0.1 to
Using a heat medium with a particle size of 2.5 mm particles accounting for at least 70% by weight of the total heat medium, raw material diamide lime is supplied in an amount of 0.1 to 5 times the weight of the heat medium per hour, and the superficial velocity of the combustion gas is 0.8 ~3.0 m/sec, and a fluidized roasting method characterized by taking out the calcined quicklime powder by a carry-over method. 2. The roasting method according to claim 1, wherein the residence time is 20 to 60 seconds. 3. The roasting method according to claim 1 or 2, wherein the roasting is performed in an oxidizing atmosphere. 4. Convey diamide lime from two or more pneumatic injection ports in the center direction of the furnace body, or two or more pneumatic injection ports in the circumferential direction, or a circumferential injection port and two or more pneumatic injection ports in the opposite direction. The roasting method according to any one of claims 1 to 3, in which gas is supplied into a fluidized bed formed by a heat medium in a roasting furnace.