JPS6250409B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a fluidized chlorination process for producing zirconium tetrachloride ( _ZrCl4 ) gas by reacting zirconium oxide (ZrO2) with chlorine in a fluidized bed in the presence of a reducing agent carbon, and in particular, it relates to a fluidized chlorination process for producing zirconium tetrachloride ( _ZrCl4 ) gas by reacting zirconium oxide (ZrO2) with chlorine in the presence of a reducing agent carbon. Concerning improvements in the process of fluidized chlorination of zirconium oxide by combustion. The fluidized chlorination method of zirconium oxide effectively prevents the contamination of impurities such as iron and aluminum chlorides into the produced zirconium tetrachloride, and makes it possible to recover high-purity zirconium tetrachloride.
It is considered a useful method. Fluidized chlorination of zirconium oxide basically involves charging zirconium oxide and reducing agent carbon into a shaft furnace, injecting chlorine from the bottom of the furnace to form a high-temperature fluidized bed, and then releasing the generated zirconium tetrachloride gas from the top of the furnace. It is recovered, introduced into a condenser, and collected as powdered zirconium tetrachloride, and the reaction according to the following formula is involved: ZrO ₂ +C + 2Cl ₂ →ZrCl ₄ +CO ₂ ...(1) ZrO ₂ +2CO + 2Cl ₂ →ZrCl ₄ ＋2CO ₂ ……(2) ZrO ₂ ＋2C＋2Cl ₂ →ZrCl ₄ ＋2CO ……(3) By-product COx becomes CO at high temperature and CO ₂ at low temperature
Therefore, equation (3) requires a high temperature of 1000℃ or higher.
For long-term operation, it is necessary to carry out the reaction at a temperature below 1000℃ in order to suppress the occurrence of ZrO ₂ in the furnace.
It is necessary to carry out fluid salination in reactions (1) and (2) at 1000°C or lower. By the way, in order to advance the above reaction, it is necessary to maintain the fluidized bed at a high temperature, but since the reaction biomaturation by the above reaction is not sufficient, it is necessary to carry out ripening. One of these reheating methods is the electric heating method, which is typified by resistance heating and induction heating methods, but both have practical difficulties in dealing with the material of the equipment against the strong corrosivity of chlorine. There is. The resistance method cannot produce materials suitable for corrosion-resistant electrical heating materials, and the induction method cannot produce materials suitable for structural materials that prevent chlorine leakage. The induction method has been put to practical use by making the furnace tube an integral structure of graphite and making the graphite function as an induction heating material, but due to manufacturing limitations of the graphite furnace tube material, the capacity per furnace is small and it is not industrially possible. This method has serious drawbacks, such as the need to install several furnaces in parallel, and the unavoidable wear and tear of the furnace cylinder material due to reaction with oxides and abrasion. Furthermore, the electrothermal method is not an advantageous method from the viewpoints of equipment cost, maintenance cost, and power cost. Another reheating method is the excess carbon combustion method.
This is a method in which carbon is additionally included in the charge other than for the reduction reaction, oxygen is blown into the furnace together with chlorine gas from the bottom of the furnace, and the reaction heat is used for heat supplementation. This method is very advantageous compared to the above electrothermal method in terms of equipment and temperature control. However, there are many problems that need to be overcome when this excess carbon combustion method is applied to actual operations, and zirconium oxide fluidized chlorination operation using oxidation using the excess carbon combustion method has not been carried out satisfactorily for a long time. do not have. The excess carbon combustion type fluidized chlorination method is based on the assumption that a fluidized bed temperature of 1000°C or lower is used, since as mentioned above, ZrO ₂ buildup will adhere to the furnace wall at temperatures above 1000°C, making long-term operation difficult. If that happens
Practical chlorination efficiency cannot be obtained unless the particle size of ZrO ₂ and C is reduced to fine powder. On the other hand, _ZrO2
When C is made into fine powder, the cylinder velocity cannot be increased to prevent the fine powder from scattering, and if the free board is made large to prevent carry over, the heat dissipated from the furnace body increases.The fine powder sticks to each other and becomes extremely There is a tendency to form soft pseudo-particles (2-3 mmφ), which causes many problems such as difficulty in fluidization. Oxygen injection also presents significant disadvantages in furnace operation. First, grain welding and flow disturbances occur due to the generation of heat spots. In other words, the local and rapid combustion heat of O ₂ immediately after injection should be thermally diffused throughout the fluidized bed by active fluidized mixing. That is, as a result of weakening the thermal diffusion force, grain welding and flow disturbance due to local overheating are likely to occur. Second, in the local O ₂ combustion zone directly above the gas injection baffle plate, O ₂ is converted into ZrO ₂ and C
It is easy to selectively burn out only C from the mixed fluidized bed, oxidize chloride, and create oxide pseudoparticles (agglomerates). In this way, improvements have been made to ensure long-term efficient operation under conflicting conditions such as regulating the fluidized bed temperature, ensuring a predetermined chlorination rate, making the charging material finer, and the adverse effects of oxygen injection. There is a lot of room left. For example, in Japanese Patent Publication No. 36-21302, a binder is added to zirconium oxide and carbon powder, the mixture is molded, this is fired to make it porous, the fired body is crushed and sifted, and the resulting material is used as a charge. It states that it is used. However, this method requires a large amount of equipment and cost for pretreatment because it requires kiln calcination, and it is difficult to control the operation to maintain the ratio of zirconium oxide and carbon. There is a need to develop a method that does not require this kind of charring. As a result of extensive studies on the mixing state, heat balance, side effects of O ₂ injection, fluidization state, etc. in fluidization, the present inventor has hereby proposed a fluidized chlorination operation using excess carbon combustion that significantly reduces the above-mentioned drawbacks. successfully established. As a general condition for fluidized chlorination, it is important that the C grains be present in close proximity to the _two ZrO grains, and it is necessary to obtain a complete mixed state in terms of both solid-solid mixing and fluidized mixing in gas contact. be. The effect of solid-solid mixing increases dramatically as the particle size decreases due to the specific surface area and proximity effect. On the other hand, the fluidization mixing in gas contact deteriorates as the powder becomes finer due to a decrease in fluidization energy and agglomeration between fluids, which causes fluidization problems. As a charge for fluidized chlorination that balances these conditions, it is very suitable to use ZrO ₂ and C particles prepared as fine particles that have been kneaded and summed to a completely mixed state. I discovered something.
Since the fine particles have strong cohesiveness, a large number of agglomerated particles containing a mixture of ZrO ₂ and C fine particles are formed during kneading. Such mixed agglomerates can be fluidized. In this way, by utilizing the cohesive properties of fine particles, ZrO ₂ and C
Both solid-solid mixing and fluid mixing can be measured at once. It has been found that adding coarse C grains to the above-mentioned fine powder mixed charge also has the function of controlling the chlorination state and stabilizing the flow of the fine powder, which is actively coagulating. It is necessary to keep the amount of oxygen blown into the furnace as small as possible in order to minimize the harmful effects of oxygen. If an active fluidized bed containing fine and coarse C particles can be formed, the amount of oxygen required for heat supplementation can be minimized. Furnace materials should be selected to maximize the heat insulation effect of the furnace. A stable and active fluidized bed is formed by ejecting gas from the porous distribution plate at high speed and establishing a fluidizing gas velocity (cavity velocity) sufficient to obtain the desired fluidization. The fine powder deposited on the dispersion plate is crushed and fluidized by the high-speed gas jet. Under these considerations, the present invention basically provides a method for fluidized chlorination of zirconium oxide using an excess carbon combustion method in a shaft type chlorination furnace.
A mixture of finely powdered zirconium oxide and finely divided carbon is thoroughly mixed, and then coarse grained carbon is added to the mixture in an amount of 10 to 40% based on the total weight ratio of the carbon constituting the fluidized bed. Provided is a chlorination method characterized by forming an active fluidized bed by blowing chlorine gas and oxygen gas through a nozzle hole at high speed. The present invention will be explained in detail below. FIG. 1 schematically shows a chlorination furnace in which the present invention is implemented. The chlorination furnace 1 is equipped with a porous dispersion plate 3 at its bottom,
Chlorine gas and oxygen gas are supplied to the lower chamber 4 of the dispersion section. A feeding device 5 for feeding the charge is provided in the center of the furnace. The innermost part of the furnace body is designed to minimize the amount of oxygen blown into the furnace body, to maximize the heat generated by the exothermic reaction, and to minimize the heat dissipated from the relatively large freeboard section 7. It is composed of a brick structure 9, a heat insulating material 10 impermeable to condensable chlorides, and a steel plate 11 covering the outer periphery. For example, the heat insulating material 10 is (1) made of an inorganic material (silicate) that is not easily affected by chlorine gas, and (2) has a closed cell structure that does not lose its heat insulating function due to the penetration of condensable gas. As the material, foamed glass bricks (blocks) or micro balloons such as barite and shirasu balloons can be used. The steel plate 11 is heated at temperatures below 200°C, preferably at 50°C, in order to protect against chlorine gas so as to constitute a completely gas-tight mantle.
It is preferable to maintain insulation between the front and back. The charge forms a fluidized bed in the column 20 in the lower part of the furnace with chlorine gas and oxygen gas blown up from below. The produced zirconium tetrachloride exits through outlet 6. In the present invention, the charge is made by kneading and mixing fine powder, preferably zirconium oxide with a size of 50μ or less, and carbon, and then adding coarse particles, preferably 100 to 1000
The feeding device 5 contains carbon particles with a size of μ.
supplied through. Since the fine powder has an inherent tendency to agglomerate as described above, most of the fine powder forms agglomerated particles in which zirconium oxide and carbon are mixed during kneading. Agglomerated grains apparently behave as a single grain when fluidized, so unlike fine powder grains as they are, they can form an active fluidized bed if appropriate fluidization conditions are applied. In particular, the mixing of coarse carbon has an extremely useful effect in stimulating fluidization and stabilizing the flow of aggregates. Although coarse carbon depends on other flow condition factors, it generally accounts for 10 to 10% of the total carbon that makes up the fluidized bed.
It is desirable to make up 40%. Further, since the reaction rate of coarse carbon is much slower than that of fine carbon, the chlorination state is controlled by a small charging/mixing ratio. As the carbon material, calcined oil coke with few impurities is preferred from the viewpoint of reaction characteristics in chlorination. Chlorine gas and oxygen gas are injected at high velocity through the porous distribution plate. Conventionally, this gas injection speed was selected simply from the viewpoint of uniform gas dispersion, but in the present invention, it is increased to, for example, 90 m/sec because of the role of controlling the fluid particle size by crushing cohesive particles. The high-velocity injection gas crushes and blows up the coarse particles 21 that inevitably accumulate on the dispersion plate, thereby promoting the maintenance of a stable fluidized state up to the upper part of the fluidized bed. To obtain stable flow conditions, the fluidizing gas velocity (void velocity) must be 0.2 to 0.2 at the furnace cross section on the dispersion plate.
Preferably, the speed is 0.8 m/sec. When the fluidized bed 20 is closely observed, it can be distinguished into a layer 22 in which the fluid is actively flowing and a layer 23 in which the fine powder is relatively loosely suspended. Even if the particles in the layer 23 fly out of the fluidized bed, they still remain in the freeboard section 7.
It settles in the inverted cone that connects the fluidized bed and the carrier overflow, thus minimizing the amount discharged as carrier overflow. Since the consumption rate of coarse carbon is much slower than that of fine carbon, it is necessary to adjust the amount of coarse carbon to be supplied in order to maintain the intended coarse carbon mixing rate in the fluidized bed. This can be done by extracting and analyzing samples from fluidized bed formulation sample holes and managing the feedstock accordingly. As a result of small-scale plant experiments, the present inventor found that by changing the chlorination furnace to the configuration shown in FIG. 2, it was possible to further stabilize the flow. Second
In the figures, the same members as in FIG. 1 are designated by the same numbers. The difference between FIG. 1 and FIG. 2 is that in FIG. 2, the fluidized bed formation region is funnel-shaped. It is desirable that the upper diameter of the funnel be 2 to 5 times that of the lower diameter. By doing so, the fluidized bed becomes more stable, and the amount of fine particles flying out from the bed is significantly reduced. Therefore, escape of unreacted raw materials is greatly reduced. As a result of the formation of an active fluidized bed, the amount of oxygen blown can be reduced to 1/4 to 1/3 of the conventional amount, and the adverse effects of oxygen blown are significantly reduced. That is, the generation of heat spots is suppressed by reducing the amount of oxygen and active fluidization, and the generation of oxide aggregates in the local oxyfuel combustion zone 21 is minimized by using fine powder and reducing the amount of oxygen. Fine powder of zirconium oxide can now be easily prepared by many methods proposed by the applicant. Carbon fines are also possible by using fine coke. In this way, fluid chlorination of zirconium oxide can be performed while minimizing the amount of blown oxygen and maximizing the chlorination efficiency. Example 1 First case with fluidized bed diameter of 200φ and freeboard part diameter of 500φ
In a small fluidized fluidized furnace as shown in the figure, zirconium oxide with dimensions of 50μ or less (average 20μ) and carbon of 50μ or less (average 20μ) are thoroughly mixed in advance in a mixer and supplied as a C20-30% mixture. The operation was carried out by adding an average of 500 microns (100 to 1000 microns) of coarse carbon to the furnace so that it accounted for 10 to 40% of the content in the furnace. Blowing gas Cl ₂ 50/min, O ₂ 50/min
min, total 100/min, rectifier plate hole jet speed 90m/
sec, cylinder speed 0.2m/sec, fluidized bed temperature 900~
Under the condition of 1000℃, there was no or trace amount of unreacted chlorine in the furnace top gas. It was also possible to drive smoothly for 10 days.
There was no occurrence of scratches on the fluidized bed wall or rectifying plate. The produced chloride contained some carry over of ZrO ₂ and C as shown in Table 1, but it was at a level that would pose no problem for practical use.

[Table] Example 2 In a small fluidized furnace having the configuration shown in Fig. 2 with a fluidized bed diameter of 200φ and a free board diameter of 500φ, and with enhanced heat retention, the blown gas, Cl ₂ 85/min, O ₂ 15/min, total 100/min, and the other conditions were the same as in Example 1, but the amount of unreacted chlorine in the furnace top gas was zero or a trace amount. The system operated smoothly for 10 days, and there were no stains on the fluidized bed walls or rectifier plates. The quality of the produced chloride is shown in Table 2, and zirconium chloride of a quality that poses no practical problems was obtained.

【table】 [Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a chlorination furnace in which the present invention is implemented, and FIG. 2 is a sectional view of a miso improving furnace. 1: Chlorination furnace, 3: Dispersion plate, 4: Gas blowing lower chamber, 5: Raw material feeding device, 7: Freeboard section,
9: Brick layer, 10: Fireproof layer, 11: Steel plate, 2
0: Column (fluidized bed).

Claims (1)

[Claims] 1. In a method for fluidized chlorination of zirconium oxide using an excess carbon combustion method in a shaft-type chlorination furnace, finely powdered zirconium oxide and finely divided carbon are thoroughly kneaded, and coarse particles of carbon are added to the resulting kneaded material to form a fluidized bed. A mixture of 10 to 40% carbon based on the total weight ratio is charged to a chlorination furnace, and chlorine gas and oxygen gas are blown in from the bottom of the furnace at high speed to form an active fluidized bed. Characteristic fluid chlorination method. 2. The method according to claim 1, wherein the finely divided zirconium oxide and carbon are on the order of 50 μm or less. 3. The method according to claim 1, wherein the coarse carbon has a size of 100 to 1000 microns. 4. The method according to claim 1, wherein the chlorination furnace is covered with a heat insulating material impermeable to condensable chloride gas. 5. The method according to claim 1, wherein the freeboard of the chlorination furnace has a size sufficient to prevent carryover of fluidized bed particles. 6. The method according to claim 1, wherein the fluidized gas velocity is 0.2 to 0.8 m/sec (calculated at 1000°C) expressed as a cavity velocity at the bottom of the fluidized bed. 7. The method according to claim 1, wherein the bottom of the chlorination furnace is funnel-shaped and a fluidized bed is formed there. 8 The gas injection speed from the furnace bottom rectifier plate hole is 90m/
The method according to claim 1, wherein the time is longer than seconds.