JPS6033526B2 - Hydrogen fluoride separation method - Google Patents

Description

[Detailed description of the invention]

The present invention separates hydrogen fluoride from hydrogen fluoride-containing gas using a fluidized solid adsorbent made of at least one selected from alumina, sodium aluminate, and solid adsorbents similar to these. The present invention relates to a method for separating hydrogen fluoride. Special face 1986-8668, which was previously filed by the present applicant.
In No. 3 (Japanese Patent Publication No. 59-12331), a gas containing hydrogen fluoride is introduced into a bag as a fluidizing gas into a fluidized bed reactor, and at this time, the above-mentioned sulfur reacts with the solids charged therein ( (adsorbent) to form an expanded and expanded fluidized bed, and the concentration of the solids in this fluidized bed, that is, the solid adsorbent, decreases from the bottom to the top, and the rate at which the solids are mainly discharged from the top increases. By carrying out the bagging of the gas, hydrogen fluoride is separated from the gas even with solid matter in a fluidized state. For recovery reasons for economical reasons and for the prevention of environmental pollution, it is increasingly necessary to remove certain components contained in the gas from the gas. Such removal is carried out by a wet method such as rinsing, or by a dry method in which solids are separated. Of particular concern is the removal of hydrogen fluoride from waste gases. Complex salt compounds such as cryolite are used as fluxes in electrolytic processes for producing aluminum. For this reason, the waste gas contains hydrogen fluoride in an amount of about 1000 F/N or less, usually about 100 F/N, although it depends on the degree of suction and dilution. In addition to the above-mentioned wet refinement method, various dry adsorption methods are known as methods for removing hydrogen evolution. This dry method avoids the corrosion problems inherent in the wet method. For example, in GB 848,708, a larger amount of dry adsorbent (e.g. limestone, calcium carbonate, slaked lime, quicklime, alumina, activated alumina or magnesium oxide) than is theoretically required to remove hydrogen fluoride is used. It has been proposed to simultaneously inject the gas to be purified into a conduit leading to the backfill. In this case, fine particles (preferably 200 mesh or less) of adsorbent are forced by gas to the backfilter, but separation of the adsorbent, ie, solids, before reaching the filter should be avoided. This is because the adsorbent adheres to the vertically extending bags of the backfill, forming a dust layer that acts as a filter cake for the subsequent gas. The disadvantages of this method are that the residence time of the solids in the gas stream is short, that solids tend to be deposited in veins, and that the filter must be cleaned regularly. . In another method (Canadian Patent No. 613352),
Gaseous hydrogen fluoride is removed from the waste gas of the electrolysis process in less than 200 minutes. In this case, the following waste gas at 880m9HF/N is 1.5
Gas residence times of less than 1 second flow through an alumina layer of ~10% loss on ignition, which is periodically removed. Fluoride-rich alumina is fed directly to the electrolyte, of which 3-20% is utilized as an adsorbent. In a preferred embodiment of this known method, alumina is added to the air stream and sent to a backfilling station, where the alumina forms a ventilation layer in the form of a dust layer and serves to remove hydrogen fluoride. It is. This dust layer is also removed periodically. This method also has in practice the same drawbacks as mentioned at the beginning. Federal Republic of Germany Patent Application Publication No. 1
No. 091994 discloses that activated alumina having a specific surface area of 150 mm/g or more is used to improve the temperature range from room temperature to 650 mm/g.
It is described that a gas containing up to 1% by volume of hydrogen fluoride is purified at a temperature of preferably 100 to 45,000 °C. In this case, it is particularly preferred to use 1 part by volume of activated alumina per 80 parts by volume of gas and to feed the activated alumina with a particle size of about 3 to 12 skins countercurrently to the gas flow. As a result, the gas has a residual content of 3 per 1 pure gas.
It is purified until it becomes a 9 on a scale of 0 to 40. In this method,
Activated alumina particles have to be made and also the applicable gas velocity in the alumina layer is 0.1-0.3 m/s
Since it is an EC, it has the disadvantage that the cross-sectional area of the device must be increased from a technical standpoint. US Patent No. 3
No. 503184 describes that the waste gas of an electrolytic cell of 1240 below 9 HF/〆 is treated in a dense fluidized bed with a bed height of 5 to 30 cm at 5 to 85 qC. In this case, 2575 k9 of oxide per 1 kg of hydrogen fluoride,
That is, alumina is added to the gas. The residence time of the gas in the fluidized bed is 0.25 to 1.9 seconds. A filter is also provided to separate dust entrained in this gas. In this method, very low gas velocities of about 0.3 m/sec are applied, since only the required density of the fluidized bed can be maintained.
Moreover, a large amount of solid matter is fed into the filter bag, which must be cleaned very often, which causes problems such as wear and tear of the filter bag. be. Exchange surface (A cape tauschflash
Due to the need for e) to be as large as possible and as dense as possible, the gas velocity in the adsorption layer is usually relatively low in the aforementioned methods. However, in this case, the gas flow rate per unit volume of the device is not high, so it cannot be an economical gas purification method. In order to eliminate these drawbacks and to make the adsorption effect very effective especially when the gas flow rate is high, hydrogen fluoride-containing gas is charged to the fluidized bed reactor as a fluidizing gas. , the gas forms an expanded and expanded fluidized bed together with the solids introduced therein, and the solids concentration of this fluidized bed decreases from the bottom to the top, and the solids are mainly discharged from the top. It was proposed that the charging of the gas be carried out at a rate of
Said Tokko Sho 46-186 Porridge No. 3 (Toku Sho 59-12331
Patent Application No. 2056096 of the Federal Republic of Germany, which is a corresponding application of the Federal Republic of Germany (Federal Republic of Germany). The process according to DE 22 25 686 A1 is generally carried out under the same conditions. Now,
In a method for separating hydrogen fluoride from gas even with a substance in a fluid state (adsorbent), the above-mentioned method is based on the above-mentioned patent application No. 2056096 of the Federal Republic of Germany.
Iso No. 3 (Samurai Ko Sho 59-112331) charges a gas containing hydrogen fluoride as a fluidizing gas to a fluidized bed reactor, and at this time, the gas is mixed with the solids charged therein. The gas is charged into bags at such a rate that an expanded and expanded fluidized bed is formed, and the solids concentration of the fluidized bed decreases from the bottom to the top, and the solids are mainly discharged from the top. and, according to the present invention, the solids discharged together with the gas (i.e., at least one selected from alumina, sodium aluminate, and solid adsorbents similar thereto) are directly fed to the fluidized bed reactor. As a whole, the method according to the invention of Japanese Patent Application No. 12331/1983, which already has advantages in itself, has been greatly improved.
In particular, it has been proposed that its economy can be improved and its operation can be simplified. Of course, the above-mentioned patent application 1986-866
In the case of the method according to the invention of No. 83 (Japanese Patent Publication No. 59-12331), it has already been considered to use an electrostatic precipitator to collect and remove fine particles, but as mentioned above, It was unexpected that the solids discharged in high density together with the gases from the fluidized bed reactor could be separated almost quantitatively by electrostatic precipitators alone. An electrostatic precipitator is used to separate the solids discharged in the gas stream.The system consisting of an adsorber and separator operates with a hitherto unknown low pressure drop, thereby reducing operating costs. The advantage is that this can be significantly reduced, especially in the case of processing large amounts of gas. In a preferred embodiment of the invention, the gas-solid suspension is adjusted with water to a powder resistance of 1 to 20 mm, preferably 1 to 10 mm. The amount of water required for this is already contained in the suspension under extreme weather conditions, but in general:
In order to obtain the above-mentioned powder resistance, it is necessary to supply water or steam at appropriate points. In this case, it is particularly preferred to feed the water directly to the fluidized bed reactor.
Surprisingly, the adsorption of hydrogen fluoride is not impaired by the supply of water and/or steam. This fact is surprising. This is because the adsorption power of the solid substance for hydrogen fluoride is greatly reduced by water, and there is therefore a risk that the final gas of the required purity cannot be obtained. In order to obtain a sufficiently high hydrogen fluoride loading, i.e. adsorption amount, of the solid, the separated solid is circulated through a fluidized bed reactor to form a circulating fluidized bed.
It is preferable to configure .cht). For circulating the solids into the fluidized bed reactor, feed devices known per se may be used. Particular preference is given to pneumatically transporting the solids. In the main field of application of the present invention, namely the separation of hydrogen fluoride from waste gases from the electrolytic production of aluminum using fluxes, the solids are selected from among alumina, sodium aluminate and similar solid adsorbents. The waste gas usually contains at least one selected species, and the waste gas usually also contains impurities, and these impurities are separated together by a solid material charged for adsorbing hydrogen fluoride. These impurities are in the form of gases or small solid particles and consist of, for example, carbon, sulfur, iron, silicon, carbon and/or vanadium, or even compounds of these elements. If such impurities are circulated together with used solids in the electrolytic process using a flux and become large in the electrolyte, problems occur. That is, it contaminates the molten aluminum metal and also reduces the current efficiency of the electrolytic furnace. In order to avoid this problem, in a preferred configuration of the present invention, solid matter is fractionated into different particle size ranges in an electrostatic precipitator having a plurality of dust collection areas (Feld) and a plurality of dust bins (SPubbunkers). do. In this case, the majority of the impurities have a concentration or degree of accumulation (Anreicherungs ad) that is more than three times higher in the fine-grained fraction separated by this electrostatic precipitator and are thus separated from the phase-grained fraction. is removed. The fine-grained fraction is either dumped or treated appropriately, for example for recovery as a solid (adsorbent). A preferred embodiment according to the invention furthermore provides that, together with the fractional separation of the solids, the coarse fraction of the solids is recycled to the fluidized bed reactor in order to obtain a sufficiently high loading of hydrogen fluoride, so that the circulating fluidized bed form. The solids having an average particle size of 20-300 μm are charged and the gas velocity of the fluidized bed is adjusted to 1
It is preferable to adjust to ~ arc/sec. In this case, the average residence time of the gas in the fluidized bed reactor is about 1 to 19 seconds. By adjusting the temperature of the gas mass suspension to a certain value in the range of 45 to 85 q○, optimum conditions can be obtained with respect to the temperature of the dust advance in the electrostatic precipitator. In principle, temperatures above 22,000 are possible, but
Since the waste gas to be treated according to the invention is generally not produced at such high temperatures, it plays only a secondary role. In a further preferred embodiment of the invention, the waste gas containing hydrogen fluoride is introduced into the fluidized bed reactor through one or more inlets configured like a Venturi tube, thereby allowing the fluidized bed reactor and the electroconcentrator to It is possible to further reduce the pressure losses occurring in the system consisting of the dust device. Furthermore, a reflection separator with low pressure loss (Pral-l
If an absorber (abscheider) is incorporated into a fluidized bed reactor, it can provide better contact between the waste gas and the solids, as well as increase the residence time of the solids and their hydrogen evolution load. However, this reduces processing efficiency (Dmchsatzlej
stung) will not decrease. According to the invention,
By controlling the feed rate of the solids and also controlling the discharge rate by means of suitable bagging and circulation devices, the average concentration of solids in the fluidized bed of the fluidized bed reactor is varied and thereby the material It is possible to vary the exchange surface over a wide range. For example, the preferred average concentration of solids for the system pressure drop is adjusted to a value of up to 10k9/〆 for the reactor volume. The amount of solids recycled per hour may be 5 to 100 times the amount of solids present in the fluidized bed of the fluidized bed reactor. Next, embodiments of the present invention will be described with reference to drawings and specific examples. In the vertical reaction column 2, i.e., a fluidized bed reactor, there is a feed device 16.
The fine particulate adsorbent is charged by the gas distribution device 1.
A raw material gas is introduced as a fluidizing gas. In this case, the flow rate of the fluidizing gas is increased so that a gas-solids sanction is formed over the entire height of the fluidized bed reactor. A reflection separator 15 is included to increase the residence time of the solids. The concentration of the adsorbent is lowered or lowered in the fluidized bed reactor, and most of the adsorbent is discharged from the suspension outlet 3. The discharged adsorbent is separated in an electrostatic precipitator 4 connected downstream of the reaction column 2 and collected in a dust bin 5. From this dust bin, a part of the accumulation is circulated through line 9 to the reaction column 2, and another part is fed through line 10 to the electrolyzer. Before being fed to the electrolyzer, the solids are passed through a combustion device 14 where most of the carbon is burned off. The waste gas from which hydrogen fluoride has been removed is discharged from the electrostatic precipitator 4 through the waste gas conduit 12. The difference between the process diagram in Figure 2 and that in Figure 1 is that solids are fractionated and separated into different particle size ranges,
This separated solid matter is collected in the dust bins 5, 6, 7 and the river. The particulate fraction that accumulates in the dust bin 8 is discharged via a conduit 11 and is, for example, dumped. On the other hand, a portion of the solids separated into the dust bins 5, 6, and 7 is circulated through the conduit 9 to the fluidized bed reaction tower 2, and the other portion is supplied through the conduit 10 to the electrolytic cell. In the embodiment of the present invention shown in FIG. 2, in order to obtain optimal dust collection conditions in the electrostatic precipitator 4, water is supplied to the fluidized bed reactor 2 through the conduit 13 to maintain a gas-solids suspension. , that is, the powder resistance is adjusted. Next, this embodiment will be explained with reference to a specific example. Specific Example 1 (Related to FIG. 1) The fluidized bed reaction tower 2 used in the experiment had a cylindrical portion diameter of 0.88 h and a height of 6 m. The electrostatic precipitator 4 had a single dust collection area and one dust bin 5. AI20 with ignition loss of 1% by weight
3 was used as a solid (adsorbent), which was obtained by calcination in a fluidized bed. This solid had a comparative area (according to the BET method) of approximately 25〆/g and an average particle size of 40r. *Waste gas having a hydrogen chloride content of 25 9/N and a temperature of 7500 was introduced into the fluidized bed reaction tower 2 from the inlet of a venturi tube-like gas distribution device 1 at a rate of 5000 N/h. A pile 203 of 6k9/h was supplied by the supply device 16. The gas velocity in the fluidized bed reactor corresponded to a velocity of 2.7 m/sec measured when the reactor was empty. A gas-solid suspension having a solid content of 250 g/N was discharged from its outlet 3 and introduced into an electrostatic precipitator 4. Solids were separated at a rate of 1250 k9/h. 6k9/h of solids, corresponding to the feed of fresh M203, were separated and fed through conduit 10 to the combustion device 14, where the carbon was burnt off and then sent to the electrolyzer. The remaining portion of the separated solids was recycled to the fluidized bed reactor column 2 via conduit 9. Fluidized bed reactor 2 has a total of 18k
There was an AI203 of 9, corresponding to an average solids concentration of 4.5 kg/. The pressure loss in the entire system formed by the fluidized bed reaction tower 2 and the electrostatic precipitator 4 was 120 days and 20 days (water column). Dust content is 1
A gas having a hydrogen fluoride content of 9/N of 00 and a hydrogen fluoride content of 1M/N or less was discharged from the conduit 12. Specific example 2 (related to FIG. 2) Fluidized bed reaction tower 2 shown in FIG. 1, electrostatic precipitator 4 having two dust collection areas and four dust bins 5, 6, 7, 8
An experiment was conducted using The above specific example 1 is used as AI203 packed in a bag as a solid product.
A material with the same properties as in the case of was used. Waste gas having a hydrogen fluoride content of 35/9/N and a temperature of 80:00 was supplied to the fluidized bed reaction tower 2 at a rate of 580/h. The supply device 16 supplied 14k9/h of N203. Gas velocities in the fluidized bed reactor were measured when the reactor was empty. It supported a speed of 3.3h/sec. In addition, 601/h of water was introduced through the conduit 13, which caused the gas to be separated in the electrostatic precipitator 4.
For example, the powder resistance of the solid suspension was adjusted and the temperature of the suspension was lowered to 60°C. Then, 175 g/N of the gas-solids suspension was discharged from the outlet 3 and introduced into the electrostatic precipitator 4, where the solids were fractionated. A total of 1000 k9/h of solid matter was separated on the dust pins 5, 6, 7, and 8. Of this, a portion corresponding to the amount of fresh AI203 introduced into the fluidized bed reaction tower 2 is led from the conduit 10 to the electrolytic cell, and is further accumulated in the dust bin 8 at a rate of 1.5k9/h. The remaining solids, except for the finest particulate fraction, were circulated through conduit 9 to the fluidized bed reactor. The fine particle fraction collected in the dust bin 8 and discharged via the conduit 11 contained three times as many impurities as the average impurity content of the total amount of N203. In other words, the average content (wt%) of the total amount of alumina is 4.5% for F and 1.3% for C.
%, S is 0.3%, and Fe203 is 0.25%, whereas the impurity amounts (wt%) for the fraction separated in the dust bin 8 are 12-5% for F and 3% for C. -7%, S is ○
-9%, and Fe203 was 0.7%. The 12k9 of AI203 present in the fluidized bed reactor 2 corresponded to a solids concentration of 3k9 per volume of the reactor. The pressure loss in the entire system constituted by the fluidized bed reaction tower 2 and the electrostatic precipitator 4 was 11 to 20 days (water columns). The purified gas was discharged through the conduit 12, and its combined dust content was less than 9/N of 30, and its fluorine content was 0.8.
It was 9/Nth. What follows belongs to embodiments of the present invention. {1] Hydrogen fluoride is removed from hydrogen fluoride-containing gas using a fluidized solid adsorbent made of at least one selected from alumina, sodium aluminate, and solid adsorbents similar to these. During separation, a fluidized bed with a very low density is formed by the gas and the solid adsorbent such that the concentration of the solid adsorbent in the fluidized bed decreases from the bottom to the top and the mass of the solid adsorbent increases. Said hydrogen fluoride-containing gas is introduced into the fluidized bed reactor as a fluidizing gas at such a rate that a portion is discharged upwards, and said gas is discharged from said fluidized bed reactor along with said gas. A method for separating hydrogen fluoride, in which a solid adsorbent is separated in a separator, and the separated solid adsorbent is circulated to the fluidized bed reactor to form the fluidized bed, wherein the separator comprises: An electrostatic precipitator immediately following the fluidized bed reactor is used to separate the body adsorbent discharged from the fluidized bed reactor together with the gas in the electrostatic precipitator, and A method characterized in that the average concentration of the solid adsorbent in the fluidized bed reactor is adjusted to a value of up to 10 kg per reactor. ■ The method described in item 1 above, characterized in that the powder resistance of the gas-solid suspension is adjusted by adding water to a value of 1 to 20 cm or less, which is suitable for dust collection, preferably 1 pi IQ.c or less. . {3} A method according to item 1 or 2 above, characterized in that the gas-solids suspension is adjusted to be suitable for dust collection by supplying water to the fluidized bed reactor. '4) Any one of the above items 1 to 3, characterized in that the solid matter is fractionated and separated into mutually different particle size ranges in an electrostatic precipitator having a plurality of dust collection areas and dust bins, respectively. The method mentioned in section 1 or around number.

[5] The method as set forth in item 4 above, characterized in that the solids separated as fractions in the particle size range are recycled to the fluidized bed reactor for the formation of a circulating fluidized bed. (i) When the particle size of the adsorbent is 20 to 300 μm, the velocity of the fluidizing gas is adjusted to 1 to instant/sec, or one or more of the above items 1 to 5. The method described in. '7- The temperature of the gas-solid suspension was set to 40
Items 1 to 6 above, characterized in that the adjustment is made to 8yo.
[Either of Sections] Methods mentioned in Sections or Numbers. (1) In any one or more of the above items 1 to 7, the waste gas containing hydrogen fluoride is introduced into the fluidized bed reactor through an inlet formed like a Venturi tube. The method mentioned. (9) The method described in any one or more of items 1 to 8 above, characterized in that the residence time of the solids is extended by incorporating a reflection separator into the fluidized bed reactor. .

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which Fig. 1 is a process flow diagram showing a method for separating hydrogen fluoride from waste gas in an electrolytic process, and Fig. 2 is a process diagram showing a method for separating hydrogen fluoride from waste gas in an electrolytic process, and Fig. 2 shows a method for separating hydrogen fluoride from waste gas in an electrolysis process. FIG. 2 is a process flow chart showing a method of separating hydrogen fluoride from waste gas of an electrolytic process using an electrostatic precipitator. In addition, in the symbols used in the drawings, 2 is a reaction tower,
4 is an electrostatic precipitator, 5, 6, 7, and 8 are dust bins, 14 is a combustion device, 15 is a reflection separator, and 16 is a supply device. FIG, IFi9.2

Claims (1)

[Claims] 1. When separating hydrogen fluoride from a hydrogen fluoride-containing gas using a fluidized solid adsorbent made of at least one selected from alumina, sodium aluminate, and a solid adsorbent similar to these. , a fluidized bed having a very low density is formed by the gas and the solid adsorbent and the concentration of the solid adsorbent in this fluidized bed decreases from the bottom to the top and a large portion of the solid adsorbent is The hydrogen fluoride-containing gas is introduced into the fluidized bed reactor as a fluidizing gas at such a rate that the solids are discharged from the fluidized bed reactor along with the gas. A method for separating hydrogen fluoride, wherein an adsorbent is separated in a separator, and the separated solid adsorbent is circulated to the fluidized bed reactor to form the fluidized bed. An electrostatic precipitator immediately following the fluidized bed reactor is used to separate the solid adsorbent discharged from the fluidized bed reactor together with the gas in the electrostatic precipitator, and A method characterized in that the average concentration of the solid adsorbent in the bed reactor is adjusted to a value of up to 10 kg/m^2 of this reactor.