KR830001540B1 - Preparation of Hydrogen Fluoride - Google Patents

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Description

Preparation of Hydrogen Fluoride

The figure is a flow diagram illustrating plant equipment for carrying out the process of the invention.

The present invention relates to a method for producing hydrogen fluoride (HF) obtained by thermal hydrolysis treatment of a fluorine-containing substance in an expandedfluidized bed and cooling the gas emitted at this time.

It is well known that fluorine-containing substances are released at high temperatures in the presence of water vapor (thermohydrolysis), and high concentrations of hydrogen fluoride can be recovered by condensation or scrubbing of the released hydrogen fluoride.

The liberation of hydrogen fluoride by the thermal hydrolysis method is particularly meaningful because waste materials from the production of aluminum by electrolysis can be used. For example, when producing aluminum by fused salt electrolysis, usually cryolite or similar fluorine-containing solvents are used, where the fluorine-containing components are attached to the lining of the electrolyzer. These linings should be changed from time to time, depending on the behavior of the electrolyzer or the time the lining has been running, which will contain 10-15% (by weight) of fluorine.

Hydrogen fluoride may also be separated by dry cleaning the gas released from molten salt electrolysis. Alumina is used as a chemical adsorbent, which contains hydrogen fluoride and also adsorbs other impurities (carbon, sulfur, iron, silicon, phosphorus, or vanadium) in the released gas, thereby continuing to melt salt electrolysis. It must be handled because it cannot be used.

In addition to recovering useful materials such as aluminum and alkali metals (US Pat. No. 4,113,832), however, it is known that waste materials can be used by thermal hydrolysis (see German specifications 2,346,537 and 2,403,282). The above-mentioned thermal hydrolysis is carried out in an expanded fluidized bed, for example, in the presence of an appropriate amount of water vapor at a temperature of 1100-1350 ° C. Alkali fluoride or hydrogen fluoride is separated from the exhaust gas and the thermohydrolyzed solid residue is dissolved and filtered through an alkaline solution to produce hydrated alumina. Alkali fluoride

Disadvantages of the above methods are that the heat released by the gases released is wasted, and the gas velocity is significantly increased by spraying water to cool it. The method of cooling by mixing cold gas is disadvantageous because it dilutes particularly unnecessary gas even if it is a matter of low hydrogen fluoride content. The use of indirect cooling eliminates these problems, while causing corrosion or erosion problems and depositing powder on the cooling surface, which lowers the thermal conductivity, resulting in large structural losses in cleaning or large cooling surface changes. This is difficult to handle.

It is an object of the present invention to present a method which avoids the disadvantages of the known methods, in particular the above mentioned points, and in particular makes it possible to utilize the heat of the emitting gas usefully, and also to ensure that the structure loss is not large.

The present invention cools the discharge gas by direct contact with the solids circulating in the separation circuit, and the solids are recooled in the cooler, where significant heat is available.

Another method of the present invention may utilize waste from the production of aluminum by electrolysis. Fluorite or other fluorine-containing minerals may also be treated, which may favor hydrogen fluoride by thermal hydrolysis.

Depending on the nature of the feedstock, the fuel used to heat to the required reaction temperature is required. The reaction temperature is usually 1000-1400 ° C. Liquid and gas as well as solid fuels are used and are introduced directly into the expandable fluidized bed. If the feedstock is high enough in carbon, i.e. using normally discarded lining material, no fueling is required.

The most suitable and simply method of cooling the discharge gas is to contact the discharge gas with the recooled solid in at least one suspended heat exchanger.

The solid is recooled in a fluidized bed cooler, which takes several steps. Its operating pattern and design depend mainly on the nature of the feed material. If the fuel content of the solid is high enough to achieve the required reaction d temperature conditions in the expansion fluidized bed, the solid may be recooled to utilize heat. For example, it can be used to generate water vapor. The resulting hot offgas is preferably recycled into the fluidized bed reactor. Fluidized beds with several cooling chambers, whether fueled separately or the thermal hydrolysis process is maintained on its own

The expandable fluidized bed used in the present invention is well known per se. In the orthodox fluidized bed, the dense phase and the upper gas layer are separated by a sudden difference in density, whereas the expanded fluidized bed shows a density distribution without boundary phase. There is no sudden density change between the concentrated phase and the upper gas layer, but the solid concentration in the reactor gradually decreases from bottom to top. In a particularly preferred arrangement, the oxygen-containing gas to be burned is fed to the fluidized bed in two different streams of air, and the gas absorbed by the exhaust gas and the solids separated therefrom are recycled to the lower part of the fluidized bed. This type of operation results in weak combustion in two stages, eliminating the formation of hot spots and NOx gases, and recycling of solids separated from the exhaust gas can lead to very high system temperatures consisting of fluidized bed reactors, separators and recovered dust. Keep it constant

Any gas that does not actually have an adverse effect on the nature of the emitting gas can be used as the flow gas. Inert gases, ie recycled discharge gases, nitrogen, steam and the like are suitable. In order to make the combustion occur violently, it is preferable to supply oxygen-containing gas to the reactor as a fluid gas.

Specifically expressing the present invention.

1. Inert gas is used as the flow gas.

In this case a combustion gas containing oxygen as the secondary gas should be supplied at at least two levels.

2. Oxygen-containing gas is used as the flow gas.

In this case, the secondary gas may be supplied at several levels, but only at one level.

When secondary gases are supplied at different levels, each level should be desirable. The volume ratio of the flow gas to the secondary gas should be between 1: 20-2: 1. The secondary gas is adequately supplied to be 30% of the height of the reactor and at least 1m above the level at which the flow gas enters. If the secondary gas is supplied at multiple levels, the top secondary gas level will be at the 30% limit. This level is best to ensure that there is adequate space for the first combustion to occur, so that a nearly complete reaction between the combustion material and the oxygen-containing gas occurs and the oxygen-containing gas, whether fluid or secondary gas, is supplied at a low level. do. On the other hand, an area with a sufficient combustion reaction is given in the space of the secondary gas injection water unit. The gas velocity of the secondary gas injection water unit entering the fluidized bed reactor is usually 5-15 m / sec. The ratio of the diameter to the height of the fluidized bed reactor should be chosen such that the residence time of the gas is 0.5-8 seconds, preferably 1-4 seconds.

The average diameter of the particles in the feedstock should be 30-250 micrometers. This degree is suitable for the flow conditions, and the reaction time can be shortened sufficiently.

The range of suspension densities that must be maintained in the fluidized bed varies but up to 100 kg / m 3. To minimize pressure loss, the average suspension density is maintained at 10-40 kg / m 3 above the secondary gas injection means. Using the Proud and Archimedes numbers to determine the operating conditions, the following ranges are obtained.

The feedstock is fed to the fluidized bed reactor in the usual way, preferably via one or more lances, for example under the flow of compressed air. Since the mixing of the cross sections is good, the number of supply lances is relatively small, and one lance is sufficient when the reactor is small.

An excellent advantage of the present invention is that because of the use of recooled solids, the release gas is suddenly cooled like a shock and thus prevents corrosion or erosion, and no powder residues affecting heat exchange are deposited. By using a fluidized bed cooler, the solid is cooled and gives a lot of heat to the cooling fluid. Since the cooling solid is circulated separately from the solid undergoing thermal hydrolysis, it does not contain H F except the initial reaction. There is therefore no loss of H F in the recooling stage. It is also possible, for example, at a stage subsequent to the addition of a recooled solid

The invention will be explained in more detail in the drawings and examples.

The feedstock, water and, if necessary, fuel are supplied in the form of a flow through the lances (4), (5) and (6) to provide a fluidized bed reactor (1), a cyclone separator (2). And return conduit (3). After reacting for a sufficient time, the thermally hydrolyzed residue derived from the feed material is filtered through conduit 7 or filtered to recover available material.

The exhaust gas from the fluidized acid reactor 1 enters the suspended heat exchanger 8 and undergoes the first cooling stage by contact with the circulating solids supplied through the conduit 9. Solids and gases are separated in subsequent separator 10. The gas enters a second suspended heat exchanger 11 through which a recooled solid is supplied via a pneumatic conveyor 12. As the gas is cooled further, it separates from the solid in another separator 13. Powder debris in the HF-containing gas is precipitated in the precipitator 14, and the gas discharged therefrom is connected to the absorption or condenser through the conduit 15.

Solids remaining in separator 10 are sent to conduit 16 to fluidized bed cooler 17 where they pass through four cooling chambers.

In the cooling chamber, the solids indirectly exchange heat capacity with the oxygen-containing gas, which flows back to the solid to remove dust and flows through the conduit 18 as a fluid gas reactor 1. Is sent to. The cooled solid is finally cooled in two cooling chambers (here cooled with water) in series and sent to the compressed air carrier 19.

Oxygen containing gas receives a significant amount of additional heat from the solids in the fluidized bed cooler 17 and passes through the separator 20 to collect dust. The gas is sent from the separator 20 to the fluidized bed reactor 1 via a conduit 21 as a secondary gas. The dust collected in the electrostatic settler 14 is circulated through the conduit 22 to the fluidized bed cooler 17.

In the fluidized bed cooler (17), conduit (12), suspended heat exchanger (11), separator (13), suspended heat exchanger (8), separator (10), and conduit (16), When depleted, the solid is transferred to a circulating fluidized bed through a conduit 23 which is a side cycle, or fed to a circuit comprising a cooler 17 via a conduit 24.

Conduits 25, 26 and 27 are passages for supplying a fluid gas or a carrier gas.

Example 1

The feedstock is the dry lining material left in the electrolyzer when producing aluminum by melting point electrolysis, with an average particle size of 100-200 micrometers. The bulk density is 1.1 kg / L and contains 26 weight% carbon and 15 weight% fluorine (calculated by F).

Because of its high carbon content, thermal hydrolysis takes place in-house. That is, no fuel supply is necessary. The gas amounts mentioned below are based on standard conditions.

The lining material is fed to the fluidized bed reactor 1 at a rate of 5000 kg / h via conduit 4, and 20 ° C. of water is also fed at a rate of 3.1 m 3 / h through conduit 6. At the same time, the reactor 1 is supplied with a flow gas of 300 ° C. at a rate of 3000 m 3 / h through the conduit 18, and a secondary gas of 400 ° C. is supplied at a rate of 9500 m 3 / h through the conduit 21. The fluid gas and the secondary gas are preheated in the fluidized bed cooler 17. In the circuit consisting of a fluidized bed reactor (1), a fan separator (2) and a recirculation furnace (3), the solids circulating in the suspended state in the fluidized bed reactor (1) by selecting the fluid state and the operating variables are secondary gas conduits (21). ), The average density is about 100kg / m ₃ , and on the secondary gas conduit 21, the average density is about 20kg / m 3. In order to fully recycle the solid in the fluidized-acid reactor 1, the solid of the recirculation circuit 3 is supplied with air at a rate of 200 m 3 / h. The temperature of the circuit is about 1100 ° C.

After 1 hour, the treated residue was recovered through conduit 7 at a rate of 3000 kg / h equivalent to the feed rate and cooled in a separate cooler. The bulk density of the treated residue was 1 kg / l and the residual contents of fluorine and carbon were less than 1 wt% and 0.1 wt%, respectively.

The gas released from the reactor 1 is cooled by the solids obtainable in the process. To do this, the discharge gas at 1100 ° C. exiting the fan separator 2 is cooled to 590 ° C. by a solid at 280 ° C. in a suspended heat exchanger 8, which is subjected to 50,000 kg / h through conduit 9. As supplied at a rate, the gas was cooled and itself became 590 ° C.

This heated solid is sent from separator 10 to conduit 16 to fluidized bed cooler 17.

In the second suspended heat exchanger (11), the exhaust gas from the separator (10) is brought into contact with a solid at 80 ° C, at which time the solid is condensed into the compressed air at a rate of 50,000 kg / h in the cooler (17). It was transferred through. Gas and solids are separated in separator 13, where a solid at 280 ° C. can be obtained. The gas cooled to 280 ° C. is sent from the separator 13 to the electrostatic precipitator 14 at a rate of 19,500 m 3 / h, where it is sent back to where hydrogen fluoride is recovered.

The composition of the exhaust gas was as follows.

The solid separated in separator 10 is sent through conduit 16 to fluidized bed cooler 17 at a rate of 50,000 kg / h, where it is cooled through four cooling chambers, which are sent to reactor 1. It cools by heat-exchanging with air, and water is supplied to the next two cooling chambers. The fluidized bed cooler 17 is supplied with fluid gas at a rate of 9500 m 3 / h and air at a rate of 3000 m 3 / h, which are used for indirect heat exchange. These two air streams are drawn through conduits 21 and 18, respectively.

Water was supplied to the cooling chamber cooled by water in the fluidized bed cooler 17 at a rate of 95 m 3 / h. In the above cooling chamber, the water at 40 ° C. became 90 ° C., while the solid was cooled to 80 ° C. The cooled solid is recycled through the conduit 27 to the suspended heat exchanger 11 at a rate of 2500 m 3 / h with the aid of air at a pressure of 500 millibars above the atmospheric pressure of 60 ° C.

Example 2

Hydrogen fluoride is obtained from fluorspar with an average particle size of 100-200 μm, a density of 1.2 kg / 1 and a content of 95% by weight of CaF ₂ .

Unlike Example 1, a fuel supply was needed.

The flow acid reactor 1 has 1210 kg / h coal through conduit 6, 1540 kg / h die (calculated as CaF ₂ ) through conduit 4, and 3100 l / h of water through conduit 5 (20 degreeC) was supplied, respectively.

The reactor 1 was supplied with a flow gas of 400 ° C. through a conduit 18 at a rate of 30000 m 3 / h, and a secondary gas at 550 ° C. was supplied through a conduit 21 at a rate of 7000 m 3 / h. These two air streams are sent from the cooler 17. In the fluidized bed reactor 1 the suspension has an average density of 100 kg / m 3 below the conduit 21 and an average density of 25 kg / m 3 above the conduit 21. The reactor was operated at a temperature of 1120 ° C. As in Example 1, air was supplied at a rate of 200 m 3 / h from the recirculation furnace 3 so that solids could be sufficiently recycled to the reactor 1. The reaction time was maintained for 90 minutes.

Treated residue is drawn through conduit 7 at a rate of 1230 kg / h, such as feed rate. The residue contains burned lime, which can be used in the building industry.

Unlike Example 1, the emitter was cooled by an extraneous solid consisting of alumina. Gas and solid were each advanced through the same passage as in Example 1.

The solid was allowed to circulate through the suspended heat exchanger, separator, fluidized bed cooler 17 through the conveying conduit 12 at a rate of 40,000 kg / h. A carrier gas at 60 ° C. is drawn through conduit 7 at a rate of 2100 m 3 / h. The residue contains burned lime, which can be used in the building industry.

Unlike Example 1, the emitter was cooled by an extraneous solid consisting of alumina. Gas and solid were each advanced through the same passage as in Example 1.

The solid was allowed to circulate through the suspended heat exchanger, separator, fluidized bed cooler 17 through the conveying conduit 12 at a rate of 40,000 kg / h. A carrier gas at 60 ° C. was supplied at a rate of 2100 m 3 / h at a pressure of 500 millibars above atmospheric pressure. The temperature of the discharge gas and the solid was 290 ° C in the suspended heat exchanger 11 and the separator 13, and 610 ° C in the heat exchanger 8 and the separator 10. The gas capable of recovering hydrogen fluoride emerges at a rate of 16,750 m 3 / h through the conduit 15, the other composition ratio being as follows.

When the solid supplied to the fluidized bed cooler 17 through the conduit 16 is cooled, the indirectly heated air is dust-free flow gas to the reactor 1 through the conduit 18 at a rate of 3000 m 3 / mh. The air sent indirectly and indirectly is sent to reactor 1 via conduit 21 at a rate of 7000 m 3 / h as secondary air. 40 ° C. water is supplied to the cooling chamber cooled with water in the fluidized bed cooler at a rate of 67 m 3 / h and heated to 90 ° C., while the solid is cooled to 80 ° C.

Claims (1)

By supplying a fluorine-containing substance, it is thermally hydrolyzed in an expanded fluidized bed to produce a gas containing hot hydrogen fluoride and a material entrained in the gas from the fluidized bed, and then separating the entrained material from a gas containing hot hydrogen fluoride. The gas is cooled by removal of hydrogen fluoride by quenching the gas containing hot hydrogen fluoride by recirculating to the fluidized bed and in direct contact with the solid at a temperature below the temperature of the gas containing hot hydrogen fluoride in a suspended heat exchanger. A method for producing hydrogen fluoride, comprising a step of allowing a solid to be cooled and then sending a hot solid to a fluidized bed cooler to recover heat, and recycling a portion of the cooled solid to a quench stage.

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