SE467952B - SET AND DEVICE TO INCREASE THE EXTENSION OF USE FOR A DRY SORBENT - Google Patents

Description

467 952 '2 and the design of the contact reactor.

As alumina is a highly abrasive dust, increased recycling of the separated material and thus increased dust concentration means that wear on transport lines and dust separators increases. This wear also results in the alumina being contaminated by the worn material, for example iron from the transport lines, and in the particle size of the alumina being reduced. Reduced size of the alumina particles means i.a. that fine alumina particles are spread in the process hall surrounding the electrolysis furnaces, which is not desirable from a work environment point of view. Increased dust concentration in the dust collector also means that the pressure drop and thus the energy consumption in it increases.

If high-speed alumina particles collide with metallic surfaces, alumina can be deposited on the surfaces and form coatings, which can then come loose from the surfaces in the form of sharp and hard alumina shells. Since the above-mentioned dust collectors usually consist of a hose filter, the hoses of which would be torn apart by these "shells" in a short time, the dust collector is usually provided with a pre-separator, which separates these "shells" from the exhaust gases before passing them through the filter hoses. In the pre-separator, however, the coarse alumina particles are also separated, which means that the coarse sorbent particles with the largest surface area and thus the greatest reaction potential are not deposited in the dust accumulated on the outside of the hoses, in which the remaining gaseous pollutants are brought into close contact with the alumina. particulate pollutants.

Since the alumina only stays in the reactor for a few seconds, but remains on the hoses until they are cleaned, which takes place approximately 1-10 times per hour, the residence time of the alumina on the filter hoses is a few hundred times greater than in the reactor. This means that the fine alumina particles, which need a short time to react with the gaseous pollutants, have a long total residence time, while the coarse alumina particles, which need a long time to react with the gaseous pollutants, have a short total residence time. In order to increase the residence time of the coarse particles and thus the degree of utilization of the alumina, it is thus forced to recycle the alumina a large number of times, which entails various inconveniences for the exhaust gas treatment plant.

US-4,501,599 proposes, for example, that fresh and recycled 3,467,952 alumina be added to the exhaust gases from the electrolysis furnaces in a special mixing chamber, before being introduced into a dust separator for separating reacted and unreacted alumina and dust brought from the electrolysis furnaces. The function of the mixing chamber is to provide an intimate mixture between the gaseous pollutants of the exhaust gases and the alumina, so that the majority of these pollutants are brought into contact with the alumina and converted into particulate pollutants which can be separated in the dust collector.

The dust separator in this case consists of a textile barrier filter, which is fitted with a pre-separator for separating the coarse particles. As a result, the coarse particles are only brought into contact with the gaseous impurities in the mixing chamber. As the residence time in the mixing chamber is short, only some of these particles, despite the intimate mixing in the chamber, have time to react with these contaminants before they are separated in the pre-separator. Despite the provision of the complicated and expensive mixing chamber, even in this case the material separated in the textile barrier filter must be circulated several times between the mixing chamber and the barrier filter in order to obtain an acceptable use of the sorbator.

DE-38 01 913 proposes that the fresh sorbent be added to the exhaust gases immediately before their entry into a hose filter, which functions both as a contact reactor and a dust separator. The material separated in the hose filter thus only needs to be recycled internally inside the filter to be brought back into contact with crude exhaust gases.

There is also no separate separation of the coarse particles of the separated material, but both fine and coarse particles are circulated together in the filter. The coarse dust thus has a residence time in the filter as long as the fine dust. This means that the exhaust gas treatment plant does not need to be equipped with a special pre-separator, contact reactor or special lines for transporting the separated material from the hose filter to the contact reactor. This provides both a simple and inexpensive system, while at the same time reducing the surfaces that can be exposed to wear.

Since the internal recirculation of the separated material takes place with the aid of a part of the partially purified exhaust gases, a recirculation of the exhaust gases is also obtained here. This means that the volume flow and thus the speed of the exhaust gases inside the filter increases, which results in a greater wear on the filter hoses and a reduction in the concentration of the gaseous contaminants. The latter in turn leads to a lower efficiency for the sorption process. Because the exhaust gases are caused to flow at a high speed through a pipe inside the filter, before they are brought into contact with the filter hoses, there is also a great risk that a "shell" will form inside the filter, see page 2, second full paragraph.

Just before the separated material is brought into contact with the crude exhaust gases, it is passed over perforated dust joint plates, through which holes a part of the separated material is diverted to the lower part of the filter housing for further transport to the electrolysis furnaces. The selection of which particles of the separated material are not to be recycled back to the exhaust gases is thus made completely randomly, which also applies to the exhaust gas treatment plant according to the above-mentioned American patent. This means that fresh, reactive sorbent particles can be diverted after a circulation inside the filter, while those sorbent particles that have already been recycled several times and have a high degree of saturation are recycled to the exhaust gases.

In other words, there is no control over how many times the fresh sorbent is circulated before it is removed to the electrolysis furnaces, resulting in a low utilization rate for the sorbent.

DESCRIPTION OF THE PRESENT INVENTION TECHNICAL PROBLEM It is thus a technical problem to achieve a high degree of utilization of the sorbent while at the same time giving as little wear as possible to the components of the exhaust gas treatment plant.

OBJECT OF THE INVENTION The object of the present invention is therefore to solve the above-mentioned technical problems of achieving a high degree of utilization of the sorbent while minimizing wear.

SUMMARY OF THE INVENTION The above object is achieved by introducing a larger proportion of the process gas at the sorbent inlet of the dust collector than at its sorbent outlet 467 952 by means of a control means arranged in the gas inlet, whereby the sorbent supplied via the sorbent inlet is directed towards the sorbent outlet. at the same time as it is circulated at least twice inside the dust separator, without simultaneous return of contaminated process gas.

The dust collector consists of a textile barrier filter with a gas inlet for supplying the polluted process gas, a gas outlet for removal of the purified process gas, at least one sorbent inlet for supplying fresh sorbent and at least one, sorbent outlet separated from the sorbent inlet for sorbent effluent. and according to the invention it has a control means extending across the gas inlet for controlling the introduction of the polluted process gas into the blocking filter and the introduction of the sorbent into the polluted process gas, the surface of the control means increasing in the direction from the blocking filter's sorbent inlet to its sorbent outlet. GENERAL DESCRIPTION OF THE INVENTION According to the present invention, the above-mentioned problem of achieving a high degree of utilization of the sorbent is solved while the wear is minimized by providing such control of the movement of the fresh sorbent inside the dust separator that no fresh sorbent particles are removed from dust. circulated at least twice inside it. Wear is minimized by circulating internally inside the dust collector, without causing high-velocity sorbent particles to collide with any metallic surfaces, and by no simultaneous return of contaminated process gas, see pages 3 and 4, the last two and first paragraphs, respectively. .

The sorbent is preferably circulated 2 - 100, especially 2 - 20, times inside the dust separator.

A larger proportion of the process gas is introduced at the sorbent inlet of the dust collector than at its sorbent outlet. This causes the process gas to flow in such a way inside the dust collector that the sorbent, during its circulation inside the dust collector, is forced to move in such a way that crushing of the sorbent is avoided.

The sorbent is preferably caused to perform a helical movement during its circulation inside the dust separator.

The process gas is preferably imparted to a turbulent flow configuration upon insertion into the dust collector. To achieve the above control of the movement of the fresh sorbent inside the dust collector, it is designed as a textile barrier filter with a gas inlet for supplying the polluted process gas, a gas outlet for removing the purified process gas, at least one sorbent outlet for supplying sorbent, at least one sorbent outlet separate from the sorbent inlet for removal of recycled sorbent and a means extending across the gas inlet for controlling the introduction of the contaminated process gas into the barrier filter and the introduction of the sorbent into the contaminated process gas.

When the sorbent outlet is separated from the sorbent inlet, the fresh sorbent must be moved a certain distance inside the barrier filter before it can be removed from it. During this movement, the sorbent is caused, by the flow of the process gas, which is controlled by the control means, to move in such a way that it is supplied to and separated from the process gas several times, thereby ensuring a high utilization of the sorbent. g The textile barrier filter is preferably a hose filter.

The surface of the guide means preferably increases in the direction from the sorbent inlet of the barrier filter to its sorbent outlet. This ensures that a larger proportion of the process gas is introduced at the point in the barrier filter where the fresh sorbent is supplied than at the place where the recycled in the sorbent is removed. This means that the concentration of the sorbent particles is highest at the place in the barrier filter where the degree of saturation of the sorbent particles is highest.

The guide means is preferably designed as a serrated plate.

This ensures that sorbent particles are spread over a larger part of the cross-sectional area of the gas inlet than would have been the case if the control member had been designed as a straight plate. The plate's teeth also create vortices in the process gas, ie the process gas is given a turbulent flow configuration. These effects result in a more even distribution of the sorbent particles in the process gas.

The length of the teeth of the plate preferably decreases in the direction from the sorbent inlet to the sorbent outlet.

One or two sorbent inlets are preferably arranged at one or two of the sides of the barrier filter, while one or two sorbent outlets are preferably arranged at another or two other sides of the barrier filter.

A sorbent outlet is preferably arranged at one side of the barrier filter, while a sorbent outlet is preferably arranged at another side of the barrier filter.

The sorbent outlet is preferably arranged at an opposite side to one side.

The control means preferably extends from one side of the gas inlet, which is arranged in connection with one side of the blocking filter, to its opposite side, which is arranged in connection with the opposite side of the blocking filter.

DESCRIPTION OF THE PROPOSED EMBODIMENT The invention will be described in more detail below with reference to the accompanying drawings.

Fig. 1 schematically shows, in a side view, a device according to the present invention.

Fig. 2 shows the device according to Fig. 1 in a view seen from the front.

Fig. 3 shows the device according to Figs. 1 and 2 in a view seen from above.

The device shown in Fig. 1 consists of a hose filter 1, which comprises a filter housing 2 with a gas inlet 3 for introduction of the polluted process gas to be purified, for example exhaust gases from electrolysis furnaces for reduction of alumina, and a gas outlet 4 for removal of the purified the process gas. The interior of the filter housing is by means of a plate 5 divided into a lower filter chamber 6 for the polluted gas and an upper filter chamber 7 for the purified gas, which are connected to the gas inlet 3 and the gas outlet 4, respectively.

The hose filter also comprises longitudinally and transversely arranged filter hoses 8, usually 100 - 800 pieces, especially 540 pieces. These felt hoses are releasably mounted at their upper, open end in the plate 5. Their length varies between 3 and 8 meters, usually 6 meters, and their diameter varies between 100 and 300 mm, usually 130 mm. The distance between two adjacent hoses varies in length between 130 and 500 mm, usually 160 mm, and in transverse between 130 and 500 mm, usually 220 mm.

The lower filter chamber 6 consists of a bottom part 9 and a filter part 10, in which the filter hoses 8 are arranged. The bottom part 9 has a vertical, front wall 9a, two vertical, opposite side walls 9b, 9c, and an inclined, rear wall 9d, which serves as the bottom for the 467 952 M 8 filter housing 2. This configuration means that the vertical section of the bottom part takes the form of a right-angled triangle, see Fig. 1, while its cross-section takes the form of a rectangle, see Fig. 3. The filter part 10 has a vertical, front wall 10a, two vertical, opposite side walls 1Db, 1Dc and a vertical, rear wall 10d, which means that both its vertical and cross-sections take the shape of a rectangle.

As shown in Fig. 2, a sorbent inlet 11 for supplying fresh sorbent particles, such as alumina particles, is arranged in one of the side walls 9b of the bottom part, while a sorbent outlet 12 for circulating sorbent particles is arranged at the opposite side wall 9c. A baffle plate 13 for diverting recycled sorbent particles to the sorbent outlet 12 is rotatably connected to the upper end of the sorbent outlet. This baffle plate extends vertically up to the lower end of the filter hoses, see Fig. 2, and longitudinally to the rear wall 9d of the bottom part, see Fig. 3. It also appears from Fig. 3 that the angular deviation of the baffle plate 13 relative to the side wall 9c of the bottom part 9 is denoted by angle ß.

The gas inlet 3 is located at the lower ends of the walls of the bottom part 9 and has a vertical, front wall 3a, two vertical, opposite side walls 3b, 3c and a vertical, rear wall 3d. This means that both its vertical and cross-sections take the form of a rectangle, see Figs. 1 and 3. To prevent the crude gas from flowing past the sorbent outlet 12, where the presence of sorbent particles is low, the side wall 3c of the gas inlet is placed one piece inside the side wall 9c of the bottom part. These side walls are connected to each other by means of a partition wall 14 with a vertical portion I4a, which is connected to the side wall 3c of the gas inlet, and an inclined portion 14b, which is connected to the side wall 9c of the bottom part.

The side wall 3b, on the other hand, is arranged directly below the side wall 9b of the bottom part, in which the sorbent inlet 11 opens, see above.

An inclined, serrated plate 15 is placed across the upper end of the gas inlet 3 and is attached at its rear edge to the lower end of the rear wall 9d of the bottom part 9. This plate is designed so that the tips of its teeth 16 are placed at the same distance from the front wall 3a of the inlet, while the distance between the roots of the teeth and the front wall 3a decreases in the direction from the side wall 3b to the side wall 3c, i.e. the length of the teeth 16 decreases in this direction. The surface of the plate, on the other hand, increases in this direction, see Fig. 3, and thus covers a larger part of the cross-sectional area of the gas inlet at the side wall 3c than at the side wall 3b. Fig. 3 also shows that the roots of the teeth lie along a straight line which forms an angle α with the rear edge of the plate.

As can be seen from Fig. 1, the entire filter part 10 is not provided with filter hoses, but the first row of filter hoses is arranged approximately 1 meter from the front wall 10a of the filter part. As a result, a flow channel 17 for the polluted gas is formed inside the lower filter chamber 6 directly above the gas inlet 3.

Nozzle tubes 18 with nozzles 19 are arranged in the upper filter chamber 7 so that a nozzle 19 is placed above the upper, open end of each filter hose 8. During the cleaning of filter hoses, these are supplied with a short, strong compressed air pulse from a pressure tank (not shown) via the nozzle tubes 18 and the nozzles 19 according to a well-defined cleaning program.

The function of the hose filter will be described in more detail in the following.

The process gas contaminated with gaseous impurities, such as hydrogen fluoride, and particulate pollutants, such as fluorine-containing dust, is introduced via the gas inlet 3 into the bottom part 9 of the lower filter chamber 6. The process gas is brought into contact with the sorbent particles via the plate 15. most of the cross-sectional area of the gas inlet and is mixed with the entire incoming process gas.

This mixing is facilitated by the vortices created in the process gas by the plate teeth. The adsorbent particles are thus mixed with the process gas and its gaseous pollutants, which are to some extent sorbed by the sorbent particles and converted into particulate pollutants.

The process gas then flows up through the flow channel 17 and into the filter hoses 8 at a speed of about 0.025 - 0.04 m / S, after which it flows out into the upper filter chamber 7 via the upper, open ends of the filter hoses. From there, the process gas is led via the gas outlet 4 to a chimney (not shown) for emissions into the atmosphere.

As the process gas passes through the filter material of the filter hoses, which for example consists of polyester, its particulate pollutants are deposited on the outside of the filter hoses. During the passage of the particulate pollutants deposited on the outside of the filter hoses, the remaining gaseous pollutants of the process gas are sorbed by unsaturated sorbent particles and separated from the process gas.

During the cleaning of the filter hoses, the particles accumulated on the filter hoses then fall down on the rear wall 9d of the bottom part 9 and slide along it down to the plate 15, which reinserts the particles into the contaminated process gas. Since the process gas mainly flows in between the filter hoses from the flow channel 17, the falling movement of the sorbator 4e7 952 v m the particles is not substantially counteracted by upflowing process gas.

This means that the particles are not returned to the filter hoses, without having passed the plate 15.

Due to the fact that the plate 15 covers a larger part of the cross-sectional area of the gas inlet at the side wall 3c, where the recycled sorbent particles are removed via the sorbent outlet 12, than at the side wall 3b, where the fresh sorbent particles are supplied via the sorbent inlet 11, a larger part of the process gas 9b than at the opposite side wall 9c. As the process gas tends to be evenly distributed over all the filter hoses 8, the uneven distribution of the process gas over the cross-sectional area of the gas inlet causes the gas introduced at the side wall 9b to flow in the direction of the opposite side wall 9c and thereby cause the sorbent particles to move to the filter. in the direction of the sorbent outlet. As a result, the fresh sorbent particles introduced at the side wall 9b of the bottom part via the sorbent inlet 11 are forced to move towards the sorbent outlet 12 at the side wall 9c while being caused to perform a helical movement. This gentle movement ensures that the sorbent particles are not crushed during their recirculation inside the lower filter chamber 6.

How many times the fresh sorbent particles are circulated inside the lower filter chamber is determined by the magnitude of the angles m and ß.

Namely, an increase of the angle α means that the plate 15 covers a larger part of the cross-sectional area of the gas inlet at the side wall 3c, whereby the pitch of the helical turns increases. An increase in the angle ß, on the other hand, means that a larger proportion of the circulating particles are removed. The number of circulations with the values of a and ß shown in Fig. 3 is about 10.

Since the volume flow of the process gas is smaller at the side wall 9c of the bottom part than at the side wall 9b, the concentration of the sorbent particles increases in the direction of the sorbent outlet 12, where the sorbent particles have a higher degree of saturation and thus have the worst quality. This means that an acceptable separation of the gaseous pollutants of the process gas is also obtained in the bottom part 9 and the filter part 10 closest to the side walls 9c and 10c. The invention is of course not limited to the embodiment described above, but can be modified in various ways within the scope of the appended claims.

For example, the bottom part 9 may be provided with two sorbent inlets and a sorbent outlet, instead of being provided with a sorbent inlet 11 and a sorbent outlet 12. The sorbent outlet may be arranged in the side walls 9b and 9c of the bottom unit, while the sorbent outlet may be arranged in the middle. the side walls at the rear wall 9d of the bottom end. It is also possible to provide the bottom unit 9 with two sorbent tufts and one sorbent top, the sorbent tops being able to be arranged at the side walls 9b and 9c of the bottom part, while the sorbent top can be arranged midway between the side walls of the rear wall 9d.

For example, the gas inlet 3 and the filter chambers 6 and 7 may be formed with a circular shape for a rectangular cross-section.

Claims (10)

_. _ 467 952 'a P A T E N T K R A V A method of increasing the degree of utilization of a dry absorbent and / or adsorbent, hereinafter referred to as sorbent, for absorption or adsorption of gaseous pollutants, such as hydrogen fluoride, from a polluted process gas, such as exhaust gases from electrolytic furnaces, wherein the sorbent after its reaction with the gaseous the pollutants are separated in a dust separator (1), which has a gas inlet (3) for the supply of the polluted process gas and a gas outlet (4) for the removal of the purified process gas, after which a part of the separated sorbent is returned to the polluted the process gas through an internal circulation inside the dust collector, fresh sorbent being supplied to the dust trap (1) via at least one sorbent inlet (11), while circulating sorbent is removed from the dust separator via at least one sorbent outlet (12) separated from the sorbent inlet that a larger proportion of the process gas is introduced at the sorbent inlet (11) of the dust collector (1) than at its sorbent outlet (12) with or a control means (15) arranged in the gas inlet (3), whereby the sorbent supplied via the sorbent inlet is caused to move in the direction of the sorbent outlet at the same time as it is circulated at least twice inside the dust separator, without simultaneous return of contaminated process gas. 2. A method according to claim 1, characterized in that the sorbent is circulated 2 - 100, preferably 2 - 20, times inside the dust separator (1). Apparatus for carrying out the method according to any one of the preceding claims for increasing the utilization rate of a dry absorbent and / or adsorbent, hereinafter referred to as sorbent, for absorption or adsorption of gaseous pollutants, such as hydrogen fluoride, from a polluted process gas, such as exhaust gases from electrolytic furnaces. comprising a dust separator in the form of a textile barrier filter (1) with a gas inlet (3) for supplying the polluted process gas, a gas outlet (4) for removing the purified process gas, at least one sorbent inlet (11) for supplying fresh sorbent, at least one sorbent outlet (12) separate from the sorbent inlet (12) for removing circulating sorbent, characterized by a control means (15) extending across the gas inlet (3) for controlling the introduction of the polluted process gas into the barrier filter ( 1) and the introduction of the sorbent into the contaminated process gas, the surface of the control means (15) increasing in the direction from the sorbent inlet (11) of the barrier filter to its sorbent outlet (12). Device according to Claim 3, characterized in that the textile barrier filter consists of a hose filter (1). Device according to claim 3 or 4, characterized in that the guide means is designed as a saw-toothed plate (15). Device according to claim 5, characterized in that the length of the teeth (16) of the plate (15) decreases in the direction from the sorbent inlet (11) of the blocking filter (1) to its sorbent outlet (12). Device according to one of Claims 3 to 6, characterized in that one or two sorbent inlets (11) are arranged at one (9b; 9d) or two (9b, 9c) sides of the barrier filter and in that one or two sorbent outlets (12 ) are arranged at another (9c; 9d) or two other (9b, 9c) sides of the barrier filter. Device according to claim 7, characterized in that a sorbent inlet (11) is arranged at one side (9b) of the blocking filter and that a sorbent outlet (12) is arranged at another of the sides (9a, 9c, 9d) of the blocking filter. Device according to claim 8, characterized in that the sorbent outlet (12) is arranged at a side (9c) opposite one side (9b). Device according to claim 9, characterized in that the control means (15) extends from one side (3b) of the gas inlet (3), which is arranged in connection with one side (9b) of the blocking filter (1), to its opposite side ( 3c), which is arranged in connection with the opposite side (9c) of the barrier filter.