DE2804742A1 - METHOD FOR CLEANING UP EXHAUST GASES CONTAINING METAL CHLORIDE - Google Patents

Description

Aluminum Company of America, Pittsburgh, Pennsylvania, 7th St.A.

Process for cleaning exhaust gases containing metal chloride

This application is a continuation-in-part application of US patent application Serial No. ₀ 765 34-6 dated February 3, 1977 "

The invention relates to exhaust gas treatment and more specifically to the treatment of exhaust gases in the production of aluminum chloride which contain minor amounts (15% or less) of HCl, COCIp and vaporized metal chlorides hydrolyzable to HCl and the corresponding metal oxides.

Halogen-containing gases and vapors, such as phosgene (COOL ·,), HCl, silicon tetrachloride, titanium tetrachloride, ferric chloride, and aluminum chloride, as well as CIp contained in the exhaust gas of an aluminum chloride reaction chamber, must be removed from the gas before it is released into the atmosphere even if they are present in low condentrations, such as 15 % or less. Although it is known that

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ζ. Bo silicon tetrachloride with water to form a gelatinous Fiderschlags reacts, which is generally referred to as silica gel, this reaction is not and should not be desired In practice, because of the clogging of the pipes and kettles, avoided after the formation of such a gelatinous Precipitation can occur.

U.S. Patent 1,461,399 (Lowe) shows that when silicon chloride is contacted with a jet of steam, above the dehydration temperature from silica to silicon chloride to silica and hydrogen chloride according to the reaction

+ 2 H ₂ O >> 4HCl +

wirdo hydrolyzed In practice it has been found, however, that this conversion takes place at ordinary steam temperatures of about 10O ⁰ C with only low reaction rates. R.IOHudson shows in "The Vapor Phase Hydrolysis of NOn-Metallic Chlorides" published in Volume 11 of the International Congress of Pure Applied Chemistry London Proceedings, 1947, that this reaction must be carried out at much higher temperatures. The author reports that Daubree has found that silicon tetrachloride and water vapor react in red heat in the presence of oxygen to form highly crystallized silicon dioxide. Hudson then explains that because oxygen and silicon tetrachloride do not react unless higher temperatures are used, that one is the one

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Vapor phase hydrolysis at temperatures of the order of 700 C show «. Hudson then proves this experimentally by stating tests which ^{have been carried out in the temperature range from 25 to 10O 0} C, with evidently no vapor phase hydrolysis of silicon tetrachloride took place, at least without occurrence of a slight deposition of a material which he called "silicon"("silicon" ) called _o Hudson then states that he observed a reaction with the formation of highly crystallized silicon dioxide at a temperature of 400 ⁰ O _o

It is also known to form metal oxides from metal halides in fluidized beds ,, Z refer ₀ B. the US Patents 3,043,657, 3,043,659 and 3 04-3660 (Hughes, inter alia, _o) on the formation of metal oxides, vie Z ₀ B ₀ titanium dioxide or silicon dioxide, by reacting the corresponding chloride with oxygen or air in a fluidized bed at temperatures of 500 ^° C. or higher, according to US Pat. No. 3,642,441 (Van Weert), metal chlorides are converted into a fluidized bed with steam or water vapor implemented. VMerum the bed is, however, at an elevated temperature of 600 ⁰ C or higher by combusting a gas such "B. Propane, operated in the fluidized bed »

Although these reactions indicated, of course, the problem of eliminating metal chlorides, such as, for example, silicon chloride, without Dissolve the formation of undesired gelatinous products, make the temperatures provided for carrying out the reactions such Procedure economically unattractive It is also too

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note that these references include the formation of such The aim of oxides from concentrated chloride vapors is not the purification of gases which contain small amounts or traces contained in chlorides

It is the aim of the invention to provide a method for cleaning exhaust gases, which contain halogenated gases, which by converting the gases to solid metal oxides without excessive application of heat can be hydrolyzed, propose, this goal and Further objects of the invention can be found in the following description and the drawing in more detail,

In accordance with the invention comprises contacting the exhaust gases 15 wt _o - contained% or less gaseous halogenated compounds including metal chlorides, for converting said hydrolyzable metal chlorides into oxides and HCl with steam at a temperature of 100 to 150 ⁰ C, while the gases through a bed flows from solid particles selected from the class consisting of carbon and metal oxides of groups IIA, IIIA, IVA, IVB and mixtures thereof, and then contacts the gases with liquid water at a temperature of 20 to 100 ^° C to remove HCl vapors from it.,

In a preferred embodiment, the gases are first passed through a dust filter and then through a bed of activated carbon to remove at least some of the halogenated compounds to remove. An extracting gas is then passed through the

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Bed of activated carbon passed to the halogenated deposited on it To remove compounds, the extracting gas containing the metal chlorides is then mixed with water vapor in the presence of particulate carbon, metal oxides of the groups HA, HIA, IVA, IVB or mixtures thereof are contacted as described above. The HCl formed is dissolved in liquid water absorbed to form an aqueous hydrochloric acid solution.

The base is then passed through a bed of activated charcoal in the presence of water to hydrolyze _{any COCl 2} in the gases to HCl and Co _2. The gases are then scrubbed to remove sulfur oxides and passed through an incinerator to oxidize Co to COp «.

The only drawing is a flow diagram showing the exhaust treatment system the invention explained

After the drawing currents exhaust gases at 2, which effluent gases may be a ChIorierungssystems, formed at the metal chlorides, is initially through the conduit 4 to the dust filter 6, the appropriate of a cloth or ceramic filter material, such as, for _o example of wool, which Can remove particles of only ΊΟ microns _o The gases then flow either dm? · *, A line 10 or through a line 12 to an adsorber 20 made of activated carbon. The gases are passed through line 12 when they contain more than 1000 ppm CIp. The gases in line 12 flow through a chlorine converter 14, which is not part of the

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finding isto

The carbon adsorber 20 contains activated carbon with a particle size range from preferably 2.38 to 4.76 mm. The gases will passed through the adsorber 20 at a speed of 6 to 18 m / min, so that a residence time in the adsorber of is given for about 3 s. In order to achieve the greatest possible adsorption of the metal chlorides, such as B. of aluminum chloride, silicon chloride or titanium chloride to ensure from the gas stream is preferred a second carbon adsorber of similar dimensions 22 in series with the carbon adsorber 20, and with this connected by a line 16 is used.

The line 18 leads the gases freed from their metal chloride components to the HCl absorber 30, which is kept at a temperature of 20 to 100 ⁰ O. A number of the same absorbers 30, 40 and 46, as indicated in the drawing, are preferably used for Removal of HCl from the gas used _o The HCl absorber can be a packed column _{filled with polypropylene (such as Z 0} B ₀ MASPAG, manufactured by Clarkson Controls and Equipment Company). The HCl absorber 30 can also consist of other suitable devices, such as Z ₀ B ₀ of tray columns, which facilitate gas-liquid contact, water or weak hydrochloric acid (0 to 20 % HcI) is added to the top of the absorber 30 through the Line 32 is supplied and flows in countercurrent to the base stream, whereby the HCl components are extracted from the gases. The one on line 32

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- ίο -

passing water or _o the incoming there acid may originate from HCl absorbers 4-0 or 46 or from an external source ,. The HCl units are an aqueous through the conduit 34 in the form of HCl solution with an HOL concentration of about 32 wt _o -% removed. The HCl components can also be removed from the system by the absorber 40 or 46 _Q

The gases leave the HCl absorber 30 generally through the Line 36, from which they reach the HCl absorber 40. on the other hand The gases can also reach the HCl absorber 46 or the hydrolyzer 50 directly. Further HCl proportions will be extracted from the gases when the absorbers 40 and 46 are used

The gases leave the HCl absorber through line 48, from which they reach a hydrolysis vessel 50, in which COC ^ is converted to HCl and Co ₂ by contacting the gases with HpO or weak hydrochloric acid in the presence of activated carbon. The vessel 50 contains activated carbon preferably with a particle size of 2.38 to 4.76 mm _o HCl is removed in aqueous form through line 54, a portion of which can be returned to hydrolyzer 50 through lines 56, 58 and pump 60 _o The remainder of the HCl can be passed back to the HCl absorber 46 through line 52 «. On the other hand, the line 52 can be connected to the absorber 30 or 40 _o Water to be filled is fed to the hydrolyzer 50 through the line 62,

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The gases leaving the hydrolyzate 50 flow to the scrubber 80 through line 64 _O WyOH or Na ₂ CO ₅ , and H _? 0 are fed to the scrubber 80 through the line 66 in sufficient quantities to keep the pH value at 5.6 and to selectively wash SOp but not COp from the gases flowing in. The gases exiting scrubber 80 are then passed through line 68 to CO incinerator 84- where CO with air or oxygen from line 86 to CO _? The gases exiting incinerator 84 through line 90 can be vented to the atmosphere by any suitable means.

The metal chlorides, which are denoted by M Cl in the drawing and which, by definition, must also be hydrolyzable to HCl and the corresponding metal oxides, are extracted from the gases by the adsorber 20 or 22 and then removed from the activated carbon bed located therein for renewal of the bed by an extracting gas is passed through the adsorber 24 in the drawing at a temperature of about 100 to 400 ^° C., preferably of about 250 ^° C., at a speed of about 3 to 15 m / min for a period of about 4 to 16 hours , which corresponds to the adsorber 20 and 22 and can be exchanged with them. The extracting gas, which can be nitrogen or any other inert or non-reactive gas, such as _o ZoB. CO ₂ , leaves the adsorber 24 together with the entrained metal chloride through the line 26 and flows to a hydrolymator 70, which is a fluidized bed, ie a

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Bed of fluids contains particles which consist of carbon or metal oxides of the classes HA, IHA, IVA, IVB or mixtures thereof with a particle size range of 0.044 to 0.30 mm. Steam at a temperature of 100 to 150 ⁰ C enters the bed of fluid particles in the hydrolyzer 70 through line 72 and is mixed with the gas to hydrolyze the metal chlorides to metal oxides and HCl, so that, for example, SiCl ^ SiO ₂ + HCl yields o The metal oxides remaining in the bed and the extracting gas and HCl leave the bed through line 74, which is connected to line 18, just before entering the HCl absorber 30, from which the hydrogen chloride from the metal chloride hydrolyzer 70, as described above, ο is removed

The adsorbers 20, 22 and 24 are, as mentioned above, interchangeable and can, as shown in the drawing, be arranged in series. In the embodiment shown, after complete regeneration, the adsorber 24 replaces the adsorber 22, which in turn replaces the adsorber 20 _o The adsorber 20, which contains the majority of the adsorbed metal chlorides, is then regenerated, as described above for the adsorber 24 _o In each In this case, the most cleaned adsorber is used as the second adsorber in the series to ensure complete adsorption of the metal chlorides from the gas.,

That entering hydrolyzer 70 through line 72

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Water is maintained at a temperature above its dew point. Simply, the water may consist of steam "at atmospheric pressure". The hydrolyzate 70 is maintained at a temperature sufficient (generally around 100 ⁰ O) to thereby ensure that the hydrolysis reaction between the metal chloride and the water vapor above the dew point of the mixed gas stream takes place and prevents the formation of gelatinous material in the bed from fluid particles, which would otherwise lead to clogging of the reaction vessel. This may conveniently be effected by external heating, such as Z ₀ B ₀ by an outer Steam jacket or the like can be achieved.

It has been found that the reaction of silicon chloride is somewhat temperature dependent, and significantly with an increase in temperature above 100 ⁰ C decreases _o Z ₀ Bo has been found that for a given bed volume, at a given speed and a given molar ratio of HPO to SiCl lead ^ a temperature of 100 ⁰ C at atmospheric pressure to a conversion of about 95% silicon chloride came), while a temperature of 125 ° C under otherwise identical conditions leads to only 70% conversion and a temperature of 150 ⁰ C again under otherwise Under the same conditions, the conversion reduced to below 25 %. The temperature in the hydrolyzer should therefore preferably not rise above about 110 to 115 ° C. A large excess of water vapor is required to achieve the desired hydrolysis of the metal chloride to metal oxide. The molar ratio of HpO to M Cl should be at least about 10 and can even be

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The solid material used in the bed consists of particulate carbon or metal oxide classes HA, HIA, IVA, IVB, or mixtures thereof. Ordinary river sand can be used. If a fluidized bed is used, the solid material such as ZoB should be used. Sand, can be crushed to a particle size of 44 x to 297 microns. However _, when using materials such as river sand, it is necessary to set up a cleaning stage beforehand to reduce the iron content of the sand. For example, a river sand has an iron content of about 1 to 2% total iron have _o For reasons which are not yet fully explained, the presence of iron seems to interfere with the process. The leaching of river sand with concentrated hydrochloric acid is a convenient method of removing iron oxide from the sand _o By such leaching of the iron content is reduced to such a low value as 0.3 wt .-%, can be reduced whereby the operational problems. If silica is used in the particle bed, it is preferably quartzite blown sand. Such sand contains less than about 0.03 wt% iron. It has also been found that AlpO can be used in place of silica. However, the additional cost of alumina cannot justify its use as a substitute material from an economic point of view.

The space time of the gas in hydrolyzer 70 can vary

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from as little as 0.03 and preferably 0.065 minutes to much longer periods of time, of a minute or more, depending on the speed of the hydrolyzer flowing gas, the ratio of water vapor to M Cl gas in the reaction vessel and the height of the bed. The relationship of the Spacetime versus bed height and velocity can be expressed by the following equation:

Bed height

Spacetime =

speed

The hydrolysis can be carried out in a static, fluid or entrained bed. A fluid bed is preferred. The velocity of the gases (the total velocity of steam and metal chloride gases) flowing through a fluidized bed should be at least about 0.1 cm / sec to allow for minimum fluidization in the specified particle size range. The speed is preferably about 1 to 200 cm / s for particles with a size of 0.07 ² l to 0.149 mm "

When using fluid beds with internal diameters greater than 0.25 m - or the equivalent dimension for non-round beds, the steam should, as has been determined, be at the bottom of the While the metal chloride gases are injected into the bed at least 0.05 "to 0.076 m above the steam inlet

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should be. Furthermore, the entry speed of the Metal chloride gases in beds of such size or larger dimension are at least 42.7 M / S "around the Prevent bedding material from forming lumps. For fluidized beds narrower than 0.25 m, the injection point for the metal chloride and the velocity of the metal chloride gas are Typically, the length of the nozzle in the bed should be less than critical than 1/5 of the inside diameter of the fluidized bed container Conventional bag filters, such as those made of matted Teflon, can be used to retain the particles in the fluidized bed container will,,

It should also be noted that the use of a fluidized bed appears to be particularly effective with regard to the removal of vapors or mists that result from the hydrolysis of metal chlorides, especially titanium tetrachloride O

The bed height is also important and must be at least 10 cm be, with about 40 to 60 cm or more advantageous for the height are, in turn, a sufficient residence time or space time of the gases within the bed in the specified particle size range and to enable the specified gas velocity range «,

The following examples, which show the hydrolysis of silicon chloride

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explain rid, serve to describe the metal chloride hydrolysis part of the procedure.

example 1

Leached with acid river sand with a particle size range 74-149 microns was charged into a tubular reactor having a diameter of 2.54 cm to a height of about 26 cm The reaction vessel was heated to a temperature of about 100 ⁰ O vapor and gaseous Silicon chloride was fed to the lower part of the reaction vessel at a rate of about 3 »5 to 4.2 cm / s at atmospheric pressure plus the pressure attributable to the bed level, so that a total residence time in the reaction vessel of about 0. 1 min was given. Table I explains the percentages for the conversion of the silicon chloride for various experiments in which the molar ratio of HpO to silicon chloride was varied Amount of deionized water contained, determined. After each experiment, the trap was weighed again and a liquid sample from each trap was 0.1 nor-. Based on this titration, the amount of HCl in the trap could be calculated. Using the reaction equation SiCl ^ + 2H ₃ O = 4HCl + SiO ₂ , the amount of silicon chloride used during the test was based on the amount of HCl found in the water trap expected

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Werdeno This calculation enables a double check the amount of silicon chloride used, determined by weighing the silicon chloride charge flask before and after each Testsο The water trap and the exhaust pipe were then put in

put a drying oven with a temperature of 120 to 150 0 _o to water and acid to be vaporized in the 3PaIIe en The exhaust pipe and the remaining solid residue was rated as 100% of silicon dioxide (SiOP) consisting. This solid residue gives the SiCl ^ which has not been hydrolyzed in the fluidized bed, again ο Using the above equation and the weight of solid substances found in the trap and the evaporation pipe, the amount of silicon chloride converted was calculated. The percent silicon chloride conversion was then calculated using the following formula:

g unreacted silicon chloride 100 χ (1 -

g silicon chloride added to the reaction vessel

An analysis of the solid material found in the water and the evaporator tube after a normal test showed that 92 to ° A % of the material was silica. Accordingly, assuming that 100 % silica was present in the solid material remaining in the water trap and exhaust pipe after drying enables a calculation of the percentages of silicon chlorido reacted

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Table I.

Silicon chloride implementation v _o HPO / SiCl ^ molar ratio

HpO / SiOl ^ molar ratio conversion of SiCl ₄ to silicon dioxide in percent

15 96

20 98

28 99

36 100

45 100

71 100

The results show that using a velocity of 3.5-4.2 cm / sec and a bed height sufficient to provide about 0.1 minute space-time, conversions of 95 % or greater using a wide range of HgO -to-silicon chloride ratios can be achieved.

Example 2

The same experiment was repeated, each increasing the speed to 4.5 to 5 cm / s and the bed height to about Was decreased 20 cm so that there was a space time of about 0.065 min. As can be seen from Table II, this reduced residence time a molar ratio of H

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from at least about 35 to 40 are desirable

Table II

B ^ O / SiOl ^ ratio conversion of SiOl ^ to silicon dioxide in percent

16 74

36 96

62 99

78 92

Example 3

The same reaction was carried out again, under Use of a hollow tube reaction vessel «, The space-time became The results obtained increased significantly by reducing the overall velocity of the gas through the reaction vessel are given in Table III below

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gabeile III

Space time in min HpO / SiCl ^ molar ratio conversion of SiOl ^, to silicon dioxide

S 0.18 59.1 17.9

0.24 73 65.6

0.25 113 79

0.33 33 80.3

0.36 97 93

0.41 57 81.0

When comparing these results with the results in Table I, wherein the residence time of 0.1 min under the same conditions resulted in a conversion of over 95 % using a molar ratio of H ₂ O to silicon tetrachloride of less than 20, can then be seen that the presence of silicon dioxide in the bed of the reaction vessel according to the invention greatly shortens the space time which is required to achieve a high percentage conversion of silicon tetrachloride to solid silicon dioxide.

Example 4-

The experiment of Example 1 was repeated, using a constant molar ratio of H ₂ O / SiCl ^ of 63 but changing the bed temperature from 100 to 125 and 150 ° C. and using a velocity of 4.6 cm / s and a space time of 0.077 min.

Table IV

Conversion of SiOl ^, to silicon dioxide

in percent bed temperature in ⁰ G

98 % 100

70 % 125

24 % 150

The results show that at a given speed,

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a given space-time and a given molar ratio higher Temperatures lead to a decrease in the percentage conversion of silicon chloride to silicon dioxide.

Example 5

Several series of tests were carried out in a manner similar to the test of Example 1 in order to show the effect of space-time on the percentage conversion by varying the bed height. In this I ¹ all the gas velocity ranged from about 6.6 to 7> 6 cm / s. When carrying out two experiments, the first series of tests had a water-to-silicon chloride ratio was carried out from about 34 to 36 »while the second series of tests with such a ratio of about 56 to 70 _° In each case the bed temperature at about 10O ⁰ C was held.

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- 24 Table V

Molar ratio of EUO to silicon chloride Bed height in cm Conversion of silicon chloride to

___________________ silicon dioxide in percent

34-46 10 36

34-46 20 50 co

c 34-46 30 62 cc

2 34-46 40 72

"54-46 50 75 V>

O -F

co 34-46 60 78

* ° 56-69 10 56

56-69 20 "73

56-69 30 78

56-69 40 86

56-69 50 90

56-69 60 92

The results show that an increase in space-time increases the percentage conversion of SiCl ₇ . The results also show that a longer space time is required when the molar ratio of HpO to silicon chloride is below about 50 ,,

Example 6

Another experiment was carried out according to Example 1, but using a space time of about O ₁ CW- to 0.05 min at an HpO to silicon chloride ratio of about 33 53 and a change in the velocity to reflect the effect of the gas velocity to show the percentage conversion of silicon chloride

! Table Vl

Conversion of silicon chloride to silicon dioxide in! Percent

Speed cm / s ,8th 3 ,8th 6th 15th 21st ,1 25th

95 75 4-2 27 30

In this case, the bed height increased with increasing speed increased in order to keep the spacetime approximately constant. It can therefore be seen that, although the same spacetime

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was applied, higher gas velocities actually lead to a reduced percentage conversion _o Therefore, the space time should be increased if the gas velocity is above about 6 cm / s, if particles with a size of 74 to 149 microns are used _o

Example 7

14.2 to 20.5 nr / min exhaust gas from a reaction vessel was fed to the exhaust gas treatment system. The DasStromzusammensetzung corresponded to 34 to 49% CO _2, 17.5 his 19.8% CO, 5.5 to 6.6 ⁰ Jo HCl 0.20 to 0.26% COCl _2, 0.14 to 0,15% SiCl ^, below 0.01 % Cl ₃ and the remainder Np ₀ An aqueous HCl solution was formed from 28 to 30% hydrochloric acid · The HCl solution did not contain any gelatinous materials »Less than 10 ppm COCl ₂ was in determined from the gas leaving the COClp hydrolyser. Neither COClp was found in the exhaust pipe. The COClp content in the exhaust pipe was less than 0.05 ppm. After 30 hours of operation the first adsorber with about 4.5 mvmin a gas stream at 90 ⁰ C with the following composition (75% H _2, 11% Cl _2, 14% CO) was for 4 hours regenerated The adsorbent was then washed with 3.2 up to 5.6 m ⁵ / min N ₂ at 115 to 300 ⁰ C for 4 hours 2/3 by weight, high purity sand (PGS Oklahoma No. ₀ 1, dry) contained “The bed was about eight feet high and diameter

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of 1.68 mo. In addition, steam was introduced into the chloride hydrolyzer at a rate of approximately 7 »6 kg / min. The temperature of the fluidized bed was maintained at 377-3 * 8 ° K, the temperature of the regeneration gas was about 453 ⁰ K; the velocity of the regeneration gas through the feed nozzles was 91 »5" to 122 m / s · The gases leaving the chloride hydrolyzer were cooled and HCl removed in one of the HCl absorbers · No gelatinous precipitation was detected in any of the HGl absorption towers, nor was there any evidence of agglomeration of the fluidized bed. About 193 kg of SiCl ^ were regenerated from the carbon adsorber

Dr · Ve _o / Mü

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e e r e i t e

Claims (1)

Patents Γ 1 J method for cleaning exhaust gases with a content of gaseous metal chlorides hydrolyzable to HOl and the corresponding metal oxides up to 15 wt .-%, characterized in that the gases are contacted with water vapor at a temperature of 100 to 150 G while the gases are allowed to flow through a bed of solid particles chosen from the class consisting of carbon and metal oxides of groups HA, IHA, IVA, IVB and mixtures thereof, thereby converting the metal chlorides into HGl and the corresponding metal oxides, then the gases contacted with liquid water at a temperature of 20 to 100 ⁰ G in order to remove HGl vapors therefrom, and the gases passed through a bed of activated carbon in the presence of water, thereby hydrolyzing GOGl _p to the gases HCl and GO ₂ . 2ο Method according to claim 1, characterized in that the gases are first passed through a bed of activated carbon in order to remove at least part of the halogen compounds, and then extracting gas is passed through the carbon bed 8U9833 / 0823 ORiGiKAL INSPECTED the halogenated compounds that have been terminated thereupon removing said contacting the gases with water in the bed of solid particles. 3ο Method according to claim 1, characterized in that the extracted gases are contacted with HpO vapor using an HpO / M Cl ratio of at least 10 and up to 75, thereby ensuring complete hydrolysis of the metal chlorides. 4. The method according to claim 3 » characterized in that the hydrolysis is carried out at a temperature of 100 to 115 ° 0. 5. The method according to claim 3, characterized in that the particles in the bed now have a particle size range from 0.044 to 0.297. 6. The method according to claim 5 » characterized in that the particles have an iron content of less than 0.3 wt .-%, 7. Method according to claim 3j, characterized in that the space-time of the gases in the said bed of solid particles is approximately 0.03 to 1 minute, _o 8. The method according to claim 7> characterized in that the velocity of the gases in said bed is 1 to 20 cm / s 809833/0828 is _o 9ο procedure according to. Claim 8, characterized in that said bed has a minimum height of at least 10 cm, _o 10o method according to claim 1, characterized in that the gases are washed in a scrubber, maintaining a pH value of about 5 »6 by adding sufficient NaOH or Na ₂ CO ,, and thereby sulfur dioxide after the OOClg hydrolysis stage selectively removed « 11 · The method according to claim 10, characterized in that the washed gases are burned in order to oxidize any partially oxidized carbon compounds to GOp « 809833 / 082Ö