CA1115028A - Process and an apparatus for the recovery of metal oxides, especially for magnesium oxide, in industrial scale - Google Patents
Process and an apparatus for the recovery of metal oxides, especially for magnesium oxide, in industrial scaleInfo
- Publication number
- CA1115028A CA1115028A CA309,484A CA309484A CA1115028A CA 1115028 A CA1115028 A CA 1115028A CA 309484 A CA309484 A CA 309484A CA 1115028 A CA1115028 A CA 1115028A
- Authority
- CA
- Canada
- Prior art keywords
- brine
- spraying
- concentrated
- waste gas
- tower
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
- C01B13/14—Methods for preparing oxides or hydroxides in general
- C01B13/18—Methods for preparing oxides or hydroxides in general by thermal decomposition of compounds, e.g. of salts or hydroxides
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/02—Magnesia
- C01F5/06—Magnesia by thermal decomposition of magnesium compounds
- C01F5/10—Magnesia by thermal decomposition of magnesium compounds by thermal decomposition of magnesium chloride with water vapour
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Inorganic Chemistry (AREA)
- Life Sciences & Earth Sciences (AREA)
- Geology (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
- Treating Waste Gases (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention provides a process for the recovery of metal oxides from contaminated starting materials on an indus-trial scale, in which the starting materials are dissolved in hydro-chloric acid and from the brine thus obtained pure metal oxide and hydrogen chloride are formed by thermal decomposition of the brine in a decomposition furnace after pretreatment of said brine, in which pre-treatment the brine is concentrated by intimate contact with waste gases containing hydrogen chloride from the decomposition furnace the improvement in which the brine to be concentrated is sprayed in a spraying zone in a stream of the waste gas, brine droplets so produced are collected after having passed through the stream of waste gases, and at least a portion of the brine so collected is sprayed at least once in the stream of waste gas and collected after having passed through the stream of the waste gas and fed into a common discharge of the concentrated brine, the pH-value of the discharging concentrated brine being maintained in a preselected range by controlling the amount of the brine subjected to said repeated spraying in the stream of waste gas.
The present invention provides a process for the recovery of metal oxides from contaminated starting materials on an indus-trial scale, in which the starting materials are dissolved in hydro-chloric acid and from the brine thus obtained pure metal oxide and hydrogen chloride are formed by thermal decomposition of the brine in a decomposition furnace after pretreatment of said brine, in which pre-treatment the brine is concentrated by intimate contact with waste gases containing hydrogen chloride from the decomposition furnace the improvement in which the brine to be concentrated is sprayed in a spraying zone in a stream of the waste gas, brine droplets so produced are collected after having passed through the stream of waste gases, and at least a portion of the brine so collected is sprayed at least once in the stream of waste gas and collected after having passed through the stream of the waste gas and fed into a common discharge of the concentrated brine, the pH-value of the discharging concentrated brine being maintained in a preselected range by controlling the amount of the brine subjected to said repeated spraying in the stream of waste gas.
Description
The present invention relates to a proc9~s ~o~ ~h~
recovery of metal oxides, especially of magnesium oxicle, from contaminated star-ting materials, on an industrial scale, in which process the starting materials are first dissolved in hydroch~ri4 acid and from the brine thus obtained pure metal o~ide and hydro-gen chloride are formed by thermal decomposition in a decomposition furnace after pretreatment of said brine, by which pre-treatment the brine is concentrated by intimate contact with the waste gases containing the hydrogen chloride of the decomposition furnace.
In conventional processes of this type the brine *o be concentrated,on the one han~ and the waste gas of the furnace used for the thermal decomposition of the brine,on thç other hand, are fed to a wet washing apparatus, in which the waste gas is contacted intimately with the brine, by which contact the hot waste gas containing both dusty solid material, which has been carried from the decomposition furnace by the stream of the waste gas, and the hydrogen chloride is dedusted. The waste gas also passes a great proportion of its heat content to the brine and water is evaporated from the brine resulting in a concentration thereof. In addition also hydrogen chloride gas from the waste gas is absorbed by the brine.
In conventional apparatuses for the preparàtion of magnesium oxide operating according to the above described process, difficulties arise from the fact that the dusty material contained in the waste gas and consisting mainly of magnesium oxide dissolves only verysparingly in the essentiallyneutral magnesiumchloride brine, which results in an undesired settling of the solid material on the installations provided in the wet washing apparatuses, over which the brine is trickling and the wet washing apparatuses become blocked. A possible operating method to avoid such blockages would be a procedure in which the brine is sufficiently acid, so as to eliminate the formation of blockages by dissolving the dusty magne-3~
: ' :
!
f~
- sium oxide. Ilowever, such a procedure is not economical, as simultaneously with the addition of hydrochloric acid also water would be added to the brine, which water would have to be evaporated in the decomposition furnace with additional expenditure of energy. In the most cases an acid content in the brine flowing off from the concentrator is not desired and neutrali~ation of this acid would be associated with an undesired additional expenditure.
The present invention provides a process of the above .
mentioned type, in which the dusty material carried along with the ;
waste gas of the combustion furnace is absorbed by the brine to be concentrated and removed by the concentrator without causing any blockages in the concentrator without the need to add hydrochloric acid to the brine and without the demand for an undesired low pH~
value in the brine leaving the concentrator, and in which process the p~-value of the brine leaving the concentrator may be maintained in a narrow range due to the subsequent further treatment thereof, so that in the further treatment of the brine practically constant conditions are present.
According to the present invention there is provided a process for the recovery of metal oxides from contaminated starting ?
materials on an industrial scale, in which the starting materials are dissolved in hydrochloric acid and from the brine thus obtained pure metal oxide and hydrogen chloride are formed by thermal decom-position of the brine in a decomposition furnace after pretreatment of said brine, in which pre-treatment the brine is concentrated by intir,late contact with waste gases containing hydrogen chloride from the decomposition furnace the improvement in which the brine to be concentrated is sprayed in a spraying zone in a stream of the waste gas, brine droplets so produced are collected after having passed through the stream of waste gases, and at least a portion of the brine so collected is sprayed at least once in the stream of waste gas and collected after having passed through the stream of the
recovery of metal oxides, especially of magnesium oxicle, from contaminated star-ting materials, on an industrial scale, in which process the starting materials are first dissolved in hydroch~ri4 acid and from the brine thus obtained pure metal o~ide and hydro-gen chloride are formed by thermal decomposition in a decomposition furnace after pretreatment of said brine, by which pre-treatment the brine is concentrated by intimate contact with the waste gases containing the hydrogen chloride of the decomposition furnace.
In conventional processes of this type the brine *o be concentrated,on the one han~ and the waste gas of the furnace used for the thermal decomposition of the brine,on thç other hand, are fed to a wet washing apparatus, in which the waste gas is contacted intimately with the brine, by which contact the hot waste gas containing both dusty solid material, which has been carried from the decomposition furnace by the stream of the waste gas, and the hydrogen chloride is dedusted. The waste gas also passes a great proportion of its heat content to the brine and water is evaporated from the brine resulting in a concentration thereof. In addition also hydrogen chloride gas from the waste gas is absorbed by the brine.
In conventional apparatuses for the preparàtion of magnesium oxide operating according to the above described process, difficulties arise from the fact that the dusty material contained in the waste gas and consisting mainly of magnesium oxide dissolves only verysparingly in the essentiallyneutral magnesiumchloride brine, which results in an undesired settling of the solid material on the installations provided in the wet washing apparatuses, over which the brine is trickling and the wet washing apparatuses become blocked. A possible operating method to avoid such blockages would be a procedure in which the brine is sufficiently acid, so as to eliminate the formation of blockages by dissolving the dusty magne-3~
: ' :
!
f~
- sium oxide. Ilowever, such a procedure is not economical, as simultaneously with the addition of hydrochloric acid also water would be added to the brine, which water would have to be evaporated in the decomposition furnace with additional expenditure of energy. In the most cases an acid content in the brine flowing off from the concentrator is not desired and neutrali~ation of this acid would be associated with an undesired additional expenditure.
The present invention provides a process of the above .
mentioned type, in which the dusty material carried along with the ;
waste gas of the combustion furnace is absorbed by the brine to be concentrated and removed by the concentrator without causing any blockages in the concentrator without the need to add hydrochloric acid to the brine and without the demand for an undesired low pH~
value in the brine leaving the concentrator, and in which process the p~-value of the brine leaving the concentrator may be maintained in a narrow range due to the subsequent further treatment thereof, so that in the further treatment of the brine practically constant conditions are present.
According to the present invention there is provided a process for the recovery of metal oxides from contaminated starting ?
materials on an industrial scale, in which the starting materials are dissolved in hydrochloric acid and from the brine thus obtained pure metal oxide and hydrogen chloride are formed by thermal decom-position of the brine in a decomposition furnace after pretreatment of said brine, in which pre-treatment the brine is concentrated by intir,late contact with waste gases containing hydrogen chloride from the decomposition furnace the improvement in which the brine to be concentrated is sprayed in a spraying zone in a stream of the waste gas, brine droplets so produced are collected after having passed through the stream of waste gases, and at least a portion of the brine so collected is sprayed at least once in the stream of waste gas and collected after having passed through the stream of the
- 2 -, .
waste gas and fed into a common discharge of the concentrated brine, the pH-value of the discharging concentrated brine being maintained in a preselected range by controlling the amount of the brine subjected to said repeated spraying in the stxeam of waste gas.
The process of the invention is characterized in that the brine to be concentrated is sprayed in a stream of waste gas and that the brine droplets are collected after having passed through the stream of the waste gas and that at least a portion of the brine so collected is sprayed again one or several times in the stream of waste gas and collected after having passed through the stream of the waste gas and fed into the common discharge of the concentrated brine, the pH value of the discharging concentrated S
brine being maintained in a preselected range by controlling the amount of the brine subjected to the repeated sprayinq proceduxe in the stream of the waste gas. An intimate contact of the brine to be concentrated with the waste gas is effected by spraying the brine to be concentrated in the stream of the waste gas without the need to provide any installations in the zone of this contact on which installations solid material could deposit, so that in spite of the very intimate contact by the fine distribution of the sprayed brine with the stream of waste gas which permits a substantially complete dedusting thereof no breakdowns due to blockages occur.
It i5 possible to adapt the degree of the mutual contact between the brine to be concentrated and the waste gas of the decomposition urnace extensively to the desired operating conditions by the choice of the size of the brine droplets which are formed during the spraying of the brine, and by the extent of the repeated ~ S~re~m B spraying procedures of the brine in the ~ of waste gas which degree deterMines the heat transfer fromthe waste gas to the brine and therewi~h the concentration of the brine and the dedusting of the waste gas and the absorption of hydrogen chloride from the
waste gas and fed into a common discharge of the concentrated brine, the pH-value of the discharging concentrated brine being maintained in a preselected range by controlling the amount of the brine subjected to said repeated spraying in the stxeam of waste gas.
The process of the invention is characterized in that the brine to be concentrated is sprayed in a stream of waste gas and that the brine droplets are collected after having passed through the stream of the waste gas and that at least a portion of the brine so collected is sprayed again one or several times in the stream of waste gas and collected after having passed through the stream of the waste gas and fed into the common discharge of the concentrated brine, the pH value of the discharging concentrated S
brine being maintained in a preselected range by controlling the amount of the brine subjected to the repeated sprayinq proceduxe in the stream of the waste gas. An intimate contact of the brine to be concentrated with the waste gas is effected by spraying the brine to be concentrated in the stream of the waste gas without the need to provide any installations in the zone of this contact on which installations solid material could deposit, so that in spite of the very intimate contact by the fine distribution of the sprayed brine with the stream of waste gas which permits a substantially complete dedusting thereof no breakdowns due to blockages occur.
It i5 possible to adapt the degree of the mutual contact between the brine to be concentrated and the waste gas of the decomposition urnace extensively to the desired operating conditions by the choice of the size of the brine droplets which are formed during the spraying of the brine, and by the extent of the repeated ~ S~re~m B spraying procedures of the brine in the ~ of waste gas which degree deterMines the heat transfer fromthe waste gas to the brine and therewi~h the concentration of the brine and the dedusting of the waste gas and the absorption of hydrogen chloride from the
- 3 -waste gas by the brine. Suprisingly the pH-value of the brine leaviny the concentrator may be maintained in the desired range by controlling the amount of the brine subjected to the repeated spraying procedures without the need to add any acid. -Preferably, the brine droplets from the first spraying procedure and also the brine droplets from subsequent spraying procedures are collected in a sump a~ranged below the spraying zone, from which sump the concentrated brine is withdrawn from the further treatment and also the brine to be subjected to further spraying procedures in the stream of waste gas. In such a way a good solution of the dusty material being only suspended in the brine is achieved, which dusty material has been separated from the stream of the waste gas. The control of the process may be achieved simply with a pH-measuring device, the sensor of which is arranged in the sump of the spraying tower. .
It is advantageous to spray the brine being sprayed for the first time in the stream of waste gas separated from that brine which has been already sprayed once in the stream of the waste gas, as thereby the size of the droplets may be selected with more .
freedom. ~ :~
As the stream of waste gas has very often a relatively great velocity also a portion of the brine droplets sprayed in the ~:
stream of the waste gas is carried along Erom the waste gas. It is advantageous to separate particles of the brine carried along from the waste gas o the furnace leaving the spraying zone of the brine to be concentrated, to collect them and to feed them into the discharge of the brine to be concentrated, so as to use this valuable brine for the recovery of magnesium o~ide and to avoidany impairment of the production of hydrochloric acid from the hydrogen chloride . ~.
present in the waste gas. ~ ~.
The present invention also provides an apparatus for carrying out the process of the invention, which apparatus is ;~
.
, , . . : . .. .
provided with a dissolving vessel, a decomposition furnace, a brine concentrator t~nrough which is passed the wasts gas of the decompo-sition furnace and adsorption means ~or the hydrogen chloride. The apparatus of the invention is characterized in that ~he brine con-centrator is in the form of a spraying tower, to the upper spraying nozzles of which the brine to be concentrated is fed and from tAe sump of which the concentrated brine is withdrawn for further treat-ment, which tower is provided with a brine conveying pump, the _ inlet sucking side of which is connected with the sump of the spraying tower and the pressure side of which is connected througha line with the spraying nozzles of the spraying tower, and that in the zone of the sump of the spraying tower or ln a flowing path of the brine withdrawn from the sump the sensor of a pH-measuring device is arranged which controls the passage through the brine conveying pump. It is especially advantageous that the apparatus of the invention is constructed very simply and safely which construction may be realized with low expenditure.
It is also possible to collect the brine droplets which are sprayed for the first time in the stream of the waste gas separated from those droplets which derive from further spraying procedures, the brine intended for the further spraying procedures being withdrawn from the collecting vessel of the first spraying procedure. The control of the pH-value o the concentrated brine may be achieved such that the brine leaving the brine concentrator from a portion which has been sprayed only once, and anoth~r portion which has been spayed several times is mixed and that the ratio of these two portions is varied. Instead of such a variation or additionally thereto also the number of the spraying procedures, if repeated spraying is intended or the conveying capacity oE a ~ -brine conveying pump arrangedina sprayingcycle in which the spraying distance serving for repeated spraying may be varied for the control of the pH-value; however, it is also possible to control the amount .
- 5 ~
, : . . : . .
- of waste gas passing the spraying distance serving for repeated spraying o~ the brine instead of such measures or ad~itionally thereto for controlling the pH-value.
The present invention will be further illu~trated by way o~ the accompanying drawings in which: :
Figure 1 is a diagrammatic representation of the apparatus for carrying out the processofthe inventionin theform ofa.principle scheme;
Figure 2 shows the inventive embodiment of a concentrator of such an apparatus in form of a spraying tower and . ~ ?
Figùre 3 shows another embodiment of such a concentrator in form of a spraying tower arrangement.
The app~ratus shown in Figure 1 comprises a dissolving vessel 1 provided with an agitator 2. The starting materials ;
containing metal ions, especially magnesium ions are introduced in ~;
this dissolving vessel 1, as shown by the arrow 3 and hydrochloric acid in which the starting materials are d.issolved, is introduced into the dissolving vessel 1 via a line 4. The contaminated metal and magnesium chloride solution obtained after reaction of the starting materials with the hydrochloric acid is withdrawn from the dissolving vessel 1 through a line 5 and passed into a precipit-ation vessel 6, in which impurities of the brine are caused to precipitate. The precipitated impurities are removed from the brine B ~ a filter device 7. From the filter device 7 the brine passes into a concentrator 9 via a line 8, in which concentrator 9 it is :
intimately contacted wi.th hot waste gases from a decomposition .~
furnace 10, which furnace serves for the thermal decomposi.tion of : .
the metal, especially magnesium chloride brine to give metal- and ,~
megnesium oxide and hydrogen chloride. The waste gas coming from ;~
3Q . the furnace 10 provided with burners 11 passes a cyclone separator 1~, which separates a great proportion of the dust carried along by . ~-the waste gas which dust isrecycled intothe furnacelO. The cleaned ~
... . . . ,, .. . . ::
2~
,. .
waste gas enters lnto the concentrator 9 via line 13, in which concentrator 9 it delivers a grea~ proportion of its heat to the metal and magnesium chloride brine passing through the concentrator 9. By evaporation of the solution water of the brine the concen-tration of the bri~e is increased and the brine itself heated.
Simultaneously the brine passing through the concentrator 9 absorbs any residual dust in the waste gas from the furnace 10. Also some hydrogen chloride contained in the waste gas from the ~urnace 10 is absorbed by the brine. The brine leaving the concentrator 9 is fed to the decomposition furnace 10 via line 14 and the metal- and magnesium oxide formed in this decomposition furnace 10 is discharged at the bottom 15 thereof.
If desired or necessary, the brine may be subjected to further purification procedures between the filter device 7 and the concentrator 9 and also between the concentrator 9 and the decompo-sition furnace 10.
After passing the concentrator 9 the waste gas from the decomposition furnace 10 passes to the absorption column 17 via line 16, to which water is supplied by the line 18. The hydrogen chloride contained in the waste gas is absorbed in the water and purified waste gas leaves the absorption column 17 at the outlet 20.
The hydrochloric acid formed in the absorption column 17 is recycled then to the dissolving vessel 1 via the line 4.
The concentrator shown in Figure 2 is in the form of a spraying tower 25, which is provided with spraying nozzles 26, to which the brine to be concentrated is fed via the line 8. The waste gas containing hydrogen chloride and leaving the decomposition furnace 10 is also fed to the spaying tower 25 via the line 13.
During the passage through the spraying tower 25 this waste gas comes into intimate contact with the brine droplets of the brine sprayed by the spraying nozzles 26 in the spraying tower 25, the brine being heated intenslvely by the hot waste gas and a part of ' ; '' ;, , . . . .
water of the brine being evaporated. The ~rine droplets also absorb the dust particles present in the waste gas. The brine droplets falling downwards in the spraying tower 25 are collected in the sump 27 of -the spraying tower 25. From the sump 27 th~ ?
concentrated brine is passed to further treatment through the line 14, in which a stop valve 28 controllable by the height of the liquid level is conveniently inserted.
- A further brine line 30 provided with a sieve 31 leads fxom the sump 27 to the inlet side of a brine pump 32, which pump is connected via a line 33 with further spraying nozzles 34 arranged in the spraying tower 25. A control valve 35 is present in the line 33, which valve is controlled by a pH-measuring device 36, the sensor of which is arranged in the sump 27. However, said sensor 37 could be arranged also in the flow path of the brine withdrawn from the sump 27, e.g. in the lines 30, 33 or 14.
Thus, the pH-value of the brine being in the sump 27 may be maintained within a selected rangel as by controlling the amount of brine being sprayed several times in the spraying tower 25 ;;~
through which the waste gas passes, the amount of the hydrogen chloride absorbed from the brine may be varied.
Having passed through the spraying tower 25 the waste gas passes to the droplet separator 41 via the line 40, in which separator the brine droplets carried along by the waste gas in the ~praying tower 25, are separatad from the waste gas. These brine droplets are collected in the droplet separator 41 and recycled to the spraying tower 25 by the line 42. The waste gas leaving the droplet separator 41 is conducted via the line 16 to absorption means in which the hydrogen chloride is absorbed for preparing the hydrochloric acid.
The spray tower arrangement shown in Figure 3 comprises two spraying apparatuses, each of which is in the form of a spraying tower. However, instead of providing two spraying towers 25a, 25b ~ 8 -.. . . . .
z~ .
it would be possible to arrange these spray~n~ appara~u~e~ tn a common housing through which the waste gas is passed. Each of the two spraying apparatuses of the arrangement of Figure 3 comprises a set of spraying nozzles 26a, 26b and a collecting vessel for collecting the sprayed brine droplets. These collecting vessels are shown in their simplest form by the lower part of the spraylng tower housing, in which the sump 27a and 27b respectively is formed.
The brine to be concentrated is fed via the line 8 to the set of spraying nozzles 26a and the waste gas from the decomposition 10furnace of the apparatus is introduced via the line 13 into the spraying tower 25a. The total of the brine subiected only to one spraying procedure in the stream of waste gas is fed from the sump 27a~on the one hand,via line 44 provided with a control valve 45 9 and a brine pump ~6 to the set of spraying nozzles 26b of the spraying tower 25b where it is again sprayed and,on the other hand, via line 47 provided with a control valve 48 to the discharge line 14 for the concentrated brine. The spraying tower 25b is provided also with a line 30 from the sump 27b, said line 30 being provided with a brine pump 32, which also feeds the set of spraying nozzles 2026b. The amount of the brine sprayed from the sump 27b via the set of nozzles 26b is controlled by a pH-measuring device 36, the sensor of which is present in the line 14. Furthermore the plI-value is influenced by adjustment of the ratio of the brine leaving the sump through the lines 44 and 47. In the arrangement of Figure 3 the waste gas is fed to the spraying tower 25b via line 49 after passing the spraying tower 25a and leaves it through the line 16. It is also possible to feed a portion of the waste gas leaving the spraying tower 26a directly to the line 16 so as to control the pH-value.
The process of the present inventlon is illustrated by the following exarnples:
X~Qple 1 3125 1 of a solution o~ MgC12 having a concerltration of 400 g of MgC12/1 are sprayed in the spray-roasting furnace 10 of the axrange-ment of Figure 1 and roasted by means of the combu~tion of 437 Nm of natural gas with 4707 Nm3 of air. 418 kg of MgO is obtained which is discharged at 15 from the furnace 10. The fumes bf the furnace 10 pass through the cyclone separator 12 and enter the concentrator 9 through the line 13. The fumes have a temperature -of 370C at the entrance of the concentrator 9and ato~al volume of 13,585 Nm3 corresponding to an operating volume of 35,500 m3 under an operating pressure of 0.90 bar. The composition of the fumes is as follows:
nitrogen ~N2) 3742 Nm3 ~ ~;
carbon dioxide (CO2)459 Nm3 ~ ;
water vapor (H2O)3551 Nm3 hydrogen chloride (E~Cl)578 Nm3 oxygen (2) 85 Nm3 _ ;
dust transfer (MgO)106 kg The fumes enter the concentrator shown in Figure 2 through ~ ~
. .
the line 13; at the same time 4000 1 of magnesium chloride brine are sprayed by the nozzles 26. The magnesium chloride brine reacts with the fumes and a concentrated magnesium chloride brine having 400 g of MgC12/1 in an amount of 3125 1 is obtained. The dedusted fumes leave the concentrator through the line 40 and are l.iberated from brine droplets carried along in the droplet collector 41, so that a ~ `
gas mixture with a temperature of about 100C having the composition:
N 3742 Nm3 C2 459 Nm3 H2O ~ 4660 Nm3 HCl 462 Nm3 2 85 Nm3 and a total volume of totally 9407 Nm3 or 14,441 m3 is sucked through the line 16 at a -temperature of 100C and pressure of 0.89 bar and conducted to -the absorption column 17. This waste gas is free of dust. To assist the reaction and to improve the separation of dust, brine is sucked off from the concentra-tor sump 27 through the brine line 30 by means of the pump 32 and sprayed by the nozzles 3~, so that the brine is repeatedly sprayed. The adjustment of the amount of the brine subjected to repeated spraying procedures to 12~500 l yields a pH-value of 7 in the concentrated brine discharging through the line 14, said brine being turbid also by MgO-particles obtained from the fumes.
Example 2:
The process is in accordance with Example l with the exception that the amount of brine to be subjected to repeated ; spraying procedures is adjusted to 16pO0 1. ~ pH-value of 6 is obtained in the concentrated brine discharging through the line 14.
No undissolved ~lgO-particles are present in the brine.
Example 3:
The process is operated in accordance with Example l and the amount of the brine to be sprayed repeatedly is adjusted to 25J000 l. A pH-value of 1 is obtained in the brine discharging through the line 14.
Example 4:
The process is operated in accordance with Example l and the amount of the brine to be sprayed repeatedly is controlled by the pH-measuring device 36. The control is adjusted such that the value 35 wil~ be opened further, when the pH-value of the corrcentrate increases above 6.3 and the free cross-section thereof will be reduced, when the pH-value of the concentrate decreases below 5.7.
In such an operation the pH-value of the brine present in the sump varies between 5 and 7; the brine does not contain any solid in suspension. The amount of concentrate sprayed by the nozz~es 34 is in average 15,736 1 and the variation margin is about + 2000 l.
5 ~ ~2~ ~
It should be men-t~on ~ th~ ~he pr~ce~9 ~nd -~bo apparatu~
of the present invention may be used especially advantageously, if the concentrated metal brine and magnesium chloride brine respec-tively is subjected to a further purification before it is subjected to thermal decomposition.
.. - " :
,. ~"''' ;~
~ . -' ' ' ~ "'''.
. .
:
....
;
It is advantageous to spray the brine being sprayed for the first time in the stream of waste gas separated from that brine which has been already sprayed once in the stream of the waste gas, as thereby the size of the droplets may be selected with more .
freedom. ~ :~
As the stream of waste gas has very often a relatively great velocity also a portion of the brine droplets sprayed in the ~:
stream of the waste gas is carried along Erom the waste gas. It is advantageous to separate particles of the brine carried along from the waste gas o the furnace leaving the spraying zone of the brine to be concentrated, to collect them and to feed them into the discharge of the brine to be concentrated, so as to use this valuable brine for the recovery of magnesium o~ide and to avoidany impairment of the production of hydrochloric acid from the hydrogen chloride . ~.
present in the waste gas. ~ ~.
The present invention also provides an apparatus for carrying out the process of the invention, which apparatus is ;~
.
, , . . : . .. .
provided with a dissolving vessel, a decomposition furnace, a brine concentrator t~nrough which is passed the wasts gas of the decompo-sition furnace and adsorption means ~or the hydrogen chloride. The apparatus of the invention is characterized in that ~he brine con-centrator is in the form of a spraying tower, to the upper spraying nozzles of which the brine to be concentrated is fed and from tAe sump of which the concentrated brine is withdrawn for further treat-ment, which tower is provided with a brine conveying pump, the _ inlet sucking side of which is connected with the sump of the spraying tower and the pressure side of which is connected througha line with the spraying nozzles of the spraying tower, and that in the zone of the sump of the spraying tower or ln a flowing path of the brine withdrawn from the sump the sensor of a pH-measuring device is arranged which controls the passage through the brine conveying pump. It is especially advantageous that the apparatus of the invention is constructed very simply and safely which construction may be realized with low expenditure.
It is also possible to collect the brine droplets which are sprayed for the first time in the stream of the waste gas separated from those droplets which derive from further spraying procedures, the brine intended for the further spraying procedures being withdrawn from the collecting vessel of the first spraying procedure. The control of the pH-value o the concentrated brine may be achieved such that the brine leaving the brine concentrator from a portion which has been sprayed only once, and anoth~r portion which has been spayed several times is mixed and that the ratio of these two portions is varied. Instead of such a variation or additionally thereto also the number of the spraying procedures, if repeated spraying is intended or the conveying capacity oE a ~ -brine conveying pump arrangedina sprayingcycle in which the spraying distance serving for repeated spraying may be varied for the control of the pH-value; however, it is also possible to control the amount .
- 5 ~
, : . . : . .
- of waste gas passing the spraying distance serving for repeated spraying o~ the brine instead of such measures or ad~itionally thereto for controlling the pH-value.
The present invention will be further illu~trated by way o~ the accompanying drawings in which: :
Figure 1 is a diagrammatic representation of the apparatus for carrying out the processofthe inventionin theform ofa.principle scheme;
Figure 2 shows the inventive embodiment of a concentrator of such an apparatus in form of a spraying tower and . ~ ?
Figùre 3 shows another embodiment of such a concentrator in form of a spraying tower arrangement.
The app~ratus shown in Figure 1 comprises a dissolving vessel 1 provided with an agitator 2. The starting materials ;
containing metal ions, especially magnesium ions are introduced in ~;
this dissolving vessel 1, as shown by the arrow 3 and hydrochloric acid in which the starting materials are d.issolved, is introduced into the dissolving vessel 1 via a line 4. The contaminated metal and magnesium chloride solution obtained after reaction of the starting materials with the hydrochloric acid is withdrawn from the dissolving vessel 1 through a line 5 and passed into a precipit-ation vessel 6, in which impurities of the brine are caused to precipitate. The precipitated impurities are removed from the brine B ~ a filter device 7. From the filter device 7 the brine passes into a concentrator 9 via a line 8, in which concentrator 9 it is :
intimately contacted wi.th hot waste gases from a decomposition .~
furnace 10, which furnace serves for the thermal decomposi.tion of : .
the metal, especially magnesium chloride brine to give metal- and ,~
megnesium oxide and hydrogen chloride. The waste gas coming from ;~
3Q . the furnace 10 provided with burners 11 passes a cyclone separator 1~, which separates a great proportion of the dust carried along by . ~-the waste gas which dust isrecycled intothe furnacelO. The cleaned ~
... . . . ,, .. . . ::
2~
,. .
waste gas enters lnto the concentrator 9 via line 13, in which concentrator 9 it delivers a grea~ proportion of its heat to the metal and magnesium chloride brine passing through the concentrator 9. By evaporation of the solution water of the brine the concen-tration of the bri~e is increased and the brine itself heated.
Simultaneously the brine passing through the concentrator 9 absorbs any residual dust in the waste gas from the furnace 10. Also some hydrogen chloride contained in the waste gas from the ~urnace 10 is absorbed by the brine. The brine leaving the concentrator 9 is fed to the decomposition furnace 10 via line 14 and the metal- and magnesium oxide formed in this decomposition furnace 10 is discharged at the bottom 15 thereof.
If desired or necessary, the brine may be subjected to further purification procedures between the filter device 7 and the concentrator 9 and also between the concentrator 9 and the decompo-sition furnace 10.
After passing the concentrator 9 the waste gas from the decomposition furnace 10 passes to the absorption column 17 via line 16, to which water is supplied by the line 18. The hydrogen chloride contained in the waste gas is absorbed in the water and purified waste gas leaves the absorption column 17 at the outlet 20.
The hydrochloric acid formed in the absorption column 17 is recycled then to the dissolving vessel 1 via the line 4.
The concentrator shown in Figure 2 is in the form of a spraying tower 25, which is provided with spraying nozzles 26, to which the brine to be concentrated is fed via the line 8. The waste gas containing hydrogen chloride and leaving the decomposition furnace 10 is also fed to the spaying tower 25 via the line 13.
During the passage through the spraying tower 25 this waste gas comes into intimate contact with the brine droplets of the brine sprayed by the spraying nozzles 26 in the spraying tower 25, the brine being heated intenslvely by the hot waste gas and a part of ' ; '' ;, , . . . .
water of the brine being evaporated. The ~rine droplets also absorb the dust particles present in the waste gas. The brine droplets falling downwards in the spraying tower 25 are collected in the sump 27 of -the spraying tower 25. From the sump 27 th~ ?
concentrated brine is passed to further treatment through the line 14, in which a stop valve 28 controllable by the height of the liquid level is conveniently inserted.
- A further brine line 30 provided with a sieve 31 leads fxom the sump 27 to the inlet side of a brine pump 32, which pump is connected via a line 33 with further spraying nozzles 34 arranged in the spraying tower 25. A control valve 35 is present in the line 33, which valve is controlled by a pH-measuring device 36, the sensor of which is arranged in the sump 27. However, said sensor 37 could be arranged also in the flow path of the brine withdrawn from the sump 27, e.g. in the lines 30, 33 or 14.
Thus, the pH-value of the brine being in the sump 27 may be maintained within a selected rangel as by controlling the amount of brine being sprayed several times in the spraying tower 25 ;;~
through which the waste gas passes, the amount of the hydrogen chloride absorbed from the brine may be varied.
Having passed through the spraying tower 25 the waste gas passes to the droplet separator 41 via the line 40, in which separator the brine droplets carried along by the waste gas in the ~praying tower 25, are separatad from the waste gas. These brine droplets are collected in the droplet separator 41 and recycled to the spraying tower 25 by the line 42. The waste gas leaving the droplet separator 41 is conducted via the line 16 to absorption means in which the hydrogen chloride is absorbed for preparing the hydrochloric acid.
The spray tower arrangement shown in Figure 3 comprises two spraying apparatuses, each of which is in the form of a spraying tower. However, instead of providing two spraying towers 25a, 25b ~ 8 -.. . . . .
z~ .
it would be possible to arrange these spray~n~ appara~u~e~ tn a common housing through which the waste gas is passed. Each of the two spraying apparatuses of the arrangement of Figure 3 comprises a set of spraying nozzles 26a, 26b and a collecting vessel for collecting the sprayed brine droplets. These collecting vessels are shown in their simplest form by the lower part of the spraylng tower housing, in which the sump 27a and 27b respectively is formed.
The brine to be concentrated is fed via the line 8 to the set of spraying nozzles 26a and the waste gas from the decomposition 10furnace of the apparatus is introduced via the line 13 into the spraying tower 25a. The total of the brine subiected only to one spraying procedure in the stream of waste gas is fed from the sump 27a~on the one hand,via line 44 provided with a control valve 45 9 and a brine pump ~6 to the set of spraying nozzles 26b of the spraying tower 25b where it is again sprayed and,on the other hand, via line 47 provided with a control valve 48 to the discharge line 14 for the concentrated brine. The spraying tower 25b is provided also with a line 30 from the sump 27b, said line 30 being provided with a brine pump 32, which also feeds the set of spraying nozzles 2026b. The amount of the brine sprayed from the sump 27b via the set of nozzles 26b is controlled by a pH-measuring device 36, the sensor of which is present in the line 14. Furthermore the plI-value is influenced by adjustment of the ratio of the brine leaving the sump through the lines 44 and 47. In the arrangement of Figure 3 the waste gas is fed to the spraying tower 25b via line 49 after passing the spraying tower 25a and leaves it through the line 16. It is also possible to feed a portion of the waste gas leaving the spraying tower 26a directly to the line 16 so as to control the pH-value.
The process of the present inventlon is illustrated by the following exarnples:
X~Qple 1 3125 1 of a solution o~ MgC12 having a concerltration of 400 g of MgC12/1 are sprayed in the spray-roasting furnace 10 of the axrange-ment of Figure 1 and roasted by means of the combu~tion of 437 Nm of natural gas with 4707 Nm3 of air. 418 kg of MgO is obtained which is discharged at 15 from the furnace 10. The fumes bf the furnace 10 pass through the cyclone separator 12 and enter the concentrator 9 through the line 13. The fumes have a temperature -of 370C at the entrance of the concentrator 9and ato~al volume of 13,585 Nm3 corresponding to an operating volume of 35,500 m3 under an operating pressure of 0.90 bar. The composition of the fumes is as follows:
nitrogen ~N2) 3742 Nm3 ~ ~;
carbon dioxide (CO2)459 Nm3 ~ ;
water vapor (H2O)3551 Nm3 hydrogen chloride (E~Cl)578 Nm3 oxygen (2) 85 Nm3 _ ;
dust transfer (MgO)106 kg The fumes enter the concentrator shown in Figure 2 through ~ ~
. .
the line 13; at the same time 4000 1 of magnesium chloride brine are sprayed by the nozzles 26. The magnesium chloride brine reacts with the fumes and a concentrated magnesium chloride brine having 400 g of MgC12/1 in an amount of 3125 1 is obtained. The dedusted fumes leave the concentrator through the line 40 and are l.iberated from brine droplets carried along in the droplet collector 41, so that a ~ `
gas mixture with a temperature of about 100C having the composition:
N 3742 Nm3 C2 459 Nm3 H2O ~ 4660 Nm3 HCl 462 Nm3 2 85 Nm3 and a total volume of totally 9407 Nm3 or 14,441 m3 is sucked through the line 16 at a -temperature of 100C and pressure of 0.89 bar and conducted to -the absorption column 17. This waste gas is free of dust. To assist the reaction and to improve the separation of dust, brine is sucked off from the concentra-tor sump 27 through the brine line 30 by means of the pump 32 and sprayed by the nozzles 3~, so that the brine is repeatedly sprayed. The adjustment of the amount of the brine subjected to repeated spraying procedures to 12~500 l yields a pH-value of 7 in the concentrated brine discharging through the line 14, said brine being turbid also by MgO-particles obtained from the fumes.
Example 2:
The process is in accordance with Example l with the exception that the amount of brine to be subjected to repeated ; spraying procedures is adjusted to 16pO0 1. ~ pH-value of 6 is obtained in the concentrated brine discharging through the line 14.
No undissolved ~lgO-particles are present in the brine.
Example 3:
The process is operated in accordance with Example l and the amount of the brine to be sprayed repeatedly is adjusted to 25J000 l. A pH-value of 1 is obtained in the brine discharging through the line 14.
Example 4:
The process is operated in accordance with Example l and the amount of the brine to be sprayed repeatedly is controlled by the pH-measuring device 36. The control is adjusted such that the value 35 wil~ be opened further, when the pH-value of the corrcentrate increases above 6.3 and the free cross-section thereof will be reduced, when the pH-value of the concentrate decreases below 5.7.
In such an operation the pH-value of the brine present in the sump varies between 5 and 7; the brine does not contain any solid in suspension. The amount of concentrate sprayed by the nozz~es 34 is in average 15,736 1 and the variation margin is about + 2000 l.
5 ~ ~2~ ~
It should be men-t~on ~ th~ ~he pr~ce~9 ~nd -~bo apparatu~
of the present invention may be used especially advantageously, if the concentrated metal brine and magnesium chloride brine respec-tively is subjected to a further purification before it is subjected to thermal decomposition.
.. - " :
,. ~"''' ;~
~ . -' ' ' ~ "'''.
. .
:
....
;
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a process for the recovery of metal oxides from contaminated starting materials on an industrial scale, in which the starting materials are dissolved in hydrochloric acid and from the brine thus obtained pure metal oxide and hydrogen chloride are formed by thermal decomposition of the brine in a decomposition furnace after pretreatment of said brine, in which pretreatment the brine is concentrated by intimate contact with waste gases containing hydrogen chloride from the decomposition furnace the improvement in which the brine to be concentrated is sprayed in a spraying zone in a stream of the waste gas, brine droplets so produced are collected after having passed through the stream of waste gases, and at least a portion of the brine so collected is sprayed at least once in the stream of waste gas and collected after having passed through the stream of the waste gas and fed into a common discharge of the concentrated brine, the pH-value of the discharging concentrated brine being maintained in a preselected range by controlling the amount of the brine subjected to said repeated spraying in the stream of waste gas.
2. A process as claimed in claim 1 wherein the brine droplets from a first spraying and brine droplets from subsequent sprayings are collected in a sump arranged below the spraying from which sump the concentrated brine is withdrawn for further treatment and also brine to be subjected to further spraying in the stream of waste gas.
3. A process as claimed in claim 2 wherein the brine subjected to subsequent spraying in the stream of waste gas is sprayed separately from the brine to be subjected to the first spraying.
4. A process as claimed in claim 1, 2 or 3 wherein the waste gas leaving the spraying zone of the brine being concentrated or subjected to a treatment to separate entrained brine particles which particles are collected and fed into the discharge of the concentrated brine.
5. A process as claimed in claim 1, 2 or 3 in which the metal oxide is magnesium oxide.
6. An apparatus for the recovery of metal oxides from contaminated starting materials which comprises a dissolving vessel, a decomposition furnace, a brine concentrator through which waste gas from the decomposition furnace is arranged to be passed and absorption means for hydrogen chloride, the brine concentrator being in the form of a spraying tower having upper spraying nozzles to which the brine to be concentrated is arranged to be fed and a sump from which the concentrated brine is arranged to be withdrawn for further treatment, which tower is provided with a brine conveying pump, the inlet side of which is connected with the sump of the spraying tower and the pressure side of which is connected through a line with spraying nozzles of the spraying tower and a sensor of a pH-measuring device being arranged in the sump of the spraying tower or in a flow path of the brine withdrawn from the sump, said measuring device being arranged to control passage of the brine through the brine conveying pump and thus maintain the pH value of the concentrated brine in a preselected range.
7. An apparatus as claimed in claim 6 in which the spraying nozzles fed by the brine conveying pump are independent of the spraying nozzles to which the brine to be concentrated is arranged to be fed, when it enters the spraying tower for the first time, the spraying nozzles fed by the brine conveying pump being arranged beneath the other spraying nozzles.
8. An apparatus for the recovery of metal oxides from contaminated starting materials which comprises a dissolving vessel, a decomposition furnace, a brine concentrator through which waste gas from the decomposition furnace is arranged to pass, and absorp-tion means for hydrogen chloride, the brine concentrator being in the form of a spraying lower arrangement, which comprises at least two spraying towers arranged in the stream of waste gas, each of which have a set of spraying nozzles and a collecting vessel arranged there beneath, the spraying nozzles of a first spraying tower being connected with a feed line of the brine to be concentrated and for feeding the spraying nozzles of a second spraying tower a feed line connected with a collecting vessel of the first spraying tower is provided, and both the collecting vessel of the first spraying tower and that of the second spraying tower being connected with a line discharging the concentrated brine, and a sensor of a pH-measuring device being arranged in the flow path of the concentrated brine, which measuring device controls the amount of brine flowing to the spraying nozzles of the second spraying tower and/or the amount of waste gas passing a spraying zone of the second spraying tower and thus maintain the pH-value of the concentrated brine in a preselected range.
9. An apparatus as claimed in claim 8, in which a further line provided with a brine conveying pump and connected with the collecting vessel of the second spraying tower is provided to feed the spraying nozzles of the second spraying tower.
10. The apparatus of claim 6, 7 or 8 including a droplet separator in the discharge line for the waste gas of the spraying tower or the spraying tower arrangement the liquid discharge of which leads into the collecting vessel of the spraying tower and the spraying tower arrangement respectively.
11. An apparatus for the recovery of metal oxides from contaminated starting materials which comprises a dissolving vessel, a decomposition furnace, a brine concentrator through which waste gas from the decomposition furnace is arranged to be passed and absorption means for hydrogen chloride, the brine concentrator being in the form of a spraying tower having spraying nozzles to which the brine to be concentrated is arranged to be fed and a sump from which the concentrated brine is arranged to be withdrawn for further treatment, the spraying nozzles being connected by a feed line with said sump for recirculation of concentrated brine and a sensor of a pH-measuring device being arranged in the flow path of the concentrated brine, which measuring device controls the amount of brine flowing to the spraying nozzles and/or the amount of waste gas passing a spraying zone of the spraying nozzles and thus maintain the pH-value of the concentrated brine in a preselected range.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AT605877A AT352081B (en) | 1977-08-22 | 1977-08-22 | PROCESS FOR THE LARGE-SCALE PRODUCTION OF METAL OXIDES, IN PARTICULAR MAGNESIUM OXIDE, AND DEVICE FOR CARRYING OUT THE PROCESS |
| ATA6058/77 | 1977-08-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1115028A true CA1115028A (en) | 1981-12-29 |
Family
ID=3582443
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA309,484A Expired CA1115028A (en) | 1977-08-22 | 1978-08-16 | Process and an apparatus for the recovery of metal oxides, especially for magnesium oxide, in industrial scale |
Country Status (10)
| Country | Link |
|---|---|
| AT (1) | AT352081B (en) |
| BR (1) | BR7805368A (en) |
| CA (1) | CA1115028A (en) |
| DE (1) | DE2834560A1 (en) |
| ES (1) | ES472721A1 (en) |
| FR (1) | FR2401098A1 (en) |
| GB (1) | GB2006175B (en) |
| GR (1) | GR65340B (en) |
| IL (1) | IL55334A (en) |
| IT (1) | IT1115567B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT392464B (en) * | 1988-08-10 | 1991-04-10 | Veitscher Magnesitwerke Ag | MAGNESIUM OXIDE IN THE FORM OF A FINE POWDER AND ITS USE |
| EP2821368A1 (en) * | 2013-07-03 | 2015-01-07 | PURAC Biochem BV | Method for processing magnesium chloride solutions |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE721358C (en) * | 1935-08-14 | 1942-06-02 | Metallgesellschaft Ag | Production of magnesium oxide from water-containing magnesium chloride solutions or melts |
| FR1299386A (en) * | 1961-09-05 | 1962-07-20 | Zentrale Forschungsstelle Fuer | Process for producing magnesium oxide from solutions or salts containing magnesium chloride |
| DE2608567A1 (en) * | 1975-03-19 | 1976-09-30 | Oesterr Amerikan Magnesit | Aq. magnesium chloride soln. concn. in thermal oxide prodn. - by introducing into hot waste gas from calciner and sintering furnace |
| AT347403B (en) * | 1975-11-20 | 1978-12-27 | Veitscher Magnesitwerke Ag | METHOD FOR THE LARGE ENGINEERING OF MAGNESIUM OXIDE HIGH PURITY |
-
1977
- 1977-08-22 AT AT605877A patent/AT352081B/en not_active IP Right Cessation
-
1978
- 1978-08-07 DE DE19782834560 patent/DE2834560A1/en not_active Ceased
- 1978-08-07 GR GR56953A patent/GR65340B/en unknown
- 1978-08-11 IL IL55334A patent/IL55334A/en unknown
- 1978-08-16 CA CA309,484A patent/CA1115028A/en not_active Expired
- 1978-08-17 FR FR7823994A patent/FR2401098A1/en active Granted
- 1978-08-21 GB GB7834004A patent/GB2006175B/en not_active Expired
- 1978-08-21 BR BR7805368A patent/BR7805368A/en unknown
- 1978-08-21 ES ES472721A patent/ES472721A1/en not_active Expired
- 1978-08-21 IT IT68947/78A patent/IT1115567B/en active
Also Published As
| Publication number | Publication date |
|---|---|
| DE2834560A1 (en) | 1979-03-01 |
| IL55334A (en) | 1981-10-30 |
| GR65340B (en) | 1980-08-18 |
| BR7805368A (en) | 1979-05-02 |
| GB2006175A (en) | 1979-05-02 |
| AT352081B (en) | 1979-08-27 |
| IT1115567B (en) | 1986-02-03 |
| GB2006175B (en) | 1982-04-21 |
| ATA605877A (en) | 1979-02-15 |
| FR2401098A1 (en) | 1979-03-23 |
| IL55334A0 (en) | 1978-10-31 |
| FR2401098B1 (en) | 1983-01-28 |
| ES472721A1 (en) | 1979-10-16 |
| IT7868947A0 (en) | 1978-08-21 |
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