GB2068920A - Dry-scrubbing fluoride- containing gases - Google Patents
Dry-scrubbing fluoride- containing gases Download PDFInfo
- Publication number
- GB2068920A GB2068920A GB8004808A GB8004808A GB2068920A GB 2068920 A GB2068920 A GB 2068920A GB 8004808 A GB8004808 A GB 8004808A GB 8004808 A GB8004808 A GB 8004808A GB 2068920 A GB2068920 A GB 2068920A
- Authority
- GB
- United Kingdom
- Prior art keywords
- alumina
- gas
- fines
- fraction
- bag filter
- 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.)
- Withdrawn
Links
- 239000007789 gas Substances 0.000 title claims abstract description 46
- 238000005203 dry scrubbing Methods 0.000 title abstract description 5
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims abstract description 41
- 239000002245 particle Substances 0.000 claims abstract description 10
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229910000040 hydrogen fluoride Inorganic materials 0.000 claims abstract description 7
- 239000000356 contaminant Substances 0.000 claims abstract description 5
- 238000011144 upstream manufacturing Methods 0.000 claims abstract description 5
- 239000004411 aluminium Substances 0.000 claims abstract description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 3
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 3
- 238000004519 manufacturing process Methods 0.000 claims abstract description 3
- 238000000034 method Methods 0.000 claims description 8
- 229930195733 hydrocarbon Natural products 0.000 claims description 5
- 150000002430 hydrocarbons Chemical class 0.000 claims description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 4
- 229910052799 carbon Inorganic materials 0.000 claims description 4
- 239000011362 coarse particle Substances 0.000 claims description 4
- 238000004064 recycling Methods 0.000 abstract 1
- 239000000463 material Substances 0.000 description 8
- 239000007787 solid Substances 0.000 description 7
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 239000003463 adsorbent Substances 0.000 description 3
- 238000001354 calcination Methods 0.000 description 3
- 239000004215 Carbon black (E152) Substances 0.000 description 2
- 239000011230 binding agent Substances 0.000 description 2
- 239000010419 fine particle Substances 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 238000005201 scrubbing Methods 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 238000001179 sorption measurement Methods 0.000 description 2
- 239000002912 waste gas Substances 0.000 description 2
- 238000004131 Bayer process Methods 0.000 description 1
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 1
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000012717 electrostatic precipitator Substances 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 239000011737 fluorine Substances 0.000 description 1
- 229910052731 fluorine Inorganic materials 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 239000011236 particulate material Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/02—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by adsorption, e.g. preparative gas chromatography
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Analytical Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
In the "dry-scrubbing" of the off- gas from an electrolytic reduction cell for the production of aluminium, particulate alumina (2) is entrained in the gas (1) to adsorb hydrogen fluoride and at least part of the alumina is separated from the gas by means of a bag filter (8) to which a fines fraction alumina is supplied direct. Such fines fraction alumina may be separated from the alumina feed before contact with the off-gas. Alternatively a coarse fraction alumina is separated from the off-gas, e.g. in cyclone (4), before entry into the bag filter (8) and the fines fraction alumina is supplied to the bag filter by recycling a part (10) of the fines particle recovered by the filter. Part of the separated coarse fraction may be recycled (3) to the off-gas upstream of the cyclone (4). Unrecycled fines may be calcined (9) for removal of organic contaminants and then fed, together with unrecycled coarse fraction (6) to the reduction cell. <IMAGE>
Description
SPECIFICATION
Improvements in dry scrubber systems for adsorption of reactive gases
The present invention relates to the dry scrubbing of gases with particulate solids for the removal of reactive components from a gas stream. The invention is particularly directed to the removal of hydrogen fluoride from the off-gas from electrolytic reduction cells for the production of aluminium.
The off-gas includes quantities of hydrogen fluoride, arising from the reaction of the fluoride fluxes in the electrolytic cells with water vapour.
The off-gas also contains very finely divided carbon released from the carbon anodes, heavy hydrocarbons in the case of such anodes that contain pitch binders, and other solids including finely divided metallic impurities such as iron which originate in the raw materials supplied to the cells. It is necessary that the hydrogen fluoride content of such off-gas should be substantially reduced before the gas is vented to the atmosphere.
It is well known that hydrogen fluoride can be removed from such off-gas by a "dry scrubbing" technique in which the hydrogen fluoride is removed by contacting the gas with a solid reactant, normally alumina, which is removed from the gas stream by a bag filter or electrostatic precipitator.
It is common practice to entrain the whole or a part of the alumina, for a group of reduction cells in the off-gas from the cells to recover HF from the off-gas, before the alumina is fed to the cells. In that way at least a proportion of the emitted HF and other fluorine values are adsorbed onto the feed alumina and recycled to the cells with the feed alumina.
In conventional procedure, as used for scrubbing the off-gas from electrolytic cells equipped with prebake anodes, the entrained alumina is caught in bag filters. The bag filter catch may be forwarded wholly to the electrolytic cell or partly recirculated for re-entrainment in the off-gas.
Alumina from Bayer process plants includes particles in a quite wide particle range. It has already been shown in British Patent
No. 1,416,344 to be desirable to classify the alumina particles after contacting the off-gas from
Soderberg cells with alumina, because it has been found that, proportionately, the fine particles pick up much more of the tarry hydrocarbon droplets which distil from the binder of Soderberg cell anodes. Since it is undesirable to return the collected tarry material to the cells, the separation of the alumina fines from the remainder of the feed provides a means of eliminating a major proportion of the tarry material from the alumina feed on the alumina fines, which may then be subjected to calcination to remove the tarry contaminant.
In carrying out the procedure of British Patent
No. 1,416,344 the alumina particle-laden off-gas has been passed through a cyclone-type separator to remove the coarser particles, constituting at least 80% (and more usually 90% or higher) by weight of the alumina particle entrained in the gas. The off-gas exhausting from the cyclone-type separator has then been forwarded direct to a bag-filter to collect the fines. The filtered off-gas is then discharged to atmosphere and the fines material collected on the bag filter are subjected to calcination to remove the hydrocarbon contaminant. These calcined fines are then either added to the coarse material collected in the cylone separator or are forwarded to a separate process plant for reclaim by reason of their contamination by other materials, such as iron, which it is undesirable to recycle to the electrolytic cells.
In the first of these alternatives a proportion of the recombined coarse and fine particles are returned to the inlet end of the entrainment duct upstream of the cylone-type separator.
It has now been realised in accordance with the present invention that for a given feed rate the scrubbing efficiency, in terms of removal of a selected reactive gaseous component of a waste gas, of a dry scrubber system of the type in which a particulate adsorbent material is entrained in a waste gas and then separated therefrom by a bag filter can be improved by forwarding a fines fraction of the particulate adsorbent material direct to the bag filter.
The term "bag filter" in the present context is employed broadly to cover any form of filtering apparatus in which the gas stream passes through a layer of collected solid particles. Because of the high relative particle-to-gas concentration in the collected layer on the filter a substantial proportion of the reactive gaseous component is adsorbed in the solid particles on the filter and the best adsorbent use of the fines fraction of the particulate material is made at the filter.
In a system in which there is no separation of a fines fraction upstream of the filter, it is preferred to introduce a means by which a fines fraction is led to the filter. This may be achieved in a variety of ways. For example a fines fraction may be separated from the fresh feed alumina before introduction into off-gas stream and forwarded direct to the filter or alternatively a special fine alumina with a higher active surface may be supplied direct to the filter. As a further alternative the dry-scrubbing system may be modified by introducing a separator (such as, for example, a cylone) into the duct upstream of the filter to filter off a coarse particle fraction which is forwarded direct to the cells or in part recirculated for entrainment in the gas duct.As a yet further alternative the solids, recovered from the filter, may be treated to separate a fines fraction and the fines fraction thus recovered may be returned to the filter.
In accordance with the present invention a proportion of the fines before calcination are recycled direct to the filter instead of being recycled to the filter after passage through the entire gas/solids contact system.
One form of system for putting the present invention into effect is illustrated in the accompanying diagrammatic drawing.
The off-gas from a group of reduction cells is led into a contact duct 1, into which a stream of fresh feed alumina is introduced at 2 and a stream of coarse recycled alumina is introduced at 3. The contact time of the alumina particles thus entrained in the gas is at least 3 seconds and may be up to 10 seconds or higher. The feed rate of recycled alumina is preferably at least equal to the feed rate of fresh alumina feed and is commonly 1.5-2 times the feed rate of fresh alumina.
At the outlet end of duct 1 the gas stream is led into a cyclone-type separator 4, in which a coarse alumina fraction is separated and led out through a conduit 5. A part of the coarse alumina fraction, which forms about 90% of the alumina entrained in the gas in duct 1, is recycled to 3 and a further amount is led away via conduit 6 to the reduction cells.
The off-gas from the separator 4 is led via conduit 7 to a bag filter 8, in which the remaining alumina fines in the off-gas are filtered off. In accordance with the present invention, a proportion (usually a major proportion) of the stream of fines from the housing of the bag filter 8 is recycled directly to the filter. The balance is forwarded to a calciner 9, in which the material is subjected to an oxidizing treatment for removal of contaminant carbon and hydrocarbons.
All of the calcined fines are introduced into the coarse particle fraction feed in conduit 6.
The gaseous discharge from the calciner 9 is also returned through a separate conduit to the duct 7 or the bag filter 8 to secure re-adsorption of any HF distilled off in the operation of the calciner 9.
The filtered tail gas from the filter housing is led off via conduit 1 1 to a stack for discharge to atmosphere.
Claims (4)
1. A process for the removal of hydrogen fluoride from the off-gas from electrolytic reduction cells for the production of aluminium in which fresh particulate feed alumina is entrained in the gas stream and in which at least a fines fraction of said particulate feed alumina is separated from said gas stream in a bag filter to form a layer of alumina particles through which said off-gas passes before discharge to atmosphere characterised in that an alumina fines fraction is supplied direct to said bag filter.
2. A process according to claim 1 further characterised in that said alumina fines fraction is separated from the feed alumina before contact with said off-gas.
3. A process according to claim 1 further characterised in that a coarse particle fraction alumina is separated from the off-gas at a location upstream of said bag filter and is at least in part recirculated for contact with said off-gas and fines fraction alumina is collected on said bag filter.
4. A process according to claim 3 further characterised in that one fraction of the fines, collected in the bag filter, is recycled to the bag filter and a further fraction of the collected fines is subjected to an oxidising treatment for removal of contaminant carbon and hydrocarbons.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8004808A GB2068920A (en) | 1980-02-13 | 1980-02-13 | Dry-scrubbing fluoride- containing gases |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8004808A GB2068920A (en) | 1980-02-13 | 1980-02-13 | Dry-scrubbing fluoride- containing gases |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2068920A true GB2068920A (en) | 1981-08-19 |
Family
ID=10511318
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8004808A Withdrawn GB2068920A (en) | 1980-02-13 | 1980-02-13 | Dry-scrubbing fluoride- containing gases |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2068920A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4534778A (en) * | 1982-10-25 | 1985-08-13 | Air Industrie | Installation for injecting a powdery material, particularly an adsorbent material, into a contact column |
| RU2493500C2 (en) * | 2010-03-18 | 2013-09-20 | Владимир Петрович Шустов | Device to purify air from gas pollution and solid particles |
| CN105797529A (en) * | 2016-05-23 | 2016-07-27 | 成都弗吉亚科技有限公司 | Coal-fired boiler smoke three-section type treatment method |
-
1980
- 1980-02-13 GB GB8004808A patent/GB2068920A/en not_active Withdrawn
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4534778A (en) * | 1982-10-25 | 1985-08-13 | Air Industrie | Installation for injecting a powdery material, particularly an adsorbent material, into a contact column |
| RU2493500C2 (en) * | 2010-03-18 | 2013-09-20 | Владимир Петрович Шустов | Device to purify air from gas pollution and solid particles |
| CN105797529A (en) * | 2016-05-23 | 2016-07-27 | 成都弗吉亚科技有限公司 | Coal-fired boiler smoke three-section type treatment method |
| CN105797529B (en) * | 2016-05-23 | 2019-03-08 | 成都弗吉亚科技有限公司 | A kind of fire coal boiler fume three-stage processing method |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |