GB2106488A - Process for removal of sulphur oxides from waste gases - Google Patents
Process for removal of sulphur oxides from waste gases Download PDFInfo
- Publication number
- GB2106488A GB2106488A GB08226294A GB8226294A GB2106488A GB 2106488 A GB2106488 A GB 2106488A GB 08226294 A GB08226294 A GB 08226294A GB 8226294 A GB8226294 A GB 8226294A GB 2106488 A GB2106488 A GB 2106488A
- Authority
- GB
- United Kingdom
- Prior art keywords
- liquor
- sorbent
- sodium
- alkaline
- sodium carbonate
- 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
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- 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
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/46—Removing components of defined structure
- B01D53/48—Sulfur compounds
- B01D53/50—Sulfur oxides
- B01D53/501—Sulfur oxides by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
Abstract
The waste gas is contacted with a sorbent comprising one or more of sodium bicarbonate, trona and activated sodium carbonate and then the spent sorbent is dissolved in an alkaline liquor. The liquor is then carbonated to precipitate trona or sodium bicarbonate which is separated and heat activated and returned to the process as sorbent. The liquor is then treated with an alkaline earth metal oxide or hydroxide to precipitate the sulphur as sulphates and sulphites. <IMAGE>
Description
SPECIFICATION
Process for removal of sulphur oxides from waste gases
This invention relates to a process for absorbing sulphur oxides from industrial waste gases with a solid sorbent for regenerating the solid sorbent for reuse.
In the combustion of fossil fuels, and in many industrial processes, a serious problem is presented by the combustion of the sulphur-containing components therein. The noxious sulphur oxides produced are an environmental pollutant and in recent years considerable effort has been made to remove the sulphur oxides from the combustions gases exhausted to the atmosphere. Several methods for removing such oxides are known (see, for example, U.S. Patent Specification No. 3,852,410 and U.S.
Patent Specification No. 3,846,535) but it is believed that all prior art processes have certain disadvantages.
According to the present invention there is provided a method for the removal of sulphur oxides from an industrial waste gas containing the same which method comprises:
(a) contacting said gas with a solid sorbent which is one of or a mixture of two or more of activated sodium carbonate, sodium bicarbonate and trona in an amount sufficient to react with substantially all of the sulphur oxides present in said gas to form solids of unreacted sorbent, sodium sulphite, sulphate, and mixtures thereof, and a waste gas substantially free of sulphur oxides.
(b) dissolving said solids in an alkaline liquor containing an alkalinity carrier to form soluble sodium compounds;
(c) carbonating the resultant alkaline sodium liquor from step (b) and cooling to a temperature sufficient'to form crystals of sodium bicarbonate or trona;
(d) separating the crystals from the liquor of step (c) and recycling said crystals to step (a) or heating said crystals for a time and temperature sufficient to form activated sodium carbonate and recycling said activated sodium carbonate to step (a); and
(e) removing carbon dioxide from the cooled liquor of step (c), adding a precipitant selected from the alkaline earth metal hydroxides, oxides and mixtures thereof to the resultant liquor to render it alkaline and form insoluble solids comprising alkaline earth metal sulphates, sulphites and mixtures thereof, separating said insoluble solids and recycling the resultant alkaline liquor to step (b).
Briefly, the method of the invention comprises treating the waste gas containing sulphur oxides (hereinafter for convenience referred to as sulphur dioxide) with a solid sorbent which is one of or a mixture of two or more activated sodium carbonate, sodium bicarbonate and trona which can remove 90 percent or more of the sulphur dioxide.Trona is the mineral name for Na2CO3. NaHCO3 ~ 2H2O and activated sodium carbonate can be formed from sodium bicarbonate or trona or a mixture thereof by calcining at a temperature ranging from about 700C to about 200 C. For example, activated sodium carbonate can be prepared from sodium bicarbonate having a characteristic particle dimension of about 50 microns by calcination over a period of about 10 to about 30 minutes at a temperature of about 1 50 C. The clean gas is vented and the unreacted solids, sodium sulphites, sulphates and mixtures thereof, are dissolved in a basic liquor that is alkaline enough to convert carbonic acid to bicarbonate, said liquor containing an alkalinity carrier, such as, for example, borate ion or ammonia or, preferably, both, to form soluble sodium compounds. The alkalinity carrier serves the function of effecting the alkalinity transfer from the precipitant to the liquid phase. The alkalinity carrier has an acid form and a base form. Carbonation of the resultant liquor forms a sodium precipitate containing bicarbonate or trona or mixtures thereof.
The precipitate is separated from the carbonated liquor and the liquor treated with a precipitant selected from the alkaline earth metal hydroxides, oxides and mixtures thereof to form insoluble alkaline earth metal sulphates, sulphites and mixtures thereof. Suitable alkaline earth metals include calcium, barium and strontium. After removing the solids, the liquor is recycled to treat spent sorbent.
The presence of borate ion (such as supplied in boric acid) in the method provides several distinct advantages. For one, it permits the use of lower flow rates in the regeneration loop of the process.
Another important advantage is that, since borate ion does not degrade chemically or biologically to any significant extent there is little loss of borate ion in the system, which accordingly reduces the amount of material utilized in the process. Moreover, since the borate ion does not act as a reducing agent in the regeneration loop or in the solid waste disposal area the sulphites and/or sulphates present are not reduced to noxious sulphur compounds as, for example, hydrogen sulphite which can present serious health and disposal problems. The use of ammonia instead of or in addition to borate ion provides similar advantages.
For a better understanding of the invention, reference will now be made, by way of example, to the accompanying drawing which is a schematic flow diagram of the method of the invention.
Referring to the drawing, a flue gas containing sulphur dioxide is fed via a conduit 2 to a gas-solid contactor 4. Contactor 4, which can take many forms (e.g. fixed bed, moving bed, fluidized bed, etc.), is suitably a baghouse collector employing tube type fabric filter dust collecting surfaces preloaded with a suitable sorbent which is introduced into contactor 4 via conduit 6. Alternatively, the sorbent may be introduced into the gas stream upstream of the contactor 4. On passing through the contactor 4, the sulphur dioxide in the flue gas reacts with the sodium-containing sorbent to produce sodium sulphite and sulphate, leaving a flue gas substantially free of any sulphur dioxide and which is vented from contactor 4 via a conduit 8.
A solids product is removed from contactor 4 via a conduit 10 and transferred to a spent sorbent storage vessel 12. At this point, the solids product will comprise unused sorbent initially in gas-solid contactor 4 plus soluble (sodium) sulphite and/or sulphate resulting from the reaction of the sorbent with the sulphur dioxide in the flue gas and any particulate matter originally contained in the flue gas, such as fly ash. The solids product is transferred to a mixing tank 16 via a conduit 14 where it is admixed with an alkaline recycle liquor containing borate ion from a line 18 and makeup chemicals which can include Na2B4O7, Na2CO3, N a2SO4, NaCI or various mixtures thereof. In the mixing tank 16, the soluble sulphite and/or sulphate, which were formed by the reaction of the sulphur dioxide with the sorbent, are dissolved.The liquor from mixing tank 1 6 is transferred via a conduit 22 to a fly ash filter 24 where any fly ash is removed and disposed of via a conduit 26. Conduit 26 may go to a reaction tank 64 when not all of the sodium sulphite or sulphate from spent sorbent vessel 1 2 dissolved in mixing tank 1 6. The liquor free of fly ash leaves filter 24 via a conduit 28, and is introduced into a carbonator 30, where it is reacted with CO2 which is introduced into carbonator 30 via conduit 32. Clean flue gas is a convenient CO2 source. Excess CO2 leaves carbonator 30 via conduit 34 for venting to the atmosphere or, if preferred, to the clean gas stack via conduit 8. Bicarbonate ions are formed which are transferred via a conduit 36 to crystallizer 38 where they are converted to solid sodium bicarbonate or trona or mixtures thereof which crystallizes out of solution.Carbon dioxide may also be added to the crystallizer 38 to drive the crystallization of sodium bicarbonate toward completion. The sodium bicarbonate crystallized in crystallizer 38 is transferred via a conduit 40 to a sodium bicarbonate filter 42. The sodium bicarbonate and/or trona recovered from filter 42 is transferred via a conduit 46 to dryer/ calciner 48 where it is either dried and transferred via a conduit 52 to regenerated sorbent storage vessel 54 or is dried and calcined to form an activated sodium carbonate which is likewise transferred via conduit 52 to regenerated sorbent storage vessel 54.
The liquid from filter 42 passes via conduit 44 into a carbon dioxide stripper vessel 56 where it is contacted countercurrently with a stripper (e.g., steam) introduced in the lower portion of stripper vessel 56 via conduit 58. A portion of the CO2, other undissolved gases and any remaining stripper is vented from stripper vessel 56 via conduit 60. This C02-containing gas may be added to carbonator 30 or crystallizer 38. The CO2 stripped liquor from stripper vessel 56 is introduced, via conduit 62, into reaction tank 64 where it is contacted with an alkaline precipitant, preferably lime, introduced via line 66. In raction tank 64, the precipitant reacts with the soluble sodium sulphite and/or sulphate to produce, for example, insoluble calcium sulphate and/or calcium sulphite and regenerate the alkaline liquor.The mixture in reaction tank 64 is transferred via conduit 68 to a sludge dewatering vessel 70 where the insoluble calcium sulphate and/or sulphite is disposed of via conduit 72, the liquid from vessel 70 being recycled, as noted above, to mixing tank 16 via conduit 18.
As can be seen from the drawing, the method comprises two basic steps: viz, a sorption step and a regeneration step. In the sorption step, the sluphur dioxide in the flue gas is contacted with the sorbent and converted into soluble sulphate and/or sulphite compounds. In the regeneration step, or loop, the sulphur species is ultimately purged from the process as an insoluble sulphur compound and the sorbent is regenerated for reuse in the sorption step.
The sorbent is preferably a sodium carbonate obtained by calcining a sodium-containing compound, such as sodium bicarbonate or trona or a mixture thereof, at a temperature of from about 70 to about 2000 C. It has been found that while sodium carbonate which has been produced by crystallizing directly from solution does not act as an effective sorbent in the process of the present invention, sodium carbonate produced by calcining sodium bicarbonate or trona makes an excellent sorbent and is easily obtained by calcining the precipitated sodium bicarbonate produced in crystallizer 38.
To remove the soluble sulphites and/or sulphates from the system, a precipitant comprising an alkaline earth metal hydroxide, oxide or mixture thereof is employed. Thus, for example, the process can employ an oxide or hydroxide of calcium, barium or strontium or mixtures. The preferred alkaline earth metal is calcium.
As noted above in connection with the description of the drawing, the method, with advantage, employs a carbon dioxide stripper. The stripper, which can be, for example, any gas-liquid countercurrent contactor, serves to remove excess CO2 which would otherwise be precipitated as calcium carbonate in vessel 64, thereby increasing the use of lime in the process. The CO2 stripper can be, for example, steam or an oxygen-containing gaseous medium such as air.
As pointed out above, the method of the invention utilizes an alkalinity carrier such as the borate ion in the liquor in mixing tank 16. The ultimate source of alkalinity in the process is supplied by the precipitant (hereinafter for convenience referred to as lime) added to the reaction tank 64. However, without the use of some medium to transfer alkalinit, -om the solid phase (lime) to the liquid phase, the alkalinity of the solution would be rapidly depleted during the carbonation step. Accordingly, for a given circulation rate in the system, production of sodium bicarbonate in the carbonator would be greatly reduced. This would necessitate an increased pumping or circulation rate in the system to the point where the process would become economically not feasible.The bore ion serves the function of effecting the alkalinity transfer from the lime to the liquid phase and can thus be considered as "alkalinity carrier". This alkalinity carrier has an acid form (boric acid) and a base-form (borate ion), being in the base form as it leaves reaction tank 64. The clear liquid which is removed from ash filter 24 and which is used to dissolve the gas-solid contactor solids from contactor 4 is pumped to the carbonator 30 where the liquid phase alkalinity of the carrier is now exchanged for liquid phase bicarbonate alkalinity. This liquid phase bicarbonate alkalinity is now converted to the solid phase alkalinity of the sodium bicarbonate in the crystallizer. The alkalinity carrier in the clear liquid from the crystaliizer 38 is now in the acid form, i.e. boric acid.Upon entering reaction tank 64, the boric acid once again contacts the solid phase alkalinity provided by the lime, and is converted into the basic form and the cycle repeated.
Preferred alkalinity carriers include boric acid and, when activated sodium carbonate is the sorbent, ammonia. It will be apparent that the alkalinity carrier can be added in its acid or base form.
Thus, for example, the borate ion may be added in the form of boric acid (acid form) or sodium tetraborate (base form), while the ammonia can be added in the form of ammonium sulphate or chloride or the like (acid form) or as ammonia gas (base form). Advantageously, both boric acid and ammonia are employed to minimize the possibility of boric acid precipitation in the crystallizer.
The limits for borate and ammonia may be determined from the following consideration. As alkalinity carriers, it is desirable to maximise their concentration. Boric acid solubility will limit the amount of borate that may be circulated. The solubility of boric acid decreases with a decrease in temperature. The coolest part of the circulating loop is the crystallizer effluent. In the crystallizer effluent almost all of the borate in the solution exists as un-ionized boric acid, H3BO3 [or B(OH)3 ] . The solubility of boric acid is dependent on solution composition as well as temperature. Solution composition is determined by both site specific factors (e.g., how much HCI or NO, are removed from the flue gas) and operating conditions. It is thus not possible to fix the maximum workable borate concentration without knowledge of these factors.The order of magnitude of the borate solubility may be obtained from solubility data reported by Linke (Linke, William F. Solubilities: Inorganic and Metal-Organic
Compounds. K-Z. Volume II, 4th Ed., American Chemical Society, Washington, D.C. 1 965).
Concentration, g/100 g H20 mole H3BO2 Temp. H3BO3 0C NaCI KCI Na2SO4 (saturated) KgH2O
25 0 0 0 5.43 0.88
35 0 0 0 7.19 1.16
35 36.8 0 0 8.2 1.33
35 33.2 0 11.9 9.6 1.55
35 0 41.0 0 11.6 1.88
35 0 0 53 13.1 2.12
The limitation on ammonia concentration is the vapour pressure of ammonia. This is greatest at high temperature and pH. An upper limit is the total solution vapour pressure (water, ammonia, and
CO2) of the solution equal to five atmospheres absolute (60 psig). For both borate and ammonia these general considerations apply anywhere in the system.
The following Examples illustrate preferred embodiments of the invention.
EXAMPLE 1
Flue gas containing 700 Ib. mole/hr. of SO2 was treated with 760 Ib. mole/hr. of activated sodium carbonate and reacted with 90 percent of the sulphur dioxide in the flue gas. The resulting solids were collected in a baghouse. The solids from the baghouse were dissolved using 1350 gal./min. of a recirculated liquor containing 2.6 m borate, 6.5 m sodium and other dissolved species such as chlorides, sulphites, sulphates, carbonates, calcium, etc. Also, makeup soda ash and borate were dissolved into the liquor at the rate of 28.6 Ib. mole/hr. and 6.4 lb. mole/hr., respectively. The resulting liquor was then carbonated with 760 Ib. mole/hr. of CO2 from a combination of clean flue gas, and CO2 recycled from the other parts of the process in the carbonator and crystallizer.The carbonated liquor was cooled to 950F in the crystallizer to precipitate 1 520 lb. mole/hr. of sodium bicarbonate. The sodium bicarbonate solids were separated from the liquor, dried and calcined at 3000F to form an activated sodium carbonate which was recycled to the baghouse to treat the flue gas. The separated liquor was passed through a CO2 stripping column to remove 90 Ib. mole/hr. of carbon dioxide from the liquor. The liquor leaving the CO2 stripping column was treated with 660 Ib. mole/hr. of lime in a reaction tank to precipitate calcium sulphite and/or calcium sulphate solids. These solids were separated from the slurry leaving the reaction tank and constituted the waste product. The separated liquor was recycled as noted above to dissolve the baghouse solids.
EXAMPLES II S Ill
These Examples were run in accordance with the general procedure of Example 1, but for the
presence or absence of an alkalinity carrier as indicated in the following Table. The results obtained
show that the circulation rate would be increased at least a thousandfold (if even technically feasible)
without the alkalinity carrier.
molality, moles/KgH2O Circulation Rate
Example Ammonia Borate gpm o 2.6 1,350
II 1.3 1.3 1,350 Ill 0 0 1,350,000+
Claims (13)
1. A method for the removal of sulphur oxides from an industrial waste gas containing the same which method comprises:
(a) contacting said gas with a solid sorbent which is one of or a mixture of two or more of activated sodium carbonate, sodium bicarbonate and trona in an amount sufficient to react with substantially all of the sulphur oxides present in said gas to form solids of unreacted sorbent, sodium sulphite, sulphate, and mixtures thereof, and a waste gas substantially free of sulphur oxides.
(b) dissolving said solids in an alkaline liquor containing an alkalinity carrier to form soluble sodium compounds;
(c) carbonating the resultant alkaline sodium liquor from step (b) and cooling to a temperature sufficient to form crystals of sodium bicarbonate or trona;
(d) separating the crystals from the liquor of step (c) and recycling said crystals to step (a) or heating said crystals for a time and temperature sufficient to form activated sodium carbonate and recycling said activated sodium carbonate to step (a); and
(e) removing carbon dioxide from the cooled liquor of step (c), adding a precipitant selected from the alkaline earth metal hydroxides, oxides and mixtures thereof to the resultant liquor to render it alkaline and form insoluble solids comprising alkaline earth metal sulphates, sulphites and mixtures thereof. separating said insoluble solids and recycling the resultant alkaline liquor to step (b).
2. A method according to Claim 1, wherein said alkalinity carrier comprises borate ion.
3. A method according to Claim 2, wherein said liquor containing said borate ion contains, in addition, dissolved ammonia.
4. A method according to Claim 1,2 or 3, wherein said sorbent comprises trona.
5. A method according to Claim 1,2,3 or 4, wherein said sorbent comprises sodium bicarbonate.
6. A method according to Claim 1,2,3,4 or 5, wherein said sorbent comprises activated sodium carbonate.
7. A method according to Claim 1,2,3,4,5 or 6, wherein said precipitant comprises calcium oxide.
8. A method according to Claim 1,2,3,4,5,6 or 7, wherein said precipitant comprises calcium hydroxide.
9. A method according to Claim 2 or any one of Claims 3 to 7 when appendant to Claim 2, wherein boric acid is employed to provide the borate ion.
10. A method according to Claim 2 or 3, wherein an activated sodium carbonate sorbent is employed with boric acid and ammonia alkalinity carrier.
11. A method according to Claim 2 or any one of Claims 3 to 7 when appendant to Claim 2 wherein sodium tetraborate is employed to provide the borate ion.
12. A method according to any one of Claims 1 to 11, wherein in step (c) CO, is added to drive the crystallization of the sodium bicarbonate toward completion.
13. A method according to Claim 1, substantially as hereinbefore described with reference to the accompanying drawing.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US30336081A | 1981-09-18 | 1981-09-18 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2106488A true GB2106488A (en) | 1983-04-13 |
| GB2106488B GB2106488B (en) | 1984-08-22 |
Family
ID=23171738
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08226294A Expired GB2106488B (en) | 1981-09-18 | 1982-09-15 | Process for removal of sulphur oxides from waste gases |
Country Status (6)
| Country | Link |
|---|---|
| AU (1) | AU546792B2 (en) |
| CA (1) | CA1171242A (en) |
| DE (1) | DE3233200C2 (en) |
| FR (1) | FR2513140A1 (en) |
| GB (1) | GB2106488B (en) |
| ZA (1) | ZA826570B (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010072793A1 (en) * | 2008-12-22 | 2010-07-01 | Solvay Sa | Process for the joint production of sodium carbonate and sodium bicarbonate |
| CN101862589A (en) * | 2010-06-30 | 2010-10-20 | 马鞍山钢铁股份有限公司 | Desulfurization process for sintering flue gas |
| CN103025661A (en) * | 2010-06-22 | 2013-04-03 | 索尔维公司 | Process for the joint production of sodium carbonate and sodium bicarbonate |
| US9868644B2 (en) | 2011-12-23 | 2018-01-16 | Solvay Sa | Process for the joint production of sodium carbonate and sodium bicarbonate |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3846535A (en) * | 1972-09-05 | 1974-11-05 | Continental Oil Co | Method for absorbing sulfur oxides from gaseous mixtures and regenerating the absorbent |
| US3823676A (en) * | 1972-10-10 | 1974-07-16 | Warren Cook Chem Inc | Method of reducing sulphur dioxide emissions from coal |
| US3852410A (en) * | 1972-12-07 | 1974-12-03 | American Air Filter Co | Sulfur dioxide and particulate contaminant removal from industrial stack gases |
| DE2459272C3 (en) * | 1974-12-14 | 1978-08-17 | Fa. Hermann Wegener, 3000 Hannover | Compound for removing environmentally harmful gases, in particular sulfur oxides, hydrogen sulfide and hydrogen halides from industrial waste gases |
-
1982
- 1982-08-27 AU AU87801/82A patent/AU546792B2/en not_active Ceased
- 1982-09-07 DE DE3233200A patent/DE3233200C2/en not_active Expired
- 1982-09-08 ZA ZA826570A patent/ZA826570B/en unknown
- 1982-09-15 GB GB08226294A patent/GB2106488B/en not_active Expired
- 1982-09-17 FR FR8215715A patent/FR2513140A1/en active Granted
- 1982-09-17 CA CA000411700A patent/CA1171242A/en not_active Expired
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010072793A1 (en) * | 2008-12-22 | 2010-07-01 | Solvay Sa | Process for the joint production of sodium carbonate and sodium bicarbonate |
| US8784756B2 (en) | 2008-12-22 | 2014-07-22 | Solvay Sa | Process for the joint production of sodium carbonate and sodium bicarbonate |
| CN102264644B (en) * | 2008-12-22 | 2015-07-15 | 索尔维公司 | Process for joint production of sodium carbonate and sodium bicarbonate |
| CN103025661A (en) * | 2010-06-22 | 2013-04-03 | 索尔维公司 | Process for the joint production of sodium carbonate and sodium bicarbonate |
| US8865096B2 (en) | 2010-06-22 | 2014-10-21 | Solvay Sa | Process for the joint production of sodium carbonate and sodium bicarbonate |
| CN101862589A (en) * | 2010-06-30 | 2010-10-20 | 马鞍山钢铁股份有限公司 | Desulfurization process for sintering flue gas |
| US9868644B2 (en) | 2011-12-23 | 2018-01-16 | Solvay Sa | Process for the joint production of sodium carbonate and sodium bicarbonate |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2513140A1 (en) | 1983-03-25 |
| ZA826570B (en) | 1983-07-27 |
| CA1171242A (en) | 1984-07-24 |
| FR2513140B1 (en) | 1985-03-15 |
| AU546792B2 (en) | 1985-09-19 |
| DE3233200A1 (en) | 1983-04-14 |
| DE3233200C2 (en) | 1986-07-31 |
| GB2106488B (en) | 1984-08-22 |
| AU8780182A (en) | 1983-03-24 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |