CA1162031A - Method of purifying a gas containing sulphur dioxide components therein - Google Patents
Method of purifying a gas containing sulphur dioxide components thereinInfo
- Publication number
- CA1162031A CA1162031A CA000386579A CA386579A CA1162031A CA 1162031 A CA1162031 A CA 1162031A CA 000386579 A CA000386579 A CA 000386579A CA 386579 A CA386579 A CA 386579A CA 1162031 A CA1162031 A CA 1162031A
- Authority
- CA
- Canada
- Prior art keywords
- phase
- gas
- solid
- absorbent
- liquid
- 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.)
- Expired
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Abstract
ABSTRACT OF THE DISCLOSURE
Purification of gases from sulphur dioxide components according to the dry method means that the gas is contacted with an absorbent in a solid phase, which yields a relatively low reaction rate. In order to increase the reaction rate according to the invention, the gas is contacted with a mixture consisting partially of a solid absorbent phase and partially a liquid phase on the surface of the solid phase.
At the purification of flue gases from sulphur dioxide hot gas is contacted with an absorption liquid in a drying apparatus, where evaporation of the water supplied and a reaction between sulphur dioxide and the absorption substance take place simultaneously, whereafter the solid product phase is separated from the gas in a dust separator and a slower, secondary absorption reaction is operative. In order to achieve a higher reaction rate in the dust separator, a substance is added to the flue gas which, together with other chemical species derived from the gas or the solid absorbent forms a liquid phase distributed over the surface of the solid phases. The liquid phase usually contains water and has a good solubility for reactants and reaction products.
Purification of gases from sulphur dioxide components according to the dry method means that the gas is contacted with an absorbent in a solid phase, which yields a relatively low reaction rate. In order to increase the reaction rate according to the invention, the gas is contacted with a mixture consisting partially of a solid absorbent phase and partially a liquid phase on the surface of the solid phase.
At the purification of flue gases from sulphur dioxide hot gas is contacted with an absorption liquid in a drying apparatus, where evaporation of the water supplied and a reaction between sulphur dioxide and the absorption substance take place simultaneously, whereafter the solid product phase is separated from the gas in a dust separator and a slower, secondary absorption reaction is operative. In order to achieve a higher reaction rate in the dust separator, a substance is added to the flue gas which, together with other chemical species derived from the gas or the solid absorbent forms a liquid phase distributed over the surface of the solid phases. The liquid phase usually contains water and has a good solubility for reactants and reaction products.
Description
0 ~ ~
Gases can be purified from sulphur dioxide c~nents by contacting with an absorbent in a liquid phase twet method) or in a solid phase (dry method). The present invention relates to a substantially dry method. As the dry method includes reaction steps implying diffusion into a solid phase, one of its disadvantages is a relatively low reaction rate.
The object of the present invention is to reduce the impact of the said disadvantage.
In general terms, the present invention provides a method for purifying a gas containing sulphur dioxide components therein, which method comprises contacting said gas with a mixture consisting of (i~ a solid absorbent phase and (ii) a liquid, hydrous phase, which liquid phase is derived from a hygroscopic salt selected from the group consisting of FeC13, Fe(N03)3, Fe(N03)2, Al(N03)3, Ca(N03)2, Mg(C103)2, MnC12, K2SO40MgSO4, NaAl(S04)2, NaC10, Na3P04, Na2SiO3, Na2S04, and ~n(N03)2 which hygroscopic salt is thermodynamically stable at the prevailing water partial pressure and temperature of said gas and which at least partly covers said solid absorbent phase, and preparing said mixture by adding to said solid absorbent phase said hygroscopic salt.
By effecting a liquid aquous phase with a high solubility for the participating reactants on the surface of the solid absorbent particles, the reaction steps, viz dissolving of the sulphur dioxide component, diffusion, separation of absorbent and precipitation of reaction product, proceed substantially more rapidly than the correspond-ing reaction steps when only gaseous and solid reactants are present. The absorbent may be an oxide, a carbonate or a hydroxide of an alkali metal. The liquid phase, may be derived from a hygroscopic salt, which at the prevailing gas temperature and gas water content is a molten hydrate.
~ ~2031 In recent years a process for absorbt~on of sulphur dioxide from a hot flue sas has come into use which in the literature ~s referred as "dry scrubb~ng". The process substantially co~prises a drying step and a filtering step, and it operates as follows: The ho~ gas is contac~ed in a drying apparatus with an atomized aqueous suspension or an aqueous solution capable to react with sulphur dioxide. In the drying apparatus evaporation of the supplied water ~akes place and simultaneously a react~on between sulphur dioxide and the absorbent occurs. As the gas leaves the drying apparatus, the major part of the supplied water has evaporated, the gas temperature has decreased, the water vapour conten~ of the gas has increased, and part of the sulphur dioxide has been absorbed and now is bound to the solid reaction product. The gas thereafter passes a dust separator where the solfd product remain~ng absorbent and any o~her solid ma~erial i5 separa~ed from the gas. Part of the separated dust may be further recycled ~nto the absorption liquid in order to increase ~he u~ilization of the absorbent.
This process often results in inco~plete utilization of the absorben~ during the driving period. After said period the reaction between the sulphur d~oxide and the absorbent proceeds in the dust separator. This reac~ion, however, proceeds relatively slowly, since the reaction steps occur in solid phases.
The present invent~on has also ~he object of bringing about a h~gher reaction rate during said latter process step.
1 1~2031 This higher reaction rate is obtained by adding to the gas a limited amount of substances such as hygrosoopic salts which under the conditions prevail~ng in the dust separ~tor form on the surface of the solid particles a l~quid ~queous phase w~h sufficient solubility for the reactants. As the reactlon steps, viz.
solution of sulphur dioxide, diffusion of reactants and precip~tation of product, proceed substant~ally more rapid than the corresponding steps in a sol~d phase, the net e~fect thereof is an increase ot the ~otal reaction rate. In order to prevent the operation of the dus~ separator from being jeopardized, the volume of the 7iqu~d phase must be small in relatlon to the volume of the solid phases, and in order to achieve a good effect, the ~quid phase ~ust be well d1str~bu~ed over ~he ~urface of ~he solid phases.
For example, the added hygroscopic substance ma~ constitute a maximum of about 20 percent, and preferably is no greater than about 50 percent by volume of said solid phase present at said dust separator. Examples of compounds~ the hydrate of which has the property of, under the conditions preva~ling a~ ~he absorption of sulphur dioxide from flue gases of fossil-fired boi7ers, being ~n liquid phase are a.o. FeC13, FetN03~3~ Fe(N03)2, Al(NO3)3, Ca(N0)3)2, Mg(C103)2, MnCl~9 K2S04 -MgS04, NaAl(S04)2, NaClO, Na3P04, Na2SiO3, Na2S04, Zn(N03)2O
E~ample __ In a pilo~ plan~ with a capacity of 10 000 Nm /h comprising a dry~ng apparatus, into which atomized absorption ligu~d is ~njected, and a fabric filter as the dust separator, tests were carried out for determining the capacity with and w1thout the addition of so~e of the aforesaid substances. Calcium hydroxide was used as absorbent which was added in an amount correspond~ng to a mole ratio Ca/S02 = 1,1 (calculated vn ingoing gas). The ~ngoing gas had a temperature of 140C and an S0~-content of 850 ppm.
>,~
~ 1~203~
r~he filtering velocit~ of the fabric filter was 92 m/h. The gas temperature after passing through the fabric filter was 70C. The following S02 absorption efficiencies were measured.
Test NoO Addition Eff~e~ency
Gases can be purified from sulphur dioxide c~nents by contacting with an absorbent in a liquid phase twet method) or in a solid phase (dry method). The present invention relates to a substantially dry method. As the dry method includes reaction steps implying diffusion into a solid phase, one of its disadvantages is a relatively low reaction rate.
The object of the present invention is to reduce the impact of the said disadvantage.
In general terms, the present invention provides a method for purifying a gas containing sulphur dioxide components therein, which method comprises contacting said gas with a mixture consisting of (i~ a solid absorbent phase and (ii) a liquid, hydrous phase, which liquid phase is derived from a hygroscopic salt selected from the group consisting of FeC13, Fe(N03)3, Fe(N03)2, Al(N03)3, Ca(N03)2, Mg(C103)2, MnC12, K2SO40MgSO4, NaAl(S04)2, NaC10, Na3P04, Na2SiO3, Na2S04, and ~n(N03)2 which hygroscopic salt is thermodynamically stable at the prevailing water partial pressure and temperature of said gas and which at least partly covers said solid absorbent phase, and preparing said mixture by adding to said solid absorbent phase said hygroscopic salt.
By effecting a liquid aquous phase with a high solubility for the participating reactants on the surface of the solid absorbent particles, the reaction steps, viz dissolving of the sulphur dioxide component, diffusion, separation of absorbent and precipitation of reaction product, proceed substantially more rapidly than the correspond-ing reaction steps when only gaseous and solid reactants are present. The absorbent may be an oxide, a carbonate or a hydroxide of an alkali metal. The liquid phase, may be derived from a hygroscopic salt, which at the prevailing gas temperature and gas water content is a molten hydrate.
~ ~2031 In recent years a process for absorbt~on of sulphur dioxide from a hot flue sas has come into use which in the literature ~s referred as "dry scrubb~ng". The process substantially co~prises a drying step and a filtering step, and it operates as follows: The ho~ gas is contac~ed in a drying apparatus with an atomized aqueous suspension or an aqueous solution capable to react with sulphur dioxide. In the drying apparatus evaporation of the supplied water ~akes place and simultaneously a react~on between sulphur dioxide and the absorbent occurs. As the gas leaves the drying apparatus, the major part of the supplied water has evaporated, the gas temperature has decreased, the water vapour conten~ of the gas has increased, and part of the sulphur dioxide has been absorbed and now is bound to the solid reaction product. The gas thereafter passes a dust separator where the solfd product remain~ng absorbent and any o~her solid ma~erial i5 separa~ed from the gas. Part of the separated dust may be further recycled ~nto the absorption liquid in order to increase ~he u~ilization of the absorbent.
This process often results in inco~plete utilization of the absorben~ during the driving period. After said period the reaction between the sulphur d~oxide and the absorbent proceeds in the dust separator. This reac~ion, however, proceeds relatively slowly, since the reaction steps occur in solid phases.
The present invent~on has also ~he object of bringing about a h~gher reaction rate during said latter process step.
1 1~2031 This higher reaction rate is obtained by adding to the gas a limited amount of substances such as hygrosoopic salts which under the conditions prevail~ng in the dust separ~tor form on the surface of the solid particles a l~quid ~queous phase w~h sufficient solubility for the reactants. As the reactlon steps, viz.
solution of sulphur dioxide, diffusion of reactants and precip~tation of product, proceed substant~ally more rapid than the corresponding steps in a sol~d phase, the net e~fect thereof is an increase ot the ~otal reaction rate. In order to prevent the operation of the dus~ separator from being jeopardized, the volume of the 7iqu~d phase must be small in relatlon to the volume of the solid phases, and in order to achieve a good effect, the ~quid phase ~ust be well d1str~bu~ed over ~he ~urface of ~he solid phases.
For example, the added hygroscopic substance ma~ constitute a maximum of about 20 percent, and preferably is no greater than about 50 percent by volume of said solid phase present at said dust separator. Examples of compounds~ the hydrate of which has the property of, under the conditions preva~ling a~ ~he absorption of sulphur dioxide from flue gases of fossil-fired boi7ers, being ~n liquid phase are a.o. FeC13, FetN03~3~ Fe(N03)2, Al(NO3)3, Ca(N0)3)2, Mg(C103)2, MnCl~9 K2S04 -MgS04, NaAl(S04)2, NaClO, Na3P04, Na2SiO3, Na2S04, Zn(N03)2O
E~ample __ In a pilo~ plan~ with a capacity of 10 000 Nm /h comprising a dry~ng apparatus, into which atomized absorption ligu~d is ~njected, and a fabric filter as the dust separator, tests were carried out for determining the capacity with and w1thout the addition of so~e of the aforesaid substances. Calcium hydroxide was used as absorbent which was added in an amount correspond~ng to a mole ratio Ca/S02 = 1,1 (calculated vn ingoing gas). The ~ngoing gas had a temperature of 140C and an S0~-content of 850 ppm.
>,~
~ 1~203~
r~he filtering velocit~ of the fabric filter was 92 m/h. The gas temperature after passing through the fabric filter was 70C. The following S02 absorption efficiencies were measured.
Test NoO Addition Eff~e~ency
2 FeCl 3 74
3 FeS04 83
4 Fe(N03)3 81 Al (N03)3 71 6 Ca (N03 ) 2 76 7 NaAl (S04)2 78 8 Na2S04 74 9 Zn~N03)~ 77 :
~:
::
~:
~:
::
~:
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for purifying a gas containing sulphur dioxide components therein, which method comprises contacting said gas with a mixture consisting of (i) a solid absorbent phase and (ii) a liquid, hydrous phase, which liquid phase is derived from a hydroscopic salt selected from the group consisting of FeCl3, Fe(NO3)3, Fe(NO3)2, Al(NO3)3, Ca(NO3)2, Mg(ClO3)2, MnCl2, K2SO4°MgSO4, NaAl(SO4)2, NaClO, Na3PO4, Na2SiO3, Na2SO4, and Zn(No3)2 which hygroscopic salt is thermodynamically stable at the prevailing water partial pressure and temperature of said gas and which at least partly covers said solid absorbent phase, and preparing said mixture by adding to said solid absorbent phase said hygroscopic salt.
2. A method as defined in claim 1, wherein said gas consists of flue gas, said purifying process comprises a drying and absorption step, and a dust separation and secondary absorption step, and said solid absorbent is in liquid form, and said absorption liquid and said liquid phase are added to said flue gas, said hygroscopic salt under conditions prevailing in the dust separator being adapted to distribute said liquid phase over the surface of said solid phase.
3. A method as defined in claim 1 or 2, wherein said sulphur dioxide components of said gas react with said absorbent to produce reaction products, and said liquid phase is aqueous and has good solubility for reactants and reaction products.
4. A method as defined in claim 2, wherein said added hydroscopic salt constitutes a maximum of 20 percent by volume of said solid phase present at said dust separator step.
5. A method as defined in claim 1 or 2, wherein said absorbent is selected from the group consisting of calcium hydroxide, calcium carbonate, magnesium calcium carbonate, sodium carbonate, sodium hydroxide or mixtures thereof.
6. A method as defined in claim 2, wherein the added hygroscopic salt is at least partially extracted from fly ash separated from the flue gas.
7. A method as defined in claim 2, wherein the added hygroscopic salt is at least partially extracted from gaseous substances in the flue gas.
8. A method as defined in claim 2, wherein said contacting step comprises atomizing said absorption liquid, and said hygroscopic salt is mixed in said absorption liquid prior to its atomization.
9. A method as defined in claim 2, wherein the added hygroscopic salt is added to the flue gas by means of a special atomization device.
10. The method of claim 2, wherein said added hygroscopic salt constitutes a maximum of 5 percent by volume of said solid phase present at said dust separator.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000386579A CA1162031A (en) | 1981-09-24 | 1981-09-24 | Method of purifying a gas containing sulphur dioxide components therein |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000386579A CA1162031A (en) | 1981-09-24 | 1981-09-24 | Method of purifying a gas containing sulphur dioxide components therein |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1162031A true CA1162031A (en) | 1984-02-14 |
Family
ID=4121019
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000386579A Expired CA1162031A (en) | 1981-09-24 | 1981-09-24 | Method of purifying a gas containing sulphur dioxide components therein |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1162031A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6902714B2 (en) * | 2000-10-05 | 2005-06-07 | F. L. Smidth A/S | Method for reducing the SO2 emission from a plant for manufacturing cement clinker and such plant |
-
1981
- 1981-09-24 CA CA000386579A patent/CA1162031A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6902714B2 (en) * | 2000-10-05 | 2005-06-07 | F. L. Smidth A/S | Method for reducing the SO2 emission from a plant for manufacturing cement clinker and such plant |
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| MKEX | Expiry |