ABSORPTION PROCESS
United States Patent 3593497
Absorption process comprising supplying SO3 or water containing gas through a gas supply conduit disposed in the upper portion of a vertical tube having an outlet opening at its lower end; supplying absorbent liquid through a liquid supply conduit disposed in the tube, providing a bath of said liquid disposed below the outlet opening of the tube, passing unabsorbed gas through a gas-filled space, disposed below a horizontal, gas-permeable plate which succeeds the tube and is contained in a housing which communicates with a gas space below the outlet opening of the vertical tube, through said plate and through a layer of the liquid disposed on top of and carried by the gas-permeable plate which layer of liquid is agitated by said gas flowing through the gas permeable plate and through the liquid thereon, discharging the liquid from said layer; and venting unabsorbed gas through a gas outlet opening in the upper portion of the housing.
US Patent References:
/1050866.html
Snow - January 1913 - 1050866
/2696275.html
Pring - December 1954 - 2696275
Fractionating columns
Chu - February 1961 - 2973189
Gas scrubber
Najarian - January 1963 - 3075751
Method for the recovery of deodorizer distillates
Jackson et al. - February 1968 - 3369344
/1050866.html
Snow - January 1913 - 1050866
/2696275.html
Pring - December 1954 - 2696275
Fractionating columns
Chu - February 1961 - 2973189
Gas scrubber
Najarian - January 1963 - 3075751
Method for the recovery of deodorizer distillates
Jackson et al. - February 1968 - 3369344
Inventors:
Grimm, Hugo (Frankfurt am Main, DT)
Dorr, Karl-heinz (Mainz)
Dorr, Karl-heinz (Mainz)
Application Number:
04/794509
Publication Date:
07/20/1971
Filing Date:
01/28/1969
View Patent Images:
Export Citation:
Assignee:
Metallgesellschaft A. G. (Frankfurt, Main, DT)
Primary Class:
Other Classes:
95/235, 261/21, 423/522, 261/116, 423/243.010, 261/114.100
International Classes:
B01D53/14; C01B17/80; C01B17/00; B01F3/04
Field of Search:
261/21,114,116 55/250 23/174,167,168
US Patent References:
| 3456928 | COMBINED BLAST FURNACE SCRUBBER AND DUST CATCHER | July 1969 | Selway |
Primary Examiner:
Miles, Tim R.
Claims:
What we claim is
1. Process for absorbing SO3 or water from a gas containing such with liquid sulfuric acid, which comprises providing a vertical tube having an outlet opening at its lower end; feeding said gas through a gas supply conduit disposed in the upper portion of the tube; feeding liquid sulfuric acid through a supply conduit disposed in the tube; providing a bath of sulfuric acid disposed below the outlet opening of the tube; contacting said gas and said liquid and passing unabsorbed gas through a gas-filled space which is disposed below the outlet opening of the vertical tube; then through a horizontal, gas-permeable plate which succeeds the tube and is contained in a housing and then through a layer of sulfuric acid carried by the gas-permeable plate, agitating said sulfuric acid on said plate by gas flowing therethrough; draining sulfuric acid from said layer through a drain; and recovering unabsorbed gas through a gas outlet opening in the upper portion of the housing; providing a drain for sulfuric acid disposed below the outlet opening of the vertical tube; providing means for supplying sulfuric acid to the agitated layer of sulfuric acid on the gas-permeable plate; and providing means for supplying said sulfuric acid to said tube from said bath extending through the housing all.
2. Process according to claim 1, herein said gas is passed through a plurality of agitated layers of sulfuric acid carried on superposed horizontal, gas-permeable plates.
3. Process according to claim 1, including liquid-stripping by means of a layer of packing elements provided above the agitated layer.
4. Process according to claim 1 including disposing the sulfuric acid bath under the vertical tube on a level such that the sulfuric acid flows at a controlled rate owing to a static head and/or a flow gradient into the agitated layer on the gas-permeable plate.
5. Process according to claim 1, herein the vertical tube is a Venturi tube.
6. Process according to claim 5, including separating the vertical tube from the housing and connecting the gas space below the outlet opening of said tube by a conduit to the gas space below the gas-permeable plate in the housing.
7. Process according to claim 6, including providing a bath of sulfuric acid on the bottom of the housing.
8. Process according to claim 6, including supplying sulfuric acid into a distributing trough which is disposed in the middle of the agitated layer on the gas-permeable plate.
9. Process according to claim 1, wherein the vertical tube is contained in the housing and the gas-permeable plate surrounds the lower portion of the tube.
10. Process according to claim 9, herein the means for supplying sulfuric acid to the agitated layer on the gas-permeable plate opens into an annular distributing space which surrounds the vertical tube and has outlet openings leading into the agitated layer.
11. Process according to claim 9, herein a baffle is provided protruding above the surface of the bath on the bottom of the housing disposed on said bottom under the outlet opening of the vertical tube.
1. Process for absorbing SO3 or water from a gas containing such with liquid sulfuric acid, which comprises providing a vertical tube having an outlet opening at its lower end; feeding said gas through a gas supply conduit disposed in the upper portion of the tube; feeding liquid sulfuric acid through a supply conduit disposed in the tube; providing a bath of sulfuric acid disposed below the outlet opening of the tube; contacting said gas and said liquid and passing unabsorbed gas through a gas-filled space which is disposed below the outlet opening of the vertical tube; then through a horizontal, gas-permeable plate which succeeds the tube and is contained in a housing and then through a layer of sulfuric acid carried by the gas-permeable plate, agitating said sulfuric acid on said plate by gas flowing therethrough; draining sulfuric acid from said layer through a drain; and recovering unabsorbed gas through a gas outlet opening in the upper portion of the housing; providing a drain for sulfuric acid disposed below the outlet opening of the vertical tube; providing means for supplying sulfuric acid to the agitated layer of sulfuric acid on the gas-permeable plate; and providing means for supplying said sulfuric acid to said tube from said bath extending through the housing all.
2. Process according to claim 1, herein said gas is passed through a plurality of agitated layers of sulfuric acid carried on superposed horizontal, gas-permeable plates.
3. Process according to claim 1, including liquid-stripping by means of a layer of packing elements provided above the agitated layer.
4. Process according to claim 1 including disposing the sulfuric acid bath under the vertical tube on a level such that the sulfuric acid flows at a controlled rate owing to a static head and/or a flow gradient into the agitated layer on the gas-permeable plate.
5. Process according to claim 1, herein the vertical tube is a Venturi tube.
6. Process according to claim 5, including separating the vertical tube from the housing and connecting the gas space below the outlet opening of said tube by a conduit to the gas space below the gas-permeable plate in the housing.
7. Process according to claim 6, including providing a bath of sulfuric acid on the bottom of the housing.
8. Process according to claim 6, including supplying sulfuric acid into a distributing trough which is disposed in the middle of the agitated layer on the gas-permeable plate.
9. Process according to claim 1, wherein the vertical tube is contained in the housing and the gas-permeable plate surrounds the lower portion of the tube.
10. Process according to claim 9, herein the means for supplying sulfuric acid to the agitated layer on the gas-permeable plate opens into an annular distributing space which surrounds the vertical tube and has outlet openings leading into the agitated layer.
11. Process according to claim 9, herein a baffle is provided protruding above the surface of the bath on the bottom of the housing disposed on said bottom under the outlet opening of the vertical tube.
Description:
This invention relates to an absorption process and apparatus therefore. It more particularly refers to such process in which gaseous or solid components are absorbed from gaseous fluids with liquid fluids. It most particularly refers to absorbing SO 3 and/or drying SO 2 -containing gases, including air, with liquid sulfuric acid.
Various processes are known for an absorption of SO 3 or moisture from gases with the aid of sulfuric acid.
The absorption and drying towers now in general use for this process have an acid-resisting lining and are provided with baffles. In these towers, the gas rises and the absorbing acid trickles down from above. These towers have the disadvantage that they must have a considerable height, require high initial construction costs and are heavy. Besides, absorbing acid must be pumped at high rates to great heights which is expensive.
Immersion absorbers have also been proposed, wherein the gas is introduced by means of a tube or bell which is immersed in the absorbing acid. The gas rises through the acid and subsequently leaves the absorber (see German Pat. Nos. 133,247; 133,933; 211,999; 882,539; U. S. Pat. Applications 692,018; now Pat. No. 3,415,741, 722,981; 737,233). These immersion absorbers have not been commercially successful in practice here large throughputs were required.
It has also been proposed to use so-called foam absorbers. To produce a high degree of absorption, these processes must use a plurality of series-connected stages, which involve a large overall height (see Chem. Technik, 16, 1964, page 350).
It is also known to use Venturi tube scrubbers for a wet cleaning of gases which contain dust or mist (see Printed German Applications 1,173,433; 1,176,099; Hegenbarth: Herstellung der Schwefelsauve, 1952, page 60).
It is also known to absorb gaseous constituents by means of liquids in Venturi tubes. To this end, a plurality of Venturi tubes are connected in series and successively supplied with the gas and the liquid. These processes and apparatus have the disadvantage that liquid must be circulated at high rates and a plurality of absorption stages are required for one absorption operation (Chemical Engineering, Aug. 16, 1965).
An absorption and drying process and apparatus is known, which utilizes an absorber housing, through the top of which a vertical Venturi tube extends, which has an outlet opening at its lower end. The tube is gastightly sealed to the top of the housing. The supply conduits for the gaseous and liquid fluids are connected in the top portion of the Venturi tube. The lower portion of the Venturi tube is surrounded by a gas-permeable plate, which extends as far as to the housing all and separates the absorber into upper and lower portions. A liquid bath is disposed at the bottom of the housing and the surface of said bath is spaced from the underside of the gas-permeable plate so that there is a gas-filled space between the bath surface and the gas-permeable plate. A layer of the liquid fluid is carried by the plate and communicates by risers with the bath on the bottom of the apparatus and is agitated by the gas flowing through the plate. A drain is provided on the level of the surface of the liquid layer on the plate. A gas outlet opening is provided in the upper housing portion above the layer (see Belgian Pat. No. 695,150).
An absorption process carried out in this apparatus avoids the disadvantages of the previously described processes and apparatus but has certain disadvantages for very large throughouts. Besides, only an acid having a given concentration and consistency can be produced in a process carried out one absorption apparatus.
Therefore, present industrial absorption process use absorption towers substantially exclusively. In most cases these towers contain packing elements.
It is therefore an object of this invention to provide an absorption, drying and scrubbing process which uses an apparatus having very small dimensions, low initial cost, low operating costs and permits an optimum absorption and drying of gases and an optimum scrubbing of gases to remove low concentrations of solids therefrom.
Other and additional objects of this invention will become apparent from a consideration of this entire specification, including the claims and drawing.
These objects are accomplished according to one aspect of this invention by the provision of a process of absorbing gaseous constituents from gaseous fluids and/or for drying gases, such as air or others, and/or for purifying gaseous fluids and for scrubbing them to remove solids, which processes are performed with liquid fluids, preferably for absorbing SO 3 and/or drying SO 2 -containing gas or air with sulfuric acid. This process used an apparatus comprising a vertical tube having an outlet opening at its lower end; a gas supply conduit disposed in the upper portion of the tube; a liquid supply conduit disposed in the tube; a bath of liquid fluid absorbent, which bath is disposed under the outlet end of the tube; a horizontal, gas-permeable plate which succeeds the tube and is contained in a housing; a gas-filled space, which is disposed under the plate and communicates with the gas space under the outlet opening of the vertical tube; a layer of liquid fluid, which is carried by the gas-permeable plate and is agitated by the gas flowing therethrough; a drain for discharging the liquid fluid from said layer; and a gas outlet opening in the upper portion of the housing. In this apparatus, a drain is provided for the bath of the liquid fluid absorbent disposed below the outlet end of the vertical tube and means are provided for supplying the liquid fluid absorbent to the agitated layer of the liquid fluid absorbent on the gas-permeable plate extending through the housing wall.
The vertical tube may be partly filled with packing elements.
The vertical tube consists preferably of a Venturi tube. The process is preferably carried out by supplying the liquid fluid in a finely divided state into the vertical Venturi tube, preferably through a nozzle. Absorbent liquid is supplied to the Venturi tube through a liquid supply conduit disposed in the tube. The absorbent liquid together with absorbed gas components passes don the Venturi tube and forms a bath below the outlet opening of the tube while unabsorbed gas passes over this bath and then up through the horizontal, gas-permeable plate and through a layer of absorbent liquid disposed thereon. The still unabsorbed gas passes out of the system while the enriched absorbent is collected.
Where the liquid fluid is corrosive, the apparatus may be entirely or partly made from or lined with ceramic or other corrosive-resistant material.
The gas-permeable plate may consist of any desired material, provided that its mechanical and chemical properties are compatible with the operating conditions. The plate is suitably composed of a plurality of segments. It may be provided with bores or slots or may consist of a porous gas-permeable plate. The cumulative area of the openings in the gas-permeable plate is determined by pressure drop of the gases flowing therethrough desired.
If required by the operating conditions, a plurality of horizontal gas-permeable plates are superposed and the rising gases passed successively and serially therethrough from bottom to top. Each of said plates suitably carries an agitated layer of the liquid fluid.
In this multiple arrangement, each plate may be provided with separate means for supplying and draining the liquid fluid absorbent thereon. Alternatively, the pressure loss of the gas in the plates may be adjusted so that the liquid fluid absorbent is supplied only to the uppermost plate and is permitted to trickle at a controlled rate through the upper and intermediate plates until it reaches the lowermost plates.
The gas outlet opening disposed in the upper portion of the housing is preferably provided with a drop separator, such as a knockout box or the like, which are per se known, which separates entrained liquid particles from the discharging gas.
A separation of entrained liquid particles may also be ensured by connecting the gas outlet opening to a separator vessel in which part of the liquid contained in the exhaust gas is separated. The gas outlet opening of this separator may be provided with a drop separator.
The drop separators consist preferably of superimposed horizontal demisters (wire mesh filters) and may also be used as a post-absorption means.
For a partial separation of the liquid particles contained in the gases, swirl separators may be provided before and after the drop separators, and a liquid stripping means in the form of a packed layer may be disposed over the agitated layer.
In one embodiment of the invention, the process is carried out with the vertical tube separate from the housing and the gas space disposed below the outlet end of the tube communicates through a connecting conduit to the gas space below the gas-permeable plate in the housing.
In this case, a bath of the liquid fluid absorbent may be provided on the bottom of the housing under the gas-permeable plate, although such bath of the liquid fluid absorbent under the gas-permeable plate is not required.
The bath of the liquid fluid absorbent on the bottom of the housing may be connected to the bath under the vertical tube.
The means for supplying the liquid fluid absorbent to the agitated layer on the gas-permeable plate preferably discharges into a distributing trough, which is disposed on the gas-permeable plate in the middle of the agitated layer. The liquid fluid absorbent is discharged through openings in the bottom or top of the trough. The size of the openings may be selected to ensure such a discharge rate that the residence time of the liquid fluid absorbent in the agitated layer until said fluid reaches the drain is approximately the same in all parts of the layer. In this design, the drain preferably consists of a trough, which surrounds the agitated layer and which receives the liquid fluid absorbent in a controlled manner.
Separate cycles may be provided for the liquid fluid absorbent flowing through the vertical tube and forming the agitated layer in the housing, respectively, or a combined cycle may be provided for both purposes.
Where a combined cycle is used, a preferred design comprises a bath disposed on such a level under the vertical tube that the liquid fluid absorbent flows at a controlled rate into the agitated layer on the gas-permeable plate under the action of the static head and/or gradient of the liquid fluid absorbent.
In another embodiment of the invention, the process is carried out with the vertical tube disposed in the housing and the gas-permeable plate surrounding the lower portion of the tube. In this embodiment, the bath and the gas space under the vertical tube are, respectively, the same as the bath and gas space on the bottom of the housing.
The means for supplying the liquid fluid absorbent to the agitated layer on the gas-permeable plate opens preferably into an annular distributing chamber, which surrounds the vertical tube. The liquid is discharged as described hereinbefore.
A baffle plate protruding above the bath on the bottom of the housing may be provided on the bottom of the housing, preferably under the outlet opening of the vertical tube. This baffle plate ensures a uniform distribution and reversion of the gases.
The process according to the invention is particularly suitable for an absorption of the SO 3 content of contact catalysis sulfuric acid plant gases and for this purpose may be used as an intermediate absorption and/or as a final absorption. A special advantage resides in that the process may be operated as a hot absorption. In this case, the apparatus may be disposed on such a level, owing to its low overall height and light weight, that the hot absorbing acid may flow owing to a natural gradient or static pressure into the preceding or succeeding process stages.
For certain purposes, such as the drying of moist air or SO 2 -containing gases with sulfuric acid, or for the production of oleum, the liquid fluid absorbent must be maintained at a relatively low temperature. Cooling elements, such as cooling pipe coils, are then preferably provided in this case in the agitated layer. These cooling coils have a cooling fluid passed therethrough in order to absorb and remove any surplus heat. Owing to the highly favorable heat transfer coefficients, heat can be removed at very high rates and therefore small cooling elements are sufficient.
The process and apparatus of this invention is suitable for any desired throughput within wide limits and for a production of acids differing in concentration and consistency in one absorption unit.
Some exemplary procedures which may be utilized to absorb SO 3 by means of sulfuric acid and in the operation of this apparatus as a dryer will now be described without limiting the scope of this invention.
Example 1.
The vertical Venturi tube is operated as a preliminary dryer and is supplied with 72 percent -- 78 percent, cold sulfuric acid, which is withdrawn from the bath at the bottom of the container. The sulfuric acid may be light-colored or dark (contaminated by gaseous constituents).
The agitated layer is operated as a post-dryer and supplied with 95 percent -- 98 percent, light-colored or dark sulfuric acid, which is withdrawn from the agitated layer.
Example 2.
The vertical Venturi tube is operated as an absorber for oleum and is supplied with 20 percent -- 36 percent cold oleum, which is withdrawn from the bath at the bottom of the container.
The agitated layer is operated as a final absorber and is supplied with 98.5 percent -- 99 percent cold sulfuric acid, which is withdrawn from the agitated layer.
Example 3.
The vertical Venturi tube is operated as an absorber for oleum as in Example 2.
The agitated layer is operated as a final absorber and supplied with 98.5 percent -- 99 percent hot sulfuric acid, which is withdrawn from the agitated layer.
Example 4.
The vertical Venturi tube is operated as the first stage of a monohydrate absorber and is supplied with cold or hot 98.5 percent -- 99.5 percent sulfuric acid, which is withdrawn from the bath at the bottom of the container.
The agitated layer is operated as the second stage of a monohydrate absorber and supplied with cold or hot 98.5 percent -- 99.5 percent sulfuric acid, which is withdrawn from the agitated layer.
Example 5.
The vertical Venturi tube is operated as in Example 4. The second stage consists of to agitated layers, which are superimposed. The upper layer is supplied with cold or hot 98.5 percent -- 99.5 percent sulfuric acid, which is then transferred into the lower layer and withdrawn from the latter.
Example 6.
The vertical Venturi tube is operated as in Example 4. The agitated layer is operated as in Example 4. A small layer of Raschig rings is provided above the agitated layer and acts as an after-absorber. The Raschig ring layer may be so closely spaced above the agitated layer that the former is moistened by the latter. Alternatively or additionally, moistening may be effected by a supply of sulfuric acid from above onto the Raschig ring layer.
Example 7.
The vertical Venturi tube operates as a monohydrate absorber and is supplied with dark sulfuric acid which comes from the dryer and is withdrawn from the bath at the bottom of the container.
The agitated layer is operated as a monohydrate absorber and supplied with bright sulfuric acid, which is withdrawn from the agitated layer. Only water for adjusting the desired concentration is added to this cycle.
The apparatus, according to the invention, and some procedures will now be explained by way of example with reference to FIGS. 1 to 5 and the absorption of SO 3 with sulfuric acid.
FIGS. 1 to 4 are a diagrammatic transverse sectional view showing the embodiment in which the vertical tube and housing are separate.
FIG. 5 is similar to FIGS. 1--4 but shows the embodiment in which the vertical tube is disposed in the housing.
FIGS. 1--4.
A gas mixture consisting of SO 3 , O 2 , H 2 (and for the intermediate absorption also SO 2 ) is introduced into a vertical Venturi tube 1 through a gas supply conduit 2 disposed in the upper portion of the tube 1. Sulfuric acid is injected through a nozzle device 3. In the Venturi tube, the sulfuric acid is intimately mixed with the gas so that part of the SO 3 content of the gas is absorbed. The mixture of gas and sulfuric acid leaves an outlet opening 4 of the Venturi tube, flows through a gas space 5 under the outlet opening 4 and is impinged on a sulfuric acid bath 6. Part of the injected sulfuric acid is absorbed by the bath 6. The remaining gas mixture flows through a connecting conduit 7 into a housing 8, where it flows through a gas space 9 and through a gas-permeable plate 10, enters an agitated sulfuric acid layer 11, then flows through a wire mesh filter 12 and then leaves the housing 8 through a gas outlet opening 13. The remaining SO 3 content is largely absorbed by the agitated layer 11 of sulfuric acid. The droplets of moisture contained in the gas are separated in the wire mesh filter 12. At the same time, an after-absorption is effected in this filter. Cooling pipes 14 (shown only on one side), provided with an inlet 15 and an outlet 16 for the coolant, are disposed in the agitated layer 11.
FIG. 1 shows the sulfuric acid being pumped from the bath 6 at a controlled rate through a drain 17 by a pump 18. This sulfuric acid flows through an acid cooler 19 and is partly discharged as product through a conduit 20 and partly reinjected through a conduit 21.
In the housing 8, the gas-permeable plate 10 is surrounded by a discharge trough 22, which receives sulfuric acid as the volume of the agitated layer 11 of sulfuric acid increases. This sulfuric acid flows through a downcoming tube 23 into a sulfuric acid bath 24 at the bottom of the housing 8 and is withdrawn through a drain 25 at a controlled rate by a pump 26. This sulfuric acid flows through acid coolers 27 and is partly discharged as product through a conduit 28 and partly returned to the apparatus through a supply means 29. The sulfuric acid is distributed by a trough 30, which extends across the width of the plate 10, preferably in the middle thereof, which is provided with outlet openings.
In FIG. 2, the bath 6 of sulfuric acid is connected by a drain 17a to the bath 24 for sulfuric acid so that there is no acid cycle connected to the Venturi tube. Part of the acid which has been cooled in the acid cooler 27 is reinjected into the Venturi tube by a conduit 31.
In FIG. 3 there is no bath of sulfuric acid at the bottom of the housing 8 under the gas-permeable plate. There is no acid cycle connected to the bath in the housing 8. Part of the acid which has been cooled in the acid cooler 19 is returned through a conduit 32 to the supply means 29.
In FIG. 4, a drain 17b for the bath 6 is also the means 29b for supplying sulfuric acid to the agitated layer 11 of sulfuric acid. A trough 30b, for distributing the acid in the layer 11, surrounds the gas-permeable plate 10. A drain trough 22b extends across the width of the plate 10 in the middle thereof and supplies acid through a pipe 23b into the bath 24.
In FIG. 5, the Venturi tube 1 is contained in the housing 8. The bath 6 of sulfuric acid under the outlet end 4 of the Venturi tube 1 is the same as the bath 24 of sulfuric acid on the bottom of the housing. The gas space 5 under the Venturi tube 1 is the same as the gas space 9 under the gas-permeable plate 10.
The withdrawn amounts of liquid absorbent are replaced through conduits 33 and 34.
Various processes are known for an absorption of SO 3 or moisture from gases with the aid of sulfuric acid.
The absorption and drying towers now in general use for this process have an acid-resisting lining and are provided with baffles. In these towers, the gas rises and the absorbing acid trickles down from above. These towers have the disadvantage that they must have a considerable height, require high initial construction costs and are heavy. Besides, absorbing acid must be pumped at high rates to great heights which is expensive.
Immersion absorbers have also been proposed, wherein the gas is introduced by means of a tube or bell which is immersed in the absorbing acid. The gas rises through the acid and subsequently leaves the absorber (see German Pat. Nos. 133,247; 133,933; 211,999; 882,539; U. S. Pat. Applications 692,018; now Pat. No. 3,415,741, 722,981; 737,233). These immersion absorbers have not been commercially successful in practice here large throughputs were required.
It has also been proposed to use so-called foam absorbers. To produce a high degree of absorption, these processes must use a plurality of series-connected stages, which involve a large overall height (see Chem. Technik, 16, 1964, page 350).
It is also known to use Venturi tube scrubbers for a wet cleaning of gases which contain dust or mist (see Printed German Applications 1,173,433; 1,176,099; Hegenbarth: Herstellung der Schwefelsauve, 1952, page 60).
It is also known to absorb gaseous constituents by means of liquids in Venturi tubes. To this end, a plurality of Venturi tubes are connected in series and successively supplied with the gas and the liquid. These processes and apparatus have the disadvantage that liquid must be circulated at high rates and a plurality of absorption stages are required for one absorption operation (Chemical Engineering, Aug. 16, 1965).
An absorption and drying process and apparatus is known, which utilizes an absorber housing, through the top of which a vertical Venturi tube extends, which has an outlet opening at its lower end. The tube is gastightly sealed to the top of the housing. The supply conduits for the gaseous and liquid fluids are connected in the top portion of the Venturi tube. The lower portion of the Venturi tube is surrounded by a gas-permeable plate, which extends as far as to the housing all and separates the absorber into upper and lower portions. A liquid bath is disposed at the bottom of the housing and the surface of said bath is spaced from the underside of the gas-permeable plate so that there is a gas-filled space between the bath surface and the gas-permeable plate. A layer of the liquid fluid is carried by the plate and communicates by risers with the bath on the bottom of the apparatus and is agitated by the gas flowing through the plate. A drain is provided on the level of the surface of the liquid layer on the plate. A gas outlet opening is provided in the upper housing portion above the layer (see Belgian Pat. No. 695,150).
An absorption process carried out in this apparatus avoids the disadvantages of the previously described processes and apparatus but has certain disadvantages for very large throughouts. Besides, only an acid having a given concentration and consistency can be produced in a process carried out one absorption apparatus.
Therefore, present industrial absorption process use absorption towers substantially exclusively. In most cases these towers contain packing elements.
It is therefore an object of this invention to provide an absorption, drying and scrubbing process which uses an apparatus having very small dimensions, low initial cost, low operating costs and permits an optimum absorption and drying of gases and an optimum scrubbing of gases to remove low concentrations of solids therefrom.
Other and additional objects of this invention will become apparent from a consideration of this entire specification, including the claims and drawing.
These objects are accomplished according to one aspect of this invention by the provision of a process of absorbing gaseous constituents from gaseous fluids and/or for drying gases, such as air or others, and/or for purifying gaseous fluids and for scrubbing them to remove solids, which processes are performed with liquid fluids, preferably for absorbing SO 3 and/or drying SO 2 -containing gas or air with sulfuric acid. This process used an apparatus comprising a vertical tube having an outlet opening at its lower end; a gas supply conduit disposed in the upper portion of the tube; a liquid supply conduit disposed in the tube; a bath of liquid fluid absorbent, which bath is disposed under the outlet end of the tube; a horizontal, gas-permeable plate which succeeds the tube and is contained in a housing; a gas-filled space, which is disposed under the plate and communicates with the gas space under the outlet opening of the vertical tube; a layer of liquid fluid, which is carried by the gas-permeable plate and is agitated by the gas flowing therethrough; a drain for discharging the liquid fluid from said layer; and a gas outlet opening in the upper portion of the housing. In this apparatus, a drain is provided for the bath of the liquid fluid absorbent disposed below the outlet end of the vertical tube and means are provided for supplying the liquid fluid absorbent to the agitated layer of the liquid fluid absorbent on the gas-permeable plate extending through the housing wall.
The vertical tube may be partly filled with packing elements.
The vertical tube consists preferably of a Venturi tube. The process is preferably carried out by supplying the liquid fluid in a finely divided state into the vertical Venturi tube, preferably through a nozzle. Absorbent liquid is supplied to the Venturi tube through a liquid supply conduit disposed in the tube. The absorbent liquid together with absorbed gas components passes don the Venturi tube and forms a bath below the outlet opening of the tube while unabsorbed gas passes over this bath and then up through the horizontal, gas-permeable plate and through a layer of absorbent liquid disposed thereon. The still unabsorbed gas passes out of the system while the enriched absorbent is collected.
Where the liquid fluid is corrosive, the apparatus may be entirely or partly made from or lined with ceramic or other corrosive-resistant material.
The gas-permeable plate may consist of any desired material, provided that its mechanical and chemical properties are compatible with the operating conditions. The plate is suitably composed of a plurality of segments. It may be provided with bores or slots or may consist of a porous gas-permeable plate. The cumulative area of the openings in the gas-permeable plate is determined by pressure drop of the gases flowing therethrough desired.
If required by the operating conditions, a plurality of horizontal gas-permeable plates are superposed and the rising gases passed successively and serially therethrough from bottom to top. Each of said plates suitably carries an agitated layer of the liquid fluid.
In this multiple arrangement, each plate may be provided with separate means for supplying and draining the liquid fluid absorbent thereon. Alternatively, the pressure loss of the gas in the plates may be adjusted so that the liquid fluid absorbent is supplied only to the uppermost plate and is permitted to trickle at a controlled rate through the upper and intermediate plates until it reaches the lowermost plates.
The gas outlet opening disposed in the upper portion of the housing is preferably provided with a drop separator, such as a knockout box or the like, which are per se known, which separates entrained liquid particles from the discharging gas.
A separation of entrained liquid particles may also be ensured by connecting the gas outlet opening to a separator vessel in which part of the liquid contained in the exhaust gas is separated. The gas outlet opening of this separator may be provided with a drop separator.
The drop separators consist preferably of superimposed horizontal demisters (wire mesh filters) and may also be used as a post-absorption means.
For a partial separation of the liquid particles contained in the gases, swirl separators may be provided before and after the drop separators, and a liquid stripping means in the form of a packed layer may be disposed over the agitated layer.
In one embodiment of the invention, the process is carried out with the vertical tube separate from the housing and the gas space disposed below the outlet end of the tube communicates through a connecting conduit to the gas space below the gas-permeable plate in the housing.
In this case, a bath of the liquid fluid absorbent may be provided on the bottom of the housing under the gas-permeable plate, although such bath of the liquid fluid absorbent under the gas-permeable plate is not required.
The bath of the liquid fluid absorbent on the bottom of the housing may be connected to the bath under the vertical tube.
The means for supplying the liquid fluid absorbent to the agitated layer on the gas-permeable plate preferably discharges into a distributing trough, which is disposed on the gas-permeable plate in the middle of the agitated layer. The liquid fluid absorbent is discharged through openings in the bottom or top of the trough. The size of the openings may be selected to ensure such a discharge rate that the residence time of the liquid fluid absorbent in the agitated layer until said fluid reaches the drain is approximately the same in all parts of the layer. In this design, the drain preferably consists of a trough, which surrounds the agitated layer and which receives the liquid fluid absorbent in a controlled manner.
Separate cycles may be provided for the liquid fluid absorbent flowing through the vertical tube and forming the agitated layer in the housing, respectively, or a combined cycle may be provided for both purposes.
Where a combined cycle is used, a preferred design comprises a bath disposed on such a level under the vertical tube that the liquid fluid absorbent flows at a controlled rate into the agitated layer on the gas-permeable plate under the action of the static head and/or gradient of the liquid fluid absorbent.
In another embodiment of the invention, the process is carried out with the vertical tube disposed in the housing and the gas-permeable plate surrounding the lower portion of the tube. In this embodiment, the bath and the gas space under the vertical tube are, respectively, the same as the bath and gas space on the bottom of the housing.
The means for supplying the liquid fluid absorbent to the agitated layer on the gas-permeable plate opens preferably into an annular distributing chamber, which surrounds the vertical tube. The liquid is discharged as described hereinbefore.
A baffle plate protruding above the bath on the bottom of the housing may be provided on the bottom of the housing, preferably under the outlet opening of the vertical tube. This baffle plate ensures a uniform distribution and reversion of the gases.
The process according to the invention is particularly suitable for an absorption of the SO 3 content of contact catalysis sulfuric acid plant gases and for this purpose may be used as an intermediate absorption and/or as a final absorption. A special advantage resides in that the process may be operated as a hot absorption. In this case, the apparatus may be disposed on such a level, owing to its low overall height and light weight, that the hot absorbing acid may flow owing to a natural gradient or static pressure into the preceding or succeeding process stages.
For certain purposes, such as the drying of moist air or SO 2 -containing gases with sulfuric acid, or for the production of oleum, the liquid fluid absorbent must be maintained at a relatively low temperature. Cooling elements, such as cooling pipe coils, are then preferably provided in this case in the agitated layer. These cooling coils have a cooling fluid passed therethrough in order to absorb and remove any surplus heat. Owing to the highly favorable heat transfer coefficients, heat can be removed at very high rates and therefore small cooling elements are sufficient.
The process and apparatus of this invention is suitable for any desired throughput within wide limits and for a production of acids differing in concentration and consistency in one absorption unit.
Some exemplary procedures which may be utilized to absorb SO 3 by means of sulfuric acid and in the operation of this apparatus as a dryer will now be described without limiting the scope of this invention.
Example 1.
The vertical Venturi tube is operated as a preliminary dryer and is supplied with 72 percent -- 78 percent, cold sulfuric acid, which is withdrawn from the bath at the bottom of the container. The sulfuric acid may be light-colored or dark (contaminated by gaseous constituents).
The agitated layer is operated as a post-dryer and supplied with 95 percent -- 98 percent, light-colored or dark sulfuric acid, which is withdrawn from the agitated layer.
Example 2.
The vertical Venturi tube is operated as an absorber for oleum and is supplied with 20 percent -- 36 percent cold oleum, which is withdrawn from the bath at the bottom of the container.
The agitated layer is operated as a final absorber and is supplied with 98.5 percent -- 99 percent cold sulfuric acid, which is withdrawn from the agitated layer.
Example 3.
The vertical Venturi tube is operated as an absorber for oleum as in Example 2.
The agitated layer is operated as a final absorber and supplied with 98.5 percent -- 99 percent hot sulfuric acid, which is withdrawn from the agitated layer.
Example 4.
The vertical Venturi tube is operated as the first stage of a monohydrate absorber and is supplied with cold or hot 98.5 percent -- 99.5 percent sulfuric acid, which is withdrawn from the bath at the bottom of the container.
The agitated layer is operated as the second stage of a monohydrate absorber and supplied with cold or hot 98.5 percent -- 99.5 percent sulfuric acid, which is withdrawn from the agitated layer.
Example 5.
The vertical Venturi tube is operated as in Example 4. The second stage consists of to agitated layers, which are superimposed. The upper layer is supplied with cold or hot 98.5 percent -- 99.5 percent sulfuric acid, which is then transferred into the lower layer and withdrawn from the latter.
Example 6.
The vertical Venturi tube is operated as in Example 4. The agitated layer is operated as in Example 4. A small layer of Raschig rings is provided above the agitated layer and acts as an after-absorber. The Raschig ring layer may be so closely spaced above the agitated layer that the former is moistened by the latter. Alternatively or additionally, moistening may be effected by a supply of sulfuric acid from above onto the Raschig ring layer.
Example 7.
The vertical Venturi tube operates as a monohydrate absorber and is supplied with dark sulfuric acid which comes from the dryer and is withdrawn from the bath at the bottom of the container.
The agitated layer is operated as a monohydrate absorber and supplied with bright sulfuric acid, which is withdrawn from the agitated layer. Only water for adjusting the desired concentration is added to this cycle.
The apparatus, according to the invention, and some procedures will now be explained by way of example with reference to FIGS. 1 to 5 and the absorption of SO 3 with sulfuric acid.
FIGS. 1 to 4 are a diagrammatic transverse sectional view showing the embodiment in which the vertical tube and housing are separate.
FIG. 5 is similar to FIGS. 1--4 but shows the embodiment in which the vertical tube is disposed in the housing.
FIGS. 1--4.
A gas mixture consisting of SO 3 , O 2 , H 2 (and for the intermediate absorption also SO 2 ) is introduced into a vertical Venturi tube 1 through a gas supply conduit 2 disposed in the upper portion of the tube 1. Sulfuric acid is injected through a nozzle device 3. In the Venturi tube, the sulfuric acid is intimately mixed with the gas so that part of the SO 3 content of the gas is absorbed. The mixture of gas and sulfuric acid leaves an outlet opening 4 of the Venturi tube, flows through a gas space 5 under the outlet opening 4 and is impinged on a sulfuric acid bath 6. Part of the injected sulfuric acid is absorbed by the bath 6. The remaining gas mixture flows through a connecting conduit 7 into a housing 8, where it flows through a gas space 9 and through a gas-permeable plate 10, enters an agitated sulfuric acid layer 11, then flows through a wire mesh filter 12 and then leaves the housing 8 through a gas outlet opening 13. The remaining SO 3 content is largely absorbed by the agitated layer 11 of sulfuric acid. The droplets of moisture contained in the gas are separated in the wire mesh filter 12. At the same time, an after-absorption is effected in this filter. Cooling pipes 14 (shown only on one side), provided with an inlet 15 and an outlet 16 for the coolant, are disposed in the agitated layer 11.
FIG. 1 shows the sulfuric acid being pumped from the bath 6 at a controlled rate through a drain 17 by a pump 18. This sulfuric acid flows through an acid cooler 19 and is partly discharged as product through a conduit 20 and partly reinjected through a conduit 21.
In the housing 8, the gas-permeable plate 10 is surrounded by a discharge trough 22, which receives sulfuric acid as the volume of the agitated layer 11 of sulfuric acid increases. This sulfuric acid flows through a downcoming tube 23 into a sulfuric acid bath 24 at the bottom of the housing 8 and is withdrawn through a drain 25 at a controlled rate by a pump 26. This sulfuric acid flows through acid coolers 27 and is partly discharged as product through a conduit 28 and partly returned to the apparatus through a supply means 29. The sulfuric acid is distributed by a trough 30, which extends across the width of the plate 10, preferably in the middle thereof, which is provided with outlet openings.
In FIG. 2, the bath 6 of sulfuric acid is connected by a drain 17a to the bath 24 for sulfuric acid so that there is no acid cycle connected to the Venturi tube. Part of the acid which has been cooled in the acid cooler 27 is reinjected into the Venturi tube by a conduit 31.
In FIG. 3 there is no bath of sulfuric acid at the bottom of the housing 8 under the gas-permeable plate. There is no acid cycle connected to the bath in the housing 8. Part of the acid which has been cooled in the acid cooler 19 is returned through a conduit 32 to the supply means 29.
In FIG. 4, a drain 17b for the bath 6 is also the means 29b for supplying sulfuric acid to the agitated layer 11 of sulfuric acid. A trough 30b, for distributing the acid in the layer 11, surrounds the gas-permeable plate 10. A drain trough 22b extends across the width of the plate 10 in the middle thereof and supplies acid through a pipe 23b into the bath 24.
In FIG. 5, the Venturi tube 1 is contained in the housing 8. The bath 6 of sulfuric acid under the outlet end 4 of the Venturi tube 1 is the same as the bath 24 of sulfuric acid on the bottom of the housing. The gas space 5 under the Venturi tube 1 is the same as the gas space 9 under the gas-permeable plate 10.
The withdrawn amounts of liquid absorbent are replaced through conduits 33 and 34.