Title of Invention

"AN IMPROVED WET SCRUBBER FOR A SIMULTANEOUS SCRUBBING OF PARTICULATE

Abstract An improved wet scrubber for simultaneous scrubbing of particulate and gaseous matters in a gas-liquid, gas-liquid-solid contacting unit, comprising a vertical column (1), a multi orifice antenna type sparger (5) is provided between the first stage (15) and the second stage (1) of the three-stage bubble column, a sedimentation chamber (8) is connected to the column (1) through a valve (9) and the water from the said sedimentation chamber is recirculated through a valve (10) and pump (11) to the top of the second stage (1) at inlet (17) and gaseous pollutants (13) are pumped through the bottom of the first stage (15) of the column characterized in that within the second stage (1) of the column, as combination of small apertured horizontal contraction disks (3) with an aperture (7) and large apertured horizontal expansion screen with 4/5 mesh (8) alternately placed to impose, sequentially, sudden and slow disturbances which leads to a high very high inter-phase transfer.
Full Text -2-
FIELD OF THE INVENTION:
This invention relates loan improved wet scrubber for simultaneous scrubbing of particiulate and gaseous matters in a gas-liquid/gas-Hquid-solid, contacting unit.
This invention further relates to an improved wet scrubber for simultaneous scrubbing of particulate and gaseous matters in a gas-liquid/gas-liquid-solid, contacting unit, which achieves intense inter-phase mixing without any mechanical device with moving parts.
BACKGROUND OF THE INVENTION:
Good inter-phase mixing is essential for successful gas-liquid/gas-liquid-solid contacting operations in a gas disposal system (bubble column). In commonly available bubble columns, bubbles are sparged into a liquid column at the bottom and as the bubbles rise through the liquid, they coalesce and reduce the effective area for gas-liquid contact.
There are disadvantages associated with the bubble columns known in the art.
One of the main disadvantages is that the continuous generation and splitting of bubbles to regenerate new surface area demands developing highly efficient gas-llquid/gas-llquid-solld contacting systems. Such requirements are seldom achieved in industrial practice, as these are associated with mechanical complications and high energy dissipation.

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Another disadvantage associated with the known wet scrubbers of the art is that because of the physical and chemical properties of gas and liquids, commercially available bubble columns mostly give single-stage contacting which are not more than 60 to 70% efficient with regard to transfer or mass or chemical species. However, present pollution control legislation demands almost 100% removal of pollutants from an exhaust effluent stream.
OBJECTS OF THE INVENTION:
It is therefore an object of the present invention to the propose an Improved wet scrubber for simultaneous scrubbing of particular and gaseous matters which reduces processing costs and overcomes aft the drawbacks mentioned above with relation to the prior art.
Another object of the present invention is to propose an improved wet scrubber for a gas-llquid solid contacting system, which is highly compact and at the same time operates in multi-stage series mode to yield very high overall efficiency without adding on to the capital cost of additional equipment or specialised maintenance procedure.

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Yet another object of the present invention is to propose an improved wet scrubber in which the number of stages can be easify varied to achieve very high efficiency even when (he individual stage efficiencies are limited by physical parameters of the system.
Still another object of the present invention is to propose an improved wet scrubber which versatile, have no moving parts and easy to fabricate, install and maintain.
A further object of the present invention is to propose an improved wel scrubber in which solids can be handled without serious erosion or plugging problems.
A still further object of the present invention is to propose an improved wet scrubber with little floor space requirements and low capital investment.
Yet a further object of the present invention is to propose an improved wet
scrubber which achieves bubble breakup and regeneration through the hydrodynamic instabilities in two-phase flow, sudden flow contractions followed by controlled flow expansion and contraction lead to instabilities which lead to continuous regeneration, breakup and regeneration of bubble

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Surface area. The scrubber operates in a number of stages and improved gas dispersion and mixing enhances both individual stage efficiencied and overall column efficiency. The number of stages is proposed to be varied to achieve very high efficiency even when the individual stage efficiencies are limited by physical parameters of the system.
According to the present invention there is provided an improved wet scrubber for simultaneous scrubbing of particulate and gaseous matters in a gas-liquid/gas-liquid-solid contacting unit, comprising, a vertical column, a multi-orifice antenna type sparger provided at between the first stage and the second stage of the three-stage bubble column, a sedimentation chamber connected to the column through a vaive and the water from the said sedimentation chamber is recirculated through a valve and pump to the top of the second stage column at inlet and gasous pollutants are pumped through the bottom of the first stage of the column characterized in that within the second stage vertical column, a combination of small apertured horizontal contraction disks and with an aperture and large apertured horizontal expansion screen with 4/5 mesh alternately placed to impose sequentially, sudden and slow disturbances which leads to a very high inter-phase transfer.

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The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to the non-limiting exemplary embodiments of the invention represented in the accompanying drawings.
Fig 1 shows a schematic diagram of the improved 'scrubber; and
Fig 2 shows in tabular form the comparison of power consumption and hydrodynamic characteristic for various gas-liquid contacting equipments with the present invention. SUMMARY OF THE PRESENT INVENTION .
The device of the present invention is highly versatile, compact and efficient gas dispersed system commonly known as bubble column, which can be used as a wet scrubber to control air pollution, for adding oxygen to waste water for removing BOD, as simple gas absorbers for absorbing a soluble gas and
as two/three phase chemical reactors or as bio-reactors and
fermenter, etc. In between the first stage (15) and the second
stage (1) of an experimental three-stage column bubbles are generated in the size range of 3-6mmf using a unique multi-orifice antenna type sparger (5). The sparger (5) design

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has been tailored to give identical velocities through individual
orifices, to insure uniform generation of relatively large
bubbles. The antenna type sparger (5) covers more than 95%
of total column area and distributes the bubbles uniformly over the entire cross section of the column. Because of the construction of the sparger (5) with 144 holes each of 1.6 mm and due to the high gas velocity maintained at the sparger (5) orifices, the bubbles rise almost vertically in this section wihotit bubble pairing or bubble coalescence- At the end of this stage, the bubbles are allowed to deform and collapse in response to the sudden flow disturbance imposed on them. This is achieved by constricting the flow cross-sectional area to about 25^ of the original column diameter by using a relatively small aperture . construction disk (3) at least one and upto 3 such construction disk (3) is placed alternatively and equally spaced with at least one end upto 3 expansion screens (2) with 4/5 mesh (6). On reaching the lower surface of the disk (3) bubbles slide radially toward the central axtal opening (6,7) of the disks (2,3). Migration of the bubbles towards this opening (6.7) leads to bubble crowding, direct impaction, infringement and bubble coalescence.

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As the constricted passage gets choked with bubbles trying to move upwards, all the bubbles collapse into a single large bubble or slug. Vigorous bubble collapse create very turbulent churning action at the disk opening (6,7). However, on passing through this disk opening (6,7), the superficial gas velocity increases to sixteen times the original empty column superficial velocity a velocity which leads to the breakup of the larger bubbles at the upper part of the disk (2,3). In this section (section -II or State II, (1) a relatively large apertured expansion screen (2) is positioned above the small apertured disk (3) to prevent bubble migration to the wall of the column (1) and to insure axial movement of the bubble swarms. Furthermore, this increase in flow area reduces the forward velocity of the bubbles due to reduction in the pressure of the liquid surrounding the bubbles leads to stretching of the bubble surface.
The bubbles deform and split under the influence of intrinsic instabilities as well as in homogeneities in the pressure field. Above and equidistant from the expansion screen, a second smaller contraction disk (3) has been provided again to create bubble crowdng, coalescence and bubble regeneration as described above. Break up of the bubbles in the liquid continuum entraps the solid particls (e.g. flyash in the exhaust of a Thermal Power

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Plant) in water which are continuously washed out by the stream of the flowing liquid (L). The second stage column (l) is provided with flanges (4) at the top and bottom for connection of the first stage (15) at the bottom and to the third stage (16) at the top- Inlet column, The liquid is sprayed at two or three points.along the

verticie height of the second sta&e of the column (r)with course water sprays (17).
The third stage (16) of the babble column is L-shaped and the outlet (12) for the clean gas has a diameter equal to the opening (?) of the small diameter horizontal contraction disk(3). The resulting slurry containing flyash can be continuously sedimented out and withdrawn from the column through a sedimentation chamber (8). The resulting relatively clean water being recirculated to the top of the column*

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Acid formed in the water by the absorption of acidic gaseous emissions needs to be only partial1y neutralised for flyash which are alkaline. Or is neutralised by a system which adds alkaline solution to the water as necessary to maintain the Hat a nominal value . Water containing the formed sediment at the bottom of the sedimentation chamber may be pumped to one or more sedimentation tanks and clarifiers where a sludge is fprmed and the remaining water is either disposed of or recycled for further use. Within the vertical, a dynamic system is established which is held stable both mechanically and chemically during continuous operation.
Simultaneously gaseous pollutants (13) are also absorbed by the highly turbulent liquid films created in the system due to continuous and very vigorous bubble formation, bubble bursting
and bubble re-formation.
The device is very versatile and the intensity of
gas-liquid-solid mixing can be easily regulated by controlling the aperture diameters _(6,7) and relative position of the aperture disks (2,3)

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The device maintains high liquid (slurry) phase contact
for the reaction to take place and excellent heat transfer properties for easy temperature control. The system has high
interface mass transfer rates at low energy input and a very high percentage upto 99.9% efficiency of removal of flyash laden
so2.

The device is extremely versatile and can be adusted to
generate bubbles of different sizes by adjusting the apertured disks (2,3) (aperture diameter (7) and mesh (6) ) and relative distance between them in the vertical column (l). It would be possible to induce shear-free mixing for shear sensitive material.
The power consumption is low and is 200 to 4 50W/M3 of the vessel. The column (l) and the contraction/expansion disks (2,3) may be made of any suitable material, like concrete, steel,
plastic or glass.
The device has high turn-down ratio and can operate with
high efficiency over a wide range of flow rates. The overall efficiency can be calculated by the formulae:

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The different values of n1,n2,n3 are n1 =0.60-0.70, n2 =0.85-0.90,n3=0.85-0.90 nT =0.99-0.995 and in many cases 100% where n1,n2,n3 are individual stage efficiencies and nT
is the overall efficiency of the system.
The above formulae indicates that even difficult devices
can be treated to achieve very high efficiency, even when the individual stage efficiencies are not very high. In this case, large number of stages should be used.
Table 1 of figure 2 shown in tabular form the comparison of power consumption and hydrodynamic characteristics for various gas-liquid contacting equipments with the present invention,
The invention described hereinabove is in relation to the non-limiting embodiments and as defined by the accompanying claims.

-13-WE CLAIM:
1. An improved wet scrubber for simultaneous scrubbing of particulate and gaseous matters in a gas-liquid, gas-liquid-solid contacting unit, comprising a vertical column (1), a multi orifice antenna type sparger (5) is provided between the first stage (15) and the second stage (1) of the three-stage bubble column, a sedimentation chamber (8) is connected to the column (1) through a valve (9) and the water from the said sedimentation chamber is recirculated through a valve (10) and pump (11) to the top of the second stage (1) at Inlet (17) and gaseous pollutants (13) are pumped through the bottom of the first stage(15) of the column characterized in that within the second stage (1) of the column, as combination of small apertured horizontal contraction disks (3) with an aperture (7) and-large apertured horizontal expansion screen with 4/5 mesh (6) alternately placed to impose, sequentially, sudden and slow disturbances which leads to a high very high inter-phase transfer.
2. The improved wet scrubber as claimed in claim 1 wherein said column can be constructed in a number of vertical stages (15,16) operating in series.

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3. The improved wet scrubber as claimed in claim 1 wherein said multi-
orifice antenna type sparger (5) placed in a lowest stage of said three-
stage column (15,16) produce bubbles in the size of 3-6mm,
4. The improved wet scrubber as claimed in claim 3 wherein said multi-
orifice antenna type sparger (5) covers more than 95% of the total column
area for distribution of uniform bubbles.
5. The improved wet scrubber as claimed in claim 1 wherein said small
apertured contraction disk (3) with aperture (7) restricts the cross-
sectional flow area to atleast 25%.
6. The improved wet scrubber as claimed in anyone of claims 1 and 5
wherein said large apertured horizontal expansion screen (2) having a 4/5
mesh (6) is positioned above said small apertured horizontal contraction
disk (3),
7. The improved wet scrubber as claimed in anyone of claims 1,5 and 6
wherein the total opening (6) area of the expansion screen (2) is bigger
than the opening (7) of the small aperture contraction disk (3).

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8. The improved wet screen as claimed in claim 1 wherein ihe antenna
sparger (5) is provided with 144 number of orifices, each pf 1,6 mm
diameter.
9. The improved wet scrubber as claimed in claim 1 wherein the contraction
disk (3) can be made from any material like concrete, steel, plastics and
glass.
10. The Improved wet scrubber as claimed In claim 1 wherein the 99.9% of
flyash and SO2 is removed from air-SO2 flyash gaseous pollutants (13).
11. An improved wet scrubber for simultaneous scrubbing of particulate and gaseous in a gas-liquid, gas-liquld-solid contacting unit, as herein described illustrated in the accompanying drawings.

An improved wet scrubber for simultaneous scrubbing of particulate and gaseous matters in a gas-liquid, gas-liquid-solid contacting unit, comprising a vertical column (1), a multi orifice antenna type sparger (5) is provided between the first stage (15) and the second stage (1) of the three-stage bubble column, a sedimentation chamber (8) is connected to the column (1) through a valve (9) and the water from the said sedimentation chamber is recirculated through a valve (10) and pump (11) to the top of the second stage (1) at inlet (17) and gaseous pollutants (13) are pumped through the bottom of the first stage (15) of the column characterized in that within the second stage (1) of the column, as combination of small apertured horizontal contraction disks (3) with an aperture (7) and large apertured horizontal expansion screen with 4/5 mesh (8) alternately placed to impose, sequentially, sudden and slow disturbances which leads to a high very high inter-phase transfer.

Documents:

00673-cal-2000 abstract.pdf

00673-cal-2000 claims.pdf

00673-cal-2000 correspondence.pdf

00673-cal-2000 description(complete).pdf

00673-cal-2000 drawings.pdf

00673-cal-2000 form-1.pdf

00673-cal-2000 form-18.pdf

00673-cal-2000 form-2.pdf

00673-cal-2000 form-3.pdf

00673-cal-2000 form-5.pdf

00673-cal-2000 g.p.a.pdf

00673-cal-2000 letters patent.pdf

00673-cal-2000 reply f.e.r.pdf


Patent Number 207112
Indian Patent Application Number 673/CAL/2000
PG Journal Number 21/2007
Publication Date 25-May-2007
Grant Date 23-May-2007
Date of Filing 07-Dec-2000
Name of Patentee INDIAN INSTITUTE OF TECHNOLOGY
Applicant Address KHARAGPUR 721 302
Inventors:
# Inventor's Name Inventor's Address
1 PROF BISWAS MANINDRA NATH INDIAN NATIONAL OF DEPT. OF CHEMIKCAL ENGINERING OF INDIAN INSTITUTE OD TECHNOLOGY, KHARAGPUR -712 302
PCT International Classification Number B01D-47/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA