Multi-level Gas Scrubber with Multiple Flooded Scrubber Heads

Abstract

The present invention relates to a wet scrubbing head design whose horizontal orientation and flooded operating characteristics allow complete wet scrubbing at multiple interaction zones each with different neutralizing reagents. The capacity for multiple scrubbing zones improves overall pollutant removal efficiency by adding polishing interaction zones for particulate and acid gas removal systems or by broadening the range of pollutants being removed by operating with a different neutralizing solution or a combination of these operating conditions. The flooded head design approach allows a single scrubber to accomplish high levels of removal efficiency for multiple pollutants which reduces cost, and footprint interaction complexities of the multiple devices it replaces. Flooded head scrubbers have application in combustion flue gas pollutant removal and in chemical and industrial applications that generate dust, odors and acid gases.

Claims

1. A vertically-oriented scrubber apparatus for removing a plurality of distinct contaminants from a contaminated gas stream, comprising: a) a scrubber vessel having a ceiling, a floor, a cylindrical wall connecting the ceiling to the floor, a plurality of vertically-spaced heads, a velum above each head, a gas inlet, an induced draft fan, and a gas outlet; b) a submerged lower head positioned horizontally across the lower end of the scrubber vessel, wherein the submerged lower head includes a horizontal plate having a plurality of narrow slots extending throughout; c) a first scrubbing fluid reservoir disposed within the bottom end of the scrubber vessel below the submerged lower head, and a first reaction zone volume to a desired level above the submerged scrubbing head, the first scrubbing fluid selected to remove a first group of contaminants from the contaminated gas stream; d) a first scrubbing fluid inlet extending into a first velum above the submerged head, first spraying means in fluid connection with the first scrubbing fluid inlet for spraying the first scrubbing fluid into the first scrubbing fluid reaction zone volume, and a first scrubbing fluid outlet in the floor; e) a first flooded head extending horizontally across the entire cross-section of the scrubber vessel at a position above the first scrubbing fluid inlet, wherein the first flooded head comprises a plate having a plurality of narrow slots extending throughout; f) a second scrubbing fluid reaction zone volume disposed to a desired level above the first flooded head, the second scrubbing fluid selected to remove a second group of contaminants from the contaminated gas stream; and g) a second scrubbing fluid inlet extending into a second velum above the first flooded head, second spraying means in fluid connection with the second scrubbing fluid inlet for spraying the second scrubbing fluid into the second scrubbing fluid reaction zone volume, and a second scrubbing fluid outlet above the first flooded head passing through the scrubber vessel wall.

2. A vertically-oriented scrubber apparatus for removing a plurality of distinct contaminants from a contaminated gas stream, comprising: a) a scrubber vessel having a ceiling, a floor, a cylindrical wall connecting the ceiling to the floor, a plurality of vertically-spaced heads, a velum above each head, a gas inlet, an induced draft fan, and a gas outlet; b) a first scrubbing fluid reservoir disposed within the bottom end of the scrubber vessel to a desired level, the first scrubbing fluid selected to remove a first group of contaminants from the contaminated gas stream; c) a first flooded head extending horizontally across the scrubber vessel at a position above the gas inlet, defining a first velum between the first scrubbing fluid reservoir and the first flooded head, wherein the first flooded head comprises a plate having a plurality of narrow slots extending throughout; d) a first scrubbing fluid reaction zone volume disposed to a desired level above the first flooded head, the reaction zone volume in fluid connection with the reservoir via one or more overflow tubes, each extending from the first scrubbing fluid reservoir through the first flooded head to a desired level above the first flooded head; f) a first scrubbing fluid inlet extending through the wall into a second velum above the first flooded head, first spraying means in fluid connection with the first scrubbing fluid inlet for spraying the first scrubbing fluid into the second scrubbing fluid reaction zone volume, and a first scrubbing fluid outlet in the floor; g) a second flooded head extending horizontally across the entire cross-section of the scrubber vessel at a position above the first flooded head, defining a second velum between the first scrubbing fluid reaction zone volume and the second flooded head, wherein the second flooded head comprises a plate having a plurality of narrow slots extending throughout; h) a second scrubbing fluid reaction zone volume disposed above the second flooded head to a desired level, the second scrubbing fluid selected to remove a second group of contaminants from the contaminated gas stream; and i) a second scrubbing fluid inlet extending into a third velum above the second flooded head, second spraying means in fluid connection with the second scrubbing fluid inlet for spraying the second scrubbing fluid into the second scrubbing fluid reaction zone volume, and a second scrubbing fluid outlet above the second flooded head passing through the wall of the scrubber vessel.

3. The scrubber apparatus of claim 1, further comprising: a) one or more additional flooded heads extending horizontally across the entire cross-section of the scrubber vessel and serially stacked vertically above the other heads, each defining an additional velum in relation to the head below; b) one or more additional scrubbing fluid reaction zone volumes, each disposed above a corresponding flooded head to a desired level, each additional scrubbing fluid selected to remove a desired additional group of contaminants from the contaminated gas stream; and c) one or more additional scrubbing fluid inlets extending through the wall into the corresponding additional velum above the corresponding additional flooded head, additional corresponding spraying means in fluid connection with the additional scrubbing fluid inlet for spraying the additional scrubbing fluid into the corresponding additional scrubbing fluid reaction zone volume, and one or more corresponding additional scrubbing fluid outlets above the corresponding flooded head passing through the wall of the scrubber vessel.

4. The scrubber apparatus of claim 2, further comprising: a) one or more additional flooded heads extending horizontally across the entire cross-section of the scrubber vessel and serially stacked vertically above the other heads, each defining an additional velum in relation to the head below; b) one or more additional scrubbing fluid reaction zone volumes, each disposed above a corresponding flooded head to a desired level, each additional scrubbing fluid selected to remove a desired additional group of contaminants from the contaminated gas, stream; and c) one or more additional scrubbing fluid inlets extending through the wall into the corresponding additional velum above the corresponding additional flooded head, additional corresponding spraying means in fluid connection with the additional scrubbing fluid inlet for spraying the additional scrubbing fluid into the corresponding additional scrubbing fluid reaction zone volume, and one or more corresponding additional scrubbing fluid outlets above the corresponding flooded head passing through the wall of the scrubber vessel.

5. The scrubber apparatus of claim 2, wherein the gas inlet is located at the top end of the vessel and a gas inlet duct conducts the gas to a position below the lowermost head.

6. The scrubber apparatus of claim 2, wherein the gas inlet is located at the side of the vessel and a gas inlet duct conducts the gas to a position below the lowermost head.

7. The scrubber apparatus of claim 2, wherein the size of the slots in the flooded heads are selected to prevent passage therethrough of scrubbing fluid in the presence of pressurized gas below the flooded heads.

8. A method of removing multiple contaminants from a contaminated gas stream, the method comprising the steps of: a) introducing a first scrubbing fluid into the apparatus of claim 1 to a desired fluid level above the submerged scrubber head; b) introducing a second scrubbing fluid into the apparatus of claim 1 to a desired level above the flooded scrubber head; c) cooling a contaminated process gas using a prior art gas conditioner; d) introducing the cooled contaminated gas under pressure from an induced draft fan into the apparatus of claim 1 at a position below the submerged scrubber head; e) allowing the gas to pass upwardly through the submerged scrubber head to transfer a first group of contaminants from the contaminated gas into the first scrubbing fluid in a first scrubbing fluid reaction zone volume above the submerged scrubber head; f) allowing the gas to continue passing upwardly through the flooded head to transfer a second group of contaminants from the contaminated gas into the second scrubbing fluid in a second scrubbing fluid reaction zone volume above the flooded head; g) spraying the exiting gas to remove additional contaminants and slow the gas flow velocity; h) allowing the exiting gas to exit the scrubbing apparatus; i) separately removing first and second scrubbing fluids from the scrubber vessel to maintain a desired level of each scrubbing fluid; and j) cleaning drained scrubbing fluids for reuse in the scrubbing apparatus.

9. The use of the scrubber apparatus of claim 1 to remove multiple contaminants from a contaminated gas stream according to the method of claim 8.

10. The method of claim 9, further comprising the additional step (ff) after step (f) of: ff) allowing the gas to continue passing upwardly through one or more serially vertically stacked additional flooded heads to transfer one or more additional groups of contaminants from the contaminated gas into one or more additional scrubbing fluids in each of one or more additional scrubbing fluid reaction zone volumes above each of the corresponding flooded heads.

11. A method of removing multiple contaminants from a contaminated gas stream, the method comprising the steps of: a) introducing a first scrubbing fluid into the apparatus of claim 2 to a desired fluid level above the first flooded scrubber head; b) introducing a second scrubbing fluid into the apparatus of claim 2 to a desired level above the second flooded scrubber head; c) cooling a contaminated process gas using a prior art gas conditioner; d) introducing the cooled contaminated gas under pressure from an induced draft fan into the apparatus of claim 2 at a position below the first flooded scrubber head; e) allowing the gas to pass upwardly through the first flooded head to transfer a first group of contaminants from the contaminated gas into the first scrubbing fluid in a first scrubbing fluid reaction zone volume above the first flooded head; f) allowing the gas to continue passing upwardly through the second flooded head to transfer a second group of contaminants from the contaminated gas into the second scrubbing fluid in a second scrubbing fluid reaction zone volume above the second flooded head; g) spraying the exiting gas to remove additional contaminants and slow the gas flow velocity; h) allowing the exiting gas to exit the scrubbing apparatus; i) separately removing first and second scrubbing fluids from the scrubber vessel to maintain a desired level of each scrubbing fluid; and j) cleaning drained scrubbing fluids for reuse in the scrubbing apparatus.

12. The use of the scrubber apparatus of claim 2 to remove multiple contaminants from a contaminated gas stream according to method of claim 11.

13. The method of claim 11, further comprising the additional step (ff) after step (f) of: ff) allowing the gas to continue passing upwardly through one or more serially vertically stacked additional flooded heads to transfer one or more additional groups of contaminants from the contaminated gas into one or more additional scrubbing fluids in each of one or more additional scrubbing fluid reaction zone volumes above each of the corresponding flooded heads.

14. The use of the apparatus of claim 1 to remove from a contaminated gas stream multiple contaminants selected from the group of contaminants comprising particulate matter, metals, hydrogen chloride, hydrogen fluoride, nitrous oxide, nitric oxide, carbon dioxide, and sulfur dioxide.

15. The use of the apparatus of claim 2 to remove from a contaminated gas stream multiple contaminants selected from the group of contaminants comprising particulate matter, metals, hydrogen chloride, hydrogen fluoride, nitrous oxide, nitric oxide, carbon dioxide, and sulfur dioxide.

16. A scrubber apparatus for removing multiple contaminants from a contaminated gas stream, comprising a scrubber vessel having a series of vertically-stacked scrubber heads, each scrubber head flooded with a different scrubbing fluid to create a separate scrubbing fluid reaction zone volume above each scrubber head, each scrubbing fluid selected to remove a desired group of contaminants from the contaminated gas stream, wherein the contaminated gas flows under pressure from below the lowermost scrubber head upwardly through the series of flooded scrubber heads.

17. A method of removing multiple contaminants from a contaminated gas stream, the method comprising the steps of: a) introducing a first scrubbing fluid into the apparatus of claim 16 to a desired fluid level above the first scrubber head; b) introducing a second scrubbing fluid into the apparatus of claim 16 to a desired level above the second scrubber head; c) cooling a contaminated process gas using a prior art gas conditioner; d) introducing the cooled contaminated gas under pressure from an induced draft fan into the apparatus of claim 16 at a position below the first scrubber head; e) allowing the gas to pass upwardly through the first head to transfer a first group of contaminants from the contaminated gas into the first scrubbing fluid in a first scrubbing fluid reaction zone volume above the first head; f) allowing the gas to continue passing upwardly through the second head to transfer a second group of contaminants from the contaminated gas into the second scrubbing fluid in a second scrubbing fluid reaction zone volume above the second head; g) spraying the exiting gas to remove additional contaminants and slow the gas flow velocity; h) allowing the exiting gas to exit the scrubbing apparatus; i) separately removing first and second scrubbing fluids from the scrubber vessel to maintain a desired level of each scrubbing fluid; and j) cleaning drained scrubbing fluids for reuse in the scrubbing apparatus.

18. The use of the apparatus of claim 16 to remove from a contaminated gas stream multiple contaminants selected from the group of contaminants comprising particulate matter, metals, hydrogen chloride, hydrogen fluoride, nitrous oxide, nitric oxide, carbon dioxide, and sulfur dioxide.

19. A flooded scrubber head for a wet gas scrubbing vessel, the flooded head comprising: a) a horizontal plate extending across the entire lateral cross-section of the scrubbing vessel, the head having one or more rows of ports for the upward passage therethrough of contaminated gases into a scrubbing fluid reaction zone volume above the head, wherein the entire perimeter of the head is adjacent to the inner circumference of the scrubbing vessel, and the size, shape and angle of the ports is selected to prevent the scrubbing fluid from passing downward through the ports in the presence of pressurized gas below the head.

20. The flooded wet scrubber head of claim 19, wherein the head further comprises one or more accelerator plates extending upwardly perpendicular to the head between the one or more rows of ports into the scrubbing fluid reaction zone volume.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0024] A detailed description of the preferred embodiment is provided below by way of example only and with reference to the following drawings in which:

[0025] FIG. 1A is a top view of a schematic drawing of one embodiment of the flooded scrubber head of the present invention;

[0026] FIG. 1B is a lateral cross-sectional view through 1B-1B of the flooded scrubber head depicted in FIG. 1A;

[0027] FIG. 1C is a blow-up schematic view of one corner of the embodiment of a flooded scrubber head shown in FIG. 1A;

[0028] FIG. 2 is a cross-sectional view of a multiple level scrubber having the flooded scrubber head of the present invention at each scrubbing level; and

[0029] FIG. 3 is a schematic of an embodiment of a system where initial scrubbing is performed by a submerged scrubbing head and the flooded scrubber head of the present invention is used for scrubbing on subsequent levels above the initial head.

DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention provides a means of creating multiple wet scrubbing interaction levels 2, 4 within a single scrubber vessel 11, each level of which is capable of scrubbing 100% of the gas flow with a different scrubbing fluid. The present invention uses a scrubber head design whose horizontal orientation and flooded operating characteristics allow the stacking of multiple heads within a single wet scrubber body. The ability to incorporate additional scrubbing interaction zones in a single system provides the opportunity to increase overall removal efficiency for pollutants such as particulate matter, acid gases or metals by adding polishing steps or to remove additional regulated pollutants by utilizing other neutralizing reagents. By incorporating the flooded scrubber heads of the present invention in wet scrubber designs the resulting system will have lower capital costs, a smaller footprint and higher efficiency removal of multiple pollutants.

[0031] Referring to FIGS. 1A to 1C, the scrubbing head 50 is shown as a generic form to demonstrate the elements of the head. The head 50 operates in a horizontal orientation. The head may be manufactured from any sheet or plate material with sufficient strength, stiffness, and thermal and chemical resistance properties. Typical materials are metal plate with the preferred materials being stainless steel. The horizontal cross-sectional shape of the head conforms to the shape of the scrubber body so as to allow a sealed fit between the periphery of the scrubber head and the inner circumference of the scrubber vessel. The head contains a plurality of ports 61 that may be in any shape, number and orientation to the head. The preferred port shape is a slot with length in the range of 125 to 200 mm with a preferred width of 2 mm. The spacing 63 of the ports is typically in the range of 20 to 25 mm. The margins 65 between the ports and the edge of the head are uniform with a preferred distance of 40 mm. The head may contain accelerator plates 71 oriented at right angles to the head. The accelerator plates equally divide the space between the rows of ports 61. The margin 65 between the accelerator plates and the ports 61 is maintained at a preferred distance of 40 mm. The accelerator plates are typically 150 mm in height and contain scuppers at the head deck level to allow the lateral transfer of scrubbing fluid. The accelerator plate is of the same material as the scrubber head. Other parameters for the ports, margins, and accelerator plates are permitted within the scope of the invention.

[0032] Referring to FIG. 2, there is depicted an example of a scrubber system incorporating the flooded scrubber heads of the present invention which is comprised of a scrubbing vessel (11) containing two flooded heads 12, 14.

[0033] The process of gas contamination removal using the system of FIG. 2 begins with introduction of the contaminated gas 1 from a combustion or industrial process that generates particulate matter, acid gases and metals that require removal. The gas enters a lowermost plenum 3 bounded by a reservoir of a first scrubbing fluid 31 (or a solid membrane) below and a flooded head 12 above. The gas enters under positive pressure created by an induced draft fan (not shown). The gas pressure is sufficient to support a desired depth of a first scrubbing fluid on the heads 12, 14 and to overcome the pressure drop incurred by the gas as it passes through the ports in the heads. Preferred pressure at the lowermost plenum 3 is 450 mm of water. The gas rises through the ports in the lowermost head 12 at a velocity in the range of 20 to 25 meters per second. The gas enters a turbulent first scrubbing fluid reaction zone volume 33 where the gas and first scrubbing fluid are aggressively mixed. The first scrubbing fluid is selected for it reactivity with a first group of contaminants targeted for removal. The first scrubbing fluid level on the lowermost head 12 is controlled by overflow tubes that pass through the head to the first scrubbing fluid reservoir 31 that is typically located in the base of the scrubber vessel 11. The overflow first scrubbing fluid 37 is replaced by conditioned first scrubbing fluid 34 from a first scrubbing fluid inlet distribution header 13 in order to maintain fluid level and reactivity with the contaminants being removed. In addition to chemical reactivity, the aggressive turbulence created in the wet scrubber will efficiently remove particulate matter from the gas and transfer it to the scrubbing fluid. After exiting the turbulent first scrubbing fluid reaction zone volume the gas rises under the remaining pressure to repeat the process, passing through a second flooded head 14 into a turbulent second scrubbing fluid reaction zone volume 35. For illustrative purposes the depth of the second scrubbing fluid reaction zone volume 35 is controlled by a second scrubbing fluid outlet, which may be a plurality of overflow troughs 23 that transfer the second scrubbing fluid from the scrubber vessel and route it to a second scrubbing fluid reservoir not shown. Using this approach, the second scrubbing fluid on head 14 can be a different scrubbing fluid than that on head 12, thus allowing polishing or alternative contaminants to be removed. Second scrubbing fluid on head 14 is constantly replaced with conditioned scrubbing fluid 36. The decontaminated gas 7 exiting the second scrubbing fluid reaction zone volume 35 can be ducted to the stack or further processes. Using this same approach, additional flooded scrubbing heads may be serially added vertically within the scrubber body for further polishing or removal of other air pollutants as required by the process.

[0034] Referring to FIG. 3, there is shown an example of a system comprising a scrubbing vessel 11 containing a submerged lowermost head 22 beneath a flooded head 14 functioning as a second scrubbing head.

[0035] The process in FIG. 3 begins with the contaminated gas 1 from a combustion or industrial process that generates particulate matter, acid gases and metals that require removal. The gas is ducted to the submerged scrubber head 22. The gas enters under positive pressure created by an induced draft fan (not shown). The gas pressure is sufficient to overcome the pressure created by the depth of a first scrubbing fluid on the lowermost head 22 and support the depth of a second scrubbing fluid to be supported on the second flooded head 14. Additional gas pressure is incorporated into the design to overcome the pressure drop incurred by the gas as it passes through the ports in the heads and losses incurred in the ducting of the gas. Preferred pressure at the lowermost plenum 3 is 450 mm of water. The gas rises through the ports in the submerged head 22 at a velocity determined by the design of the head. The gas enters a turbulent first scrubbing fluid reaction zone volume 33 where the gas and first scrubbing fluid are aggressively mixed in a turbulent first scrubbing fluid reaction zone volume. The first scrubbing fluid is selected for its reactivity with a first group of contaminants targeted for removal. The first scrubbing fluid level on the submerged head 22 is controlled by sensors such as differential pressure sensors which activate control valves to regulate the flow of fluid exiting for recirculation via a first scrubbing fluid outlet 32 in the floor of the vessel. Conditioned first scrubbing fluid 34 is added through a first scrubbing fluid inlet distribution header 13 in order to maintain reactivity with the contaminants being removed. In addition to chemical reactivity, the aggressive turbulence created in the wet scrubber will efficiently remove particulate matter from the gas and transfer it to the scrubbing fluid. After exiting the turbulent first scrubbing fluid reaction zone volume 33 the gas rises under the remaining pressure to repeat the process, passing through flooded head 14 into a turbulent second scrubbing fluid reaction zone volume 35. For illustrative purposes the depth of the second scrubbing fluid reaction zone volume 35 is controlled by a second scrubbing fluid outlet, which may be a plurality of overflow troughs 23 that transfer the second scrubbing fluid from the scrubber vessel and route it to a second scrubbing fluid reservoir (not shown). Using this approach, the upper flooded head 14 can operate with a different scrubbing fluid than is used on the submerged head 22 thus allowing polishing or the addition of alternative reagents to remove other regulated contaminants. Second scrubbing fluid on the flooded head 14 is constantly replaced with conditioned second scrubbing fluid 36 carried by second scrubbing fluid inlet distribution header 15. The decontaminated gas 7 exiting the second scrubbing fluid reaction zone volume can be ducted to the stack or further processes. Using this same approach, additional flooded scrubbing heads may be serially added vertically within the scrubber vessel for further polishing or removal of other air pollutants as required by the process.

[0036] One or more flooded scrubbing heads as embodied in the present invention offer advantages over the current art represented by submerged scrubbing heads. Among the advantages is the ability to supply wet scrubbing of 100% of the gas at multiple levels of interaction zones with different neutralizing reagents within a single scrubbing body. This attribute allows a single scrubbing device to remove a broader range of pollutants at higher removal efficiencies. Scrubbers utilizing the flooded head design will have a smaller and highly flexible footprint, lower capital cost, scalability and capacity to remove multiple pollutants in a single device. The flooded head has application in combustion processes including coal, biomass and municipal solid waste where the primary pollutants targeted for removal are particulate matter, acid gases including sulphur dioxide, hydrogen chloride and hydrogen fluoride, metals including mercury. In addition, scrubbers used in chemical and industrial processes requiring the removal of dust, odors and acid gases are candidates for flooded head designs in both new and retrofit installations.

[0037] From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objectives herein set forth, together with other advantages which are obvious and which are inherent to the system. It will be understood that certain features and sub-combinations are of utility and may be employed with reference to other features and sub-combinations. This is contemplated by and is within the scope of the claims. Many possible embodiments may be made of the invention without departing from the scope of the claims. It is to be understood that all matter herein set forth and shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense. It will be appreciated by those skilled in the art that other variations of the preferred embodiment may also be practiced without departing from the scope of the invention.