Wet scrubber nozzle system and method of use for cleaning a process gas

Abstract

A wet scrubber (10) useful for cleaning a process gas (F) comprising at least a first spray level system (40) and a second spray level system (48) arranged compactly vertically above the first spray level system (40) in a wet scrubber tower (14). Each spray level system (40, 48) is equipped with a plurality of atomizing flattened relatively wide spray angle nozzles (56) for atomizing an absorption liquid (AL) supplied thereto for contact and intermixing with the process gas (F) for removal of environmental pollutants therefrom.

Claims

1. A wet scrubber for cleaning a process gas comprising: a wet scrubber tower, at least a first spray level system to which an absorption liquid is supplied for atomization by nozzles comprised in the first spray level system, and a second spray level system which is arranged vertically above the first spray level system in the wet scrubber tower and to which an absorption liquid is supplied for atomization by nozzles comprised in the second spray level system; each spray level system inlet is horizontally arranged by at least 10 to 20 degrees from the other for a concomitant horizontal offset of the nozzles arranged thereon and arranged within a compact vertical height; each spray level system comprising a tubular portion, a number of tubular extensions extending perpendicularly from the tubular portion, and nozzles fluidly connected to the tubular portion and to the number of tubular extensions; and each nozzle is a flattened wide spray angle nozzle atomizing absorption liquid within interior of wet scrubber tower for environmental pollutant removal from a process gas comprising environmental pollutants passed through wet scrubber tower to produce a cleaned process gas.

2. A wet scrubber according to claim 1, wherein the compact vertical height is approximately 0.3 to 0.5 meter.

3. A wet scrubber according to claim 1, wherein the process gas is passed through wet scrubber tower at an approximate velocity of 5-15 m/s.

4. A wet scrubber according to claim 1, wherein the absorption liquid is a limestone slurry or an alkaline sodium solution.

5. A wet scrubber according to claim 1, wherein the absorption liquid is an ammoniated solution or an amine solution.

6. A wet scrubber according to claim 1, wherein the nozzle spray angle is approximately 150 to 180 degrees.

7. A wet scrubber according to claim 1, wherein the environmental pollutant is sulphur dioxide.

8. A wet scrubber according to claim 1, wherein the environmental pollutant is an acid gas.

9. A method of cleaning a process gas comprising an environmental pollutant using a wet scrubber comprising: compactly arranging at least first and second spray level systems each equipped with a plurality of flattened wide spray angle nozzles within an interior of a wet scrubber tower, with each spray level system comprising a tubular portion, a number of tubular extensions extending perpendicularly from the tubular portion, and the plurality of flattened wide spray angle nozzles fluidly connected to the tubular portion and the tubular extensions; horizontally arranging absorption liquid inlets for each of the at least first and second spray level systems at least 10 to 20 degrees apart one from the other for a concomitant horizontal offset of the nozzles arranged thereon; supplying absorption liquid through the absorption liquid inlets to each of the at least first and second spray level systems via separate spray level system pumps for absorption liquid atomization by the plurality of flattened wide spray angle nozzles; and passing an upward vertical flow of process gas through the wet scrubber tower for absorption liquid contact and environmental pollutant removal to produce a cleaned process gas.

10. The method of claim 9, wherein the at least first and second spray level systems are compactly arranged within approximately 0.3 to about 0.5 meter vertical height.

11. The method of claim 9, wherein the absorption liquid inlets are horizontally offset by approximately 10 degrees one from the other.

12. The method of claim 9, wherein the flattened wide spray angle nozzles provide a spray angle of approximately 150 to about 180 degrees.

13. The method of claim 9, wherein the process gas flows vertically upward through the wet scrubber tower at a velocity of about velocity of 5-15 m/s.

14. The method of claim 9, wherein the absorption liquid is a limestone slurry, an alkaline sodium solution, an ammoniated solution or an amine solution.

15. The method of claim 9, wherein the environmental pollutant is sulphur dioxide, carbon dioxide or an acid gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject invention is described in more detail below with reference to the appended drawings in which:

(2) FIG. 1 is a schematic side perspective partial cut-away view of a wet scrubber in accordance with a first embodiment.

(3) FIG. 2 is a schematic top view of a spray level system of the wet scrubber of FIG. 1 taken along line II-II just below mist eliminators.

DESCRIPTION OF PREFERRED EMBODIMENTS

(4) FIG. 1 illustrates a wet scrubber 10. The wet scrubber 10 is operative for removing at least a portion of the sulphur dioxide content and similar environmental pollutants comprised in a process gas, in the form of a flue gas, F, generated in a boiler 12 operative for combusting a fuel, such as coal, oil, peat, waste and the like. Process gas and flue gas F are considered synonymous and used interchangeably throughout the subject description.

(5) Wet scrubber 10 comprises a vertical open circular or round wet scrubber tower 14 with interior 16, a process gas inlet 18 arranged in a base portion 20 of wet scrubber tower 14 for flow of flue gas, F, from fluidly connected boiler 12. Flue gas F from boiler 12 flows into fluidly connected interior 16, of wet scrubber tower 14 for cleaning and flows out of process gas outlet 22 arranged in an upper portion 24 of wet scrubber tower 14 as a cleaned flue gas, CF. Cleaned flue gas CF is flue gas from which at least a portion of the sulphur dioxide content and similar environmental pollutants has been removed. As illustrated in FIG. 1 as a vertical, upwardly pointed arrow, flue gas F travels substantially vertically upward inside interior 16 of wet scrubber tower 14 and out of wet scrubber tower 14 as cleaned flue gas CF.

(6) An absorption liquid tank 26 is arranged at the bottom 28 of base portion 20 of wet scrubber tower 14. Absorption liquid tank 26 is equipped with a fluidly connected oxidation arrangement 26a. An absorbent, such as fresh limestone, CaCO.sub.3, or an alkaline sodium solution, is supplied to absorption liquid tank 26 from a fluidly connected absorbent supply device 30 fluidly connected to a limestone or alkaline sodium solution storage area 32 and a supply pipe 34. It will be appreciated that absorption liquid tank 26 may, as an alternative, be positioned outside of wet scrubber tower 14, and that the supply of limestone or alkaline sodium solution could, as an alternative, enter wet scrubber 10 at other locations, as a dry powder, a slurry or both.

(7) Wet scrubber 10 further comprises a first circulation pump 36 which circulates in a fluidly connected absorption liquid circulation pipe 38, an absorption liquid, sometimes referred to as a limestone slurry or an alkaline sodium solution. Absorption liquid is pumped by first circulation pump 36 from absorption liquid tank 26 through fluidly connected circulation pipe 38 to an absorption liquid inlet 40a at point of entry 40b into wet scrubber tower 14 fluidly connected to first spray level system 40 arranged horizontally across interior 16 in mid portion 42 of wet scrubber tower 14 adjacent base portion 20. Wet scrubber 10 further comprises a second circulation pump 44 which circulates in a fluidly connected absorption liquid circulation pipe 46, an absorption liquid from fluidly connected absorption liquid tank 26. Absorption liquid is pumped by second circulation pump 44 through fluidly connected circulation pipe 46 to an absorption liquid inlet 40a at point of entry 40b into wet scrubber tower 14 fluidly connected to second spray level system 48 arranged horizontally across interior 16 in mid portion 42 of wet scrubber tower 14 vertically about 0.3 to about 0.5 meters above first spray level system 40. Wet scrubber 10 further comprises a third circulation pump 50 which circulates in a fluidly connected absorption liquid circulation pipe 52, an absorption liquid from fluidly connected absorption liquid tank 26. Absorption liquid is pumped by third circulation pump 50 through fluidly connected circulation pipe 52 to an absorption liquid inlet 40a at point of entry 40b into wet scrubber tower 14 fluidly connected third spray level system 54 arranged horizontally across interior 16 in mid portion 42 of wet scrubber tower 14 above second spray level system 48. Wet scrubber 10 further comprises a fourth circulation pump 50a which circulates in a fluidly connected absorption liquid circulation pipe 52a, an absorption liquid from fluidly connected absorption liquid tank 26. Absorption liquid is pumped by fourth circulation pump 50a through fluidly connected circulation pipe 52a to an absorption liquid inlet 40a at point of entry 40b into wet scrubber tower 14 fluidly connected to fourth spray level system 54a arranged horizontally across interior 16 in mid portion 42 of wet scrubber tower 14 above third spray level system 54. Distance CC illustrated in FIG. 1, is determined by measuring from the vertical mid-point of the point of entry 40b of one spray level system, e.g., the first spray level system 20, to the vertical mid-point of the point of entry 40b of another spray level system, e.g., the fourth spray level system 54a. Distance CC is preferably approximately 0.3 m to about 0.5 m per spray level system within distance CC. Distance CC is significantly reduced in the subject embodiment due to use of a plurality of flattened relatively wide spray angle nozzles 56 equipped on each spray level system without unwanted absorption liquid spray interference between adjacent spray level systems that causes decreased sulphur dioxide removal efficiency. A greater distance CC is less preferable, since a greater distance CC increases the overall vertical height of wet scrubber tower 14 required, thus increasing investment and operating costs. It will be appreciated that a wet scrubber 10 could comprise more or less than four spray level systems, for example 2 to 10 spray level systems arranged in interior 16 of wet scrubber tower 14.

(8) First spray level system 40 comprises a tubular portion 58 equipped with a number of fluidly connected atomizing nozzles 56 to finely distribute absorption liquid supplied thereto by pump 36. Absorption liquid is finely distributed by nozzles 56 to achieve effective contact between the absorption liquid and the flue gas flowing upwardly through interior 16 of wet scrubber tower 14. All or some of nozzles 56 may, for example, be commercially available nozzles capable of providing the desired flattened relatively wide spray angle, for instance widened flat fan-like sprays or widened hollow sprays, manufactured by Spraying Systems in Wheaton, Ill. 60187 USA, Bete Fog Nozzle in Greenfield, Mass. 01301 USA and Lechler in St. Charles, Ill. 60174 USA. This type of flattened relatively wide angle of approximately 150 to about 180 degrees atomizing nozzle is operative for a liquid flow of about 17 m.sup.3/hour, corresponding to 17000 liters/hour, or 280 liters/minute, at a spraying pressure measured using water, of about 0.5 bar.

(9) Second spray level system 48 is similar if not identical to first spray level system 40 and comprises a tubular portion 60 equipped with a number of fluidly connected atomizing nozzles 56. Third spray level system 54 comprises a tubular portion 62 equipped with a number of atomizing nozzles 56. Fourth spray level system 54a comprises tubular portion 62a with a number of atomizing nozzles 56.

(10) A mist eliminator 64 is located above fourth spray level system 54a or the upper most spray level system in the wet scrubber tower 14. Mist eliminator 64 arranged horizontally across interior 16 in upper portion 66 adjacent to process gas outlet 68, removes at least a portion of the absorption liquid droplets entrained by cleaned flue gas, CF. Hence, absorption liquid droplets are removed from cleaned flue gas CF as the cleaned flue gas flows upwardly through interior 16 of wet scrubber tower 14, prior to exiting wet scrubber 10 via process gas outlet 68.

(11) In wet scrubber 10, sulphur dioxide, SO.sub.2, and similar such acid gases in the flue gas reacts with limestone, CaCO.sub.3, or alternatively an alkaline sodium solution, in the absorption liquid to form calcium sulphite, CaSO.sub.3, which is subsequently oxidized to form gypsum, CaSO.sub.4. The oxidation of calcium sulphite is preferably performed by bubbling air or oxygen gas through the absorption liquid using oxidation arrangement 26a fluidly connected to an air or oxygen source 26b via source pipe 26c. Hence, the absorption liquid comprises, in addition to the limestone, also small amounts of calcium sulphite and, as a major constituent, gypsum. Gypsum formed through this process is removed from wet scrubber 10 via a fluidly connected disposal pipe 70 to a fluidly connected gypsum dewatering unit 72. The dewatered gypsum may be commercially used, for example in wallboard production.

(12) In addition to sulphur dioxide, SO.sub.2, wet scrubber 10 removes, at least partly, other contaminants from the flue gas also. Examples of such other contaminants include sulphur trioxide, SO.sub.3, hydrochloric acid, HCl, hydrofluoric acid, HF, and other acidic process contaminants. Still further, wet scrubber 10 may also remove, at least partly, other types of contaminants from the flue gas, such as for example dust particles and mercury.

(13) FIG. 2 illustrates a schematic top view from line II-II of FIG. 1 of the spray level systems within interior 16 of wet scrubber tower 14. Each of the spray level systems has the same principal design equipped with a number of fluidly connected perpendicular tubular extensions 74 forming a grid with and extending from the spray level tubular portions 40, 48, 54 and 54a. Atomizing nozzles 56 fluidly connect to tubular extensions 74 and also optionally tubular portions 40, 48, 54 and 54a so that the plurality of nozzles 56 are rather evenly distributed over the entire horizontal cross-section of wet scrubber tower 14 interior 16.

(14) Typically, the number of nozzles 56 in each spray level system 40, 48, 54, 54a would range from about 4 to about 500. In accordance with one embodiment, substantially all of the absorption liquid supplied to nozzles 56 is sprayed in all directions within interior 16, i.e., into the flow of flue gas through wet scrubber tower 14. As such, nozzles 56 atomize absorption liquid supplied thereto and generate a spray cloud SC of absorption liquid. In this spray cloud SC is an intense intermixing of flue gas F and absorption liquid AL. Typically, vertical flue gas velocity may be approximately 5 to 15 m/s, often 6 to 10 m/s, through wet scrubber tower 14. However, absorption liquid AL in the spray cloud SC dissipates, clears or drains from the flue gas F quite slowly. Slow absorption liquid AL dissipation results in bubbling beds of turbulence within wet scrubber tower 14. The intense mixing of absorption liquid AL and flue gas F in the spray clouds SC results in increased sulphur dioxide absorption levels and thereby efficient removal of sulphur dioxide from flue gas F. Absorption liquid AL eventually drains from spray cloud SC, after having a relatively long average residence time in the spray cloud SC before draining therefrom.

(15) Within wet scrubber tower 10, nozzles 56 are arranged so that at least half of the absorption liquid supplied thereto is sprayed in a horizontal, perpendicular to flue gas flow direction. In fact, all of the absorption liquid may be sprayed in a generally horizontal, perpendicular to flue gas flow direction, as an alternative to spraying in all directions. Spraying absorption liquid in spray cloud SC in a generally horizontal direction or alternatively in all directions from each of the spray level system is arranged to cover the entire interior 16 spray zone represented by distance CC with a spray cloud SC formed upon flue gas F contacting absorption liquid AL. Absorption liquid AL sprayed from nozzles 56 clean a process gas more efficiently and at a lower cost than the prior art wet scrubber and method described above.

(16) It will be appreciated that numerous variants of the embodiments described above are possible within the scope of the appended claims.

(17) A method of using the subject wet scrubber 10 comprises compactly arranging at least first and second spray level systems 40, 48 each equipped with a plurality of flattened relatively wide spray angle nozzles 56 within approximately 0.3 to approximately 0.5 meter of interior 16 wet scrubber tower 14 vertical height distance CC, arranging absorption liquid inlets 40a for each of the at least first and second spray level systems 40, 48 with points of entry 40b into the wet scrubber tower 14 horizontally offset at least approximately 10 to approximately 20 degrees apart one from the other, supplying absorption liquid AL through the absorption liquid inlets 40a to the at least first and second spray level systems 40, 48 for absorption liquid AL atomization by the plurality of flattened relatively wide spray angle nozzles 56, and passing an upward vertical flow of process gas F through the wet scrubber tower 14 at a velocity of 5 to 15 m/s for process gas F and absorption liquid AL contact. The process gas F and absorption liquid AL contact provides for sulphur dioxide and similar environmental pollutant removal to produce a cleaned process gas CF.

(18) Hereinbefore, a method and a wet scrubber for removing sulphur dioxide from a process gas are described. It will be appreciated that the described method and wet scrubber may also be utilized for removing other contaminants from a process gas. For example, the subject method and wet scrubber could be utilized for removing carbon dioxide from a process gas. The removal of carbon dioxide from the process gas may, in such a case, often be conducted in a wet scrubber which is of a similar type or the same type as the wet scrubber operating for sulphur dioxide removal, but which is located downstream, with respect to the direction of process gas flow, of the wet scrubber in which sulphur dioxide is removed. Furthermore, while limestone may often be part of the absorption liquid in a sulphur dioxide removing wet scrubber, a carbon dioxide removing wet scrubber may utilize another type of absorption liquid, for example an absorption liquid comprising an ammoniated solution or an amine solution.

(19) To summarize, a wet scrubber tower 14 cleaning a process gas F comprises a first spray level system 40 and a second spray level system 48 which is arranged compactly, e.g., within 0.3 to 0.5 meter vertically above the first spray level system 40 within interior 16 of wet scrubber tower 14, each spray level system 40, 48 comprising nozzles 56 operative for atomizing absorption liquid AL in a flattened relatively wide spray angle in a horizontal direction perpendicular to the flow of flue gas F through the wet scrubber tower 14 or in all directions within wet scrubber tower 14. The atomized absorption liquid AL contacts the process gas F for process gas F and absorption liquid AL intermixing to remove sulphur dioxide and produce a cleaned flue gas.

(20) While the invention has been described with reference to a number of preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another.