Method and apparatus for cleaning a contaminated air stream

Abstract

A method and apparatus for cleaning a contaminated air stream, the method comprising the step of passing the contaminated air stream through a multistage cleaning reactor, wherein at least two stages of the multistage cleaning reactor comprise marine shell material.

Claims

1. A method of cleaning a contaminated air stream, the method comprising: passing the contaminated air stream through a multistage cleaning reactor, wherein at least two stages of the multistage cleaning reactor comprise a marine shell material, wherein at least one of bulk density, or level of calcium carbonate of the marine shell material in one of the at least two stages differs from that of the marine shell material in another of the at least two stages of the multistage cleaning reactor.

2. The method as claimed in claim 1 wherein at least one stage of the multistage cleaning reactor comprises an inert crumb rubber biotrickling material.

3. The method as claimed in claim 2 wherein the at least one stage of the multistage cleaning reactor further comprises a biological element.

4. The method as claimed in claim 1 wherein the marine shell material comprises whole or partially whole sea shells.

5. The method as claimed in claim 1 further comprising irrigating each stage of the multistage cleaning reactor with water.

6. The method as claimed in claim 5 further comprising purging the irrigation water to remove contaminants from the reactor.

7. The method as claimed in claim 5 further comprising heating the irrigation water.

8. The method as claimed in claim 5 further comprising controlling the purging of the irrigation water.

9. A method of cleaning a contaminated air stream, the method comprising; passing the contaminated air stream through a multistage cleaning reactor, wherein at least two stages of the multistage cleaning reactor comprise a marine shell material; and further comprising passing the contaminated air stream through one of: at least one stage of the multistage cleaning reactor containing American clam shells, and then through at least one stage containing mussel shells; or at least one stage of the multistage cleaning reactor containing oyster shells, and then through at least one stage of the multistage cleaning reactor containing queen scallop shells; or at least one stage of the multistage cleaning reactor containing American clam shells, and then through at least one stage of the multistage cleaning reactor containing queen scallop shells; or at least one stage of the multistage cleaning reactor containing oyster shells, and then through at least one stage of the multistage cleaning reactor containing cockle shells; or at least one stage of the multistage cleaning reactor containing American clam shells, and then through at least one stage of the multistage cleaning reactor containing cockle shells; or at least one stage of the multistage cleaning reactor containing queen scallop shells, and then through at least one stage of the multistage cleaning reactor containing cockle shells.

10. An apparatus for cleaning a contaminated air stream, the apparatus comprising a multistage cleaning reactor and means for passing the contaminated air stream through the multistage cleaning reactor, wherein at least two stages of the multistage cleaning reactor comprises a marine shell material, wherein at least one of bulk density, or level of calcium carbonate of the marine shell material in one of the at least two stages differs from that of the marine shell material in another of the at least two stages of the multistage cleaning reactor.

11. The apparatus as claimed in claim 10 wherein at least one stage of the multistage cleaning reactor comprises an inert crumb rubber biotrickling material.

12. The apparatus as claimed in claim 10 further comprising means for irrigating each stage of the multistage cleaning reactor with water.

13. The apparatus as claimed in claim 12 further comprising means for heating the irrigation water.

14. The apparatus as claimed claim 12 further comprising means for purging the irrigation water to remove contaminants from the reactor.

15. An apparatus for cleaning a contaminated air stream, the apparatus comprising: a multistage cleaning reactor and means for passing the contaminated air stream through the multistage cleaning reactor; wherein at least two stages of the multistage cleaning reactor comprises a marine shell material; and wherein: at least one stage of the multistage cleaning reactor containing American clam shells, and at least one stage of the multistage cleaning reactor containing mussel shells; or at least one stage of the multistage cleaning reactor containing oyster shells, and at least one stage of the multistage cleaning reactor containing queen scallop shells; or at least one stage of the multistage cleaning reactor containing American clam shells, and at least one stage of the multistage cleaning reactor containing queen scallop shells; or at least one stage of the multistage cleaning reactor containing oyster shells, and at least one stage of the multistage cleaning reactor containing cockle shells; or at least one stage of the multistage cleaning reactor containing American clam shells, and at least one stage of the multistage cleaning reactor containing cockle shells; or at least one stage of the multistage cleaning reactor containing queen scallop shells, and at least one stage of the multistage cleaning reactor containing cockle shells.

16. The method as claimed in claim 1, further comprising a non-transitory computer-readable medium having computer-executable instructions adapted to cause a computer system to perform the method of passing the contaminated air stream through the multistage cleaning reactor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is an apparatus for cleaning a contaminated air stream in accordance with one embodiment of the invention,

(3) FIG. 2 is a graph of results of using the apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) Referring to the drawings there is illustrated one embodiment of an apparatus according to the invention for cleaning a contaminated air stream.

(5) The apparatus is suitable for and may be employed to clean a contaminated air stream originating from waste water treatment processes or treatment processes for the by-products of waste water treatment such as bio solids dewatering, drying, pasteurising or physical and chemical and thermal hydrolysis prior to digestion.

(6) The apparatus 1 comprises a multi-stage reactor, in this embodiment showing three stages, 1, 2, and 3. The only requirement is for the reactor to comprise at least two stages, with no maximum number of stages.

(7) Each stage of the reactor comprises filtration material through which air is passed to be cleaned. At least two reactor tanks house marine shell material to filter the air.

(8) Marine shell material may be sourced as a secondary by-product from the food industry and may comprise whole or partially whole sea shells. The marine shell material may be mussels shell material, and/or oyster shell material, and/or cockles shell material, and/or American quahogs shell material (US clam shells commonly found along the eastern seaboard of USA), and and/or queen scallops shell material. These marine shell materials are widely available and inexpensive. Bottom-dredged mussel shells may be used for their large size, density and weight, which are typically older than rope grown muscles. Shell material of differing botanical species may be used in the same system.

(9) There are enormous and advantages in using the spent shell of shell fish. Firstly, it is a by-product of various food operations in that oysters, whelks, mussels, clams and so on are processed in factories which produce a large amount of spent shells which then have to be disposed of, causing pollution. In any event, the disposal of such shells is expensive. Anything that removes the necessity to spend money on the disposal of the shells but additionally makes them a valuable commodity is obviously extremely advantageous. It has long been appreciated that spent shells of shell fish are a major source of calcium material. It would be wrong to underrate the disposal problem experienced by many shell fish processors. A further advantage of the use of spent shells is that they are of a particularly useful shape in that some of the shells will be broken, others will have their full structural integrity and so on, so that the bed formed by the use of the spent shells will be a bed that will ensure adequate flow of gases and adequate retention and moisture by providing a sufficient number of shells which will form individual liquid reservoirs. It has been found that mussel shell or, more correctly, a half mussel shell is particularly advantageous as there is a large amount of mussel shell available after processing in factories. It is particularly appropriate to use such a shell as it is not alone efficient in use, but equally needs to be disposed of on a regular basis. Thus, the raw material for the initial preparation of the system packing, together with its replacement when the shell used has passed its useful life, is readily available and inexpensive. Further, mussel shell is particularly structurally rigid.

(10) It has been found that mussel shells are one of the most reactive media giving extremely high efficiency and elimination capacities. Mussels shells however have a relatively low bulk density hence the combination of high efficiency and low bulk density gives excellent treatment but a reduced media life on high H.sub.2S applications.

(11) Oyster shells and American Clams on the other hand are a larger shell with a smaller surface area and a higher bulk density. These shells are not as reactive and removal efficiency and elimination capacity tends to be lower than mussels shells. The combination of the reduced efficiency and higher bulk density shell however gives a much longer media life.

(12) Use of marine shell material in the reactor tank facilitates a physical and chemical/catalytic reaction and a biological reactions favourable to neutral pH between the marine shell material and the contaminated air stream. The shell media is particularly suited for the removal of organic sulphur compounds, volatile organic compounds and organic sulphur compounds. Shell media comprises high levels of calcium carbonate which neutralises acid by-products from biological oxidation of sulphur compounds.

(13) Where two stages of shell material are used, it is advantageous to use larger heavier shell material in one stage, followed by smaller more reactive shell material in a subsequent stage. The second shell stage may be a polishing stage wherein the shells buffer and maintain a neutral pH which is required for capture and degradation of volatile organic compounds and volatile organic siloxane.

(14) For high H.sub.2S applications, it may be beneficial to incorporate a crumb rubber stage prior to the first shell stage. A biological element may be added to the crumb rubber stage. Crumb rubber acts as a prefiltration media for removing high levels of H.sub.2S by a combination of physical and chemical/catalytical/biological means in a low pH environment. The rubber material may be of automotive origin and is widely available and inexpensive. Where crumb rubber is used, it is granulated or shredded into small pieces. As the crumb rubber material is inert, the crumb rubber material offers an almost indefinite media life.

(15) The combination of passing the contaminated air stream through both the rubber material and a dual stage marine shell material has been found to result in highly efficient improved cleaning of the contaminated air stream, in particular in the case of high concentrations of hydrogen sulphide (H.sub.2S) and/or organic sulphur, or VOCs in the contaminated air stream. Similar to shell material, rubber material is a widely available and inexpensive, recovered material.

(16) Each stage comprises a reactor chamber housing filtration material, and a pumped recirculating tank 10 which acts as a reservoir to store water for irrigating the filtration medium. The recirculating tank shown in FIG. 1 comprises an irrigation pump 12 and a heater 14 for heating the recirculation water. Each stage comprises at least one spray nozzle 16 to spray water onto the filtration material to irrigate it. Each spray nozzle is fed water via pipe 18 from the reservoir of water formed in the recirculating tank 10. A strainer, diaphragm valve and a pressure gauge are also provided within pipe 18. The arrangement of the reactor chamber over the recirculation tank facilitates the recirculation of the irrigation water and the formation of a water seal to prevent air leaking from the system. The reactor chamber has an air and water permeable floor to hold the filtration medium in place. A water inlet 20 feeds water into each recirculating tank. An overflow pipe 22 is also provided. FIG. 1 also shows a heat exchanger adjacent the overflow outlet pipe. At least one ventilation fan 24 is provided in communication with the outlet of the last stage to transport treated air to atmosphere or for further processing.

(17) Each reactor chamber has an inlet port 4 and an outlet port 6. In the embodiment shown in FIG. 1, the outlet port 6a of the reactor chamber of the first cleaning stage is in air stream communication with the inlet port 4b of the reactor chamber of the second cleaning stage 2. The outlet port 6b of the reactor chamber of the second cleaning stage 2 is in air stream communication with the inlet port 4c of the reactor tank 5 of the third cleaning stage 3. The outlet 6 of stages 1 and 3 is in the recirculating tank 10, while the outlet 6b of the middle stage 2 is in the reactor chamber.

(18) As illustrated in FIG. 1, the contaminated air stream enters the inlet port 4 of the reactor chamber of the first cleaning stage 1, and the cleaned air stream may exit through the outlet port 6c of the reactor tank of the third cleaning stage 3. Arrows demonstrate the direction of flow of air through the multiple stages of the system. In the first stage air flows downwards, in the second upwards and in the third downwards.

(19) The system relies on a continuous recirculation of the water, where at least 95% of the water is recirculated. It may be necessary to purge 5% of the water, however the actual percentage of purged water will depend on the conductivity/pH of the recirculation water. If a crumb rubber stage is included, that stage will have a high purge water rate due to the resultant low pH in that stage.

(20) It will be appreciated that the apparatus may operate by means of a combination of physical adsorption and chemisorption, followed by biological oxidation and breakdown, if crumb rubber is used in an upstream stage and marine shells in a downstream stage.

(21) The apparatus of FIG. 1 provides multi-stage cleaning using crumb rubber and marine shell technology. The multiple stages improve the efficiency of the cleaning process by a combination of increased contact with the surface area resulting from higher face velocities and increased mass transfer from the gaseous to the liquid and solid phase by resulting from increased back pressure at increased face velocities.

(22) The apparatus is effective at removing a large percentage of the contaminants from the contaminated air stream, for example between 95% and 99% of the contaminants from the contaminated air stream. In one test, the apparatus of FIG. 1 achieved between 95% and 99% removal of H.sub.2S from the gas stream containing approximately 2000-2800 ppm H.sub.2S. H.sub.2S is removed by way of absorption and chemisorption followed by the biological degradation in each stage containing marine shell material.

(23) TABLE-US-00001 Average Efficiency Average Range Efficiency Range Elimination Elimination Media % % g/m3/hr g/m3/hr Crumb Rubber 33 0-40 2.90 0.9-6.7 Crumb Rubber + 46.5 28-78 5.30 4-32.2 Biological Crumb Rubber + 72 58-99 17.40 8.06-29.17 Biological + Cleaning Semi Crushed 70.8 7-100 14.80 3.6-42 Quahogs Queen Scallops 56 21-95 13.80 1.8-27 Cockle-Mussel 60.4 18-99 13.79 1.9-56.6 Blend 1 Cockle-Mussel 76 56-99 21.70 8.5-43.3 Blend 2

(24) FIG. 2 illustrates the results of this testing performed using these various types of marine shell material versus solely crumb rubber material.

(25) The average removal efficiency was 62.5%-70.8%. The average elimination capacity was 12.8-14.8 (g/m.sup.3/hr). The removal efficiency and elimination capacity was improved for the cockle/mussel mix compared to a 100% cockle mix. The removal efficiency was 50-70%. The elimination capacity was 12-21.7 (g/m.sup.3/hr). Queen scallops provide successful treatment and in the overall performance hierarchy would come third after mussel and Quahogs and before cockles and oysters for H.sub.2S. Significant improvement in the crumb rubber efficiency and the elimination capacity was achieved by incorporating the biological component of the marine shell material and performing in-situ cleaning.

Example 2

(26) The following table lists the results of testing performed using various mixtures of marine shell material.

(27) TABLE-US-00002 Average Average Average Loading Elimination Removal m.sup.3/m.sup.3/ Capacity Media % hr g/m.sup.3/h Mussels/Queen 72.67 77.1 17.40 Scallops Mussels/Cockles 64.80 85.8 17.10 Mussels/Semi 71.00 68.6 14.85 Crushed Quahogs

(28) The mussel/queen scallop mix gave the highest elimination capacity followed by mussel/cockle and mussel/quahog. The multi pass or layered approach is superior to blending medias. Performance was improved by using a higher efficiency spiral nozzle.

(29) The invention is not limited to the embodiment hereinbefore described, with reference to the accompanying drawings, which may be varied in construction and detail. It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

(30) The words comprises/comprising and the words having/including when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.