AU688633B2

AU688633B2 - Air emission control system

Info

Publication number: AU688633B2
Application number: AU40316/95A
Authority: AU
Inventors: Ian McCoy; Christopher Nash; Warrick Norris
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-12-08
Filing date: 1995-12-08
Publication date: 1998-03-12
Anticipated expiration: 2015-12-08
Also published as: AU4031695A

Description

Patents Act 1990 CHRISTOPHER NASH, IAN MCCOY AND WARRICK

NORRIS

ORIG INAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Air Emission Control System The followinig statement is a full description of this invention icluding the best method of performing it knownl to us:- Technical Field The present invention is directed to an air emission control system for the removal of pollutants from air emissions. In particular, the present invention is directed to the removal of pollutants in air emissions from buildings.

Background Art As public awareness of the detrimental effects of air pollution has increased, government bodies have acted accordingly and have placed, or are in the process of placing, stricter air emission requirements for industry in Australia. Traditionally, many industries have vented untreated gaseous emissions and pollutants directly from factories without concern to the overall effect on the air quality of the environment. Many industries are now faced with the problem of effectively removing pollutants from air emissions produced during their activities. For example, the mushroom, sludge 15 compost industry is now faced with the problem of removing particulate matter and noxious organic and inorganic pollutants in emissions from the composting procedure prior to release to the environment. Regulations will •.soon be in force to prevent direct venting of emissions from factories and sheds to the immediate environment prior to removal of pollutants from the 20 emissions.

Other industries, including paint shops, foundries, smelters and electroplating factories, are also faced with this problem of removing noxious fumes and particulate matter from emissions prior to venting to the immediate environment. There is therefore a need for an efficient and 25 economic air emission control system adaptable focr use in a variety of industrial applications.

o. The present inventors have develcopd tn air emission control system that is particularly adapted for the removal of pollutants from air emissions.

Summary of Invention Accordingly, in a first aspect, the present invention consists in an air emission control system for treatment of ambient air containing emissions derived from a biological source, the system comprising: an air inlet adapted to remove the ambient air emissions from the biological source; a means to pass air via the inlet through the system; 'LI a wet scrubber adapted to produce a spray of treatment liquid in the scrubber such that, when the air passes through the spray, at least some pollutants in the air are removed; a liquid collection means adapted to collect spent liquid including pollutants from the wet scrubber; a condenser adapted to control moisture in the air after treatment in the wet scrubber; a filter means adapted to further remove pollutants from the treated air; an air outlet; and a means to return at least some of the spent liquid containing pollutants to the biological source.

Preferably, the means to pass air through the system is a fan. It would be appreciated by one skilled in the art that any means known to the art to pass air through a system would be suitable.

Preferably, the wet scrubber is a spray tower comprising a plurality of spray rings each having a plurality of spray jets, positioned within the tower to generate the spray. Wet scrubbers are well known to the art and known scrubbers would be adaptable for the present system.

20 The treatment liquid can comprise any chemical or mixtures thereof known to the art to remove pollutants. Water has been found to be particularly suitable to remove biological pollutants that can be returned to the biological source, In another preferred form, the treatment liquid is sodium hydroxide solution (caustic solution) at a concentration of up to 25 w/v. It would be appreciated by one skilled in the art, however, that the type and concentration of treatment chemical, if any, in the treatment liquid call be varied to suit the amount and types of pollutants in the air to be treated.

The spray tower used in the system of the present invention would operate within the standard requirements known to the art. The liquid to air ratio would be in the order of 1.3-2.7 litres per cubic metre. The pressure drop within the tower would be in the order of 0.25-0.5 kPa. The size of the system would be adapted according to the amount of air to be treated and also to the types of pollutants that should be removed by the system.

Preferably, the collection means is in the form of a collection tank such that the chemical treatment liquid drains from the wet scrubber into the 3/1 tank. The spent chemical treatment liquid including the pollutants may be further treated in situ or may be removed in or from the tank for further treatment or complete recycling to the biological source.

An advantage of the present invention is that it allows the return of at least some of the pollutants to the biological source. As many of the pollutants from biological sources, for example mushroom composting, contain nitrogen and sulphur compounds which can be metabolised or utilised by the biological source, it is an advantage to be able to recycle these pollutants. Furthermore, when water is used as the treatment liquid, recycling the spent water provides a further cost benefit to the user and reduces the problem of disposal and/or further treatment of the spent liquid.

In order to monitor the treatment process, its preferred that the condenser further includes a means to measure pH and/or redox potential of the moisture in the air. The system may further include means to adjust the a a a pH and/or redox potential of the moisture such that the moisture in treated air is maintained at a desired pH and/or redox potential.

The air emission control sys tem is particularly adaptable to computer-based automatic control. The efficiency of removal of pollutants can be monitored at the various stages throughout the system and changes can be made automatically through such control.

Preferably, the filter means includes a chemical filter and a particulate filter. More preferably the chemical filter is an activated carbon filter and the particulate filter removes particulates less than about 2 microns.

In one preferred form, the system further includes a prefilter positioned before the wet scrubber being adapted to remove particulate from the air prior to chemical treatment. In another form, a vent scrubber is positioned before the wet scrubber being adapted to pass high pressure water across the air to remove particulates from the air prior to treatment in the wet scrubber.

The air outlet may be positioned so that the treated air is vented to the immediate environment. Alternatively, the outlet may be positioned in a building from which the untreated air was removed. In this form, the system allows the recycling of air from a desired area forming a closed environment, When the system is used for the treatment of air produced or emitted from o mushroom or windrow composting, it is preferred that the air is removed O'r" from the building at or near the ceiling and the air outlet is positioned in the form of vented pipes in the floor of the building under the compost. This 25 allows the treated air to be passed through the compost or windrow and also allows the control of moisture to the compost by adjusting the moisture content of treated air prior to return to the building.

Reference to a building includes any form of enclosed environment ranging from a temporary membrane arrangement to a permanent structure like a factory.

The present system is adapted for use in many different industries where release of untreated polluted air emissions is becoming a problem. In particular, the present system can be particularly adapted for the removal and treatment of air from biological processes, for example, mushroom 35 composting. Alternatively, the system may be adapted for the treatment of pollutants emitting fromn many indus trial plants, for example, paintworks and spray booths, smelters and elec troplaters.

In a preferred emibodiment of the present invention, the building from which the air is removed and tr'eated by the system is substantially sealed, such that substantially all polluted air canl be removed and treated b the systemn over a given period. The systLem is adaptable such that preferably each hour would result in the turnover of the air in the building. In the forml where the air outlet is not positioned within the building, there will be a need to provide a means of adding fresh air back into the building. This may be achieved by a fan or the like to control the addition of air to the building without allowing the escape of untreated polluted air from the building.

In a further preferred embodiment of [lhe present invention, the air emission system further includes a smnoke detector. In this form, the air emission control system may be used as a means of controlling fire or smoke by substantially renioving the air froml within the building so as to extinguish any fire therein. In this form, the air removed by the system would be vented to the outside and substantially no replacement air would be allowed to pass back into the building.

In a second aspect, the present invention consists in a method for removal of pollutants from air emissions comprising treating emissions with the air control system of the first aspect of the present invention.

Brief Description of Drawings In order that the invention may be more clearly understood, the invention will be further described by way of example with reference to the 25 accompanying drawing, wherein: Fig. 1 is a schematic representation of anl air control system according to [lie pr1esent iniventioni.

Detailed Description of Invention Referring to Fig. 1, air emission control system 10 comprises anl air inlet 20, a fan 30, a wet scrubber 40, a liquid collection tank 50, a condenser 60, an air filter 70, and anl air outlet In use, air is removed from a building '12 and passed through the air inlet 20 by the fanl 30 through piping 22. The air passes along the direction of the arrows through the fan 30 into a wet scrubber 40 in the form of a spray tower com-prising a plurality of jet rings, each including a plurality of spray jets positioned throughout the scrubber 40, The wet scrubber 40 includes twenty spray rings 42 each having a plurality of spray jets 44 positioned around the wall of the scrubber 40, Such that when the air passes through the scrubber 40 it must pass through a spray of chemical treatment liquid forced out through the spray jets 44. Many pollutants in the air can be removed by treatment in the wet scrubber.

The treatment liquid flows to the base 46 of the wet scrubber 40 andl collected via pipe 52 in a liquid collection tank The air passes through the wet scrubber 40 into a condenser 60 such that moisture may be controlled in the air prior to passing through the filter 70. The filter 70 comprises two filters including a particulate filter 72 which removes particles less than 2 microns and an activated carbon filter 74 which removes further pollutants pr'esent in the air. The air then exits from the filter 70 and passes out through the air outlet 80, resulting in the removal of the desired pollutants from the air, The wet scrubber 40 in the form of a spray tower operates having a liquid to air ratio of from -1.3-2.7 litres per cubic metre and is operated under a pressure drop from 0,25-0,5 kPa. The chemical treatment liquid is in the form of sodium hydroxide solution (caustic solution) of up to 20%/w/v. The caustic treatment removes inorganic and organic chemicals. Other chemical treatment means, however, may be used in the scrubber and such chemicals may include sodium metabisuiphite, soda ash, chlorine or detergents having a caus-tic base.

The size of the air emission control system would be adapted depending on the size of the building or the amount of air that mu st be Soso. 25 treated. If a large air space, for example a large building, must have its air treated, then it is possible to locate a number of air control emission systemns throughout the building to treat the air, The system 10 can be placed on the 6 6outside of the building having the respective inlets 20 positioned in the uipper air space of a building and the air outlet 80 positioned in the lower level of the building. If the air is 'to be recirculated, then it is preferred that the building is substantially sealed, such that air emissions from the buidig assthouh te iremssion control system of the present invention. Alternatively, tbhe systenm can be housed within the building so as to reduce noise to the outside environmi-ent and improve the aesthetics of the does 35 site, 7 It is possible, however, that iii situations where it is not necessary to recycle and control the air returning to the building, then the air outlet would be positioned outside the building and the treated air released into the surrounding environment, The system 10 can include a valve arrangement 85 to allow control of air emitted through the internal outlet or external outlet 801.

Furthermore, in order to monitor the air being treated within the system, the condenser 60 may include a means for measuring p1H and/or redox potential 62,64 of the moisture in the air. In order to control the pH and/or redox potential of moistuLre, it is possible to add a further means 66 within which to control either or both of these parameters. Such measuring and control means may be connected to automatic circuitry such that the p11 and/or redox potential may be controlled to the desired values automatically.

This type of control is well known by persons skilled in the art and the present invention is particularly adaptable to this form of control.

The air emission control system 10 may further include a smoke detector 90 so that, in the case of fire, the system may be used to control the amount of air being removed or rep~laced into the building. It would therefore be possible to rem-ove air via the inlet 20 but vent the treated air away from the building by closing the valve 85 to the internal outlet 80 thus removing the air and extinguishing thle fire. Under this type of fire control, it: would be necessary to ensure that no people are present in the building to :::*:ensure that no person would be asphyxiated. An alarm system could be installed to be activated when air is vented out of the building in case of fire..

25 The air emission control system of the pjresent invention is particularly adaptable for the use in mushroom composting plants. In this form, the air is removed from the ilet 20 above the compost in or near the ceiling of the plant and the treated air would be returned through the air outlet in the form of vented ducts running through the floor under the compost. In this form, the returning air may be moisture laden or warmed so as to control the moisture and temperature of the air returning to -the compost. Alternatively, the treated air may be cooled prior to returning to the compost so as to control the amount of fermientation occurring in the compost.

It will be appreciated by one skilled ini the art that the air control system of the presenit invention is adaptable for other industries requiring air, emission treatment, such as spray painters, smelters, electroplaters and the like.

In order to ensure that the air emission control system is functioning to the desired level, air sampling may be carried out at various stages through the system so as to measure the efficiency of the treatment stages.

For example, the quality of the air may be measured between the wet scrubber 40 and the condenser 60, before and after entry to the filter Such routine measurement would ensure that the system is functioning and will allow the manipulation of the treatment conditions at any of the stages and also ensure that all treatment processes are functioning at the required level. The measurement sampling and monitoring can be placed under the control of a computer so that the system can be run automatically.

The present invention is suitable to remove many pollutants from air emissions including sulphides, nitrates/nitrites, inorganic acids, organic compounds and particulate material.

Furthermore, the present invention may be constructed in situ or may be made as a mobile unit that can be moved from site to site, It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

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Claims

1. An air emission control system for treatment of ambient air containing emissions derived from a biological source, the system comprising: an air inlet adapted to remove ambient air emissions from the biological source; a means to pass air via the inlet through the system; r wet scrubber adapted to produce a iay of chemical treatment liquid in the scrubber such that, when the air passes through the spray, at least some pollutants in the air are removed; a liquid colltEtion means adapted to collect spent liquid including pollutants from the wet scrubber; a condenser adapted to control moisture in the air after treatment in the wet scrubber; 15 a filter means adapted to further remove pollutants from the treated air; an air outlet; and a means to return, t least some of the spent liquid containing pollutants to the biological source. 20

2. The system according to claim 1, such that the means to pass air through the system is a fan.

3. The system according to claim 1 or 2, such that the wet scrubber is a spray tower comprising a plurality of spray rings each including a plurality of spray jets positioned within the tower to generate the spray. 25

4, The system according to any one of claims 1 to 3, such that the *treatment liquid is water.

5. The system according to any one of claims 1 to 4, such that the collection means is in the form of a tank such that the treatment liquid drains from the wet scrubber into the tank.

6. The system according to any one of claims 1 to 5, such that the filter means includes a chemical filter and a particulate filter.

7. Th system according to claim 6, such that the chemical filter is an activated carbon filter.

8. The system according to claim 6 or 7, such that the particulate filter removes particles less than 2 microns.

9. The system according to any one of claims 1 to 8 having the outlet positioned in a different area from where the air is removed.

The system according to any one of claims 1 to 8 having the outlet positioned in the same area from where the air was removed such that the treated air is returned thereto.

11. The system according to claim 10, having the air inlet positioned at or near the ceiling of a building and the air outlet is in the form of a vented pipe positioned in the floor of the building.

12. The system according to any one of claims 1 to 11, further including a means to measure pH and/or redox potential of moisture in the air.

13. The system according to claim 12 further including means to adjust the pH and/or redox potential of the moisture in the air.

14, The system according to any one of claims 1 to 13 further including a smoke detector.

15. A method for removing pollutants from ambient air emissions :derived from a biological source, the method comprising: drawing ambient air from the biological source through an air inlet by a fan to a wet scrubber adapted to produce a spray of treatment liquid in the scrubber such that, when the air passes through the spi'ay, at least some 20 pollutants in the air are removed with the liquid; collecting spent liquid including pollutants from the wet scrubber; passing the treated air through a condenser such that the amount of moisture in the air is controlled; passing the air through a filter means adapted to further remove 25 pollutants from the air; passing the treated air through an air outlet; and returning at least part of the spent liquid to the biological source.

16. The method of claim 15 wherein the air emissions are derived from a mushroom composting plant,

17. The method of claim 16 wherein after treatment the air is returned to the mushroom composting plant.

18. An air emission control system for treatment of ambient air containing emissions derived from a biological source substantially as described with reference to the drawing. cA dnk-- u -J 0..Y 11

19. A method for removing pollutants from air emissions derived from a biological source substantially as described with reference to the drawing. Dated this 28th day of November 1997 CHRISTOPHER NASH, IAN MCCOY and WARRICK NORRIS Patent Attorneys for the Applicant: F.B. RICE CO. 00 *a a a a* C I I ABSTRACT The invention relates to an air emission control system comprising an air inlet, means to cause air to move through the system, a wet scrubber for chemical treatment of the air, a means to collect removed pollutants from the wet scrubber, a condenser to control the moisture content of the treated air, a filter means and an air outlet. 00 S *5 090*a 0.. *o Po l *og