WO2002013949A1

WO2002013949A1 - Method and apparatus for elimination of odour gases

Info

Publication number: WO2002013949A1
Application number: PCT/FI2000/000700
Authority: WO
Inventors: Sakari Savikko
Original assignee: Sakari Savikko
Priority date: 2000-08-17
Filing date: 2000-08-17
Publication date: 2002-02-21
Also published as: AU2000265743A1

Abstract

Method and apparatus for elimination of odour gases, such as nitrogenous and sulphurous odour compounds produced as a decomposition product of organic waste. According to the invention odour gases are eliminated in an absorption reactor (7) in such a manner that in a porous honeycomb (10) located in the absorption reactor (7) the binder solution (19) of the odour compounds is by means of a circulation pump (2) and a circulation circuit (3) brought in contact with the malodorous air current moistened to 100 % relative humidity. The binder solution (19) is spread in small drops on top of the honeycomb, from which the binder solution flows downwards through the honeycomb. The odour gases are conveyed through the honeycomb counter-current, i.e. upwards from a lower level. The nitrogenous and sulphurous odour compoounds in the odour gases bind themselves chemically to the binder solution which flows further to a circulation container (11). The saturated binder solution is conveyed to a sewer, whereafter the circulation container is re-filled with an active binder solution from a storage container (18). The apparatus for elimination of odour is activated for example by a flow switch (17) or an odour sensor (21) coupled to the outlet pipe (8) of the absorption reactor.

Description

METHOD AND APPARATUS FOR ELIMINATION OF ODOUR GASES

METHOD ACCORDING TO THE INVENTION

The invention relates to for elimination of malodorous odour gases produced as a decomposition product of organic waste.

The field of application of the method according to the invention covers all such targets in which for example nitrogenous and sulphurous odour compounds flow to the environment and cause significant odour problems. Such targets include for example pumping plants of sewage networks, sewage treatment plants, composting plants for organic waste, animal by-product treatment plants, pig houses, industrial sewage treatment plants as well as extract air channels in air conditioning systems. It is characteristic to ail these targets that the odours are produced as a result of a decomposition process of organic waste. The scope of application of the method does not cover such areas in which for example pure hydrocarbons evaporate, because they do not contain sulphur or nitrogen atoms.

STATE OF THE ART

Existing methods for odour elimination can be divided into three types.

The first group includes different filters. For example active carbon and peat function as filtering agents. By means of these methods it is only possible to attain a partial decrease in the odour intensity. Odour gases are typically very complex chemical gas mixtures. By means of most sensitive gas chromatographic devices for separation and analysis it is possible to provide evidence of hundreds of different molecules in gas mixtures produced by bacteriological decomposition. Each molecule has, of course, its own properties in relation to the surfaces of other materials and such surface absorption material does not exist which would react i.e. bind all foreign molecules from the air. Naturally, the filters cause a significant flow resistance in the network, wherein it is not possible to use them without the support of other technical devices such as blowers.

The second group consists of methods in which the aim is to change the odour compounds chemically into a less malodorous form. Typical reagents include different oxidizers. Both oxygen and ozone are used for this purpose. The result is the same as the one obtained with filters. Some compounds become oxidized and others do not, and the result is only a partial decrease in the odour intensity.

The third widely used method for elimination of odour nuisances is based on masking the air. This method is, of course, very questionable, because the aim is merely to mislead the human nose by covering the actual detrimental stench with a strong odorant.

OBJECT OF THE INVENTION

It is an object of the present invention to introduce a method and an apparatus that do not contain the above-described drawbacks.

CHARACTERISTICS OF THE METHOD ACCORDING TO THE INVENTION

According to the method of the invention, malodorous odour gases are moistened, whereafter they are conveyed through a layer containing binder solution, such as a honeycomb, in which the odour gases are brought in contact with the binder solution, wherein malodorous compounds, such as nitrogenous and sulphurous odour compounds are absorbed and bound chemically to the binder solution.

The invention is based on a known chemical property, as well as on the combination of properties of known chemical equipment technology.

EMBODIMENTS OF THE METHOD ACCORDING TO THE INVENTION

According to a preferred embodiment of the method according to the invention malodorous odour gases are moistened preferably to 100 % relative humidity, whereafter the odour gases are allowed to form with the binder solution such an aqueous phase reaction which specifically reacts i.e. binds in itself the compounds in gaseous form in which sulphur or nitrogen atom forms a part of the molecule.

The moistening of odour gases to a humidity as close as possible to the 100 % relative humidity is advantageous because evaporation of the chemicals in the binder solution to the open air is thus prevented. In other words, the binder solution can be maintained active in the cycle of the process as long as possible.^"

According to a second preferred embodiment of the method according to the invention the binder solution is spread on the porous honeycomb in such a manner that the binder solution runs through the honeycomb, wherein odour gases are conveyed through the honeycomb, preferably upwards from a lower level.

According to a third preferred embodiment of the method according to the invention, the binder solution that has run through the porous honeycomb is allowed to run preferably to a recycling container, whereafter the binder solution is recycled and spread on the honeycomb again.

According to a fourth preferred embodiment of the method according to the invention the activity of the binder solution is measured with a concentration sensor or the like and when the reagents of the binder agent have been consumed under a predetermined limit, the binder solution in the circulation is removed and changed into a new active binder solution.

According to a fifth preferred embodiment of the method according to the invention malodorous odour gases are allowed to flow freely through the porous honeycomb, preferably upwards from a lower level as a result of the lifting force caused by the difference in temperature between the odour gases and the ambient air, such as open air, and the binder solution is allowed to run through the porous honeycomb downwards from an upper level under the influence of gravity.

The method according to the invention is especially advantageous because it is not absolutely necessary to use energy-consuming blowers in the process since it is possible to utilize the chimney effect based on the difference in temperature between the gases in different spaces. In this way it is possible to convey gases from inside to the colder open air, but equally well from one room to another, if there exists a difference in temperatures between them. The above-presented method differs from methods of prior art in that respect that it fully eliminates the odours caused by decomposition of organic materials. When the method was tested experimentally, the human nose was used as a measuring instrument in elimination of odours, the human nose being the only measuring instrument available for real odour nuisances. There are, of course, several kinds of electronic sensors, but their applicability is at its best only in the detection and monitoring of one or more predetermined gas components. The presented invention utilizes the chemical property, that it is possible to produce such an aqueous phase reaction which specifically reacts i.e. binds in itself the gaseous compounds in which sulphur or nitrogen atom forms a part of the molecule. The compounds existing in odour gas mixtures typically contain a very small amount of nitrogen or sulphur, but when they are removed from the air this is perceived as total elimination of odours.

All pumping plants for sewage, sewage treatment plants, composting plants for organic waste, animal by-product treatment plants, pig houses, industrial sewage treatment plants and extract air channels of air conditioning systems contain ventilating pipes and exhaust openings of extract air channels to attain and ensure a faultless and secure operation of the systems. All these ventilating pipes and exhaust openings of extract air channels are open to the open air. A problem that is widely known and often experienced is caused by the fact that these ventilating pipes and exhaust openings of extract air channels spread odours in their environment which are perceived malodorous and which cause problems e.g. for living comfort.

APPARATUS ACCORDING TO THE INVENTION

The invention also relates to an apparatus for elimination of malodourous odour gases produced as a decomposition product of organic waste.

CHARACTERISTICS OF THE APPARATUS ACCORDING TO THE INVENTION

The apparatus according to the invention is characterized in that it contains: a chamber, such as an absorption reactor containing a honeycomb or a similar porous layer, a feeding device for feeding and spreading the binder solution on the honeycomb, a moistening apparatus for moistening the odour gases, and a channel or the like for conveying the moistened odour gases in the honeycomb of the chamber for contact with the binder solution.

It is characteristic to a preferred embodiment of the apparatus according to the invention that in the absorption reactor the honeycomb is primarily a horizontal porous layer whose surface area is large and the flow resistance at low flow speeds of gases is small, - that the feeding device of the binder solution is located above the honeycomb, and said feeding device contains means for spreading the binder solution on top of the honeycomb in drops as an even fall of rain without a pressurized shower effect, and that the absorption reactor contains a discharge pipe of the binder solution to discharge the binder solution run through the honeycomb from the absorption reactor.

A second preferred embodiment of the apparatus according to the invention is characterized in - that a circulation container is connected to the discharge pipe of the binder solution in the absorption reactor to collect the binder solution discharged from the absorption reactor, and that a pipe-like circulation circuit and a circulation pump are connected to the circulation container to convey the binder solution to the honeycomb of the absorption reactor again.

A third preferred embodiment of the apparatus according to the invention is characterized in that a concentration sensor measuring the activity of the binder solution is connected to the circulation circuit of the absorption reactor, a discharge pipe or the like and means for discharging the used binder solution from the circulation container on the basis of a predetermined control signal of the concentration sensor are connected to the circulation container, - and that a storage container and filling means for filling the circulation container with the active binder solution are connected to the circulation container. A fourth preferred embodiment of the apparatus according to the invention is characterized in that the moistening device located in the odour gas inlet channel or the like is a cellular moistening device in which odour gases can be brought preferably to 100% relative humidity by means of cold tap water, and that the inlet opening of odour gases in the inlet pipe is placed below the honeycomb in the absorption reactor to convey odour gases upwards from a lower level through the honeycomb as a result of a lifting force caused by the difference in temperature between the odour gases and open air.

A fifth preferred embodiment of the apparatus according to the invention is characterized in that the outlet pipe of the absorption reactor comprises a flow switch and/or at least one odour sensor that detects the flow of extract air.

The elimination of odour gas compounds from an air current takes place in a special absorption reactor. The purpose of this reactor is to bring the binder solution in contact with the malodorous air current in such a manner that the contact surface is large and the contact time sufficient. The flows in the reactor move counter-current, wherein the evaporation that has taken place in the reactor flows together with the flow towards the open air. When the contact surface is large, the evaporation potential i.e. the chemical losses are also significant. To prevent this, the malodorous air current saturated to 100 % relative humidity is supplied to the reactor, wherein evaporation and thereby chemical losses to the open air do not occur, and the operating costs of the system are as small as possible. The air that is purified from odour gases flows to the open air.

EXAMPLE OF AN EMBODIMENT

In the following, the invention will be described by means of an example by referring to the appended drawing that shows the absorption reactor according to the invention and the peripheral apparatus of the same.

DESCRIPTION OF THE DRAWING The drawing shows an absorption reactor 7 according to the invention in which the elimination of malodorous odour gases takes place in the following manner. Air containing malodorous odour gases flows away from an odour source 1 via a pipe 6 into the absorption reactor 7, in which the air is lifted up through a porous honeycomb 10 as a result of the chimney effect and further exits the absorption reactor 7 via an outlet pipe 8. The outlet pipe 8 contains a flow switch 17 that detects whether air flows in the outlet pipe 8 and which is the direction of the flow. If an air current does not exist in the pipe 8 or the current is directed towards the absorption reactor 7, the odour elimination method is not activated. However, if the air current is directed outwards from the absorption reactor 7 in the outlet pipe 8, i.e. upwards in the drawing, the flow switch 17 activates the odour elimination process.

Alternatively, the flow switch 17 may be replaced or supplemented with at least one odour sensor 21, which detects odours in the outlet pipe 8. By means of the odour sensor 21 it is possible to attain a function similar to the one attained with the flow switch 17, i.e. the activation of the odour elimination process when malodorous gases flow outwards in the outlet pipe 8. An especially important factor in view of odour gas elimination is an odour sensor that detects for example hydrogen sulphide H₂S, because this compound is very malodorous.

The function of the odour elimination process starts in such a manner that in the outlet pipe 8 the flow switch 17 or odour sensor 21 detecting the flow of malodorous extract air gives an activation command. Thus, at the same time a circulation pump 2 of the binder solution for the odour compounds and a magnetic valve 4 of a cold water pipe 16 connected to the general water distribution system 15 are activated in the circulation circuit 3, said magnetic valve opening the flow of water to a moistening cell 5. The moistening of the incoming malodorous air current takes place in the moistening cell 5, which is for example a conventional cellular moistening device 5 used generally in air conditioning, the dimensions of which are determined according to the incoming malodorous air current. In the part of the pipe 6 after the moistening device 5 before the absorption reactor 7, the relative humidity of the incoming malodorous air is 100% RH (RH= relative humidity).

Below the outlet pipe 8 located topmost in the absorption reactor 7 and leading to the open air, there is a spreader 9 of a binder solution 19, which scatters the binder solution 19 as an even fall of rain over the entire cross-section of the absorption reactor 7, on top of the honeycomb 10. The spreader 9 of the binder solution 19 is of such a type that pressurized shower effect is not produced therein. In other words, the spreader 9 is not a nozzle requiring dynamical pressure, because the flow resistance of air must be small to enable the flow of air in external air pressure.

In the absorption reactor 7, the binder solution 19 of odour gases falls down on top of the extremely porous layer 10 as an even fall of rain. The porous layer 10 is of such a type that the flow resistance therein at very low flow rates, such as under 0.5 m/s, is very small. Furthermore, the porous layer 10 has such a structure that its surface is very large when compared to its volume, for example over 1000 m²/1 m³. Honeycomb structures known as such are used as the porous layer 10, and it is necessary that they endure the effects of water and chemicals.

When the binder solution 19 has fallen down on top of the porous honeycomb structure 10, it starts to flow through the honeycomb 10 under the influence of gravitation. In the absorption reactor 7, a saturated humid malodorous air current rises against the flow of the binder solution 19, and enters in contact with the binder solution 19 in the porous honeycomb 10. The thickness of the honeycomb 10 is dimensioned in such a manner that the time is sufficient for the desired chemical reactions to take place. Thus, nitrogenous and sulphurous odour compounds bind themselves chemically to the binder solution 19 flowing from the lower part of the absorption reactor 7 back to the circulation container 11. From the circulation container 11 the binder solution 19 is conveyed back to the circulation pump 2 and further to the absorption reactor 7 via the spreader 9 to the honeycomb 19.

Because the binder solution 19 supplied to the absorption reactor 7 loses its strength in use, a concentration sensor 12 is constantly used to measure the activity of the binder solution 19. When the binder solution 19 has become saturated, i.e. when the reagents of the same have been consumed, the concentration sensor 12 gives a control signal which opens a magnetic discharge valve 13 in the circulation container 11. Thus, the saturated binder solution 19 is emptied out from the circulation container 11 for example to a general sewer duct 20. The binder solution 19 emptied to the general sewer duct 20 is fully environmentally compatible and suitable to be discharged to a sewer, and therefore it can be safely either emptied to a general sewer network or taken to a refuse disposal site.

When the circulation container 11 has become empty, a filling pump 14 in the storage container 18 is activated and the circulation container 11 is filled up again with the active binder solution 19 from the storage container 18. After the circulation container 11 has been emptied and re-filled the circulation pump 2 of the circulation circuit 3 of the binder solution is activated and the elimination of odour gases continues.

During the act of changing the saturated binder solution into a new, active binder solution, the flow of odour gases from the odour source 1 to the open air can be stopped if the process permits. The flow of odour gases can be stopped for example by closing the valve installed in the outlet pipe 8, which is not shown in the drawing.

It is not, however, necessary to interrupt the flow of odour gases. This results from the fact that although the flow and supply of the binder solution to the honeycomb 10 is stopped, the honeycomb 10 does, however, contain some binder solution at all times. Typically this is sufficient for continuing the absorption reaction with the odour gases for such a long period of time that the circulation of the new active binder solution and supply of the same to the honeycomb 10 can be started.

Claims

Claims:

1. A method for elimination of malodorous odour gases produced as a decomposition product of organic waste, characterized in that the malodorous odour gases are moistened, whereafter they are conveyed through a layer (10) such as a honeycomb containing binder solution of odour compounds (19), in which layer the odour gases are brought into contact with the binder solution, wherein malodorous compounds, such as nitrogenous or sulphurous odour compounds are absorbed and bound chemically to the binder solution.

2. The method according to claim 1 , characterized in that the malodorous odour gases are moistened most advantageously to 100% relative humidity, whereafter the odour gases are allowed to form such an aqueous phase reaction with the binder solution (19) that specifically reacts with i.e. binds in itself the gaseous compounds in which sulphur or nitrogen atom forms a part of the molecule.

3. The method according to claim 1 or 2, characterized in that the binder solution (19) is spread on top of the porous honeycomb (10) in such a manner that the binder solution runs through the honeycomb (10) wherein odour gases are conveyed through the honeycomb preferably upwards from a lower level.

4. The method according to claim 1 , 2 or 3, characterized in that the binder solution (19) that has run through the porous honeycomb (10) is most advantageously run to a recycling container (11) whereafter the binder solution is recycled and spread on top of the honeycomb again.

5. The method according to any of the claims 1 to 4, characterized in that the activity of the binder solution (19) is measured with a concentration sensor (12) or the like, and when the reagents of the binder solution have been consumed below a predetermined limit, the binder solution in the circulation is disharged and changed into a new, active binder solution.

6. The method according to any of the claims 1 to 5, characterized in that malodorous odour gases are allowed to flow freely through the porous honeycomb (10), preferably upwards from a lower level as a result of a lifting force caused by the difference in temperature between the odour gases and the ambient air, such as open air, and that the binder solution (19) is allowed to flow through the porous honeycomb downwards from an upper level under the influence of gravity.

7. An apparatus for elimination of malodorous odour gases produced as a decomposition product of organic waste, characterized in that the apparatus contains a chamber (7) such as an absorption reactor, containing a honeycomb (10) or a corresponding porous layer, feeding device (9) for feeding and spreading binder solution (19) on the honeycomb (10), a moistening device (5) for moistening the odour gases, and a channel (6) or the like for conveying the moistened odour gases to the honeycomb (10) of the chamber (7) for contact with the binder solution

(19).

8. The apparatus according to claim 7, characterized in that in the absorption reactor (7) the honeycomb (10) is primarily a horizontal porous layer whose surface area is large and the flow resistance at low flow speeds of gases is small, - that the feeding device (9) of the binder solution (19) is located above the honeycomb (10), and said feeding device contains means for spreading the binder solution (19) on top of the honeycomb (10) in drops as an even fall of rain without a pressurized shower effect, and that the absorption reactor (7) contains a discharge pipe of the binder solution (19) to discharge the binder solution flown through the honeycomb

(10) from the absorption reactor.

9. The apparatus according to claim 7 or 8, characterized in that a circulation container (11) is connected to the discharge pipe cf the binder solution (19) in the absorption reactor (7) to collect the binder solution discharged from the absorption reactor, and and that a pipe-like circulation circuit (3) and a circulation pump (2) are connected to the circulation container (11) to convey the binder solution (19) to the honeycomb (10) of the absorption reactor again.

10. The apparatus according to claim 7, 8 or 9, characterized in that a concentration sensor (12) measuring the activity of the binder solution (19) is connected to the circulation circuit (3) of the absorption reactor (7), that a discharge pipe or the like and means (13) for removing the used binder solution (19) from the circulation container on the basis of a predetermined control signal of the concentration sensor (12) are connected to the circulation container (11), and that a storage container (18) and filling means (14) for filling the circulation container with the active binder solution (19) are connected to the circulation container (11 ).

11. The apparatus according to any of the claims 7 to 10, characterized in that the moistening device (5) located in the odour gas inlet channel or the like (6) is a cellular moistening device in which odour gases can be brought preferably to 100 % relative humidity by means of cold tap water, and that the inlet opening of odour gases in the inlet pipe (6) is located below the honeycomb (10) in the absorption reactor (7) to convey odour gases upwards from a lower level through the honeycomb as a result of a lifting force caused by the difference in temperature between the odour gases and open air.

12. The apparatus according to any of the claims 7 to 11, characterized in that the outlet pipe (8) of the absorption reactor (7) comprises a flow switch (17) and/or at least one odour sensor (21 ) that detects the flow of extract air.