FR2719774A1 - Deodorisation of gases by passing through successive filters in a tower - Google Patents

Abstract

In a process for the deodorisation of malodorous gases, such as polluted air, gas for purification crosses at least one filter (4,5 and 6) with a hydro-absorbent filling (40,50 and 60) impregnated with a treatment liquid (16 and 17). A pressurised water supply (11) leads to spray nozzles (18) above or below each filter bed. Valves (14 and 15) feeding water to the sprays are opened and closed according to a timer (10), which also controls valves (12 and 13) dosing chemical additives.

Description

 The subject of the present invention is a method for deodorizing smelly gaseous effluents, as well as the device for implementing said method.

 It is known that smelly gases are released in particular during the treatment of sludge in wastewater treatment plants, during the manufacture of compost, or the treatment of animal waste as well as in certain industrial manufacturing operations. It is most often exhaust air, but it can also be smoke or other gaseous effluents loaded with smelly products.

 The proportion of smelly substances is most often extremely reduced, of the order of a few milligrams per m3 of gas, and in many cases it may be only a few fractions of milligrams per m3, nevertheless producing a significant nuisance.

 It is known practice to use gas washers to purify these gaseous effluents, in particular by using washing solutions containing chemicals.

Thus, by way of example, the smelly products of the ammonia or amine type are removed by washing using dilute acid solutions, the hydrogen sulfide and the mercaptans using an alkaline solution containing bleach or other oxidant.

 It is also known to purify stale air using biofilters, which contain microorganisms. The filtering layer of such a biofilter absorbs smelly products, which are oxidized by microorganisms. These bisfilters must nevertheless be regularly supplied with nutritive salts necessary for the proliferation of microorganisms, while their pH must be maintained at a suitable value by adding chemicals to the watering solution.

 The use of gas washers is preferably carried out in a closed circuit in order to avoid an unnecessary loss of chemicals, which requires the use of pumps, while the purification of gases frequently requires the use of several stages. successive washing cycles.

 However, the implementation of pumps, and their constant energy consumption, make expensive deodorization installations of this type, a disadvantage to which are added noise, the risk of breakdowns and the costs entailed by their monitoring.

 The object of the present invention is to remedy these drawbacks of existing devices by proposing a process for deodorizing smelly gaseous effluents which does not require the use of pumps.

 The present invention thus relates to a process for deodorizing smelly gaseous effluents which is essentially characterized in that it consists in using at least one filter containing a water-absorbent filling body, which is sprayed at regular intervals with pressurized water added with appropriate chemicals, watering being carried out at determined time intervals so as to allow satisfactory impregnation of said filling body.

 To this end, in accordance with the invention, the filter contains a layer of filling body of sufficient thickness so that said filling body retains, between two successive sprinklers, a humidity which makes it possible to ensure the effectiveness of the treatment with screw of the gaseous effluent which passes through said filter.

 As a filling body which can be used in the process according to the invention, mention may be made of expanded clay granules, cellular concrete or expanded glass, or water-absorbing fibers, and more generally any water-absorbing product suitable for this purpose. use.

 The duration of the watering of the filter with the water loaded with the appropriate chemicals is of course a function of the thickness of the filling layer and of the water pressure, nevertheless it is generally of the order of 2 to 3 seconds, generally representing less than a tenth of the time separating two successive waterings.

 The water used for watering the filter can be local distribution water, the pressure in the distribution pipes is generally between 4 and 6 bars.

 Prior to watering the filter, water is added with a suitable quantity of the appropriate chemical (s), the mixing being carried out punctually, at the time intervals determined for watering the filter.

 The method according to the invention has the considerable advantage, compared to existing methods, of using only measured quantities of water, without resorting to the use of pumps requiring installation in a closed circuit.

 This results in significant savings, both at the installation stage of the device used and at the energy consumption during operation of said device.

The present invention also relates to a device allowing the implementation of the method according to the invention, said device being characterized essentially in that it comprises in combination
a) a pressurized water supply;
b) at least one filter enclosing a layer of a water-absorbent filling body, above or below which is arranged a spray bar, and into which the stale air supply pipe emerges
c) at least one container containing an aqueous solution of at least one suitable chemical
d) at least one injector connected at the inlet to the water inlet and at the outlet to the watering boom, and also connected to said container containing said chemical;
e) at least one clock controlling at predetermined intervals the opening and closing of at least two solenoid valves arranged, the first between the water inlet and the injector, and the second between the injector and the container containing the chemical solution.

 The injector used in the device according to the invention is a conventional type injector, comprising an inlet port for pressurized water, an outlet port connected to the spray bar and an opening for connection to the container containing the chemical solution, which is sucked into said injector, during the simultaneous opening of the two solenoid valves, by a venturi effect.

 The device according to the invention can comprise several successive filters each intended to be impregnated with a different chemical solution, depending on the products to be removed from the air to be purified. In this case the successive filters can advantageously be placed one above the other so as to constitute a purification tower.

 At least one of the filters used can also consist of a biofilter, the active substance of which consists of at least one microorganism. In this case, the chemical solution with which the said filter should be impregnated will consist of a solution of suitable nutritive salts added, where appropriate, with substances regulating the pH.

 The characteristics and advantages of the present invention will emerge more clearly from the description which follows and which relates to the appended drawing, it being understood that this description does not have any limiting character with respect to the invention.

In the attached drawing
- Figure 1 schematically shows a first embodiment of a device according to the invention.

 - Figure 2 schematically shows a second embodiment of a device according to the invention.

 If we refer first to Figure 1, we see in this figure that a device according to the invention comprises a pipe 1 for supplying air to be deodorized, which is sucked in by a fan 2 and sent into a treatment tower 3 provided at its upper end with an outlet 8 for purified air.

 Tower 3 comprises three successive filters 4, 5, 6 comprising three layers 40, 50, 60 of a water-absorbent filling body, for example balls of expanded clay.

 The lower filter 4 is surmounted by a spray bar 19 provided with nozzles 18 suitably arranged and oriented so as to spray the entire surface of the layer 40.

 Between the upper filters 5 and 6 is placed a second watering ramp 20 provided with nozzles 18 oriented partly upwards and partly downwards, so as to be able to water the entire surface of the layers 50 and 60.

 The spray bars 19 and 20 are each connected to the outlet of an injector 9, 9 ′, the inlet of which is connected to a pipe 11 for supplying pressurized water on which a solenoid valve 14, respectively 15 is disposed. , electrically connected to a clock 10.

 The injector 9 is furthermore connected to a line 17 ′ connected to a container 17 containing for example a solution of sulfuric acid intended to be sprayed onto the lower filter 4 of the tower 3 so as to impregnate the layer 40, which is then intended to absorb the ammonia and / or the amines contained in the air to be deodorized. A solenoid valve 13 electrically connected to the clock 10 is placed on the line 17 ′ at the outlet of the container 17.

 The injector 9 ′ is connected to a line 16 ′ connected to a container 16 containing for example a solution of bleach and soda, intended to be sprayed, by the spray bar 20, on the two filters 5 and 6 so as to impregnate the layers 50 and 60, with a view to absorbing for example hydrogen sulphide and / or the mercaptans contained in the air to be deodorized. A solenoid valve 12 electrically connected to the clock 10 is disposed on the line 16 'at the outlet of the container 16.

 The periodic watering of the filters 4, 5 and 6 is controlled by the clock 10 adjusted so as to trigger at regular intervals the opening of the solenoid valves 12, 13, 14 and 15. The injector 9 is then filled with a mixture of water and the solution of bleach and soda, which is injected, through the spray bar 19, onto the layer 40 of the filter 4. The same applies to the injector 9 ', which ensures the mixing of the water and the sulfuric acid solution and its injection on the filters 5 and 6 through the spray bar 20.

 A tray 38 disposed in the tower 3 below the two upper filters 5 and 6 collects the overflow of irrigation water which flows, through a pipe 39, to a sewer 7 in which the overflow of irrigation water from the filter 4 also flows through a pipe 39 '.

 The periodicity and duration of each watering are predetermined and entered in the form of data in the clock 10, this data being of course a function of various factors, including the thickness and the surface of the water-absorbent layers used, and the temperature ambient.

 The stale air entering the device through line 1, leaves through outlet 8 of tower 3 after passing through the three filters 4, 5 and 6 which rid it of smelly substances.

 Referring now to FIG. 2, it can be seen in this figure that another device according to the invention firstly comprises a biofilter 22 which the gas supplied through the pipe 21 passes from top to bottom under the effect of suction of a fan 23 disposed at the outlet of the biofilter 22, which sends it to a purification tower 24 provided with four superimposed filters 25, 26, 27 and 28 each comprising a layer of water-absorbent granular and porous water-absorbent material at regular intervals.

Three spray bars 37 are disposed respectively above the filters 25 and 26 and between the filters 27 and 28, each being connected to the output of an injector 34 whose input is connected, through a solenoid valve 33, to a water supply pipe 35 under
Each injector 34 is on the other hand connected, through a solenoid valve 33 ′, to a container, respectively 29, 30 and 31, each containing a solution of an appropriate chemical, the container 29 a solution of bleach, container 30 a sodium hydroxide solution and container 31 a sodium hyposulfite solution.

 In the same way the biofilter 22 is surmounted by a spraying boom 37 connected to the outlet of an injector 34 connected at the inlet, through a solenoid valve 33, to the water pipe 35, and also connected, through a solenoid valve 33 ', to a container 32 containing a solution of ammonium phosphate and acetic acid.

 The various solenoid valves are electrically connected to a clock, not shown in the figure, which ensures the watering, at regular intervals, of the various filters by the water of the pipe 35, after mixing, in each injector 34, with the solution of the appropriate chemical.

The water and energy consumption of such a device is extremely low, because for 10,000 m3 of gas to be treated, the following quantities are sufficient per hour
Water 80 i / h Acetic acid 10 g / h
Soda 5 g / h Bleach 10 g / h while the energy consumption is 4kWh / h.

 Such an installation makes it possible to remove hydrogen sulfide, mercaptans and amines above 99.9 l, and aldehydes and ketones above 99.5 t.

 The air leaving the installation no longer contains smelly substances.

Claims (13)

1) Method for deodorizing smelly gaseous effluents, in particular stale air, in which the gas to be purified passes through at least one filter containing a layer of a water-absorbent filling body impregnated with a treatment liquid, characterized in that the impregnation of said layer of filler body is carried out by sprinkling with the aid of pressurized water added with suitable chemicals and in that said sprinkling is carried out at predetermined time intervals, for a period of time also predetermined . 2) Method according to claim 1, characterized in that the pressurized water used is local distribution water. 3) Method according to claim 1 or claim 2, characterized in that the duration of watering is equal to one tenth or less of the time separating two successive waterings. 4) Method according to any one of the preceding claims, characterized in that the gas passes through several filters each containing a hydroabsorbent filling body, said filters being impregnated with solutions of different chemicals.  5) Method according to any one of the preceding claims, characterized in that at least one of the filters used is a biofilter. 6) Method according to claim 5, characterized in that the biofilter is sprayed with water added with nutritive salts and optionally with pH regulating substances.  7) Method according to L any one of the preceding claims, characterized in that the filling body of each filter is in the form of porous granules of expanded clay, cellular concrete or expanded glass. 8) Device for the deodorization of smelly gaseous effluents, in particular stale air, comprising at least one filter (4, 5, 6) containing a layer (40, 50, 60) of a water-absorbent filling body and at least a container (16, 17) containing an aqueous solution of a suitable chemical, characterized in that it further comprises  a) an inlet (11) of pressurized water  b) at least one spray bar (19, 20) arranged above or below each filter (4, 5, 6)  c) at least one injector (9, 9 ') connects the inlet to the water inlet (11) and the outlet to the watering boom (19, 20), and also connected to the container (16, 17) containing the chemical solution  d) at least one clock (10) controlling, at predetermined time intervals, the opening and then the closing of solenoid valves (12, 13, 14, 15) arranged, one (14, 15) between the water supply (11) and the injector (9, 9 ') and the other (12, 13) at the outlet of the container (16, 17) containing the chemical, so as to cause the periodic watering of each filter (4 , 5, 6) with water added with a chemical. 9) Device according to claim 8, characterized in that it comprises several successive filters (4, 5, 6) arranged one above the other in a purification tower (3). 10) Device according to claim 8 or claim 9, characterized in that the gas to be purified is supplied by a line (1) using a fan (2) which introduces it to the base of the filter (4 , 5, 6) or from the purification tower (3), from which it emerges via an outlet (8) arranged at the upper end of said filter (4, 5, 6) or of said purification tower ( 3). 11) Device according to one of claims 8 to 10, characterized in that it comprises at least one biofilter (22). 12) Device according to claim ll, characterized in that the gas to be purified crosses the biofilter (22) from top to bottom under the suction effect of a fan (23) which is disposed at the outlet of said biofilter (22 ) and which sends it to a purification tower (24) fitted with several overlapping filters (25, 26, 27, 28). 13) Device according to claim 11 or claim 12, characterized in that the biofilter (22) is regularly sprayed with water added with nutritive salts and / or ae pH regulating substances.