GAS TREATMENT SYSTEM AND METHOD

Abstract

Disclosed is a process for treating a stale gas, involving the following steps: circulation of the stale gas in a gas/liquid contactor, called a contactor, and then circulation of the stale gas in a filter unit, called a filter unit, the process involving, in the contactor, placing a circulating liquid in contact with the stale gas, the circulating liquid having a temperature of between 2 and 15 C., preferably between 5 and 10 C., and also to a treatment unit for performing the process including a gas/liquid contactor and a filter unit.

Claims

1. A process for treating a stale gas, comprising: circulating the stale gas in a gas/liquid contactor, called a contactor, and then circulating the stale gas in a filter unit, called a filter unit, the process including, in the contactor, placing a circulating liquid in contact with the stale gas, said circulating liquid having a temperature of between 2 and 15 C.

2. The process as claimed in claim 1, wherein the circulation of the stale gas in the contactor involves circulation of the stale gas in a direction opposite to a direction in which the liquid circulates in the contactor.

3. The process as claimed in claim 2, wherein the circulation of the stale gas in the contactor involves: circulating the stale gas in a direction identical to a direction in which the liquid circulates in the contactor, circulating the stale gas in a direction opposite to a direction in which the liquid circulates in the contactor.

4. The process as claimed in claim 1, further comprising: injecting the stale gas into a first part of the contactor, called the co-current part, in which the stale gas circulates in the same direction as the direction in which the liquid circulates in said first part of the contactor, and circulating the stale gas in a second part of the contactor, called the counter-current part, in which the stale gas circulates in the direction opposite to the direction in which the liquid circulates in said second part of the contactor, and circulating the stale gas in the filter unit.

5. The process as claimed in claim 1, further comprising placing the stale gas and the liquid circulating in the contactor in contact with a heat exchanger.

6. The process as claimed in claim 1, further comprising circulating a cooling liquid in the heat exchanger, said cooling liquid having a temperature of between 2 and 15 C.

7. The process as claimed in claim 1, further comprising: injecting the liquid circulating in the contactor into the second part of the contactor or, respectively, into the first part of the contactor, and then reinjecting the liquid which has circulated in the second part of the contactor into the first part of the contactor or, respectively, into the second part of the contactor.

8. The process as claimed in claim 1, further comprising a step of heating the stale gas prior to the circulation of the stale gas in the filter unit.

9. The process as claimed in claim 1, wherein the process is performed for the removal of odorous volatile organic compounds (VOCs).

10. The process as claimed in claim 1, wherein the stale gas is stale air.

11. The process as claimed in claim 1, wherein the stale gas is biogas.

12. A stale gas treatment unit comprising: a gas/liquid contactor, called a contactor, in which the stale gas circulates, a filter unit, called a filter unit, in which the stale gas circulates; said stale gas treatment unit being designed to perform the process as claimed in claim 1.

13. The stale gas treatment unit as claimed in claim 12, wherein the unit is arranged so that a liquid circulating in the contactor is injected into a second part of the contactor or, respectively, into a first part of the contactor, and so that the liquid which has been injected into the second part of the contactor is reinjected into the first part of the contactor or, respectively, into the second part of the contactor; said liquid circulating in the contactor having a temperature of between 2 and 15 C.

14. The stale gas treatment unit as claimed in claim 12, wherein: the first part of the contactor, called the co-current part, is arranged so that the stale gas circulates in a same direction as a direction in which the liquid circulating in the contactor circulates in said first part of the contactor, and the second part of the contactor, called the counter-current part, is arranged so that the stale gas circulates in an opposite direction to a direction in which the liquid circulating in the contactor circulates in said second part of the contactor.

15. The process of claim 1, wherein said circulating liquid has a temperature of between 5 and 10 C.

16. The process as claimed in claim 2, further comprising: injecting the stale gas into a first part of the contactor, called the co-current part, in which the stale gas circulates in the same direction as the direction in which the liquid circulates in said first part of the contactor, and circulating the stale gas in a second part of the contactor, called the counter-current part, in which the stale gas circulates in the direction opposite to the direction in which the liquid circulates in said second part of the contactor, and circulating the stale gas in the filter unit.

17. The process as claimed in claim 3, further comprising: injecting the stale gas into a first part of the contactor, called the co-current part, in which the stale gas circulates in the same direction as the direction in which the liquid circulates in said first part of the contactor, and circulating the stale gas in a second part of the contactor, called the counter-current part, in which the stale gas circulates in the direction opposite to the direction in which the liquid circulates in said second part of the contactor, and circulating the stale gas in the filter unit.

18. The process as claimed in claim 2, further comprising placing the stale gas and the liquid circulating in the contactor in contact with a heat exchanger.

19. The process as claimed in claim 3, further comprising placing the stale gas and the liquid circulating in the contactor in contact with a heat exchanger.

20. The process as claimed in claim 1, further comprising circulating a cooling liquid in the heat exchanger, said cooling liquid having a temperature of between 3 and 10 C.

Description

DESCRIPTION OF THE FIGURES AND EMBODIMENTS

[0139] Other advantages and features of the invention will become apparent on reading the detailed description of implementations and embodiments which are in no way limiting, and from the following appended drawings:

[0140] FIG. 1 is a schematic representation of a first embodiment of the process and of the treatment unit according to the invention;

[0141] FIG. 2 is a schematic representation of a second embodiment of the treatment unit and of the process according to the invention.

[0142] Since the embodiments described below are in no way limiting, it is notably possible to consider variants of the invention comprising only a selection of described features, isolated from the other described features (even if this selection is isolated within a sentence including these other features), if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection comprises at least one feature, which is preferably functional without structural details, or with only part of the structural details if this part only is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0143] In addition, the embodiments below are described in relation with the treatment of stale air, but can also be applied to the treatment of biogas.

[0144] With reference to FIG. 1, a first embodiment describes a treatment process according to the invention and also a treatment unit according to the invention.

[0145] FIG. 1 presents a process for treating odors and odorous VOCs of stale air 3 resulting from a process for treating wastewater or waste treatment facilities. The stale air 3 is introduced 1 into the treatment unit 13 at a temperature of between 35 C. and 55 C. The process involves circulation 31, 32 of the stale air 3 in a gas/liquid contactor 2, called the contactor 2, and circulation 4 of the stale air in a filter unit 5, called the filter unit 5. The process involves placing a liquid 6 circulating 61, 62 in the contactor 2 in contact with the stale air 3 circulating 31, 32 in the contactor 2. The circulating 61, 62 liquid 6 has a temperature of between 5 and 10 C. This temperature may, in certain cases, range between 2 and 15 C. The placing of the liquid 6 circulating 61, 62 in the contactor 2 in contact with the stale air 3 circulating 31, 32 in the contactor 2 is direct contact.

[0146] The liquid 6 circulating 61, 62 in the contactor 2 is water.

[0147] The circulation 31, 32 of the stale air 3 in the contactor 2 involves circulation 32 of the stale air 3 in a direction opposite to a direction 61 in which the liquid 6 circulates in the contactor 2.

[0148] The flow rate of the liquid 6 circulating 61, 62 in the contactor 2 relative to the flow of stale air 3 circulating in the contactor 2 is less than 10 l/m.sup.3. According to the invention, the flow rate of the liquid 6 circulating 61, 62 in the contactor 2 relative to the flow of stale air 3 circulating in contactor is from 2 to 4 ml/m.sup.3, advantageously 3 l/m.sup.3.

[0149] With reference to FIG. 2, the liquid 6 circulating 61, 62 in the contactor 2 circulates in a single vertical direction 67 in which the liquid 6 flows.

[0150] The circulation 31, 32 of the stale air 3 in the contactor 2 involves circulation 31 of the stale air 3 in a direction identical to the direction 61 in which the liquid 6 circulates in the contactor 2 and circulation 32 of the air stale 3 in a direction opposite to the direction 62 in which the liquid 6 circulates in the contactor 2. According to, the step of circulation 31 of the stale air 3 in a direction identical to the direction 61 in which the liquid 6 circulates in the contactor 2 is performed prior to the step of circulation 32 of the stale air 3 in a direction opposite to the direction 62 in which the liquid 6 circulates in the contactor 2.

[0151] The process according to the invention involves injection 1 of the stale air into a first part 21 of the contactor 2, called the co-current part, in which the stale air 3 circulates 31 in the same direction as the direction in which the liquid 6 circulates 61 in said first part 21 of the contactor 2. Equivalently, this step may be described as circulation 31 of the stale air 3 in co-current with the liquid 6 circulating 61 in the contactor 2. Next, the process involves circulation 32 of the stale air 3 in a second part 22 of the contactor 2, called the counter-current part 22, in which the stale air circulates 32 in the opposite direction to the direction in which the liquid 6 circulates 62 in said second part 22 of the contactor 2. Equivalently, this step may be described as circulation 32 of the stale air 3 in counter-current to the liquid 6 circulating 62 in the contactor 2. Next, the process involves circulation 4 of the stale air 3 in the filter unit 5. At the outlet of the treatment unit 13, the process involves discharging 16 the treated air 17.

[0152] Subsequent to the step of circulating 62 stale air in the second part 22 of the contactor 2, the process includes a step of heating 9 the stale air 3 prior to circulation 4 of the stale air 3 in the filter unit 5. The step of heating 9 the stale air 3 is thus performed subsequent to the step of circulating 61 the liquid 6 in the first part 21 of the contactor 2. During the heating step, the stale air 3 is heated to a temperature 5 C. higher than its temperature at the outlet of the contactor 2.

[0153] The process involves injection 63, into the first part 21 of the contactor 2, of the liquid 6 circulating 61, 62 in the contactor 2, followed by recovery 66 of the liquid 6 which has circulated 61 in the first part 21 of the contactor 2. The recovery 66 of the liquid 6 is followed by reinjection 64, into the second part 22 of the contactor 2, of the liquid 6 which has circulated 61 in the first part 21 of the contactor 2.

[0154] Subsequent to the circulation 62, in the second part 22 of the contactor 2, of the reinjected 64 liquid 6, the process involves recovery 65 of the liquid 6 which has circulated 61, 62 in the contactor 2.

[0155] The recovered 65 liquid 6, which has circulated 61, 62 in the contactor 2 is removed for the purpose of its subsequent treatment and/or recycling.

[0156] The process involves placing stale air 3 circulating 31, 32 in the contactor 2 and liquid 6 circulating 61, 62 in the contactor 2 in contact 7 with a heat exchanger 8.

[0157] The liquid 10 circulating in the heat exchanger, called the cooling liquid 10, is water.

[0158] The step of placing the stale air 3 and the liquid 6, circulating 31, 32, 61, 62 in the contactor 2, in contact 7 with the heat exchanger 8 is performed concomitantly with the step of circulating 31 the stale air 3 in co-current with the liquid 6 circulating 61 in the contactor 2. In other words, the step of placing the stale air 3 and the liquid 6 circulating 31, 32, 61, 62 in the contactor 2 in contact 7 with the heat exchanger 8 is performed in the first part 21 of the contactor 2. The cooling liquid 10 circulating in the heat exchanger 8 has a temperature of between 5 and 10 C. This temperature may, in certain cases, range between 2 and 15 C.

[0159] The cooling liquid 10 injected 101 into the heat exchanger 8 is identical to the liquid 6 injected 63 into the contactor 2. The cooling liquid 10 injected 101 into the exchanger 8 and the liquid 6 injected 63 into the contactor 2 come from a refrigerating unit 11 fed with industrial water 12. The cooling liquid 10 is recovered 102, at the outlet of the heat exchanger 8, and is reinjected 103 into the cooling liquid 10 circuit. According to the invention, the cooling liquid 10 is reinjected 103 into the refrigerating unit 11.

[0160] With reference to FIG. 2, a second embodiment describes a treatment unit according to the invention and also a process according to the invention.

[0161] FIG. 2 presents a unit 13 for treating stale air 3. The treatment unit 13 comprises a gas/liquid contactor 2, called the contactor 2, in which the stale air 3 circulates 31, 32 and a filter unit 5 in which the stale air 3 circulates 4. The treatment unit 13 is arranged so that the stale air 3 circulates 31, 32 in the contactor 2 then circulates 4 in the filter unit 5. The stale air 3 is injected 1 into the first part 21 of the contactor 2. The stale air is injected 1 into the contactor 2 at a temperature of between 35 and 55 C. The treated air 16, leaving the treatment unit 13, is discharged 17 into the atmosphere.

[0162] The stale air 3 treatment unit 13 is designed to perform the process according to the invention.

[0163] According to the invention, the filter unit 5 is an active charcoal filter unit 5.

[0164] The stale air 3 treatment unit 13 is arranged so that the liquid 6 circulating 61, 62 in the contactor 2 is injected 63 into a second part 22 of the contactor 2 and so that the liquid 6 which has been injected 63 into the second part 22 of the contactor 2 is reinjected 64 into the first part 21 of contactor 2. The liquid 6 circulating 61, 62 in the contactor 2 has a temperature of between 5 and 10 C. This temperature may, in certain cases, range between 2 and 15 C.

[0165] The placing of the liquid 6 circulating 61, 62 in the contactor 2 in contact with the stale air 3 circulating 31, 32 in the contactor 2 is direct contact. The injections 63 and 64 of liquid 6 into the contactor 2 are performed by spraying via nozzles.

[0166] The stale air 3 treatment unit 13 is arranged so that the flow rate of the liquid 6 circulating 61, 62 in the contactor 2 relative to the flow rate of stale air 3 circulating in the contactor 2 is less than 10 l/m.sup.3. According to the invention, the flow rate of the liquid 6 circulating 61, 62 in the contactor 2 relative to the flow rate of stale air 3 circulating in contactor 2 is between 2 and 4 L/m.sup.3, for example 3 l/m.sup.3.

[0167] The liquid 6 circulating 61, 62 in the contactor 2 is water.

[0168] The liquid 6 circulating 61, 62 in the contactor 2 circulates in a single vertical direction 67 in which the liquid 6 flows by gravity.

[0169] The first part 21 of the contactor 2, called the co-current part 21, is arranged so that the stale air 3 circulates 31 in the same direction 67 as the direction in which the liquid 6 circulating 61, 62 in the contactor 2 circulates 61 in said first part 21 of the contactor 2. The second part 22 of the contactor 2, called the counter-current part 22, is arranged so that the stale air 3 circulates 32 in the opposite direction to the direction 62 in which the liquid 6 circulating 61, 62 in the contactor 2 circulates 62 in said second part 22 of the contactor 2.

[0170] The contactor 2 is a cyclone type contactor 2. The circulation 31 of the stale air 3 in the first part 21 of the contactor 2 takes place in a downward swirling movement 31 around the central zone 22 of the contactor 2. The circulation 32 of the stale air 3 in the second part 22 of the contactor 2 takes place in a substantially rectilinear upward movement 32 in the central zone 22 of the contactor 2.

[0171] The cyclone type contactor 2 has a cylindrical shape. The central zone 22 extends along the axis of revolution of the contactor 2.

[0172] The second part 22 of the contactor extends from the outer walls of the central zone 22 to the inner walls 23 of the contactor 22, i.e. the inner walls 23 of the first part 21 of the contactor 2.

[0173] The stale air 3 treatment unit 13 comprises a heat exchanger 8 arranged so that the stale air 3 and the liquid 6 circulating 31, 32, 61, 62 in the contactor 2 come into contact with an exchange surface of the exchanger 8. Inside the exchange surface 81 circulates a cooling liquid 10, the temperature of which is between 5 and 10 C. This temperature may, in certain cases, range between 2 and 15 C.

[0174] The cooling liquid 10 is water.

[0175] The heat exchanger 8 is a tubular exchanger 8. The exchanger 8 comprising a bundle of circular tubes 81 extending around the central zone 22.

[0176] The cooling liquid 10 and the liquid 6 circulating 61, 62 in the contactor 2 are recovered, respectively 102 and 66, in a tank 14, then reinjected 64 into the first part 21 of the contactor 2.

[0177] The tank 14 forms part of a recirculation circuit.

[0178] The cooling liquid 10 injected 101 into the heat exchanger 8 is identical to the liquid 6 injected 63 into the contactor 2. The cooling liquid 10 injected 101 and the liquid 6 injected 63 come from a refrigerating unit 11 fed with industrial water 12. The cooling liquid and the liquid 6 which has circulated 62 in the second part 22 of the contactor 2 are recovered 102, 66 at the outlet of the heat exchanger 8, in a tank 14.

[0179] The stale air 3 treatment unit 13 is arranged so that the liquid 6 which has circulated 61, 62 in the contactor 2 is recovered 65 for the purpose of its subsequent treatment. The liquid 6 is recovered 65 subsequent to the circulation 61, in the first part 21 of the contactor 2, of the reinjected 64 liquid 6.

[0180] The recovered 65 liquid 6, which has circulated 6, 61, 62 in the contactor 2, is removed for the purpose of its subsequent treatment and/or recycling.

[0181] The stale air 3 treatment unit 13 comprises an element 9 for heating the stale air 3, arranged so that the stale air 3 is heated before circulating 4 in the filter unit 5. The stale air 3 is heated to a temperature 5 C. higher than its temperature at the outlet of the contactor 2.

[0182] The heating element 3 comprises a hot filament 15 positioned on the path of circulation of the stale air 3 so as to heat the stale air 3.

[0183] Although, according to the embodiments presented, the main intended application, for the process and the treatment unit 13, is the treatment of odors and odorous VOCs, the process and the treatment unit 13 according to the invention also perform the removal of:

[0184] hydrophilic VOCs, and/or

[0185] odorous hydrophilic VOCs, and/or

[0186] dusts, and/or

[0187] particles, and/or

[0188] odorous compounds other than VOCs, and/or

[0189] nonodorous VOCs.

[0190] Although, according to the embodiments presented, the main intended application, for the process and the treatment unit 13, is the treatment of stale air 3 originating from wastewater or sludge, in particular sludge resulting from water treatment, or from waste treatment facilities. The process and the treatment unit 13 are also suitable for treating any type of stale air 3 containing elements such as mentioned above.

[0191] The stale air 3 injected 1 into the contactor 2 has a temperature above 5 C. In general, when the stale air 3 comes from a water treatment process, it has a temperature above 18 C., notably between 40 C. and 50 C.

[0192] The process and the treatment unit 13 are suitable for treating stale air 3 containing VOCs present in concentrations of greater than 10 mg/m.sup.3, preferably between 10 and 1000 mg/m.sup.3, more preferably between 10 and 35 500 mg/m.sup.3.

[0193] The efficiency of the process and of the treatment unit 13 is such that it allows circulation 31, 32, 4 of stale air 3 at a flow rate of between 100 and 20 000 m.sup.3/h. For optimal treatment performance, the circulation 31, 32, 4 of stale air 3 is performed at a flow rate of between 500 and 5000 m.sup.3/h. In other words, between 500 and 5000 m.sup.3 are injected into the contactor 2 and are recovered at the outlet of the contactor 2, and thus of the filter unit 5, per hour.

[0194] Needless to say, the invention is not limited to the examples that have just been described and numerous amendments may be made to these examples without departing from the scope of the invention.

[0195] Thus, in variants that may be combined with each other of the embodiments described previously:

[0196] the stale air 3 injected 1 into the contactor 2, or into the treatment unit 13, has a temperature above 5 C., and/or

[0197] the stale air 3 injected 1 into the contactor 2, or into the treatment unit 13, has a temperature of between 15 and 60 C., and/or

[0198] the stale air 3 injected 1 into the contactor 2, or into the treatment unit 13, has a temperature of between 5 and 80 C., and/or

[0199] the flow rate of the liquid 6 circulating 61, 62 in the contactor 2 relative to the flow of stale air 3 circulating in the contactor 2 is less than 20 l/m.sup.3, and/or

[0200] the cooling liquid 10 and/or the liquid 6 circulating 61, 62 in the contactor 2 have a temperature of 5 C., and/or

[0201] the temperature of the cooling liquid 10 is equal to the temperature of the liquid 6 circulating 61, 62 in the contactor 2, and/or

[0202] the liquid 6 circulating 61, 62 in the contactor 2 and/or the cooling liquid 10 is industrial water filtered at 250 m, and/or

[0203] the process involves: [0204] injection 63 of the liquid 6 circulating 61, 62 in the contactor 2 into the second part 22 of the contactor 2, and then [0205] reinjection 64 of the liquid 6 which has circulated 61 in the second part 22 of the contactor 2 into the first part 21 of the contactor 2, and/or

[0206] the process includes a step 9 of heating the stale air 3 prior to the circulation 4 of the stale air 3 in the filter unit 5, and/or

[0207] the stale air 3 is heated to a temperature above 3 C., and/or

[0208] the stale air 3 is heated to a temperature of between 5 and 35 C., preferably between 10 and 30 C., and/or

[0209] the stale air 3 is heated to a temperature of 25 C., and/or

[0210] the cooling liquid 10 is recovered 102, at the outlet of the heat exchanger 8, and is reinjected: [0211] into the contactor 2, and/or [0212] into a circuit for the liquid 6 circulating 61, 62 in the contactor 2, and/or

[0213] the circulation 31 of the stale air 3 in the first part 21 of the contactor 2 takes place in an ascending swirling movement 31 around the central zone 22 of the contactor 2; the circulation 32 of the stale air 3 in the second part 22 of the contactor 2 takes place in a substantially rectilinear downward movement 32 in the central zone 22 of the contactor 2, and/or

[0214] the efficiency of the process and of the treatment unit 13 is such that it allows circulation 31, 32, 4 of stale air 3 at a flow rate of between 250 and 10 000 m.sup.3/h,

[0215] the unit 13 for treating stale air 3 is arranged so that the liquid 6 circulating 61, 62 in the contactor 2 is injected 63 into a first part 21 of the contactor 2 and so that the liquid 6 which has been injected 63 into the first part 21 of the contactor 2 is reinjected 64 into second part 22 of the contactor 2, and/or

[0216] the refrigerating unit 11 may be any device designed to produce cold, such as: [0217] a gas compression system, or [0218] a gas absorption system, or [0219] a heat pump system, or

[0220] the cooling liquid 10 and the liquid 6 circulating 61, 62 in the contactor 2 are recovered, respectively 102 and 66, in a tank 14 to be reinjected 64: [0221] into a cooling liquid circuit 10, and/or [0222] into a circuit for the liquid 6 circulating 61, 62 in the contactor 2, and/or [0223] into the second part 22 of the contactor 2, and/or

[0224] the contactor is a contactor of the following type: [0225] spray column, or [0226] packed column, or [0227] tray column, or [0228] bubble column, or [0229] falling-film column, and/or

[0230] the treatment unit 13 comprises several contactors 2, and/or

[0231] when the treatment unit 13 comprises several contactors 2, the contactors 2 are arranged in series.

[0232] Furthermore, the various features, forms, variants and embodiments of the invention can be combined with each other in various combinations provided that they are not incompatible or mutually exclusive.