Process and plant for the thermal abatement of malodorous emission from a purification plant with energy recovery from said abatement

Abstract

A process and a plant for the thermal abatement of foul air containing malodorous substances. A flow of foul air containing malodorous substances as combustive air is fed into the combustion chamber of a unit for production and recovery of energy, and a flow of exhaust gas is obtained. The flow of exhaust gas is fed into a scrubber for the abatement of polluting substances, whereby the scrubber uses water for the washing of the flow of exhaust gas, producing a flow of low-temperature purified gas and a heated washing liquid. The heated washing liquid is conveyed to at least one heating jacket of a storage tank for the biological treatment of sewage of the aforementioned purification plant.

Claims

1. A process for the thermal abatement of malodorous emissions from a purification plant with energy recovery from said abatement, said process comprising the steps of: feeding a flow of foul air containing malodorous substances emitted from a purification plant, as combustive air into a combustion chamber of a unit for production and recovery of energy, thus producing a flow of exhaust gas; feeding said flow of exhaust gas into a scrubber for the abatement of polluting substances, said scrubber using water for the washing of said flow of exhaust gas, thus producing a flow of purified gas and a heated washing liquid; transferring said flow of purified gas to a system for release into the atmosphere, for emission of said flow of purified gas into the atmosphere; conveying said heated washing liquid to a heating jacket of a storage tank for the biological treatment of sewage, said storage tank being comprised in said purification plant.

2. The process according to claim 1 comprising the further steps of: carrying out an indirect heat-exchange between said heated washing liquid and said sewage, obtaining a cooled washing liquid; conveying said cooled washing liquid upstream of said purification plant.

3. The process according to claim 1, wherein said purification plant is a plant for the treatment of waste waters and/or digestates.

4. The process according to claim 3, wherein said storage tank for the biological treatment of waste waters is a tank for de-nitrification of waste waters or a tank for the oxidation/nitrification of waste waters and/or is a digester for anaerobic digestion of the sludges produced in said plant for the treatment of waste waters and/or digestates.

5. The process according to claim 4, wherein said storage tank for the biological treatment of sewage is kept at a temperature comprised between 15° C. and 45° C.

6. The process according to claim 5, wherein said storage tank for the biological treatment of sewage is kept at a temperature comprised between 35° C. and 45° C.

7. The process according to claim 3, wherein said scrubber is fed with purified water, exiting said plant for the treatment of waste waters and/or digestates, as washing water.

8. The process according to claim 1, comprising the further steps of: transferring a heat-exchange fluid to said unit for production and recovery of energy, thus obtaining a flow of heated heat-exchange fluid; conveying said heated heat-exchange fluid to a sludge dryer of said purification plant; carrying out an indirect heat-exchange between said heated heat-exchange fluid and said sludges, obtaining a cooled heat-exchange fluid and dried sludges.

9. The process according to claim 8, wherein said heat-exchange fluid is diathermic oil.

10. A system for the thermal abatement of malodorous emissions from a purification plant with energy recovery from said abatement, said system comprising the following units: a pipe for collecting foul air containing malodorous substances coming from said purification plant; a unit for the production and recovery of energy comprising a combustion chamber in fluid communication with said collecting pipe; a scrubber for polluting substances in fluid communication with said combustion chamber, said scrubber being fed with water for the washing of an exhaust gas flow exiting from said combustion chamber and comprising an abatement chamber, a discharge opening for a washing liquid and a flow conveyor for a purified and cooled exhaust gas flow; a distribution header for said washing liquid in fluid communication with said discharge opening, said distribution header being in fluid communication with a heating jacket of at least one tank for the biological treatment of sewage of said purification plant, wherein said unit for the production and recovery of energy comprises heating means for an indirect heat-exchange between a heat-exchange fluid circulating therein and said exhaust gas.

11. The system according to claim 10 comprising the following units: an entry pipe for conveying said heat-exchange fluid to said heating means, said entry pipe being in fluid communication with said heating means; an exit pipe for the transfer of said heat-exchange fluid from said heating means to the heating jacket of at least one sludge drier of said treatment plant, said exit pipe being in fluid communication with said heating means and with said heating jacket of said sludge drier.

12. A method of revamping a purification plant comprising a system for conveying foul air containing malodorous substances, a deodorizing unit connected to said system for foul air and a system for release of purified air into the atmosphere, which is connected to said deodorizing unit, said method comprising the steps of: providing a collecting pipe and connecting it to said system for conveying foul air; providing a unit for production and recovery of energy, said unit comprising a combustion chamber; connecting said collecting pipe to said combustion chamber; providing a scrubber for polluting substances and connecting it to said combustion chamber, said scrubber being fed with water for washing an exhaust gas flow exiting from said combustion chamber, and comprising a discharge opening for a washing liquid and a flow conveyor for a purified and cooled exhaust gas flow; providing a distribution header and connecting said discharge opening for a washing liquid thereto, said distribution header being in flow communication with a pre-existing heating jacket of a tank for the biological treatment of sewage of said plant; connecting said flow conveyor to said system for release of purified air into the atmosphere.

13. The revamping method according to claim 12, wherein said purification plant is a plant for the treatment of waste waters and/or digestates.

14. The revamping method according to claim 13, wherein said scrubber is connected with a pre-existing effluent duct, in which purified water exiting from said plant for the treatment of waste waters and/or digestates flows, so that said scrubber can be fed with said purified water as washing water.

15. The revamping method according to claim 12, wherein said unit for production and recovery of energy comprises heating means for an indirect heat exchange between a heat-exchange fluid circulating in said means, and said exhaust gas, the method comprising steps of: connecting an entry pipe for conveying a heat-exchange fluid, to said heating means; arranging an exit pipe for the transfer of said heat-exchange fluid from said heating means to a pre-existing heating jacket of a sludge drier of said purification plant and connecting said heating means to said heating jacket; connecting said exit pipe to said heating jacket.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows in schematic form a system for the thermal abatement of malodorous emissions from a purification plant with energy recovery from said abatement;

(2) FIG. 2 shows in schematic form a different embodiment of a system for the thermal abatement of malodorous emissions from a purification plant with energy recovery from said abatement;

(3) FIG. 3 shows in schematic form a revamped waste water and digestate treatment plant comprising a system for the thermal abatement of malodorous emissions with energy recovery according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(4) FIG. 1 shows a system 1, indicated overall by 1, for the thermal abatement of malodorous emissions from a purification plant with energy recovery from said abatement, which implements the process according to a mode of implementation of the present invention; this system comprises the following units: a pipe 2 for collecting foul air containing malodorous substances coming from a purification plant; a unit 3 for the production and recovery of energy comprising a combustion chamber 4 in fluid communication with the aforesaid collecting pipe 2; a scrubber 5 for polluting substances in fluid communication with the said combustion chamber, said scrubber 5 is fed with water for washing an exhaust gas flow exiting from the combustion chamber and comprises an abatement chamber 6, a discharge opening 8 for a washing liquid and a flow conveyor 10 for a purified and cooled exhaust gas flow; a distribution header 15 for a washing liquid in fluid communication with the discharge opening 8 for a washing liquid and with a heating jacket of at least one tank for the biological treatment of sewage of the plant.

(5) Preferably, the flow conveyor 10 for a flow of purified and cooled exhaust gas is connected to and in fluid communication with a system for release into the atmosphere, not shown here because entirely conventional, preferably included in the plant in question.

(6) Preferably the scrubber 5 for polluting substances may be of the type described in European Patent EP 0,749,772 B1.

(7) With reference to FIG. 2, this shows a different embodiment of a system for the thermal abatement of malodorous emissions from a purification plant with energy recovery from said abatement, according to the present invention, which implements a process according to a mode of implementation of the present invention, already described with reference to the summary.

(8) More specifically, in accordance with the aforementioned particular embodiment of a system 1 according to the present invention, the unit 3 for the production and recovery of energy may comprise heating means 20, preferably a heat exchanger, for indirect heat exchange between a heat-exchange fluid circulating in these means and said exhaust gas.

(9) Moreover, the system 1 may further comprise: an entry pipe 19 intended for conveying a heat-exchange fluid, preferably a diathermic oil, to the heating means 20 and in fluid communication therewith; an exit pipe 21 for the transfer of the heat-exchange fluid from the heating means 20 to the heating jacket of at least one sludge drier of the purification plant, the exit pipe 21 being in fluid communication with the heating means 20 and with the heating jacket of said sludge drier.

(10) The remaining elements of the system shown in FIG. 2 are structurally and/or functionally equivalent to corresponding elements of the system 1 for thermal abatement of malodorous emissions previously described in FIG. 1 and these elements are attributed the same reference numbers as the latter.

(11) With reference to FIG. 3 a plant for the treatment of waste waters and digestates, denoted overall by 100, is described, said plant comprising a system 1 for abatement of malodorous emissions with energy recovery according to the present invention.

(12) The elements of the abovementioned system shown in FIG. 3 are structurally and/or functionally equivalent to corresponding elements of the system for thermal abatement of malodorous emissions previously described in FIG. 2 and these elements are attributed the same reference numbers as the latter.

(13) More specifically, the plant 100 comprises a preliminary treatment zone where the waste waters undergo screening, degritting and oil and grease removal.

(14) A primary duct 121 for foul air connected to a system 180 for conveying the foul air extends from the preliminary treatment zone 101.

(15) Downstream of the preliminary treatment zone there is a biological treatment zone 102 where the pre-treated waste waters undergo a first de-nitrification step and a second oxidation/nitrification step.

(16) The biological treatment zone 102 may comprise at least one tank for biological treatment of sewage, comprising in turn a heating jacket, for maintaining a temperature not higher than 45° C., preferably comprised between 35° C. and 40° C., inside the at least one tank for biological treatment of the sewage.

(17) The at least one tank for biological treatment of sewage which may be included in the zone 102 and said heating jacket are not shown because they are entirely conventional.

(18) A secondary duct 122 for foul air connected to the system 180 for conveying the foul air extends from the preliminary treatment zone 102.

(19) Downstream of the biological treatment zone 102 there is a tertiary treatment zone 103 for sedimentation/settling and filtration of aerated waste waters from the zone 102.

(20) Downstream of the tertiary treatment zone 103 there is located and connected a discharge outlet 104 for releasing the purified waste water into the environment or for transfer thereof to a disinfection zone, not shown since entirely conventional, downstream of which the purified waste water may be reused in the plant or conveyed in an industrial aqueduct for reuse.

(21) A sludge treatment line 105 extends from the biological treatment zone 102 and/or from the tertiary treatment zone 103.

(22) The sludge treatment line 105 comprises a pre-thickening zone 106 in which the density is increased by means of settling and elimination of resultant water which may be transferred into the preliminary treatment zone 101 of the plant 100.

(23) A tertiary duct 128 for foul air connected to the system 180 for conveying the foul air extends from the pre-thickening zone 106.

(24) The sludge treatment line comprises a digestion zone 107, situated downstream of the pre-thickening zone 106, where the thickened sludges undergo an anaerobic digestion step at a temperature typically of between 37° C. to 45° C. for a time period of about 15 to 20 days inside digesters.

(25) The sludge treatment line 105 comprises a dehydration and drying zone 108 situated downstream of the digestion zone 107, where the digested sludges are first dehydrated and then dried. The dehydration and drying zone 108 comprises a drier, not shown since entirely conventional, comprising in turn a heating jacket inside which a diathermic fluid flows.

(26) At the output of the drier there is a line 109 for the vapour condensation and a dried sludge recovery line 110.

(27) The foul air conveying system 180 is connected to and in fluid communication with a collecting pipe 2 included in a system 1 for abatement of malodorous emissions from the plant 100 for treatment of waste waters and digestates with energy recovery from said abatement.

(28) Moreover, the conveyor 10 of the system 1 according to the present invention shown in FIG. 3 is connected to and in fluid communication with a system 182 for release into the atmosphere of purified air from the waste water and digestate treatment plant 100.

(29) At the same time, the discharge opening 8 is connected to and in fluid communication with a distribution header 15 which is in turn connected to the zone 102, more specifically is in fluid communication with the heating jacket of the at least one biological treatment tank comprised therein; the header 15 is also connected to the zone 107, more specifically is in fluid communication with the heating jacket of digester included therein.

(30) The plant 100 is also connected to a pre-existing effluent duct 125 connected to the discharge outlet 104 inside which purified water from the plant flows, so as to be able to supply said scrubber with purified water as washing water.

(31) The plant 100 revamped in accordance with a revamping method according to the present invention further comprises an entry pipe 19 intended for conveying a heat-exchange fluid to the heating means 20 and in fluid communication with said means.

(32) The entry pipe 19 is connected to and is in fluid communication with the heating jacket of the drier included in the dehydrating and drying zone 108.

(33) At the same time, an exit pipe 21 for the transfer of the heated heat-exchange fluid to the heating jacket of this drier for the sludges of the plant is installed downstream of the heating means 20; the exit pipe 21 has the function of placing the heating means 20 in fluid communication with the heating jacket of the drier included in the dehydration and drying zone 108 and allows a heated heat-exchange fluid to be transferred to said jacket

(34) The revamped plant 100 described above is effectively realized by means of a revamping method according to the present invention, previously described with reference to the summary of the present invention.

(35) In particular, the revamping method according to the present invention allows the implementation of a system 1 according to the present invention operating in synergy with a pre-existing purification plant, preferably for the treatment of waste waters and digestates, such as that shown in FIG. 3, by making simple modifications thereto.

(36) In particular, as explained in detail further above, it is necessary only to connect the system 180 for conveying the foul air to the collecting pipe 2, connect the distribution header 15 to the cooling jacket of the biological treatment tanks which are to be heated and kept at a suitable temperature with the flow of washing liquid heated by means of the system 1 and, finally, connect the conveyor 10 to a pre-existing system 182 for release into the atmosphere.

(37) With reference to the latter in particular, it should be said that the treatment system 1 is perfectly compatible with a pre-existing system for release of purified air into the atmosphere forming part of a pre-existing purification plant. In fact, the system 1 allows a cooled and purified flow of air to be transferred at temperatures compatible with the materials used to manufacture the pipes of the aforementioned release system, usually plastic material.

(38) Furthermore, the revamping method according to the invention does not envisage necessary decommissioning of the pre-existing deodorizing unit 181 since the latter may be retained as an auxiliary and/or back-up apparatus.

(39) Moreover, the revamped plant 100 described above, comprising a fully operative system 1 according to the present invention, advantageously allows the abatement process to be implemented according to a particular mode of implementation of the present invention.

(40) From the description above it can be seen that the process for the abatement of malodorous emissions according to the present invention solves the technical problem and achieves numerous advantages, the first one being the fact that it is possible to perform effective and practically complete abatement of malodorous substances arising from a flow of foul air from a purification plant.

(41) Since this abatement is performed thermally a large quantity of heat is produced, also owing to the intrinsic heat value of the thus combusted malodorous substances of the foul air, which may be advantageously recycled inside the plant.

(42) At the same time, said abatement is performed by recycling a heated washing liquid as heat-exchange liquid in order to heat and keep at the required temperature the enzymatic treatment tanks of the purification plant in question, which otherwise would have to be heated in a different manner.

(43) Moreover, with the process according to the invention, it is possible to recover further thermal energy produced inside a system for implementing the said process, by means of recycling of a heated heat-exchange fluid, said fluid being transferred to a sludge drier of the purification plant in question.

(44) Therefore, in a particularly innovative and advantageous manner, the present invention provides a single process for the production of thermal energy necessary for operation of the purification plant and for abatement of malodorous emissions.

(45) In addition, in order to reduce further the consumption levels and make the process according to the invention even more sustainable in economic terms, another advantage consists in the possibility of using biogas, optionally produced by the digestion of sludges inside the purification plant, in order to feed the energy production and recovery unit according to the present invention.

(46) Moreover, with a view to saving resources, with the abatement process according to the present invention not only is it possible advantageously to feed a scrubber with purified water output from a waste water and/or digestate treatment plant, instead of with mains water, but also it is possible to transfer, once cooled, the washing water output from the heating jackets of the tanks of the biological treatment plant upstream of a waste water and/or digestate treatment plant where it can be combined with the waste waters and/or digestates to be treated.

(47) In other words, for the same production capacity, the system proposed for implementation of the process according to the present invention is able to ensure operation at lower costs compared to a system needed to obtain this production capacity using the methods of the prior art.