EFFECTIVE DEODORIZATION FOR BIOLOGICAL DEPURATIONS SEWAGE PLANTS
Thanks to the acquired experience and know-how, TWT is a reference in designing and manufacturing installations for process fluid treatment.
The scrubbers built by TWT are made with thermoplastic materials (such as polypropylene, PPS or PVC), both in horizontal axis configuration and vertical axis configuration. The functioning process includes a countercurrent washing between the ricirculated liquid, vaporized by the distribution nozzles, and the gas to be treated. The contact surface is increased by means of high efficiency packing materials, which ease the contacts between the two phases.
In the horizontal scrubbers the liquid meets the gas perpendicularly to its flow, in those with vertical axis the washing is in countercurrent. For a proper operation of the scrubbers is sometimes necessary the use of chemical products such as adsorption adjuvant, can be also necessary to design consecutive washing stages. The dosing of the chemical reagents, suitable to the used process, happens in a automatic way, under the control of the equipment for the PCS/DCS plant management, which controls the solution discharge and the process parameters.
Our abatement towers are designed to treat gases and odour generating vapors with air flow rate from 2.000 up to 500.000 m3/h and to guarantee the full respect of the emission limits stated by the international standards A.I.A. (Autorizzazione Integrata Ambientale).
FIVE STAGES WET SCRUBBER
One of the most innovative plants we built is the one installed in the Sewage treatment plant of the City of Monza, conceived to solve the problems related to the emissions and the odours coming from the sludge treatment line of the urban sewage treatment plant.
The plant is designed with 5 washing and deodorization stages, built in two towers (wet scrubbers) working in series for the abatement of the vapours transported by the mixed air flow constituted by the air draft coming from the tanks of sludge oxidation, from the tanks of primary sludge collection, from the tanks of the sludge digested by the anaerobic stabilization, from the tanks of the sludge mechanically thickened and from the post combustor of the thermal sludge treatment unit.
TREATED AIRFLOW
The first abatement tower has inside two separated chemical washing stages, the second one has three (the first two equal to the ones of the first tower, plus a neutral final washing). The contact time and the definition of the project parameters are in compliance with what provided by the guide lines of Regione Lombardia.
The mentioned washing stages have packed beds filled by random rings to reach the best contact with the aspirated gasses. The structure of the described rings creates a thick mesh layer on which the washing liquid sprayed and the polluted air, in upward motion, go in contact: in that very moment begins the chemical reaction that causes the neutralization of the pollutants in the air flow. After the washing stages, in both towers, the vapours cross a demister.
The fumes, then, are conveyed to the treatment unit with a activated carbon filtration system, as safety measure. The installation, designed that way and automatically managed by a DCS supervisor is able to reduce the odour from 10.000 u.o/m3 to 500 u.o/m3 after the wet scrubber, solving what was a critical point for the neighborhood.
