La Motta, Franesco (2017) Innovative processes for submicron particle removal. [Tesi di dottorato]

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Item Type: Tesi di dottorato
Resource language: English
Title: Innovative processes for submicron particle removal
La Motta,
Date: 10 April 2017
Number of Pages: 145
Institution: Università degli Studi di Napoli Federico II
Department: Ingegneria Chimica, dei Materiali e della Produzione Industriale
Dottorato: Ingegneria dei prodotti e dei processi industriali
Ciclo di dottorato: 29
Coordinatore del Corso di dottorato:
Di Natale, FrancescoUNSPECIFIED
Date: 10 April 2017
Number of Pages: 145
Keywords: Condensational growth, particulate matter
Settori scientifico-disciplinari del MIUR: Area 09 - Ingegneria industriale e dell'informazione > ING-IND/25 - Impianti chimici
Date Deposited: 25 Apr 2017 18:04
Last Modified: 08 Mar 2018 13:49
DOI: 10.6093/UNINA/FEDOA/11840

Collection description

The removal of fine (FP dp < 2000 nm) and ultrafine particles (UFP dp <100 nm) from anthropogenic flue gases is becoming a priority of environmental chemical engineering because of their toxicity for humans and their contribution in climate change. In fact, once inhaled, particles finer than 300-500 nm penetrate the deepest regions of the lungs and even cross the cellular membranes, reaching the circulatory system and causing a wide range of health problems. In addition, fine and ultrafine particles affect atmosphere and climate characteristics in complex and sometimes still undetermined ways, according to their physical nature. In general, the presence of high particles contamination in the atmosphere is associated to reduction of visibility in cities and scenic areas, cloud formation, secondary reactions of atmospheric pollutants and radiative forcing phenomena. Fine and ultrafine particles are primarily emitted by combustion processes some of which are located close to high population density area (vehicular traffic, harbours, industrial areas, residential heating) increasing significantly the exposure risk: while the overall particle exposure appears as a limited concern, regional effects are often significant and affect a wide fraction of the world population. Following the pertinent regulation on air quality and pollution control, the design of conventional fine particle abatement devices was optimised to achieve a very high reduction (even higher than 99.5%) of the emitted particles in mass. Therefore, they are very effective in removing the largest particles (whose weight highly influences the mass removal efficiency) but are far less efficient toward the particles ranging from 100 to 2000 nm, range called Greenfield Gap. To this end, new technologies able to effectively handle both coarse, fine and ultrafine particles are under development. Among them, it is worth mentioning wet electrostatic precipitators, agglomerates, wet electrostatic scrubbers, pool scrubbing and condensational growth assisted treatment units. The rationales for using condensational growth as a pre-treatment are that the liquid-solid aerosols can be more easily captured because, their size is larger than the critical regions and the presence of a water shell may favour their sticking with the water-gas interface. Condensational growth can be adopted to increase the removal efficiency of different wet particle removal technologies. The purpose of this work was to study an innovative system to remove fine and ultrafine particles. The concept design was to couple the gas treatment devices with the condensational growth aimed to enhance the particles collection. Among the removal techniques, the work focused on the bubble columns and the wet electrostatic scrubbers. The concept design consisted to pre-treat particles laden gas in a growth unit in order to generate a solid-liquid aerosol with larger size that, fed to the removal units, was more easily captured. The growth unit consisted in a growth tube (GT), made up by a glass cylinder high 40 cm and with an internal diameter of 1.5 cm. The concept of the growth unit was to make in contact the aerosol with a warmer liquid film. The supersaturation levels depended on the temperature gradient and the gas velocity. The bubble column (BC) consisted in a glass bottle filled with distilled water (ID= 10 cm, H= 20 cm) having a porous ceramic distributor (D=8 mm) placed 1 cm above the bottom from which the gas enters the bottle and a gas outflow at the bottle cap. The wet electrostatic scrubber (WES) consisted in a cylinder in plexiglass 40 cm high and with an internal diameter of 4.5 cm. It is equipped with an electrospray unit that houses on the top of the chamber. The lateral surface of the reactor presents two 10 mm holes for gas inlet and outlet. Two different set of experiments were carried out. A first set of experiments was carried out to measure the aerosol growth obtained in the GT and to verify the conditions at which the heterogeneous condensation took place. The second one was meant to measure the particles abatement in the GT, BC, WES and the entire GT-BC and GT-WES systems. The experiments were performed at a gas flow rate of 48 L/h with the GT operated at liquid temperature between 30 and 70°C. Five different materials were tested: sodium chloride, titanium dioxide, carbon black and calibrated nanoparticles of polystyrene with a mean volume diameter of 100 and 200 nm. The aerosol was generated by an aerosol generator (TOPAS ATM 221) and monitored by two different diagnostic system: the TSI 3340, based on a light scattering measure, and a TSI 3910, based on the electrical mobility measure. The experimental results on the particle growth showed that at the exit of the GT the initial wide distribution changed towards more narrow shape and moved towards larger particles. This behaviour was observed for all the materials and the mode of their distributions at the highest temperature was roughly 350 nm. Moreover, the supersaturation levels established in the GT for each film temperature were evaluated and it was observed that the particles started to grow at supersaturation level much lower than that one predicted by the classical theory. A deep investigation of the physic of the condensational growth was accomplished in order to explain these experimental evidences. The experimental results on the particle abatement showed that the GT contributed to the particle removal and had a “cut-off” for particles larger than 500 nm. The tests run with the whole systems showed that indeed the efficiencies of both the BC and the WES improved significantly when the particle growth was observed. The BC had the maximum increment of roughly 100% at 70°C for all the tested aerosols, while the WES had the maximum improvement at 50°C for most of the tested particles, suggesting the presence of an optimum between the particles growth process and its capture mechanisms.


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