Biological and Chemical Scrubbings of Vented gas from hot-melting operation of recycled nylon plastics
| Autor: | Kuan-po Chen, 陳冠博 |
|---|---|
| Jazyk: | en_US |
| Rok vydání: | 2014 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 102 This study aimed to develop a biotrickling-biofilter process and a two-stage chemical scrubbing process to absorb and oxidize VOCs in vented gas from hot-melt granulation of waste nylon at 250oC as a renewable raw material. The gas contains fumes and volatile organic compounds (VOCs) with unpleasant plastic-burning odors which may arise complaints when smelled by nearby residents. A pilot-scale biotrickling-biofilter consisting of an acrylic column (14 cm sq. × 120 cm H) was used for the test. The column was initially packed with 19.6 L of prepared fern chips to a height of 100 cm. A 20-L nutrient solution tank with an effective volume of 16 L and a circulation pump with a pumping rate of 10 L min-1 were provided for moistening and nutrition of the biomedia. The bio-treated gas vented from the bio column was either vented to the atmosphere or introduced to a column of 5.2 cm inner diameter packed with 30 g of cylinder-type granular activated carbon (GAC) of 2-3 mm in diameter and length. The GAC was intended to adsorb residual VOCs or odorous compounds from the bio-treated gas. Results of the biotreatment test indicate that oxygen- and nitrogen-containing hydrocarbons as well as paraffins were major VOCs (volatile organic compounds) emitted from thermal smelting of recycled nylon at 250oC. With operation conditions of media pH of 5.5-7.0, EBRT (empty bed retention time) of 6-12 s, influent THC (total hydrocarbons) concentrations of 0.65-2.61 mg m-3, and volumetric organic loading of 0.05-0.85 g m-3 h-1, the fern chip packed biofilter with nutrients of milk, potassium dihydrogen phosphate, and glucose could achieve an overall THC removal efficiency of around 80%. Burnt odor emitted from the smelting of the recycled nylon could be eliminated by the biofilter. Estimations indicate that for scrubbing 1000 actual cubic meters (Am3 @25oC) of the exhaust gas and the total cost of chemicals and electricity is around US $0.41 (NTD 12.2). In the chemical scrubbing process, sodium hypochlorite (NaOCl) solutions were used to scrub and oxidize the VOCs and the associated odors from the hot-melting exhaust. An alkaline hydrogen peroxide (H2O2) solution was followed to remove chlorine (Cl2) emitted from the oxidative solution. Laboratory scrubbing bottles with a liquid volume of 300 mL were used with the hot melt gas injected into the system at a rate of 1 L min-1 at 25oC. Results from the chemical scrubbing tests indicate that by purging the test gas through a solution with available chlorine (Cl2) of 15-95 mg L-1 at an adjusted pH (6.54-10.8), and then through a solution with pH in the range of 12.0-12.4 and 0.35% H2O2, 95% of the VOCs in the range of 15.0-28.5 ppm (expressed as methane equivalent) were removed. The pungent burnt plastic odor in the test gas was almost completely removed. Estimations indicate that it requires around 0.058, 0.0517, and 0.0949 kg of NaOCl solution (12% available Cl2), H2O2 solution (35% H2O2), and sodium hydroxide solution (45% NaOH), respectively, for scrubbing 1000 normal cubic meters (Nm3) of the exhaust gas and the total chemical costs is around US $0.07 (NTD 2.1). This study has developed a new, effective, and economic process for reducing odorous compounds in hot-melt gas. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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