Regenerative Thermal Oxidation of Airborne N, N-Dimethylformamide and Its Associated Nitrogen Oxides Formation Characteristics
Abstract In this study, a two-bed electrically heated regenerative thermal oxidizer (RTO) was used to test the thermal destruction and oxides of nitrogen (NOx) formation characteristics in burning airstreams that contain either N, N-dimethylformamide or dimethylformamide (DMF) mixed with methyl ethyl ketone (MEK). The RTO contained two 0.152 m × 0.14 m × 1 m (L × W times] H) beds, both packed with gravel particles with an average diameter of approximately 0.0111 m and a height of up to 1 m with a void fraction of 0.42 in the packed section. The thermal recovery efficiency (TRE) and the gas pressure drop over the beds were also studied. Experimental results reveal that, with a valve shifting time (t s) of 1.5 min, a superficial gas velocity (U g) of 0.39 m/sec (evaluated at an influent air temperature of around 30 °C) and preset maximum destruction temperatures (T S) of 750–950 °C, no NOx was present in the effluent gas from the RTO when it was loaded with DMF-free air. When only DMF was present in the influent air, the average destruction efficiencies exceeded 96%, and increased with the influent DMF concentration from 300 to 750 mg/N∙m3. The “NOx-N formation/DMF-N destruction” mass ratios were in the range 0.76–1.05, and decreased as the influent DMF concentration increased within the experimental range. When both DMF and MEK were present in the influent gas, the NOx formation ratio was almost the same and the DMF destruction efficiency increased with the influent MEK/DMF ratio from 150/300 to 4500/300 (mg/mg) and in the preset temperature range. The NOx formation ratios were in the range 0.75–0.96. The TRE decreased as U g increased but was invariant with T s. The Ergun equation was found to suffice in the estimation of the pressure drop when the gas flowed over the packing beds.
Assessment of the strategies for reducing VOCs emission from polyurea-formaldehyde resin synthetic fiber leather industry in Taiwan
This study provides a novel attempt to assess the effectiveness of control strategies for reducing volatile organic compounds (VOCs) emission from polyurea-formaldehyde resin synthetic fiber leather (PU) industry. Dimethyl formamide (DMF), major content of solvents, accounts for roughly 2500 tonnes/year to avoid excessive viscosity of polyurea-formaldehyde and to increase facility in working. The other solvent contents, methyl ethyl ketone (MEK) and toluene, are used as carrier of DMF. Emission of these VOCs from solvent causes serious odor problems. It is important to know the VOCs pollution sources and emission characteristics before treating the VOCs in PU industry. In this study, 80 stacks in five factories were tested to evaluate emission characteristics at each VOCs source. After examining the VOCs concentrations in the flue gases and contents in the PU, the DMF emission rate before treatment and from fugitive source is 2300 and 80 tonnes/year, respectively. To reduce VOCs emission rate, it is important to assess reducing solvent content in painting and increasing control efficiency of treatment equipment. In this study, the zeolite rotator is recommended to be used as effective control equipment.
Solitary Orbital Paget Disease: A Case Report
Purpose: To describe the clinical findings in a patient who had developed painless supraorbital prominence. Methods: Clinical and histopathological findings of the case are reviewed and presented. Results: The patient had an isolated histologically confirmed Paget disease of the orbit. Local excision of the lesion was performed. Conclusion: Paget disease can present not only as a diffuse process but also as a painless, solitary lesion of the orbit.