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.
Treatment of gaseous toluene using a regenerative catalytic oxidizer over supported copper oxide catalysts.
Abstract Regenerative catalytic oxidizers (RCO) are conveniently used to control the emissions of volatile organic compounds (VOCs), because of their high thermal recovery efficiency (TRE) and low cost. In this work, three catalysts were prepared by impregnation, and used in RCOs to test their performance in toluene oxidation, TRE, the difference between the temperatures of the inlet and the outlet gases (Td), and pressure drop under various operational conditions. Experimental results demonstrate that 10 wt% CuCo/(G) catalyst is the best catalyst in an RCO because it is effective in treating toluene with a toluene conversion of up to 95% at the heating zone temperature (Tset) = 400°C under various conditions. The 10 wt% CuCo/(G) catalyst has the greatest tolerance against the effects of inlet toluene concentration and gas velocity (Ug), and exhibits the best performance in terms of TRE, Td, and pressure drop. The TRE range was from 90.2% to 92.9% and Td ranged from 18.2°C to 30.9°C under various conditio...
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.