EFFECT OF FEEDING OXYGEN FRACTION ON GAS EMISSION AND SOLID RESIDUE FROM OXIDATIVE THERMAL TREATMENT OF OILY SLUDGE

摘要

Oily sludge is one of the major industrial wastes and a large portion of it contains combustible components with high heating values. One of the current major methods to dispose of oily sludge is oxidative thermal treatment. Experiments were performed in this study to understand the effects of its operating conditions on the gas emission and solid residue from the oxidative thermal treatment of oily sludge. The experimental conditions employed were: gas flow rate of 50 cm~3/min (value at 298 K) for 300 mg dry waste, a constant heating rate (HR) of 5.2 K/min, the oxygen concentrations in air of 1.09, 4.83, 8.62 and 20.95 vol. % , and the temperature (T) range of 378 ～925 K. Experimental results showed that the residual mass fractions (Ms) were about 78.95, 28.49, 8.77 and 4.13 wt. % for the HR of 5.2 K/min at the oxidative thermal decomposition temperatures (Ts) of 563, 713, 763 and 873 K for 20.95 vol. % O_2, respectively and the Ms for 8.62, 4.83 and 1.09 vol. % O_2 at the T of 873 K were 4.87, 7.94 and 9.44 wt. %, respectively. Higher O_2 concentration enhanced the oxidative thermal decomposition reactions and reduced the residual mass. The major emitted gases were CO, CO_2, hydrocarbons (HCs), H_2O and H_2. The HCs mainly consisted of low molecular paraffins, especially C_1. Also, experimental results showed that the formation of HCs involved two major peaks at 20.95 and 8.62 vol. % O_2. The total accumulated masses of HCs of 20.95 and 8.62 vol. % O_2 in 425～925 K were 64,923 and 72,593 μg/L, respectively. The T ranges corresponding to the maximum production rates of CO_2, and of CO, HCs and H_2 were 788 ～ 813 K and 713 ～ 738 K for the O_2 concentration in air of 20.95 vol. % , respectively. The incineration efficiencies η_i ( =CO_2/(CO_2 + CO)) of oily sludge for the accumulated gas emission in the range of 425～925 K were 46.34 and 50.11 for 20.95 and 8.62 vol. % O_2, respectively. However, the values of η_i for the instantaneous gas emission at 913 K were about 96.9 and 95.78% for 20.95 and 8.62 vol. % O_2, respectively. The effect of oxygen concentration on the η_i was not so obvious. After the combustion of the emitted gases, high T was needed in order to increase the value of η_i to become greater than 99.9%.