ABSTRACT

In order to the intensification of gas–liquid mass transfer of MDEA-containing wastewater during wet air oxidation (WAO) process, the microbubbles and millimetre bubbles were applied by fine-pore sparger (5 and 20–30 μm) and single pore sparger (6.35 mm), respectively. Effect of the superficial gas velocity on the average microbubble size, gas holdup and oxygen mass transfer coefficient (K_La) of MDEA-containing wastewater at the ambient conditions was studied. The results showed that the microbubbles (less than 1 mm) were beneficial to enhance mass transfer process and had a higher dissolved oxygen concentration during WAO process of MDEA-containing wastewater owing to higher gas holdup and larger oxygen mass transfer coefficient. The COD removal ratio was 66% at low superficial gas velocity (u_g= 0.3 cm/s) in WAO process by microbubbles, while it achieved at high superficial gas velocity (u_g= 3.0 cm/s) by millimetre bubbles. The critical oxygen mass transfer coefficient K_La was 0.183 min⁻¹ of MDEA-containing wastewater by 20–30 and 5 μm fine pore sparger, which was 2∼5 times more than that of single pore sparger (<0.1 min⁻¹). The microbubbles could improve dissolved oxygen concentration and enhance the formation of hydroxyl radical at short time with atmospheric pressure. During the WAO process, the MDEA would be converted into intermediates including formic acid, acetic acid, ammonium, nitrite and nitrate. The WAO process with microbubbles could significantly improve the gas–liquid mass transfer performance at low superficial gas velocity and greatly reduce air consumption for MDEA-containing wastewater.

摘要

为了加强湿式空气氧化（WAO）过程中含 MDEA 废水的气液传质，采用细孔分布器（5 和 20-30 μm）和单孔分布器（ 6.35 毫米），分别。研究了在环境条件下，表观气体流速对含MDEA 废水的平均微泡尺寸、气体持量和氧气传质系数 (K _{L a) 的影响。}结果表明，微气泡（小于1 mm）有利于增强传质过程，并且在含MDEA废水的WAO过程中具有较高的溶解氧浓度，这是由于较高的含气量和较大的氧传质系数。COD 去除率在低表观气速 (u _g= 0.3 cm/s) 在 WAO 过程中通过微泡实现，而在高表观气体速度 (ug ₌ 3.0 cm/s) 下通过毫米气泡实现。20~30和5 μm细孔分布器的含MDEA废水的临界氧传质系数K _L a 为0.183 min ^{-1 ，是单孔分布器（<0.1 min -1 ）的2~5倍}）。微泡可以在大气压下短时间内提高溶解氧浓度并促进羟基自由基的形成。在 WAO 过程中，MDEA 将转化为中间体，包括甲酸、乙酸、铵、亚硝酸盐和硝酸盐。带有微泡的WAO工艺可以显着提高低表观气速下的气液传质性能，并大大降低含MDEA废水的空气消耗量。