Field Enhancements of Packed-Bed Performance for Low-Concentration Acidic and Basic-Waste Gases from Semiconductor Manufacturing Process

Abstract

Low-concentration acidic and basic-waste gas pollutants contribute significantly in the total emission of a facility. Previous results show that the control of high volumetric flow rate (∼ 500 m³/min), low-concentration acidic (<1 ppm by vol) and basic (<3 ppm by vol) gases from semiconductor process vent, by conventional wet scrubbing technique is a challenging task. This work was targeted to enhance the performance of packed beds for high-volumetric flow rate, low-concentration acidic (HF, HCl), and basic (NH₃)-waste gases from the semiconductor manufacturing process. The methodology used to meet the goal was the application of fine-water mist over the inlet stream before entering to the packed bed and use of the surfactant with mist/packed-bed liquid in low concentration. An experimental study was carried out in two acid-packed beds to optimize the operating conditions, such as pH of the liquid, circulating liquid flow rate, blow-down cycle, and so forth. The relationship among liquid pH, liquid ionic concentration, and the removal efficiency of the packed bed for the pollutants has been discussed considering chemical equilibrium, two-film theory, and Henry’s law. For the potential utilization of scrubbing water, the dependency of the efficiency on blow-down cycle was studied, and a mechanism is suggested. The proposed water-mist surfactant system was installed in two acid-packed beds, and performance of the packed beds was compared. The background efficiencies of the acid-packed beds for HF, HCl, and NH₃ were found max to be (n = 11) 53, 40, and 27%, whereas after installation of the system, they increased significantly and became 76 ± 13% (n = 10), 76 ± 8% (n = 7), and 78 ± 7% (n = 7), respectively, for inlet concentrations of HF and HCl <1 ppm and NH₃ <14 ppm. The mechanism by which the surfactants operate to enhance the removal in scrubbing process is suggested considering the hydrodynamic effect and the interfacial effect with the charge-generating characteristic of surfactants on water surface, when dissolved into water. The results show that a proposed rectification system can effectively reduce the emission rates below the regulatory level (0.6kg/hr) at the present conditions of the facility.