Optimization of Ammonia Absorption Using Acid Spray Wet Scrubbers

Abstract

<abstract> <bold><sc>Abstract.</sc></bold> Packed-bed wet scrubbers are effective for abatement of ammonia (NH₃) emissions from animal feeding operations (AFOs) but result in high air resistance. Spray scrubbers generally have relatively low air resistance and high NH₃ removal potential. This study aimed to develop a spray scrubber module (SSM) through optimization of the design and operating parameters of spray scrubbing for recovering NH₃ emissions from the exhaust air streams of animal facilities. The design parameters, including nozzle type, scrubber column size and geometry, and number of stages of the spray scrubber module, were optimized. Effects of operating parameters such as acid concentration, superficial air velocity, retention time, and inlet NH₃ concentration were quantified. Superficial air velocity adversely affected scrubber performance significantly due to its direct relationship with air residence time. The inlet NH₃ concentration was inversely proportional to the scrubber efficiency. The SSM was optimized as a hexagonal scrubber column with a diameter of 45.7 cm (18 in.) equipped with three stages of PJ40 spray nozzles, spraying 1% (w/v) H₂SO₄ scrubbing liquid counter-current to the exhaust air stream with superficial gas velocity of 3 to 4 m s^-1, equivalent to air retention times of 0.55 to 0.41 s. The SSM recovered about 91% of the NH₃ at an operating liquid pressure of 0.51 MPa, a superficial air velocity of 4 m s^-1, and an inlet NH₃ concentration of 30 ppm_v when operated with a single stage of spraying. For high inlet NH₃ concentration of 100 and 400 ppm_v, the SSM was able to reduce NH₃ by 86% and 74%, respectively, when operated at a maximum pressure of 0.62 MPa with three stages of spray nozzles and a superficial air velocity of 4 m s^-1. The pressure drop of the spray scrubber was mainly caused by the mist eliminator. The total static pressure drop of the SSM was under 15 Pa when the air velocity ranged from 2 to 4 m s^-1. The results of this study demonstrate that acid spray scrubbers could be a very effective and feasible NH₃ mitigation technology for U.S. animal farms.