A prototype acid spray scrubber for absorbing ammonia emissions from exhaust fans of animal buildings
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Date
2007-07
Journal Title
Journal ISSN
Volume Title
Publisher
American Society of Agricultural and Biological Engineers
Abstract
Mitigation of ammonia (NH3) emissions from animal production buildings has been a challenge because of the
large volume of low NH3 concentration laden air being released. Among emission mitigation technologies for concentrated
animal feeding operations, acid spray scrubbers have the greatest potential for adaptation to the existing large animal
facilities because of their lower fan airflow reduction, ability to simultaneously remove particulate and gaseous pollutants,
and viability for zero or less waste generation by recycling effluents as liquid fertilizer. A multi-stage wet scrubber prototype
that can be operated with a maximum of three stages was developed and optimized for reducing NH3 emissions using simulated
conditions typically encountered at an animal building exhaust. The parameters optimized for a single-stage wet scrubber
include nozzle type, nozzle operating pressure, sulfuric acid concentration, spray coverage, and air retention time. The
optimized single-stage wet scrubber settings can remove emissions from 60% ±1% at 5 ppmv inlet NH3 concentration (IAC)
to 27% ±2% at 100 ppmv IAC at a normal exhaust superficial air velocity (SAV) of 6.6 m s-1. A high concentration of droplets
inside the contact chamber increased the rate of inter-collision between droplets, which led to high droplet coagulation and
decreased surface area for gas-liquid contact. These phenomena were prevented by operating the nozzles in the higher stages
co-current to the airflow and by using fewer nozzles in higher stage. The two-stage and three-stage wet scrubbers were
therefore optimized by determining the least number of nozzles in each stage that provided the most effective NH3 removal.
The optimized two-stage scrubber could remove NH3 emissions from 60% ±0% at 5 ppmv IAC and 35% ±1% at 100 ppmv
IAC. The optimized three-stage scrubber could remove emissions from 63% ±3% at 5 ppmv IAC and 36% ±3% at 100 ppmv
IAC. Airflow retention time was found to significantly affect NH3 absorption. Reducing the superficial air velocity to 3.3 m
s-1 from 6.6 m s-1, which increased the air retention time from 0.2 s to 0.4 s, improved NH3 removal efficiencies to 98% ±3%
at 5 ppmv IAC and 46% ±2% at 100 ppmv IAC for the single-stage scrubber. Similarly, the performance of the two-stage
scrubber at a SAV of 3.3 m s-1 improved to 77% ±0% at 20 ppmv IAC and 57% ±1% at 100 ppm IAC. Lastly, the performance
of the three-stage scrubber at a SAV of 3.3 m s-1 improved to 70% ±1% at 30 ppmv IAC and 64% ±1% at 100 ppmv IAC.
It was observed that the three-stage wet scrubber did not increase the overall wet scrubber performance, as predicted
theoretically. Further studies are needed so that the application of these scrubber designs becomes feasible for treating air
emissions from animal buildings. The wet scrubber caused an additional backpressure of 27.5 Pa, resulting in about 8%
airflow reduction for a fan operating at 12.5 Pa.
Description
Keywords
air emissions, air treatment, ammonia absorption, ammonia emissions, animal buildings
Citation
R. B. Manuzon et al, "A prototype acid spray scrubber for absorbing ammonia emissions from exhaust fans of animal buildings," Transactions of the ASABE 50, no. 4 (2007)