Abstract:
Fugitive emissions of odour and other pollutants from inside structures provide many challenges for monitoring, modelling and control. Capture using extraction allows treatment of these emissions before discharge up a stack. However the quantity that escapes capture is difficult to estimate and depends on ambient wind, size and orientation of openings, location of the source within the structure, and extraction air flow.
This paper presents an example assessment of effectiveness of capture inside a structure containing liquid waste. The pressure differential between inside and outside the structure was measured across openings. Fluctuations in pressure were large relative to the values being measured, so both an inclined manometer and a digital manometer were used. Wind speeds and direction was also measured on site.
Pressures typically ranged from -2 Pa to +1 Pa, but positive pressures only occurred for 1% of time. The average pressure differential was -0.73 Pa. As expected, higher negative pressures were measured across a smaller opening. Higher wind speeds coincided with larger pressure fluctuations. The ratio of opening area to enclosure area ranged from 0.002 to 0.003, within the USEPA guideline of 0.05. Average velocities across openings were calculated based on area and pressure differential, and found to be approximately 0.66 m/s inward, which meets ACGIH recommendation of 0.25 m/s. Despite there being some periods of escape, the velocity was within 0.25 m/s for 92% of time. We calculated that fugitive emissions ranged from 1 to 8% during the measurement period. The ventilation rate of 13 m3/m2h is within a recommended design criterion.
Authors: Andrew Martin
Theme: Odour assessment, management and control
Keywords: fugitive, odour, capture, pressure, monitoring
Presented at: Clean Air Society of Australia and New Zealand (CASANZ)’s International Clean Air and Environment Conference, September 2022
