Ventilation Modeling for Dubai's Deep Sewer Tunnels

摘要

Under the Dubai Municipality's ambitious Deep Strategic Sewerage Tunnel (DSST) program, wastewater will be collected from Deira (DSST-DR) and Bur Dubai (DSST-BD) catchment areas and conveyed to large terminal pumping stations (TPS), one located at the tunnel terminus for both DSST-DR and DSST-BD, lifting to Al Warsan (WSTP) from 64 m and Jebel Ali (JSTP) wastewater treatment plants from 90 m respectively. Accurate prediction of ventilation dynamics and sizing odor control facilities are essential to prevent release of foul air from deep sewer tunnels beneath the streets of Dubai. Friction between the wastewater and tunnel headspace works not only to accelerate the sewer air but also could causes air ejection and odour release from the sewer. As the fast-moving wastewater can accelerate air, joining a slow-moving wastewater can retard air movement when the wastewater dramatically decelerates. When this happens, the fast-moving air from upstream collides with slow-moving air segment and generates a high pressure zone. The pressure created could be small but could also be enough to push out odorous air and cause complaints. It was determined that natural friction drag effect is not sufficient to keep the deep sewer tunnels under negative pressure. Ventilation model developed for Dubai's deep sewer tunnels revealed that forced ventilation coupled with air jumper configuration at the Vortex Drop Shaft (VDS) provide much better ventilation maintaining negative pressure within the tunnels. For DSST-DR tunnel, in addition to an Odor Control Facility (OCF) at the TPS, two regional OCFs and two VDS with air jumpers are required. For DSST-BD tunnel, in addition to an OCF at the TPS, three regional OCFs and three VDS with air jumpers are required. Each OCF provides 500 Pascal draft pull pressure at the tunnel.