Air Contaminants and Industrial Ventilation

Emission from stack

Thermal inversion



• Subsidence inversion :The subsidence inversions are formed by the slowly sinking air being heated by adiabatic compression. The subsiding layers are more stable than they were at their original higher altitudes. Subsiding air almost never continues downward to the earth's surface. Near the earth's surface there is always, however slight, some turbulent mixing taking place. This slow sinking is almost always counteracted by the turbulent mixing. Therefore, since subsiding air almost never reaches the ground, "subsidence inversions" are always found well above ground level.
• frontage inversion

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Comtaminated plume patterns

• Cone shape (normal)
• Fan shape (due to thermal inversion)
• Loop

  Air Quality Standard

  • Hazardous air pollutants
  • National Ambient Air Quality Standard (NAAQS)

    SO2 (0.50 ppm 3-hrs Average)

    NOx (0.053 ppm Annual mean)

    CO (9 ppm 8-hr Average)

    Ambient ozone (.08 ppm 8-hr Average)

    PM 2.5 (65 µg/m3 24-hr Average)

    PM 10 (150 µg/m3 24-hr Average)

    Lead (1.5 µg/m3 Quartely Average)

  AIR CONTAMINATION AND INDUSTRIAL VENTILATION

  Indutrial Ventilation

  • Supply Systems are uses for creating a comfortable environment such as HVAC and replacing exhaust from the plant. It can be considered as dilution control systems Typical system consists of air inlet, filter, heating and/or cooling equipment, fan, ducts,and grill or plenum. Some systems may include recirculation.
  • Exhuast System are classified in to two generics
    • General exhaust system can be used to remove the contaminants generated in space by flashing out given space with the large quantilties of air so that the average concentration is reduced to safe level.
    • Local exhuast system was designed to capture the a contaminant at or near the source. The general sytem is comprised of four basci elements; Hood, ducts, air cleaning device, and fan.

  Basic design

• Principle of air flow

  Q = Volumetric flow per minute

  V = Average velocity Ft/Min

  A = Cross-sectional area Square Ft

  Static pressure (SP) =

  Velocity pressure (VP) =

  Air flow velocity V = 4005 (VP)1/2 at 70 F and 14.7 PSI

   

• Calculating dilution and ventilation rate

   

• Design crteria

  

  Face velocity

  Capturing velocity

  Slot velocity

  Duct velocity

   

• Fume hood design

   

• Welding bench design

  Clean Air Act

  Maximum achievable control tcenology (MACT)