Session 4, Unit 7 Plume Rise

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Session 4, Unit 7Plume Rise
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Qualitative Descriptions

• Plume rise ?h
• Hhs ?h
• Driving forces
• Buoyancy
• Momentum
• Different phases
• Initial phase
• Thermal phase
• Breakup phase
• Diffusion phase

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Qualitative Descriptions

• Influencing factors
• When there is no downwash
• Exit velocity
• Stack diameter
• Stack gas temperature
• Ambient temperature
• Wind speed
• Atmospheric stability
• Wind shear
• Downwash

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Holland Plume Rise Formula

• Simple
• More suitable for power plant
• For neutral conditions
• The wind speed u is adjusted to the stack height.
• For non-neutral conditions

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Briggs Plume Rise Formulas

• More complicated
• Buoyancy flux parameter
• Momentum flux parameter

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Briggs Plume Rise Formulas

• Determination of buoyancy dominated or momentum
  dominated plumes
• Calculate (?T)c
• For unstable or neutral (A-D)
• For Fb lt55
• For Fb?55
• For stable (E,F)
• If ?T (Ts-Ta) ? (?T)c , its buoyancy dominated
• If ?T (Ts-Ta) lt (?T)c , its momentum dominated

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Briggs Plume Rise Formulas

• For buoyancy dominated plume under unstable or
  neutral conditions (A-D)
• x distance at which atmospheric turbulence
  begins to dominate entrainment
• For Fb?55 m4/sec3, x34 Fb2/5
• For Fblt55 m4/sec3, x14 Fb5/8
• xfdistance to the final rise, m
• xf3.5x
• Final plume rise

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Briggs Plume Rise Formulas

• For buoyancy dominated plume under stable
  conditions (E and F)
• Stability parameter, s
• Default values for
• 0.02 K/m for E stability
• 0.035 K/m for F stability

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Briggs Plume Rise Formulas

• Final plume rise
• Distance to final rise

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Briggs Plume Rise Formulas

• For momentum dominated plume under unstable or
  neutral conditions (A-D)
• For momentum dominated plume under stable
  conditions (E,F)
• Calculate both and use the lower one.

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Briggs Plume Rise Formulas

• Gradual rise
• Distance lt distance to final rise (i.e., xltxf)
  and Buoyancy dominated plume

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Briggs Plume Rise Formulas

• Distance lt distance to final rise (i.e., xltxf)
  and momentum dominated plume
• Jet entrainment coefficient
• Unstable conditions (A-D)

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Briggs Plume Rise Formulas

• Xdownwind distance with max value of
• Xmax49Fb5/8 for 0ltFblt55 m4/sec3
• xmax119Fb2/5 for Fbgt 55 m4/sec3
• Stable conditions (E,F)
• with

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Briggs Plume Rise Summary
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Buoyancy Induced Dispersion

• Air entrainment due to boiling-like action
  enlarges the plume
• Small impact on ground level concentration in
  most cases
• The impact can be reflected in ?
• Initial plume size
• Effective dispersion coefficients

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Session 4, Unit 8Averaging Time, Multiple
Sources, and Receptors

• Chimney, Building, and Terrain Effects

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Averaging Time

• The concentration calculated from the Gaussian
  equations should represent the averaging time
  that is consistent with the averaging time of ?
• Short-term ? 1 month
• Long-term gt 1 month

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Averaging Time

• If longer averaging time is desired, use the
  following power law
• P0.17-0.75, suggested value is 0.17

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Crosswind Averaging

• Integrate y from -? to ?
• Average over a sector

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Crosswind Averaging

• Average over a sector considering distribution of
  wind speeds and stability classes
• ISCLT3 and STAR

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Crosswind Averaging

• Smoothing transition from sector to sector
• Weighted smoothing function, WS
• Smoothed average concentration

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Multiple Sources

• The max from each source do not exactly overlap
• Use of multiple stack factor
• More accurate method modeling with a consistent
  coordinate system

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Receptors

• Receptor grid
• Cartesian coordinate system
• Polar coordinate system
• Single stack, but the origin of the coordinate
  system is not at the stack base
• Multiple stacks
• Presentation of results
• Concentration isopleths

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Example Calculation

• Chapter 10

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Chimney Effects

• Stack tip downwash
• Low pressure behind stack
• u is at the stack top level
• No plume rise (plume sink)
• Avoid stack tip downwash

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Building Effects

• General description
• Expanded meaning of building
• Reduce building effects rule of thumb
• hsgt2.5hb
• Too conservative for tall thin buildings

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Briggs Procedure to Minimize Downwash

• Five steps
• Correction for stack induced downwash
• Correction for building effects
• Determine if plume is entrained in the cavity.
  If entrained, treat it as a ground level source
• Buoyancy effect
• Calculate downwind concentration

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Cavity

• Description
• Cavity length
• Short buildings (L/H?2)
• L affects cavity length xr
• Long buildings (L/Hgt2)
• L does not affect cavity length xr

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Cavity

• Max cavity width
• Its location long x direction
• Max height

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Cavity

• Concentrations within cavity

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Wake Downwind of Cavity

• Treated as a ground level source
• Turner method (virtual source)
• Gifford method
• Gifford-Slade method (total dispersion
  parameters)
• Huber-Snyder method

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Sources Downwind of Buildings

• Briggs method
• Beyond 3?b ? no building effect
• Within 3?b ? treat them as ground level sources

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Complex Terrain

• Definition
• Simple terrain
• Complex terrain
• Intermediate terrain
• Plume behavior in complex terrain

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Complex Terrain

• Modeling approaches
• Briggs
• Egan
• Bowne
• Modified dispersion coefficients
• ISC3 (COMPLEX 1) to be discussed later

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GEP Stack Height

• Definition
• Greater of
• 65 m
• HGH1.5L (for stacks in existance on Jan 12,
  1979, HG2.5H)
• Structures to be considered within 5L
• In modeling analyses, no credit is given for
  stack height above the GEP