CIEG 434 Air Pollution Control

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CIEG 434 Air Pollution Control
Review of some things you should know

• Ideal gas law Mass/energy balance Bernoulli
  equation and applications of the above

Note you can see the calculation spreadsheets
explaining any worked example here. To do this,
exit the show by right-clicking then select Edit
slides. Then right-click on the answer and
select Worksheet ObjectOpen.
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Ideal Gas Law

• PV nRT, ? mass/vol, so PM ?RT
• R 0.08206 L-atm-mol-1-K-1
• (Table 1.5 has R in lots of combinations of
  units)
• At STP (P1 atm, T25oC298K), this gives
• molar volume of any ideal gas as
• V/n RT/1 24.466 L/mol

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Ideal Gas Law

• MW molecular weight (actually, mass)
• units grams/mole (g/mol)
• mol is sometimes referred to as gmol

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Ideal Gas Law

• To treat air as an ideal gas, we need its
  molecular weight
• Air is approximately 78 N2, 21 O2, 1 Ar
• Assuming N2, O2, and Ar are ideal gases,
• MW of air 0.78(28) 0.21(32) 0.01(40)
  28.964 29 (g/mol, kg/kmol, lb/lbmol)

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Unit Conversions Using Ideal Gas Law

• Common units for gases ppm, ppb, ?g/m3
• Common units for particulates ?g/m3, mg/m3
• Gaseous concentrations in ppm and ppb are on a
  volume basis, not a mass basis

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Unit Conversions Using Ideal Gas Law

• Concentration in ppm
• (mole fraction, volume fraction, or partial
  pressure) x 106
• Concentration in ppb
• (mole fraction, volume fraction, or partial
  pressure) x 109
• Note I prefer to use the notations ppmv and
  ppbv to clearly indicate that these are
  volume/volume measurements. However, this is
  invariably the case when dealing with airborne
  substances.
• How to convert between ppm and ?g/m3?

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Unit Conversion Examples

• The secondary NAAQS (National Ambient Air Quality
  Standard) for SO2 is 0.5 ppm. Convert the
  concentration to ?g/m3.
• Answer

(Click to see spreadsheet calcs)

• California's air quality standard for NO2 is 470
  ?g/m3. Express the concentration in ppm.
• Answer

(Click on table to see spreadsheet calcs)
Note to see the calculation spreadsheet, you
have to exit the show by right-clicking then
select Edit slides. Then right-click on the
answer and select Worksheet ObjectOpen.
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Unit Conversion Examples (cont'd)

• An air containing 50 ppm Cl2 passes through a
  10-in. duct at 250oF and 100 psig. The gas
  velocity is uniform at 25 ft/s. What is the
  emission rate of chlorine (in lb/d)?
• Ans

(Click on table to see spreadsheet calcs)
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Mass / Energy Balance

• Maccum Min - Mout Mformed - Mconsumed
• Eaccum Ein - Eout Eproduced - Econsumed
• (e.g., 1st law of thermo DU Q - W)

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Mass Balance Example
Example 1.11 (p. 38)
What is the NO2 in the humid air? Answer
(Click on table to see spreadsheet calcs)
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Bernoulli Equation

• u2/2 ?dP/? gz constant (frictionless flow)
• For small ?P and incompressible flow, energy per
  unit mass is constant u2/2 P/? gz
• u12/2 P1/? gz1 u22/2 P2/? gz2 losses

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Bernoulli Equation

• If using the average cross-sectional flow for u
  in the Bernoulli equation, the average kinetic
  energy (u2) will be poorly estimated.
• include a kinetic energy correction factor,

(a 2 for laminar/circular, 1.01-1.1 for
turbulent flow)
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Bernoulli Equation

• One application of Bernoulli's equation is
  flowrate measurement (venturi orifice meters)
• Without heat/work or Dz, and if u2A2 u1A1

• If a1 a21, and A2/A1 B2, we get equ. 1.17

• If ideal gas, r PM/RT (equations 1.20-1.24)

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Bernoulli Equation Energy Balance

• Besides the 3 mechanical energies, a fluid also
  has internal energy (per unit mass), U
• Total energy per mass u2/2 P/? gz U
• u2/2 PV gz U (V vol/mass 1/?)
• H u2/2 gz ( H enthalpy U PV)
• Q - W (DH aDu2/2 gDz) . m

Note! Equ. 2.7 in Cooper Alley has a in the
denominator instead of the numerator. This is
incorrect but, of course, does not matter if a is
assumed as unity.
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Bernoulli Equation

• For orifice meter,

• For venturi meter,

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Energy Balance Example
Example 2.2 (p. 82) Calculate the heat removed
by cooling water.