air pollution control l 16
Post on 20-Jan-2015
586 Views
Preview:
DESCRIPTION
TRANSCRIPT
L-19 and L-20Dispersion of Pollutants: Gaussian
Dispersion Model (GDM)
Air pollution and Control
(Elective -I)
Stability classes
Stability Classes
• Developed for use in dispersion models
• Stability classified into 6 classes (A – F)
• A: strongly unstable – Large lapse rates
• B: moderately unstable
• C: slightly unstable
• D: neutral- Less or zero lapse rate
• E: slightly stable – mild inversion
• F: moderately stable – moderate to severe inversion
Pasquill’s Stability table
Air Quality ModelOutput:
Concentration Distribution
Input 1:Emissions
Input 2:Meteorology
Input 3:Atmospheric
Chemistry
Input 4:Surface Properties
General Structure of Air Pollution Models
5Prof S S Jahagirdar, NKOCET
Air Pollution modeling :Parameters in Models
1. Source Parameters (Emission Characteristics)Emission rates of pollutants (mass/time)Physical location of sourceTemperature of gas releasePlume Rise
2. MeteorologyAtmospheric temp.Atmospheric stability (needed for Dipersion
coefficients) Wind velocity
3. Atmospheric ChemistryChemical Reaction in the atm.Depositions (wet or dry)
4. Surface Parameters (Properties)Surface geometry, roughness, seas, urban or rural
areas etc6
Why Use Dispersion Models?
• Predict impact from proposed and/or existing development
– NSR- new source review
– PSD- prevention of significant deterioration
• Assess air quality monitoring data
– Monitor location
• Assess air quality standards or guidelines
– Compliance and regulatory
• Evaluate AP control strategies
– Look for change after implementation7
Why Use Dispersion Models?
• Evaluate receptor
exposure
• Monitoring network
design
– Review data
– Peak locations
– Spatial
patterns
• Model Verification
8
Model Assumptions• Gaussian dispersion modeling based on a
number of assumptions including
– Steady-state conditions (constant source emission strength)
– Wind speed, direction and diffusion characteristics of the plume are constant
– Mass transfer due to bulk motion in the x-direction
– Conservation of mass, i.e. no chemical transformations take place
– Wind speeds are >1 m/sec.
– Limited to predicting concentrations > 50 m downwind
9
10
11
• Horizontal dispersion coefficient
12
• Vertical dispersion coefficient
13
Atmospheric Stability Classes
14
Dispersion Coefficients: Horizontal
15
Dispersion Coefficients: Vertical
16
17
Maximum Ground Level Concentration
Under moderately stable to near neutral conditions,
zy k ss 1
The ground level concentration at the center line is
2
2
21 2
exp0,0,zz
H
uk
QxC
ss
The maximum occurs at
2 0/
HddC zz ss
Once sz is determined, x can be known and subsequently C.
,0,0 exp 1 0.1171y z y z
Q QC x
u us s s s
---------------- Eq - A
Put in Eq - A
How to use GDM?Need to know proper orientations of both
Source and Receptor:Source at (0,0,H) and Receptor at (x,y,z) C(x,y,z;H)
Pollutant Emission Rate from source: Q (mass of pollutant/time) NOT Volume flowrate of Stack gas
Atmospheric Stability Category (A, B, C. etc.)
18
Wind velocity at stack height : u
Dispersion Coefficients : σy and σz (can be determined from graphs)
Effective Stack height: H = hs + Δh Calculation of Plume rise (Δh ) by any one formula (Refer lecture on plume rise)
THEN USE GDM C(x,y,z;H) =….
19
Example - 1
• A stack in an urban area is emitting80 g/s of NO. It has an effectivestack height of 100 m. The windspeed is 4 m/s at 10 m. It is a clearsummer day with the sun nearlyoverhead. Estimate the ground levelconcentration at a) 2 km downwindon the centerline and b) 2 km
downwind, 0.1 km off the centerline.20
Example
1. Determine stability class
Assume wind speed is 4 km atground surface. Descriptionsuggests strong solar radiation.
Stability class B
21
Example
2. Estimate the wind speed at the effective stack height
Note: effective stack height given – no need to calculate using Holland’s formula
10
1002.0
1
212 4
p
z
zuu
22Prof S S Jahagirdar, NKOCET
p
Example
3. Determine σy and σz
σy = 290
σz = 220
290
220
23
Example
4. Determine concentration using Eq 11-12
a. x = 2000, y = 0
22
220
100
2
1exp
290
0
2
1exp
)6.5)(220)(290(
80)0,100,2000(
C
33 μg/m g/m 3.641043.6)0,2000( 5 C
24Prof S S Jahagirdar, NKOCET
Example
4. Determine concentration using Eq 11-12
a. x = 2000, y = 100
22
220
100
2
1exp
220
100
2
1exp
)6.5)(220)(290(
80)0,2000(
C
)0,100,2000(C
25Prof S S Jahagirdar, NKOCET
L-20Problems on GDM
Air Pollution and Control
Elective -I
26
Prof S S Jahagirdar, NKOCET
Example-2
• An industrial boiler is burning at 12 tons (10.9 mton) of 2.5% sulfur coal/hr with an emission rate of 151 g/s. The following exist : H = 120 m, u = 2 m/s, y = 0. It is one hour before sunrise, and the sky is clear. Determine downwind ground level concentration at 10 km.
Stability class =
sy =
sz =
C(10 km, 0, 0) =
27
Exercise-3
• If emissions are from a ground level source with H = 0, u = 4 m/s, Q = 100 g/s, and the stability class = B, what is downwind concentration at 200 m?
At 200 m:
sy =
sz =
C(200 m, 0, 0) =
28
Go to Additional problems
29
Objective Questions
Q1. GDM is used for _____________________
______________________________________.
Q2. σy and σz values depend upon __________.
Q3. In GDM ‘H’ is _________ ___________.
Q4. Greater the wind speed and mixing heights _______________ will be the concentration of pollutants.
Q5. Max ground level concentration is given by _________________ .
30
Theory Questions
Q1. What are assumptions made in Gaussian dispersion model?
Q2. What is Gaussian dispersion equation? Explain meaning of each and every term in it. Also give its different forms.
Q3. Write about how to use GDM.
Q4. What is use of Dispersion models?
Q5. Discuss parameters needed for air pollution modeling.
31
top related