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Prof. Jiakuan Yang
Huazhong University of Science and Technology
Air Pollution Control Air Pollution Control EngineeringEngineering
Lecture Lecture 7-1 7-1 General ideas in air pollution controlGeneral ideas in air pollution control
Ⅰ Three alternative for air pollution control
Ⅱ air pollution control systems and equipment
Ⅲ Fluid velocities in air pollution control
equipment
Ⅳ Minimizing volumetric flow rate and pressure
drop
Ⅴ Efficiency, penetration, nines
Questions for the Last Lecture
1. What are three alternatives for air
pollution control?
2. Please give three logical approaches to
improving dispersion.
3. How to deal with the collected pollutants in
down-stream pollution control device?
Answer (1)
Process change and pollution prevention
Down-stream control device
Improving dispersion
Answer (2)
Tall stack
Intermittent control schemes
Relocate the plant
Answer (3)
Reuse the collected pollutants if the
concentration is high enough to
recovery, such as, raw materials, fuels
Ultimate disposal of the rest pollutants
by landfill or combustion.
Ⅴ Efficiency, penetration, nines
Downstream control device
C0
Q1C1Q0C0
C1
Q0C0 Mass flow rate of contaminant into the device
Q1C1 Mass flow rate of contaminant out of the device
Ⅴ Efficiency, penetration, nines
00
11
00
1100 1CQ
CQ
CQ
CQCQ
00
111CQ
CQefficiencyp
1p
Efficiency
penetration
nines 99% 99.9%90%
Ⅴ Efficiency, penetration, nines
(2) 11 2112211
222 CQCQ
CQ
CQ
00
331CQ
CQoverall
)1(11 1001100
111 CQCQ
CQ
CQ
Q1C1Q3C3
Q2C2Q0C0
(3) 11 3223322
333 CQCQ
CQ
CQ
Ⅴ Efficiency, penetration, nines
1 2 3
1 1
2 2
3 3
1 2 3
1
1
1
1
1
overall
overall overall
PP P
P
P
P
P PP P
3210033 111
(3) in to (2) and (1)
CQCQ
substitute
321
33
1111
in to CQ
overall
overallsubstitute
In the terms of penetration
Ⅵ Homogeneous and non-homogeneous pollutants
•CO, SO2 are homogeneous
Every CO molecule is identical to every other CO molecule .
•Particles are not homogeneous
different particle with various sizes .
Ⅶ combustion
Most air pollutants are created and released in
processes involving combustion, transportation , fuel
combustion , industrial processes, solid wastes
incineration , miscellaneous .
Ⅶ combustion
(1) basic combustion equation
OHy
xCOOy
xHC yx 222 24
(2) Heat of combustion
In combustion , we will have removed a finite amount of energy in the form of heat , called the heat of combustion .
The higher heating value, water is condensed .
The lower heating value, water as gas less than the higher heating value by the amount of that latent heat of condensation .
Ⅶ combustion (3) Explosive or combustible limits
Too rich to burnFlammable
ymethane
T, 0 F
0.0 0.40.30.20.1 0.5
2000
Too
lean
to b
urn
1000
3000
4000
0
UE
L
LE
L Sto
ichi
omet
ric
Ⅶ combustion
1 mol CH4 need 2 mol O2.
O2 in air is about 21%, so the needed air is 2/0.21.
Stoichiometric mixture (理论完全燃烧混合物 )
The mixture of air and combustible gases in the state of complete combustion.
OHCOOCH 2224 22 1 2
(3) Explosive or combustible limits
(volume % methane ) mol % methane =
21.02
1
1
= 0.095 = 9.5%
Ⅶ combustion
LEL (Lower Explosive Limit) , leans limit
A lower limit value, less than which mixture will not burn, expressed as the concentration of the combustible gas .
UEL (Upper Explosive Limit ) ,rich limit
(3) Explosive or combustible limits
Ⅶ combustion
LEL and UEL often are expressed in the ratio of the mole
percent of methane in the limit mixture to that in the
stoichiometric mixture.
UEL%164095.0
1555.0
LEL %46095.0
0436.0
(3) Explosive or combustible limits
Ⅶ combustion
Two types expressions
y methane = volume%
y methane, in the limit mixture
y methane, in the stoichiometric mixture
Fig. 7.4, Page 181
Table 7.1, Page 179
(3) Explosive or combustible limits
n
n A/F
fuel
air
fuel
air
M
M
Ⅶ combustion (3) Explosive or combustible limits
Mass of air
Mass of fuel
Ⅶ combustion
products change
(4) The volume and composition of combustion products
volume change
Fuel (CxHy)
Air(O2、 N2
)
Products of combustionOH
yxCOO
yxHC yx 222 24
4n
1)1(21.0
1n y/2x
n y/2 x out mol Total
1121.0
1
2
y x
21.0
179.0
2
y x
79.02
y xout mol Total
stoich
stoich
total
yx
XE
n
xE
n
nEE
X
EnnXn
stoich
stoich
stoich
stoichdrydry
(4) The volume and composition of combustion products The faction of excess air
humidity
Product of CO2Product of H2O Humidity N2 Excessive of Oxygen
Ⅷ Changing Volume Flow rate
Air flow in Air flow out
m· =100lbm/min
T = 500 0F =260 ℃1atm
m· =100lbm/min
T = 300 0F = 148.9 ℃1atm
Q=? Q=?
/756.0
60
45359.0100m
skgs
kg
Ⅷ Changing Volume Flow rate
0.45359kg1lb
60second1min
rate flow Massm
rate flow VolumeQ
m· Q
(1) Standard International Units, SI, metric Units
Ⅷ Changing Volume Flow rate
MP
RTQ
m
(1) Standard International Units, SI, metric Units
510013.129
202738.314mQ
=0.627 scms
=0.627 scm / s
=0.627 Nm3/s
Standard Cubic Meters per Second
Normal Cubic Meters per Second
Standard flow rate
Ⅷ Changing Volume Flow rate
(1) Standard International Units, SI, metric Units
Actual flow rate
P
PstdstdT
T ) (scms QQ
stdPP
)20273(
260)(2730.627Q
=1.14 acms
=1.14 acm/s
=1.14 am3/s
Actual Cubic Meters per Second
Ⅷ Changing Volume Flow rate
(2) British UnitsStandard flow rate
Minuteper feet Cubic Standard means scfm
1329scfm
60(3.281)0.627
60/1
(3.281) ) scms ( QQ
3
3
3.281ft 1m 60second1min
Ⅷ Changing Volume Flow rate
(2) British UnitsActual flow rate
Minuteper Feet Cubic Standard Actual means acfm
2146acfm
)20273(
260)(2731329
T
T ) Q(scfmQ
std
This Lecture and the Next Lecture
This Lecture: Chapter 7 Page 160~196
Page 202~205
The Next Lecture: Chapter 8 Page 209~246
Exerciser
Page 203, 7.5
Page 204, 7.12
Page 205, 7.19, 7.21
1. Please explain a typical air pollution control system.
2. The below table shows the Lean Limit and Rich Limit of Toluene(C7H8). What are the stoichiometric mixture, LEL, and
UEL for the combustion of Toluene in air, expressed in yToluene
(volume percentage of Toluene in air) respectively?
FuelMolecular
WeightExplosive Limit %
stoichiometricLean Rich
Toluene 92 43 322
Some deviceAir flow Air flow out
m=10 kg/s T=227℃ Q=?
m=10 kg/s T=127℃ Q=?
3. The following figure shows some kind of device with a gas flow in and out. The gas has the properties of air, and a flow rate of 10 kg/s. The pressure is close to atmospheric(1 atm). At standard conditions the temperature is 20 . What are the volumetric flow rates in and out? T℃he results should be expressed as four types in scms, acms, scfm and acfm respectively.
3. A typical coal has the following ultimate analysis by weight: H, 6.0%; C, 60.0%; N, 1.0%; S, 2.0%; O, 7.0%; ash 10.0%. It is burned with 20% excess air with humidity 0.0116 mol/mol dry air, and combustion is complete.(1) Determine SO2 concentration (ppm) in the gases of combustion p
roducts.(2) A rate of 1000 kg/h of dry coal is used in combustor, and the temperature of the gases of combustion products is 100 0C. What is the gas flow rate of the gases of combustion products in actual cubic meter per second (acms) at the actual conditionings (100 0C and 1 atm)?
CombustorAir
Coal Gases of combustion products
y SO2 = ? (ppm)
Gas flow rate =? (acms)
DISCUSSION
Topics about Air pollution:
Introducing yourself
Interesting news or information about air pollution your
having read or heard
Your opinions on this Air Pollution course
Your suggestions for Chinese Air Pollution
Other familiar issues about Air Pollution