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