Prof. Jiakuan Yang Huazhong University of Science and Technology Air Pollution Control Engineering

Questions for the Last Lecture 1.Please Give the Equations of Control Efficiency and Penetration. 2. Please Explain the Following Terms: (1) Stoichiometic Mixture (2) LEL (3) UEL (4) A/F (5) scms (6)Nm 3 /s (7) acfm

Answer

Stoichiometric mixture is the mixture of air and fuel (combustible gas) in the state of complete combustion. LEL (Lower Explosive Limit) is the lower limit value less than which mixture is too lean to burn, also called Lean Limit. UEL (Upper Explosive Limit) is the upper limit value more than which mixture is too rich to burn, also called Rich Limit.

Answer A/F is the ratio of mass of air to mass of fuel. scms means Standard Cubic Meters per Second Nm 3 /s means Normal Cubic Meters per Second. acfm means actual cubic feet per minute.

Lecture 8 Lecture 8 The nature of Particulate Pollutants Particulate pollutants (the most common air pollutants) Volatile Organic Compounds (VOCs) Sulfur Oxides Nitrogen Oxides The four major air pollutants

Lecture 8 Lecture 8 The nature of Particulate Pollutants Nonhomogeneous pollutants Particulate pollutants are not chemically uniform, have different size, shape, and chemical compositions.

Lecture 8 Lecture 8 The nature of Particulate Pollutants Ⅰ Diameter of particles Ⅱ Primary and secondary particles Ⅲ Forces acting on particles Ⅳ Terminal gravitational settling velocity Ⅴ Behavior of Particles in the Atmosphere Ⅵ Summary

Ⅰ Diameter of particle diameter of sphere (1) Definition diameter of a sphere of equal volume

Ⅰ Diameter of particles (2) unit 1 μ m=10 -6 m, micrometer 1mm=10 -3 m, millimeter 1nm=10 -9 m, nanometer( 纳米） 1Ǻ= m, Ǻugström （埃）

Ⅰ Diameter of particles (3) dimension of typical material human hair about: 50 μ m page of the book: 100 μ m thick

Ⅰ Diameter of particles 4) Different dimension sizes have different effects on human health. Particulate pollutants causing significant air pollution are in the size range from 0.01 to 10 μ m.

Ⅰ Diameter of particles ① Lung-damaging dust, from 0.5 to 5μm ② >10 μ m, removed in our noses and threats. ③ 5~10 μm, removed in the trachea or bronchi. ④ <5 μm, getting to the lung.

Ⅰ Diameter of particle ⑤ Inhalabe particles. Refer to all particles smaller than 10 μ, PM 10 ⑥ respirable particles (refer to all particles) smaller than 3.5 μ. ⑦ Fine particles, smaller than 2.5μ, PM 2.5. The smaller the particles size, the more damage to human health.

Ⅱ Primary and secondary particles (1) How fine particles generate >10 μ 0.1 to 10 μ Crushing and grinding process Combustion, evaporation, or condensation processes Mechanical method Chemical or phase change

Ⅱ Primary and secondary particles (1) How fine Particles generate extreme grinding and milling operation Paint pigments 0.1~5 μ Ground talc 0.5~50 μ extreme grinding with water Example, Page211

Ⅱ Primary and secondary particles (1) How fine particles generate Example Page211 Burning cigarette Smoke, which consists of small drops of condensed hydrocarbons Transparent, gaseous hydrocarbons, too hot to condense

Ⅱ Primary and secondary particles Example Nanomaterials by vaporization and condensation process Vacuum pump Laser or plasma (1) How fine particles generate

Ⅱ Primary and secondary particles (2) state of particles Solid Dust (1~10,000 μ) Fume (0.001~1 μ) Liquid Mist (0.001~10 μ) Spray (10~10,000 μ) smog (0.001~2 μ ) Fog (0.001~50 μ) Atmospheric dispersoids

Ⅱ Primary and secondary particles (3) secondary particles Secondary particles are formed in the atmosphere from gaseous pollutants which are called as the precursors. Precursors: 前驱物

Ⅱ Primary and secondary particles For example Secondary particles Tobacco smoke sulfuric Mist Black smoke of car CxHyCxHy SO 2 precursors (3) secondary particles CxHyCxHy

Ⅱ Primary and secondary particles (4) primary particles Primary particles are found in the atmosphere in the form in which they were emitted. For example Fly ash ZnO Fume Coal dust Cement dust

(5) Differences between Primary and Secondary particles Ⅱ Primary and secondary particles Primary Secondary diameter >1 μ <1 μ generation mechanical Condensation or chemical reaction state solid liquid

Ⅲ Forces acting on particles electrostatic Van der Waals gravity inertial D2D2 D3D3 Surface forces Volume force Surface forces Volume force 1 D

Ⅲ Forces acting on particles Gravity causes the fall and separation of particles. Electrostatic and Van der Waals agglomerate the particles into larger particles.

Ⅲ Forces acting on particles The basic strategy of control for particulate pollutants is to agglomerate them into larger particles that can be easily collected. This can be done by forcing the individual particles to contact each other or by contacting them with drops of water.

Ⅳ Terminal gravitational settling velocity (1) Forces acting on particles in a fluid Assuming a single particle, no the electrostatic and Van der Waals. Forces between the particle and other particles can be ignored. buoyancy gravity

Ⅳ Terminal gravitational settling velocity buoyancy weight Drag force a (1) Forces acting on particles in a fluid Particle falls down, getting an acceleration v : v 0 Drag force takes place. Initially, v = 0

Ⅳ Terminal gravitational settling velocity (1) Forces acting on particles in a fluid buoyancy gravity Drag force a μ ---- the viscosity of the fluid According to Newton's law for viscosity

Ⅳ Terminal gravitational settling velocity (1) Forces acting on particles in a fluid The drag force increases as the velocity increases until it equals the gravity minus the buoyancy. At this time, the velocity is terminal setting velocity, the sum of the forces acting is zero, so the particle continues to move at a constant velocity.

Ⅳ Terminal gravitational settling velocity (1) Forces acting on particles in a fluid Why drag force is not considered in the air parcel model?

Ⅳ Terminal gravitational settling velocity (1) Forces acting on particles in a fluid Stokes’ law So ρ air can be ignored, buoyant 0

This Lecture and the Next Lecture  This Lecture:  Chapter 8 Page 209~227 Page 239~243  The Next Lecture:  Chapter 9 page 249~328

Exerciser Page Page

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