2025年大气污染与控制工程考试复习整理.docx

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大气复习资料
概念解释
Globe warming: Global warming is the increase in the average measured temperature of the Earth's near-surface air and oceans since the mid-twentieth century, and its projected continuation.
VOCs: Volatile organic compounds are those organic liquids or solids whose room temperature vapor pressure are greater than about psia(=) and whose atmospheric boiling points are up to about 500℉, which means most organic compounds with less than 12 carbon atoms.
Wet scrubber: A device that collects particles by contacting the dirty gas stream with liquid drops. OR A device removes particulates from a gas steam by bringing the particles into contact with a liquid. The particles attach to the liquid and can be removed in a slurry solution.
Temperature inversions: It is a phenomenon that the temperature increases with the height increasing. That stability also lessens the exchange of wind energy between the air layer near the ground and high altitude winds. OR A temperature inversions is a thin layer of the atmosphere where the decrease in temperature with height is much less than normal.
ESP: Electrostatic precipitator, which is like a gravity setter or centrifugal separator, but electrostatic force drives the particles to the wall. And it is effective on small particles below about 5μm in diameter.
SNCR: short of “selective non-catalyst reduction”. It is the process that involves injecting either ammonia or urea into the firebox of the boiler at a location where the flue gas is 760 -1100℃ (1,400 and 2,000 °F) to react with the nitrogen oxides. The resulting product of the chemical redox reaction is elemental nitrogen (N2), carbon dioxide (CO2), and water (H2O).
SCR: short of “selective catalyst reduction”. It is a means of converting nitrogen oxides (NOx), also referred to as NOx with the aid of a catalyst into diatomic nitrogen (N2) and water (H2O), under the condition of 320-400℃（600-750℉）
6NO+4NH3→5N2+6H2O, 4NO+4NH3+O2→4N2+6H2O, 2NO2+4NH3→3N2+6H2O.
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Thermal NO: Thermal NOx refers to NOx formed by the simple heating of oxygen and nitrogen, either in a flame or by some other external heating, ., a lighting bot.
: Particle with the aerodynamic diameter less than um, which is also called Respirable Particles.
Alternative fuel: Several other fuels except of conventional gasoline and diesel, which have been used for many years in slighutly modified automobile engines, for reasons of cost and availability.
A/F ratio: Air to fuel ratio for auto engines. For any hydrocarbon fuel with formular CxHy, so n stoich oxygen =x+y/4. For complete combustion of this fuel, the equation is CxHy + (x+y/4)O2→xCO2+y/2 O2, so (A/F)=
Lean bum ：Lean burn refers to the use of lean mixtures in an internal combustion engine .The air-fuel can be as high as 65:1 ,so the mixture has considerably less fuel in comparison to the stoichiometric combustion ratio (:1 for petrol , for example ).
Photochemical smog: It is the chemical reaction of sunlight, nitrogen oxides and volatile organic compounds in the atmosphere, which leaves airborne particles and ground-level ozone. Photochemical smog is a light blue and it is the secondary pollutants in the atmosphere.
Aerodynamic diameter: Airborne particles have irregular shapes, and their aerodynamic behavior is expressed in terms of the diameter of an idealized spherical particle known as Aerodynamic diameter.
HEPA: High Efficiency Particulate Air. It is a type of air filter that used for removing solid particles from gas steams that contain few of them.
Plume rise: the plume rising a distance △h above the top of the stack before leveling out.
Primary Particles: Particles found in the atmosphere in the form in which they were emitted, for examples, NO,CO,SO2
Point Sources: small number of large sources that emit larger amounts per source, at higher elevations (power plants, smelters, cement plants, etc.) called point sources
Answer following questions
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Which are the main constituents for the ground level ozone formation?
Ozone is formed when the following constituents are present.
Nitrogen oxides, Volatile Organic, Compounds, Sunlight, High temperature(>18 ℃)
NO+VOC+O2+Sunlight→NO2+O3
Please list five major types of wet scrubbers.
Plate Scrubber（板式）； Packed Scrubber（填料式）； Preformed Spray Scrubber（喷雾式）；Gas-Atomized Spray Scrubber（气体雾化）；Centrifugal Scrubber （离心式）；
Impingement-Entrainment Scrubber（冲击夹带式）；Mechanically Aided Scrubber（机械辅助式）；Moving Bed Scrubber（移动床式）。
How to control VOCs pollution by prevention? Two examples.
Substitution(替代): Replacing gasoline as a motor fuel with compressed natural gas or propane is a form of substitution.
Process Modification(过程修改): Replacing gasoline-powered vehicles with electric-powered vehicles is a form of process modification.
Leakage（渗漏） Control: Storing large amounts of gasoline in floating roof tanks.
Please introduce the process of forced-oxidation Limestone Wet Scrubbing briefly？
SO2+H2O→H2SO3 ; CaCO3+ H2SO3→CaCO3+CO2+H2O; 2CaCO3+O2→CaCO4
What are the differences between SCR and SNCR in NOx treatment?
(What is the most differences points between SCR and SNCR?)
SCR is a catalyst process where the temperature is between 600 and 750℉. However, SNCR is a process that without catalysts and it is at higher temperature between 1,400 and 2,000 °F.
Can TWC be applied in the treatment of diesel exhaust (emission of diesel engine)? fWhy？
·The characteristic of emission of diesel engine: Ample PM and Excessive O2, Lower temperature;
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·The difficulty in the reaction of solid-gas-solid.
NO. 1) The characteristic of emission of diesel engine is ample PM, excessive O2, and lower temperature. But this is not TWC reaction conditions. 2) It is difficult to react solid-gas-solid.
Key: The mixture process of fuel and air for gas engines is distinguished from that for diesel engines, hence the character of one type engine is different from the other one: there are mainly five gases (NOX, HC, CO and O2, CO2) in the exhaust of gas motors, while there are ample O2 and four other gases mentioned above in the tailpipe emission of diesel engine. And the presence of abundant O2 would inhibit the performance of TWC.
Moreover, the contact and reaction of solid-solid-gas resulting in the difficulties for catalysts to oxidation the particulate in the exhaust of diesel engine, while the contact and reaction of solid-gas-gas occur in the exhaust of gasoline engine and the latter reaction is easier.
What kinds of indoor air pollutants are mostly concerned by public?
Random
Combustion by-products
CO, CO2, SO2, Formaldehyde(甲醛), Hydrocarbons(碳氢化物), NOx
Particulates, polyaromatic hydrocarbons(PAHs)
Cigarettes d)Volatile organic compounds (VOCs) e) Biological contaminants
Basic strategy of control for particulate pollutants (Three aspects). /List the technology strategy for the control of particles.
Impaction 碰撞 Interception 截留 Diffusion 扩散
By forcing the individual particles to contact each other,
By contacting them with drops of water,
By preventing the emission of gaseous pollutants.
Give names of three typical kinds of combustion reactors. Which has lowest operator temperature among those reactors?
1. Direct flame incineration
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2. Thermal incineration
3. Catalytic incineration (has lowest operator temperature)
What are the major development problems of Forced-oxidation limestone wet scrubbing?
1) Corrosion due to Cl building up
2) Solid deposition
3) Poor reagent utilization
4) Poor solid-liquid separation
What are primary air pollutants and secondary air pollutants? Any example?
Primary air pollutants are directly from the sources, for examples, NO, CO, SO2.
The secondary air pollutants are from the primary pollutants, such as NO2, NO3, fine particles. NO+CH+O2+sunlight → NO2+O3
How to reduce the formation of NOx in flue gas by modifying the combustion processes?
(p459)
1) Low excess air;
2) Air staged combustion;
3) Fuel shagged combustion;
4) Fuel gas recirculation (FGC).
Please explain the formation of acid rain?
Sulfur oxides and nitrogen oxides
NOx+ H2O→HNO3 (NOx: NO , NO2) nitric acid
SO2+ H2O→H2SO4 sulfuric acid
What are basic principles of electrostatic Precipitators (six activities)?
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·Ionization(离子化) - Charging of particles
·Migration(迁移) - Transporting the charged particles to the collecting surfaces
·Collection(搜集) - Precipitation of the charged particles onto the collecting surfaces
·Charge dissipation(电荷消耗) - Neutralizing the charged particles on the collecting surfaces
·Particle dislodging(使颗粒移动) - Removing the particles from the collecting surface to the hopper
·Particle removal(颗粒迁移) - Conveying the particles from the hopper to a disposal point
三、Calculation
1) Estimate the concentration of carbon monoxide at the downwind edge of a city. The city may be considered to consist of three parallel strips, located perpendicular to the wind. For all of the strips the wind velocity equals 3 m/s. The properties of each of the strips are described in the following table,
Name of strip
Length, km
Emission rate
q, g/s·km2
Mixing height
H, m
Upwind suburbs
5
100
400
Downtown
2
500
500
Downwind suburbs
5
100
400
Solution： c1=0+(100*5000)/(3*400)= μg/m3
c2=+(500*)/(3*500)=
c3=+(100*5000)/(3*400)=
2) An ESP is designed to treat 540,000 acfm（actual cubic feet per minute） with 99% efficiency. Assuming an effective drift velocity of m/s, calculate the required plate area and the number of plates. The plate size is tall by 3m long(A =－Q×㏑(1－η)/ωp, acfm＝1ft3/min, 1m=, 1m2＝1550 in2＝ ft2).
Solution：1ft3/min=(1/)3m3/min= m3/min
540000acfm=540000* m3/min= m3/s
A= -()ln(1-)=
N==604
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3) We wish to treat an airstream containing fraction (%, 5000ppm) toluene, moving at a flow rate 2240m3/h at 0℃ and 1 atm, so as to remove 99% of the toluene by water absorption. Estimate the required water flow rate. Here Henry’s law constant is 10000 atm.
Solution：
4）A power plant flue gas contains 1000ppm of SO2 and is emitted at a rate of 224m3/s at 546K and 1 atm. A Forced-oxidation limestone wet scrubbing system is to be used to achieve 90% removal of the SO2. Calculate the amount of CaSO4·2H2O contained in the final solid product in t/d.
Solution： =(101325*224*1000*10-6)/(*546)=
SO2~ CaSO4·2H2O so n（caso4）=n（so2）=*90%=
m= *172g/mol *3600*24s/d *10-6 t/d= t/d
5）A power plant emits 36 kg/h of SO2 at height H=120m and the wind speed is 2 m/s. Dispersion Coefficients: σy=40m and σz=30m, Estimate the ground-level concentration of SO2 from this source at a distance 1km directly downwind?
Solution：u=2m/s , H=120m, Q=36kg/h=10g/s , y=0 , z=H=120 , x=1000m
=
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6）A power plant flue gas contains 1000×10-6 （1000ppm）of NOx，and is emitted at a rate of at 546K and 1 atm. The NOx is 90%mol NO, balance NO2. A selective catalytic reduction system is to be used to remove the NOx. Calculate the minimum of ammonia needed in kg/h.
Solution： 4NO+4NH3+O2→4N2+6H2O 2O+4NH3+O2→3N2+6H2O
PV=nRT n=(101325**1000*10-6)/(*546)=
n(no)=*2mol/s= so n(no2)=-=
n(NH3)= n(no)+2* n