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Air Pollution

Example Q0: Pollutant Concentration

Concentration Estimation (Y- and Z-directional dispersion constants)

April 22, 2011 arunku@civil.iitd.ac.in 7

Example Q1: Pollutant Concentration (repeat using empirical relationship for sigma y and sigma z) and compare.

Pollutant Concentration (ppm or µg/m3)

– µg/m3 = [ppm * g mol/mass* 1000]/[L/mol]

– At 0°C and 1 atm pressure (760 mm Hg), the volume of– At 0°C and 1 atm pressure (760 mm Hg), the volume ofthe gas is 22.4 L/mol.

Example Q3: Pollutant Concentration

– A sample of air analyzed at 0deg C and 1 atm pressureis reported to contain 9 ppm of CO. Determine theequivalent CO conc. in µg/m3 and mg/L?

Solution (Q3): Pollutant Concentration

– gm molecular mass of CO = 12+ 16=28 g/mol

– At 0deg C and 1 atm pressure (i.e., 760 mm Hg),volume of gas is 22.4 Liters/mol.

– Conc. (µg/m3 ) = 11.250 mg/m3

Example Q4: Gaseous and Particulate Emission

Air Pollution Control

A) Stationery Sources

– Pre-combustion controls (improved fuel quality)

– Combustion controls (improved combustion process)

– Post-combustion controls (capture emissions after theyare formed but before they are released to the air)

Example Q5: Particle removal efficiency in cyclones

– An air stream with a flow rate of 7 m3/s is passedthrough a cyclone of standard proportions. Thediameter of the cyclone is 2 and the air temperature is77degC.

– Calculate (i) Removal efficiency for a particle with a– Calculate (i) Removal efficiency for a particle with adensity of 1500 g/m3 and a diameter of 10 µg, if a bankof 64 cyclones with diameters of 24 cm are usedinstead of the single large unit.

Solution Q5:Particle removal efficiency in cyclones

– B= D/4=0.24m/4=0.06m

– H=D/2=0.12m

– Cross section area of entrance=bh=0.06*0.12=0.072m2

– As we have 64 similar units=> total entrance area• =64*0.072 m2 = 0.45 m2

– Inlet velocity = (7m3/s)/(0.45m2)= 15.5 m/s

– Calculate d50 ???

– Calculate d/d50

– Use efficiency vs. (d/d50) plot to find out efficiency forcalculated d/d50 value?

1) Electrostatic Precipitators

Intense electric field ionizes particles.

They move under the under the influence of electric field to grounded collecting surface

Electrostatic Precipitator

• Consists of alternating plates and wires, a large directcurrent potential is established between them– As gas stream passes between the wire and the plate,

gas molecules are ionized, ions attach to the particles,giving them a net negative charge

– The particulates then migrate to the plate where they– The particulates then migrate to the plate where theystick and can later be removed

Electrostatic Precipitator

• Efficiency usually > 98%, including submicron particles– Uses: electric power plants, acid production facilities

etc

– Can accommodate large flow rates, solid or liquidparticles, low operation and maintenance costs, butare expensive and require a lot of spaceare expensive and require a lot of space

Q6: Electrostatic Precipitator-Example Problem

• We want to remove fly ash particles from stack gasesflowing at 10m3/s.

• Drift velocity (w) can be written as• w=3*105 .(dp) where dp is particle diameter in (m)

Calculate plate area requirement to collect a 0.5 micronCalculate plate area requirement to collect a 0.5 micronparticle with 90% efficiency?

Comment on effect of area increase on efficiency?

2) Filtration

• Gas stream drawn or pushed through fabric that prevents particle

passage

• Generally used for particles < 5 µm

Filtration

Bag house

Filtration

• Two configurations:

– Deep bed filter: Used for relatively clean gases and low volumes,e.g., air conditioning systems

– The Baghouse: for dirty industrial gas with large volumes

• Many applications (e.g. cement crushing, feed and grainhandling and sanding machines)handling and sanding machines)

• Effective removal of small particles, but are large and expensive

3) Liquid Scrubber

• For particulate matter that is wet, corrosive or very hot

• Particle pollutant can be removed by injecting water intothe gas stream

• Particles/droplets grow and removed by cyclone

Liquid Scrubber (SO2 control)

Fine limestone (CaCO3) is mixed with water to create a slurry.SO2 is absorbed by the slurry producing CaSO3 or CaSO4 precipitate,which is removed as a sludge.

Flue Gas De-sulfurization (FGD)

• Flue gas (gas that exits via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator)

– Or the combustion exhaust gas produced at power plants

• FGD have reaction chemistries based on lime (CaO), caustic • FGD have reaction chemistries based on lime (CaO), caustic soda (NaOH), soda ash (Na2CO3) or ammonia (NH3)

• Limestone slurry is sprayed onto the flue gas, SO2 is absorbed by the slurry, producing calcium sulfate or calcium sulfite, which is then removed as a sludge.

4) Absorption

• Transfer pollutant from a gas phase to a liquid phase (gas dissolves in the liquid)

– scrubbers (liquid droplets absorb the gas)

– towers (a thin film of liquid absorbs the gas)

• Process depends on:• Process depends on:

– solubility of pollutant &

– creating a large air/liquid surface area

• Primarily for soluble inorganic gases, e.g. NH3, Cl2, SO2

Absorption

5) Adsorption

• Gas to solid mass transfer (pollutant “sticks” to solidsurface)

• Adsorbents1. activated carbon,

2. molecular sieves,

3. silica gel,

4. activated alumina (large active surface area per unit volume)

• At some point, adsorbent becomes saturated and needsregeneration

• Commonly used for: hydrocarbons, solvents, H2S, SO2,NO2

Adsorption

6) Combustion

• Used when the contaminant in the gas stream isoxidizable to an inert gas

• Typically CO and hydrocarbons• Typically CO and hydrocarbons

B) Motor Vehicles

– Cleaner gasoline

– Exhaust system controls (catalytic converter)

– Improved engines

– Alternative fuels

Hazardous Waste Management

Hazardous Wastes

Hazardous Wastes

• A waste with properties that make it dangerous orpotentially harmful to human health or the environment.

• Forms:

– Liquids, solids, contained gases, or sludges.

• It can be the by-products of manufacturing processes orsimply discarded commercial products, like cleaning fluidsor pesticides.

Characteristics

Ignitability

Corrosivity

Reactivity

Toxicity

Special Categories of Hazardous Wastes

• Hazardous waste mixtures

• Wastes derived from the management of hazardous wastes

• Hazardous waste contained in a nonwaste container

• Low-level radioactive mixed wastes• Low-level radioactive mixed wastes

• Special rules for recycling

The “Cradle-to-Grave” Regulatory Approach: Regulatory Requirements

1. Generators: identify, properly handle, and insure proper disposal of all wastes

2. Transporters: Comply with Hazardous Materials Transportation Act and meet other requirements on Transportation Act and meet other requirements on packaging, handling, and documenting waste shipments

3. Hazardous waste management or treatment, storage and disposal facilities: meet general and specific facility standards, groundwater monitoring, closure/post-closure activities, financial responsibility requirements

Hazardous Waste Management Units

• Storage Units

– Container storage units

– Tank systems

– Surface impoundments

• Disposal Units

– Landfills

– Land treatment units

– Thermal treatment units– Waste piles

– Containment buildings

– Thermal treatment units

– Chemical, physical and biological treatment units

– Underground injection wells

Waste Management Options

WASTE REDUCTION

• Source segregation

• Process

WASTE TREATMENT

• Land treatment• Thermal conversion• Physicochemical

• Biological

WASTE DISPOSAL

• Landfill• Deep-well injection

• Underground modification

• Material

Recovery

• Stabilization• Ecosystem

Assimilation

• Underground

storage• Surface Storage

most desirable least desirable

Pollution Prevention Incentives

1. Reduce – waste management costs– raw material costs– secondary costs– liability

2. Increase2. Increase– compliance safety margin– trust by regulators

3. Enhance public image

Treatment Strategies for Hazardous Wastes

• Objectives1. neutralize the waste;

2. recover energy or material resources from a waste;

3. render the waste less hazardous; or

4. make the waste safer to transport, store, or dispose. 4. make the waste safer to transport, store, or dispose.

Treatment Technologies -1

• Incineration: is the high temperature burning (rapid oxidation) of awaste, usually at 1600 to 2500 degrees F (i.e., controlled-flamecombustion or calcination). It destroys organic constituents in wastematerials.

• Waste-to-Energy Incineration: This is usually associated withmunicipal waste combustion where the waste is burned at a hightemperature. Heat energy is recovered from the combustion processtemperature. Heat energy is recovered from the combustion processand is usually used to generate steam and or electricity.

Treatment Technologies -2

• Boilers: This device is used to treat hazardous waste. Boilers usecontrolled flame combustion and recover thermal energy in the form ofsteam or heated gases.

• Steam stripping: This treatment technology is used to remove organiccompounds from liquid waste streams and it involves direct applicationof stream to the liquid and subsequent condensation of the extractedorganic compounds. It not only removes hazardous constituents fromthe waste stream but it also can have the added benefit of making thethe waste stream but it also can have the added benefit of making theconstituents less toxic.

Treatment Technologies -3

• Physical removal: This process removes the hazardous constituentsfrom waste streams by separation techniques, such as ion exchange,adsorption, reverse osmosis, chelation, solvent extraction,crystallization, precipitation, distillation, filtration, evaporation, etc. Theremoved hazardous constituents may require further treatment tomake them less toxic.

• Carbon adsorption: Use of activated carbon to adsorb hazardouswaste constituents (both gaseous and aqueous waste streams).

• Chemical oxidation: Use of strong oxidizing agents (e.g.hypochlorite, peroxides, persulfates, percholorates, permanganates,etc) to break down hazardous waste constituents to render them lesstoxic or mobile.

• Chemical reduction: Use of strong reducing agents (e.g. sulfurdioxide, alkali salts, sulfides, iron salts, etc) to break down hazardouswaste constituents to render them less toxic or mobile.

Treatment Technologies -4

• Deactivation: Removal of the hazardous nature of the waste byneutralizing the characteristics of ignitability, corrosivity, and/or reactivity.

• Neutralization: Here, low pH acidic corrosive waste streams are usuallyneutralized by containing bases and high pH corrosive waste streams areusually neutralized by adding acids.

• Extraction: Removal of hazardous constituents from either gaseous orliquid waste streams by means of settling, filtration, adsorption,liquid waste streams by means of settling, filtration, adsorption,absorption, solvents, or other means. Further treatment is required in thiscase.

• Stabilization: This process reduces the mobility of the hazardousconstituents of a waste or that makes the waste easier to handle. Themost common stabilization agents added to waste streams are Portlandcement, lime, fly ash, and cement kiln dust.

Treatment Technologies -5

• Treatment in tanks: mechanical settling, gravity settling, chemicaloxidation, and neutralization, etc.

• Biological treatment: Treatment using bacteria, fungi, or algae toremove and degrade the hazardous constituents (aerobic, anaerobictreatment)

Household Hazardous Wastes

Indoor PesticidesAnt sprays and baits

Cockroach sprays and baits

Flea repellents and shampoos

Bug sprays

Houseplant insecticides

Moth repellents

Mouse and rat poisons

and baits

Automotive ProductsMotor oil

Fuel additives

Carburetor and fuel

injection cleaners

Air conditioning refrigerants

Starter fluids

Automotive batteries

Transmission and brake fluid

Antifreeze Workshop/Painting SuppliesAdhesives and glues

Furniture strippers

Oil or enamel based paintLawn and

Garden

Cleaning ProductsOven cleaners

Drain cleaners

Wood and metal

cleaners and polishes

Toilet cleaners

Tub, tile, shower cleaners

Bleach (laundry)

Pool chemicals

Oil or enamel based paint

Stains and finishes

Paint thinners and turpentine

Paint strippers and removers

Photographic chemicals

Fixatives and other solvents

Garden ProductsHerbicides

Insecticides

Fungicides/wood

preservatives

MiscellaneousBatteries

Mercury thermostats or thermometers

Fluorescent light bulbs

Driveway sealer