Air Pollution Control and Measurement Lecture Notes

Flashcards covering particulate pollutants, filtration mechanisms, stack sampling, legislation philosophies, and industrial pollution control equipment.

Impaction

A filtration mechanism where large particles having too much inertia to follow a curving streamline of air around filter fibers collide with a fiber and get trapped.

Diffusion

A filtration mechanism where Brownian movement increases the probability of smaller particles bumping into and being captured by a filter fiber.

Electrostatic attraction

A mechanism where particles are pulled to and adhere to fibers because both the filter paper and the particles carry electrostatic charges.

Pore size

A factor where a smaller measurement increases filter efficiency.

Filter loading

The accumulation of captured particles that helps trap incoming ones, though effectiveness ends if the filter becomes clogged.

Traverse points

Specific points located at the center of equal areas in a stack's cross-section where samples must be collected to achieve a representative sample.

Isokinetic Sampling

A sampling condition for particulates $> 3\,\text{m}$ where the gas velocity in the stack ($V_g$) equals the velocity at the top of the probe nozzle ($V_{p}$).

Dry Gas Meter (DGM)

An instrument that measures the velocity, temperature, pressure, and volume of air at a particular traverse point (not average chimney conditions).

Anderson Multi Stage Impactor

A device consisting of several stages of stainless steel plates with circular holes of successively smaller diameters used to separate particles by size ranges.

Best Technology Emission Standard

A philosophy requiring all members of a class to employ the best techniques currently available for minimizing pollutant emissions.

Prohibitive Emission Standard

A regulation that forces the use of better technology by banning certain acts, such as the open burning of combustible waste.

Visible Emission Standard

A standard that limits the particle emission rate by regulating the opacity of smoke from chimneys.

Numerical Emission Standard

A standard that limits the concentration of pollutants, such as the $1.5\,\text{g/mile}$ limit for hydrocarbons in automobiles.

Air Quality Standard Philosophy

A philosophy based on zero damage where a threshold value of a pollutant is deemed not to endanger health or the environment.

Emission Tax Philosophy

A strategy where emitters are taxed for exceeding levels based on the quantities of emissions, assuming the environment has a finite absorptive capability.

Cost-Benefit Philosophy

The principle of accepting that some damage is unavoidable and deciding rationally how much damage to accept versus how much to spend to reduce it.

Smoke

A submicrometer particulate aerosol from a combustion source that obscures vision.

Smoke Density Meter

A device that projects a constant light beam across a stack to a photoelectric sensor to measure percentage obscuration.

Ringelmann Method

A quick visual method of assessing smoke opacity by comparing smoke to a standardized 6-point scale chart ranging from 0 (clear) to 5 (100% black).

Inertial Seperation (Cyclone)

A technique effectively used for particulates $> 10\,\mu\text{m}$ where centrifugal force is imparted to particles via a tangential gas stream.

Ascending vortex

The part of a cyclone separator that carries the clean gas stream out upwards.

Descending vortex

The part of a cyclone separator that carries particulates downwards into the hopper.

Bag house filter

A system of tubular bags, ranging from $120-400\,\text{mm}$ in diameter, that achieves high efficiency ($> 99\%$) for particles $> 1\,\mu\text{m}$.

Electrostatic Precipitator (ESP)

Equipment that uses high-voltage electrical fields (over $40000\,\text{V}$) to charge dust particles and draw them to grounded collecting plates.

Corona effect

The phenomenon where discharge wires carrying high voltage negatively charge dust particles within an ESP.

Mechanical rappers

Devices used in an ESP to shake dust loose from collecting plates into bottom collection hoppers.

Wet scrubbers

Pollution control devices that rely on the collision and coalescence between dust particles and liquid droplets to increase particle mass so they fallout.

Venturi Scrubber

A device where water is atomized at a throat by high-velocity gas (up to $100\,\text{m/s}$) to collect fine particles.

Packed bed tower

A scrubbing system containing a mist eliminator and a packing section where liquid is sprayed to clean dirty gas.

Scrubbing liquid criteria

The requirements for a liquid to be inexpensive, non-toxic, non-corrosive, non-flammable, chemically stable, and have high gas solubility.

Biofiltration

The control of air pollution using biologically active materials such as compost, peat, or soil.

Aerobic degradation

A process in biofilters where complete biodegradation results in $\text{CO}_2$, water, and microbial biomass.

Condensation

A control mechanism used for the recovery of valuable products and volume reduction by increasing pressure or decreasing temperature.

Face velocity

One of several factors, including pore size and filter loading, that efficiency of filtration depends on.

$$V_p > V_g$$

A condition described as more than 100% isokinetic where the streamline converges in the probe and less particles are collected.

$$V_p < V_g$$

A condition described as less than 100% isokinetic where the streamlines diverge and more particles are collected.

Photoelectric sensor

A component in a smoke density meter that provides electrical output based on the percentage of light obscuration.

Air purging

A maintenance action for smoke density meters to keep the optics accurate.

Ringelmann Chart Distance

The specific distance (about $15\,\text{m}$) at which an observer should stand so chart lines appear to merge into a uniform shade.

$\text{SO}_2$ + alkaline ammonia

A specific chemical combination used in scrubbing to enhance collection efficiency.

$\text{H}_{2}\text{S}$ + diethanolamine

A treatment combination used in gas scrubbing to remove reduced sulfur compounds.

Inertial Collector Advantages

Simple construction, low cost, low space requirements, and no moving parts.

Bag house efficiency

High collection effectiveness reaching $> 99\%$ for particles larger than $1\,\mu\text{m}$.

Venturi throat velocity

Gas speeds reaching up to $100\,\text{m/s}$ used to smash water into a fine spray for scrubbing.

Filtration Velocity

The operational speed for bag filters, typically ranging from $0.3-6\,\text{m/min}$.

Mist eliminator

A component in scrubbers designed to remove liquid droplets from the gas stream before it exits.

Biofilter bed height

The typical measurement of the filter material layer, which is approximately $1\,\text{m}$.

Soil beds

A type of biofilter material consisting of biologically active mineral soil.

Cyclonic separator

A device used in conjunction with a venturi scrubber to remove larger drops after water and gas coalescence.

Standardized 6-point scale

The grading system used in the Ringelmann Method to assess smoke density from 0 to 5.