TOPIC 2 : AIR POLUTION ENGINEERING

Outline of topic 2:

AIR EMISSIONS MODELLING AND SAMPLING

AIR POLLUTION ABATEMENT EQUIPMENTS

IntroductionWHAT IS YOUR UNDERSTANDING?

• Who are you ?• What is your role?• We have any ISSUES for these?• Are you important for this ISSUES…….?

INTRODUCTION

AIR POLLUTANT AIR POLUTION

Any solid, liquid, or gaseous substance presence in the

atmosphere in such concentration as may be or tend to be injurious to

human beings or other living creatures or plants, property or

environment.

The presence of air pollutants in the atmosphere of any air.

Major affected area by air pollution is the atmosphereContribution of air pollution also can be dispersed to other environmental components and overall the whole biosphere is affected

Region of the atmosphere

Region concern: Troposphere

• main concern for air pollution • this is the region where we live

• The region of stratosphere also need to be concerned for the – transportation of pollution– particularly the debris of above ground (atomic bomb tests

or nuclear disaster)– and volcanic eruption

• Ozone layer is also located at the stratosphere

CLASSIFICATION OF AIR POLLUTANT

A) Primary pollutantIt is a direct emission from the sourceAre SOx , CO , NOx , Pb , hydrocarbon (PAH)

Example: SO2

from chimney or stack CO, NOx and hydrocarbons emitted by motor vehicles

Primary pollutant can react with the other substances in atmosphere and produce secondary pollutantExample:Primary pollutant react with water vapour in the presence of sunlight to form new set of pollutants

B) Secondary pollutant It is formed by complex reaction between primary pollutants

by thermal, chemical or photochemical reactions with radical molecules

Generally are sulfuric acid (H2SO4), ozone (O3), formaldehydes and peroxy-acyl-nitrate (PAN), etc.

Example: By thermal action SO2

can be oxidised to SO3 which, dissolved in water,

gives rise to the formation of H2SO4mist (with the assistance of catalyst reaction by manganese and iron oxides)

C) Organic pollutant– Are those of biological origin– Such as Pollen, Bacteria, Organic compounds-Polycyclic

aromatic hydrocarbon (PAH)

D) Non-organic pollutant– Gaseous pollutant - priority gaseous which have been

identified to be toxic or carcinogenic or nuisance)

– Such as CO2, CO, SO2, O3

– Non-gaseous pollutant - occupy the atmosphere with a wide variety of suspended particulate matter (SPM), which can take form of both solid and liquid, ranging in size from a few nanometres (nm) to 0.5 mm.

– Such as dust, fume, mist, smoke, spray

AIR SAMPLING AND MODELING

Measuring and Estimating Levels of Air Pollution

Air samples are collected usually to find out:

what pollutants are in the air What are the levels (or concentration) of the pollutants found

Note: i) To determine whether levels of pollution in the air that people breathe could be harmful to their health

ii) Illness can result depending on the level of contamination, duration of exposure or pre-existing health condition

Measuring Devices

No single device can measure every air pollutant because each air

pollutant is different:

Some pollutants are particles

Some are gases

Some pollutants break down in sunlight

Some do not break down in sunlight

Some pollutants react very quickly when they land on surfaces

Some are very stable

Most common approaches to measuring air pollution

A) Filter sampling

- to measure the amount of particles in the air- samples are collected using devices that have filters

with very small holes in them- as air flows through the device, gases will pass through

the filters, but particles in the air are trapped.- laboratories can then find out what contaminants are in

the particles and measure the amount of particles that landed on the filters

B) Canister sampling

- to measure gases in air, samples are often collected in small containers called canisters

- a pump are used to pull air into the canister- after the sampling period is over, the canister is

full of compressed air- a laboratory can then measure the amounts of

gaseous pollutants in the canister

Air Modeling

An air modeling is a mathematical tool that use to understand how

contaminants move in the air

In order to use an air model, relevant data related to area of study

are needed

Scientifically, sound modeling can result in a better understanding of

the overall exposure to specific contaminants

Note: Because extensive sampling data are not available for many sites, air models are the best tools available for estimating exposure to air pollution.

Air Models

• can be used to estimate a substance’s concentration over different time frames, such as a given day or an entire year.

• can be used to estimate the level of multiple substances in the air as a result of emissions from a single source or multiple sources.

• can estimate a substance’s concentration at a wide range of locations.

• can be used to estimate levels of air pollution in residential areas.

• can offer insights into where contaminants deposit in greatest quantities.

• can help identify areas where air sampling should take place.

Note: Even though a model may be used to measure a source-specific contaminant, there may be other sources of air pollution (such as motor vehicle traffic, airports, wind-blown dust and burning) that may be affect the result.

Example:Air modeling is used to estimate the amount of contaminants in the air that people breathe, and the amount of contaminants that might have been deposited in the residential areas.

Models inputs: source of contamination and local weather conditions.Models output: estimations levels of air pollution and the amount of air

contaminations that might land on the ground Analysis: analysis is to first run the models, then critically review the results and finally document the findings.

Note: i) Though many models are quite advanced, none are perfect. Outputs from models should be viewed simply as estimates of actual conditions.

ii) Even though a model may be used to measure a source-specific contaminants, there may be other sources of air pollution (such as motor vehicle traffic, airports, wind-blown dust and burning) that may affect the result.

ENVIRONMENTAL RISK ASSESSMENT

Environmental risk is defined as “ any risk, hazard or chances of bad consequences that may be brought upon the environment” (Environmental Act, 1974).

Elements of Environmental Risk Assessment (ERA)- The ERA will examine the magnitude of the effect, the pathways and

transport mode of the particular hazard/pollutant to the receptor and commonly uses predictive exposure modeling tools to determine the relative risk factors.

- The end receptor is usually defined which in the case of a human health risk assessment, the end receptor is the human population within the zone of impact while in an ecological risk assessment, the end receptor may be particular plant or faunal species.

Step Risk Assessment Process

Air Pollution Monitoring and ModelingAir pollutant risk assessment + result of studies on health effects +

exposures to the pollutant with results of studies = level of people’s

exposures at different distances from the source of the pollutant

Level 1 Level 2

-Usually less sophisticated in the scope and technique of measurement as well as modeling- Measurement are short-term spot samples that provide an immediate value with typical accuracy of only between 20 to 50%- Air dispersion models are normally used as preliminary screening tool due to the larger error range inherent in the model Exp: SCREEN3 which models a single source and is unidirectional.

-Applies more advanced techniques of air sampling and more complex models which require extensive meteorological data-A longer term measurement utilizing more permanent monitoring equipment with a much higher accuracy- US EPA models used to estimate concentration from point, line and area sources Exp: ISCST3 (short term < 24h) and ISCLT3 (long term > 24h)

Air Pollution Abatement Equipments

PREVENTING AND MINIMIZING AIR POLLUTION

Considerations for controlling pollutants without the addition of specific treatment devices:

– Eliminate leaks or vents of the pollutant– Change raw materials, fuels, or processing step to reduce

or eliminate the pollutant– Reduce the quantity of pollutant released or the quantity

of carrier gas to be treated– Use equipment for dual purposes

AIR POLLUTION CONTROL DEVICES

PARTICULATES

• Control techniques for particles focus on capturing the particles emitted by a pollution source

• Characteristics of the particulate exhaust stream affect the choice of the control device

• Characteristics include:– the range of particle sizes– the exhaust flow rate– the temperature– the moisture content– various chemical properties (explosiveness, acidity,

alkalinity, and flammability)

Objectives of using control devices:

Prevention of nuisance Prevention of physical damage to property Elimination of health hazards to plant personnel and to the general population Recovery of valuable waste products

Common control devices used to remove

particulates

Electrostatic precipitators

Fabric filters

Venturi scrubber

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Cyclones

Settling chamber

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Electrostatic Precipitators (ESPS)• A particle control device that uses electrical forces to move the particles

out of the flowing gas stream and onto collector plates• The ESP places electrical charges on the particles, causing them to be

attracted to oppositely charged metal plates located in the precipitator• The particles are removed from the plates by "rapping" and collected in a

hopper located below the unit• The removal efficiencies for ESPs are highly variable; ex: for very small

particles alone, the removal efficiency is about 99 percent

ELECTROSTATIC PRECIPITATORS

Fabric Filters/Baghouse• It remove dust from a gas stream by passing the stream through a porous

fabric• The fabric filter is efficient at removing fine particles and can exceed

efficiencies of 99% in most applications• The selection of the fiber material and fabric construction is important to

baghouse performance• Fiber material- must have adequate strength characteristics at the

maximum gas temperature expected and adequate chemical compatibility with both the gas and the collected dust

• One disadvantage of the fabric filter is that high-temperature gases often have to be cooled before contacting the filter medium

FABRIC FILTERS/BAGHOUSE

Venturi Scrubbers• Use a liquid stream to remove solid particles• Gas laden with particulate matter passes through a short tube with flared

ends and a constricted middle• This constriction causes the gas stream to speed up when the pressure is

increased• A water spray is directed into the gas stream either prior to or at the

constriction in the tube• The difference in velocity and pressure resulting from the constriction

causes the particles and water to mix and combine• The reduced velocity at the expanded section of the throat allows the

droplets of water containing the particles to drop out of the gas stream• Effective in removing small particles (removal efficiencies of up to 99%)• One drawback of this device-production of wastewater

VENTURI SCRUBBERS

Cyclones• A particulate-laden gas enters tangentially near

the top of the cyclone• The gas flow is forced into a downward spiral

simply because of the cyclone’s shape and the tangential entry.

• Centrifugal force and inertia cause the particles to move outward, collide with the outer wall, and then slide downward to the

bottom of the device.• Near the bottom of the cyclone, the gas

reverses its downward spiral and moves upward in a smaller inner spiral.

• The cleaned gas exits from the top through a “vortex-finder” tube, and the particles exit from the bottom of the cyclone through a pipe sealed by a spring loaded flapper valve or rotary valve

Settling Chambers• Settling chambers use the force of gravity to remove solid

particles• The gas stream enters a chamber where the velocity of the

gas is reduced• Large particles drop out of the gas and are recollected in

hoppers• Because settling chambers are effective in removing only

larger particles, they are used in conjunction with a more efficient control device

SETTLING CHAMBERS

GASEOUS POLLUTANTS• The most common method for controlling gaseous pollutants is the

addition of add-on control devices to recover or destroy a pollutant

• There are four commonly used control technologies Absorption Adsorption Condensation Incineration

• The choice of control technology depends on the pollutant(s) that must be removed the removal efficiency required pollutant gas stream characteristics specific characteristics of the site

Absorptiono Gaseous pollutant is dissolved in a liquid

Adsorptiono The binding of molecules or particles to a surfaceo In this phenomenon molecules from a gas or liquid will be attached in a

physical way to a surface

Condensationo Process of converting a gas or vapour to liquido Any gas can be reduced to a liquid by lowering its temperature and/or

increasing its pressure

Incineratoro Most used to control the emissions of organic compounds from process industries

Thermal incinerator general case

Catalytic incinerator

• RECORD AND INVENTORY