air and noise pollution environmental protection and control

Post on 05-Apr-2017

114 Views

Category:

Environment

2 Downloads

Preview:

Click to see full reader

TRANSCRIPT

Syed Jeelani Basha

Asst.Prof

JNTUK syllabus

Air Pollution control

equipments and

methods

• For particulate matter

1. Settling chambers

2. Fabric filters

3. Scrubbers

4. Cyclones

5. Electrostatic

precipitators

• For Gaseous

pollutants

1. Absorption

2. Adsorption

3. Combustion

Source correction methods

Raw material changes

Process changes

Equipment modification & replacement

Objectives of control equipment

o Prevention of nuisance

o Prevention of physical damage to property

o Elimination of health hazards to plant personnel

o Recovery of valuable waste product

o Minimization of economic losses

o Improvement of product quality

Particulate control equipment

o Gravitational settling chambers

o Fabric filters

o Scrubbers

o Cyclone separator

o Electrostatic precipitators

o Efficiency of a separating device

η= quantity of particulates collected from gas/ quantity of particulates present initially

Gravitational settling chamber

o Used to remove particles with size greater than 50 μm.

o Velocity of flue gas reduced in large chamber.

o Particles settle under gravitational force.

Vs= hV/ L ----------- (i)

L= length of chamber

V= horizontal velocity of carrier gas

Vs= settling velocity of particulates

h= height through which particulates travel before

settling down

By stokes law

Vs= g( p- )D2/18μ --------- (ii)

D= dia of particle

g= acceleration due to gravity

ρp= density of particle

ρ = density of gas

μ= viscosity of gas

From eq- i and ii

D= [18Vhμ/ Lg ( p- )]1/2

D = is minimum size of particle that can be

removed in a settling chamber

Advantages

o Low initial cost.

o Easy to design.

o Low pressure drop.

o Low maintenance cost.

o Dry and continuous disposal of solid particulates.

Disadvantages

o Require large space.

o Less collection efficiency.

o Only larger size particles can be collected.

Application

o Industrial application is limited.

o Used widely for removal of large solid

particulates from draft furnace, kilns.

o Sometimes used in process industry, food and

metallurgical industry.

o Used as pre-cleaners for high efficiency

collectors.

Cyclone separator o Centrifugal force is utilized to separate the

particulate matter.

o It can remove 10 to 50 μm particle size.

o Used mostly in industries.

Dp, min= [9 μ B/ V Nt( p- )] ½

Dp, min= dia of smallest particles that can be

removed cm

μ = viscosity of the fluid

B= width of cyclone inlet duct

V= avg. inlet velocity

Nt= no of turns made by gas stream in cyclone

p = density of particles

= density of fluid

o Design factor having greatest effect on

collection efficiency is cyclone diameter.

o Smaller dia, higher is efficiency, because

centrifugal action increase with decreasing radius

of rotation.

o Cyclone efficiencies > 90 % with particle dia of

10 μ

o > 95 % with particle dia 20 μ.

Efficiency

o Conventional efficiency

o High efficiency- smaller body dia to create greater separating force.

o Increase collection efficiency, if increase in dust particle size, dust particle density, gas inlet velocity, inlet dust loading, cyclone body length (no of gas revolutions)

o Decrease collection efficiency due to increase in gas viscosity, cyclone dia, gas outlet dia, inlet width, and inlet area

Operating problems

o Erosion

o Corrosion

o Material build up

Advantages

o Low initial cost.

o Require less floor area.

o Simple construction and maintenance.

o Can handle large volume of gas at high temp.

o No moving parts

Disadvantages

o Requires large head room.

o Less efficiency for smaller particles (<10μm).

o Sensitive to variable dust load and flow rate.

Applications

o Control gas borne particulates from industries

like cement, feed and grain processing, food and

beverage processing, mineral processing, paper

and textile industries and wood working

industries.

o Used in recovery of catalyst ducts in petroleum

industry and reduction of fly ash emission.

Electrostatic precipitators

o Works on the principle of electrical charging

of particulate Matter (-ve) and collecting it in a

(+ve) charged surface.

o 99% efficiency.

o Can remove particle size range of 0.1 μm to 1

μm.

Six major components

o A source of high voltage

o Discharge electrodes and collecting electrodes

o Inlet and outlet for gas

o A hopper for disposal of collected material

o An electronic cleaning system

o An outer casing to form an enclosure around

electrodes

Principles

o Gas stream passed two electrodes.

o High potential difference is maintained.

o Out of two electrodes, one is discharging other

collecting.

o Potentials of 100 kv are used.

o Ionization creates active glow zone called

“corona”. o Gas ionization is dissociation of gas molecules

into free ions.

o As particulates pass through field, they get

charged and migrate to oppositely charged

electrode.

o Particles deposited on collecting electrodes, lose

charge and removed mechanically by rapping.,

vibration or washing to a hopper.

Single stage and two stage precipitators

o Single stage gas ionization and particulate

collection in a single stage.

o Two stage, particle ionized in first chamber and

collected in second chamber.

o Industrial precipitators single stage design.

o Two stage used for lightly loaded gases.

o Single stage for more heavily loaded gas streams.

Efficiency

o General collection efficiency is high, nearly

100%

o Installations operate 98 and 99% efficiency.

o Acid mist and catalyst recovery efficiencies in

excess of 99%.

o Carbon black, because of agglomeration

tendency collection efficiency less than 35%.

E= 1- e -Utf

E= collection efficiency

f= specific collecting area of precipitator,

expressed as sq m of collecting electrode area

per cubic m of gas handled per s.

Ut= migration velocity of particle towards

collection electrode

e= napierian log base

Design parameter

o Volumetric flow rate

o Composition

o Temperature

o Dew point

o Dust particle conc.

o Size of particle

o Bulk density

o Tendency of allgomorate

Advantages

o High collection efficiency.

o Particles may be collected dry or wet.

o Can be operated at high temp. (300-450˚c). o Maintenance is normal.

o Few moving parts.

Disadvantages

o High initial cost.

o Require high voltage.

o Collection efficiency reduce with time.

o Space requirement is more.

o Possible of explosion during collection of

combustible gases or particulates.

Application

o Cement factories

o Pulp and paper mills

o Steel plants

o Non- ferrous metal industry

o Chemical industry

o Petroleum industry

o Carbon black industry

o Electric power industry

Fabric filters or cloth filters o Flue gas is allowed to pass through a woven

fabric, which filters out particulate matter.

o Small particles are retained on the fabric.

o Consists of numerous vertical bags 120-400

mm dia and 2-10 m long.

o Remove particles up to 1 μm.

o Its efficiency up to 99%.

Factors affecting efficiency

Efficiency decrease due to

o Excessive filter ratio:- ratio of carrier gas vs

gross filter area

o Improper selection of filter media:- temp.

resistance, resistance to chemical attack and

abrasion resistance taken into consideration.

Operating problems

o Cleaning

o Rupture of cloth

o Temperature

o Bleeding

o Humidity

o Chemical attack

Filter cleaning

o Rapping

o Shaking

o Back wash

o Pulse jet

Filter medium

o Carrier gas temp.

o Carrier gas composition

o Gas flow rate

o Size and shape of dust particles

Fabric Max.

operatin

g temp.

(˚ C)

Acid

resistance

Alkali

resistance

Abrasion

resistance

Tensile

strength

Kg/cm2

Cotton 82 Poor Good Very good 4920

Wool 93 Very good Poor Fair to

good

1755

Nylon 93 Poor to

fair

Excellent Excellent 5625

Dacron 135 Good Good Very good 5625

Polypropyl

ene

93 Excellent Excellent Excellent 7730

Fiber glass 290 Fair to

good

Fair to

good

Fair 14,060

Physical properties of bag filters

Advantages

o Higher collection efficiency for smaller than 10 μm

particle size.

o Performance decrease becomes visible, giving

prewarning.

o Normal power consumption.

Disadvantages

o High temp. gases need to be cooled.

o High maintenance and fabric replacement cost.

o Large size equipment.

o Fabric is liable to chemical attack.

Application

o Metallurgical industry

o Foundries

o Cement industry

o Chalk and lime

o Brick works

o Ceramic industry

o Flour mills

Scrubbers or wet collectors

o Particulate matters are incorporated into liquid droplets

and removed from the gas stream.

o Flue gas made to push up against a down falling water

current.

o Particulate matter mix up with water thus falls down

and gets removed.

Collection mechanism

o Impingement

o Interception

o Diffusion

o Condensation

Types of scrubbers

o Spray towers

o Venturi scrubbers

o Cyclone scrubbers

o Packed scrubbers

o Mechanical scrubbers

Spray towers

Venturi scrubber

Cyclone scrubber

Packed scrubbers

Mechanical scrubbers

Advantages

o Simultaneously remove particulates and gaseous

pollutants.

o Hot gases can be cooled down.

o Corrosive gases can be recovered and neutralize.

Disadvantages

o Lot of waste waters produced.

o Poses freezing problem in cold countries.

o Maintenance cost is high when corrosive materials are

collected.

Choice of equipment

1. Particulate size

2. Particulate loading

3. Efficiency required

4. Properties of carrier gas

1. Composition 6. Humidity

2. Temp. 7. Combustibility

3. Pressure 8. Reactivity

4. Viscosity 9. Toxicity

5. Density 10. Electrical property

5. Flow characteristics of carrier gas 1. Flow rate

2. Variation in flow rate

6. Specific property of contaminant 1. Composition 6.Toxicity

2. Contaminant phase 7. Hygroscopicity

3. Solubility 8. Agglomerating

characteristics

4. Combustibility 9. Electrical and sonic

properties

5. Reactivity 10. Catalyst poisoning

7. Allowable pressure drop

8. Contaminate disposal

9. Capital and operating cost of equipment

10. Ease of maintenance and reliability

Economical aspects

1. Cyclones:- cheap to install, power consumption

moderate, maintenance cost normal.

2. Filters:- expensive to install, power consumption

moderate. Maintenance cost high.

3. Electrostatic precipitators:- most expensive regarding

installation, power consumption moderate to low as

pressure drops. Maintenance cost moderate

4. Scrubbers :- installation cost moderate, maintenance

cost not high, high rate of power consumption.

Control of gaseous contaminants

Methods of control include:

o Absorption

o Adsorption

o Secondary combustion

Absorption

o Effluent gas passed through absorbers

(scrubbers), which contain liquid absorbent.

o Efficiency depends on 1. Amount of surface contact between gas and liquid

2. Contact time

3. Conc. of absorbing medium

4. Speed of reaction between the absorbent and gases

o Absorbents used to remove SO2, H2S, SO3, F

and oxides of nitrogen.

Equipments using principles of absorption for

removal of gaseous pollutants

o Packed tower

o Plate tower

o Bubble cap plate tower

o Spray tower

o Liquid jet scrubber absorbers

Gaseous

pollutants

Common absorbents used in solution form

SO2 Dimethylaniline, ammonium sulphite,

ammonium sulphate, sodium sulphide, calcium

sulphite, alkaline water,

H2S NaOH and phenol mix (3:2), tripottasium

phosphate, sodium alamine, sodium

thioarsenate, soda ash

HF Water, NaOH

NOX Water, aqueous nitric acid

Adsorption

o Surface phenomenon, require large solid surface

o Adsorption towers use adsorbents to remove the

impurities from the gas stream.

o The impurities bind either physically or chemically to

the adsorbing material.

o The impurities can be recovered by regenerating the

adsorbent.

o Adsorption towers can remove low concentrations of

impurities from the flue gas stream.

Construction and Operation

o Adsorption towers consist of cylinders packed with the

adsorbent.

o The adsorbent is supported on a heavy screen

o Since adsorption is temperature dependent, the flue gas

is temperature conditioned.

o Vapor monitors are provided to detect for large

concentrations in the effluent. Large concentrations of

the pollutant in the effluent indicate that the adsorbent

needs to be regenerated.

Advantages of Adsorption Towers

o Very low concentrations of pollutants can be removed.

o Energy consumption is low.

o Do not need much maintenance.

o Economically valuable material can be recovered during

regeneration.

Gaseous pollutants Adsorbents used in solid form

SO2 Pulverized limestone or

dolomite, alkalized alumina

H2S Iron oxide

HF Lump limestone, porous sodium

fluoride pellets

NOX Silica gel

Organic solvent vapours Activated carbon

Secondary combustion

o Flame or catalytic combustion can be utilized

when gases or vapors to be controlled.

o Fume and vapor incinerators

o After burners

o Flares, either with steam injection or venturi

flare

o After burners on incinerators met with varying

success depending on kind of after burner used

and type of incinerator.

o Flare design for smokeless combustion gases of

variable composition and wide range of flow

rates.

o Venturi flares, mix air with gases in proper ratio

prior to ignition to achieve smokeless burning.

Fume incinerators

o When conc. of combustible portion of gas

stream below flammable range, catalytic

combustion process used.

o Used to control effluent gases, fumes and odors

from refineries, burning waste, cracking gases,

chemical plants, paint and enamel ovens.

Method is expensive when

1. Fuel values of gaseous discharge low

2. Moisture content of discharge is high

3. Exhaust volume is extremely large

Factors considered in design of incinerators are

1. Sufficient air for combustion reaction

2. Adequate temp.

3. Adequate retention time

o Incineration equipment, single combustion

chamber.

o Combustion chamber proportioned that gas

velocity, gas flow patterns, established produce

adequate retention time.

o Avg. retention time 0.2-0.3 s at temp. 650 ˚C and higher.

Noise Pollution

Contents

• Noise

• Noise Standards

• Sources of Noise Pollution

• Causes of Noise Pollution

• Effects of Noise Pollution

• Control of Noise Pollution

• IS14000

What is Noise?

• In simple terms, noise is unwanted sound. Sound is a form

of energy which is emitted by a vibrating body and on

reaching the ear causes the sensation of hearing through

nerves.

• Sounds produced by all vibrating bodies are not audible.

The frequency limits of audibility are from 20 HZ to 20,000

HZ.

• Sounds of frequencies less than 20 HZ are called infrasonics

and greater than 20,0000 HZ are called ultrasonics.

A noise problem generally consists of three inter-related

elements

1. The source,

2. The transmission path and

3. The receiver.

This transmission path is usually the atmosphere

through which the sound is propagated, but can include the

structural materials of any building containing the receiver

How it is computed?

• The intensity of sound is measured in sound pressure

levels (SPL) and common unit of measurement is decibel,

dB.

• If the sound levels are measured in terms of pressure,

then, sound pressure level, LP is given by,

The LP is measured against a standard reference

pressure

, which is equivalent to zero decibels.

Day-night equivalent noise levels (Ldn):

The day night equivalent noise levels of a community

can be expressed as

where,

Ld = day-equivalent noise levels (from 6AM - 9 PM), dB

Ln = night equivalent noise levels (from 9 PM - 6 AM), dB

Characteristics of Noise

• Sound pressure

• Frequency

• Duration

• Time of the day

• Location

Kinds of Noise

• Continuous

• Variable

• Impulse or Impact

• Chemical Noise

• Instrumental Noise

Variable Noise

Impulse Noise

Continuous Noise

Sources of Noise Pollution

• Household Sources

• Social Events

• Commercial and Industrial Activities

• Transportation

Household Sources

• Food Mixer

• Grinder

• Vacuum Cleaner

• Washing machine and Dryer

• Air Conditioner

• Cooler

• TV

• Loud speaker

Social Events

• Places of Worship

• Discos and Functions

• Political Parties

• Markets where people sell goods with

loudspeaker.

When these events are not often, they can be

termed as nuisance rather than noise pollution.

Commercial and Industrial Activities

• Printing Presses

• Manufacturing Industries

• Construction Sites

Sources of Construction Noise

• Pneumatic Hammers

• Air Compressors

• Bulldozers

• Loaders

• Dump Trucks

• Pavement breakers

Sources of Industry Noise

• Fans

• Motors

• Compressors mounted outside

Transportation

• Road Traffic Noise

• Aircraft Noise

• Noise from Rail Roads

Causes of Noise Pollution

• Poor Urban Planning

• Sounds from Motor Vehicles

• Sounds from Musical Instruments

• Car Alarms

• Office Equipment

• Factory Machinery

• Construction Work

• Barking Animals

• Appliances

• Audio Instruments

• Loud Speakers

• Noise Created by People

Effects of Noise Pollution

• Effects on Human

• Effects on Animals

• Effects on Environment

Effects on Human • Hearing Impairment

• Interference with Spoken Communication

• Decrease in Efficiency

• Lack of Concentration

• Fatigue

• Sleep Disturbances

• Cardiovascular Disturbances

• Disturbance in Mental Health

• Impaired Task Performance

• Negative Social Behavior and Annoyance reactions

• Abnormal Fetus

• Temporary or Permanent Deafness

Diseases Caused by Noise Pollution

• High Blood Pressure

• Heart Attack

• Deafness

• Stress

Effect on Animals

• Damages Nervous system

• They become Dangerous and Attacking

• Raise Metabolism

• Death of Certain Species

• Genetic and Evolutionary Problems

Effects on Environment

• Breakage of Earth Barrier

• Damages Buildings, bridges and Monuments

Control of Noise Pollution

1. Control at Source

2. Control in the Transmission Path

3. Using Protective Equipment (Receiver)

Control at Source

• Reducing the Noise Levels from Domestic Sectors

• Maintenance of Automobiles

• Use of Economic instruments

• Control over Vibrations

• Low Voice Speaking

• Prohibition on Usage of loudspeakers

• Selection of Machinery

• Maintenance of Machines

Control in the Transmission Path

• Installation of Barriers

• Installation of Panels and Enclosures

• Green Belt development

Using Protection Equipment

• Job Rotation

• Exposure Reduction

• Hearing Protection

• Protection at the Receiver End

Ear plugs

Noise Control Techniques

• Sound insulation

• Sound Absorption

• Vibration Damping

• Vibration Isolation

• Urban Planning

• Public Education and Awareness

IS14000

• ISO 14000 is a family of standards related to environmental

management that exists to help organizations

1. minimize how their operations (processes, etc.) negatively

affect the environment (i.e., cause adverse changes to air,

water, or land)

2. comply with applicable laws, regulations, and other

environmentally oriented requirements

• ISO 14000 is similar to ISO 9000 quality management in

that both pertain to the process of how a product is

produced, rather than to the product itself.

ISO 14000 refers to a series of standards on environmental

management tools and systems. ISO 14000 deals with a

company's system for managing its day-to-day operations

and how they impact the environment.

1. The Environmental Management System and

Environmental Auditing address a wide range of issues

to include the following:

2. Top management commitment to continuous

improvement, compliance, and pollution prevention.

3. Creating and implementing environmental policies,

including setting and meeting appropriate targets.

4. Integrating environmental considerations in operating

procedures.

5. Training employees in regard to their environmental

obligations.

6. Conducting audits of the environmental management

system.

top related