air control devices

8/3/2019 Air Control Devices

1/35

AIR POLLUTION CONTROL DEVICES: for CRITERIA

POLLUTANTS including VOCs

1. Ground Level O32. CO

3. SO24. NO2

5. Pb6. Particulate Matter

a) PM10b) Total Suspended Particulate Matter (TSP)

Particles ranging in size from 0.1 micrometer to about 30

micrometer in diameter are referred to as total

suspended particulate matter (TSP). TSP includes a broad

range of particle sizes including fine, coarse, and

supercoarse particles.


2/35

National Ambient Air Quality Guideline for Criteria Pollutants:

Philippine Clean Air Act of 1999 (R.A. 8749)

utants

Short Terma Long Termb

m g/Ncm ppm

Averaging

Time m g/Ncm ppm Averaging Time

Suspended Particulate

Matterc TSP

PM-10

230d150f 24 hours24

hours

9060 1 yeare1 yeare

Sulfur Dioxidec 180 0.07 24 hours 80 0.03 1 year

Nitrogen Dioxide 150 0.08 24 hours

Photochemical

Oxidants as Ozone

14060 0.070.03 1 hour8

hours

Carbon Monoxide 35

mg/Ncm10

mg/Ncm

309 1 hour8

hours

Leadg 1.5 3 monthsg 1.0 1 year


3/35

Good 0.000 0.034

Fair 0.035 0.144

Unhealthy for

sensitive groups

0.145 0.224

Very Unhealthy 0.225 0.304

Acutely unhealthy 0.305 0.604

Emergency 0.605 0.804

Sulfur Dioxide (ppm) [24-hour]


4/35

Good None

Fair None

Unhealthy for sensitive

groups

People with respiratory disease, such as asthma, should

limit outdoor exertion.

Very unhealthy Pedestrians should avoid heavy traffic areas. People with

heart or respiratory disease, such as asthma, should stay

indoors and rest as much as possible. Unnecessary trips

should be postponed. People should voluntarily restrict

the use of vehicles.

Acutely unhealthy People, should limit outdoor exertion. People with heart

or respiratory disease, such as asthma, should stay indoors

and rest as much as possible. Unnecessary trips should be

postponed. Motor vehicle use may be restricted. Industrial

activities may be curtailed.

Emergency Everyone should remain indoors, (keeping windows and

doors closed unless heat stress is possible). Motor vehicle

use should be prohibited except for emergency situations.

Industrial activities, except that which is vital for public

safety and health, should be curtailed.


5/35

AIR POLLUTION CONTROL DEVICES

1. NOx CONTROL and REMOVAL

Fuel switching

Conversion to a fuel with a lower nitrogen content or one that

burns at a lower temperature may result in a reduction ofNOx

emissions.

Combustion of natural gas or distillate oils tends to result in lowerNOx emissions than is the case for coal or heavy fuel oils.

technical constraints and the availability and costs of alternative

fuels are major considerations in determining the viability of fuel

switching.

fuel switching may result in greater emissions of other criteriapollutants.


6/35

Fuel DenitrificationFuel denitrification of coal or heavy oils could, in principle, be used to

control fuelNox formation.

Denitrification currently occurs as a side benefit of fuel pretreatment to

remove other pollutants, such as pretreatment of oil by desulfurization

and chemical cleaning, or solvent refining of coal for ash and sulfur

removal.

The low denitrification efficiency

and high costs of these processes do

not make them attractive on the

basis ofNOx control alone, but they

may prove cost effective on the basisof total environmental impact.


7/35

PROCESS MODIFICATION POST PROCESS MODIFICATION

Low NOx burners Selective catalytic reduction

Natural gas burner/reburn Selective noncatalytic reduction

Water/stream injection Nonselective catalytic reduction

Staged combustion

Flue gas recirculation

Low excess air

Staged overfire air


8/35

NOx

NOx

NH3NOx

NH3NOx

N2H2O

N2H2O

FLUE

GAS

CLEAN

FLUE GAS

CATALYST BED

Removal of NOx by SCR

SELECTIVE CATALYTIC REACTOR (SCR)

4NO + 4NH3

+ O2

4N2

+ 6H2

O

2NO2 + 4NH3 + O2 3N2 + 6H2O

2NO + (NH2)2CO + O2 2N2 + 2H2O + CO2


9/35

CONTROL OF SULFUR DIOXIDE EMISSIONS

1. PROCESS MOFIFICATION OPTIONSFuel Switching

Coal Washing

Coal Gasification and Liquefaction

Fuel Switching

Many coal-fired facilities attempt to reduce these emissions byswitching to coal with a lower sulfur content, such as subbituminous

coal which generally contains less sulfur than bituminous coal.


10/35

Coal Gasification and Liquefaction

Organic sulfur, which is part of themolecular structure of the coal,

cannot be removed by washing or

other physical cleaning processes.

Chemical desulfurization of

organic sulfur from coal is extremely

expensive.

Coal gasification and liquefaction

can remove much of the organic

sulfur, but results in a substantial loss

of total available heating value.

Coal Washing

Much of the sulfur in coal is in pyrite (FeS2) or in mineral sulfate

form, much of which can be removed by washing or other physicalcleaning processes.

However, disposal of the solid or liquid wastes formed during these

processes can be difficult and/or expensive.


11/35

Desulfurization of Oil and Natural Gas

The sulfur in crude oils and natural gas can be removedeasily and economically and the elemental sulfur recovered

as a by-product can be sold as a raw material.

The steps in the desulfurization of oil or natural gas are:

R-S + H2 H2S + R (where R represents any organic

group)

H2S + 3/2 O2 H2O + SO2

2H2S + SO2 2H2O + 3S2H2S + SO2 2H2O + 3S


12/35

Fluidized Bed Combustion

Also, combustion of crushed coal in a bed of a sorbent material

(fluidized-bed combustion) can reduce SO2 emissions. Sulfur dioxide inthe coal reacts with limestone or dolomite in the bed to form gypsum.


13/35

2. POST PROCESS MODIFICATION

Dry and wet scrubbing

are the most common

technologies to

desulfurize flue gas.

Slurries of sorbent and

water react with SO2 inthe flue gas.

SO2 emission control contd..


14/35


15/35

Particulate Matter CONTROL

1. PROCESS MODIFICATIONS

Process controls typically used to control particulate

matter emissions include fuel switching, coal cleaning,

and good combustion practices.

Particulate matter," also known as particle pollution or PM, isa complex mixture of extremely small particles and liquid

droplets. Particle pollution is made up of a number of

components, including acids (such as nitrates and sulfates),

organic chemicals, metals, and soil or dust particles.


16/35

2. POST-PROCESS AIR POLLUTION CONTROL DEVICESFour classes of control equipment are used to remove

PM from gas streams:

a. Mechanical collectors such as cyclones

b. Electrostatic precipitators

c. Fabric filters, also referred to as baghouses

d. Wet PM scrubbers


17/35

CYCLONE

Cyclones are essentially cylinders

with inlet and outlet ducts for theair stream. A vortex is created in the

cylindrical section of the cyclone

either by injecting the air stream

tangentially or by passing the gas

through a series of vanes. As the

particulate-laden gas is forced to

change

direction in the vortex, the inertia of

the particles forces them tocontinue in the original direction,

collide with the outer wall, and slide

downward to the bottom of the

device to be collected in a hopper.


18/35


19/35

ELECTORSTATIC PRECIPITATORS

Electrostatic precipitators use an electrostatic field to chargeparticulate matter in the flue gas stream. The charged

particles then migrate to a grounded collection surface. The

collected particles are periodically dislodged from the

collection surface by vibration or rapping.


20/35


21/35

FABRIC FILTERS

* also referred to as baghouses* capable of achieving the highest particulate removal

efficiencies of all the particulate control devices.


22/35

A fabric filter system consists of several filtering elements

(bags), a bag cleaning system, and dust hoppers contained

in a main shell structure. Fabric filters remove dust from agas stream by passing thestream through a porous

fabric. The fabric does some

of the filtering, but plays a

more important role by

acting as a support medium

for the layer of dust that

quickly accumulates on it.

The dust layer (cake) isresponsible for the highly

efficient filtering of small

particles, but also increases

the resistance to gas flow.


23/35

PM WET SCRUBBER

Wet PM scrubbers control PM and acid gases, with somecontrol of organics. Wet PM scrubbers are applied as a

post-process technique to:

1. Scrub particulates from incinerator exhausts;

2.Control particulate and gaseous emissions

simultaneously;3. Control acid gases;

4. Control sticky emissions that would otherwise plug

filter-type collectors;

5. Recover soluble dusts and powders; and6. Control metallic powders such as aluminum dust that

tend to explode if handled dry.


24/35

How does WET PM Scrubbers work?

Wet PM scrubbers remove particles from gas by capturing

the particles in liquid droplets (usually water) and

separating the droplets from the gas stream. The goal is to

cause the tiny pollutant particle to be lodged inside the

collecting droplet and then to remove the larger dropletfrom the gas stream. In general, the smaller the target

droplet, the smaller the size of particulate that can be

captured and the more densely the droplets are packed, the

greater the probability of capture.


25/35


26/35

CONTROL OF VOLATILE ORGANIC COMPOUNDS

1. PROCESS MODIFICATION STRATEGIES

Typical strategies are:

Change of coating formulation, such as conversion to water-based

paint;

Change from a VOC-based coating to a non-liquid coating such aspowder coat; and

Change to coating methods that increase transfer efficiency and

reduce total coatings used per application.


27/35

VOCs POST-PROCESS AIR POLLUTION CONTROL DEVICES

Typical post-process control devices ofVOC are:1. Carbon adsorber

2. Incinerator

3. Floating-roof storage tank

4. Vapor capture device during tank filling; and

5. Fluid capture, recycle, and reuse.

Many VOC emission sources are processes that are not enclosed or

contained and the VOC are emitted into the ambient work area. Before

the emissions can be routed to a control device, they must first be

captured.


28/35

Incinerators are used to control emission from curing

ovens, dryers, and other sources of organic vapors.Incinerators are

installed to allow

compliance with

regulatoryrequirements.

The ultimate function

of incineration is to

achieve complete

combustion. Incomplete

combustion can form

new, potentially more

toxic compounds.

INCINERATORS


29/35

TwoMajor types: Thermal and catalytic incinerators

Major Components of an incinerator:

1. Burner

- supplies air and fuel needed to provide heat.

- provides turbulent mixing and hot gas which are

necessary to oxidize the VOCs.

2. Heating/oxidizing Chamber

- acts as a holding space acts as a holding space that allows

time for all the vapors to oxidize

3. Heat recovery device

Incinerators include a recovery system to recover heat fromthe ho exhaust gases.

4. Gas stack


30/35


31/35

Non refractory linedCatalyst poisons P, Sn, Zn,Masking and fouling


32/35

Operating Principles of Incinerator Systems:

1. Proper Operating Temperature

The burner flame in the main chamber generates hot

combustion gas that heats the relatively cool VOC-

containing gas stream to the combustion temperature.

Combustion happens only when the auto-ignition

temperature.Auto-ignition temperature is the minimum temperature that

must be reached before combustion can occur (800 to

1400oF).


33/35

2. TURBULENCE

Turbulence provides the

mixing needed to bring the

organic material and the O2

together and helps transferheat between the hot

combustion gases and the

other VOC material


34/35

3. OXYGEN

- excess air is used to ensure complete combustion.-Excess air is kept low, heating the excess air requires

additional fuel.

- extreme levels of excess air can reduce incinerator

temperatures, thus reduce VOC removal efficiency

4. Residence Time

Residence time in an incinerator is measured from the time the

waste gas stream reaches the operating temperature, until the

time the waste gas leaves the combustion chamber.

It is determined by the size of the combustion chamber and the

gas flow rate through the chamber.


35/35

5. VOC Concentration

Inlet gas stream VOC concentration are limited to 500-7500

ppm.VOC concentrations are kept below 25% of the Lower

Explosive Limit (LEL) so that the incinerator flame does not

flash back to the process equipment.

air control devices

Documents