8-filters
TRANSCRIPT
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Air FiltersAC units and control
Dr. Ahmed Elsaft
College of Engineering & TechnologyMechanical and Marine Engineering Dept.
Arab Academy for Science, Technology and
Maritime Transport
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Contents
Indoor air quality
urpose o ers
Types of filters
Filters selection
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Indoor air is one of the top five environmental threats to
uman ea .
According to the World Health Organization, 30% of
Syndrome (SBS).
SBS is characterized by headaches, nausea, irritated
nasal passages, itchy eyes, and skin irritation amongbuilding occupants.
,recently ranked the Number 1 management issue by the
International Facilities Management Association.
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Indoor Air ualit IA
affects the health and well-being of occupants.
How well indoor air satisfies the three basic requirements for
uman occupancy :-
a erma accepta ty
(b) Maintenance of normal concentrations of respiratory gases(c) Dilution and removal of contaminants to levels below health
or odor discomfort thresholds.
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urpose o ers
To remove particulates from air-stream. Depends on:
Particle size
Shape Mass
Construction
Electrostatic properties
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Filter Particles larger than 2.5 m are classified as coarse dust
w e a ess an . m are cons ere as ne us .
Arrestance: A standardized synthetic dust consisting of,mass fraction of the dust removed is determined.
Dust-spot efficiency: Atmospheric dust is passed into the
air cleaner, and the discoloration effect of the cleaned airon filter paper targets is compared with that of the
.
Fractional efficiency or penetration: Uniform-sized particles
are fed into the air cleaner and the percentage removed bythe cleaner is determined.
DOP: is a penetration test where Di-Octyl Phthalate (oily.
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Filter
Group I: Panel-type filters of expanded metal. (Aluminum Filter)
Group Ill: Extended-surface filters of fine glass fibers. (Bag Filter)
roup : ea e pane - ype ers o ne syn e c ers en s. yn e c er
Group IV: Extended-area pleated HEPA-type filters of ultra fine glass fiber
paper. Biological grade air filters are generally 95% DOP efficiency; HEPA
filters are 99.97% and 99.99%; and ULPA filters are 99.999%.
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Comparative Performance of Viscous Impingement and Dry-Media Filters
Group IPanel-type filters of spun glass, open cell foams, expanded metal and screens, synthetics, textile
denier woven and nonwoven, or animal hair.
Grou II
Pleated panel-type filters of fine denier nonwoven synthetic and synthetic-natural fibers blends, orall natural fibre.
Group III- ,
fibers, or wet-laid paper of cellulose- glass, synthetic, or all-glass fibers.
Group IV
Extended-area pleated HEPA-type filters of wet-laid ultra fine glass fibre paper. Biological grade air. .
99.999%.
Notes:1. Group numbers have no significance other than their use in this figure.
. .
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FilterMeasured byEfficiencyNew ClassEurovent classType
Synthetic dustweight arrestance
65, 80, 90G4EU4
40, 60, 80,
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AHU/PAU-Filters
Air filtration is an important component to achieve
an acceptable indoor air quality. Low-efficiency filters of the panel type as pre-filter
Medium- and hi h-efficienc ba t e for filterin
the air
-
removal of objectionable odors
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Test Method for Filters with different efficiency
Weight
arrestance
Dust Spot Di-Otyl
Phthalate
DOP
Particle size of test
dust
Large particles
in atmospheric
Atmospheric dust 0.3mparticles
Means to determine
dust concentration
Precision
Balance
Change in light
transmission
Particle count
Application Low efficiency
filter
Medium efficiency
filter
High
efficiency filter
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Low Efficiency Filter
Dust spot efficiency lower than 30%
Panel type
Dimension 500mm x 500mmFilter media
Corrugated metal wire mesh
Dr and reusable-n lon
Dry and disposable Glass fibre mats
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Medium Efficiency Filter
Filter efficiency between 30% to 95%
Extended surfaces such as pleated mats or bags are used to
Increase surface area of the filter media
Increase air velocity flowing through the filter media
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High Efficiency Particulate Air Filter
It remove dust particle by filtration of the passing air;
The filter media is glass fibre of submicrometer diameter
that is formed into pleated paper mats (dry and disposable).
The erformance of filter media is measured b al ha value
which is a function of penetration in % and pressure drop
(mm).
Typical size of filter is 600mm x 600mm x 300mm
Surface filter media area may be 50 times of the face area
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High Efficiency Particulate Air Filter(Contd)
Application: meet the requirement of di-octyl phthalate (DOP) 99.97%
efficiency for dust particle 0.3m
Clean room
Clean space for microelectronic industry
Pharmaceutical industry Precision manufacturing industry
Operating theatre in hospital
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Princi les of o eration
When traveling in the air stream of the ionizing
field, positively charged dust particles areattracte an attac e to t e groun p ates.
Dust particles agglomerate at the ground plates.
that they are blown off and carried away by the airstream.
Application:
Cigarettes smoke
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Electronic air cleaner(contd)
A hi h DC otential of 1.2kV is a lied to the ionizin field.
Positive ions generated from the ionizer wire charge the dust particles. After passing the ionizing section, dust particles come to a collecting section.
This section consists of several plates alternatively grounded and insulated.
A strong electric field is produced by a DC potential of 6KV is applied to these
plates. Dust particles become positively charged which are attracted and
attached to the ground plates.
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Activated carbon filter
Principles of operation: Removal by absorption.
Activated carbon has porous surface.
carbon, bond to these surfaces and come in contact with the carbon
granules.
Reactivation or regeneration required for activated carbon at the end ofits life
Construction
.
Activated carbon is placed in special tray This special tray slides easily into position to form activated carbon beds
These activated carbon beds are sealed into the cell housing by facing
plates.
Low efficiency filter is placed as pre-filter
l Refuse storage room ventilation: removal of objectionable odour and
irritating vapour of gaseous airborne particles 3nm to 6nm in size
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Activated carbon filter
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Effects of indoor air pollution
IAQ problems which affect people
fall into three general areas: (a)
and (c) chronic health effects.
Pollutants in our indoor environment
affect work productivity. Therelationship between point sources
con am nan s an suscep e
population will determine the risk
and effect of indoor air pollution,and this is often driven by
inadequate ventilation
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selection
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2- Specific particle size range or aerosolsthat require filtration
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The most important
characteristics of the air
the air filters.
Particles less than 2.5micrometer in diameter
are generally reoffered to
as fine with those greaterthan 2.5 micrometer
being considered as
.
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Three operating characteristics thatdistinguish the various types of fi lters:
1-Efficiency: the ability of the filter to removeparticulate matter from an air-stream.
2-Air flow resistance: is the pressure dropacross the filter at a given air flow rate.
3-Dust-holding capacity: the amount of
particulate type of dust that filters can holdwhen it is operated at a specified air flowrate.
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A standardized synthetic dust consisting of
Dust spot efficiency :
into the filter, and the discoloration effect ofthe cleaned air filter paper targets is
com ared with that of that of the incominair.
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Fractional efficiency orenetration:
Uniform-sized particles are fed intothe filter and the percentage removedb the filter is determined b aphotometer or condensation nucleicounter
Particle size efficiency:Atmospheric dust is fed to the filterand air samples taken upstream and
downstream are drawn through aparticle counter to obtain efficiencyverses particle size
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Test Method for Filters with different efficiency
Weight
arrestance
Dust Spot Di-Otyl
Phthalate
DOP
Particle size of test
dust
Large particles
in atmospheric
Atmospheric dust 0.3mparticles
Means to determinedust concentration
PrecisionBalance
Change in lighttransmission
Particle count
Application Low efficiency
filter
Medium efficiency
filter
High
efficiency filter
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Straining.
openings that are smaller than the
particulate being removed
Direct interce tion.
The particles follow a fluid
that the particle contacts the fiber
and remains there
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Inertial deposition
Coated viscous material. Adhesivecoating, wire screen impingement filter
Diffusion
motion about their basic streamlines(Brownian motion), which contributes
to de osition on the fiber
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,
accumulating dust loadcauses pressure drop toincrease u to somemaximum recommendedvalue
Renewable media filters inwhich fresh media areintroduced into the air-stream as needed to
constant resistance andconsequently, constantefficienc
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Electronic filters, which if
maintained ro erl b re ularcleaning have relatively constant
pressure drop and efficiency
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a e o an ex en e sur ace con gura on
of deep space folds of submicron glass fiberpaper.
It must be capable of removing 99.97% of. .
s an ar or a s, c ean room, nuc ear,hospitals, semiconductor, electronics,pharmaceutical manufacturing and toxic-
articulate a lications
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ULPA filters can remove particles as
small as 0.1 microns.
Ultra low penetration air filters areextended media dry filters in a rigidframe that have a minimum particlecollection efficiency of 99.999% for
articles reater than or e ual to 0.12micron in size.
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Renewable media filters :(RMF)
1-Moving-curtain viscous
impingement filters.
2-Moving-curtain dry
media fi lters
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to remove and collectparticulate contaminants such
as dust, and smoke.
The filter consists of anionization section [small
-kV grounded] and col lectingplate section [a series ofparallel equally spaced with a
- .
Electronic fil ters should have an
indicator or alarm system toindicate when the high voltageis off or shorted out.
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Liquid sprayers:
Used to remove wettable solids contaminants, liquidcon am nan s an wa er so u e po u ng gases n
industrial
Ultra-violet lamps:
intensity 14,000 microwatt cm2. This would kill most
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Evaluation of fi lters
Degree of air cleanliness required.
Disposal of dust after it is removed from the air.
Amount and type of dust in the air to be filtered.
Operating resistance to air flow (pressure drop).
pace ava a e or ra on equ pmen .
Cost of maintaining or replacing filters.
.
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The most important characteristics
-the air filters.
Particles less than 2.5 micrometer
reoffered to as fine, with thosegreater t an .5 m e ng
.
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Three o eratin characteristics that distin uishthe various types of filters:
.
particulate matter from an air-stream.
. r ow res s ance: res s ance s e pressure
drop across the filter at a given air flow rate.
3.Dust-holding capacity: the amount of particulate
type of dust that filter can hold when it is operated
at a specified air flow rate.
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Typical Filter Applications Classified by Filter Efficiency and Type
Pre-filter Pre-filter/Filter Final Filter
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Arrestance:A standardised synthetic dust consisting of various particle sizes is fed to the filter.
A standardized atmospheric dust is passed into the filter, and the discoloration effect of
the cleaned air filter paper targets is compared with that of the incoming air.
ract ona e c ency or penetrat on:Uniform- sized particles are fed into the filter and the percentage removed by the filter isdetermined b a hotometer or condensation nuclei counter.
Particle size efficiency:
drawn through a particle counter to obtain efficiency verses particle size.
Mechanisms of particle
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Mechanisms of particle
collection:1. Straining.
Strain particles through membrane openings that is smaller than the particulate
being removed.
2. Direct interception.The particles follow a fluid streamline close enough to a fibre that the particle
contacts the fibre and remains there.
3. Inertial deposition.Coated viscous material. [adhesive coating, wire screen impingement filter]
4. Diffusion.Very small particles have random motion about their basic streamlines (Brownian
motion), which contributes to deposition on the fibre.
5. Electrostatic effects.Particles or media charging can produce changes in the collection of dust.
f f
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f fCommon filters are grouped as follows:
. , n w c e accumu a ng us oa causes pressure rop oincrease up to some maximum recommended value.
2. Renewable media filters, in which fresh media are introduced intothe air-stream as needed to maintain essentially constant resistance and
consequently, constant efficiency.
,
have relatively constant pressure drop and efficiency.
4. Panel filters, there are a variety of panel filters including viscous, y- y x - u , y
Particulate Air [HEPA] filters.
5. Viscous impingement filters, are panel filters made of coarsefibers with high porosity. Glass fibers, steel or aluminium mesh, and metal baffles
are used for filter media. The filter medium is often coated with a viscous
substance e.g. filter oil [adhesive] that causes particulates to impinge on the
.
HEPA filt
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HEPA filters: Stands for High Efficiency Particulate Air filters.
Made of an extended surface configuration of deep space folds of .
it must be capable of removing 99.97% of particles as small as 0.3microns.
These filters are the standard for labs clean room nuclear hos italssemiconductor, electronics, pharmaceutical manufacturing and toxic-particulate applications.
Stands for Ultra Low Penetration Air filters.
ers can remove par c es as sma as a ou . m crons.
Ultra low penetration air filters are extended media dry filters in a rigidframe that have a minimum particle collection efficiency of 99.999
ercent for articles reater than or e ual to 0.12 micron in size
Renewable Media Filters:
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Renewable Media Filters:
Types of RMF:
1. Movin -curtain viscous im in ement filters.
2. Moving-curtain dry media filters.
Using electrostatic precipitation to remove and collect
, .
The filter consists of an ionization section [small diam.-
plate section [a series of parallel equally spaced with a
positive DC volt of 4-10kV]. Electronic filters should have an indicator or alarm
system to indicate when the high voltage is off or
shorted out.
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.
used to remove wettable solids contaminants, liquid contaminates andwater soluble polluting gases in industrial areas such as hydrogen
sul hide, Sul hur dioxide, Nitro en oxide and carbon monoxide.
2. Activated Carbon Filter:The carbon sheath is heated to a high temperature to be activated. Oncens a e , e ac va e car on w a rac e a oms o e gases a
cause the odour. carbon will absorb as much as 50% of its weight inforeign gases. . . . ,
-- removes dangerous household chemical gases from things likecleaners, paints, solvents, carpets, furniture, and other materialcontaining chemical substances.
3. Ultra-Violet Lamps:Lamps give an electromagnetic (Ultraviolet) radiation of intensity 14,000
.seconds.
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va ua on o ers:
1. Degree of air cleanliness required.
. sposa o us a er s remove rom eair.
.
filtered..
drop).
5. S ace available for filtration e ui ment.6. Cost of maintaining or replacing filters.
7. Initial cost of the s stem.
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