History of HEPA
Update to today
Per Lindblom
Hollingsworth & Vose
April 22, 2010
Presentation
• Historical review
• HEPA Filter Media choices
• Next Generation Micro fiberglass HEPA media
National Defense Research Council
• The National Defense Research
Council (NDRC), solicited the
assistance of a number of
university and industrial scientists
in the search for better smoke
filters.
• This effort resulted in important
U.S. advances in the theory and
technology of aerosol filtration.
– 1942 Dr. Irving Langmuir
developed a general theory
for mechanical filtration
– 1943 LaMer and Sinclair
developed instruments to
measure the filtration
efficiency of DOP smoke
(0.30 µm) particles
Diffusion
Interception
H&V develops Gas Mask Media
• The British sent filter paper
extracted from captured German
gas mask canisters to the U.S.
Army Chemical Warfare Service
Laboratories (CWS) in the early
days of the WW II.
• NRL analyzed media from a
captured German gas mask in
early WW II
– had unusually high particle
retention characteristics,
acceptable resistance to airflow,
good dust storage, and resistance
to plugging from oil-type
screening smokes.
– H&V developed US version of
this media for gas mask. Media
would be known as CWS type 6.
The Collective Protector
• Gas masks where practical in the
field but less so for Army HQ.
• To address this type of problem,
the U.S. Army Chemical Corps
developed a mechanical blower
and air purifier known as a
“collective protector” filter unit.
• the gas mask canister smoke filter
was refabricated into a filter
constructed of deep pleats
separated by a spacer panel and
sealed into a rigid rectangular
frame using rubber cement.
Manhattan Project
• In 1942 the top secret Manhattan
Project was formed.
• The Project created potential air
pollution problems that could be
solved only by using air filters
with filter media characteristics
similar to those of the CWS filter.
• The U.S. Army Chemical Corps
became the sole supplier of highperformance filters to the
Manhattan Project
• The filters developed in the
process was called
“superinterception” or “superefficiency” filters; later referred
to as “absolute” filters
Post World War II
• CWS Filter media relied on raw
materials coming from overseas.
• AEC comissioned Arthur D.
Little to find domestic sources.
• Johns Manville and Owen
Corning developed sub-micron
diameter glass fibers.
• 1951 - an all-glass-fiber paper
made partly from super-fine glass
fibers with diameters
substantially less than 1.0 μm.
• The use of Glass allowed much
greater control of manufacturing
procedures and production of
better, more uniform papers.
The Conception of HEPA
• 1953 Walter Smith working
with Arthur D. Little
developed the ‘absolute’
filter for the AEC
• Arthur D. Little also started
the first commercial filter
manufacturing company,
the Cambridge Filter
Company.
• By 1957, three firms were
fabricating absolute filters.
• In 1960 the first laminar
flow bench was invented at
Sandia National Laboratory
The Birth of HEPA
• HEPA filters, an acronym invented by Humphrey Gilbert, from his 1961
AEC report called High-Efficiency Particulate AirFilter Units, Inspection,
Handling, Installation.
• A HEPA filter was defined as a throwaway, dry-type filter with:
–
–
–
a minimum particle removal efficiency of 99.95 percent ( which was later raised to
99.97 percent) for a 0.3-μm monodisperse particle cloud;
a maximum resistance of 1 inches water gauge (in.wg) when operated at rated airflow
capacity
a rigid frame
HEPA Filtration enables Technology.
• 1960’s NASA develops
contamination control
technology around HEPA
filtration after loosing several
unmanned satellites.
• NASA establishes clean room
standards for US Manned
Space Program in the late 60’s
• AEC –drives standards and
quality control of Filter media
• Cleanroom Technology
enables
• Lunar Landing
• Silicon Chips
Evolvement of HEPA Filters
• Customer demand of higher handling Higher Air volume at a
given efficiency.
• Using less filters in a system
• Reducing cost.
HEPA Filter Media
• HEPA media
–
–
–
–
Microfiber Glass
PTFE membrane
Synthetic Charged Media
Nanofibers
Comparison Microfiber Glass vs. Membrane
Glass
PTFE Membrane
• Depth Filters
• Randomly oriented intertangled
fibers laid into a mat.
• Surface Filter
• Biaxially stretched about 800%
into a microporous structure.
• Higher Gamma/Alpha
• Inert –no outgassing
• High Cost
– Typically using a Fourdrinier
process
– Submicron glass fibers
• Glass fiber paper has a very low
“solidity” That is, the volume of
the sheet contains a low
percentage of solid material and
a very high percentage of void
area.
• Easy to process
Next Generation Microfiber Glass
HEPA Filter Media
Per Lindblom
Paul Smith
PerForm ®
• Perfect Formation
– The importance of Formation will follow
• High Performance
• Filter Media 4 -Cost Effective Solutions
15
Evolution of Filter Manufacturer Needs
• Increasing sophistication of
equipment
• Greater emphasis on productivity
–
–
–
–
Higher pleating speeds
Minimize downtime
Reduction of waste
Minimize filter repairs / touch-ups
• Reduction in manufacturing
variance
• Improved filter performance
– Lower pressure drop for a given
efficiency/class
– Hence lower energy demand in usage
16
H&V Product Development
Objectives
Actions
1. Increase uniformity of fiber
distribution
2. Improve processability
– Elimination of
contaminants
– Reduce variation in media
– Physical properties
3. Improved Filtration
characteristics creating Higher
performance
Low pressure
drop
1. Quantitative measurement of
media formation
2. Major capital investments in
machine modifications
– In-line web analysis
– Defect detecting and tracking
3. Optimisation of the media design
17
Increase uniformity of fiber distribution
• To improve consistency of
pleat shape
• To improve laminarity of
flow through the filter
• To Increase the filter
“gamma”
– Reduce pressure drop
– Reduce energy demand
18
Measured and
predicted by
“Formation Index”
Improved Formation:
A lower Formation Index is better
H&V PerForm HEPA
Formation Index = 3.0
H&V Ashrae
Formation Index = 4.0
Typical HEPA
Formation Index = 5.2
Typical Ashrae
Formation Index = 6.5
19
Formation - Conclusions
• Formation of the media has significantly improved due to
machine and media design changes
• Lower F.I. means the media has:
– Fewer Fibre clumps and pills
– Better overall fiber distribution
– Minimal air entrapment (air bubbles)
• Lower F.I. means the media pleats better and results in:
–
–
–
–
–
Neat sharp pleat tips
Even air flow distribution
Lower filter pressure drops
Higher filter gamma
HIGHER PLEATER PRODUCTIVITY
20
Improved Processing Characteristics
Typical HEPA Media
PerForm ® H&V HEPA
Media
21
Improved Performance of the media
log
Gamma = -9.8 . 100 .
% Pen
100
Pressure Drop
• Gamma is higher when
– Pressure drop is lower
– Penetration is lower
• Two medias, with the same flat sheet gamma:
– The media with the lower formation index gives
22
• Better defined pleat tips and:
• Higher filter gamma
Influence of Formation on filter gamma
Two medias with the same flat sheet gamma, one with
better formation
23
Improved Flat Sheet Gamma
• Typical H13/H14 HEPA:
– Gamma = 12
– Pressure Drop (ΔP) = 30.5 mm H2O (max. DOP penetration 0.03%)
• PerForm ® H13/H14 HEPA:
– Gamma = 14
• 10 - 12% lower ΔP for the same efficiency.
– Pressure Drop (ΔP) = 27 mm H2O (max. DOP penetration 0.03%)
24
Improved Filtration Properties: Gamma
% CNC Penetration (0.18 mic) v Media Velocity
1
CNC Penetration
• Previous Industry
standard media
• H&V media 2007
• PerForm media 2009
0.1
0.01
0.001
0
1
2
3
4
5
6
Face Velocity, cm/s
25
Filter Media 4 cost effective solutions
Driven by higher gamma:
Both
• Higher flat sheet gamma
• Higher filter gamma
Lower Energy Costs
Filter
Design
Criteria
Less Media
26
Longer Life
Filter Media 4 cost effective solutions
Lower Energy Costs
Filter
Design
Criteria
Less Media
Longer Life
PerForm ®
– Lower pressure drop for a given efficiency
– Cost engineer by removing media area
• Increase the media face velocity and still meet spec.
• Still achieve a lower pressure drop for the same efficiency
• eg. Save 11% of the cost of the media........
27
Reducing media area
Minimum Efficiency (at MPPS) v Face Velocity for H14
Minimum Efficiency (at MPPS), %
99.99950
Standard media
99.997% efficiency
1.8cm/sec
135 Pa
99.99900
99.99850
99.99800
PerForm Media
99.997% efficiency
2 cm /sec
125 Pa !
USING 11% LESS MEDIA
99.99750
99.99700
99.99650
99.99600
99.99550
99.99500
1
1.5
2
2.5
3
3.5
Face Velocity cm/s
28
4
4.5
5
5.5
Filter Media 4 cost effective solutions
Lower Energy Costs
• Driven again by higher gamma
• Lower pressure drop means larger
delta to the final pressure drop
• Longer loading time and longer
life
29
Filter
Design
Criteria
Less Media
Longer Life
Filter Media 4 cost effective solutions
Lower Energy Costs
• Energy demand
E= (q x Δp)/ η x T x c/1000
Filter
Design
Criteria
q air flow (m3/sec)
Less Media
Δp average pressure drop (Pa)
T running time (hrs)
η fan efficiency
c cost of energy in USD per kWh
e.g
Longer Life
1 Pa, 50% eff, 600x1200mm 0.45m/s, 0.15 USD/kwh
-> $0.85
Rule of Thumb:
Every 1 Pa lower pressure drop
Saves $ 1 /yr
30
USD
Filter Media 4 cost effective solutions
Per Filter !
31
Filter Media 4 cost effective solutions
To summarise
•
Media consistency
– Minimise defects
– Measurable F.I.
•
•
•
Lower F.I.
Redesigned media
•
•
Higher gamma and Lower pressure
drops
32
•
Productivity improvements
– Less downtime
– Less scrap or re-work
– Faster pleating speeds
Filter improvements
– Sharper pleats
– Higher flat sheet gamma
– Higher filter gamma
Filter cost savings
– Cost engineer, Less media
– Lower energy demand
– Longer filter life
Thank you … Any questions?