Breathing New Life into Dust Collection
Filters
A new high-efficiency cleaning technology can enable baghouse filters to
exceed service life expectations while meeting environmental and production
requirements.
John Johnson
Posted on: 02/01/2003
Anyone who maintains baghouse dust collectors understands the significant
costs that are often associated with replacing the filters. Aside from new
filters, retainers (cages) and the labor to remove the old filters and
install new filters, there are also other cost-related issues involved. For
process-related industries, the most important issue is down time—in most
cases, when the baghouse is down, so is the process. Another consideration
is the safety and environmental exposure risk that takes place while people
are working inside the baghouse. Let’s face it: baghouse filter replacement
is a dirty, labor-intensive and time-consuming job.
One of the more common reasons manufacturers replace baghouse filters is due
to increased baghouse differential pressure, which creates air restriction
on the process side and causes reduced production. The assumption is that
once the filters can no longer properly permeate, the filter life is over.
However, for many filters, this is no longer the case. Through a new
high-efficiency cleaning method, “dead” filters are now being revitalized to
“as new” condition.
Turning Old into New
Figure 1. High-efficiency cleaning (HEC) removes dust particles within
filter media and improves air flow levels back to the filter's original
design.
Reconditioning used filters bags is not an original concept. Over the years,
a number of companies have tried unsuccessfully to clean filters using
direct cleaning methods and tools such as air cannons that send an
undetermined amount of air mass into the filter bags. Other methods—such as
laundering filters in industrial washing machines, using air lances to clean
filters from the inside and outside, and the “old beat down” method of
sending employees into the baghouse to whack the filters with
broomsticks—have also been attempted without success.
The concept of using air is the right approach, but there is a scientific
method of understanding compressed air (mass) and cleaning velocity as it
relates to static pressure of the dirty filter. In other words, you must
know how much air to use when using a dedicated cleaning source to clean a
filter that is impinged with dust particles. Using too much air will destroy
the integrity of the filter’s construction and, in some cases, cause injury
to the person handling the equipment, while using too little air will not
accomplish anything except wasting time and money.
A successful high-efficiency cleaning method was developed in Germany and
has been used at hundreds of sites since 1996. In 2001, this proprietary
filter cleaning technique* was introduced in North America and has already
been successfully implemented in several North American process-related
industries as a proven method of removing dust particles within filter media
and improving airflow levels back to the filter’s original design (see
Figure 1).
Where, When and How
The standard measurement to determine airflow restriction is differential
pressure, which is the difference between the clean and dirty sides of the
filter. Most plants that operate a baghouse system are required to monitor
and routinely record differential pressure to determine the productivity of
the baghouse and its associated filters. When the differential pressure is
determined to be “too high” because it causes flow restriction problems, the
filters must either be discarded or cleaned.
Many pulse-jet baghouses use compressed air to regularly self-clean the
filters. The compressed air is transferred from a reservoir tank through a
valve connection that sends a predetermined amount of air through a piping
device, known as the blow pipe, which is above a row of filters. The air
(energy) travels through the pipe and is directed through small orifices and
into the filters that are below the pipe. The compressed air causes a pulse
or energy source that extends down the length of the filter and knocks off
dust particles. All of this occurs while dirty air is continuously sent to
the filters for capture.
In the majority of pulse-jet baghouses, the bags are filtering and being
cleaned simultaneously. This can cause a problem known as dust
re-entrainment, in which dust that is being cleaned from the filter returns
to the filters. The cleaning energy is shared by several filters per blow
pipe, and as filters age and become impregnated with dust particles, the
effectiveness of the cleaning is slowly negated. The dust on and inside them
becomes harder to remove, and the filter requires more energy than the
baghouse cleaning equipment can provide. Filters are typically replaced once
conventional cleaning is not capable of properly removing the dust from the
filters.
High-efficiency cleaning can prolong the life of these filters by using
dedicated compressed air energy to effectively remove dust particles that
have penetrated the filter media. The cleaning technique is performed
off-line, which prevents dust re-entrainment, and filter removal is not
required. In most cases, the cost to perform the cleaning is equal to the
cost associated with the labor of removing and replacing filters.
The cleaning service is designed for pulse-jet/plenum pulse baghouses with
top-entry access. The service will work with all filter media—including
polyester, aramid, acrylic, fiberglass, spun-bond and other high performance
media, such as membrane technology—applied to any substrate, and it does not
structurally damage the filters.
Before high-efficiency cleaning is conducted on the baghouse system, a
sample filter is used to accurately predict the success of the cleaning
method in a testing chamber by mirroring the baghouse parameters. A
monitoring unit measures the fabric condition, the ability of the filter to
be cleaned and the approximate level of recovery the cleaning will provide.
Based on this information, a pressure-versus-airflow measurement is created
that illustrates the effectiveness of the cleaning. Finally, the
high-efficiency cleaning equipment independently cleans each filter with a
predetermined amount of dedicated compressed air, removing embedded dust
particles and prolonging the filter’s life.
Taking Advantage of New Technology
Baghouse operators have always looked for ways to minimize filter
replacements while meeting environmental, safety and production demands.
High-efficiency cleaning technology can achieve these goals by effectively
removing impinged dust particles, thereby increasing the filter’s throughput
function and decreasing differential pressure. Through high-efficiency
cleaning, manufacturers can turn filters that are being considered for
replacement into filters that have “as new” filtering values and extended
service lives.
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