How
often should I change my bags?
Filter bags are a consumable item. They do wear out, blind off,
burn up and get attacked by chemicals. Just like the oil and
air filter in your car they need to be replaced to keep your
collector running at optimum performance.
How long should my filter bags last?
Many factors affect bag life. Often collectors that were built
with production rates in mind are now operating at twice their
design load. Moisture and chemical upsets can take a set of bags
out at startup. Typical design criteria on new installations
should allow for a 2-year bag life. However, for difficult applications
you can expect no more than a 3-month life if there are
not other alternatives.
How do I know if I need to have a permit for my baghouse
or dust collector?
More
than likely you are required to have a permit, either state
or federal for a baghouse or dust collector. Your first point
of contact should be your local permitting authority for air
pollution sources. Permits
for businesses are usually administered at the state or local
community level. Contact your State Small
Business Assistance Program or your State
Environmental Agency for assistance with this matter.
I am right in the
middle of an extended batch run with my baghouse and the
dust collector just failed. It's going to cost me a small
fortune in penalties if I shut down to fix the baghouse.
Normally I run a clean stack. Can my local regulatory agency
cut me some slack just so I can get this batch finished?
Don't throw in the towel.
You MAY have an out. Most districts have an equipment
breakdown rule but they vary. California, one of the most advanced
states regarding air pollution regulations, describes how the
districts in their state approach this:
"The conditions that
a malfunction must meet in order to qualify for district breakdown
provisions vary from district to district. Typically, the following
are conditions for an acceptable breakdown:
1. The
breakdown must result from a failure that was unforeseeable;
2. It
must not be the result of neglect or disregard of any air pollution
control law or rule or regulation;
3. It
must not be intentional, or the result of negligence;
4. It
must not be the result of improper maintenance;
5. It
must not constitute a nuisance; and
6. It
must not be an abnormally recurrent breakdown of the same equipment."
There are reporting
and time restrictions and you WILL get a visit from an inspector
who may shut you down on the spot, but it is usually worth
a shot. At least
get a copy of your districts Breakdown Provision/Rule and go
over it before you need to make a call.
I have started to
see some smoke coming from my stack but it is barely noticeable.
How much is too much?
The
opacity of a plume is typically measured using a scale called
a Ringlemann Chart as published in the United States Review
of Mine Information Circular No. 1C8333, (May 1967), as specified
in Health and Safety Code section 41701(b). A reading of 2
or less is usually acceptable. The reading normally cannot
be done with the naked eye and requires a sampling by a qualified
technician.
Is there a formula
that I can use to determine the collection efficiency of
my baghouse?
To determine collector efficiency divide the emissions (grains\SCFM)
or mg\Cubic Meters by the incoming Grain Loading (grains\SCFM)
. This will be the collector efficiency in percentage.
Is there a formula that I can use to predict the collection
efficiency of my baghouse?
There is no single universal formula for any collector to predict
collection efficiency. Many factors come into play especially
the unique characteristics of the dust being collected.
We have changed our process to run at a higher temperature.
Now the inlet gases at the baghouse are too high for the type
of bags we have in there . What can I do?
You basically have two choices:
Condition the gases to a lower the temperature, or change the
filter bags to a type that is rated for the new higher temperature.
Gas conditioning takes on three principal methods: dilution,
radiation and evaporative.
Dilution of the exhaust gas stream by air is the easiest
and cheapest method, especially at very high temperatures. However,
air dilution requires the use of a larger baghouse to handle
the increased volume of air. Other problems can arise due to
the difficulty of controlling the intake of ambient moisture
and other contaminants from the dilution air intake.
Radiation coolingcan also be used to lower the process exhaust
gas temperature. Radiation cooling involves the use of long non-insulated
ducts that allow the gas stream to cool as heat radiates from
the duct walls. Ducts can be designed in "U"
shapes to allow more duct surface area to be exposed for radiation
cooling. Radiation cooling would not normally be very effective
to cool gas temperatures below 572oF or 300oC.
This would require substantial surface area, lengthy duct runs,
and increased fan horsepower. Precise temperature control is
difficult to maintain and there is a possibility of the ducts
becoming plugged due to particle sedimentation.
Evaporative cooling is also used to reduce exhaust gas stream
temperature. Evaporative cooling is accomplished by injecting
fine water droplets into the gas stream. The water droplets absorb
heat from the gas stream as they evaporate. Spray nozzles are
located in a quench chamber or somewhere in the duct preceding
the baghouse. Evaporative cooling gives a great amount of controlled
cooling at a relatively low installation cost. Temperature control
can be flexible and accurate. However, this cooling method may
increase the exhaust volume to the baghouse. The biggest problem
with evaporative cooling is keeping the gas temperature above
the dew point of the gas (5O2, NO2, HCl, etc.). Otherwise, gases
may condense on the bags causing rapid bag deterioration. In
addition, all moisture injected into the gas must be evaporated
to prevent corrosion of metal parts and blinding or plugging
of the bags.
I run a chemical plant and face enormous regulations not
only for my emissions but also in the manufacturing, storage
and transportation of our product(s). Are there any resources
that address the chemical industry?
There are several sources. The one comprehensive source we have
found is ChemAlliance.org
I have spark carry-over from our processing ahead of the
baghouse. How can I reduce the risk of fire in my baghouse?
Spark carry-over is a major concern. At a minimum
pin holes will develop in the media which will transfer dust
to the exhaust stack. More serious cases result in fires.
There is sophisticated equipment that detects and attempts to
extinguish sparks within the ductwork prior to the baghouse.
A crude but inexpensive method of spark reduction is the hanging
of rows of chain in the ducting so that the sparks will
strike the chain net and break up. It is often a matter
that the baghouse is too close to the spark source, thereby not
allowing enough time for the spark to die out prior to entering
the baghouse.
I have a high temperature (+300oF) baghouse that
sometimes has heat excursions 25o higher than the
rating for the media I am using. These excursions only last
a short while and then everything is back to normal. Am I really
affecting the life of the filters?
It is a misconception
that short excursions above the rated temperature of a media
do little harm. It is a fact that tensile strength effects
are cumulative so eight excursions of one hour each in a given
period would be the same as running for eight hours straight
at the same reading. Often temperature related failures occur
days after the event from a weakened bag flexing over that
period. Know your process and if you think you will be spending
any time exceeding the rated operating temperature of the media
select a media with a higher temperature rating or anticipate
a shorter bag life and the associated cost factors that go with
it. High temperature baghouses should have continuous monitoring
AND recording of temperature (strip chart, circular chart).
I just installed a new set of bags in my baghouse. Do I need
to do anything special when I go to start it up for the first
time?
Baghouse start-up after re-bagging is extremely critical. Improper
start-ups are a leading source of immediate or premature bag
failure. A well-executed start-up will insure a long useful bag
life and optimum baghouse performance. Start-up procedures vary
with both the temperature of the gas stream and the type of particulate
being collected. Unless the baghouse is being used as the actual
product recovery station for the powder, it is recommended that
bags be conditioned with a pre coat powder. This powder is introduced
near the baghouse inlet and coats the filter bags with a permeable
cakethat acts as a filter enhancement and protects the
filter surface in case of abnormal particulates at start-up.
Additionally you may elect or be required to leak test the baghouse.
Check out our Maintenance Powders section
for more information.
What is the proper fit of a filter bag onto a cage for a
pulse-jet baghouse?
The "nip" or amount of the bag that can be pinched up from the
cage, at a ring location, typically should be about ¼"-3/8" for
felts and 3/16" for woven fiberglass. Excessive pinch will cause
premature bag wear and allow for migration of dust through the
cross-section of the media. Too tight a pinch will reduce the
ability of the dust cake to release from the bag exterior.
What should I set my compressed air at for my pulse-jet baghouse?
The manufacturers of the baghouse usually have designed the
unit to operate with a specified pulse pressure. In the absence
of manufacturers recommendations some general rules can be applied.
For a typical baghouse with 10'-12' long bags the pulse pressure
should be between 80-100 psig. Bags of 6'-8' would be lower (60-80
psig) and bags of 14' or more may require 120 psig or more to
clean adequately. As a rule of thumb, the lower you set the
pressure the more energy savings you will see as long as the
inlet draw of the baghouse is operating satisfactorily.
