Q: |
On my pulse-jet collector
every time a row of bags is cleaned I get a puff of smoke
up the stack. Other than that it runs fine. What can I
do to eliminate 'puffing?' |
A: |
If
your baghouse is operating fine except for during the cleaning
cycle then you might be cleaning too frequently, have too
light a dust loading, or the material collected is not
conducive to building a dust cake in which case you should
consider using a Precoat material or modifying the operation
of the baghouse. If there is little or no dust cake on
the bags the pulse action is doing nothing more than "working"
the dust particles through the cross section of the filter
media. Check your differential pressure at the time of cleaning.
If you have "on demand" pulsing set the values to a higher
delta P. If you have timed cycle cleaning lengthen the time
between cycles.
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Q: |
How
often should I change my bags? |
A: |
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 you running at optimum performance.
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Q: |
How long should my filter bags last? |
A: |
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 2-year bag life. However,
for difficult applications you can expect maybe no more than
3 months life if there are not other alternatives.
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Q: |
How do I know if I need to have a
permit for my baghouse or dust collector? |
A: |
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 business 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.
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Q: |
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?
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A: |
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.
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Q: |
I
have started to see some smoke coming from my stack but
it is barely noticeable. How much is too much?
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A: |
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
usually cannot be done with the naked eye and requires
a sampling by a qualified technician.
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Q: |
Is
there a formula that I can use to determine the collection
efficiency of my baghouse? |
A: |
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.
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Q: |
Is there
a formula that I can use to predict the collection efficiency
of my baghouse? |
A: |
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.
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Q: |
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?
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A: |
You basically have
two choices: Condition the gases to low 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, 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
cooling can 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.
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Q: |
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?
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A: |
There are several
sources but one comprehensive source we have found is ChemAlliance.org
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Q: |
I
have spark carry-over from our processing ahead of the
baghouse. How can I reduce the risk of fire in my baghouse?
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A: |
Spark carry-over
is a major concern. At a minimum you can develop pin holes
in the media which will transfer dust to the exhaust stack.
More serious cases will 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 in order that the sparks will
strike the chain net and be broken up. It can often be
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.
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Q: |
I have a high temperature (+300oF) baghouse
that sometimes has heat excursions 25o higher than that rated 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? |
A: |
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 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).
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Q: |
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? |
A: |
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
cake. This acts as a filter enhancement and also 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.
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Q: |
What is the proper fit of a filter
bag onto a cage for a pulse-jet baghouse?
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A: |
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.
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Q: |
What should I set my compressed air
at for my pulse-jet baghouse?
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A: |
The
manufacturers of the baghouse usually have designed the
unit to operate with a specified pulse pressure. In the
absence of that 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 can set the pressure the more energy savings you will
see as long as the inlet draw of the baghouse is satisfactory
for the operation.
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