Maintaining Dust Control Equipment
Maintenance is the Key to Compliance.
By: Mark Kestner, Ph.D, President, NESCO
dust control equipment is the key to compliance. But these days it’s tough enough to maintain
production equipment much less dust controls.
Poor maintenance is the largest contributing factor to non-compliance
and the major cause of citations and fines.
control equipment for aggregate processing can be divided into three
categories: enclosures to contain it, spray systems to suppress it, and
baghouses to collect it. These deserve the same level of preventive
maintenance as your crushers, screens and conveyors. If you think your spray
system isn't a piece of production equipment, read your operating permits. They stipulate that the plant cannot be
operated unless dust controls are in good operating condition. Operating with a broken down spray system or
baghouse will put health and safety at risk and expose the plant to fines up to
$25,000 per day. If you think
regulators will let you slide, just ask the owners of a major east coast quarry
that was shut down for a month this year
until dust control equipment was restored to good operating condition.
enclosures include chutes, covers, skirts, curtains and the like. Maintenance
of dust enclosures is critical to protect employees from respirable
silica-containing dust. Dust and
spillage that leaks has to be cleaned up.
Workers who have to sweep, shovel or bobcat it can get a nose full of
dust so make sure workers have access to respirators and use them. Fabric masks offer little or no protection
against respirable dust. Whenever possible, use hoses or vacuums to
flush down or pick up spillage.
chutes, worn skirting, and torn curtains need to be repaired promptly. Much of this work can be done with in-house
labor and materials. Old conveyor
belting can be used for curtains, scrap steel for patches and covers.
systems are the principal control device at most quarries and are pretty simple
to maintain. The two most important
maintenance items are:
Spray nozzles. Nozzles
should be inspected daily. Nozzles that are
easy to see and easy to reach are easy to maintain. Nozzles that can't be seen or are hard to
reach don't get inspected and cleaned. Nozzles
can plug from the inside-out due to suspended or dissolved solids (scale) in
the water supply or from the outside-in due to deposition on spray bars.
Water filters. Water
filters and strainers need to be inspected regularly and cleaned or replaced as
necessary. The spray system should be
equipped with a pressure gauge. A
decline in spray pressure indicates a dirty strainer and will provide
maintenance personnel with a metric for frequency of inspection.
Most conventional spray systems use centrifugal pumps are
that self-lubricating and do not require any regular maintenance. If you have a "fog" system that
uses a positive displacement pump, they will require regular oil changes and
are much more susceptible to wear.
It's also a good idea to have a spare pump and motor on hand
in case of a mechanical failure or freeze damage.
Solenoid valves can be another sore point, particularly when
the water supply is dirty or contaminated with sand. Dirt and grit that builds up on the valve
seat can prevent it from closing properly.
If spray nozzles keep on running or dripping after they have been shut
off, that’s a good indication that the solenoid is dirty and needs to be
cleaned or replaced.
If you are thinking about installing a spray system, here
are some guidelines to reduce spray system maintenance:
1. Use heavy duty components designed to operate in an abusive
2. In a cold weather climates, house the pump in a heated enclosure.
3. Use the cleanest water possible, Using dirty pond or river water will make
nozzle, filter and pump maintenance a nightmare.
4. Install drain valves at all the low points. Frozen lines can delay start-up on cold
morning and that means lost production.
5. Put nozzles where they can be seen and are easy to
access. Out of sight is out of mind.
6. Consolidate all moving parts in a central location with the
pump. Solenoids and filters out in the
plant are more likely to be damaged or freeze and take more time to inspect and
7. Most nozzle pluggage occurs from the outside-in due to
deposition of wet fines that blow back onto the nozzle – particularly at
crusher discharges. Install nozzles so
that they are out of the way of this “blowback” or put a dust curtain in front
of them with a small hole that nozzles can spray through.
8. Keep a list of all nozzles and their location to facilitate
ordering and replacement
baghouses are “pulse-jet” that periodically and sequentially pulse reverse air
through the filter media to keep them clean.
differential pressure across the filter bags as measured by a magnehelic or
photohelic gauge is the best indicator of performance. High differential pressures indicate that
bags are caked up or blinded. Low
differential pressure can indicate that bags are torn or missing.
dust emissions are observed at the baghouse exhaust, this is also a pretty good
indicator that bags are torn or missing.
hopper discharge for any material build-up.
If not discovered in time, dust can fill a hopper to its inlet and plug
the unit. Whether a rotary valve, screw
or pneumatic conveyor is used to empty the hopper, it should be inspected
fans should be inspected semi-annually.
Loose or worn belts or an imbalanced impeller, will reduce the fan's
performance. Any time unusual vibration
or squealing is observed, the unit should be thoroughly inspected.
media is the most important element of the baghouse and periodic inspection
should be mandatory. Inspect the clean
air side of the baghouse for any leaks or tears in the filter media.
should also be inspected for any leaks or deposition. If the exhaust fan is not able to maintain
the air velocity in the duct of at least 3500 fpm, dust will settle out and
restrict air flow. Eddies in sharp bends
can also result in deposited dust that restricts air flow.
If you are
going to install or refurbish a baghouse, here are some guidelines to keep
maintenance costs down:
1. Make sure they are designed for heavy-duty
2.Specify materials of construction that are corrosion
resistant. Using cheap metal will result
in corrosion that eats holes in ductwork.
3. Avoid sharp bends in ducts that will quickly wear through. This is particularly true if the plant
processes hard, abrasive rock like sandstone or granite.
4. Select filter media that will hold up to your specific
stone. Again, abrasive dust will require
more resistant media. If the rock
contains any sulfides that can produce acidic corrosion when exposed to
moisture, you’ll need a filter media that is up to the task.
5. Avoid long-multiple intake ducts. To save money, many plants install a single
big baghouse with tentacles of ductwork that extend to multiple sources. It is almost impossible to balance air flows
with such an arrangement and you’ll be much better off installing multiple
baghouse with fewer and shorter intake ducts.
Maintenance - Don't wait 'til it breaks!
use wet suppression systems, dry collectors or a combination of both, institute
a routine program of preventive maintenance and make sure that the plant
pursues it with the same alacrity that they do for production equipment. The program should include a daily inspection
recording spray system pressure and/or baghouse differential pressure as well
as a log of any maintenance or repair work.
Pollution control equipment may
not put more tons into trucks, but it does protect the health and safety of
your employees that do.