How to Save Dollars on Dust Control

            Times are tough and cost control is the key to profitability.  Air quality standards are a fact of life and quarries have little choice but to spend money on control measures that will keep them in compliance.  But why spend more than you have to?  .

            What’s the difference between a million dollar and a ten thousand dollar race horse?  Does the former run one hundred times faster than the latter?  Of course not.  The difference is the nose that gets across the finish line first.  In other words, it’s the little things that count.  If you want to save money on dust control, do the little things that will add up to big savings. 

            Here ten money-saving tips to control dust from roads, piles and crushing plants.

           

No. 1 – Slow Down

            The slower a vehicle travels the less dust it produces.  On most roads, vehicles that travel at 15 mph do not produce appreciable dust emissions. A speed limit of 10 mph is even better. Is a 15 mph practical for haul routes?  If trucks can get stone up to the primary crusher fast enough at 15 mph, it makes sense.  If they can’t, calculate the minimum speed required to the maintain production rate and set speed limits accordingly.  I’ve seen haul trucks race to a primary crusher at 40 mph in a cloud of dust only to sit there for 10 minutes waiting to dump – that’s what you want to avoid.

No. 2 - Enforce Speed Limits

            Posted speed limits won’t reduce dust if they aren’t enforced.  That can be tough if truck drivers aren’t your employees.  Speed bumps can help trucks to observe speed limits but banging tailgates can cause a noise problem.  Rumble strips are more likely to slow trucks down without causing gates to bang.  Posting and rigorously enforcing speed limits is the best way to reduce dust emissions and the frequency of treating unpaved roads.  Plant management has to set the example.  If you blast around the plant in your pick-up, don’t expect anyone else to slow down.

No. 3 - Shorten Routes

            Shorten traffic routes as much as possible.  Fewer vehicle-miles traveled means less dust in the air and less road to water or chemically treat.  Use flags or other markers to delineate traffic areas and install concrete barricades to make sure trucks do not wander off of designated routes. Keep paved roads clean by restricting access to them from unpaved roads. 

No. 4 – Improve Road Structure

            Poor construction, bad drainage and lack of maintenance all aggravate dust emissions and track-out.  Inspect roads to make sure they have a proper crown, a good mix of fines and aggregates and a well-compacted surface.  When surface material has more than 30% silt, dust control measures will work but will not be cost-effective.  Put some chips or other coarse aggregate down to reduce the amount of silt on the surface.  This will reduce the frequency of treatment and the amount of water or chemical used per square yard.

No. 5 - Use Road Dust Suppressants

            A wide variety of chemical additives are used as road dust suppressants.  Just about every sticky, gooey or gummy chemical you can imagine has been used to control road dust.  They can reduce the frequency of treatment to the point where they are less costly than routine watering especially in dry, arid environments where water is hard to come by.  Vendors may be willing to provide a free trial to let you gauge effectiveness of chemicals and determine cost savings.

            If you are currently using chemicals to control road dust, try to use a waste product for this purpose.  For example, waste brine produced from oil and gas wells can be just as effective as more refined and expensive products.  Pulp and paper plants, steel mills, oil refineries and chemical plants may all be sources of waste or off-spec materials that can be used on unpaved roads.

No. 6 – Replace Tankers with Sprinklers

            Install a stationary sprinkler system instead of using a mobile tanker for road dust control.  It can cost in excess of $100,000 annually in capital and operating costs to employ a mobile tanker to water roads in a large quarry.  Stationary sprinkler systems can significantly reduce these costs depending on the distance that requires watering.  Simple computer controls can be used to optimize the frequency and duration of treatment.  Just make sure that the sprinklers are protected from errant trucks and can be drained in cold weather.

           

No. 7 – Train Loader Operators in Control Measures

            Loaders are the most active vehicles in quarries.  Train operators to take personal responsibility for dust control.  That means not overfilling buckets and spilling stone as they load trucks.  Avoiding sharp turns and rapid accelerations also helps to keep dust down.  Loading out from the lee side of a pile on windy days can also make a big difference.  In most cases, dumping quickly can help to reduce the amount of dust that gets into the air. 

No. 8 - Choke feed crushers

            Good operating practice can not only reduce dust but also improve production.  Choke feeding crushers is one example.  Crushers, particularly horizontal or vertical shaft impactors produce less airborne dust when they are operating at capacity because they are moving less air.  Some plants I’ve seen are a Frankestein mix of mis-matched equipment slapped together with screens or belts to small to keep up with their crushers.  Dust produced from impactors that are operating at less than 50% of capacity is almost impossible to control.

No. 9 - Avoid Interruptions

            Avoiding interruptions in process flow also reduces emissions and keeps production rates up.  Crushers that are “windmilling” an put ten times the dust into the air as they do when they’re loaded.  The most common reason for intermittent operation is the lack of sufficient haulage to sustain primary plant operation.  Stone runs through the plant in a burst of production followed by a burst of dust. 

No. 10 – Enclose Dust Sources

            Enclosing dust sources is one of the most cost-effective ways to reduce emission levels and your reliance on more expensive controls like wet suppression systems or baghouses.  The EPA estimates that partial enclosure of a dust source like a transfer point or hopper on three sides with a cover has a control efficiency of 70%.  Adding a simple rubber dust curtain at discharge points also helps to contain emissions.  Make sure that belt skirting is in good shape and there is enough idler support at load points to prevent dust and spillage.  Workers have their greatest exposure to respirable dust when they have to shovel or bobcat spillage caused by leaking skirts.  Much of this work can be accomplished using scrap steel, old belting and a little elbow grease.

           

Conclusion – Implement the least expensive control measures first.

            A cost-effective dust control plan designed to comply with air quality standards at the lowest possible cost requires the use of good operating and engineering practices combined with a proper wet suppression (or dry collection) system.  Good operating practice means training operators to take personal responsibility for minimizing dust.  Training them to do so is barely a blip in the budget and can have a big payoff.  Good engineering practices that emphasize the containment of dust sources can often be implemented with in-house labor and material.  Do the least expensive things first.  You’ll find that the savings that result will go a long way in reducing the costs of more expensive controls like wet suppression and dry collection systems.