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CCR Impound Regulations Spur Questions Over Dust Emissions and Wastewater Control

In recent years, incidents of leakage or breaching of surface impoundments have inspired changes in coal combustion residual (CCRs) storage regulations with regards to containment of settling ponds used for the storage of substances including fly ash, bottom ash, boiler slag and flue gas desulfurization materials. 

By Derek Schussele

Atomized mist is one of the only technologies that can deliver effective control of both surface dust and airborne particles.

In recent years, incidents of leakage or breaching of surface impoundments have inspired changes in coal combustion residual (CCRs) storage regulations with regards to containment of settling ponds used for the storage of substances including fly ash, bottom ash, boiler slag and flue gas desulfurization materials.

The Environmental Protection Agency (EPA) Rule “Hazardous And Solid Waste Management System; Disposal Of Coal Combustion Residuals From Electric Utilities” appears to be aimed directly at coal-burning generators. Instead of settling ponds, the EPA is now requiring CCR-producing companies to transition to dry storage, with very stringent rules regarding location and treatment.

CCR producers transitioning to new dry storage strategies are discovering that compliance with one regulation can have them bumping up against air quality and wastewater standards. Monitored by extremely sensitive technology, testing for airborne particulates and run-off has shown that timeworn dust suppression methods such as industrial sprinklers are no longer sufficient to maintain compliance with the current federal, state and local regulation of fugitive dust and wastewater.

CCR Pile Storage and Dust Mitigation Requirements – 1
For outdoor storage, the EPA Final Rule requires an impervious base with both run-on and run-off control leading to a lined settling pond.

CCR Regulat ion

Authors of the EPA final rule now mandate operators of sites to have, “‘Cradle-to-grave’ management, subject to requirements for composite liners, groundwater monitoring, structural stability standards, corrective actions, closure/post-closure care and financial assurance.”

The final rule further requires that owners and operators create a CCR Fugitive Dust Control Plan that gives clear instructions as to how they plan to mitigate fugitive dust emissions from their locations. EPA examples of appropriate control measures include operational changes such as reducing fall distances at material drop points, covering trucks, enforcing reduced speed limits, and reducing or halting operations during high wind events. Other measures could involve structural changes to the facility, paving and sweeping roads or locating the CCR inside of an enclosure or partial enclosure.

For outdoor storage, the EPA Final Rule restricts the placement of CCR storage piles to an impervious base with both run-on and run-off control leading to a lined settling pond. The agency suggests using wind barriers, compaction and/or vegetative shields, applying a daily cover and operating a water spray or fogging system.

Slipstream Effect – 2
Atomized mist suppresses dust more effectively than sprinklers and spray bars, creating smaller droplets that avoid the slipstream effect.

 

CCR Landfill Restricted Locations – 3

 
Preventing run-off is a critical element of dust control.

Fugitive Dust

Dust particles 200 microns or smaller are able to linger in the air. At around 100 μm these particles are considered inhalable, able to irritate the nose and throat.

Wind naturally comes to mind as a main cause of fugitive dust, but it’s only part of the problem. In most operations, the greatest amount of fugitive dust is caused by disruption from loading, offloading, conveying and transport of CCRs. For this reason, attempts to control dust only via surface suppression are largely ineffective. Surface suppression from industrial sprinklers create droplets approximately 200-10,000 μm in size. Large droplets are unsuccessful against airborne dust particles, due to a phenomenon known as the “slipstream effect.”

A slipstream is created when a solid mass moves swiftly through the air. Like air moving around an airplane wing and keeping the craft aloft, a slipstream also travels around a large falling water droplet. Smaller dust particles can get caught in this slipstream and be directed away from the droplet, remaining airborne. The greatest chance for a collision between droplets and dust particles occurs when the two are about the same size.

Developed in the last decade, atomized mist technology avoids the slipstream effect, producing millions of tiny droplets that are roughly 50-200 μm in diameter. Small enough to travel on air currents and producing virtually no slipstream, the droplets collide with particles and use their combined mass to drag them to the ground.

The largest DustBoss design features a specialized barrel with a powerful 60 horsepower (HP) industrial fan on one side and a misting ring on the other. A 10 HP (7.5 kW) booster pump sends pressurized water through the circular manifold, which is fitted with atomizing nozzles.

Wastewater Run-off

The EPA’s Final Rule restricts the placement of CCR storage piles away from an aquifer, wetland, seismic impact zone, fault area, or unstable soil. This makes the volume of run-off from dust suppression technology an even more important consideration. Generally using between 165 and 500 GPM, industrial sprinklers can fill two to three Olympic-sized swimming pools every week of operation. Atomized mist is able to deliver a fraction of the water volume.

The lower water usage of an atomized mist system helps prevent over-saturation and run-off, drastically reducing wastewater. This improved water control allows operators to better maintain compliance with local, state and federal regulations and restrictions.

Author

Derek Schussele is a dust management specialist at Dust Control Technology

 

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