One of the battles between petroleum coke storage operators and regulators often goes something like this: operators apply for permits and licenses, submit to environmental inspections, and work diligently with local and state authorities on an ongoing basis. Later, these same powers issue citations and even levy fines against the companies over air quality due to fugitive dust. Operators attempt to suppress the dust using industrial sprinklers to saturate the petcoke with thousands of gallons of water. Then the Environmental Protection Agency (EPA) files lawsuits for “pollution violations” due to excessive runoff and drainage control.
This counter-intuitive situation contains two flaws:
(A) Petcoke doesn’t fit the EPA’s definition of a pollutant. In fact, it has joined crops, minerals and dried bulk goods such as coffee on the futures exchange, and therefore is considered not a waste product but an inert, non-toxic substance.
(B) The EPA and local officials have not yet determined the final destination of the runoff at many North American storage sites, so it is unknown what is allegedly being “polluted.”
Yet the lawsuits persist.
One proposed solution for this dilemma is to manage dust and runoff by enclosing stockpiles inside a physical structure, creating strain on businesses to find the real estate and funding for such a sizable endeavor. However, there is a highly effective and less expensive method that has been proven to better control dust and drastically reduce runoff issues at the same time. The technology is called “atomized dust suppression,” and it involves shattering a water stream into millions of tiny droplets and projecting them long distances in a massive plume, where the droplets collide with dust particles and drive them to the ground.
Let’s take a look at the runoff problem:
Most operations use dikes, berms and catch basins to lead runoff away from waterways and public property. Rainfall, snow and ice runoff can be adequately managed and predicted through average rainfall and accurate modern weather modeling. Industrial sprinklers, on the other hand, can erode an unreasonable amount of product, straining containment systems and using massive amounts of water, often exceeding even the hardest downpour.
For example: a hard 3-inch per hour torrential rainfall on a 10,000 sq. ft. area will produce 18,700 gallons in one hour at the rate of 312 gallons per minute (GPM). This is enough to flood catch basins and put serious stress on drainage systems. Industrial sprinklers can use 500 GPM or even more, typically concentrated on a limited area due to the pressures required. The average municipal water pressure is only 50 PSI (more than 75 PSI and pipes would begin to leak), so a limited number of sprinkler heads can be run from each line. Industrial sprinklers need the high inlet pressure to cover an adequate area.
By using high-powered industrial sprinklers, the cost of water can become a major expenditure and cause excessive runoff. Increased water volume carries more product away and causes accumulation and clogging in catch basins. This requires more extensive runoff control systems, as well as increased man hours devoted to management.
One thing petcoke storage operators may agree with the EPA lawsuits on is that too much product is eroded through natural rainfall and the use of industrial sprinklers. The reason for this is, at the time of sale, petroleum coke should be in its driest state, since moisture content may have an impact on the price. This is why it is so important to use dust suppression methods that keep the product as dry as possible, while controlling fugitive particles.
Scientific research of soil erosion has shown “a low soil water content, and thus high negative pore water pressure, increases the cohesiveness of the soil, which results in a reduced detachability by runoff shear forces and raindrop impact” What this means is that a dry porous material will absorb water, whereas a saturated petcoke will not. Low absorption rates cause more water to stream off, carrying surface material with it.
After inspecting petcoke sites in the Detroit area in 2014, Andy Hartz, southeast Michigan district coordinator of Michigan Department of Environmental Quality, confirms that dryer material is easier to control, writing in his brief, “The more friable, drier, lighter, and finer the bulk material is, the more effective the Fugitive Dust Control methods incorporated into the Fugitive Dust Plan shall be.”
Thus, when a natural rain event occurs, material that was already saturated causes more erosion. Though it may sound counterintuitive at first, keeping petcoke storage piles drier is actually a better way of both suppressing dust and controlling runoff.
Aside from the solution state above involving expensive enclosures, Hartz added to his brief some suggestions as to how petcoke facilities could control runoff. “Example measures could include a berm or dike between the material and the shoreline or a concrete or asphalt curbing around the petcoke piles to prevent discharge to surface waters or prevent materials from migrating off of the asphalt pad,” he wrote. Unfortunately, saturating the product with 500 GPM of water from industrial sprinklers and trapping material in a contained area would quickly turn Hartz’s solution for petcoke piles into a large slurry pond.
Over the last several years, coal handling and mining facilities in various parts of the world have adopted atomized dust suppression as a solution. The technology has been proven to effectively control dust by pulling particles out of the air and dragging them to the ground using a fraction of the water, thus avoiding massive runoff.
Petcoke dust particles are similar in mass to coal dust, averaging around 50 to 100 microns (μm) in size. Gravity generally causes rainwater to form particles between 2 mm (2000 μm) and 6 mm (6000 μm) as it falls. At 6 mm, the raindrop traveling down to earth usually breaks apart into two or three smaller droplets due to opposing forces such as speed and wind velocity. An industrial sprinkler delivers a pressurized stream, which typically produces even larger droplets than 6mm, that don’t travel far enough to break apart. Large droplets from both sources — due to their mass — can cause a slipstream effect, in which the tiny dust particle gets caught in air currents moving around the droplet, preventing it from being absorbed.
The most effective atomized water droplets, on the other hand, are only 50 μm to 200 μm in size for most applications. Millions of tiny droplets are introduced into the target area, hanging suspended for an extended period of time because of their low mass. They can travel with airborne dust on air currents, giving them more opportunity to encounter particles and collide with them to neutralize the fugitive material.
Atomized dust control technology is a completely different concept from industrial sprinklers. For example, the DustBoss® DB-60 requires only 23 GPM to create a dense plume, using a 25 HP fan to throw the atomized mist up to 200 feet. With 359 degree oscillation, a single unit can cover 125,000 square feet (11,613 square meters), which is nearly 3 acres.
Instead of saturating bulk material, the atomized mist technology for dust management allows the petcoke to remain relatively dry, except for a thin surface layer, making it porous enough to absorb rainwater, but further suppressing surface dust. A well-engineered atomized misting design should be capable of running all day unattended with little to no pooling or runoff.
Runoff is expensive from many aspects: water cost, product loss, containment expenses, legal fees, maintenance costs and company reputation. Operators of petcoke storage facilities, local residents, environmental groups, and state and federal officials need to be able to agree on a list of best-practice solutions that will keep jobs in their area with as little environmental impact as possible. Given that the current approaches to dust management have not resolved all the issues involved, it’s time to consider new and alternative solutions as the industry seeks best practices to minimize dust without creating vast amounts of wastewater.
Atomized dust suppression systems allow operators to engage in environmentally responsible dust control, with considerably less product loss and reduced concerns about runoff. It’s a technology that makes good economic and ecological sense, one that deserves closer examination as an alternative to existing and proposed dust mitigation techniques.
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