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Productivity Perspectives

Kevin Parker

Kevin Parker, editorial director of Processing magazine, has been writing about process industry, automation and information-technology markets for more than 20 years.

Unique liquid-mixing method addresses viscosity, volume challenges

August 27, 2013
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An innovative way to use pneumatics to mix, blend or agitate liquid-filled tanks, vessels and basins,  has found application in the food, chemical and oil & gas industries. This mixing process, its developers say, is particularly well suited for high-viscosity liquids, such as in lubricant blending, and for large-volume storage tanks holding millions of gallons of liquids.

That’s because “pulse-air-mixing” works by the sequential release of measured amounts of compressed air or gas, underneath flat, round discs called accumulator plates, located at the bottom of a tank. The rising gas-bubble pulses move the liquid, creating a “vertical” circulation pattern in the tank.

While use of pulse-mixing is appropriate when solids need to be kept suspended in liquid, its developers say it is probably not the way to go when solids need be dissolved in a liquid-filled tank. In these cases, the shear created by a mechanical mixer contributes mightily to solids blending.

But the almost-complete lack of shear with the pulse-mixing method can be, in many other type applications, one of its biggest benefits. “It’s a major selling point,” says John Voorhies, director of sales and services, Pulsair Systems, Bellevue, Wash. “If you’re simply moving a liquid and shear is of no benefit to you than we have the advantage. Even with 10-million-gallon capacity tank results can be delivered faster, and by closely managing compressed-air usage, less energy consumed.”

Nitrogen is typically used as the agitating gas in most instances when air is not, in food, wine, chemical and petroleum industries where oxidation is a concern or the environment considered hazardous.

Originally developed and patented about thirty years ago by a company called Pulsair Systems’ founder, Dick Parks, pulse-air-mixing already today sees significant use by lubricant blenders and for large-volume storage tanks. The pulse-air-mixing process is sold as a highly engineered kit through national distributors for on-site installation by user or contractor personnel.

Given the proven efficacy of its solution and its innovative business and distribution model, the company believes other industries will find significant uses for the solution.

“With our NSF certification for potable water tanks we see growth in this area. Railroad tank cars and shipping containers have high integrity,” says Voorhies, “but also some real mixing challenges. All of our equipment is outside the tank which eliminates a number of DOT regulatory requirements from concern. The system also works extremely well in accelerating the heating of liquid products in rail tank cars by controlling the pulses of air through the bottom drain outlet. It’s also of interest that through the elimination of all electrical and electronic components, the process can be used in explosion-proof environments.”

For lubricant blenders, use of pulse-air mixing is a “natural” because mixing is accomplished independent of the liquid’s viscosity, Voorhies says. “The same holds true when two liquids of different viscosities are blended. The liquid with the higher specific gravity will of course tend to settle at the bottom of the tank.  Because the mixing action is from bottom to top, that heavier liquid is swept up and brought to the top. Other types of agitation don’t deliver this.”

As gas “squeezes” out between the accumulator plates and tank floor, it gathers at each plate into a very large, single oval-shaped bubble. Bubbles from the plates then rise to the surface: 1) the vacuum created pulls the heavier bottom liquids upwards and 2) liquids above the bubbles are pushed up and out toward the tank side and then down the tank wall, returning to the bottom.

“Strategic placement of pulse points and accumulator plates on the tank floor means virtually 100% of the tank’s contents are moved,” Voorhies says. “The extremely low surface area to volume ratio and short residence time of the air precludes any meaningful transfer between the bubbles and liquids and vice versa. This reduces the possibility of air entrainment into the liquid.”

Pulsair says its mixing method is 30-50% faster than mechanical mixers, and 75-90% faster than conventional air mixing, sparging or recirculation. Further, the larger the tank is, the greater the advantage. The mixing process is efficient and fast because is harnesses gravity to move the liquid in the tank. 

Pulsair says its mixing method uses 40-60 times less compressed air or gas than spargers and 25-75% less energy than mechanical mixing methods. For example, with pulse-mixing a 10 PH (5-30SCFM) compressor can easily mix a 1 million gallon tank.

Pulse-air-mixing operates without seals, gears, motors, shafts, impellers or baffles. There are no moving parts in the tank or vessel; the only thing that moves is the product.