Managing the Air Flow Side of Sanitation

Research Engineer John Pierson examines Pitot tube before conducting traverse of ductwork to measure air velocity.

A key challenge facing many plants today is how to adequately control air flow in processing operations. Uncontrolled or improperly controlled air flow poses a risk to plant sanitation programs because it has the potential to carry aerosols, fine particulates, and bioaerosols that may harbor organisms that can contaminate products and plant surfaces. Such uncontrolled or improperly controlled flows can also contribute to condensation problems and even become a source of nuisance odors.

Controlling air flow in plant operations ultimately requires understanding internal air movement patterns together with where and how infiltration is being introduced through external openings. This can be achieved by taking air velocity readings at key points throughout the operation. When taking these readings, it is useful to take note of inputs from controllable entry points, such as fans or air supply ducts, as well as inputs from less controllable points, such as product pass-throughs, walk-through openings to neighboring plant areas, and external window and door openings. This will help in developing subsequent strategies for better controlling air flow.

It is also useful to take temperature and humidity readings on all air flows to better understand the potential for condensation problems, particularly when air is moved from a warmer area into a cooler area. And finally, it is imperative that flow patterns be understood with regard to the risk of transporting contamination from an area where its presence can be tolerated, to one where it cannot.

In rendering operations, an additional challenge is posed by the operation of air emission treatment systems. Such systems require that air-handling systems be properly balanced to work efficiently. Imbalanced air supply systems coupled with infiltration from exterior openings can result in a dilution of odor-laden air fed through the systems, while allowing fugitive odor emissions to escape from regions where air movement is limited. Often this occurs because plants simply are unaware that their system is out of balance. One way of keeping an eye on this is to install static pressure monitors at a variety of air-handling ductwork locations.

Sound far-fetched, well it isn’t. As part of its air emissions treatment system, Perdue Farms’ Protein Plant in Accomac, Va., has implemented a static pressure monitoring system at a variety of air-handling ductwork locations. The plant is using this system to help adjust dampers to balance house air in a way that will ensure its air treatment system capacities are optimized as part of its overall odor control plan.

“This plant is in a great position to make smart decisions regarding air handling because static pressure gauges are in place to help the plant better understand the dynamics of its day-to-day processes. For example, knowing how exterior door positions affect static pressure readings can assist in determining if they could be a contributing factor should nuisance odor complaints emerge,” notes John Pierson, senior environmental research engineer with the Georgia Tech Research Institute.

Pierson explains that as a general strategy, plants should prioritize inlets so that critical processes are under the greatest draw, but no more than 10 percent greater than the system average. After any major change in the dampers (i.e., the system resistance), the fan suction and fan discharge should be measured to obtain the current total fan static pressure reading. This includes monitoring fan amperage and voltage readings so that the total fan static pressure can be compared with the fan curve or performance-rating chart. Regardless, he says, unintended openings in the overall structure must be addressed as well as ensuring air vents inside of the facility are not blocked. “The fan will draw a given amount of air along the fan curve, and it doesn’t care where that air comes from,” adds Pierson.