Troubleshooting your airflow system

Learn a few tips to ensure production changes yield their full benefit.

Joe Gosney, PE, QEP, SSOE Group

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When a manufacturer makes a process change that delivers an increase in production, it may want to hold the applause until the system has run for 4 to 12 weeks. Process changes typically alter the airflow characteristics that were part of the system’s original design criteria—for example, the amount of process air, its temperature, its humidity, and the quantity of particulates and gases.

Changes in any of these characteristics can negatively impact the system’s performance, plant efficiency, and environmental permitting.

What’s the best course of action to avoid these risks and still reach your goal of increased production? Simply, use foresight by including people with the appropriate training and experience in the project planning stage. One should be an airflow expert who will understand how your proposed process changes will impact airflow and in turn how that will affect the air transport system. He or she will start by looking at the system’s original design criteria and operational parameters as well as the current parameters.

One or more of the following may be among the solutions for trouble-free results:

• If the revised process is going to increase airflow beyond the capacity of the transport system or pollution control equipment, consider a change of fuel from natural gas combined with ambient air to natural gas and oxygen. This will remove the nitrogen from the combustion system, allowing the revised system to supply additional heat to the process, and may not require increasing the size of the pollution control system.
• Modify the size of the ductwork to handle the increase or decrease in the air volume.
• Increase the size of the pollution control equipment by adding another compartment to the bag house; change the material the bags are made out of or, if possible, increase the surface area of each bag to keep the air to cloth ratios the same; add volume to dropout boxes, or increase the number of cyclones.
• Add another section or change the collection plate configuration of the electrostatic precipitator to increase its ability to efficiently remove particulate from the airstream.
• Use more or less ambient air for cooling the airstream. If the system uses both ambient air and evaporative cooling, be sure the evaporative cooler can handle the additional heat load when the ambient air is reduced.
• Have a good understanding of the chemistry of the airstream you are dealing with. Understand when materials in the airstream will be in a gaseous, liquid, and solid state. This information is valuable in determining when and where blockages and corrosion may occur in the transport system. History may tell you a buildup in the ductwork will occur where you have a cleanout door, but an increase or decrease in temperature or volume may move the area of the blockage out of the area of the cleanout door.

Joe Gosney’s full article on airflow as a factor in production management is one of the topics in Plant Engineering’s Forecast issue, which will be published in mid-February. To receive the digital edition of Plant Engineering in time for the Forecast issue, which also will feature the 2011 Plant Engineering Salary Survey, subscribe here (it's free!).