Process Air Balancing Project Requires Different Approach

Mechanical Service Corporation was called in by an HVAC preventive maintenance customer of ours to troubleshoot a new dry product material handling system that was not working as designed.

The system, which had only been running about eight weeks, basically consisted of two large blowers pushing ambient air through a 5-inch stainless steel line at approximately 4,000 ft./min. under 2-3 PSI of pressure. Dry product had been collecting in several areas of the system, frequently slowing or stopping product flow. A dry particle counter appeared to be malfunctioning, as well.

MSC observed the product running in horizontal and vertical piping during operation, and it became clear that the current CFM/capture velocity called for in the design was not sufficient to move the product properly, particularly in the vertical runs. The problem, however, was not in the design. It was, rather, due to recent increases in product moisture content and particle size. These changes meant that the product was heavier than expected and would require a 50% increase in flow velocity to allow it to freely move through the problem areas. Fortunately, the main 50HP blower had more than enough capacity to handle this increase.

To achieve this, our service technicians cut in two 8-inch adjustable blast gates on each end of the system in the main piping to adjust overall velocities. Through some experimentation with product, we were able to adjust all of the individually-controlled dampers to a velocity just high enough to draw the product from the material handling wheels below the ovens that were feeding the material handling system. This made dialing in the proper flow for the product much easier.

Now that the system was able to successfully move the dry product through the piping to the storage hoppers, the service techs moved on to field-calibrating the dry particle flow meter. This required taking known quantities of dry product and carefully checking the weight of the product against the flow at 20% intervals to account for the five ovens producing carefully-sized products used for dosing. Flow meter accuracy was highly important to the process, so after conferring with the dry product flow meter engineer, MSC prescribed quarterly volume-to-weight calibration of the devices and added it to our existing PM agreement with the client.