When most people think yogurt, they think of slimming down. But in this case, the goal was to get bigger — at least for the yogurt manufacturer. When the manufacturer wanted to scale up its process, they called on Brooks’ partner Cross Instrumentation for help.
The company already used Brooks mass flow controllers (MFC) on another line in its facility with outstanding results. So the project engineer again reached out to Cross for help with selecting the best product for the company’s process. Cross, along with Brooks application engineers, created an elegant process solution that enabled a scale-up without any fears about contamination or spoilage.
The scale-up was on a line that produces flavored yogurt with assorted fruit fillings. The design called for a series of holding tanks for the fruit fillings. When the tanks are refilled with fruit, most of the high-purity air is displaced, while a slight positive pressure is maintained in the top (headspace) of the tank. During production, the fruit gets moving very readily and flows down to blend tanks below the holding tank. From there, it moves to either a bulk fill line or an individual fill line until the tank is empty. Then the process repeats.
When the tanks are emptied, they are steam sterilized, then backfilled with high-purity air to prevent contamination. This steam cleaning was the first hurdle. The company needed an MFC that could withstand the wet environment. The second challenge was the rapid backfill, which called for airflow as high as 70 slpm.
The yogurt manufacturer initially inquired about Brooks' 5850 MFC, which they had used on another smaller line, but the Brooks team was looking at the bigger picture.
Originally, they considered trying to control pressure in the headspace by installing a Brooks back-pressure regulator and pressure controller, “over-feeding” the air using a rotameter and venting the excess to waste, but Brooks guided them to a better process that was more cost-efficient.
In the revised design, the MFC gets its set point from the control system based on tank pressure. A pressure transducer monitors the headspace pressure, and a slight excess of air is vented using a small, fixed orifice valve. As the tank empties, the pressure transducer signals the MFC, which adjusts to the flow rate of the fruit filling leaving the tank. This method substantially reduced the amount of expensive, high-purity air required.
Brooks recommended size 3 SLA5800 Series Thermal Mass Flow Controllers, which easily accommodate the 70 slpm flow rate. The SLA5800's ability to handle a high flow rate for initial fill and still provide tight control during the emptying phase was critical to the manufacturer. The model SLAMf53 unit, which employs a Brooks NEMA 4X waterproof housing, prevents unwanted moisture from creeping into the air fill via the MFC from the wet environment.