Case Study: Thermal flowmeter optimizes control of large onion dryers for food processing plants

Sept. 14, 2021

Air/Gas Flow Meter provides precise, reliable measurement of both air flow and natural gas to operate batch systems more efficiently while improving end-product quality and reducing energy.

The engineers at a large food industry vegetable drying plant processing onions needed better humidity control to avoid batch recycling due to the variable moisture content of the onions and other vegetables. FCI’s ST50 Series Thermal Air/Gas Flow Meters were placed in multiple locations (inlet pre-heated air, re-circulation air, outlet), allowing the plant team to adjust air flow rates throughout the process depending on onion humidity levels, which ensured drying of the onions by the end of the process — with minimal batch recycling.

Industrial air blowers and dryers are necessary in a wide range of materials process control applications. They are used extensively in the production of foods, flavors, fillers, granules, powders, particles, bulk catalysts and polymers — generally anytime that raw materials must be dried to remove excess moisture content that would interfere with production or quality.

The installation of ST50 Series Flow Meters in the process control loop for air blower and dryer systems provides highly accurate hot air flow rate monitoring. The use of mass flowmeters ensures precise rate of flow measurement and totalized flow measurement for zone control and overall system operational efficiency. In addition, they can accurately measure and control and/or sub-meter natural gas flow to heaters and burners, which cuts plant energy operating costs while reducing a plant’s carbon energy footprint and increasing competitiveness.

Relying on FCI’s accurate thermal dispersion mass flow sensing technology, the ST50 Flow Meters provide accurate and repeatable direct mass flow measurement at a lower cost. With the ST50 meter, there is no need for the temperature sensors, flow computers or the other devices required with orifice plates, Venturis, vortex shedding and other flowmeters. The ST50’s unique design also provides built-in temperature compensation for reliable measurement over a wide temperature range with almost no pressure drop.

Offering a wide flow range, the ST50 Flow Meter measures air, compressed air, natural gas or nitrogen from 0.75 to 400 SFPS (0.23 to 122 MPS) in line sizes from 2 to 24 inches (51 to 610 mm). Flowmeter accuracy is up to +1% of reading, +0.5% of full scale, with repeatability of +0.5% of reading. The meter operates at temperatures from up to 0°F to 250°F (-18°C to 121°C). Turndown ratio is up to 100:1.

The flow range of the ST50 Series can be field-configured in either standard mass flow or volumetric engineering units. It features dual analog outputs: two 4-20 mA outputs, which are field assignable to flow rate or temperature and an RS232C I/O port. A 0-500 Hz pulse output for totalized flow is also available as an option. All configurations are easily user set in the field with any standard laptop to the RS232C port and/or via the wireless IR link/PDA.