Complying with governmental regulations while maintaining a high level of functioning is a challenge for plants throughout the process industries, and particularly in water and wastewater plants. Many water quality plants are using flow controls to help achieve critical operational goals. This case study shows how thermal dispersion mass flow meters can help your plant ensure compliance with stringent government regulations.
Instrumentation plays a pivotal role in meeting regulations set forth by the Environmental Protection Agency, Department of Ecology and the Department of Health. To ensure compliance with these types of regulations, the Lakehaven Utility District in Washington realized that it needed reliable flow meters for some of its most difficult applications—the air and gas flow lines serving its aeration basins and anaerobic digesters.
Thermal dispersion flow meters are well accepted in the municipal industry to provide reliable flow measurement at low flows and low pressures. That’s why the District turned to the Magnetrol® Thermatel® Model TA2 for its ease of use and ability to handle these difficult applications. The THERMATEL Model TA2 mass flow transmitter measures mass flow by detecting heat dissipation from a heated surface. The sensor contains two mass balanced elements with precision matched RTDs. The reference sensor measures the process temperature (up to +400° F [+200° C]); the second RTD measures the temperature of the heated sensor. The power to the heater is varied to maintain a constant temperature difference above the reference temperature.
There is an inherent non-linear relationship between power and mass flow. The microprocessor in the TA2 compares the power against the calibration curve and converts the power requirements to the mass flow rate. Temperature is also measured to provide temperature compensation of the mass flow over the operating range of the instrument.
Because the TA2 measures air and gas directly and has excellent low flow sensitivity, it is a smart choice for challenging applications. It can provide a high degree of accuracy that ensures compliance with stringent standards such as those the District was seeking to meet.
Adding THERMATEL Model TA2 in the aeration lines maintained a minimum flow rate to prevent the diffusers from getting plugged, while also being used in conjunction with dissolved oxygen (DO) probes to provide sufficient flow to meet the oxygen demands in the basin. On the digester gas lines, the units measured the amount of methane going to fuel the boiler to generate hot water/steam for the plant, as well as the excess methane going to flare.