An Echotel ultrasonic transmitter from Magnetrol (upper left) measures grease level through a fog of vapor at the WWTP grease receiving station. Grease is being fed from a tanker through the green hose. |
Although the plant’s original digesters were performing well and producing energy for process heating, management wanted still more efficiency from the treatment system. With the average WWTP consuming more electricity than any other municipal service - sometimes as much as 30 to 40 percent of overall energy consumption - it’s not surprising that this facility has moved steadily toward increasing self-sufficiency in energy generation. The electrical generation unit that now boosts production of digester gas, purifies it, and converts it into electricity was made possible in part by state environmental and economic opportunity agency grant initiatives.
Because of its long-standing relationship with the sanitary district, Magnetrol International was called in to address the level and flow needs for the new waste-to-gas system. The first application to be addressed was the grease receiving station at the project’s front end, a 12-foot-deep, in-ground cement repository where waste haulers offload their grease. The level measurement application was somewhat challenging because warm grease dumped during colder months can create steam that the level device must cut through in order to make accurate measurements. It was precisely for its ability to detect true level despite the compromised atmosphere that the non-contact Echotel® Model 355 ultrasonic level transmitter was selected for the grease receiving station. Each of the five floating roof digesters also utilize a pair of Model 355 ultrasonic transmitters.
At the back end of this multi-million-dollar project, three Thermatel® TA2 thermal mass flow meters monitor methane gas flow from the digesters. Initially, plant personnel did not know how much methane would be produced with any degree of certainty. Knowing the exact amount of methane was necessary in order to select the generator with the right capacity for the job. The TA2 flow meters compiled the required data and the generator was specified.
As a result of the waste-to-gas initiative, the forward-thinking sanitary district anticipates the ability to generate 50 percent of its electricity from biogas.
About the Author: Mark Mackinnon is a product support specialist for Magnetrol International.