Optimizing a digester cycle requires constant monitoring of gas flow, temperature and methane fraction to ensure all three measurements are within preset operating parameters. Based on this data, operators feed sludge to the digesters. Not long ago in Reading, Pa., the city’s wastewater treatment plant was using outdated pressure transducers to monitor biogas flow, which was not very accurate and often caused false readings. Temperature was monitored manually, taking up to four hours of a technician’s time.
Lack of real-time operating data was leading to operational latency and high costs. The methane fraction would drop below 20 percent and temperature would fall to 80°F, slowing the plant’s throughput and raising costs. When these conditions occur, a digester could sour, causing the bacteria to produce higher levels of other gases, accelerating corrosion. If the methane fraction fell too much, the plant would have to tap external natural gas sources to fuel the boilers at a cost of up to $16,000/month.
The City of Reading was able to gain real-time, multipoint data via Endress+Hauser’s Proline Prosonic Flow B 200, an ultrasonic flow measuring system specifically designed for this type of application - monitoring of wet, dirty biogas with a variable composition and low flow and pressure. The B 200 provided +/-1.5 percent flow accuracy independent of gas composition and provided continuous methane fraction, colorific value and energy flow calculations. With self-cleaning ultrasonic sensors and no moving parts, the unit was relatively maintenance-free. Pressure loss was also eliminated, as the flowmeter design allows for unobstructed gas flow.
The City of Reading has recently noticed labor savings of approximately $20,000/year by decreasing sampling and lab testing time; tear-down maintenance was cut in half, saving another $15,000/year; and the need for external natural gas to fuel the boilers was minimized, saving approximately $37,500/year in winter fuel costs. As a result of the installation of Endress+Hauser’s flow measuring system, to date, the City of Reading has saved a total of $72,500.
Endress+Hauser is exhibiting at WEFTEC.16, Booth 3745. For more information, visit www.us.endress.com.