subject: Sight Glass Crucial In Biogas Digester Tank Applications [print this page] A growing interest in alternative energy is fueling the construction of biogas facilities, which typically produce methane gas through bacteria-based anaerobic digestion (fermentation) of animal manure and other organic wastes. The end product is essentially the same as natural gas and can be used in the same ways.
Biogas production facilities typically use large concrete digester tanks, which must be equipped with sight glasses to allow observation inside the tanks. Visual monitoring is essential because foam or crust formation can slow down the digestion process. Therefore, sight glasses are installed near tank work platforms where operators use their observations to see changes going on inside the tanks, and set mixing devices at optimum positions to prevent foam and crust build-up. Fast response to these changes translates into significant biogas production efficiencies. In addition, early detection of irregularities helps ensure safe operations.
Since the methane produced is a combustible gas, and can form an explosive mixture with air, it is essential that each glass installation form a gas-tight seal to meet safety requirements. L.J. Star developed its RD300 sight window specifically to meet these requirements, and incorporated other features that aid in the monitoring of biogas processes.
The RD300 has an innovative expanding gasket that allows it to conform to irregularities in the cement walls and ports of the digester tanks. This tubular rubber gasket around its perimeter is sandwiched between high-grade steel rings. As the mounting screws are tightened, the inner and outer rings draw together and force the gasket to expand, thereby creating a gas-tight seal. In addition, the sight glass includes three angled mounting brackets that are long enough to accommodate the depth of the container wall.
Standard Specifications. The RD300 sight glass is made of high quality soda-lime glass. All metal components are made of 316Ti stainless steel (14571). The outside ring diameter is 295mm and the viewing area diameter is 220mm.
Available Options. The RD300 sight window is available with several options that are important for biogas applications. The unit may be ordered with an optional motorized wiper, a manually operated wiper, and a washer assembly. By turning a valve, operators can direct water spray on the interior of the glass. The spray tube is made of high quality stainless steel. Alternatively, the spray tube can be used to take fermentation gas samples from the container.
Monitoring is often performed remotely, in which case the RD300 can be equipped with explosion-proof lights and video cameras. The optional Lumiglas light is designed to hinge mount on the metal ring, providing directionally adjustable illumination. The optional Lumiglas VISULEX video camera can be similarly mounted to provide remote observation of processes. Both the light and camera carry Cenelec IIc explosion proof ratings (Zones 1 & 2).
Additional Information. To obtain additional information, contact L.J. Star Incorporated, P.O. Box 1116, Twinsburg, OH 44087. Phone: 330-405-3040. Fax: 330-405-3070. Email: view@ljstar.com. Or visit website: www.ljstar.com/pubs/20.htm.
