Читать книгу Automation of Water Resource Recovery Facilities - Water Environment Federation - Страница 248

If each primary clarifier has a dedicated pump, control is easier. In this instance, primary sludge pumping is done with “on-time” and “off-time”. If there are automatic valves and/or grinders associated with the pump, they will need to be included in the on–off cycle with the pump. In general, the off-time frequency should be short enough to prevent plugging at the pipe inlet. In addition, the on-time frequency should be short enough to prevent “rat holing” (i.e., pulling supernatant through the sludge, which results in thin sludge). For example, the off-time may be 30 minutes and the on-time may be 10 minutes. If the sludge blanket level is known, the time interval can be trimmed slightly so that the blanket remains at a normal level. Typically, adjustments to time because of blanket level should be made infrequently, with a single change made each day or so because the blanket level typically does not change quickly.