Читать книгу Automation of Water Resource Recovery Facilities - Water Environment Federation - Страница 249

If more than one primary clarifier shares a dedicated pump, the control gets more complicated. In this instance, each primary sludge tank valve is controlled with an “open time”. The sludge pump (along with any grinders associated with the pump) will typically run continuously or as long as any associated tank’s sludge valve is open. The valves for each clarifier will typically cycle in order, with the clarifier valve that has been closed the longest opening next. In general, the open-time frequency for each valve should be short enough so that the clarifiers waiting to remove sludge do not cause plugging at the pipe inlet and to prevent rat holing. For example, four clarifiers sharing the same pump might each have their valve open time at 10 minutes, resulting in a closed time of 30 minutes for each clarifier valve. If sludge blanket levels are known, the relative open time for each clarifier can be trimmed slightly so that the blankets remain close across all clarifiers. As stated previously, adjustments to time because of blanket level should typically be made infrequently, with a single change made each day or so because the blanket level typically does not change quickly.