The SpinPro AutoFloc Automatic Polymer Flocculation Control System is a chemical control system used to optimize flocculant and/or coagulant dosage on dewatering applications including but not limited to screw presses, belt presses, dewatering tubes (Geo-Tubes), centrifuges, clarifiers and DAF;s. The system utilizes a microprocessor based controller in conjunction with a suspended solids or color monitor to continuously monitor and regulate the effluent quality. Optional feed forward inputs of flow and suspended solids allow faster adaptation to influent steam variations. The self-tuning PID controller eliminates overdosing and insures consistent process operation.
Theory of Operation
The basic principle of the SPINPRO AutoFloc is to make small changes in the chemical dosage and look for matching variations in the feedback signal. In dewatering or clarification applications, the feedback signal represents the Total Suspended Solids (TSS) in the filtrate. Filtrate TSS has proven to be an excellent indicator of the effectiveness of polymer dosage. By measuring the change in TSS associated with small changes in chemical dosage, the controller can calculate the path of the system and determine where on the chemical dosage curve it is operating.
The polymer dosage curve above shows a typical process response to polymer dosage. In the effective dosage range, increases in chemical dosage result in improved separation and a significant decrease in filtrate TSS. In the overdosing area, or “comfort Zone,” increased polymer dosage does very little to improve separation and can often result in even higher TSS. In most processes controlled manually, operators will maintain dosage somewhere in the comfort zone. The gives the operator a cushion so that an increase in polymer demand will not cause an upset.
By utilizing the feedback principle described above, the AutoFloc determines whether its operating set point is in either the effective dosage range or in the comfort zone. If the set point is achievable without overdosing, the AutoFloc will function as a self-tuning PID controller; maintaining the effluent at the chosen set point by continuously adjusting polymer dosage.
Unlike other controllers, however, if the process changes and the set point is no longer achievable, the AutoFloc will not operate in the overdosing area trying to reach that set point. Instead, it will realize that the process is no longer responding to increases in polymer and it will reduce chemical dosage until it crosses back into the effective dosage range. It will continue to operate on the “elbow” of the dosage curve until it finds it is able to reach the desired set point without overdosing. This action eliminates overdosing, resulting in a significant decrease in polymer use.