Polymer control system
View Patent ↗A feedback control for a polymer dispensing system, which otherwise continuously adjusts the polymer feedrate so as to keep the measured streaming current of filtrate from a sludge dewatering process at one predetermined setpoint. The feedback control includes a video camera focused on sludge as it trails behind plows on a dewatering belt, a video image processing system for converting the video signal into single numbers known as “camera readings”, and a computer programmed both to compare them with a “camera reading” setpoint and to determine whether the filtrate charge is more positive or more negative than it normally is whenever the “camera reading” deviates from its setpoint by a threshold amount. A controller, activated by the computer, incrementally resets the polymer feedrate in such a direction as to restore the normal cationic charge of the filtrate. The feedback control uses the streaming current value measured immediately after each “camera reading” excursion to update the streaming current setpoint.
1. A method of automatically adjusting polymer feedrate in a sludge dewatering process in which filtrate captured from a gravity belt thickener and generated when the process is operating under optimum conditions exhibits a normal cationic charge measurable, as is the filtrate's charge generally, with a streaming current monitor, which comprises:
(a) converting images from a video camera focused on a fixed portion of the thickener's belt into single numbers known as “camera readings”;
(b) simultaneously monitoring the streaming current of filtrate from the dewatering process;
(c) determining, whenever the “camera readings” begin to deviate from a “camera reading” setpoint by a predetermined threshold, whether the filtrate charge is more positive than the normal cationic charge;
(d) incrementally resetting the polymer feedrate in such a direction as to restore the normal cationic charge of the filtrate; and
(e) updating the streaming current setpoint which is used to adjust the polymer feedrate except during a “camera reading” excursion when the “camera readings” deviate from the “camera reading” setpoint by at least the predetermined threshold, the updated streaming current setpoint being set equal to the streaming current value measured immediately after each such “camera reading” excursion.
2. The method according to claim 1 which further comprises incrementally resetting the polymer feedrate at preset intervals in such a way as to induce a “camera reading” excursion in which the “camera reading” deviates from the “camera reading” setpoint by the predetermined threshold amount.
3. The method according to claim 1 which further comprises incrementally decreasing the polymer feedrate at preset intervals in order to induce a “camera reading” excursion in which the “camera reading” deviates from the “camera reading” setpoint by the predetermined threshold amount and then immediately increasing the polymer feedrate in increments in order to end the “camera reading” excursion before a washout of the thickener's belt can occur.
4. A method of automatically adjusting polymer feedrate in a sludge dewatering process in which filtrate is captured from a dewatering belt, which comprises:
(a) converting images from a video camera focused on a fixed portion of the dewatering belt into single numbers known as “camera readings”;
(b) simultaneously monitoring the streaming current of the filtrate;
(c) converting the filtrate's measured streaming current values to cationic charge values;
(d) continuously comparing the “camera readings” with a “camera reading” setpoint;
(e) adjusting the polymer feedrate continuously so as to maintain the filtrate's streaming current values within a streaming current setpoint deadband, except when the “camera reading” deviates from the “camera reading” setpoint by at least a predetermined threshold amount;
(f) incrementally resetting the polymer feedrate, when the “camera reading” so deviates, in such a direction as to restore the filtrate's normal cationic charge, as exhibited by the filtrate when the process is operating under optimum conditions; and
(g) updating the streaming current setpoint by setting it equal to the streaming current value measured immediately upon the “camera readings” coming to within the threshold amount of the “camera reading” setpoint after an excursion outside of its threshold.