Automated Chlorination Control System: Orlando's Eagle Eye

This paper presents concepts and protocol associated with the design, start-up and operation of an automated chlorination control system based on flow, ORP and chlorine residual. The controller is unique in design and operation given it automatically switches, based upon a floating scale, between control by ORP and chlorine residual as setpoint for chlorine feed control.City staff developed the controller, in conjunction with a local vendor. The Orlando Eagle Eye controller is capable of handling process conditions that have prevented other chlorinator controllers available on the market, and tested at Water Conserv II, from functioning properly. The Water Conserv II facility, like many other plants that do not have ammonia or total nitrogen standards incorporated into effluent permits, experiences fluctuating levels of ammonia throughout the day in the final effluent. Fluctuation of ammonia in plant effluents create difficulties regulating chlorine feed rates to maintain required chlorine residuals both in the manual mode or with traditional automatic control systems.The City evaluated controllers available in the market and then began to develop and pilot the Orlando Eagle Eye when it was determined no off-the-shelf system met our needs. During the two-year development period, the City eventually identified valuable correlations between ammonia and ORP, and the proper response to increase or decrease the chlorine feed rate to effectively control the chlorine residual of the final effluent. The City documented when ammonia levels were high, as indicated by a low ORP reading, a decrease adjustment the chlorine feed rate was necessary to increase or maintain the combined chlorine residual. However, when ORP was high, indicating that the ammonia level is low, the chlorine feed rate must be increased in order to increase and achieve a free chlorine residual. The City learned that using only one setpoint signal, whether chlorine based or ORP based, could not be used for both ammonia level cases. The Orlando Eagle Eye controller determines when to use the ORP value as the control setpoint, or when to use the floating chlorine residual value as the control point, based on process conditions as identified by ORP fluctuations.This paper provides estimated cost savings recognized by reduced chlorine usage and O&M labor expended since implementing the Orlando Eagle Eye controller.