HOW MUCH CONTROL SHOULD A DISTRIBUTED CONTROL SYSTEM HAVE IN YOUR PLANT? DESIGN EXPERIENCE FOR THE CONTROL SYSTEM UPGRADE AT THE METROPOLITAN WATER RECLAMATION DISTRICT OF GREATER CHICAGO'S STICKNEY WATER RECLAMATION PLANT

The Metropolitan Water Reclamation District of Greater Chicago (MWRDGC) has nearly completed the design of improvements to the control system at its Stickney Water Reclamation Plant (WRP). The design includes the installation of a Distributed Control System (DCS) for the plant and outlying facilities.At the outset of the design process, the stated goal was to standardize controls throughout the plant. The intent was to establish hard and fast design rules that would standardize hard-wired control for basic, front-line equipment interlocks, such as motor protection and personal safety. The intent was for the DCS to provide supervisory control of equipment, allowing operational changes needed as part of the normal course of operation.As a result of the design approach used, the design of the new DCS's involvement in the electro-mechanical operation of the facility varied dramatically from process area to process area. In some areas, the DCS will replace motor control functions, including overload protection for small motors. In other areas, the DCS will be simply linked to existing PLCs, providing no more than additional operational interface capabilities to the existing system.This paper looks in detail at several of the various applications for the use of the DCS in various situations throughout the plant. This project gives an excellent opportunity to demonstrate the gamut of the extent of control that can be provided in the design of a DCS retrofit.