Safety Interlock System Integration With A PC Based Distributed Control Model

摘要

The use of Chlorine Dioxide for water treatment in North America can be traced back to 1947 when it was first used to control phenol-related taste and odor concerns in drinking water supplied from the Niagara River in New York State. In recent years, the use of chlorine dioxide as a primary disinfectant, replacing chlorine in the water treatment industry has seen growing interest due to increasing regulatory pressures. These regulatory issues have caused many Municipalities to review their treatment programs and in some cases forced them to seek alternative treatment solutions, or to better control their existing systems. ERCO Worldwide has integrated a number of control system elements, along with novel chlorine dioxide generator technologies to provide Municipalities with chlorine dioxide systems that will help them address these regulatory pressures. The resulting control strategy, while developed for a specific series of generators, would lend itself to almost any small to medium scale control system for standalone OEM packages. This control system philosophy has been based upon an open networking strategy coupled with a number of digital communication protocols, and facilitates the integration of this standalone system into the larger Municipal Water Plant Enterprise. ERCO's control system design philosophy is born out of its experiences in the chemical industry, in which large scale DCS systems are integrated with standalone safety interlock systems. However, this level of complexity and system cost were neither warranted, nor would they be supported at the Municipal Water Treatment Plant level. A control system philosophy had to be developed that could be implemented cost effectively, easily supported in the field, and would be scalable to suite anticipated requirements. It was imperative that the control system be easily integrated into the Municipal Water Plant's control scheme, despite the wide range of applied technologies implemented across North America and the diverse nature of the requirements of each customer. A PC-Based control system was designed utilizing commercially available software that integrated the system Human Machine Interface, Control Logic, Alarming, Data Logging, OPC Server and Clients, and HTML Reporting into a single development package. The PC-Based control package was linked to a programmable I/O system, via a Modbus TCP interface. The selected I/O system was modular in nature allowing the vendor to optimize the I/O capabilities of the control package with the required field instruments. The PC-Based control system was programmed with the process interlocks, while the programmable I/O was configured to run the safety interlocks. By isolating the process logic and safety interlock logic between two separate controllers; this control system enables this family of generator technology to address a number of the issues raised through the ANSI ISA S84.01 standard. The integration of PC-Based control with a programmable I/O system enabled the development of a control system that was based solely on commercially available elements which supports a number of different digital bus technologies. This package can be readily integrated into existing and anticipated plant control schemes, to facilitate the integration of the standalone controller into the overall plant control strategy.