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A totally integrated automated system
By Tony Di Stefano, Project Engineer, Siemens Energy and Automation -- Design News, August 5, 2002
Company: United Conveyor Corp. (UCC)
Location: Waukegan, IL
Engineering Services: Since 1920, United Conveyor Corp. (UCC) has devoted its efforts exclusively to the design, supply, construction and maintenance of ash handling and other abrasive material handling systems. UCC designs custom-engineered systems to meet the specific requirements of an individual power plant or utility installation, or other industrial application. Designs are based on customer specification, laboratory test data, and UCC design standards that have been proven by experience.
Project: Totally integrated automation system from Siemens Energy & Automation installed in units five and six of the Shenzhen Western Power Plant, China. The system controls a pneumatic conveying system used to transport fly ash from 88 precipitator, economizer, and air pre-heater hoppers to storage bin silos. Each unit generates 300 MW of electric power and serves both industrial and residential consumers. The units produce more than 35 tons of fly ash per hour. The fly ash is mainly used as landfill or as a binder for road repair.
Engineering Challenge: Installing an automation system with a family of processors that are designed to work seamlessly without any other program configuration or consideration by the designer. The system had to control the flow of the fly ash transported by between 4 inch Hg and 13 inch Hg negative pressure, produced by a rotary positive displacement mechanical exhauster, driven by a three-phase motor. The automation system as specified by the customer had to have a high level of redundancy and ensure a failsafe operation.
Proposed Solution: The customer wanted a totally integrated automation solution that would satisfy the requirements, and these controls were to come from a single vendor. Siemens was specified. The Siemens solution, because of its automatic copying capability between two PLC CPU's, saves engineering time due to a single program concept. It also promotes reliability through transparent redundancy.
Components and tools applied: The main rack includes two SIMATIC® S7 414H PLCs connected by fiber optics that communicate over a redundant PROFIBUS cable communicating at 19.2 kbps. It is capable of up to12 Mbaud to more than 700 I/O over a distance of approximately 200 meters, but capable of 1,000 meters. The redundant PLCs communicate with two redundant HMI PC's via Ethernet. The software used was Siemens Step 7 Project Manager programming software for the PLCs, and Siemens WinCC and Redconnect software was used on the PC-based HMI's. As a result of the features of these components, UCC and Siemens were able to configure the HMI's to be both active and on-line at the same time with the redundant PLC rack; this satisfied the customer's requirement for redundancy at both the PLC and HMI levels.
Results: The redundant PLC saves programming time and program revision during start-up because it is edited on-line just like a single PLC. There is only one program to edit and download with no special consideration by the programmer. Because of the transparent and redundant nature of the PLCs, the programmer can concentrate on programming the application and forget about the programming that is normally required to control the redundant failover, further saving time on the project while maintaining a high level of integrity.
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