OCR Text |
Show GNOCIS GNOCIS (~eneric NQx ~ontro.l .lntelli.gent ~y~tem) is an enhancement to digital control systems (DCS) targeted at improving utility. bOIler effiCiency and reducing emissions. GNOCIS is designed to operate on units burning gas, oil, or coal and is available for all combustion firing geometries. GNOCIS utilizes a neural-network model of the combustion characteristics of the boiler that reflects both short-term and longer-term trends in boiler characteristics. A constrained-nonlinear optimizing procedure is applied to identify the b~st set pOints for the plant. These recommended set points can be implemented automatically without operator intervention (closed-loop), or, at the plant's discretion, conveyed to the plant operators for implementation (open-loop). The software incorporates sensor validation techniques and is designed for continuous on-line use. The major elements of GNOCIS are shown in Figure 1. Alabama Power Company's Gaston Unit 4, a 270 MW wall-fired unit, and PowerGen's Kingsnorth Unit 1, a 500 MW tangentially-fired unit served as developmental sites for GNOCIS. Demonstrations of GNOCIS are also underway at a number of other sites including Georgia Power Company's Hammond Unit 4, Entergy's Nelson Unit 4, Duquense's Cheswick Unit 1, and PowerGen's Kingsnorth Unit 3. Results from Kingsnorth Unit 1 and Gaston Unit 4 are presented in this paper. GNOCIS development was funded by a consortium consisting of the Electric Power Research Institute, PowerGen, Southern Company, Radian International, U.K. Department of Trade and Industry, and U.S. Department of Energy. THE GASTON TRIAL The objective of the Gaston trial is to develop and demonstrate GNOCIS on a wall-fired unit. Gaston Unit 4 is a 270 MW pulverized coal unit. The Babcock and Wilcox (B&W) opposed-wall-fired boiler is Combustion Models Software -Supervisory Optimizer -Communications -Archiving -Safety Constraints DCS Integration -Operator Graphics -Configuration Modifications 1 Unit -I mplementation -Safety Constraints Plant Operators / Engineers Figure 1. Major Elements of GNOCIS arranged with nine burners (3W x 3H) on two opposing walls such that no burner has another burner directly across from it. Combustion air is supplied to the burners via common wind boxes on each side of the boiler. The unit is equipped with B&W XCL low NOx burners and six B&W EL-76 ball and race mills. Fuel is delivered to the mills by two-speed table feeders. The unit has two forced-draft fans, six primary air fans, and two flue gas recirculation fans. Combustion air is heated with Ljungstrom air preheaters. The boiler control system for Gaston Unit 4 is a Leeds and Northrup Max 1000 distributed digital control system. The control system is designed such that the unit is controlled through the CRTs -- there are no bench board mounted controls. GNOCIS Implementation The original objective at Gaston was to implement an open-loop, advisory system with no immediate plans to migrate to closed-loop operation. This objective influenced the original design philosophy in a number of respects, primarily selection and quantity of control variables, increased demand for flexible and informative operator displays, and reduced necessity for stringent recommendation checking and incorporation of safeguards. However, during the course of the project, it was determined that there were significant benefits, both in performance and ease of use of the system, if upgrades were made to GNOCIS to enable closed-loop operation. These enhancements also give the operator an easier way to implement open-loop recommendations. 2 |