Westinghouse Incorporates Proven GPC-1500 Controller Into C 0 / 0 2 Trim Package

The field-proven, microprocessorbased Model 1500 General Purpose Controller has been incorporated into the Westinghouse carbon monoxide/ oxygen (C0/02) combustion trim control package by the Combustion Control Division of Westinghouse Electric Corporation.

Labeled TC-910, The Westinghouse C0/02 trim control package now calls upon the increased power and flexibility of the GPC-1500.

The GPC-1500 controller provides complete panel instrumentation with annunciation and alarm contact outputs for as many as six control loops.

Previously, the Westinghouse TC910 package incorporated the microprocessor-based Model 1400 controller which provided dedicated control for combustion air or fuel trim. The additional control capability of the GPC-1500 enables microprocessor- based control of other important boiler parameters in addition to automatic combustion trim control.

Most combustion control experts agree that oxygen trim control provides up to 90 percent of available fuel savings in an automatic combustion trim control system. The addition of carbon monoxide flue gas analysis to the trim strategy makes the remaining 10 percent of available fuel savings in the combustion process attainable.

The TC910 system utilizes the flue gas analysis provided by the Westinghouse model 620 CO analyzer and the Hagan industrial-type, in situ excess oxygen analyzer. The Model 620 CO analyzer utilizes high resolution infrared absorption spectroscopy to determine CO flue gas content. A microprocessor located in the control room uses the difference in intensities between the infrared energy transmitted across the stack and the energy received to calculate the CO content.

The Hagan in situ, zirconium oxide, excess oxygen analyzer provides accurate, reliable measurement of excess oxygen flue gas content from directly within the boiler flue.

The TC910 control system establishes the CO measurement as the primary control parameter. A CO setpoint is established and excess air is trimmed based on the CO measurement. If a sudden boiler load change or other process upset occurs and certain preset 02 high or low limits be reached, the control of the combustion process is automatically switched to the 02 control parameter. The system then quickly returns the process to within the O, limits. At this time the trim control returns to the CO control parameters.

The GPC-1500 controller can also be programmed with a unique feedforward feature that allows the TC910 system to dynamically bias the air and/or fuel control as a function of boiler load.

The feedforward control action is totally independent of the analyzers' signals from the programmed setpoints. The control action functions as an electronic cam, producing the optimum mechanical relationship between the air and fuel linkages in the combustion process during dynamic boiler load conditions.

This action allows optimum combustion trim control at all times.

The TC910 system can also include optional Veritrak recorders for providing permanent records of important combustion and trim control data.

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Maritime Reporter Magazine, page 47, Dec 1986

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