The design and performance of steam generators supplied to thermal power plants are greatly influenced by the properties of coal burnt. All coals are not same and the variation of heating value of coal supplied to boiler results in changes in critical process parameters like pressure and temperature of main steam produced. These fluctuations are normally controlled by master pressure controller, provided the variation in heating value is within certain limits. If the heating value of coal being burnt varies substantially, a remedial measure is necessary to control the pressure and temperature fluctuations during coal fuel switching. The composition of the coal burnt currently in a boiler is determined from an online analyser, and an embedded controller computes the current heating value of the coal and suitably modifies the gains of all the controllers to arrest the undue fluctuations in pressure and temperature. A validated mathematical model for a typical 500 MW plant is used to simulate the variations in pressure and temperature of steam with normal and embedded controllers. Significant reduction in pressure and temperature variation has been achieved with an embedded controller. This article discusses the improved method of ensuring optimum boiler performance during coal fuel switchover.
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