MODELLING, SIMULATING AND OPTIMIZING BOILERS.

In the present work a framework for optimizing the design of boilers for dynamic operation has been developed. A cost function to be minimized during the optimization has been formulated and for the present design variables related to the Boiler Volume and the Boiler load Gradient (i.e. ring rate on the boiler) have been dened. Furthermore a number of constraints related to: minimum and maximum boiler load gradient, minimum boiler size, Shrinking and Swelling and Steam Space Load have been dened. For dening the constraints related to the required boiler volume a dynamic model for simulating the boiler performance has been developed. Outputs from the simulations are shrinking and swelling of water level in the drum during for example a start-up of the boiler, these gures combined with the requirements with respect to allowable water level uctuations in the drum denes the requirements with respect to drum size. The model has been formulated with a specied building-up of the pressure during the start-up of the plant, i.e. the steam production during start-up of the boiler is output from the model. The steam outputs together with requirements with respect to steam space load have been utilized to dene requirements with respect to steam drum size. The cost function has been dened as a function taking the weight of the boiler, its dynamic capability and nally the consumptions during dynamic operation of the boiler into consideration (the latter presumed constant). It has been shown that the weight of the boiler is (with an acceptable accuracy) proportional with the volume of the boiler. For the dynamic operation capability a cost function penalizing limited dynamic operation capability and vise-versa has been dened. The main idea is that it by mean of the parameters in this function is possible to t its shape to the actual application. In the paper an optimization example is shown and the results discussed. By means of the developed model it is shown how the optimum changes from a boiler favoring a good dynamic capability (i.e. a boiler with a relatively large volume) to a boiler not penalizing a limited dynamic capability (i.e. a boiler with a relatively small volume) if the shape of the cost function is changed slightly.