Overcoming Shrink-and-Swell Effect in Water Level Control Strategy on Industrial Drum Boiler

Power generation has become an increasingly competitive arena. The cost of operating power plants comes mostly from the fuel bill, which runs in the billions of dollars annually. In order to minimise the fuel bill and maximise plant efficiency, a plant’s load-following capability must be optimised, i.e. to follow the demand of power closely. A great deal of attention has been given to the controller that regulates water level (and steam pressure) at the steam-generating unit – the boiler-drum. The control strategy is complicated by the non-linear and non-minimum phase characteristics of the boiler-drum. This paper illustrates our work in the optimisation of load-following scheme by applying a 3-element controller scheme to regulate the boiler-drum’s water level. The controller is then cascaded with another feedback loop that regulates steam pressure. The results from the control scheme have shown considerable improvement over a typical boiler-drum’s water level control strategy.