Comprehensive Study for Control of Boiler Drum Level in Power Plants

Abstract

In every country, the power demand increase with the industrial and civil growth. To meet this demand, special attention must be paid to the control of power generating plants to insure stable and robust supply. The power grid in Sudan covers almost the cities with many power generating units. The increase in power generation resulted in an increase in disturbances and power swings due to faults in units or transmission lines, this power swings has a great effect on generation units and cause many unit trips. The major cause of unit trips in these circumstances is the boiler drum level. While single-element drum level control is acceptable for steady boiler load conditions; as load changes become more frequent, unpredictable, or severe, this type of level control cannot respond quickly enough to compensate for changes. More information must be included and processed to predetermine the amount of water to be added to the drum to compensate for load changes. The addition of elements (flow transmitter devices) enables the controller to predict the amount of water added to the drum to maintain drum level set-point. In this study the old control system which is used in Khartoum North Power Station Unit-3, microprocessor base control system is a black box system and analogue system, the monitoring for drum level in the mimic display by indication lamps only. This system is upgraded to a new system using DCS system which allows the operator to monitor all process variables, interlock, sequence control system and modulating control system. The study focuses on the drum level control from the startup up to full load. A design for the single element control and three element control with Metso automation software using function block diagram language is presented. A comparison between single and three element control system was made; from the study found that the fluctuation in the load for the single element control is more than three element control.