Bahman Mehran - Iran Electrical Organization

Due to the facts that superheater tubes are normafly designed within specifiied limits, any extra rise of superheater metal temperature above the limits drops the life time of these tubes drastically,therefore , one of the most important controlled varibles in steam power plant is superheater outlet steam temperature. This control loop is of great importance and requires high accuracy and safety of measuring and control equipments.In conventional control methods, in order to obtain acceptable superheater steam temperature time response against disturbances and load changing , the superheater tubes are divided into several sections and also two or three spary water injection points are installed.Each section is controlled individually via its control loop, thus the dead time problem which is caused due to superheater long tubes fairly rectified . In this paper an attempt is made to introduce new concept for reducing spray water injection points and improving system time response through state varible controller with observer based on modern control theory. This modern technique not only reduces the investment cost by reduction of spray water injection points , but increasing superheter and turbine blade life time and system robustness.