Automatic control design and application in fluidized bed coal combustion systems

Purpose of this M. Sc. Thesis is to provide the efficient and low emissions combustion by using a determined algorithm in a laboratory scaled circulating fluidized bed type coal combustion system. To be able to provide the efficient combustion, air/fuel ratio must be calculated according to bed material, bed temperature and emissions. The amount of air, which enters the combustion room, can be varied according to hydrodynamics properties, fuel properties, and amount of humidity, outer temperature and air pressure. Generally, in the moment of combustion, excess amount of air causes a decrease in the combustion temperature. Uncompleted combustion, CO and hydrocarbons are formed because of low amount of air. Automatic control is one of the most important processes in the coal burning systems, especially Fluidized Beds. A well-designed automatic control system keeps the values in desired level and guarantees the efficiency when it runs. In this project, to constitute feedback signals according to pre-determined algorithm by collecting necessary data signals from reactor and flue and control coal feed motor and air flow fan with the help of sensors, which are placed in laboratory scaled circulating fluidized bed system reactor and flue, was aimed. One of the first steps of constituting algorithm is determining and studying the parameters which affect the combustion efficiency. The effects, which are based on fuel and combustion system, affect combustion directly. After a system installed, when the fuel based difficulties are overcame, system works effectively. The efficiency of CFB combustion systems is quite high. These combustion systems, which have structure that provides three conditions of combustion, don?t need any additional filter establishment to keep the emission values in the desired intervals. Hence, the advantage about establish cost points out the system when system is compared to other combustion system The studied system as a scope of this thesis is, laboratory scaled CFB combustion system which the capacity was increased to 250kW with the last upgrades where was placed in Gazi University, Engineering and Architecture Faculty, Mechanical Engineering Department, Thermal Power Laboratory. With two differential pressure transmitters, three thermocouples on the reactor and a Zirconium Oxygen Sensor at the flue, required measurements will be taken continuously. Subsequently, the values are executing by CPU which has the algorithm to control the system between pre-determined set value intervals of temperature, pressure decrease and excess oxygen in the flue gas by increasing or decreasing the motor frequency of coal feed and motor frequency of air feed fan.