SCHEME FOR SELF-OPTIMISING COMBUSTION CONTROL OF MULTIFUEL FIRED BOILERS IN STEEL PLANTS.

Boilers in captive power plants of integrated steel plants use various byproduct gases, in addition to coal and oil. It is difficult to optimize combustion of such multi-fuel fired boilers by single component flue gas analysis. A technique of self optimization has been evolved using a microprocessor. Under steady state conditions the oxygen and combustible content in flue gas are measured and a performance index has been calculated depending upon weightage assigned. Perturbations are created in air-fuel ratio of a particular fuel to calculate change in the performance index. With the help of a mciroprocessor, the search for minimum of this index is continued to establish optimum ratio for the fuel. While doing this it has taken into consideration that this ratio does not fall below the stoichiometric ratio. Similar exercise has been carried out for other fuels. The cycle of fixing up of optimum air-fuel ratio for each fuel is done continuously on-line. The control algorithm and schematic scheme for implementation of this technique have also been discussed.