An approach to optimum combustion control using parallel type and cross-limiting type technique

In the paper, a new approach to the combustion control by introducing the parallel type air–fuel combustion control and cross-limiting type (or lead-lag type) combustion control technique designed in one control system in a boiler is presented. This new approached combustion control system is designed in such way that controlled the air–fuel ratio in furnace in parallel way for small steam demand variation and in cross-limiting way for high steam demand variation. This approach does not require any extra field instrumentation or modified process parameter. All original instruments are used to measure the process parameters for combustion control and final control elements controlled the process. It is shown that air and fuel flow can be successfully optimized for the required steam demand by new designed combustion control. The accurate air–fuel ratio obtained in the proposed technique also minimizes some problems of the conventional system like incomplete combustion during sudden load change, boiler stuck-up problem and bump problem. The complete derivation of the required mathematical models is reported in the paper. Performance of three boilers incorporated with the proposed system is observed for a long period and the performance report is presented. A very efficient performance in three boilers has been observed.

► A new approach to the combustion control by introducing the parallel type air–fuel combustion control and cross-limiting type (or lead-lag type) combustion control technique designed in one control system.
► Elimination of incomplete combustion problem, boiler stuck-up problem and bump problem during sudden load change in conventional cross limiting system.
► Optimization of air–fuel ratio.
► Improvement of efficiency of power plant and reducing the environmental effect due to incomplete combustion.
► Improvement of plant reliability and life of plant equipments.