On-line Operating Adjustment of Small Biomass Fired Boilers Optimizing CO and NO_x Emissions

摘要

Control of combustion conditions in small-scale biomass boilers for heating purposes is a specific task because it must be carried out without any high additional costs. If a basic control of heating water on a desired value is performed by means of a PI control algorithm in a PLC, it is possible to enhance this control unit with other algorithms taking care for searching optimal operating conditions. These conditions are considered from the viewpoint of energy efficiency and ecological impacts, especially emissions of unburned hydrocarbons and CO, but also nitrogen oxides are in interest. This previously minor problem has become significant with the large expansion of the small-size biomass-fired boilers. The combustion process consists of phenomena that we have little information about for an exact mathematical description. The equations of the chemical reactions are known, but in reality the combustion of biomass is much more complicated and more variable than a mathematical model can express. Therefore, techniques searching extreme are more suitable than controllers requiring a mathematical model in design or tuning. In such a way it is possible to design a controller that is able to control the combustion process effectively over the whole operation range.