Control Strategy for Small-Scale Wood Chip Combustion

The purpose is to control small-scale (< 1MWth) wood chip combustion in an inexpensive and durable way. Therefore, a hierarchical control concept is presented. The main task of the fuel feed control system, which is based on temperature and lambda measurements, is to settle the fuel feed to air feeds and to compensate for the temporary fluctuations in the fuel feed. The task of the air flow control is to set the primary and secondary air flows suitable for the power level and for the fuel moisture content. Test results of a 200 kW commercial system are presented. The process experiments indicate that the high level control system is able to adapt to varying combustion conditions and to maintain low emission levels. The control concept is adaptable also to existing systems.