A new biomass based boiler concept for small district heating systems

The primary combustion chamber is partitioned to be able to maintain the required combustion temperature even at low thermal outputs. The thermal output span is 50 kW to 500 kW, with one module operating in the range of 50-150 kW and the other in the range of 150-350 kW. The smaller module will operate during summer time when heat is demanded only for hot tap water production, which on average amounts to about 10 % of the maximum heat demand during one season. Because of the wide thermal output span that is possible, the boiler can run continuously without starts and stops, which reduces emissions of unburnt gases radically. As another possibility to handle fast heat load variations that frequently occur in smaller district heating networks, a water heat store has been installed in the system.