Biomass Heating System - Buffer Tanks

Buffer Tanks

Buffer tanks, sometimes referred to as 'thermal stores' are crucial for the efficient operation of all biomass boilers where the system loading fluctuates rapidly, or the volume of water in the complete hydraulic system is relatively small. Using a suitably sized buffer vessel prevents rapid cycling of the boiler when the loading is below the minimum boiler output. Rapid cycling of the boiler causes a large increase in harmful emissions such as Carbon monoxide, dust, and NOx, greatly re duces boiler efficiency and increases electrical consumption of the unit. In addition, service and maintenance requirements will be increased as parts are stressed by rapid heating and cooling cycles. Although most boilers claim to be able to turn down to 30% of nominal output, in the real world this is often not achievable due to differences in the fuel from the 'ideal' or test fuel. A suitably sized buffer tank should therefore be considered where the loading of the boiler drops below 50% of the nominal output – in other words unless the biomass component is purely base load, the system should include a buffer tank. In any case where the secondary system does not contain sufficient water for safe removal of residual heat from the biomass boiler irrespective of the loading conditions, the system must include a suitably sized buffer tank. The residual heat from a biomass unit varies greatly depending on the boiler design and the thermal mass of the combustion chamber. light weight, fast response boilers require only 10ltr/kW, while industrial wet wood units with very high thermal mass require 40ltr/kW