Usefulness assessment of automatic air flow control system with oxygen sensor in a 20 kW boiler with periodic wood pellet supply

Abstract

The benefits of applying automatic air flow control system with oxygen sensor in a 20 kW heating boiler with a retort furnace supplied periodically with wood pellets were examined. Boiler combustion chamber was not lined with ceramic blanket and therefore the fuel supply cycle duration (operation and stand-by) was set by the producer to just 20 seconds. Variation in time of carbon monoxide, nitric oxide, nitrogen oxides and oxygen concentrations in the flue gas, as well as correlations between: pollutant concentrations and temperature in the combustion chamber or oxygen concentration, temperature in the combustion chamber and oxygen concentration, nitric oxide and carbon monoxide concentrations were compared for different scenarios: with automatic air flow control and with constant air flow. It was concluded that applying automatic air flow control system with oxygen sensor did not significantly reduce carbon monoxide concentration (only by 10-15%). Most probably it is because the stand-by in fuel feeding is too short for the air supply fan to react. In order to reduce carbon monoxide concentration, instead of applying automatic air flow control it is preferable to obtain higher heat outputs (above 60% of its maximum value) and use higher capacity water heat storages.