Extensive reduction of toxic gas emissions of firewood-fueled low power fireplaces by improved in situ gas sensorics and catalytic treatment of exhaust gas

Two different firewood-fueled high quality fireplaces for private homes were complemented with novel in situ gas sensors for residual oxygen and CO/HC flue gas analysis and with a catalytic converter for exhaust gas treatment. The sensitivity performance of the used CO/HC mixed-potential-type sensor is characterized. Based on these two gas sensor signals and on the combustion temperature a new general strategy for automatic control of the primary and secondary air streams for firewood combustion was developed. This enabled reduction of the (toxic) CO/HC-emissions to about 50% (central heater) and 15% (tiled stove), respectively, in comparison to the emissions measured when the firing process is controlled by the algorithm of the fireplace-producer. After implementation of a catalytic converter into the flue gas channel (central heater) and post-combustion chamber (tiled stove) and adaptation of the control algorithm parameters the CO/HC-emissions were further reduced to about 25% and less than 1%, respectively. Studies of the long-term stability of the catalyst material by temperature dependent gas conversion experiments indicated that the conversion kinetics is stabilized at an onset-temperature of about 155 °C.