Abstract
Abstract. The sensing characteristics and long-term stability of different kinds of CO ∕ HC gas sensors (non-Nernstian mixed potential type) during in situ operation in flue gas from different types of low-power combustion systems (wood-log- and wood-chip-fuelled) were investigated. The sensors showed representative but individual sensing behaviour with respect to characteristically varying flue gas composition over the combustion process. The long-term sensor signal stability evaluated by repeated exposure to CO ∕ H2 ∕ N2 ∕ synthetic air mixtures showed no sensitivity loss after operation in the flue gas. Particularly for one of the sensors (Heraeus GmbH), this high signal stability was observed in a field test experiment even during continuous operation in the flue gas of the wood-chip firing system over 4 months. Furthermore, it was experimentally shown that the signals of these CO ∕ HC sensing elements yield important additional information about the wood combustion process. This was demonstrated by the adaptation of an advanced combustion airstream control algorithm on a wood-log-fed fireplace and by the development of a combustion quality monitoring system for wood-chip-fed central heaters.
Highlights
Small-scale furnaces operated in domestic households, especially wood-log-fuelled heating systems and wood-chipor pellet-fuelled central heaters, are well known to contribute considerably to air pollution with toxic emissions of uncombusted and/or partly combusted exhaust gas components (CO / HC) and particulate matter (PM) loaded with organics
The signals of CS1K, CS10K and HC plus ROC measurement (HCS) over time of a typical test sequence are given in Fig. 2 together with the Tc, the residual oxygen concentration (ROC) and the analysis of IR active flue gas components by quasi-continuous HT-FTIR analysis
The system was operated at 70 % nominal power (NP) up to 120 min, reduced to 50 % and the firing process was stopped at 225 min
Summary
Small-scale furnaces operated in domestic households, especially wood-log-fuelled heating systems and wood-chipor pellet-fuelled central heaters, are well known to contribute considerably to air pollution with toxic emissions of uncombusted and/or partly combusted exhaust gas components (CO / HC) and particulate matter (PM) loaded with organics. Our previous studies (Butschbach et al, 2009; Kohler et al, 2013a, b) have shown that firing process control can be further improved by optimization of the airstream control algorithms based on the additional introduction of an in situ gas sensor operated in the flue gas for continuous measurement of CO / HC components like carbon monoxide (CO) or hydrocarbons like formaldehyde or methane (HC); this is called a CO / HC sensor This results in a tremendous reduction of toxic gas emissions from wood-log-fuelled single-room fireplaces by up to 80 % (Ojha et al, 2017) compared to the emissions of handoperated (conventional) single-room furnaces
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