CO and NO emissions from pellet stoves: an experimental study

This work presents a report on an experimental investigation on pellet stoves aimed to fully understand which parameters influence CO and NO emissions and how it is possible to find and choose the optimal point of working. Tests are performed on three pellet stoves varying heating power, combustion chamber size and burner pot geometry. After a brief review on the factors which influence the production of these pollutants, we present and discuss the results of experimental tests aimed to ascertain how the geometry of the combustion chamber and the distribution of primary and secondary air, can modify the quantity of CO and NO in the flue gas. Experimental tests show that production of CO is strongly affected by the excess air and by its distribution: in particular, it is critical an effective control of air distribution. In these devices a low-level of CO emissions does require a proper setup to operate in the optimal range of excess air that minimizes CO production. In order to simplify the optimization process, we propose the use of instantaneous data of CO and O sub(2) concentration, instead of average values, because they allow a quick identification of the optimal point. It is shown that the optimal range of operation can be enlarged as a consequence of proper burner pot design. Finally, it is shown that NO emissions are not a critical issue, since they are well below threshold enforced by law, are not influenced by the distribution of air in the combustion chamber, and their behavior as a function of air excess is the same for all the geometries investigated here.