In a joint project with the company Paul Künzel GmbH a small heating furnace in the power range < 50kW has been developed that can be used with straw-pellets and cereal grains. Wheat and rye pellets as well as wheat and barley grains have been investigated as fuels, regarding the respective fuel properties and pollutant emissions.

It has been shown that the ash melting behaviour of the different fuels has a major impact on furnace operation. While the other fuels investigated could be used satisfactorily but with varying quality of combustion, a constant operation was not at all possible with wheat grains.

As combustion temperatures have to be kept low because of the ash melting behaviour of the fuels, the CO-values remain well above the regulatory limits. This imposes the necessity to improve the burner further. Differences in the fuel properties become apparent when dust or particle emissions are considered: rye pellets emit more than six times more particle mass than wheat pellets, while approx. 80 % of the particle mass is smaller than 1 μm in diameter (PM1). Detailed analysis of the PM1-fraction shows characteristic particle distributions for the different fuels, with the highest particle number concentrations within the diameter range of 70 to 200 nm. NOx-Emissions were also heavily dependent upon fuel properties but they could be almost halved using simple air staging and were thus maintained well below regulatory limits.