The co-combustion of pellets with pistachio shells in residential units additionally equipped by Pt-based catalyst

There are several published studies evaluating the possibilities of thermal and non-thermal utilization of pistachio hard shells in many technical sectors; however, there are no relevant data about the possibilities of usage of this homogenous biomass-based by-product as a fuel for automatic household heating appliances for partial or full substitution of standard ENplus A1 pellets, which is the aim of the presented study. The composition and basic properties of both fuels were compared as well as the flue gas composition formed during the 6 different fuel mixture combustion in two real-scale pellet burners. The mass concentration of observed pollutants (CO, total suspended particles, and C3H8) in the flue gas was strongly affected by increasing of pistachio shell mass fraction in the fuel mixture (from 10 to 100%). In comparison to the combustion of ENplus A1 pellets, CO was increased up to 25.9 times, total suspended particles up to 15.3 times, and C3H8 up to 13.7 times. Based on the results of real combustion tests, the equations were listed, describing the increase of the mass concentration of pollutants for the whole spectrum of pellets/pistachio shell ratios applied on the chosen designs of the pellet burners. The Pt-based oxidation honeycomb catalyst, additionally installed at the combustion unit outlets for flue gas purification, showed conversion rates up to 82.2% in the case of CO and up to 33.1% in the case of C3H8. This enables the reaching of the same or lower mass concentrations of mentioned pollutants in the flue gas, formed during the co-combustion of appropriately selected fuel ratios in comparison to ENplus A1 pellet combustion without the catalyst.