Influences of Fuel Bed Depth and Air Supply on Small-Scale Batch-Fed Reverse Downdraft Biomass Conversion

Abstract

The producer gas composition and the thermochemical conversion process of a small-scale reverse downdraft reactor has been investigated under ten operating conditions with different fuel bed depths and air supply rates. The operating principle of this research reactor is a batch-fed reverse downdraft process, using wood pellets as the solid biomass fuel. The oxygen-limited regime, where the fuel consumption increases nearly linearly with the air supply, has been identified, and four flow rates over the range of this regime have been investigated. The fuel bed depth was varied between one and four reactor diameters (1D (100 mm)–4D (400 mm)). The results demonstrate that increasing the primary air mass flux leads to both greater fuel consumption and higher temperatures as well as heating rates in the reaction front. Greater air supply rates and the resulting higher temperatures lead to a substantial increase in fuel conversion into permanent gases, rather than tars or char, and a rise in the cold gas effici...