Moisture content as a design and operational parameter for fast pyrolysis

Fast pyrolysis trials of wheat straw were performed in a pilot plant featuring a screw reactor and two stage condensation system. Trials differed in the moisture content of the used biomass (1.2%, 9.2%, and 23.6%) and the sweeping gas flowrate. Higher moisture feedstock seems to lead to higher bio-oil production but the largest organic liquid yield occurred at intermediate feedstock moistures. Increasing the sweeping gas flow rate at the system leads to a higher liquid yield richer in organics. Based on these results it is concluded that the highest organic liquid yield is not observed for dry feedstock because the missing water vapour leads to longer hot vapour residence time, favouring secondary gas phase cracking reactions. Information and yields obtained at the pilot were scaled up to industrial scale (500 kg h(-1) of feedstock) and used to construct an Aspen Plus (R) model that can be used to estimate heat availability in different parts of the system as well as simulate a dryer that would employ available internal process heat. This model was used to investigate the impact of using moister feedstock in the process. Enough heat is available for drying moist feedstock by using flue gas of the heat carrier loop in a different manner as in the current design.