Co-firing and microwave pre-treatment of lignocellulosic pellets for control of thermochemical conversion of biomass mixtures and sustainable energy production

Abstract

Original experimental device with heat output up to 20 kW was developed and tested with the aim to provide wider use of the locally available renewable energy resources - agriculture residues (wheat straw) for sustainable energy production and reduced effect of energy production on climate changes. To provide efficient control of thermochemical conversion of straw pellets, mixtures of straw pellets with microwave (mw) pre-treated straw or wood pellets were used, providing selective pre-treatment of the mixture components at frequency 2.45 GHz with temperatures of pre-treatment 473 K and 548 K. The effect of selective microwave pre-treatment of the mixture components on kinetics of thermochemical conversion was estimated providing complex on-line measurements of the flame temperature, produced heat and composition of the products at different stages of the mixture’s thermochemical conversion. The results of complex measurements reveal that selective microwave pre-treatment of mixture components can be used as a tool to provide control of ignition and burnout of mixtures and composition of the products. The most pronounced effect during thermochemical conversion of selectively activated mixtures was observed for the mixture of raw straw with additives of pre-treated wood pellets with mass fraction 30%, when the total amount of produced heat can be increased about 9%, produced heat energy per mass of burned mixture by more than 5%, the volume fraction of carbon-neutral CO2 emission in the products relative to that for raw straw pellets by 7% with decrease of the mass fraction of polluting NOx emissions in the products by 18% confirming cleaner sustainable heat energy production and improved heat production efficiency.