Possibility of using biomass as a microwave absorber for intensifying microwave pyrolysis of coal and polymer waste

Relevance. Desire to reduce energy sector negative impact on the environment by replacing fossil fuels with renewable and CO2-neutral biomass resources. Aim. To study the possibility of using biomass as a microwave absorber to intensify microwave pyrolysis of energy-intensive raw materials. Methods. Certified SS methods for determining the thermal characteristics and elemental composition of the organic and mineral parts of organic raw materials, the "transmission–reflection" method for measuring the imaginary (ε'') and real (ε') components of the complex permittivity, physical experiment, gas analysis. Results. It is shown that some biomass samples (wheat husk, sunflower husk, manure and cedar nut shells) effectively interact with microwave radiation, which leads to their short processing initiation times (from 72 to 94 s). This is ensured by high values ​​of the dielectric loss tangent (tg(α)>0.130), due to the composition of their organic part of the raw material, the degree of mineralization and its type, and the textural characteristics of the surface. These types of biomass can be considered as intensifying additives in microwave processing of materials with low absorption efficiency. For example, adding biomass to coal in amount of 10 to 20 wt % made it possible to reduce the microwave processing initiation time by 1.9–2.1 times, while the total process duration was reduced by 1.6–1.8 times. This contributed to a reduction in energy costs for processing by 3–21%. The greatest efficiency was achieved with the addition of 20% pine nut shells, while cattle manure demonstrated significantly lower efficiency. Joint microwave processing of biomass and polymer waste is possible, but this requires searching for optimal compositions of mixed compositions. It was shown that the presence of polymer waste in a mixture with biomass during melting prevents the occurrence of discharges between biomass particles in the microwave field. This limits the proportion of its content in the mixture. The use of biomass as a microwave absorber for intensifying the microwave pyrolysis of coal and polymer waste opens up new opportunities for the development of technologies for the thermal processing of organic waste under microwave heating conditions.