Kinetics of the Drying Process of Composite Biopellets on a Convective Drying Bench

Abstract

In Ukraine, there is a problem of overflowing sediment maps, to which activated sludge, which eventually turns into sludge deposits, is constantly added. The accumulated sludge deposits are outdated, have lost most of their nutrients, became too mineralized and are practically unsuitable for direct biofuel production. The elimination of accumulated sediments is necessary for the efficient and uninterrupted operation of treatment plants, as well as for land reclamation. However, due to the energy crisis around the world, it is possible to use them with the creation of fuels based on obsolete sludge, peat and biomass to solve this problem. Therefore, it is important to develop a technology for processing obsolete sludge into fuel pellets that can be used as fuel for, as an example, mini-CHPPs that simultaneously produce heat and electricity. Since obsolete sludge deposits have a low content of organic matter, it is proposed to create composite pellets for their better utilization, followed by their drying and combustion, in which the resulting ash will be used to make building materials. Therefore, the aim of the study was to investigate the drying processes of composite pellets on a convective plant and generalize them with a theoretical calculation. The drying processes of composite pellets based on obsolete sludge deposits, peat and biomass and identifies effective drying modes are studied in the paper. As a result, the influence of the coolant temperature on the drying time of the sludge-peat composition was determined, which shows that an increase in temperature reduces the drying time of the pellets by 1.4 times. Comparison of the drying kinetics of two- and three-component pellets at 80 °C and 120 °C indicates that the drying time of three-component pellets is by 1.1 to 1.4 times shorter than that of two-component pellets. Increasing the temperature of the coolant reduces the drying time of three-component pellets by about 1.5 times. Theoretical studies with the construction of generalized drying curves for composite pellets calculated by the method of V. V. Krasnikov showed a coincidence with experimental data. The relative and kinetic drying coefficients were calculated from the generalized drying curves and the drying speed, and the formulas for the drying time of two- and three-component pellets were obtained.