Mechanical performance and thermal behavior assessment of de-oiled microalgae-blended coal composites using statistical and ANN modeling

Abstract

Towards blended solid fuel processing technologies, the present study is first attempt to utilize de-oiled microalgae, Chlorella pyrenoidosa NCIM2738, as a binder to densify low-rank coal waste to formulate upgraded biomass-blended coal composites. The de-oiled biomass has shown similar gross calorific value (18.62 MJ/kg), sulfur content (1.45%), and low ash content (18%) in comparison to coal. Fuel characteristics of biomass-blended coal composites of 20:80 ratio showed gross calorific value (19.0 MJ/kg), fuel ratio (1.85), and low sulfur content (< 1%). The multi-objective optimization strategy is used to optimize the molding pressure, average particle size, and binder ratio for maximization of the mechanical performance indicators such as compressive strength and drop strength of biomass-blended coal composites. The maximum compressive strength and drop strength of blended composites at multi-objective optimized conditions after model validation (R2 > 0.99) are observed to be 14.6 MPa and 97.8%, respectively. Fourier transform infrared analysis is used to evaluate structural variation during coal-microalgae interaction. Thermogravimetric analysis, derivative thermogravimetric, and differential thermal analysis (TGA-DTG-DTA) are conducted to determine characteristic temperature points and heat involvement during combustion. TGA-DTG-DTA showed remarkable shifting of ignition point from 335 °C (parent coal) to 301–299 °C (blended coal composites), extended burnout temperature (47–82 °C higher than parent coal), and excessive exothermic heat involvement (3305–3363 μVs/mg) during composite combustion. Levenberg-Marquardt algorithm–based artificial neural network model was applied to validate the thermal analysis of coal, microalgae, and blended composites, which offers an excellent tool for studying thermochemical conversions. An in-depth investigation of mechanical-thermal aspect of the coal-biomass energy system will provide new possibilities to select microalgae as binder with optimized binder ratios which can apply in coal-based power plants as sustainable and affordable fuels. Graphical abstract: (Figure presented.). © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2023.