Slow pyrolysis of pistachio-waste pellets: Combined phenomenological modeling with environmental, exergetic, and energetic analysis (3-E)

Abstract

Slow pyrolysis of a pellet of pistachio waste was studied using a macro-thermogravimetric analysis. Experiments were conducted at different heating rates (5, 10, and 15 K/min), measuring the evolution of mass weight loss and CO release. Based on a dimensionless number analysis, a numerical model was formulated, comprising heat and mass balances. A kinetic expression for the release of CO was proposed. Additionally, a 3-E (environmental, exergetic, and energetic) analysis for the processing of 20 kg/h of bio-waste (case study) was applied. Experimental results showed that biochar and gas yields decreased with an increase in the heating rate (43 to 36% and 28 to 24%, respectively), while the bio-oil yield increased (29 to 40%). The slow pyrolysis model presented a good agreement with experimental results of weight loss. Furthermore, a comparison with the contracting volume model showed that internal heat transport should control the global process. The proposed kinetic model for CO release showed a good fit to experimental data, where activation energy values were 29.88 (5 K/min), 17.44 (10 K/min), and 28.79 kJ/mol (15 K/min). Finally, from the 3-E analysis and the experimental results, it can be suggested that an increase in the heating rate resulted in a higher pyrolysis exergetic efficiency (70%). It is due to an increase in the bio-oil yield with high-energy content.