Performance Analysis of a Torrefaction System with Carbonaceous Feedstock

Abstract

Indian timber market and agriculture fields are growing rapidly. According to the 2021 ITTO (International Tropical Timber Organization) report, the Indian industry has processed around 50 million m3 in 2020. Along this line, the timber industry is a major source of sawdust and it is generated in large quantities during wood processing. Sawdust is derived from a waste product of woodworking operations such as sawing, sanding, planning, and routing. It is composed of small chipping of wood. It has a great potential to be used as an alternate source of energy by employing thermochemical conversion techniques. Similarly, India is one of the largest exporters of mango in the world. Waste mango cells are generated in a huge quantity which is one of the potential sources to harvest energy. Pyrolysis is one of the suitable techniques to generate biochar, pyro-oil, and syngas from such wastes. Experiments were conducted on a batch-type vacuum pyrolysis reactor with two condenser bottle arrangements. In the first part of the experiments, sawdust was pyrolyzed at five temperatures (300°C, 350°C, 400°C, 450°C, and 500°C) with a constant heating rate of 10°C. The results indicated that with an increase in process temperature from 300°C to 500°C, biochar percentage decreases whereas syngas and bio-oil percentage increase. At higher temperature pyrolysis, energy yield in the products is higher as compared to lower temperature pyrolysis. Biochar was characterized with SEM, FTIR. The result indicated an increase in process temperature (300°C to 500°C) led to decrease the biochar yield, whereas bio-oil yield increased (27.66% - 40.00%), while heating value (22.57 MJ/kg - 25.68 MJ/kg), and carbon (43.77- 75.57%) increased. The yield of biochar declined, and the yield of bio-oil and pyrolysis gas increased with the process temperature. The energy efficiency (83.44-87.32%) and exergy efficiency (74.24- 87.45%) of the pyrolysis system increased with process temperature, and the thermodynamic analysis optimization was achieved at 500°C. According to Fourier transform infrared (FTIR) Analysis Biochar at 400°C, 450°C, and 500°C produces less smoke than biochar at 300°C and 350°C. In Biochar Analysis, there were no aromatic components (benzene, phenol, etc.) or nitrogen components present at the pick point. Additionally, as the temperature increased, the porosity of the biochar increased. Scanning Electron Microscopy (SEM) analysis showed that feedstock has an integrated structure compared to biochar; more pores were generated, and the size became smaller when the temperature increased. In the second part of the experiments, Mango waste was pyrolyzed at interaction effects of process parameters (temperature(A), heating rate(B), and residence time(C)) on the fuel properties (char yield, higher heating value, energy yield, and fuel ratio) were modeled and the optimal condition for enhanced fuel properties ware determined using response surface methodology by employing the central composite design matrix. A model equation was generated using the data obtained and the significance of the model was investigated using analysis of variance to determine if the fit of multiple regressions was significant. The result indicated to optimize the effects of process parameters on the fuel properties. At the optimum conditions (A=402°C, B=12°C/min, C= 82 min), the char yield, higher heating value, energy yield, and fuel ratio has been found to be 35.57%, 25.81MJ/kg, 47.29% and 3.49, suggesting that biochar is a potential solid fuel in power generationand an effective means to reduce greenhouse gas emissions.