Comparative pyrolysis characteristics and kinetics of agricultural food grains by thermogravimetric analysis
Anene Oguaka, Natalia Flores Quiroz, Richard Walls
Abstract
Pyrolysis precedes the development of smouldering or flaming fires in storage and processing facilities. Understanding this process and determining the parameters that characterise it is essential for controlling fires. This study analysed the pyrolysis of African food grains that are important for food security but historically have received limited attention. Cowpeas, lentils, millet, soybeans, unshelled peanuts, flax, sunflowers, shelled peanuts, and sesame were subjected to thermogravimetry in a nitrogen atmosphere at heating rates of 5, 10, 20, and 40 °C/min from ambient to 600 oC. All grains were completely dehydrated at 170 oC and started decomposing at about 180 oC. The decomposition patterns varied with the relative proportion of hemicellulose, cellulose, protein and, particularly, lipids (oil content). Pyrolysis rates peaked at lower temperatures of about 300 oC for non-oil grains but at higher temperatures of 400 oC for oil grains. Friedman and Coats-Redfern methods were used to determine activation energies (130–355 kJ/mol), preexponential factors (8.1 × 107–1.0 × 1031 s-1) and the numerical values of the complex, multistep reaction models. Oil grains (or their powder) generally have lower activation energies, are thus more reactive than non-oil grains, and therefore constitute critical consideration for fire safety in processing facilities. The work is important for developing fire engineering solutions for food facilities based on quantitative fire behaviour data.