APPLICATIO STUDY ON KINETICS OF BIOMASS PYROLYSIS IN THE FIXED BED. 1. SIMULATION AND NUMERICAL ANALYSIS OF LIGNIN THERMAL DECOMPOSITION

Abstract

A non-stationary model of the biomass thermolysis process was built based on three primary independent parallel reactions of the biomass active part conversion into gas, liquid phase and char, taking into account the secondary reactions of tar decomposition into char and light gas. It is shown that the main role in the production of mixed pyrolysis gas (primary gas and light gas) is played by the light gas generation rate due to the secondary reaction of tar decomposition into light gas. This reaction rate significantly exceeds the primary gas production rate due to the fact that the activation energy of the primary gas formation reaction lignin → gas is higher than the activation energy of the lignin → tar reactions. It was found that the rate of generation of the primary reaction lignin → char significantly outweighs the rate of tar → char production, so the latter reaction can be neglected. It is shown that as the temperature of lignin pellets increases, CO and light hydrocarbon C1.16H4 increase and carbon dioxide CO2 and H2О decrease. The consumption of volatile components in the pyrolyzer depends on the temperature distribution of biomass pellets across the pyrolyzer cross-section, which decreases towards the center of the retort, following the consumption of gaseous components decreases as they approach the axis of the pyrolyzer. The amount of mixed pyrolysis gas released and char depends on the radial coordinate r. At r = 0.047 m and time τ = 380 s, the amount of mixed pyrolysis gas is 90 % and char is 10 %, at r = 0.016 m and τ = 380 s = 83 % and = 17 %. Bibl. 13, Fig. 7.