PROPENSITY OF LOW-TEMPERATURE AND ANAEROBIC AND AEROBIC-CREATED WOOD CHARS TO SELF-IGNITION

摘要

Cases have shown that when wood is exposed to a long-term low temperature heat source with different oxygen exposure conditions, it turns into reactive chars that carry fire risk. However, there is little experimental data to explain the reactivity of preheated wood chars that are prone to self-ignition. This paper investigated the reactivity of anaerobic and aerobic wood chars created at low heat treatment temperatures (HTT) at 140°C, 150°C, 160°C and 175°C for extended durations ranging from 12 days to 152 days. Special care has been taken to prepare anaerobic wood chars by flushing vacuum oven with nitrogen when cooling down the chars to room temperature at the end of heating process. Aerobic chars were created in a carbolite oven with access to atmospheric air. Thermogravimetric analysis (TGA) and Fourier Transform Infrared spectroscopy (FTIR) were employed to determine the chemisorption and reactivity of these chars. TGA experiments were carried out at low chemisorption temperatures (CST) below 70oC before gasification set in. Using Elovich equation, rate of oxygen uptake and activation energies were calculated to describe the types of reactive sites present in low-temperature preheated wood chars, which possess altogether a different chemisorption mechanism from coal chars. FTIR was performed to provide an insight to the changes in functional groups for the bulk-scale chemisorption behavior of preheated wood chars exposed to air. Results of this study suggest that chars created at low temperature for long duration (175°C for 26 days) in both aerobic and anaerobic conditions are susceptible to chemisorption, thus, they are prone to self ignition. Vacuum-preheated wood chars possess higher intrinsic reactivity towards oxygen in comparison with air-preheated wood chars signifying by higher initial rate of chemisorption.