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 differentoxygen exposure conditions, it turns into reactive chars that carry fire risk. However, there is littleexperimental data to explain the reactivity of preheated wood chars that are prone to self-ignition. Thispaper investigated the reactivity of anaerobic and aerobic wood chars created at low heat treatmenttemperatures (HTT) at 140°C, 150°C, 160°C and 175°C for extended durations ranging from 12 days to152 days. Special care has been taken to prepare anaerobic wood chars by flushing vacuum oven withnitrogen when cooling down the chars to room temperature at the end of heating process. Aerobic charswere created in a carbolite oven with access to atmospheric air. Thermogravimetric analysis (TGA) andFourier Transform Infrared spectroscopy (FTIR) were employed to determine the chemisorption andreactivity of these chars.TGA experiments were carried out at low chemisorption temperatures (CST) below 70oC beforegasification set in. Using Elovich equation, rate of oxygen uptake and activation energies were calculatedto describe the types of reactive sites present in low-temperature preheated wood chars, which possessaltogether a different chemisorption mechanism from coal chars. FTIR was performed to provide aninsight to the changes in functional groups for the bulk-scale chemisorption behavior of preheated woodchars 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, theyare prone to self ignition. Vacuum-preheated wood chars possess higher intrinsic reactivity towardsoxygen in comparison with air-preheated wood chars signifying by higher initial rate of chemisorption.