Abstract

Fire is a naturally occurring element in many ecosystems which can have both positive and negative effects. However, in recent years the frequency of the fires and the area they affect has increased. The rapid spread of wildland fires coupled with the limited resources available to forest services to manage wildland fires highlights the urgency for accurate prediction of fire spread. Fire prediction models enable the fire management services to predict the spread of fire and prioritize firefighting efforts more effectively. Understanding reactions and mechanisms occurring during wildland fires improves the fire prediction models. During wildland fires, the biomass covering forest beds undergoes pyrolysis prior to combustion due to exposure to high temperatures. Pyrolysis is the thermal decomposition of biomass, which does not require oxygen. Volatiles generated during pyrolysis may react with oxygen and contribute to the fire spread. Detailed examination of the volatiles released during pyrolysis of the foliage provides valuable information which later can be used to improve fire prediction models. In this research, the pyrolysis behavior of plant species from three U.S. regions (southern California, northern Utah, and the southeastern U.S.) with frequent wildfires is studied. The temperature and heating rates were selected carefully, 725 °C and 180 °C/s respectively, to mimic those of wildfires. A flat flame burner was used to provide a high temperature and high heating rate zone for pyrolysis experiments. This setup was used for pyrolysis of plant samples from southern California, northern Utah, and co-pyrolysis of chamise and scrub oak. Tar was collected during pyrolysis and co-pyrolysis experiments and was analyzed by a gas chromatography mass spectrometry (GC/MS) system. To identify the high molecular weight compounds in tar from pyrolysis of Utah juniper and long leaf pine litter, the collected tar was analyzed by high performance liquid chromatography (HPLC). Gas analysis was achieved by gas chromatography thermal conductivity detector (GC/TCD). To investigate tar compounds in various flame heights, pine needles were used as fuel and samples were collected from three different regions inside the flame: near the base, the intermittent region and the plume region. These tar samples were later analyzed by GC/MS. The results from this research show that the slight disparities in the tar yield of plants from different U.S. regions (southeastern U.S., northern Utah, and southern California) is likely due to inherent chemical and physical differences between various plant species. Similar to tar, the differences in the yields of light gases from plant species is due to biomass type. Further analysis of tar from all plants showed that, with the exception of manzanita foliage and its twigs, aromatics are the major constituents of tar. This research showed that despite similarities in the chemical composition of tar from various species, it is necessary to collect and analyze tar from any specific biomass to have a better understanding of its composition. CO, CO2, CH4, and H2 were the major constituents of pyrolysis gases on a wt % basis. CO was the main component of the light gases succeeded by CO2, CH4, and H2 on a wt % basis. High heating value of tar and light gases released during pyrolysis of all plant species was estimated. The contribution of tar to the HHV of volatiles was 82 to 92% which shows the importance of tar identification to estimate the impact of pyrolysis of biomass prior to combustion of foliage. Co-pyrolysis of chamise and scrub oak did not result in any significant synergistic effects as the chemical composition of the two plant species are similar to each other.

Degree

PhD

College and Department

Ira A. Fulton College of Engineering; Chemical Engineering

Rights

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