Experimental Study On The Influence Of Particle Size,Moisture Content And Mineral Content On The Spreading Rate Of Peat Smoldering

Forest fires include crown fire, surface fire and ground fire. Ground fire is in essence the smoldering combustion of peat or humus, and characterized by long-time burning, difficulty of extinguish and to be found, no flame or heavy smoke. It can transit to flaming combustion in appropriate circumstances, causing more threatening forest fire. In order to understand ground fire, it is necessary to study the smoldering mechanism of peat or humus.Comparing with humus, peat has more uniform composition and structure, and therefore this work uses peat as the experimental material. The smoldering process of peat is influenced by the moisture content, mineral content, particle size and other parameters. As a basic physical parameter of peat, particle size affects the bulk density, porosity and thermal parameters. The moisture and mineral contents vary with the degree of peat decomposition and the distance below the surface. These parameters vary great in nature and are easy to change in experiments, so this thesis has studied the influence of particle size, moisture content and mineral content on the spreading rate of peat smoldering experimentally. The used particle sizes are:<1mm,1-2mm,2-3mm,3-4mm,>4mm; moisture contents:4.05%,10.04%,23.02%,45.47%,65.72%,91.13%,100.02%.; mineral contents:12.03%,16.93%,25.56%,36.01%,48.81%,57.00%. The conclusions are:(1) Within a certain range of particle size, the smoldering spreading rate increases with the increase of particle size. However, over this range, the spreading rate decreases with particle size increase. In these experiments, the critical range of particle diameter is2-3mm. In these experiments the peak smoldering temperature ranges from510℃to710℃and the average peak temperature decreases with the increase of particle size. By analyzing the specific surface area and apparent density influence on the smoldering, explained the experimental results.(2) The spreading rate decreases with the increase of moisture content. In these experiments, the peak temperature ranges from570℃to720℃. And the critical moisture content for smoldering occurrence is100.02%. For lower moisture contents, the moisture content has great influence on the smoldering spreading rate; while for higher moisture contents, this influence is lower. Using the forward smoldering model by semi-quantitative to calculate the different water contents smoldering peat spread rate, explained the experimental results.(3) In these experiments, the spreading rate of water evaporation front decreases firstly, then increases and finally decreases with the increase of mineral content, while the spreading rate of pyrolysis and char oxidation fronts decrease with the increase of mineral content. The peak temperature ranges from430℃to710℃. The critical mineral content for smoldering occurrence of these experiments is57.00%. Using the forward smoldering model to calculate the different mineral contents smoldering peat spread rate, explained the experimental results.