Effects of Fuel Properties on Natural Downward Smoldering of Piled Biomass Powder: Experimental Investigation

Effects of fuel properties on natural downward smoldering of piled biomass powder: experimental investigation

Fang He, Zhenqiang Gao, Bin Luo, Zhihe Li, Weiming Yi

Shandong University of Technology, Zibo, Shandong, 255049 P.R. China

Abstract: In order to obtain data for modeling validation of one-dimensional smoldering and combustion of biomass, effects of fuel type, moisture content, and particle size on natural downward smoldering of biomass powder have been investigated experimentally. A cylindrical reactor (inner size Φ26 cm × 22 cm) was built and powders of corn stalk, pine trunk, pyrolysis char and activated char from corn stalk were prepared.

Fig. 1— Schematic of the experimental set-up for the natural downward smoldering

Smoldering characteristics of the four materials, different moisture contents (between 0% and 30%, wet basis, corn stalk powder) and different particle sizes (between 20 and 100 mesh, dry corn stalk powder) were examined. Results showed that: 1) The maximum temperature in the fuel bed is only slightly affected by fuel type and particle size. It increases gradually for original biomass and decreases slowly for chars with the development of the process. 2）Propagation velocity of the char oxidation front is dominated by carbon density and ash content. And it is almost not affected by moisture content and particle size. 3) There is always a drying front in the fuel bed during smoldering of hydrocarbons even if the original material is dry. Propagation velocity of the drying front is affected by moisture content significantly, decreases from more than 10 to 3 times of char oxidation velocity with the increase of moisture content from 0 to 20%. 4) Cracks inside the fuel bed of are dominated by fuel type and particle size.

Typical results:

Fig. 2 — Effects of the fuel type on the temperature of smoldering

Temperature histories of smoldering of the four fuels are presented in Fig. 2. Maximum temperatures from thermocouples are between 450 and 750 ℃, varies with their depths.

Fig. 3 — Effects of moisture content on propagation and mass loss rate of smoldering

The time it takes for the thermocouples to reach the given temperatures（101 ℃ for drying and the maximum for char oxidation) at moisture content between 0 and 30 % is presented in Fig. 3. It shows that the drying time increases significantly with the increasing moisture content. However, there is no obvious regularity between the char oxidation time and the moisture content.

Highlight:

1. Natural downward smoldering of four materials, different moisture contents, and different particle sizes were investigated.

2. Propagation velocity of the char oxidation front differs significantly from that of the drying front.

3. Carbon density and ash content of fuel dominate propagation velocity of the char oxidation front.

4. Fuel bed of finer material is apt to have bigger cracks.

Keywords: fuel type, moisture content, particle size, biomass, smoldering