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ABSTRACT
To utilize various types of biomass as raw materials for briquette fuel, the influence of raw material on combustion behavior should be clarified. This study aimed to confirm the influence of biomass raw materials on flaming and char combustion, particularly on the duration of combustion. Cypress, bamboo, rice husk, and paper were used as raw materials for the briquettes. Several sizes of briquettes were burned in a hot airflow setup, and the mass loss (for individual samples) and the durations of flaming and char combustion were obtained. It was found that the duration of flaming combustion for each raw material is proportional to the product of the inverse square of the specific surface area and briquette density. It is suggested that these proportional constants are correlated with the mass percentage of holocellulose in the biomass, which is estimated via ultimate analysis. However, the duration of char combustion for each biomass raw material is almost proportional to the product of the inverse square of the specific surface area and the fixed carbon content of the briquette. It is suggested that these proportional constants are correlated with the mass percentage of ash content in the biomass. Thus, in our study, we were able to predict the combustion characteristics of briquettes made from various raw materials individually.
Nomenclature
| C | = | carbon ratio in the biomass sample (wt%) |
| Ccel | = | carbon ratio in cellulose (wt%) |
| Clig | = | carbon ratio in lignin (wt%) |
| Cc | = | proportional constant of the char combustion duration and ρfc(V/S)2 (m□s□kg−1) |
| Cf | = | proportional constant of the flaming combustion duration and ρ(V/S)2 (m□s□kg−1) |
| D | = | oxygen diffusion coefficient (m2□s−1) |
| Fo | = | Fourier number |
| H | = | hydrogen ration in the biomass sample (wt%) |
| Hcel | = | hydrogen ratio in cellulose (wt%) |
| Hlig | = | hydrogen ratio in lignin (wt%) |
| L | = | representative dimension (m) |
| m’ | = | oxygen supply rate (kg□s−1) |
| S | = | briquette surface area (m2) |
| t | = | time (s) |
| tc | = | char combustion duration (s) |
| tf | = | flaming combustion duration (s) |
| V | = | briquette volume (m3) |
| X | = | lignin ratio in the biomass sample |
| αs | = | thermal diffusivity (m2□s−1) |
| ρ | = | briquette density (kg□m−3) |
| ρfc | = | the fixed carbon content of the briquette (kg□m−3) |
| Δx | = | characteristic length (m) |
| Δρ | = | difference in oxygen density between ambient air and reaction zone (kg□m−3) |