Experimental Analysis of Low-Temperature Bed Drying of Wooden Biomass Particles

Abstract

This report investigates the low-temperature bed drying of biomass particles for use in a gasification process. Experimental drying equipment capable of drying up to 0.25 m 3 of biomass batchwise was constructed. The experimental result indicates that the drying equipment and applied method are appropriate to evaluate different drying parameters and their influence on the drying course. Drying parameters such as air temperature, air velocity, bed height, and type of wood are studied regarding the drying rate, final moisture content in the material, and bed pressure drop. The constant-rate and falling-rate drying period are studied to obtain an energy efficient drying process. Measurements show that the drying zone (where the actual drying occurs) progresses irregularly through the bed.

Techno-economic evaluation of biomass drying in moving beds: The effect of drying kinetics on drying costs

“…11) show that the temperature greatly influences the drying time; the lower the temperature of the drying gas, the longer the drying time needed. A similar observation has been reported in [20] and [40] where drying rates of pine bark, and sawdust and woodchips in fixed bed were studied, respectively. Figures 11A-C show that the drying time decreases considerably when the inlet air temperature increases from 50 to 70 ⁰C.…”

“…Drying curves presented in [20] and [50] also show similar behaviour even though wood species have been different in these tests, willow chips in [50] and pine bark in [20]. Results in [40] show also that drying curves for woodchips behave in the same way as they do in our tests. However, drying times are approximately 3-22 % shorter for woodchips in our studies.…”

“…Several studies [21,[40][41][42][43][44] have investigated drying biomass in a belt dryers/ fixed bed where air is used as a drying gas. Holmberg et al [21] experimentally investigated bark drying in fixed beds.…”

“…Results indicated that the linear characteristic drying rate curve can be used for bark drying with good accuracy when the bed height is 150-250 mm and the inlet air temperature is below 100 °C. Bengtsson [40] experimentally analysed low-temperature (< 100 °C) bed drying of wooden biomass particles (woodchips and sawdust). The constant drying rate and falling drying rate drying periods were studied to obtain an energy efficient drying process.…”

“…It is one of the most versatile dryers capable of handling a wide range of products, for example, animal feed, nuts, and woody biomasses [12]. Belt dryers are used for several biomasses including woodchips, bark, forest residue and sawdust [40,74]. The structure of a belt dryer is quite simple and robust.…”