Abstract
The condition of heat transfer to lignocellulosic biomass particles during thermal processing at high temperature (>400 °C) dramatically alters the yield and quality of renewable energy and fuels. In this work, crystalline cellulose particles were discovered to lift off heated surfaces by high speed photography similar to the Leidenfrost effect in hot, volatile liquids. Order of magnitude variation in heat transfer rates and cellulose particle lifetimes was observed as intermediate liquid cellulose droplets transitioned from low temperature wetting (500–600 °C) to fully de-wetted, skittering droplets on polished surfaces (>700 °C). Introduction of macroporosity to the heated surface was shown to completely inhibit the cellulose Leidenfrost effect, providing a tunable design parameter to control particle heat transfer rates in industrial biomass reactors.
Highlights
The condition of heat transfer to lignocellulosic biomass particles during thermal processing at high temperature (>400 °C) dramatically alters the yield and quality of renewable energy and fuels
A microcrystalline cellulose particle can be analogous to a boiling water droplet on a heated surface
When subjected to high temperatures (> 400 °C), long chain biopolymers such as cellulose decompose into smaller, more valuable products used for renewable fuels and chemicals
Summary
For cellulose impinging on a polished silicon surface, the solid particle transitions to a liquid droplet, after which the liquid droplet reacts to primarily form gases and vapors. At 500 °C and 600 °C, the particle area first increases, as the intermediate liquid cellulose spreads to wet the polished silicon surface This is followed by rapid decrease in area as the intermediate liquid reacts, evaporates and shrinks. At 775 °C, the heat transfer rate for the porous surfaces is higher than that observed for the polished surface These results indicate that particle liftoff from vapor generation is completely inhibited across this temperature range, which agrees with previous work that suggests that vapors and gases from an evaporating liquid droplet penetrate into surface features, such as channels and macropores, thereby suppressing the Leidenfrost effect[11,12,22,23,24,25,26]. Further research into cellulose liftoff will allow for precise design of structured surfaces for control of the reactive Leidenfrost phenomenon
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