Logistical related costs and inferior fuel performance prevent the attractive commercialization of lignocellulosic biomass conversion into biofuels. Wet torrefaction, or hydrothermal carbonization, is a pretreatment process to help converting diverse feedstocks into a homogeneous energy-denser solid fuel. The pre-treatment product has more favorable properties such as higher atomic carbon content, lower volatiles, less friability and higher hydrophobicity. Wet torrefaction is an interesting route to reduce the cost associated with lignocellulosic biomass use and conversion by improving fuel performance.
In this work, we present a kinetic study of wet torrefaction of lignocellulosic biomass. A mini-reactor was built to perform wet torrefaction of a small amount of lignocellulosic biomass at isothermal conditions. The key to obtain accurate experimental data for kinetic modeling is to heat and cool the reactor in a very short period of time. Even with a radiant heater, it usually takes 10-20 min to heat the reactor up to the temperature range of 200 – 260 °C. To solve this challenge, special reactor design was carried out by using a two-chamber reactor. The lower chamber (inside the radiant heater) is loaded with water. The upper chamber (outside the radiant heater) is connected with lower chamber with a ball valve, and loaded with biomass. When the temperature of the lower chamber reaches the desired conditions, the ball valve is opened and the biomass capsule (~0.2 g loblolly pine wrapped by stainless steel mesh) drops into lower chamber. Then the ball valve is closed and chemical reaction starts immediately. After wet torrefaction, the mini-reactor is cooled quickly by immersing into the ice-water bath. The conversion of biomass in wet torrefaction can be achieved at various reaction temperatures and reaction times. By performing the kinetic modeling, the wet torrefaction of lignocellulosic biomass is apparently first order reaction and depends significantly on temperature.
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