High Pressure and Temperature Conversion of Lignin and Black Liquor to Liquid Fuels

Abstract

A project aiming to find a method for conversion of lignin or black liquor to liquid fuels has been initiated. The conversion is supposed to take place in a high pressure and temperature reactor at near supercritical water conditions. A pilot scale autoclave station, acquired for this purpose, has been evaluated considering the heat transfer in three different units; the storage tank, the preheater and the reactor. Experiments with water have been carried out at different pressures and temperatures near the supercritical region. The temperatures of the heaters and the corresponding heated units have been measured and the results have been evaluated with mathematical models for the heat transfer. Heat transfer coefficients have been calculated both theoretically and experimentally. A difference between the theoretical and experimental overall heat transfer coefficient was found for the preheater. This difference has been investigated and the most likely cause is a small passage of air in the preheater which reduces the heat transfer from the preheater material to the water pipe. The water experiments showed that the heaters can supply enough heat to reach water temperatures near the supercritical point. Pump trials with lignin slurry at different lignin concentrations have been conducted. Slurries at higher concentrations than 10 wt% lignin could not be pumped easily with the current pump components. At these higher concentrations, the pump valves were contaminated and the flow interrupted. The results will be used in further research within the project for obtaining liquid fuels from lignin or black liquor.