Fast Pyrolysis Bio-Oils from Wood and Agricultural Residues

Abstract

Fast pyrolysis bio-oil (pyrolysis liquid) from plant residues is one alternative to replace fossil fuels and feedstocks. Fast pyrolysis liquid is a potential source of revenues for companies who have biomass residues at their disposal. Once produced, bio-oils may be shipped, stored, and utilized much like conventional liquid fuels once their specific fuel properties are taken into account. First encouraging large scale bio-oil utilization tests with published results were carried out in Stockholm in the 1990s in a heating boiler designed for heavy fuel oil. Industrial ovens are also potential users of bio-oil. Bio-oil would also be an interesting fuel for small scale distributed heat or power production. However, introducing a new fuel into the markets is not going to happen easily. Bio-oil is quite different from conventional liquid fuels, and many challenges remains to be overcome. A stepwise market introduction is proposed: bio-oil would first replace fuel oil in boilers, where its properties would not be prohibitive. Once the overall utilization chain has been proven, more demanding uses may be introduced. VTT has been developing an integrated concept, in which fast pyrolysis is integrated to a fluidized-bed boiler. The experimental work on fast pyrolysis has been focused in supporting this concept. In Scandinavia, forest residues are the most feasible feedstocks for pyrolysis. These residues contain extractive matter that yield a second liquid phase. This is both an opportunity (for recovering byproduct) and a challence (for using both phases as fuel). Agro-biomasses are more challenging feedstocks for energy use due to the high amount of alkali metals and nitrogen in the oil. In addition, they produce more water during pyrolysis, causing phase instability. In this paper, fast pyrolysis is discussed including experimental results from pyrolysis of wood and agricultural residues as well as results from a techno-economic evaluation.