Pilot-scale combustion of fast-pyrolysis bio-oil: ash deposition and gaseous emissions

Fast pyrolysis is a promising method to transform solid biomass into a liquid product called "bio-oil" with an energy density of four to five times greater than the feedstock. The process involves rapidly heating biomass to 450-600° C in the absence of air and condensing the vapor produced to give bio-oil. Typically, 50- 75% (weight) of the feedstock is converted into bio-oil that has a number of uses, for example energy production or bio-refinery feedstock. This study investigated the gaseous emissions and ash deposition characteristics resulting from bio-oil combustion in a pilot scale combustion test rig at Cranfield University. A feeding system with heated lines and heated/stirred reservoir was used to feed a spray nozzle in the combustion chamber. Ash deposit samples were collected from the resulting flue gas using three air-cooled probes that simulate heat exchanger tubes with surface temperatures of 500, 600, and 700°C. The deposits formed were analyzed using SEM/EDX and XRD techniques to assess the corrosion potential of the deposits. The results are compared to measured ash deposit compositions formed from biomass combustion. Thermodynamic modeling software was used to make predictions for the partitioning of a range of elements for bio-oil combustion and the results compared to the measured data.