Enhanced performance of gasification by blending coal into biomass in a fluidized bed two-stage system

Abstract

Biomass, blended with a small amount of coal, was fed into a fluidized bed two-stage gasifier to produce low-tar H₂-rich gas through O₂-rich gasification. The blended coal improved the energy density of biomass fuel and also worked as the bed material. For the fluidized bed two-stage gasification, large char particles of biomass and coal tend to accumulate at the bottom of the gasifier (a riser) to form a carbon-rich reaction zone there. Then, the O₂ coming from the bottom of the gasifier mainly reacts with such char, consequently suppressing its interaction with the gases including H₂ from pyrolyzer. Using O₂-rich air with an ER of 0.35 and at gasification temperatures of about 890 °C, gasifying biomass blending 10 wt% coal produced gas containing 13.3 vol% CO, 20.1 vol% CO₂, 4.3 vol% CH₄, and 9.8 vol% H₂, giving an LHV of 4.9 MJ/Nm³_d. Tar content in the produced gas gradually decreased with time, and over the last 6 h the measured content was 0.012 g/Nm³_d. Steady operation was well achieved, showing the performance without ash agglomeration for the O₂-rich gasification of biomass.