Permeability of Coal and Coal-Biomass Mixtures as Feedstocks To Reduce Net Carbon Emissions

Abstract

We describe measurements of permeability on coal-biomass mixtures, which are a potential feedstock to gasifiers to reduce net carbon emissions. Permeability is measured under anticipated dry feed stress conditions to determine the potential for fugitive gas emission from the gasifier into the feed hopper. Cylindrical samples of coal-biomass blends are housed within a triaxial apparatus capable of applying mean and deviatoric stresses and of concurrently measuring gas permeability. We measure the evolution of strain, porosity and permeability under mean stresses of 3.5, 7 and 14 MPa. Permeability is measured by pulse transmission testing using N 2 and He as the saturant and assuming the validity of Darcy's law. Porosity is measured by pressure pulse with He as saturant and assuming an ideal gas. Experiments are conducted on a range of coals and biomass blends at mixtures of 100 percent coal through 100 percent biomass. Measured permeabilities are in the range 10 -13 to 10 -16 m 2 with the 100 percent biomass blends showing lower permeabilities than the coal biomass and 100 percent coal blends. Permeabilities change in loading and unloading and exhibit hysteresis. We fit the data to connect permeability with porosity using relations for porous media where permeability changes proportionally to the cube of the change in porosity. This model performs adequately since there is little size reduction in the granular mass due to the applied isotropic loading.