Mechanical and Transport Characteristics of Coal-Biomass Mixtures for Advanced IGCC Systems

Open Access
Author:
Chandra, Divya
Graduate Program:
Energy and Mineral Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
February 03, 2012
Committee Members:
  • Derek Elsworth, Thesis Advisor
Keywords:
  • Coal-Biomass mixtures
  • Gasifier
  • Integrated Gasification Combined Cycle (IGCC)
  • Grain Breakage
  • Permeability Evolution
Abstract:
Co-firing of coal-biomass is one effective means of reducing CO2 emissions as biomass is a carbon neutral supplementary fuel. Co-feeding of biomass is technically challenging and is an unaddressed issue. We explore the relationship between mechanical, transport and critical state characteristics of coal-biomass mixtures by evaluating mixture composition, stress, strength, rhelogy and permeability of coal-biomass mixtures. We report measurements of strength and permeability evolution for uniformly graded (passing #200 mesh) granular mixtures of coal-biomass in the proportions (a) 100% sub-bituminous coal, (b) 75%-25% sub-bituminous coal-biomass and (c) 100% biomass. We observe response at confining stresses in the range 5 and 25 MPa and at strain rates of ~10-4/s. The pure biomass is the most compliant and weakest of the three mixtures and the coal the stiffest and strongest. The samples stiffen with compaction as confining stress increases. Results show strain hardening for all sample mixtures resulting from grain breakage. Work hardening behavior is characterized using a CAP model. Permeability measurements are made assuming steady state conditions. In all samples, permeability reduces with an increase in axial strain and yields permeabilities in the range 10-14 to 10-16 m2 (10 to 0.1 mD). We define the evolution of permeability as a function of changes in both porosity and grain breakage. These measurements are important in characterizing feed characteristics of dry-fed coal-biomass mixtures to prevent gas-flow back and to maintain feed rates into pressurized gasifiers.