Numerical Modeling of Chemically Reacting Carbon Particles in Dense Particulate Media

• Author / Creator

  Sahu, Pankaj Kumar

• This work presents the numerical study of chemically reacting char particles in dense particulate media applied to fixed and fluidized beds. Our main goal was to approximate 3D fixed bed particles into 2D axisymmetric geometry using a representative element, which is found in Chapter 1. Dry air was made to pass at different Reynolds number of 10, 50 and 100 into a row of 10 spherical char particles(dp = 0.02 m). The inflow temperature was kept at 1000K. We incorporated six gaseous chemical species, O2;CO;CO2;H2;H2O and N2 in addition to solid carbon, taking into account 3 heterogeneous and 4 homogeneous semi-global reactions. The particles were assumed to be non-porous. A Pseudo Steady State approach using commercial CFD solver, ANSYS Fluent™14.0 was applied to solve the Navier Stokes equation for the flow field, coupled with energy and species conservation equations. Combustion and gasification were represented by varying composition of the inlet gas as, i) YO2=0.233 and YH2O=0.001 and ii) YO2=0.11 and YH2O=0.074, respectively. Comparisons of the temperature and mass fraction of CO2 on the particle surface as well as along the axis were made. The maximum difference in axial temperatures between the two cases was observed to be 8% for Re = 10. A 2.8% maximum difference in surface averaged temperature was observed for Re = 50. Effect of the P-1 radiation model has also been investigated. The 2D and 3D simulations are illustrated and analyzed to emphasize the validity of the 2D model. Chapter 2 provides the study of influence of heat transfer in solids, as well as combustion and gasification in 2D-channel bed. Investigations were made at different Reynolds number to analyze the temperature and mass fraction of CO2 along the axis. A maximum temperature difference of 3.6% was observed along the axis for Re = 100. Study was also performed to evaluate the carbon consumption rates, temperature and mass fraction of CO2 on the particle surface. The peak axial temperature of 2750 K was seen at Re = 100 during combustion, while gasification managed to increase the peak temperature to 1900 K. Additional parameters such as the Damkohler number and Lewis number were also investigated. Chapter 3 includes comparisons between fixed bed and fluidized bed conditions using new 2D approximation. Fluidized beds-like geometry have been depicted by introducing spacing between the particles. Two different arrangements were tried, with spacing:- d and 0.5d. This model was compared to the previous chapter and it was found that the temperature in fluidized beds tends to be higher by 15% compared to fixed beds.

• Subjects / Keywords

  • Combution
  • Gasification
  • Gasifiers
  • Fluidized Beds
  • CFD
  • Fixed Beds
  • Simulations

• Graduation date

  Spring 2015

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3KD1QT5H

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.