Multi-environment PDF modeling for non-catalytic partial oxidation process under MILD oxy- combustion condition

摘要

The multi-environment probability density function approach has been applied to numerically investigate the Moderate or Intense Low-Oxygen (MILD) oxy-combustion processes encountered in the non-catalytic partial oxidation (PDX) gasifier. The multi-environment PDF approach has the form of a conventional Eulerian scheme and retains the desirable property of a particle-based method. Micro-mixing is represented via the IEM model, and the detailed chemistry is based on GRI 3.0 mechanism without NOx chemistry. In terms of the mean temperature, the present multi-environment PDF approach yields the overall agreement with the measurements in the highly fuel-rich MILD oxy-combustion situation with the strong flue gas recirculation even if there exist the certain discrepancies in the upstream region. Special emphasis is given to the effects of the fuel/oxygen injection velocity and O-2/CH4 ratio on the characteristics of the strongly recirculated MILD oxy-combustion processes. Depending on injection velocity or O-2/CH4 ratio, the present MEPDF approach well reproduces the qualitative flame transition characteristics from MILD combustion to conventional combustion. The higher fuel/oxygen injection velocity leads to the much longer jet penetration and the much higher SDR level which makes the ignition to occur at further downstream region. The relatively lower O-2/CH4 ratios maintain the basic characteristics of the MILD combustion while the highest O-2/CH4 ratio locally creates the oxy-flame like structure rather than the non-visible flame field. Based on numerical results, the detailed discussions are made for flame stabilization, auto-ignition process and precise flame structure in terms of recirculation rate, distribution of turbulent DamkOhler number, scalar dissipation rate, mean temperature and mole fraction of CH2O and OH. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.