Defining the Coal Particles

The Lagrangian Multiphase model is used to define the interaction between a discrete phase of solid coal particles and the continuous background phase of the fluid domain within the coal combustor.

Coal is defined as a multi-component coal particle consisting of the four components raw coal, char, ash, and water. The injected coal particles undergo several processes flowing through the combustor:

  • Evaporation of moisture content
  • Coal volatile formation
  • Oxidation of the remaining char

The evaporation of the moisture content of the coal particle is modeled by the coal moisture evaporation model. This model is based on a quasi-steady evaporation process where the driving force for evaporation is the departure from the vapor-liquid equilibrium using the Ranz-Marshall correlation. The Coal Devolatilization model determines the rate at which the coal volatile escapes from the coal particle and is released to the gas phase. In this tutorial, you use the half-order char oxidation model to calculate the char oxidation. With this model, char is oxidized through O 2 , H 2 O and C O 2 .

To define the coal particles:
  1. Within the Coal Combustion continuum, right-click the Models > Lagrangian Multiphase > Lagrangian Phases node and select New > Free-stream Phase.
  2. Rename the Lagrangian Phases > Phase 1 node to Coal.
  3. For the Coal phase, select the following models in order:
    Group Box Model
    Particle Type Material Particles
    Residence Time (selected automatically)
    Pressure Gradient Force (selected automatically)
    Spherical Particles (selected automatically)
    Material Multi-Component Coal
    Species (selected automatically)
    Equation of State Constant Density
    Mass Transfer Coal Combustion
    Two-Way Coupling (selected automatically)
    Energy (selected automatically)
    Coal Moisture Evaporation (selected automatically)
    Char Oxidation Half-Order Char Oxidation
    Raw Coal Devolatilization User-Defined Devolatilization
    Track Sampling Boundary Sampling
    Track File
    Optional Particle Forces Drag Force
    Optional Models Turbulent Dispersion
    Particle Radiation
    Parcel Depletion
  4. Click Close.
  5. To allow you to track particles at the outlet boundary, select the Coal > Models > Boundary Sampling node and set the following properties:
    Property Setting
    Scalars Click (Custom Editor) and select:
    • Particle > Mole Fraction > Particle Mole Fraction of Ash
    • Particle > Mole Fraction > Particle Mole Fraction of Char
    • Particle > Mole Fraction > Particle Mole Fraction of H2O
    • Particle > Mole Fraction > Particle Mole Fraction of RawCoal
    Boundaries OUTLET
  6. Expand the Half-Order Char Oxidation node, multi-select all [reaction] nodes and set the Temperature Exponent, Beta to 0.5.
  7. To prevent the tracking of very small ash particles and to reduce the calculation time, set the maximum mass fraction of ash that is tracked. Select the Coal > Models > Parcel Depletion node and set the following properties:
    Property Setting
    Depletion Criterion $ParticleMassFractionAsh>0.999
  8. To set the absorption and scattering efficiencies of the coal particles, edit the Coal > Models > Multi-Component Coal > Material Properties node and set the following properties:
    Node Property Setting
    Particle Absorption Efficiency > Constant Value 1.1
    Particle Scattering Efficiency > Constant Value 1.2
  9. Select the Coal > Models > Track File node and using (Custom Editor), select the following Scalars:
    • Particle > Particle Diameter
    • Particle > Mass Fraction > Particle Mass Fraction of Ash
    • Particle > Mass Fraction > Particle Mass Fraction of Char
    • Particle > Mass Fraction > Particle Mass Fraction of H2O
    • Particle > Mass Fraction > Particle Mass Fraction of RawCoal
    • Particle > Mole Fraction > Particle Mole Fraction of Ash
    • Particle > Mole Fraction > Particle Mole Fraction of Char
    • Particle > Mole Fraction > Particle Mole Fraction of H2O
    • Particle > Mole Fraction > Particle Mole Fraction of RawCoal
    • Particle > Particle Temperature
It is possible to estimate the kinetics of devolatilization by heating coal particles at a constant rate and monitoring the loss in mass. In this tutorial, the devolitilization rate is defined by a user-defined field function UserDevolatilizationRate that is a function of the particle temperature according to [991]:

  1. Select the Coal > Models > User-Defined Devolatilization node and set the following properties:
    Node Property Setting
    User-Defined Devolatilization Volatile Yield 0.6
    Volatile Vapor Component CoalVolatile
    User Devolatilization Rate Method Field Function
    Scalar Function UserDevolatilizationRate
  2. Save the simulation.