Biomass Gasification

Written by Prof. William Smith (University of Guelph) and Allan Leal (ETH Zurich) on Mar 31st, 2023

This tutorial demonstrates the use of Reaktoro for biomass gasification in which temperature and exit gas composition are calculated from given Fuel Ultimate Analysis and fuel-to-air ratios.

from reaktoro import *
from numpy import arange

db = NasaDatabase("nasa-cea")

# Inputs -----------------------------------------------------------------------------
massC              = 49.30  # g/mol
massH              = 5.5    # g/mol
massO              = 45.2   # g/mol
HHV                = 18.933 # kJ/g
Q                  = 0.05   # heat loss (%) with respect to HHV
fAirMin            = 0.70   # minimum value for fAir (fuel to air mass ratio)
fAirDelta          = 0.1    # step-size for fAir values
fAirNum            = 30     # number of steps for fAir
output_all_species = True   # if false, output only a few species
# ------------------------------------------------------------------------------------

fAirs = [fAirMin + i * fAirDelta for i in range(fAirNum)]

nC = massC / 12.011
nH = massH / 1.00797
nO = massO / 15.9994

h0CO2 = -393.522  # kJ/g
h0H2O = -285.83   # kJ/g

a = nH / nC
b = nO / nC

formula = ChemicalFormula(f"CH{a}O{b}")

Mfuel = formula.molarMass() * 1000  # from kg/mol to g/mol
Mair = 28.850334  # in g/mol

factor = Mfuel / Mair

HHVmol = HHV * Mfuel

h0fuel = HHVmol + h0CO2 + 0.5*h0H2O*a  # in J/mol
heatDuty = (1 - Q) * HHVmol + h0CO2 + 0.5*h0H2O*a  # in J/mol

stmodelparams = StandardThermoModelParamsConstant()
stmodelparams.G0 = 1.0e+3
stmodel = StandardThermoModelConstant(stmodelparams)

species = Species()
species = species.withName("Fuel")
species = species.withElements(formula.elements())
species = species.withAggregateState(AggregateState.CondensedPhase)
species = species.withStandardThermoModel(stmodel)

db.addSpecies(species)

gases = GaseousPhase(speciate("C H O N"))
condensedphases = CondensedPhases("Fuel H2O(l) C(gr)")

system = ChemicalSystem(db, condensedphases, gases)

specs = EquilibriumSpecs(system)
specs.pressure()
specs.enthalpy()

solver = EquilibriumSolver(specs)

temperatures = []

table = Table()

for fAir in fAirs:
    state = ChemicalState(system)
    state.temperature(25.0, "°C")
    state.pressure(1.0, "bar")
    state.set("Fuel", 1.0, "mol")
    state.set("O2", fAir * factor * 0.21, "mol")
    state.set("N2", fAir * factor * 0.79, "mol")

    props = ChemicalProps(state)
    conditions = EquilibriumConditions(specs)

    conditions.pressure(props.pressure())
    conditions.enthalpy(heatDuty, "kJ")

    conditions.setLowerBoundTemperature(298.15, "°C")
    conditions.setUpperBoundTemperature(3000.0, "°C")

    result = solver.solve(state, conditions)

    assert result.succeeded()

    table.column("Air:Fuel") << fAir
    table.column("Temperature") << state.temperature()
    table.column(f"n(Gases)") << state.props().phaseProps("GaseousPhase").amount()
    
    if output_all_species:
        for species in system.species():
            table.column(f"n({species.name()})") << state.speciesAmount(species.name())
    else:
        table.column("n(C(gr))")    << state.speciesAmount("C(gr)")
        table.column("n(CH4)")      << state.speciesAmount("CH4")
        table.column("n(CO)")       << state.speciesAmount("CO")
        table.column("n(CO2)")      << state.speciesAmount("CO2")
        table.column("n(H2)")       << state.speciesAmount("H2")
        table.column("n(H2O)")      << state.speciesAmount("H2O")
        table.column("n(N2)")       << state.speciesAmount("N2")

table.save("output.txt")

We now plot the calculated temperatures of the exit stream as a function of the fuel-to-air mass ratio.

from reaktplot import *

fig = Figure()
fig.xaxisTitle("Air:Fuel (mass ratio)")
fig.yaxisTitle("Temperature [K]")
fig.drawLineWithMarkers(fAirs, table["Temperature"], name="")
fig.height(1000)
fig.show()