Flue gas emitted from the stack of fired heaters are the main target for recovery of wasted heat. Energy engineers should calculate the amount of flue gas recoverable energy and decide whether to pursue investment projects. At this time, what energy engineers need is the flue gas enthalpy calculation library.
If know the composition of nitrogen, oxygen, argon, carbon dioxide, and water at atmospheric pressure and the discharge temperature, it is a simple procedure to calculate the enthalpy of each component in the mixed component state using the mixing rule.
Python code of flue gas enthalpy
The following Python code calculates the fluegas entalpy emitted at 500 degC with compositions of 70.0 mol% N2, 15.0 mole% O2, 5.0 mole% Ar, 5.0 mole% CO2, and 5.0 mole% H2O.
def fluegas(temp_given, temp_base, mol_n2, mol_o2, mol_arg, mol_co2, mol_h2o):
if temp_given < 0 or temp_base < 0 or temp_base > temp_given: return -1
coeff_a = [6.921525928892, 6.905598931009, 4.964694915254, 8.44682086499, 7.967187267909]
coeff_b = [0.000264324135, 0.00156659667, 0, 0.00575849121, 0.000876904142]
coeff_c = [0.000000433542006, -0.000000453431059, 0, -0.00000215927489, 0.000000575161121]
coeff_d = [-1.17644032E-10, 5.37208504E-11, 0, 3.05898491E-10, -1.47239368E-10]
mw = [28.0134, 31.9988, 39.948, 44.01, 18.0152]
wt = [0, 0, 0, 0, 0]
temp_given = temp_given * 1.8 + 32
temp_base = temp_base * 1.8 + 32
sum_mol = mol_n2 + mol_o2 + mol_arg + mol_co2 + mol_h2o
mol_n2 = mol_n2 / sum_mol
mol_o2 = mol_o2 / sum_mol
mol_arg = mol_arg / sum_mol
mol_co2 = mol_co2 / sum_mol
mol_h2o = mol_h2o / sum_mol
sum_mw = mw[0] * mol_n2 + mw[1] * mol_o2 + mw[2] * mol_arg + mw[3] * mol_co2 + mw[4] * mol_h2o
wt[0] = mw[0] * mol_n2 / sum_mw
wt[1] = mw[1] * mol_o2 / sum_mw
wt[2] = mw[2] * mol_arg / sum_mw
wt[3] = mw[3] * mol_co2 / sum_mw
wt[4] = mw[4] * mol_h2o / sum_mw
sum_h = 0
for comp in range(5):
each_ha = coeff_a[comp] * (temp_given - temp_base)
each_hb = coeff_b[comp] / 2 * (pow(temp_given, 2) - pow(temp_base, 2))
each_hc = coeff_c[comp] / 3 * (pow(temp_given, 3) - pow(temp_base, 3))
each_hd = coeff_d[comp] / 4 * (pow(temp_given, 4) - pow(temp_base, 4))
each_h = (each_ha + each_hb + each_hc + each_hd) / mw[comp] * wt[comp] * 0.556
sum_h = sum_h + each_h
return sum_h
enthalpy = fluegas(500,15,0.70, 0.15, 0.05, 0.05, 0.05)
print("flue gas enthalpy = ", enthalpy, "kcal/kg")
When run the code, you will receive the following results.
flue gas enthalpy = 121.0 kcal/kg
