Week 4 - Combustion Efficiency Calculation after Preheating

A recuperator is a heat exchanger which uses heat from the flue gases to preheat the inlet air which is used for combustion. Recuperator recovers around 80% of the heat, increase the combustion efficiency, increase in flame temperature and improves fuel efficiency.

• Effect of pre-heating on AFT

Quantity class method is used to create the mixture between methane and air . A is the instance for air and B for the methane. Preheating temperature varies from 298 to 600K

AFT is calculated for varying preheating temperature and plotted for the same.

CH4 + 2(O2 + 3.76N2) = CO2 + 2H2O + 7.52N2

No. of moles of Air = 9.52

Code:

import cantera as ct

import numpy as np

import matplotlib.pyplot as plt

gas = ct.Solution ('gri30.cti')

Air = ct.Quantity(gas)

Pre_Temp = np.linspace(298.15, 600,20)

Fuel = ct.Quantity(gas)

Fuel.TPX = 298.15, ct.one_atm, {'CH4':1564}

Fuel.moles = 1

for T in Pre_Temp:

Air.TPX = T, ct.one_atm, {'O2':0.21, 'N2':0.79}

Air.moles = 9.52

Mixture = Air + Fuel

Mixture.equilibrate('HP', 'auto')

print ('The AFT is ' + str(round(Mixture.T,4)) + 'K')

print (Mixture.T)

plt.plot(T,Mixture.T,'*',color = 'red')

plt.title('Effect of Preheating ')

plt.xlabel('preheating Temperature')

plt.ylabel('AFT')

plt.show()

Result:

Observation:

Preheating temperature increases the AFT as increasing inlet air temperature results in efficient combustion and less usage of fuel.

• Effect of pre-heating on Combustion Efficiency

Combustion efficiency is the measure of how the fuel is efficiently used in the combustion process.

For adiabatic process,

Q_out = m_reactants*h_reactants - m_products*h_products

Combustion efficiency, % = [Heat loss/(LHV*M_fuel)]*100

Code:

import cantera as ct

import numpy as np

import matplotlib.pyplot as plt

gas = ct.Solution ('gri30.cti')

Air = ct.Quantity(gas)

Pre_Temp = np.linspace(298.15, 600,20)

Fuel = ct.Quantity(gas)

Fuel.TPX = 298.15, ct.one_atm, {'CH4':1}

Fuel.moles = 1

LHV = 50*pow(10,6)

Products = ct.Quantity(gas)

Products.TPX = 1700, 101325, {'CO2': 0.094, 'H2O':0.189, 'N2':0.715}

Products.moles = 10.56

for T in Pre_Temp:

Air.TPX = T, ct.one_atm, {'O2':0.21, 'N2':0.79}

Air.moles = 9.52

Q_loss= ((Air.mass*Air.h)) + ((Fuel.mass)*Fuel.h-(Products.mass)*Products.h)

Q_supplied= Fuel.mass*LHV

Efficiency = (Q_loss/Q_supplied)

print (Fuel.mass, Air.mass, Q_loss, Q_supplied)

plt.plot(T, Efficiency, '*', color = 'red')

plt.title('Effect of Preheating on Efficiency')

plt.xlabel('preheating Temperature')

plt.ylabel('Efficiency')

plt.show()

Result:

Observation:

Preheating temperature increases efficiency as increasing inlet air temperature results in less usage of fuel, thus less energy is supplied to the process and combustion is more efficient.