Combustion Efficiency Calculation after Preheating

Objective:

1.What is the effect of preheating on the adiabatic flame temperature?

1. Change pre-heating from 298 to 600K
2. Explain your results.

For this problem, Methane is considered as fuel and combusted with air.

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

Code for the problem is given below:

import cantera as ct
import matplotlib.pyplot as plt
import numpy as py

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


A=ct.Quantity(gas)
Tmin=298
Tmax=600
 

B=ct.Quantity(gas)
B.TPX=298.15,ct.one_atm,\'CH4:1\'
B.moles=1


for T_preheating in range (Tmin, Tmax):
	A.TPX=T_preheating,ct.one_atm,\'O2:0.21, N2:0.79\'

	A.moles=2*3.76/0.79

	M=A+B

	M.equilibrate(\'HP\',\'auto\')
	
	plt.plot(T_preheating,M.T,\'+\',color=\'red\')

plt.xlabel(\'Preheating Temperature in K\')
plt.ylabel(\'Adiabatic Temperature in K\')	
plt.title(\'Effect of Preheating Air Temperature On AFT\')
plt.grid()
plt.show()

Result:

Conclusion:

1.From the graph it can be seen that adiabatic Flame varies linearly with the preheating Temperature.

2.This means as Preheating temperature increases adiabatic Flame Temperature also increases.

3.Preheating also saves Consumption of fuel.

2.Does preheating help with fuel saving? If yes, how does combustion efficiency go up as a function of pre-heating temperature? Assume that the furnace exit temperature is 1700K (For this case assume that the combustion products are CO2, H20, and N2).

1. Write the formula for combustion efficiency
2. Plot the effect of pre-heat temeprature on combustion efficiency
3. Is it right or wrong to assume a fixed furnace exit temperature? Explain your answer.

Combustion efficiency is a measure of how much available heat is generated from the process.

ncombustion=(Available Heat/Maximum heat generated)

ncombustion=Q/(mf x LHV)

Q=Heat available.

mf=mass of fuel.

LHV=Lower Heating Value.

Stoichometric Equation:

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

Mole Fraction of CH4=1/(1+2+7.52)=0.095

Mole Fraction of N2=7.52/(1+2+7.52)=0.71

Mole fraction of O2=2/(1+2+7.52)=0.189

Total no of moles at product side=10.56.

Python Code For the above problem is given below:

import cantera as ct
import matplotlib.pyplot as plt
gas=ct.Solution(\'gri30.cti\')

fuel=ct.Quantity(gas)
fuel.TPX=298.15,ct.one_atm,\'CH4:1\'
fuel.moles=1
fuel_mass=fuel.mass
H_fuel=fuel.h


products=ct.Quantity(gas)
products.TPX=1700,ct.one_atm,{\'CO2\':0.095,\'H2O\':0.1901,\'N2\':0.7148}
products.moles=10.52
mass_products=products.mass
H_products=products.h
LHV = 50e6 #J/KG.

air = ct.Quantity(gas)
air.TPX = 298.15,ct.one_atm,{\'O2\':0.21,\'N2\':0.79}
air.moles = 9.52
mass_air = air.mass
H_air = air.h


for T in range (298,600,5):
	air = ct.Quantity(gas)
	air.TPX = T,ct.one_atm,{\'O2\':0.21,\'N2\':0.79}
	air.moles = 9.52
	mass_air = air.mass
	H_air = air.h

	Q = (fuel_mass*H_fuel+mass_air*H_air-(mass_products*H_products))
	
	n_eff = (Q/((fuel_mass)*(LHV)))*100


	plt.plot(T,n_eff,\'+\',color=\'red\')



plt.grid()
plt.ylabel(\'Combustion Efficiency\')
plt.xlabel(\'Preheating Temperature\')
plt.show()

Results:

Percentage saving of Fuel:

import cantera as ct
import matplotlib.pyplot as plt
gas=ct.Solution(\'gri30.cti\')

fuel=ct.Quantity(gas)
fuel.TPX=298.15,ct.one_atm,\'CH4:1\'
fuel.moles=1
fuel_mass=fuel.mass
H_fuel=fuel.h


products=ct.Quantity(gas)
products.TPX=1700,ct.one_atm,{\'CO2\':0.095,\'H2O\':0.1901,\'N2\':0.7148}
products.moles=10.52
mass_products=products.mass
H_products=products.h
LHV = 50e6 #J/KG.

air = ct.Quantity(gas)
air.TPX = 298.15,ct.one_atm,{\'O2\':0.21,\'N2\':0.79}
air.moles = 9.52
mass_air = air.mass
H_air = air.h

Q = (fuel_mass*H_fuel+mass_air*H_air-(mass_products*H_products))
efficiency_stp=(Q/((fuel_mass)*(LHV)))*100

for T in range (298,600,5):
	air = ct.Quantity(gas)
	air.TPX = T,ct.one_atm,{\'O2\':0.21,\'N2\':0.79}
	air.moles = 9.52
	mass_air = air.mass
	H_air = air.h

	Q = (fuel_mass*H_fuel+mass_air*H_air-(mass_products*H_products))
	
	n_eff = (Q/((fuel_mass)*(LHV)))*100


	plt.plot(T,n_eff,\'+\',color=\'red\')

	saving=((n_eff/efficiency_stp)-1)*100

	plt.plot(T,saving,\'+\',color=\'blue\')

plt.grid()
plt.ylabel(\'Efficiency\')
plt.xlabel(\'Preheating Temperature\')
plt.legend([\'Combustion Efficiency\',\'Percentage Saving\'])
plt.show()

Results:

Conclusion:

1.Efficiency increases with increase in Preheating Temperature.

2.As Inlet temperature gets Preheated, it reduces the work of furnace to heat the air and hence fuel is saved.

3.As rate of Combustion increases with increase in preheating temperature, Combustion Efficeincy Increases.

4.Preheating Temperature depends on the product of the combustion, as the cycle proceeds which leads to damage of recuperator.Hence it is necessary to maintain outlet temperature of recuperator as fixed value.