As part of this assignment you will need to consult text books to determine vari
ID: 1060064 • Letter: A
Question
As part of this assignment you will need to consult text books to determine various physical properties. In all cases you must dearly state the source from which you acquire the data. 100 mol of pure methane (CH_4) is burned in a furnace with 1000 mol of dry air. Some of the energy liberated by the combustion reaction is used to heat a process stream which flows through the furnace in tubes as shown below. An analysis of the waste gases shows that no methane is present in the waste stream. a) State and balance the reaction equation for the complete combustion of methane at 25 degree C and include state symbols. b) Determine the stoichiometric oxygen demand. c) Calculate the percentage excess of oxygen. d) Given the heat of formation data shown in table 1 (overleaf) calculate the heat of combustion of methane. e) Calculate the composition of the waste gases leaving the boiler. The fuel is now changed to Butane gas which is fed to the furnace at a rate of 1 mol min^-1 with 20% excess air. The combustion reaction goes to completion. The butane and air both enter the furnace at 25 degree C. The (wet) waste gas composition is given in table 1 below and the volumetric flowrate of the waste stream is found to be 0.896 m^3min^-1 at 0 degree C and 1 atm. f) If the furnace is well insulated and the temperature of the waste gas stream is measured to be 600 degree C, how much energy is being transferred to the process stream each minute.Explanation / Answer
a) Combustion of CH4 -
CH4 (g) + 2O2 (g) --> CO2 (g) + 2H2O (l)
b) Determine the stoichiometric O2 demand
1 mol CH4 reacted with 2 mol of O2
100 moles of CH4 reacted with 2 x 100 = 200 moles of O2
So stoichiometric O2 demand is 200 moles
c) Calculate the % excess of O2
Air is a mixture of gases - 78% nitrogen and 21% oxygen - with traces of water vapor, carbon dioxide, argon, and various other components.
In 100 mol of air 21 mol of o2
1000 mol of air ( 21 /100) x 1000 = 210 moles
Excess O2 = 210 moles – 200 moles = 10 moles
The % excess of O2 = (10/200) x 100 = 5%
d) Calculate heat of combustion of methane-
Enthalpy change for a given reaction is equal to (sum of standard enthalpies of formation of products)-(sum of standard enthalpies of formation of reactant )
Hf0 CH4= - 44.9 KJ/mol
Hf0 CO2 = -393.5 KJ/mol
Hf0 H2O = -286 KJ/mol
Enthalpy change for a given reaction is equal to (sum of standard enthalpies of formation of products)-(sum of standard enthalpies of formation of reactants)
So for the given reaction ---
[-393.5 + 2 X (-286)] - [-74.9 + 0]
= -965.5 + 74.9 = -890.6 KJ/mol
Heat of combustion of methane = -890.6 KJ/mol
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