4. A liquified petroleum gas (LPG) fuel mixture has concentration (mole%):
Propane
80%
n-Butane
20%
The LPG undergoes a combustion reaction and 30% of the propane is converted, while all of
the n-butane is converted. LPG enters the reactor at a flow rate of $n_{LPG}$ = 2.00 kmol/min at
25°C.
Excess air is fed in at 25°C and the O? molar flow rate out of the reactor is 4.2 kmol/min. The
unreacted propane is fully recovered at 25°C and used in another process. The other gases,
including all H?O, are sent into the atmosphere as stack gas at temperature T? (T?>100°C).
Assume complete combustion.
a) Draw a flowchart, write assumptions and perform a DOF.
b) What is the HHV for the LPG?
c) What is the % excess air fed?
d) What is the molar composition of the stack gas on a dry basis?
e) Find the temperature of the stack gas (T?). If you cannot fully solve, set up the
solution and show what you would do.
f) Assume that the temperature T? = 1350°C. Find the volumetric flow in m³/s of
stack gas, including H?O (Assume P? = P??? = 101.3kPa).
g) What is the flow rate is SCM/s?
h) (Bonus 3 pts) If pure LPG is initially stored at T = 20°C in a tank that has some
vapor head (vapor at top of tank), what is the pressure of the tank if the LPG
(liquid feed) composition is as given above?
