Question

I'm stuck on this question. Please solution for this.

This question is from the Elementary Principles of Chemical Processes 4th edition question 9.65

9.65. Methane is burned completely with 40% excess air. The metha ne enters the combustion chamber at 25°C, the combustion air enters at 1500C, and the stack gas CO2, H20(v), O2, N2] exits at 450°C. The chamber functions as a preheater for an air stream flowing in a pipe through the chamber to a spray dryer. The air enters the chamber at 25Cat arate of 1.57x 10 m3 (STP)/h and is heated to 181°C. All of the heat generated by combustion is used to heat the combustion products and the air going to the spray dryer (i.e., the combustion chamber may be considered adiabatic) Stack gas 450°C COMBUSTION CHAMBER Air, 181°C To spray dry Air, 25°C 1.57x104 scMH CH Combustion Air 25%C 150°C (a) Draw and completely label the process flow diagram and perform a degree-ffreedom anal SIS. (kmol/h) and the volumetric flow rates (m h) of the two effluent streams. State all assumptions you make. (c) When the system goes on line for the first time,environmental monitoring of the stack gas reveals a considerable quantity of CO, suggesting a problem with either the design or the operation of the combustion chamber. What changes from your calculated values would you expect to see in the temperatures and volumetric flow rates of the effluent streams increase, decrease, cannot tell without doing the calculationsh?

Answer 1

Given data:

Methanol inlet temperature in combustor chamber = 25 deg C

Combuster air inlet temperature = 150 deg C

Air inlet temperature of combustor chamber = 25 deg C

Air flow rate = 1.57*10^4 m³/hr

a) Degrees of freedom analysis(DOF):

DOF = Number of unknowns - Number of species - Other equations

Then

Number of unknown = 4

Number of species = 1 and

Other equations = 0

Then DOF = 4-1 = 3

Degrees of freedom = 3

b) Molar flow rate of Methane

Assume methane flowrate in combustion chamber = 100 mol/sec

Molecular weight of methane = 16.04 g/mol

Density of methane at 25 deg C = 0.656 Kg/m³

Assume the methane pressure = 5 Kg/cm^2

Then

Q[L/s] = N[mol/s]*R[atmL/molK]*T[K]

Q=(100[Kg/s]*[1 Kmol/16.04Kg]*[10^3 mol/1 Kmol]*[0.082 atml/mol K]*[25+273K])/5 atm

=30.46 L/S