Chapter 9, Problem 9.65P

Methane is burned completely with 40% excess air. The methane enters the combustion chamber at 25°C, the combustion air enters at 150°C. and the stack gas [CO₂, H₂O(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 25°C at a rate of 1.57 × 10⁴m³(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).

1. Draw and completely label the process flow' diagram and perform a degree-of-freedom analysis.

Calculate the required molar flow rates of methane and combustion air (kmol/h) and the volumetric flow rates (m³/h) of the two effluent streams. State all assumptions you make.

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 calculations]?