Question

natural gas containing 95 mole% methane (ch4) and 5 mole% ethane (c2h6) is burned completely with excess air. the product of the combustion contains 0.10 mole% co, 7.2 mole% co2, 15.6 mole% h2o, 72.7 mole% n2, 4.4 mole% o2. consider a batch combustion operation with 100 moles of natural gas as feed. a) write the balanced chemical reactions. b) draw a diagram of the combustion process labelling all streams with composition and moles. c) write the stoichiometric equations that should be used for the estimation of the theoretical air. d) explain how will the excess air change if 75% of the natural is burned. you can assume that the air consists of 21 mole % o2 and 79 mole % n2.

Answer 1

The question involves writing balanced chemical reactions for the complete combustion of methane and ethane, creating a diagram of the process, deriving stoichiometric equations for theoretical air estimation, and discussing how excess air requirements change with incomplete combustion.

Step-by-step explanation:

The given information describes the complete combustion of a natural gas mixture containing methane (CH4) and ethane (C2H6).

Part A: Balanced Chemical Reactions

The balanced chemical reactions for combustion of methane and ethane are as follows:

For methane (CH4):
CH4 + 2O2 → CO2 + 2H2O
For ethane (C2H6):
2C2H6 + 7O2 → 4CO2 + 6H2O

Part B: Diagram of Combustion Process

The diagram should show inflow of 95 moles of methane and 5 moles of ethane, and outflow of the various products with the specific mole percentages given.

Part C: Stoichiometric Equations

The stoichiometric equations will relate the moles of methane and ethane to the moles of oxygen needed for complete combustion.

Part D: Excess Air

If only 75% of the natural gas is burned, the requirement for excess air would decrease proportionately to the amount of fuel not combusted, as less oxygen is necessary for incomplete combustion.