A fuel consisting of 75 mol-% methane and 25 mol-% ethane enters a furnace with 80 % excess ai

step 1 How much heat is lost and how much heat is transferred in this problem? We know that the change

A fuel consisting of 75 mol-% methane and 25 mol-% ethane...

A fuel consisting of $75 \mathrm{~mol}-\%$ methane and $25 \mathrm{~mol}-\%$ ethane enters a furnace with $80 \%$ excess air at $303.15 \mathrm{~K}\left(30^{\circ} \mathrm{C}\right)$. If $800 \mathrm{GJ}$ per $\mathrm{kmol}$ of fuel is transferred as heat to boiler tubes, at what temperature does the flue gas leave the furnace? Assume complete combustion of the fuel.

Key Concepts

Combustion Stoichiometry

This concept involves understanding the chemical reactions in which a fuel reacts with an oxidizer (typically oxygen in air) to produce combustion products such as carbon dioxide and water. It requires balancing the chemical equation to ensure mass conservation, determining the amounts of reactants needed for complete combustion, and calculating the byproducts generated. This fundamental idea serves as the basis for understanding energy production and reaction efficiency in combustion systems.

Excess Air

Excess air refers to the amount of air supplied above the stoichiometric requirement needed for complete combustion. It is used to ensure that all the fuel is burned, but it also affects the composition and temperature of the combustion products. When air is provided in excess, more nitrogen and some unused oxygen are present in the flue gases, which influences the overall heat transfer and the thermal characteristics of the combustion process.

Energy Balance in Combustion

This concept deals with applying the principles of energy conservation to a combustion process. It involves the calculation of how much of the heat released by fuel combustion is transferred to the surroundings (such as boiler tubes) and how much remains in the system, raising the temperature of the products. A proper energy balance considers both the heat released by the fuel and the sensible heat absorbed by the combustion products, which is crucial for determining exit flue gas temperatures.

Specific Heat Capacity

Specific heat capacity is a material property that indicates the amount of energy required to raise the temperature of a unit mass of a substance by one degree. In combustion and heat transfer problems, knowing the specific heat capacity of the flue gas is essential for calculating how much the temperature will increase for a given amount of transferred heat. This concept links the energy absorbed during combustion to the resulting changes in temperature, making it central to thermal analysis in combustion systems.

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