A coal from Utah which has an ultimate analysis (by mass) of...

A coal from Utah which has an ultimate analysis (by mass) of 61.40 percent $\mathrm{C}, 5.79$ percent $\mathrm{H}_{2}, 25.31$ percent $\mathrm{O}_{2}, 1.09$ percent $\mathrm{N}_{2}, 1.41$ percent $\mathrm{S},$ and 5.00 percent ash (noncombustibles) is burned with 20 percent excess air in an atmospheric pressure boiler. Calculate the mass of water in the products per unit mass of coal burned, and the dew-point temperature of the water vapor in the products.

Key Concepts

Ultimate Analysis

This concept involves determining the elemental composition of coal (or any fuel) by mass, including percentages of carbon, hydrogen, oxygen, nitrogen, sulfur, and inert materials (ash). The ultimate analysis provides the necessary data to predict the combustion products and to perform energy and mass balance calculations.

Combustion Stoichiometry

This is the quantitative study of reactants and products in a combustion reaction. It involves balancing the chemical equation based on the composition from the ultimate analysis to determine the amounts of products like CO2, water vapor, SO2, and others. This concept is essential for calculating the precise amounts of gases and vapors formed, including the water produced from the hydrogen content.

Excess Air

Excess air refers to supplying more oxygen than the theoretical (stoichiometric) requirement for complete combustion. This concept explains how additional air (and therefore additional nitrogen and water vapor) affects the final composition of the combustion products. It is critical for determining the actual quantities of reactants and products, ensuring complete combustion, and calculating dilutions in the exhaust gas.

Water Vapor Formation

In the context of fuel combustion, water vapor formation is mainly determined by the hydrogen component of the fuel. Calculating the mass of water involves converting the hydrogen content into water through the combustion reaction. Understanding this transformation is vital for determining the amount of water in the products, which is directly related to the potential for condensation and the thermal properties of the exhaust gases.

Dew Point Calculation

The dew point is the temperature at which water vapor in a gas mixture begins to condense into liquid water. This concept is important in combustion and boiler operations because it helps predict when and where condensation might occur, which can impact heat transfer and cause corrosion. Calculating the dew point requires knowledge of the water vapor concentration and the overall pressure, helping to manage and design systems that handle moisture in combustion products.

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