E3.2 Heating Value

Example 3.2: Calculate heating value of a natural gas given the following composition in volume percent:

CH₄ = 94.44, C₂H₆ = 3.4, C₃H₈ = 0.55, C₄H₁₀ = 0.5,

CO = 0.01, CO₂ = 0.57, H₂ = 0.03, N₂ = 0.5

The following table provides heat of formation for various components. This table also lists moles of oxygen required for complete combustion and moles of combustion products.

Solution

CO₂ produced = 0.944(1) + 0.068(2) + 0.017(3) + 0.020(4) + 0.0001(1) = 1.049

H₂O(l) produced = 0.944(2) + 0.068(3) + 0.017(4) + 0.020(5) + 0.0001(0) = 2.038

Enthalpy of products, SH _Products = 1.049(-94052) + 2.038(-68317.4) = -237891.4 cal

Enthalpy of feed, SH _Feed = 0.944(-17889) + 0.068(-20236) + 0.017(-24820)

+ 0.020(-29812) + 0.0001(-26416) = -18407 cal

Heat of reaction, ΔH₂₉₈ = SH _Products - SH _Feed

= -237891.4 - (-18407) = -219492 cal/mol = -395086 Btu/lbmol

High heating value, HHV = -ΔH₂₉₈ = 3.951 ´ 10⁵ Btu = 1044 Btu/ft³