Thermodynamics

Introduction To Chemical Engineering Thermodynamics Seventh Edition By J.M. Smith, H.C. Van Ness, and M.M. Abbott.

Problems 1.22

Energy cost vary greatly with energy source: coal @ $25.00/ton, gasoline @ a pump price of $2.00/gal, and electricity @ $0.1/kWh. Conventional practice is to put these on a common basis by expressing them in $/GJ. [A gigajoule is approximately 106(btu).] For this purpose, assume gross heating values of  29  MJ/kg for coal and 37 GJ/m3 for gasoline.
Rank order the three energy sources with respect to energy cost in $/GJ.
Explain the large disparity in numerical result of part (a). Discuss the advantages and disadvantages of the three energy sources.

Given :

Energy cost,
Coal: $25/ton
Gasoline: $2/gal
Electricity: $0.1/kWh
Gross heating value,
Coal: 29MJ/kg
Gasoline: 37GJ/m3

Asked :

(a) Order energy cost with basis $/GJ.
(b) Explain energy cost large disparity in numerical and discuss the advantages and disadvantages of the three energy sources.

Answer :

Remember that 1ton = 100kg
Based on appendix A, 1gal = 231(in)3 = 231(2.54x10-2m)3 = 3,785.4x106 m3 = 0.0037854 m3
1kWh = 103 J/s = 103 J/s x 3600s = 3.6x106 J = 3.6x10-3x109 J = 3.6x10-3 GJ

(a) Energy cost,
Coal: 29MJ/kg = 2,900MJ/ton = 2.9GJ/ton
$25/ton : 2.9GJ/ton = $8.62/GJ
Gasoline: $2/gal : 37GJ/m3 = $2/0.0037854m3 : 37GJ/m3 = $14.28/GJ
Electricity: $0.1kWh = $0.1/3.6x10-3GJ = $27.77/GJ

Order from the cheapest : coal, gasoline, and electricity.

(b) From part (a) the gasoline cost almost double as coal and the electricity cost almost two time the gasoline cost and more than three times the coal cost. Coal and gasoline are world primary source with oil. Large disparity cost per gigajoule still made coal one of primary source of energy.

Advantages
Coal: Cheap, available in nature, and traditionally.
Gasoline: Less pollution than coal, and available in nature.
Electricity: Renewable source, less pollution, and modern.

Disadvantages
Coal: One of most pollution, made local environment disaster, and non-renewable source
Gasoline: Flammable and non-renewable source,
Electricity: Expensive and still need mine as feed for power plants

*So, coal still one of the cheapest and has a lot mining spread in the world, it makes most of nation especially developed country still use coal as prime energy source and gasoline respectively. Electricity still hard to be main energy source because high cost and even more clean to environment but if power plant still use mining such as coal, oil, and gasoline as feed for power plant it’s still made pollution, still non-renewable and it can make more cost.

(If you find a mistake comments below)

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