Energy costs vary greatly with energy source: coal @ $25.00/ton, gasoline @ a pu
ID: 2126457 • Letter: E
Question
Energy costs vary greatly with energy source: coal @ $25.00/ton, gasoline @ a pump price of $2.00/gal, and electricity @ $0.1000/kWhr. Conventional practice is to put these on a common basis by expressing them in $ GJ-1. [ A gigajoule is approximately 106 (Btu).] For this purpose, assume gross heating values of 29 MJ kg-1 for coal and 37 GJ m-3 for gasoline.
(a) Rank order the three energy sources with respect to energy cost in $ GJ-1.
(b) Explain the large disparity in the numerical results pf Part (a). Discuss the advantages and disadvantages of the three energy sources.
Explanation / Answer
a) 1 ton = 1000 kg => Heating value of 1 ton of coal = 29 GJ / ton
1 gallon = 0.00378541 m^3 => Cost of gasoline in (/m^3) = $528.344 / gal
1 kWhr = 3.6 MJ = 0.0036GJ
So: energy costs for coal = 25/29 = 0.862 $/GJ
Costs for gasoline = 528.344 / 37 = 14.28 $/GJ
Costs for electricity = 0.1 / 0.0036 = 27.78 $/GJ
So, Coal > gasoline> 27.78
b) Large disparity occurs because even though heat content is higher for gasoline and electricity, they have to be manufactured / processed so that they can be used. This leads to higher cost of production. Also production in general is more expensive for them than coal
Coal:
Advantages: Easily available, Not much processing needed to obtain energy, cheap
Disadvantages: Non-Renewable, Comparatively low heating value, causes pollution
Gasoline:
Advantages: High heat content, comparatively cleaner fuel than coal
Disadvantages: Expensive, Causes pollution and health hazards, non-renewable
Electricity:
Advantages: No pollution, high heat content, Abundant availability - only source needs to be tapped
Disadvantages: High cost of production, Extra dependence on coal/natural gas based manufacturing, not yet tapped to full potential
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