Energy costs vary greatly with energy source: coal @ $25.00/ton, gasoline @ a pu
ID: 733883 • 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. Rank order the three energy sources with respect to energy cost in $ GJ-1. Explain the large disparity in the numerical results of Part (a). Discuss the advantages and disadvantages of the three energy sources.Explanation / Answer
In North America, the term "Btu" is used to describe the heat value (energy content) of fuels, and also to describe the power of heating and cooling systems, such as furnaces, stoves, barbecue grills, and air conditioners. When used as a unit of power, Btu per hour (Btu/h) is the correct unit, though this is often abbreviated to just "Btu". The British thermal unit (symbol Btu or sometimes BTU) is a traditional unit of energy equal to about 1.055 KJoules. It is approximately the amount of energy needed to heat 1 pound (0.454 kg) of water, which is exactly one tenth of a UK gallon or about 0.1198 US gallons, from 39 °F to 40 °F (3.8 °C to 4.4 °C). There are 1055 Joules in a BTU, and there are 3414 BTU’s in a Kilowatt-Hour. coal=25 $ per ton heating value=29 MJ /kg heating value=29000 MJ/ton =29 GJ/ton so it costs 25/29=0.86 $/ GJ gasoline=2 $ per gallon heating value=37 GJ /m3 heating value=37 GJ/m3 1 m3=264.172051242 gallon so it costs =(37/264.172)*2=0.28 $/ GJ electricity=.1 $ per kWH One Btu is approximately:0.293071 W·h (watt hours) 10^6 btu =293.071 kwh so it costs =29.3 $/ GJ comparing all we get gasoline is cheap ,next coal and electricity
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