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3.2: How much energy there is in fossil fuels?

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    85074
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    A very important characteristic of each fossil fuel type is the heat of combustion – in other words, the amount of thermal energy released in the process of burning a mass unit of a given fuel. It is listed in the table below.

    Table 3.1. Heat of combustion of fuels

    Fuel

    MJ/kg

    BTU/lb

    Hydrogen

    141.80

    61,000

    Methane (Nat. gas)

    55.50

    23,900

    Propane

    50.35

    21,700

    Butane

    49.50

    20,900

    Gasoline

    47.30

    20,400

    Kerosene

    46.20

    19,860

    Diesel

    44.80

    19,300

    Ethanol

    29.67

    12,750

    Methanol

    22.65

    9,740

    Coal (Anthracite)

    27.00

    11,600

    Coal (Lignite)

    15.00

    6,500

    Wood

    15.00

    6,500

    Peat (dry)

    15.00

    6,500

    Peat (dump)

    6.00

    2,500

    In addition, we also give the data for several other substances which are not mined, but are widely used as fuels. The names of fossil fuels or fuels derived from them are shown in bold face, and of other fuels – in regular face.

    The heat of combustion is given in the units of MJ/kg, and also of British Thermal Units per pound (BTU/lb). The latter is not a SI unit, but it is still very popular in the US.

    Hydrogen H2 does not occur naturally. Large amounts of hydrogen are used in fertilizer industry for making ammonia NH3. In the US, 95% of hydrogen used for this purpose is produced by a process called natural gas reforming. Hydrogen may be used as fuel in electric cars using fuel cells for converting it to electricity. They are real zero-emission cars (their exhaust is pure water vapor only), so they are ideal for California. However, because of their high price and a small number of refueling stations, they are not yet very popular: until mid-2018, only slightly over 3,000 of them has been sold, mostly in big CA cities. And it has to be kept in mind that the cars are zero-emission ones, yes, but CO2 is released to atmosphere when the fuel for them is produced by the natural gas reforming technology.

    Propane (C3H8) and Butane (C4H10) are gases normally dissolved in crude oil, and released during the rectification process; they are transported and sold in a liquefied form, in pressurized tanks. They are used, e.g., as a popular fuel in gas grills.

    Peat is a fossil fuel, yes, but a very “young” one. It formed at the end of the last Ice Age – not tens of millions years ago, like coal. There are few peat-fired power plants in the world, so, essentially, peat is a fossil fuel of only marginal importance.


    3.2: How much energy there is in fossil fuels? is shared under a CC BY 1.3 license and was authored, remixed, and/or curated by Tom Giebultowicz.

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