3.2: How much energy there is in fossil fuels?

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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.