Power Plant Engineering

2.8.3 NATURAL GAS
Do you know the fact that natural gas known in the short form as CNG is used in buses, trucks
etc. in Delhi? Natural gas is a fossil fuel. This is usually formed in the Earth along with petroleum. Its
main constituent is methane. It also contains small quantities of Ethane and Propane. Natural gas lique-
fied by applying high pressure is CNG (Compressed Natural Gas). In automobiles, houses and factories,
CNG is used as a fuel. It is also used as a source of hydrogen required in the manufacture of fertilizers.
Natural Gas (CNG) is generally a mixture of the lighter hydrocarbons with methane (CH
4
) pre-
dominating, often with varying fractions of nitrogen and impurities such as hydrogen sulfide. Natural
Gas meet nearly 20% of world’s energy needs. Increase in NG supplies during this century has been
almost as dramatic as those of oil. However, development of NG industry has been limited to markets
that could be economically connected by pipeline to natural gas reserves. The expense of constructing
costly pipeline networks could only be justified where there are both large reserves and an assured
demand. The future role of NG will be largely determined by transport costs and the world depends
largely on large gas reserves and resources in areas further away from major markets. World proven gas
reserves are estimated to be about 394 billion boe (1975 values) and estimated undiscovered resources
to be about 1358 billion boe. Much will depend on when and how much of the estimated undiscovered
resources in North America and Western Europe are found and developed.
Almost all of the present world production of NG is transported by pipeline. An alternative to gas
pipelines is provided by transport by tankers carrying liquefied natural gas (LNG). The technology is
commercially available since 1960s and the costs are still high. The gas must first be liquefied by cool-
ing to – 161°C, then carried in specially designed refrigerated tanks, and re-gasified at receiving termi-
nals. Approximately 25% of the energy is lost in processing the LNG, and allowing also for transport,
only about two thirds of the original supply of gas is delivered to the consumer. An LNG processing and
transport system requires high capital expenditure and this will limit the rate of growth of international
trade in LNG. NG provides a clean and convenient fuel and an important chemical feedstock.

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POWER PLANT ENGINEERING
2.8.4 COAL
Coal has been used as a fuel for several millennia in China. In Europe, coal was known to the
Greeks and called ‘anthrax’ from which the name anthracite is derived. Its use was very much limited
until the firewood crisis in England in the 16th century which led to wide spread use of coke when
Darby developed the use of coke for reducing the iron ore. The changing rates of coal production are
explained by the change in market nature. When the development of railway began, the demand for
coal increased directly but also permitted it to be transported much more cheaply. The coal market in
USA was disturbed by the rapid market growth for oil and later NG.