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Fig. 7   Black Point Power Station of CLP Power (photo courtesy: CLP Power)

Coal and natural gas are the most common fuels used in power stations to generate electricity. When the fuel is burnt, energy is released to turn a turbine. The turbine in turn drives a generator to generate electricity (for details, please see the module Electricity Generation and Transmission in Hong Kong). As a result, when we use electricity, we are indirectly using coal and natural gas. Nuclear energy provides an alternative way to generate electricity, and may become a solution to the energy crisis in the future.

Petrol and diesel

Petrol and diesel come from petroleum (crude oil). Petroleum is a complex mixture of hydrocarbons, appearing as a dark-coloured, flammable liquid in the upper layers of some areas of Earth's crust. Petroleum has to be separated into different useful parts by fractional distillation. The different parts are called fractions. Petrol and diesel are two of the fractions that can be burnt as fuels to provide power for vehicles. Diesel is denser, more oily and less volatile than petrol. Diesel also requires less refining to produce than petrol and that is why it is cheaper.

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Town gas

Town gas is not directly obtained by the fractional distillation of petroleum, but by the refining of one of the fractions called naphtha. Naphtha is treated by Catalytic Rich Gas (CRG) process at gas production plants in Hong Kong.

Fig. 8   Tai Po Gas Production Plant Fig. 9   Giant tanks for storing town gas in the Tai Po Gas Production Plant

At the end of the CRG process, town gas is obtained which consists mainly of hydrogen (49%), methane (28.5%), carbon dioxide (19.5%), and a small amount of carbon monoxide (3%) [1]. Smell is added to the town gas to ensure easy detection in case of a gas leak.

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Natural gas

Natural gas is often found together with petroleum. Its main component is the lightest hydrocarbon, methane. In Hong Kong, natural gas is not available for use at home, but is used in power station to produce electricity. Natural gas is imported to Hong Kong in a gaseous state from the Yacheng Gas Field near Hainan Island through a gas pipe under the sea. In countries like Japan, natural gas is imported in liquid state called Liquefied Natural Gas (LNG). LNG is formed when natural gas is chilled to -162 oC and condenses to liquid state. LNG is transported over long distances by special insulated LNG ships [2]. As LNG is only about one six hundredth of its original volume in gaseous state, transporting it over long distances is more economical than transporting natural gas through pipes.

Fig. 10   Natural gas is transported through pipes from Yacheng Gas Field near Hainan Island to the Black Point Power Station in Hong Kong. (Photo courtesy: CLP Power)     Fig. 11   Liquefied Natural Gas is transported by double-hulled insulated LNG ship. (Photo courtesy: LNG Shipping Solutions and CLP Power)

Liquefied petroleum gas (LPG)

LPG is found in gas well together with natural gas, and is also produced as one of the byproducts when petroleum is refined. It is a gas in room temperature and pressure. When it is stored in a pressurized tank, it is liquefied.