Producer and Blast-Furnace Gases
Producer gas is a form of water gas, a term applied to steam-process gases. It is made by burning low-grade fuel (such as lignite or bituminous coal) in a closed vessel, called a producer, while passing a continuous stream of steam and air through the producer. The resulting gas is approximately 50 per cent incombustible nitrogen derived from the air present in the producer, and is low in fuel value, having only about 28 per cent of the heating value of coke-oven gas.
Blast-furnace gas, which results from the interaction of limestone, iron ore, and carbon in blast furnaces, has some heating value because of its carbon monoxide content, but contains about 60 per cent nitrogen. Enormous quantities are produced during the operation of furnaces. Most of this gas is consumed in heating the air blast and driving the compressors for the blast. The heating value of blast-furnace gas is about 16 per cent of that of coke-oven gas.
Natural Gas
A certain amount of natural gas usually occurs in connection with petroleum deposits and is brought to the surface with the oil when a well is drilled. Such gas is called casing-head gas. Certain wells, however, yield only natural gas.
Natural gas contains valuable organic elements that are important raw materials of the petroleum and chemical industries. Before natural gas is used as fuel, heavy hydrocarbons such as butane, propane, and petrol are extracted as liquids. The remaining gas constitutes so-called dry gas, which is piped to domestic and industrial consumers for use as fuels; dry gas, devoid of butane and propane, also occurs in nature. Composed of the lighter hydrocarbons methane and ethane, dry gas is used also in the manufacture of plastics, drugs, and dyes.
Bottled Gas
Several of the lighter hydrocarbons, such as propane, butane, and pentane, and mixtures of these gases, are liquefied and employed as fuels. With so-called bottled gases, which are usually stored in steel cylinders, appliances such as cooking stoves and heaters can be used in localities where a centralized gas supply is not available. Such bottled gases are produced from natural gas and petroleum.
Liquid fuels
Petrol, mixture of the lighter liquid hydrocarbons used chiefly as a fuel for internal-combustion engines. It is produced by the fractional distillation of petroleum oil; by condensation or adsorption from natural gas; by thermal or catalytic decomposition of petroleum or its fractions; by the hydrogenation of producer gas or coal; or by the polymerization of hydrocarbons of lower molecular weight. For use in high-compression engines, it is desirable to produce petrol that will burn evenly and completely in order to prevent knocking, which is the noise and damage caused by premature ignition of a part of the fuel and air charge in the combustion chamber. The antiknock characteristics of a petrol are directly related to its efficiency and are indicated by its octane number. This is a rating that describes the performance of a fuel in comparison with that of a standard fuel containing given percentages of isooctane and heptane. The octane number given to the fuel is the same as the percentage of isooctane in the standard fuel of the same performance. The higher this number, the less likely a fuel is to cause knocking. Cracked petrol has better antiknock characteristics than straight-run petrol, and any petrol can be further improved by the addition of such substances as tetraethyl or tetramethyl lead. Since it was discovered, however, that the emission of lead from such petrols is dangerous to human beings—among other effects, raising blood pressure—research on new ways to reduce the knocking characteristics of petrol was intensified.
Low-lead petrols were introduced in the early 1970s as a result of increased public concern about air pollution. After 1975 all new cars in the United States were equipped with catalytic converters to reduce their emission of pollutants. Because even low-lead petrol “poisons” the catalyst, the proportion of leaded petrol in the United States declined from 73 per cent of the total supply in 1976 to less than 10 per cent in 1990. European countries were moving more slowly in this direction, largely by placing extra taxes on leaded petrol. Many environmentalists are looking to much-increased use of gasohol and cleaner-burning natural gas in the late 1990s.
Petroleum, or crude oil, naturally occurring oily, bituminous liquid composed of various organic chemicals. It is found in large quantities below the surface of the earth and is used as a fuel and as a raw material in the chemical industry. Modern industrial societies use it primarily to achieve a degree of mobility—on land, at sea, and in the air—that was barely imaginable less than a hundred years ago. In addition, petroleum and its derivatives are used in the manufacture of medicines and fertilizers, foodstuffs, plastic ware, building materials, paints, and cloth, and to generate electricity.
Conclusion
Different fuels have been used for different purposes. Fossil fuels have a particular disadvantage because they are very heavy pollutants, and are non-renewable. However, they are advantaged in that they are a very good source of energy. In the examples I have looked at the majority are fossil fuels which are all combusted and cause problems in the ozone layer. However there are alternatives, new research has now found hydrogen can be controlled enough to be used as a fuel. Hydrogen can supply the huge energy needs, which could particularly be used in aircraft.