Gases in Technology
Gases in Technology
Gases are mainly used in industry as fuels; as raw materials for the preparation of chemicals; as chemical agents in welding, the chemical heat treatment of metals, and the creation of inert or special atmospheres; in some biochemical processes; as heat carriers; as the active component for performing mechanical work (firearms, jet engines and missiles, gas turbines, steam and gas installations, and pneumatic transport); and as the physical medium for gas discharge (in gas-discharge tubes and other instruments). More than 30 different gases are used in technology.
Natural gases and artificially produced generator gas or by-product (coke and blast-furnace) gases are used as fuels. In ferrous metallurgy natural gas is consumed mainly in blast furnaces and open-hearth furnaces. Each year, natural gas is used in about 60 percent of the production of cement and glass and in more than 60 percent of the production of keramzit (porous clay filler) and ceramics. The changeover of glassmaking furnaces to natural gas significantly improves the qualitative and economic indexes of glass manufacturing. In the machine-building industry, gas fuel makes up about 40 percent of the fuel requirements. Heating furnaces and heat-treatment furnaces are the main consumers of gas. The use of natural gas instead of other kinds of fuel in these furnaces lowers the cost of heating and improves its quality, increases the efficiency of the furnaces, and creates better sanitary-hygienic working conditions in the plant. Natural gas satisfies about 20 percent of the fuel requirements of electric power plants in the USSR. The use of natural gas in electric power plants gives very satisfactory results. Upon conversion from solid fuel to gas, the efficiency of boiler installations at electric power plants increases by 1-4 percent, and the number of personnel may be reduced by 21-26 percent. The total decrease in fuel consumption made possible by greater efficiency and the reduced expenditure of electrical energy on internal needs of the power plant is 6-7 percent. The use of gas in low-capacity boiler furnaces increases efficiency by 7-20 percent (depending on fuel quality) over boilers using solid fuel and makes it possible to increase output by 30 percent or more. The use of natural gas to heat steam and hot-water boilers opens up new possibilities for the construction of simpler and more economical boilers that require less metal.
Some gases are also used as raw materials for the technological processes of the chemical industry: about 200 different types of chemical products are made from them. A number of the largest combines in the chemical industry of the USSR operate on natural gas.
Among the gases used as chemical agents, air (atmospheric or oxygen-enriched) and oxygen are the most widely used in the metallurgical, chemical, and allied industries. Many other gases, such as acetylene, chlorine, fluorine, and the inert gases, also have significant application in these industries.
An oxyacetylene mixture is most often used in gas welding; its flame can reach a very high temperature (about 3200° C). Atomic-hydrogen welding, in which the metal is heated by hydrogen that has been converted into the atomic state by an electric arc, is used in some cases.
The heat treatment of metals in furnaces is often accompanied by the action of chemical agents in a gaseous state. The saturation of the surface layer of steel with carbon is achieved by prolonged heating of the steel in an atmosphere of gases that dissociate, with the release of atomic carbon. Natural gas, a propane-butane mixture, and other gases are used in industrial units for gas carburizing. To avoid excessive release of soot or resinous substances, generator gas or flue gases purged of carbon dioxide and water vapor are mixed with these gases.
Gases are used as chemical agents during nitriding, cyaniding, calorizing, and chrome-plating of steel during chemical heat treatment. When steel is gas-carburized with aluminum or chromium, it is heated in aluminum chloride or chromium chloride vapors. Nitrogen, generator gas from anthracite or charcoal, the products of combustion of some gases (after carbon dioxide and water vapor have been eliminated), and the products of ammonia dissociation are used in the metal-working industry to create a special atmosphere to prevent the oxidation and decarbonization of metals, which take place when they are heated in air or flue gases.
Water vapor, carbon dioxide, and nitrogen, as well as a mixture of carbon dioxide and nitrogen (for example, the products of the combustion of a gaseous fuel with a small amount of excess air), are used as inert substances to purge equipment in which there is a danger of explosion (gasholders, gas purifiers, and pipelines). High-capacity equipment is purged with inert gases before it is filled with gases such as hydrogen. During this process atmospheric air is displaced, and the formation of an explosive gas-air mixture in the equipment is prevented.
In the electric-lamp industry, nitrogen, krypton, xenon, and other gases are used to fill incandescent lamps. By filling the lamps with inert gas, the rate of evaporation of the filament is reduced, thus increasing the lifetime of the lamps. In addition, the use of some inert gases in this way substantially increases the luminous efficiency of incandescent lamps (by up to 30 percent); this is very important, since electric lighting consumes about 20 percent of all the energy produced in the USSR. Incandescent lamps are often filled with a mixture of argon and nitrogen. Krypton and xenon are especially suitable for filling lamps because of their high density and minimal heat conduction.
Gases are also used for the intensification of some biochemical processes. Carbon dioxide and the pure products of combustion of sulfurless fuel may be used as a carbon-dioxide fertilizer. An increased amount of carbon dioxide (up to 0.3 percent) in the atmosphere of hothouses and greenhouses accelerates the growth and raises the fruit yield of some plants. The ripening of harvested vegetables and fruits, such as tomatoes and apples, may be speeded up if they are kept in an ethylene atmosphere.
Air and the products of combustion (flue gases) are used as heat carriers; the gaseous products of exothermal processes, such as the oxidation of ammonia and the production of sulfur dioxide, are somewhat less frequently used in this way. Flue gases are used as heat carriers for the direct heating of articles or materials in stoves and dryers and for the preparation and heating of intermediate heat carriers such as water vapor, hot water, or air. Flue gases may be diluted with air or waste gases to regulate the heating process. They are sometimes used to transport and dry suspended coal dust. In such cases the flue gases are not only heat carriers but also a physical medium for the transport of pulverized solids. Air is used as an intermediate heat carrier only when the contamination of the object being heated by the soot and ash contained in some flue gases is not permissible. Air is used most often as a heat carrier in dryers and in some building heating systems.
As a source of mechanical power, gases are used in gas turbines, in firearms, in jet engines and missiles, and in internal-combustion engines. Dirigibles and blimps are filled with low-density gases.
An electric discharge in gas or vapor is widely used in electrical technology. It may be used to rectify an alternating current, to transform direct current into alternating current, to generate electrical oscillations, and for lighting (gas glow lamps). By selecting the appropriate gases or metal vapors, it is possible to increase the radiation of gas-discharge lamps in a given part of the spectrum. The overall luminous efficiency of light sources may be increased in this way.
REFERENCESKortunov, A. K. Gazovaia promyshlennost’ SSSR. Moscow, 1967.
Speisher, V. A. Szhiganie gaza na elektrostantsiiakh i v promyshlennosti, 2nd ed. Moscow, 1967.
“Ispol’zovanie gaza v promyshlennykh i energeticheskikh ustanovkakh.” In the collection Teoriia i praktika szhiganiia gaza, vols. 3-4. Leningrad, 1967-68.
Riabtsev, I. I., and A. E. Volkov. Proizvodstvo gaza iz zhidkikh topliv dlia sinteza ammiaka i spirtov. Moscow, 1968.
V. A. SPEISHER