Abstract

Steam is the most important industrially used vapor and, after water, the most common and important fluid used in chemical technology. It can be generated by evaporation of water at subcritical pressures, by heating water above the critical pressure, and by sublimation of ice. Steam is used in electric power generation; for driving mechanical devices; for distribution of heat; as a reaction medium; as a solvent; as a cleaning, blanketing, or smothering agent; and as a distillation aid. Steam not only has high latent heat, moderate density, and nonpolluting properties, but also provides easy control of temperature in processes and heating application. Steam is generated from water by boiling, flash evaporation, and throttling from high to low pressure. The phase change occurs along the saturation line with the specific volume of steam larger than that of the boiling water. Thermal energy (heat of evaporation) is absorbed during the process. At the critical and supercritical pressures, the water–steam distinction disappears. The thermodynamic and physical properties of pure steam are well established over the range of pressures and temperatures used. Corrosion of containment materials and purity of water are important to steam production.