Steam Turbines
Steam turbines have been used to generate power for about 100 years, and today, they generate most of the electricity produced in the United States. Typically, steam turbines are in the 50-500 MW range, and they are widely used in CHP applications. Conventional steam turbines have multiple turbines to enhance system efficiency. The installation also requires a boiler to generate steam, fuel handling systems, and steam handling systems. The separation of boiler from the power generating equipment enables operation with wide range of fuels. Steam turbines are well suited to medium- and large-scale industrial and institutional applications where inexpensive fuels, such as coal, biomass, various solid wastes and byproducts (e.g., wood chips. etc.), refinery residual oil, and refinery off gases are available. The electrical generating efficiency of standard steam turbine power plant varies from high of 40% HHV for large, electric utility plants designed for highest practical annual capacity factor, to under 10% HHV for small, simple plants which make electricity as a byproduct of delivering steam to processes or district heating systems.

Steam turbine operates on the principle of Rankine Cycle (see figure below). Water is first pumped to medium to high pressure. It is then heated to the boiling temperature corresponding to pressure, boiled, and most frequently superheated. The turbine expands the pressurized steam to lower pressure and the steam is exhausted either to a condenser at vacuum conditions or into an intermediate temperature steam distribution system that delivers the steam to the industrial or commercial application.


Three different types of steam turbines are common. These include:

• Condensing Steam Turbines: These turbines exhaust directly to the condensers that maintain vacuum conditions at the discharge of the turbine. Typical use is at central power generation plants where maximum power and electrical generation efficiency is desired from steam supply and boiler fuel.
• Back-pressure turbines: These turbines are a non-condensing type, and exhaust the entire flow of steam to the industrial process or facility steam at conditions close to process heat requirements. The discharge pressure depends on the type of CHP application. Typical use is district heating systems and industrial processes.
• Extraction turbines: These turbines extract a portion of the steam at some intermediate pressure before condensing the remaining steam. The regulated extraction permits more steam to flow through the turbine to generate additional electricity during periods of low thermal demands.

Links to Manufacturers Skinner Power Systems Turbosteam

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