10221 Technology Description

The thermodynamic cycle for the steam turbine is the Rankine cycle. The cycle is the basis for conventional power generating stations. In this cycle, a heat source (boiler) converts water to high-pressure steam. The steam expands in a turbine to produce power. The steam exiting the turbine is condensed and returned to the boiler to repeat the process.

A steam turbine consists of a stationary set of blades (called nozzles) and a moving set of adjacent blades (called buckets or rotor blades) installed within a casing. The steam pushing the blades turns the shaft of the turbine and the connected load. A steam turbine converts pressure energy into velocity energy as it passes through the blades. The energy in high-pressure steam from a boiler* or other source** spins a steam turbine, and the turbine spins the shaft of a generator. All "steam-electric" generating plants — whether coal, natural gas, oil, nuclear, or geothermal energy powered — use this basic process.

The primary type of turbine used for central power generation is the condensing turbine. Steam exhausts from the turbine at subatmospheric pressures, maximizing the heat extracted from the steam to produce useful work. The non-condensing turbine (also referred to as a back-pressure turbine) exhausts steam at atmospheric pressures and above. In these turbines, a downstream process actually does the condensing to drive the cycle. An innovative application for steam turbines is as a replacement for pressure-reducing values. This application is generally quite small-scale, i.e., less than one megawatt. Manufacturers have lowered costs dramatically on such modular, load-following, back-pressure steam turbine generators.*** The discharge pressure is established by the specific CHP application.

The extraction turbine has opening(s) in its casing for extraction of steam either for process or feedwater heating. The extraction pressure may or may not be automatically regulated depending on the turbine design. Regulated extraction permits more steam to flow through the turbine to generate additional electricity during periods of low thermal demand by the CHP system. In utility type steam turbines, there may be several extraction points, each at a different pressure.

Modern large condensing steam turbine plants have efficiencies approaching 40 to 45%; however, efficiencies of smaller industrial or back-pressure turbines can range from 15 to 35%. Boiler/steam turbine installation costs are between $800 and $1000/kW or greater depending on environmental requirements. The incremental cost of adding a steam turbine to an existing boiler system or to a combined cycle plant is approximately $400 to $800/kW.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

Get My Free Ebook


Post a comment