Thermal power station
A thermal power plant converts heat, more thermal energy partly into electrical energy. It is also called thermal power plant or caloric power plant, and only works when two heat reservoirs are present with sufficient temperature difference. The heat is first converted into an engine into usable kinetic energy and then into electrical energy by a generator, so it can find energy conversions take place.
Many thermal power plants are steam power plants. However, there are plants that have no steam turbines or even a water circulation, such as historical power plants with steam engines or modern Diesel-/Gasmotor- or gas turbine power plants. A common feature of today's thermal power plants are the thermodynamic cycles of the working fluid, which are closed when steam power plant and the gas power plant open.
- 6.1 through cooling without cooling tower
- 6.2 Sequence cooling with cooling tower
- 6.3 Circulation cooling with cooling tower
Importance
Thermal power stations provide in most industrialized countries (except Norway, Switzerland and Austria ), a majority ( depending on the region 60-100 %) of electrical energy. The reason for this monopoly position are very large, easily exploitable energy resources in the form of fossil fuels such as oil, coal and natural gas, as well as the decades-long use of this technology. Alternative methods but steadily gaining in importance as the fossil reserves are limited.
Principle of operation
The operating principle of steam power plants is always the following:
After that, the first step is repeated again; the process is cyclical. A large part of the thermal energy in the working fluid is lost to the environment or is removed intentionally by cooling. In combined heat and power generation waste heat is also used.
Heat source
Most thermal power plants generate the heat required even by burning fossil fuels or use the waste heat from nuclear processes in the nuclear power plant. As natural sources of heat geothermal and solar radiation can be used.
Efficiency
The thermal power plants underlying Carnot cycle is its electrical efficiency principled limits, so are energy conversion considerable losses, mainly as heat, inevitable.
Material Technically, the turbine inlet temperature is currently limited to about 600 ° C. The maximum plant efficiency must be below the Carnot efficiency of ( 600-40 ) lie / (570 273 ) = 66%.
The waste heat is not used for heating, the current efficiency of a power plant is typically between 30% and 45%. Higher efficiencies can be used in systems with more than one turbine to achieve, but the technical complexity is correspondingly greater. Be practiced such systems, for example, in gas - and -steam combined cycle power plants.
A significant better utilization of the primary energy can be achieved in plants by extraction of district or process heat (combined heat and power). As a result, overall efficiencies (more precisely, total utilization ) from 60% to 70 % can be achieved, in cogeneration plants even over 90%.
Factors for the practical usability
Apart from efficiency, the following factors shall be considered:
- General amount of energy available to the primary energy source
- Exploitable deposits
- Cost per unit of energy produced
- Technical feasibility of the combustion
- Environmental impact of emissions, waste heat or ionizing radiation
- Operating risks
Cooling
Many thermal power plants use to cool the water over flowing rivers. This saves the cooling tower with its many disadvantages, and the temperature at the outlet of the steam turbine can be reduced more effectively. However, may be too warm river water. There are therefore set limits to how many degrees Celsius or at what temperature the flow may be a maximum heated to prevent tipping. This can result in summer at high water temperature shutdown of the power plant. Since the 1970s, so-called heat load plans have been established, which can be seen from the maximum temperature of the water. Another, also combinable possibility is the use of cooling towers through which the waste heat is, if you can not capitalize on the combined heat and power to the heating of adjacent residential areas or greenhouses.
Cooling methods
In each of the following described method of cooling the water by means of filtration equipment must be cleaned of dirt, so that the ever-present coarse dirt will not clog the downstream turbine condenser and make so ineffective. For this purpose, flotsam and filters, the filter protecting the individual components such as the condenser and the heat exchanger in the first place. The cooling water is then cooled down in a cooling tower or a cooling pond, it may be either released into a river or reused in the cooling circuit. Furthermore, the cooling towers of large power plants such as air scrubbers act. Your cleansing effect on the air flowing through it remains low for the environment, but the washed dust is concentrated in the cooling water and may cause significant pollution of the downstream equipment. In particular, the capacitors of the steam turbines are affected, which therefore need to be cleaned with the ball method.
Through cooling without cooling tower
As the heated cooling water is untreated back into the water, there is a once-through cooling. The once-through cooling is the most efficient and most economical form of cooling; they do but can be applied only where the heat input is not an unreasonable burden on the waters. Critical are the summer months, because it can then be an upset of the water. In Germany once-through cooling is operated mainly located in coastal regions or on the Rhine. Especially on the Rhine, the " Working Group of the Federal States for keeping the Rhine ( Rhein ARGE ) " even in 1971 presented a heat load plan of the German section of the Rhine, the still valid.
Flow cooling with cooling tower
In this method, a stream is taken the necessary cooling water, heated in the condenser and then sprayed in the cooling tower. The non-evaporated and cooled to its original temperature water is returned to the river to flush out salts and impurities. The latter would increase constantly in their concentration when the water is not discharged to the atmosphere would be used repeatedly in the tower.
Circulation cooling with cooling tower
The circulation cooling, however, always use the same water; it will be supplemented from evaporation and blow down only the losses. This technique has proven itself with a low supply of cooling water very much. However, the constant evaporation of an increase in salinity ( thickening ) of the cooling water will spring up which leads to deposits in particular calcium and magnesium carbonates ( mineral deposits ). To counteract this effect, the cooling water (for example phosphonic acid ) stabilized with chemicals. From a certain upper limit of the total salinity and total hardness dilution of the cooling water must be brought about through blow down and fresh water supply. When you initiate the blow down in urban drainage systems ( indirect discharge) or water ( direct discharge ) shall state environmental regulations. Another problem of the cooling circulation, the growth of microorganisms. In addition to the fouling hygienic problems with respirable bacteria to the cooling tower ( Legionella spp., Pseudomonas aeruginosa) are taken into account. Therefore, the cooling water is also treated with biocides and bio- dispersant.
Technical realization of the principle of thermal power plant
- Heat removal from the wild (see also Renewable energy): Geothermal power plant
- Ocean thermal power plant
- Solar thermal power plant
- Nuclear power plant (actually nuclear fission power plant) Nuclear fusion power plant ( also a form of nuclear power plants but so far only research facilities )
- Lignite-fired power plant
- Coal-fired power plant
- Waste heat power plant Müllheizkraftwerk