Today’s tutorial deals with the steam power process in more detail. The mode of operation of the different components is especially elaborated on.
2. The steam power process
Pump, steam generator and turbine
The pump serves to pump water and consequently increasing its pressure. While there is generally negative pressure (so a pressure below the ambient one) within the condenser, the pump makes sure that the pressure rises considerably (in big power plants several 100 bars are common). The higher the pressure, the higher is the efficiency of the steam power process. These high pressure do however also pose high demands on the materials used (e.g. the pipes) and thus lead to higher investment costs.
Following the pressure increase in the pump, the water flows through the pipes into the combustion chamber. In the combustion chamber the respective primary energy carrier (e.g. coal or natural gas) is burned thereby releasing heat. The water flowing through the combustion chamber is therefore heated and entirely transforms into steam. Depending on the combustion chamber, water is headed once or several times through helical pipes. The steam which is generated in the process is meant to heat up to a very high temperature. Here the same applies: The higher the temperature, the higher is the efficiency of the process. Again, the limitations of deployed materials, such as the pipes and the turbines have to be considered.
The steam that leaves the combustion chamber is then directed into a turbine. Here the steam is expanded, while the pressure declines. In the process of expansion the steam propels the paddle wheels of the turbine. Actually, the (pressure) energy which is released during the expansion of the steam is converted into the rotary motion of the turbine.
Different turbines for different pressure ranges exist. The construction of high, medium and low pressure turbines differ. The rotary motion of the turbine is transmitted to the generator via a shaft. This shaft is made of metal and tightly connection the turbine and the generator.
Generator and condenser
Magnets are fixed to a shaft in the inside of the generator (the so-called rotor do the generator). Coils, so wound up conductors, are arranged around this shaft (the so-called stator). When the shaft spins the magnetic field of the magnets changes. As the magnetic field also penetrates the coils, a changing magnetic field induces a voltage difference at the end of each of the coils. In the generator, the rotary movement of the turbine is thus transformed into electricity.
The steam that escapes the turbine (in parts it already condensed back to water) has to be returned to the pump. This closes the loop. In order to achieve a complete condensation of the steam, it is directed into a condenser.
In the condenser heat is being dissipated, respectively steam is being withdrawn, and liquid water remains. In order to dissipate the heat, a second water cycle is guided into the condenser. The two cycles do not mix in this process. The second cycle is often fed from a natural source, e.g. a river close by. A low temperature in the secondary cycle, allows a low condensation temperature, which in turn reduces the pressure in the condenser and increases the overall efficiency of the process.
The liquefied water will flow towards the pump again. Here it is important, that the water is entirely in its liquid form. Otherwise the pump might be damaged.
The chemical energy stored in the respective energy carrier (during fission the heat released), is thus transformed into heat in the first step. Subsequently, the heat that is released is transformed into a rotary movement in the turbine. Finally, electricity in generated by using the rotary movement in the generator.
The quality of a steam power process is assessed in terms of its efficiency, which will be treated in the next tutorial.
