Time:2015-07-20 15:44:07 Auther: Ailsa from ZG Boiler
Coal fired power plants use a "vapor power cycle" to produce power. Specifically, they use a "Rankine" cycle. look this up online.
1.A pump pressurizes the water above up to the line of the vapor dome. The water then enters a coal fired boiler. At this state the steam is a "compressed liquid".
2.Coal is burned to heat up the water and turn it into steam in a boiler. while inside the boiler turning to steam it is called a "saturated mixture". While in the mixture phase it goes from being a "saturated liquid" to a "Saturated Vapor" (Remember those are both within the "Saturated Mixture" umbrella. Once it exits the boiler it is outside the vapor dome it is a "Superheated Vapor".
3.The hot pressurized steam goes through a turbine and becomes a "Saturated Vapor" again. The turbines spins because of the steam pressure and enthalpy. This spinning turbine is hooked up to a generator that produces power.
4. The steam exits the turbine and goes to a condenser where it is converted back into a liquid. This convertion is converting it the mixture from a "Saturated Vapor" back to a "Saturated Liquid". Then it goes back to the pump to be re-pressurized. i.e. back to step 1.
The pressures and temperatures vary. they are usually shown through tables. Here is part of a table
Below are volumes
Temp (C) Saturation Pressure (kPa) Sat. liquid (m^3/kg) Sat Vapor (Vg)
84 57.868 0.001032 2.8261
90 70.183 0.001036 2.3593
95 84.609 0.001040 1.9808
So the saturation pressures vary with different temperatures.
The critical point is 374 (C) and 22.064 MPa. if the temperature and pressure are above this then it is it's super critical. From the above all, you may understand the steam types that coal fired power plant use.