Flow measurements in steam turbines for energy generation

A steam turbine is a device that is used to turn the high pressure of steam into the rotation of an axis. This type of turbine is primarily used in power plants, but also for other usages where large amounts of power is needed, such as sea ships in the oil- and gas industry. In this process, energy is used that is generated by cooling the steam. Therefore, it is of great importance to guarantee the correct flow of the steam. A trustworthy flowmeter is therefore essential for steam turbines.

Different Stadia of Steam

Almost everyone knows that water boils and evaporates at 100°C which creates steam. This stage of steam we call wet steam and when all water has evaporated it is called saturated water. This saturated steam is used in many processes to transfer heat (energy). Steam is therefore also one of the most reliable and energy-efficient ways to do this. There is however another stage that is called overheated steam (superheated steam). This stage is reached by heating the saturated steam further until above the boiling point. Superheated steam is not usable for heat transfer, saturated heat is much better suited for that. Superheated steam is however ideal for steam turbines.

Why does steam overheat

The biggest value of superheated steam is in the enormous amount of internal energy that can be used for kinetic reactions. This is used for mechanical expansion against the turbine blades and back-and-forth moving pistons, which produce a rotating movement of an axis. The value of superheated steam in these situations is the capacity to release a lot of internal energy and remain above the condensation temperature of water vapor, at the temperatures in which reaction turbines and piston motors work. With a steam turbine it is essential that the superheated steam does not cool off below the evaporation point, because the water droplets that are created at that point could damage or bend parts of the turbine.

Flow measurements in steam

The only measurement principle that can reliably and accurately measure the flow of steam is vortex. The vortex measurement principle is based on the fact that a turbulence in flow is caused after an obstacle in the flow. The higher the flow, the higher the turbulence. Through measuring this turbulence, the flow can be determined very accurately. The vortex measurement principle works perfectly for saturated steam. It is also appropriate to use it for overheated steam (superheated steam), as long as the instrument is provided with proper temperature compensation.

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