Losses In Steam Turbine
The steam turbines are used in oil and gas, distillery, chemical plants, food processing industry, or in industries where the steam is a by-product. While operating the steam turbine at maximum load, different losses of steam occur in a steam turbine. The turbine uses every single bit of heat drop produced by steam. But practically turbine work done is much less than the isentropic heat drop of steam used. Because at the time of operation some internal losses occurred. Practically 100% gross efficiency is not possible for any turbine. When the turbine works some factors have reduced the output of the turbine, known as the losses in a steam turbine.
Following are the major losses that occur in a steam turbine.
Admission losses, Leakage losses, Nozzle Friction losses, Blade losses, Wheel Friction losses, losses due to Mechanical friction, Residual Velocity loss, losses in regulating valves, loss due to wetness of steam, Governing losses, Exhaust losses, Radiation and convection losses, Losses due to moisture, Carryover losses.
Leakage loss – Leakage loss occurs between the shaft, bearings, nozzles, and stationary diaphragms.
Windage losses – windage loss occurs when moving rotor blades come in contact with inactive steam then there is a move of energy as of blade to steam.
Nozzle Losses – When fluid is transferring from convergent to divergent or reverse then its momentum might be lost. Pressure losses occur when fluid flows from convergent to divergent. Head losses that occur in nozzles are due to pipelines.
Friction losses occur due to the flow of steam through nozzles on moving and stationary blades.
Blade friction loss – It is due to steam gliding over the blades and friction on the surface of the blades.
Wheel friction loss – When steam passes through the rotating turbine wheel, it produces some resistance on the turbine wheel.
Losses due to mechanical fraction – This loss is for turbine bearing. It is due to the shaft and wheel bearing and also the regulating valve of the turbine. This loss may be reduced by proper lubrication of the moving parts of the turbine.
Loss in regulating valves – Before entering the steam to the turbine, it passes through the boiler’s stop and regulating valve. Steam gets throttled in these regulating valves and as a result, steam pressure will be less than the boiler pressure at the entry of the turbine.
Loss due to wetness of steam – It is due to the moisture present in the turbine. When steam passes through the lower stage of the turbine, it becomes wet. At the lower stage, the velocity of water and steam are different and will not form a homogeneous mixture. That’s why the velocity of water particle is less than that of steam and water particle has to be dragged with the steam and some part of the kinetic energy of steam is lost.
Governing loss – This loss is due to the throttling of the steam at the main stop valve of the governor.
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