summary What is the turbine? What is the principle of steam turbine? Types of steam turbine. Component of steam turbine. Problems in steam turbine.
What exactly is the turbine?Turbine is an enginethat converts energy offluid into mechanicalenergyThe steam turbine issteam driven rotaryengine.
Principle of steam turbine: The steam energy is converted mechanical work by expansion through the turbine. Expansion takes place through a series of fixed blades(nozzles) and moving blades. In each row fixed blade and moving blade are called stage.
Steam turbine:Steam Turbine System:• Widely used in CHP(combined heat and power) applications.• Oldest prime mover technology• Capacities: 50 kW to hundreds of MWs• Thermodynamic cycle is the “Rankin cycle” that uses a boiler• Most common types • Back pressure steam turbine • Extraction condensing steam turbine 5
Steam turbine: Back Pressure Steam Turbine • Steam exits the turbine at a higher pressure that the atmospheric HP Steam Advantages: -Simple configuration -Low capital cost Boiler Turbine -Low need of cooling water -High total efficiencyFuel Disadvantages: Condensate LP Process Steam -Larger steam turbine Figure: Back pressure steam turbine 6
Steam turbine: Extraction Condensing Steam Turbine HP Steam• Steam obtained by extraction from an Boiler Turbine intermediate stage Fuel• Remaining steam is Condensate LP Steam Process exhausted• Relatively high capital cost, lower Condenser total efficiency Figure: Extraction condensing steam turbine 7
Types of steam turbine: There are two main types1. Impulse steam turbine2. Reaction steam turbine
Impulse steam turbine: The basic idea of an impulse turbine is that a jet of steam from a fixed nozzle pushes against the rotor blades and impels them forward. The velocity of steam is twice as fast as the velocity of blade. Pressure drops take place in the fixed blade (nozzle).
The single stage impulse turbine: The turbine consists of a single rotor to which impulse blades are attached. The steam is fed through one or several convergent nozzles. If high velocity of steam is allowed to flow through one row of moving blades. It produces a rotor speed of about 30000 rpm which is too high for practical use.
Reaction steam turbine: A reaction turbine utilizes a jet of steam that flows from a nozzle on the rotor. Actually, the steam is directed into the moving blades by fixed blades designed to expand the steam. The result is a small increase in velocity over that of the moving blades.
Corrosion: Resultant damage: Extensive pitting of airfoils, shrouds, covers, blade root surfaces. Causes of failure: Chemical attack from corrosive elements in the steam provided to the turbine.
Creep: Resultant damage: Airfoils, shrouds, covers permanently deformed. Causes of failure: Deformed parts subjected to steam temperatures in excess of design limits.
Fatigue: Resultant damage: Cracks in airfoils, shrouds, covers, blade roots. Causes of failure: Loosing of parts (cover, tie wire, etc.) Exceeded part fatigue life design limit
Stress Corrosion Cracking: Resultant damage: Cracks in highly stressed areas of the blading. Causes of failure: caused by the combined presence of corrosive elements and high stresses in highly loaded locations.