Power land cycle of steam power generation :
The idealized cycle for a steam power plant is the Rankin cycle. As the aim is always to achieve higher efficiency, following feature exist in modem power plants :
1. Re-heating of steam after partial expansion in high pressure turbine.
2. Regeneration - bleeding part of the steam to heat the cold condensate from condenser.
3. Use of steam at high-pressures for improvement of thermal efficiency most of the power plants use high pressures usually more than l00 kg/cm3, 500 MW units being fabricated at M/s. BHEL will use steam at 170 atm.
Steam power Station > Boilers:
High steaming rates at higher pressures steam call for careful designing of boilers. A power station has to operate continuously for longer periods of time, hence boiler must be available for longer period-without need for shut downs on account of breakdowns or repairs.
On one hand a boiler furnace must have high temperature to heat the water, at the same time the gases discharged through chimney must have low temperature (to minimize losses) and least pollution producing gases. This calls for incorporating rapid heat transfer devices. The boilers in modern power plants are water tube boilers, with water walls. In addition to this super-heaters, re-heaters and economizer are installed to utilize maximum possible heat available inside the furnace. Furthermore, higher steaming rates require high flow velocities of water, steam, flue gases etc., with adequate controls and safety devices.
(Heaters in Boilers)
( Steam Turbine Arrangements )
Steam power Station > Turbines :
In order to obtain full benefit from high steam conditions, it is necessary to use large turbines. On large turbines of 100 MW and over, the cycle efficiency can be improved,by using external re-heating and expanding steam in turbine in two or three stages usually designated as high pressure, intermediate pressure and low pressure stages.
Axial flow turbines are commonly used in power plants. Maximum permissible speed for alternator being 3000 rpm, reduction gear boxes are used wherever turbine rotor speed is higher.
No comments:
Post a Comment