Turbines


TURBINE
 
Steam Turbine

A steam turbine is a prime mover, which continuously converts the energy of high pressure, high temp steam supplied by a steam generator into shaft work with the low temp steam exhausted to a condenser. The energy conversion takes place in two steps:–

  1. The high pressure & temp steam first expands in nozzle & comes out at high velocity.
  2. The high velocity jets of the steam coming out of the nozzle, impinges on blades mounted on a wheel, get deflected by an angle & suffer a loss of momentum which is absorbed by rotating wheel in producing torque. 


1.   Speed                                          
             i.        Normal speed (3000rpm)
           ii.        Low speed (less than 3000rpm)
         iii.        High speed (more than 3000rpm)

  1. Pressure
             i.        Low pressure steam turbine (up to 20Kg/cm2)
           ii.        Medium pressure steam turbine (up to 40Kg/ cm2)
         iii.        High-pressure steam turbine (above 40 up to 170Kg/ cm2)
          iv.        Super pressure turbine (above 170Kg/ cm2)

Turbine system

The turbine system comprises of:

Rotor

The rotor shaft is machined from a solid alloy steel forging. Balancing rings are also provided for adding screw type balancing weights. The wheel blades are of corrosion resisting steel and are attached to the wheels by dovetails.

Bearings
The rotating shaft of any machine must be supported in bearings. The bearings used in turbine in Renusagar power plant is mainly journal & thrust bearings

Journal bearing

Journal bearings that have the lining of low friction babit material are called sleeve bearing. Sleeve bearings may be split or full round. The lining may be heavy for large sized machinery & thin for precision machinery. Most sleeve bearings are of the split construction because of their ease in replacement & servicing.

Thrust Bearing

Thrust bearing takes up the residual axial thrust forces of the turbine that have not been compensated yet by the Labyrinth Gland sealed balancing piston & also any thrust force possibly transferred through the gear tooth coupling & transmits these forces to the front bearing housing. Chiefly the turbine load determines the magnitude of axial forces thus exerted on thrust bearing. In addition the thrust bearing serves the purpose of fixing the rotor in its axial position with respect to the turbine housing.

Exhaust End Bearing Bracket & LP Bearing

The fabricated bearings brackets are constructed integral with the exhaust end of the turbine casing. The bearing bracket has provision for oil drain & oil feed piping. The bearing assembles into a cylindrical bore that provides sealing for outside diameter.
The LP & journal bearing is tilting pad bearing. The bearing consists of 5 steel backed Babbitt lined pads assembled in a straight sealed aligning rings. The pads are provided for a slight tilting action of bearing to compensate the shaft deflection.   


HP Bearing & Thrust Bearings

The HP journal bearings consist of five steel backed shoes assembled in straight-sealed aligning rings. It has same action as LP bearing. 
The active & inactive thrust bearing assembly consists of two bearings each having a set of babbitt lined pads assembled in the base rings with a series of upper & lower leveling links assembled between the pads & the base rings. With this arrangement thrust load applied against an upper leveling link immediately behind it.

Turning gear

It is a motor driven or hydraulic operated device located it keeps the turbine & generator running at low speeds. It prevents distortions when the turbine is stopped suddenly. If the rotor is stopped suddenly the hot gases reach the upper surface of the turbine, hence the upper part is at high temp then the lower one. It may leads to sagging or bowing of the rotor. The turning gear rotates the turbine rotor at slow speed thereby enabling uniform cooling of the complete rotor.

Turbine auxiliaries

The main turbine auxiliaries are:

Condenser: It is the interface between steam and water cycle works as a heat sink. Working fluid gives up the quantity of heat that can’t be converted into work to the cooling water & gets condensed. Condenser tubes are straight tubes with smooth surface.

Steam Jet Air Ejector (SJAE): Air and non-condensable gases leaking into the condenser must be continuously evacuated from turbine/condenser system to enable the condenser to operate efficiently. A steam jet blows into the throat of the nozzle of SJAE & this high velocity jet produces a suction that draws air into throat at high velocity, thereby removing air from the condenser.  

Feed Water Heater: A regenerative cycle uses feed water heater to increase the efficiency of Rankine cycle. Two types of heaters are generally used. One is low pressure heater (LPH), which takes the steam extraction from the LP side of turbine while the other one is high-pressure heater (HPH), which takes steam extraction from HP side.
At Renusagar, five extractions are taken for regeneration.
Low-pressure heater (LPH) –2; Deaerator – 1; High-pressure heater (HPH) -2

Deaerator: The presence of certain gases like Oxygen, carbon dioxide & ammonia dissolved in water is harmful because of their corrosive attack on metal particularly at high temp. Thus in modern HP boiler to prevent internal corrosion, the feed water should be free of all dissolved gases especially Oxygen. This is achieved by using Deaerator.
It serves the following function:
  1. Heating incoming feed water.
  2. To act as a reservoir to a sudden or instantaneous demand i.e. it provides condensate storage & proper suction condition for the boiler feed pump.

Boiler feed pump (BFP): BFP is multistage pump provided    for pumping, feed water to Steam drum through the economizer.

Turbine Governing System

Governor: Its function is to keep the speed of a prime mover constant by adjusting the output of the engine to be equal to the external load on the engine in a given duration.

Control valve: The steam flow can be adjusted to the desired turbine output by opening or closing of the CVs .For this purpose; the CVs are opened or closed in succession according to predetermined sequences.

Emergency stop valve: The emergency stop valve is the principle shutting off the mechanism in the line, which connects the line steam supply with the turbine. In the event of the disturbance the emergency stop valves will interrupt the steam supply to the turbine in the minimum possible time.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
The type of emergency stop valve here under consideration is additionally equipped with a testing arrangements which permits at any time a check of the valve spindle & piston rod for free mobility without interfering with normal turbine operation.


Lubrication system

Turbine are supported on bearings proper lubrication is necessary in order to avoid:

  1. Seizure of bearing
  2. Wear of rotor
  3. To remove the heat

In Power plants following pumps are used for lubrication:

Main oil pump (MOP): it is used for lubrication of turbine bearings in running condition.

Auxiliary oil pump (AOP):  Provides oil for lubrication during turbine start up.

Emergency oil pump (EOP):  It is DC pump it provides lubrication incase of AC failure.

Jacking oil pump (JOP):  It provides initial lift to turbine during start for wedge film lubrication to set up.

Comments

Post a Comment

Popular posts from this blog

Power Plant cycle

Image
CLASSIFICATION OF POWER PLANT CYCLE Power plants cycle generally divided in to the following groups, (1) Vapour Power Cycle (Carnot cycle, Rankine cycle, Regenerative cycle, Reheat cycle, Binary vapour cycle) (2) Gas Power Cycles (Otto cycle, Diesel cycle, Dual combustion cycle, Gas turbine cycle.) CARNOT CYCLE This cycle is of great value to heat power theory although it has not been possible to construct a practical plant on this cycle. It has high thermodynamics efficiency. It is a standard of comparison for all other cycles. The thermal efficiency (η) of Carnot cycle is as follows: η= (T1– T 2)/T 1 where, T1 = Temperature of heat source T2 = Temperature of receiver RANKINE CYCLE Steam engine and steam turbines in which steam is used as working medium follow Rankine cycle. This cycle can be carried out in four pieces of equipment joint by pipes for conveying working medium as shown in Fig. 1.1. The cycle is represented on Pressure Volume P-V and S-T diagra...
Read more

BLOG Meant for

This blog covers the following areas pertaining to instrumentation and control. • Pressure • Flow • Level • Temperature • Neutron Flux • Control Pressure • explain the basic working principle of pressure measuring devices, bourdon tube, bellows, diaphragm,      capsule, strain gauge, capacitance capsule; • explain the basic operation of a differential pressure transmitter; • explain the effects of operating environment (pressure, temperature, humidity) on pressure detectors; • state the effect of the following failures or abnormalities:  over-pressuring a differential pressure cell or  bourdon tube;  diaphragm failure in a differential pressure cell;  blocked or leaking sensing lines; and  loss of  loop electrical power. Flow • explain how devices generate a differential pressure signal: orifice,  venturi, flow nozzle, elbow, pitot tube, annubar; • explain how each of the following will affect the ind...
Read more