STEAM TURBINE

CONTENT

I. Introdution

II. Working principle

III. Construction

IV. Operation

What is the Turbine?What is the Turbine?

TURBINE is a power machine to drive working machine such as TURBINE is a power machine to drive working machine such as compressor, pump, electrical generator.compressor, pump, electrical generator.

Steam TurbineSteam Turbine Gas Turbine Gas Turbine Water TurbineWater Turbine

Steam TurbineSteam Turbine

Gas TurbineGas Turbine

Water TurbineWater Turbine

Steam turbines are made in a variety of sizes ranging from Steam turbines are made in a variety of sizes ranging from

small <0.75 kW (<1 hp) units (rare) used as mechanical drives small <0.75 kW (<1 hp) units (rare) used as mechanical drives

for pumps, compressors and other shaft driven equipment, to for pumps, compressors and other shaft driven equipment, to

1 500 000 kW (1.5 1 500 000 kW (1.5 GW; 2 000 000 hp) turbines used to ; 2 000 000 hp) turbines used to

generate electricity.generate electricity.

Selection of steam turbine type depend on the overall process Selection of steam turbine type depend on the overall process

requirement and configuration as well as project/ operation requirement and configuration as well as project/ operation

cost reason.cost reason.

Parts and equipmentParts and equipment

Steam turbine can be classified as the Steam turbine can be classified as the following:following:

• By steam supply and exhaust conditions:By steam supply and exhaust conditions: Back pressure Turbine or none condensing turbine.Back pressure Turbine or none condensing turbine. Condensing Turbine.Condensing Turbine. Extraction Steam Turbine.Extraction Steam Turbine. Induction Steam TurbineInduction Steam Turbine Reheat Steam TurbineReheat Steam Turbine• By Blades and Stages design:By Blades and Stages design: Impulse TurbineImpulse Turbine Reaction Turbine.Reaction Turbine.

Non-Condensing Steam Turbine:Non-Condensing Steam Turbine:Non-condensing or back pressure turbines are most widely used Non-condensing or back pressure turbines are most widely used for process steam applications. The exhaust pressure is controlled for process steam applications. The exhaust pressure is controlled by a regulating valve to suit the needs of the process steam by a regulating valve to suit the needs of the process steam pressure.pressure.

Condensing Steam TurbineCondensing Steam Turbine

Condensing turbines are most commonly found in electrical Condensing turbines are most commonly found in electrical power plants. These turbines exhaust steam from a boiler in a power plants. These turbines exhaust steam from a boiler in a partially condensed state, typically of a quality near 90%, at a partially condensed state, typically of a quality near 90%, at a pressure well below atmospheric to a condenser.pressure well below atmospheric to a condenser.

Extraction Steam Turbine:Extraction Steam Turbine:In an extracting type turbine, steam is released from various In an extracting type turbine, steam is released from various stages of the turbine, and used for industrial process needs or sent stages of the turbine, and used for industrial process needs or sent to boiler feed water heater to improve overall cycle efficiency. to boiler feed water heater to improve overall cycle efficiency. Extraction flows may be controlled with a valve, or left Extraction flows may be controlled with a valve, or left uncontrolled.uncontrolled...

Induction Steam TurbineInduction Steam Turbine

Induction turbines introduce low pressure steam at an Induction turbines introduce low pressure steam at an intermediate stage to produce additional power.intermediate stage to produce additional power.

Reheat Steam TurbineReheat Steam Turbine

In a reheat turbine, steam flow exits from a high pressure section In a reheat turbine, steam flow exits from a high pressure section

of the turbine and is returned to the boiler where additional of the turbine and is returned to the boiler where additional

superheat is added. The steam then goes back into an superheat is added. The steam then goes back into an

intermediate pressure section of the turbine and continues its intermediate pressure section of the turbine and continues its

expansion. Using reheat in a cycle increases the work output expansion. Using reheat in a cycle increases the work output

from the turbine and also the expansion reaches conclusion from the turbine and also the expansion reaches conclusion

before the steam condenses, there by minimizing the erosion of before the steam condenses, there by minimizing the erosion of

the blades in last rows.the blades in last rows.

Impulse & Reaction TurbinesImpulse & Reaction Turbines

Impulse TurbinesImpulse Turbines

Impulse Steam TurbineImpulse Steam Turbine

On Impulse Turbine a thermal expansion take place only in the On Impulse Turbine a thermal expansion take place only in the nozzles and static energy is converted to the kinetic energynozzles and static energy is converted to the kinetic energy

There is no pressure different at inlet and outlet of blades on There is no pressure different at inlet and outlet of blades on the rotor, because the thermal expansion only in the nozzles. It the rotor, because the thermal expansion only in the nozzles. It means no thrust force acting on the rotor disc.means no thrust force acting on the rotor disc.

Reaction Steam TurbineReaction Steam Turbine

Reaction stage

Thermal expansion occurs both in the nozzles and blades. The impulse force

comes from the kinetic energy which is converted in the nozzles, and

reaction force created in the blades comes due to decreasing steam pressure.

These two forces produce the rotation torque of the blades on the rotor. On

this type, differential pressure between the inlet and outlet of blades

generates thrust force to turbine shaft. Therefore, to reduce the thrust force

acting on the shaft, shaft diameter is equal to the diameter of the blade root,

and blades are mounted on shaft directly.

Impulse and Reaction TurbineImpulse and Reaction Turbine

Actually, Steam turbine using in the refineries are combined impulse and Actually, Steam turbine using in the refineries are combined impulse and reaction to get more advantages and less disadvantagesreaction to get more advantages and less disadvantages

NozzleNozzle

Thrust & Radial bearingsThrust & Radial bearings

Journal BearingJournal Bearing

Self Equalizing tilting padSelf Equalizing tilting pad

Sealing ProblemSealing Problem

Labyrinth effectivenessLabyrinth effectiveness

Sealing of Steam TurbineSealing of Steam Turbine

Monitoring systemMonitoring system

Function of Trip Throttle Valve (TTV)Function of Trip Throttle Valve (TTV)

Adjustment of steam flow to turbine during Adjustment of steam flow to turbine during start-up.start-up.

Close valve quickly as the pressure of Close valve quickly as the pressure of control oil lose due to interlock trip of control oil lose due to interlock trip of turbine or push the button trip.turbine or push the button trip.

Partial stroke test of TTV.Partial stroke test of TTV.

Trip Valve and Control ValveTrip Valve and Control Valve

Trip ValveTrip Valve

Trip Throttle ValveTrip Throttle Valve

Trip Throttle ValveTrip Throttle Valve

Throttle valve operationThrottle valve operation

Condensing system(Cond)Condensing system(Cond)

• Air in condenser is sucked by steam ejector and send to inter cooler Air in condenser is sucked by steam ejector and send to inter cooler together with ejector driving steam. In inter cooler steam is cool together with ejector driving steam. In inter cooler steam is cool down by condensed water and convert to water and returns to down by condensed water and convert to water and returns to condeser through siphon tube.condeser through siphon tube.

• Air in inter cooler is suck again by steam ejector and send to after Air in inter cooler is suck again by steam ejector and send to after cooler and only water in after cooler return to condenser through cooler and only water in after cooler return to condenser through steam trap and air goes to outside.steam trap and air goes to outside.

Assume that:- Steam stream meets all the conditions about pressure and temperatue before to be taken to turbine.- All the systems including: electrical, control, pneumatic system, closed cooling water system, condensate system, feed water system, boiler) in normal operation condition. No more failure on the devicesThe steps for starting turbine as following:

Start-up Procedure

OPERATION

1. Placing the turbine lubrication oil system in service:- Start one duty pump and place the remain in spare- Test change over- Check parameter: pressure,temperature, condition of cooler,

filter..

2. Running turning gear system: - Turning gear is done before start up and after shutdown turbine.- The turning gear times depend on the outage duration of turbine

(start up) or metal temperature (shutdown), may be from severe hours to one day in case of start up.

Less than one day: 2 hours Up to7 days: 6 hoursUp to 30 days: 12 hoursOver 30 days: 24 hoursNormally, a motor is used for turning gear. The turning speed varies

from above ten rpm to hundred rpm.

3. Placing the turbine governing system (or EHC) in service:

- Start the hydraulic pump, check header pressure- Check condition of valve and pipe is not abnormal- Trip test (by push Emergency stop button)- Setting initial loading (for generator driven) or no-load

speed (compressor or pump driven) and loading limiter (gradient)

4. Pre-runup checks of turbine valves- In order to detect valve malfunction before steam admitted to the

turbine- If having any problem in valve operation , it must be repaired

before turbine start up- The valves are tested including stop valves and control valves- During the valve checks, the turbine isolating valves close to

prevent steam flow through the turbine. Once valve completely checked, these valve open to allow steam flow to the emergency stop valve.

5. Place the condensate cooling water (ccw) system in service:-Start ccw pump, check the parameters-Place the condensate cleaning system in service-Place vacumn the primary system (for water box) in service (if installed)-Monitoring parameters..

6. Place the gland sealing steam system in service:- To sealing turbine before pulling condensate vacumn- Before start up, gland sealing steam is extracted from the

live steam system ( or auxiliary steam systeam) and decreased both pressure and temperature (pressure: sligher than atmospheric about 30-40 mbar, temperature: different from metal temperature about 50oC)

- Check the gland steam condenser in normal condition

7. Pulling condenser vacumn: Doing before start up:-To reduce the tendency of the LP turbine exhause to overheat-To prevent excessive flow – induced vibration of moving blades in the turbine last stageActivities:-Start the vacumn pumps or ejectors.-Monitoring the condensate pressure below 150 mbara

8. Placing the LP turbine exhaust cooling system in service:

- Supply the cooling spray water to protect the LP turbine last stages, condensate tubes from overheating when turbine exhaust temperature is high.

- The control valve will open and closing base on exhaust temperature.

9. Turbine warm-up -To reduce thermal stress caused by temperature different between live steam and turbine metal -Normally, a control valve is used to extract steam from live steam and taken to the turbine. The temperature rising of turbine metal is limited and depend on the initial turbine metal temperature, may from 30-100oC/hour.-After temperature different between live steam and turbine metal below 50oC, can finish warm-up step.

10. Start - up turbine:Base on initial turbine metal temperature, can classify 3 start up

modes:- Cold start: Turbine metal temperature < 150o C- Warm start: Turbine metal temperature :150o C - 410o C- Hot start: Turbine metal temperature > 410o C

Before start up, operators must carefully check performance of all the system concerned are normal and ready, example: vacumn pressure, lube oil pressure and temperature, position of drain valve….-Setting the speed target, run up rate, initial loading, holding speed, warm up time.. base on mismatch diagram. Carefully check in case of auto-setting.-Press start button to run up turbine.-The control valve will slowly open and steam flow to the turbine for rotary-Turning gear disengaged and turbine run up base on start up curve.

Start up curve

Start up on DCS

Monitoring in operation:- Critical speed- Shaft eccentricity- Thermal stress- Shaft vibration- Differential Expansion - Temperature: lube oil temperature, bearing metal temperature- Turbine exhaust hood: Vacumn, temperature, - Steam qualities: Silica, conductivity, pH