bab 8 - turbine
TRANSCRIPT
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TURBINE
8.1 Background
Steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and
converts to useful mechanical work. The steam turbines are split into three separate stages,
High Pressure (HP), Intermediate Pressure (IP) and Low Pressure (LP) stage. After the steam
has passed through the HP stage, it is returned to the boiler to be re-heated to its original
temperature although the pressure remains greatly reduced. The reheated steam then passesthrough the IP stage and finally to the LP stage of the turbine.
Figure 8-1. View of the Internals of a Typical Power Station Steam Turbine
Steam turbines are generally configured in many different ways. Several IP or LP stages can be
incorporated in to the one steam turbine. A single shaft or several shafts coupled together may
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be used. Either way, the principles are the same for all steam turbines. The configuration is
decided by the use to which the steam turbine is put, co-generation or pure electricity
production.
Turbines are one of the major components of any thermal power plant, generate steam for
power generation. The brief details of typical boiler used in 210 MW thermal power plant is
given in the Table 8-1.
Table 8-1: Brief specifications of turbine
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8.2 Steps Involved In Conducting the Energy Audit
The steps involved in conducting energy audit of turbines are:
Data collection
Observations and Analysis
Exploration for energy conservation measures
Report preparation
8.3 Data Collection
The following data sheets give brief specifications to be collected. It is suggested to obtain the
comprehensive technical specifications of Turbines and its associated equipment.
8.3.1 Specification of turbine and associated equipment
a. Turbine
Collect the detailed design specifications of the turbine. The following Table 8-2 gives the list
of specifications to be collected for energy audit study in addition to following specific
details.
Type of the turbine
Make and model
No of stages (for HP, IP and LP)
Number of cylinders
No of main and reheat valves
Construction details of HP, IP LP
Turbine extraction systems
Control systems Type of governing
Type of sealing
Year of installation
Major modifications carried out during the recent past
The design specifications to be collected are given in the following Table 8-2
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Table 8-2: Design Specifications of turbine
Particulars Unit MCR NCR
Rated output MW
Turbine Heat rate Kcal/kWh
Efficiency of the turbine %
Steam flow for rated output tph
HP inlet steam pressure Kg/cm2
HP inlet steam temperature OC
HP exhaust steam pressure Kg/cm
2
HP exhaust steam temperature OC
IP inlet steam pressure Kg/cm2
IP inlet steam temperature OC
IP exhaust steam pressure Kg/cm2
IP exhaust steam temperature OC
LP inlet steam pressure Kg/cm2
LP inlet steam temperature OC
LP exhaust steam pressure Kg/cm2
LP exhaust steam temperature OC
Condenser vacuum mmWC
Cooling water inlet temperature to condenser OC
Cooling water outlet temperature to condenser OC
Cooling water flow through the condenser m3/h
Super heater spray tph
Reheater spray tph
8.4 Instruments Required
The following instruments are required for conducting turbine energy audit:
Temperature Indicator & Probe
Pressure gauges
Flow measuring instrument (steam and water)
Ultrasonic leak detector
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While conducting the turbine efficiency test, measurements of steam flow pressure and
temperatures are very essential. Calibrated on line instruments can also be used for conducting
the test
8.5 Measurements & Observation Be Made
While conducting the audit, the following measurements (temperature and pressure) are
necessary
Feed water at Inlet & Outlet of Heaters
Main steam
HP turbine extraction Hot reheat steam, Cold reheat Steam
IP extraction
IP Exhaust
In addition to the above, the following measurements are required:
Condenser back pressure
Cooling water flow and temperatures
Generator output
Barometric pressure
Reheater spray (flow)
Superheater spray (flow)
Feed water (flow)
8.6 Observations and Analysis
8.6.1 System familiarization and operational details
Detailed interactions with the plant personnel have to be carried out to get familiarization for
system detail and operational details. The brief details of the entire system have to be given in
the report along with the specifications. PG test reports of the turbine and associated
equipment data need to be collected. The consolidated data sheets need to be given in the
report for reference.
During the familiarization on power plant and its operation, plants observation and past data
should be obtained pertaining to the:
Past performance trends on turbine loading, operation,
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PLF Major constraint in achieving the high PLF, load or efficiency
Major renovation and modifications carried out in the recent past
Operational failures leading to in efficient operation
Tripping
Performance of associated equipment (condenser, boiler, etc)
Plant side initiatives to improve the performance and efficiency of the Turbine
All major observations arrived at during the discussions, which affect the performance and
energy efficiency of the turbine, it is suggested to verify the records and history.
8.6.2 Turbine heat rate evaluation and efficiency
The trials are to establish heat rate (kcal/kWh) and turbine efficiency under, as run conditions
have to be carried out. The efficiency method given in this procedure is the enthalpy drop
efficiency method. This method determines the ratio of actual enthalpy drop across turbine
section to the isentropic enthalpy drop.
This method provides a good measure for monitoring purposes. Each section of the turbine
must be considered as a separated turbine. Each section should be tested and results are
trended separately. While conducting the tests, it has to be ensured that, it is conducted over
normal operating load range. The following gives the data sheet for measurements:
The following Table 8-3 gives the data sheet for measurements and observations for conducting
as run test for turbine efficiency evaluation
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Table 8-3: Data sheet for turbine efficiency evaluation
Operating parameters Symbol Unit As run data
Date -
Duration h
Avg. Unit load MW
% of NCR %
Frequency Hz
Speed rpm
Control valve A % open
Control valve B % open
Main steam flow tph
Feed water flow tph
HP turbine inlet temperature (left/right)OC
HP turbine inlet Pressure (left/right) Kg/cm2
IP turbine inlet temperature (left/right) OC
IP turbine inlet Pressure (left/right) Kg/cm2
LP turbine inlet temperature (left/right)OC
LP turbine inlet Pressure (left/right) Kg/cm2
Condenser vacuum (A/B) MWC
LP gland steam line pressure Kg/cm2
LP gland steam line temperature OC
Super heater spray tph
Reheater spray tph
Others
Ext. to Feed Heaters Pressure
Ext. to Feed Heaters Temp
Turbine heat rate is given by:Q1 Main steam flow Kg/h
H1 Main steam enthalpy Kcal/kg
h2 Feed water enthalpy Kcal/kg
H3 Hot reheat enthalpy Kcal/kg
H2 Cold reheat enthalpy Kcal/kg
Q2 Reheat steam flow Kcal/kg
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Turbine cylinder efficiency is given by:
The following Table 8-4 data sheets given in the can be used for turbine cylinder efficiency
evaluation.
Table 8-4: Turbine efficiency evaluation data sheet
Operating parameters Unit DesignAsrun
Deviation fromdesign
Remarks
Avg. Unit load MW
% of NCR %
Frequency Hz
Speed rpm
Main steam parameters -
Pressure Kg/cm2
TemperatureOC
Enthalpy Kcal/kg
Entropy Kcal/kg/OC
Exhaust steam parameters -
Pressure kg/cm2
TemperatureOC
Enthalpy Kcal/kg
Entropy Kcal/kg/OC
Actual enthalpy drop Kcal/kg
Isentropic enthalpy drop Kcal/kg
Cylinder efficiency %
The above table can be used for all stages such as HP, IP and LP turbines.
After evaluating the turbine heat rate and efficiency evaluation, check for the deviation from the
design and identify the factors contributing for the deviations. The major factors to be looked
into are:
Main steam and reheat steam inlet parameters
Turbine exhaust steam parameters
Reheater and super heater spray
Passing of high energy draining
Loading on the turbine
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Boiler loading and boiler performance
Operations and maintenance constraints
Condenser performance and cooling water parameters
Silica deposition and its impact on the turbine efficiency
Inter stage sealing, balance drum and gland sealing
Sealing fins clearances
Nozzle blocks
Turbine blade erosion
Functioning of the valves
Operational status of HP heaters Performance of reheaters
8.6.3 HP Feed Heaters and LP Feed Heaters
Collect the specifications given in the for HP heater Table 8-2.
Table 8-2: Specifications of HP heaters
Unit HP heater # HP Heater # HP heater #
Heater position (horizontal/vertical) -
H P heater ID code & number -
No of zones (De-superheating,condensing, drain cooling)
-
No of tubes No
Surface area m2
Tube size (OD x thickness) mm
Feed water inlet temperatureOC
Feed water inlet temperatureOC
Extraction steam flow tph
Extraction steam pressure Kg/cm2
Pressure drop (water side) mWC
TTDOC
DCA Drain cooler approachtemperature
OC
Temperature raiseOC
Similarly collect the specifications of LP heaters.
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8.6.4 H P Heaters and LP heaters
The performance of the feed water heaters can be analyzed by monitoring:
The terminal temperature difference,
Drain cooler approach temperature,
The pressure drop on the feed water side
Temperature side across the heater
The approach temperature (DCA)
Use the following data sheet Table 8-3 for compilation of data of HP heaters (as an example, if
the plant has three HP heaters HPH-5, HPH-6 & HPH-7)
Table 8-3: Data sheet for HP heaters
Unit HPH 5 HPH 6 HPH 7
Design Actual Design Actual Design Actual
Feed water entering temp. OC
Feed water entering press. kg/cm2g
Feed water leaving temp. OC
Feed water leaving press. kg/cm2
HPH shell press. kg/cm2
HPH extraction temp. ppm
HPH extraction press. kg/cm2
HPH drain temp. OC
Feed water diff. pressure. kg/cm2
While collecting the heater wise parameters, collect the following
Unit load MW
Main steam pressure
Main steam temperature
Feed water flow
Super heater attemperation flow
Reheater attemperation flow
Boiler feed pump discharge pressure
HPH levels
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Condenser vacuum
Barometric pressure
After the collecting the above data, evaluate the following
Terminal temperature difference TTD
Heater drain cooler approach temperature difference DCA
Temperature rise across TR
Terminal temperature difference, TTD = tsat- tfw out
where:
Drain cooler approach temperature, DCA inOC = tdrain- tfw out
where:
Temperature raise TR = tfw in - tfw out
where:
While conducting the energy audit of HP heaters, check for the following, the above three
performance parameters are deviating from the design and actual raise in feed water
temperature is low:
Excessive make up
Poor water heater performance
High terminal temperature difference
Excessive venting (worn vents, altered set point, vent malfunctioning)
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High water level (tube leaks, improper setting)
Header partition leaks
Non condensable gases on shell side
Excessive tube bundle pressure drop (excessive number of tubes plugged, tubes folded
internally)
High drain cooler approach temperature
Drain cooler inlet not submerged
Low water level (improper setting, excessive FW heater drain bypass improper setting
/bypass valve left open/bypass malfunctioning/bypass valve leaks)
Excessive tube bundle pressure drop (excessive number of tubes plugged/tubes folded
internally)
Feed water heater bypassed
FW heater bypass valve leaking
Similar approach shall be followed for LP heaters. Based on the above, if the HP heaters
performance is poor, then additional load on economizer can be estimated by using the data
sheet.
8.6.5 Key observations and Analysis
This forms the major component of energy audit system the details should be given in details
pertaining to the section mentioned in the earlier sections:
High Reheater Spray
Superheater Spray
Deviation from Design parameter Main steam Pressure, temperature, flow
Condenser Vacuum.