maintenance report
TRANSCRIPT
(December 15, 2009 to March 31, 2010)
Submitted To:Mr. Mushtaq Ahmad Principal Engineer (Mechanical) Block-II
Submitted by: Muhammad Arshad Mukhtar Trainee Engineer (Mechanical) Block-II
CONTENTSSummary 4
CHAPTER 1:
Maintenance Overview
1.1 What is Maintenance?? 8
1.2 Types of Maintenance 8
Preventive Maintenance
Breakdown Maintenance
Scheduled Maintenance
Predictive Maintenance
1.3 Responsibilities of Maintenance Engineer (Mechanical) 10
1.4 Responsibilities of Maintenance department 11
1. Routine PMs
2. Planed outages
3. Forced outages 4. Calibration
1.5 Objectives and targets of Mechanical Maintenance Block-II 13
1.6 Maintenance activities of Gas turbine 13
1. Combustion Inspection (CI)
2. Hot gas path inspection (HGPI)
3. Major overhauling (MOH)
1.7 Maintenance activities of Steam turbine 13
1. Minor overhauling
2. Major overhauling
2
1.8 Data Sheet operating Hours 14
CHAPTER 2:
Case Studies
2.1 Case Study No 1
Washing of GT-8 20
2.2 Case Study No 2
Condenser Tubes Leakage 26
2.3 Case Study No 3
Gear Box Replacement 30
2.4 Case Study No 4
Booster Air Compressor 35
2.5 Case Study No 5
High Differential Pressure Problem 39
2.6 Case Study No 6
Circulating Water Pump 42
2.7 Case Study No 7
Hydraulic Power System 49
2.8 Case Study No 8
Atomizing Air System 75
3
Summary
“All activities involved in keeping system’s equipment working are termed as
maintenance. Objective of the maintenance is to maintain the system capability &
minimize total costs.”
I was deputed in Mechanical maintenance Block II. Here I have spent about four
months. During this period major emphasis has been given to the observation of the
maintenance activities performed by the maintenance staff which includes attending
to the PMs as well as break-down maintenance. The aim has been to get familiarized
with the mechanics of the hardware used at the plant, their maintenance procedures,
manpower handling and utilization, documentation and planning activities. CI
activities were also observed during this tenure. Besides this different tasks were
performed which were assigned by seniors.
Case Studies
The following case studies were done during this tenure.
1. Washing of GT 5-8
2. Condenser Tubes Leakage
3. Gear Box Replacement
4. Booster Air Compressor
5. High Differential Pressure Problem
6. Circulating Water Pump
7. Hydraulic Power System
8. Atomizing Air System
4
Presentations
I have also given training to the mechanical staff on the following topics.
1. Mechanical power transmission
2. GT-5 spread problem
3. Hydraulic power pack system
4. Water treatment system
5. Centrifugal Pumps
Systems
Line tracing of the following systems has been completed:
1. Fuel Oil forwarding & filtration Skid GT-5-8
2. Fuel oil system GT 5-8
3. Lube Oil System GT 5-8
4. Gas Skid GT 5-8
5. Cooling and sealing air system GT 5-8
6. Atomizing Air System GT 5-8
7. Turbine cooling water system GT 5-8
8. Lube Oil System ST 11-12
Challenges/faults to KB2MM during Training
During this period I have seen so many problems which were rectified by mechanical
section. The following were the major problems which were list down.
1. HP feed water pump jam due to damaged balance sleeve
2. Repairing of gear box
3. Tripping of GT 7 due to hydraulic oil filter leakage
4. HP feed water pump vibration high due to bearings damage
5. Leakage of water from closed cooling water of GT cooling system (cooler was
leak) so it was isolated.
6. Atomizing air temp remained high at GT-5
7. Auxiliary hydraulic oil pump running continuously
5
8. Replacement of bleed v/v NO 3 at GT- 6
9. Water cooler cleaning , vacuum improvement
10. Flue gas leakage from broken bolt after CI
11. GT- 8 fire , Manual shut down of machine (due to electrical short circuiting)
12. High spread problem at GT 5
13. Fuel shortage Problem
14. Leakage from flow divider junction box
15. Fire on GT 6. tripping of M/c but not fond any reason
16. STG 11 trip due to HP drum level high
17. GT 8,7,5 tripping with following indication
18. heavy skid trouble
19. low liquid fuel pressure trip
20. heavy fuel pressure low
21. HSD down stem differential pressure high
22. STG 12 trip due to tripping of GT 7,8
23. Vacuum pump jam due to impeller damage
24. Acid Unloading pump (Centrifugal pump impeller replacement…..Teflon)
25. Main fuel oil pump repairing
26. Neutralization pump
27. BSDG Compressor piston rings changed
28. Gear box repairing (wheel rubbing with upper casing)
29. LP Evaporator (leakage)
30. Inspection of lifting tackle
a. Chain Block
b. D Shackle
c. Eye Bolt
d. Sling Wire
e. Sling wire Endless
f. Polyester Sling
g. Beam Trolley
31. Replacement of 2nd stage nozzle during CI
32. Replacement of torque converter during CI Due to Seizing
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Modifications
Some systems were modified for efficiency improvement.
1. New line was installed at booster air compressor
2. HRSG Isolation valve
3. Sump tank modification
7
1.1 What is Maintenance??
Maintenance may be defined as, "All actions which have the objective of retaining or
restoring an item in or to a state in which it can perform its required function. The
actions include the combination of all technical and corresponding administrative,
managerial, and supervision actions."
1.2 Types of Maintenance
(a) Preventive Maintenance
(b) Breakdown Maintenance
(c) Scheduled Maintenance
(d) Predictive Maintenance
Preventive Maintenance
A system of scheduled, planned or preventive maintenance tries to minimize the
problems of breakdown maintenance. It is a stitch in time procedure.
It locates weak spots (such as bearing surfaces, parts under excessive vibrations, etc.)
in all equipments, provides them regular inspection and minor repairs there by
reducing the danger of unanticipated breakdown. The underlying principle of
preventive maintenance is that prevention is better than cure.
Objectives of Preventive Maintenance
(i) To minimize the possibility of unanticipated production interruption or major
breakdown by locating or uncovering any condition which may lead to it?
(ii) To make machine tools always available and ready for use.
(iii) To maintain the optimum productive efficiency of the machine tools.
(iv) To maintain the operational accuracy of the machine tools.
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(v) To reduce the work content of maintenance jobs.
(vi) To achieve maximum production at minimum repair cost.
(vii) To ensure safety of life and limb of the machine tool operators.
Scheduled Maintenance
Scheduled maintenance is a stitch in time procedure aimed at avoiding breakdowns.
Breakdowns can be dangerous to life and as far as possible should be minimized.
Scheduled maintenance practice incorporates; inspection, lubrication, repair and
overhaul of certain equipments which if neglected can result in breakdown.
Inspection, lubrication, servicing of these equipments are included in the
predetermined schedule. Scheduled maintenance practice is generally followed for
overhauling of machines; cleaning of water and other tanks, etc.
Predictive Maintenance
In predictive maintenance, equipment conditions are measured periodically or on a
continuous basis and this enable maintenance men to take a timely action such as
equipment adjustments, repair or overhaul. Predictive maintenance extends the
service life of equipment without fear of failure.
It is comparatively a newer maintenance technique. It makes use of human senses or
other sensitive instruments such as Audio gauges, Vibration analyzers, Amplitude
meters, and Pressure, temperature and resistance strain gauges to predict troubles
before the equipment fails.
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Breakdown Maintenance
Breakdown maintenance implies that repairs are made after the equipment is out of
order and it cannot perform its normal function any longer, an electric motor of a
machine tool will not start, a belt is broken.
Under such conditions, operation department calls on the maintenance department to
rectify the defect. The maintenance department checks into the fault and makes the
necessary repairs. After removing the fault, maintenance engineers do not attend the
equipment again until another failure or breakdown occurs.
Causes of Equipment Breakdown
Failure to replace worn out parts.
Lack of lubrication.
Neglected cooling system.
Indifference towards minor faults.
External factors (such as too low or too high line voltage, wrong fuel, etc.)
Indifference towards equipment vibrations, unusual sounds coming out of the
rotating machinery, equipment getting too much heated up.
1.3 Responsibilities of Maintenance Engineer (Mechanical)
Following are the responsibilities of Mechanical Maintenance Engineer.
1. Responsible for all mechanical maintenance and overhauling activities of
respective Block.
2. Provide supervision, leadership, specialist knowledge and expertise to his team for
mechanical maintenance and fault finding/trouble shooting.
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3. Identify, evaluate, plan and assign / execute preventive & corrective maintenance
jobs as per OEM recommendations.
4. Ensure timely response of job cards raised to his section.
5. Establish and maintain good working relations and coordination with Operation and
other sections.
6. Monitor stores stock to ensure availability of minimum quantity of required spare
parts.
7. Initiate spare parts requisition timely for the procurement of spare parts/material.
8. Act as Accepter / Issuer as per KAPCO Safety Rules subject to his nomination /
authorization.
9. Ensure implementation of KAPCO Safety Rules by his team.
10. Assist PE Mechanical in preparation and control of Sectional Budget.
11. Assist PE Mechanical in preparation of specifications, evaluation of bids, follow
up and execution of CAPEX & MRR projects, etc.
12. Assist PE Mechanical in appropriate management of resources and cost effective
maintenance.
13. Train and develop staff to improve their technical knowledge, commercial
awareness.
14. Implement IMS in his area of responsibilities.
15. Perform any other relevant task assigned by his seniors.
1.4 Responsibilities of Maintenance department:
The following are the responsibilities of Mechanical Maintenance department.
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1. Routine PMs
2. Planed outages
3. Forced outages
4. Calibration
1. ROUTINE PMs
Receiving of PMs/Work Orders
Daily Planning
Receiving of Safety Documents
Assigning of Work
Execution of Work
Closing of Job Cards
2. PLANED OUTAGES
Receiving of Outage Plan
Pre-Outage Meetings
Receiving of Work Orders
Daily Planning
Obtaining Safety Documents
Daily Progress Meeting
Assigning of Work
Execution of Work
Filling of Protocols
Closing of Outage Job Cards
Submission of Outage Maintenance Report
3. FORCED OUTAGES
Communication of Problem
Arrival of Maintenance Team at Site
Commencement of Work
Completion of Work
Closing of Job Cards
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4. CALIBRATION
Receiving of work orders
Execution of Calibration
Closing of jobs
Calibration Record
Storage and Record of Tools/Instruments
1.5 Objectives and targets of Mechanical Maintenance Block-II
The objectives and targets of the mechanical section are
1. To reduce forced outage of block II units due to Mechanical fault from
135GWH to 122 GWH.
2. To reduce No of trips of maintenance Block II units from 6 to 5 due to
Mechanical.
3. To maintain the thermal efficiency of maintenance Block II units above 42.30
%.
4. To limit overdue PM jobs of Mechanical section to 6 %.
5. To ensure the manpower utilization at least 78 % of Mechanical II section.
1.6 Maintenance activities of Gas turbine
1. Combustion Inspection (CI)
2. Hot gas path inspection (HGPI)
3. Major overhauling (MOH)
1.7 Maintenance activities of Steam turbine
1. Minor overhauling
2. Major overhauling
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1.8 Data Sheet operating Hours
Unit Maintenance EOH Duration (Days)
5-8 Combustion
Inspection
7500 10
Hot Gas Path
Inspection
22500 45
Mojor
Overhauling
45000 45
11-12 Minor
Overhauling
25000 10
Major
Overhauling
50000 45
Activities during CI
The following are the maintenance of combustion inspection.
Preparation and removal of turbine compartment roof.
Removal of liquid fuel lines
Removal of atomizing air lines
Removal of gas fuel lines
Removal of liquid fuel check valves.
Removal of fuel nozzles
Unbolt and open up combustion chamber covers
Remove x-fire tube retainers and x-fire tubes
Removal of combustion liners & Flow sleeves
Unbolt and remove transition pieces.
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Removal of 11th stage cooling sealing air Lines extraction valves & conduit.
Place mechanical support jacks under unit casings
Removal of turbine casing bolts & upper half first stage nozzle eccentric pin
Removal of upper half turbine casing
Take turbine clearances check. Fill protocol
Remove lower half second and third stage nozzle radial retaining pins &
plugs.
Remove lower half second and third stage nozzle segments
Remove upper half second and third stage nozzle radial retaining pins & plugs
Remove upper half second and third stage nozzle segments
Stage nozzle segments check valves
Dismantling & cleaning of fuel nozzles & fill protocols
Assembly and bench test fuel nozzle & check valve assembly (pressure test)
replacement of fuel nozzle & check valve assembly parts if required
Inspect combustion liners & fill protocols
Inspect x-fire tubes & retainers & fill protocols
Inspect transition pieces & fill protocols
Inspect combustion chamber flow sleeve & fill protocols
Inspect combustion wrapper & fill protocols
Inspect first stage nozzle crackness and fill protocol.
Repair/ welding of turning vanes.
Cleaning of t/b casing faces, taping, bolts, and segment slit & pins holes etc.
Activities during MOH
The following are the maintenance activities during MOH.
Removal of accessory gear coupling, checking of acc gear alignment, and
installation of rotating fixture.
Preparation and removal of three pieces of turbine compartment roof
Removal of exhaust and inlet duct access panels
Removal of turbine compartment side panels
Preparation and removal of t/b compartment roof.
Removal of liquid fuel lines
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Removal of atomizing air lines
Removal of gas fuel lines
Removals of liquid fuel check valves.
Removal of fuel nozzles
Unbolt and open up combustion chamber covers
Remove x-fire tube retainers and x-fire tubes
Removal of combustion liners & Flow sleeves
Unbolt and remove transition pieces.
Removal of 11th stage cooling sealing air Lines extraction valves & conduit.
Place mechanical support jacks under unit casings
Removal of turbine casing bolts & upper half first stage nozzle eccentric pin
Removal of upper half turbine casing
Take turbine clearances check. Fill protocol
Remove lower half second and third stage nozzle radial retaining pins &
plugs.
Remove lower half second and third stage nozzle segments
Remove upper half second and third stage nozzle radial retaining pins & plugs
Remove upper half second and third stage nozzle segments
Stage nozzle segments check valves
Dismantling & cleaning of fuel nozzles & fill protocols
Assembly and bench test fuel nozzle & check valve assembly (pressure test)
replacement of fuel nozzle & check valve assembly parts if required
Inspect combustion liners & fill protocols
Inspect x-fire tubes & retainers & fill protocols
Inspect transition pieces & fill protocols
Inspect combustion chamber flow sleeve & fill protocols
Inspect combustion wrapper & fill protocols
Inspect first stage nozzle crackness and fill protocol.
Repair/ welding of turning vanes.
Cleaning of t/b casing faces, taping, bolts, and segment slit & pins holes etc.
Unbolt and remove forward and after compressor casing
Unbolt and remove upper half inlet casing (bell mouth)
Unbolting & remove compressor discharge casing,
Remove upper half exhaust diffuser, exhaust hood and air cone
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Remove lower half first stage nozzle eccentric pin & horizontal nozzle clamps.
Remove lower half first stage nozzle
Remove the upper half of the 1st stage nozzle support ring and cleaning
Remove the inner compressor discharge casing
Remove upper half 2nd & third stage nozzle retaining pins & plug
Remove upper half 2nd & third stage nozzle segments
Checking rotor thrust and compressor clearances.
Take initial readings of IGV, noting backlash, bush clearances and fill
protocol
Remove upper half #1, #2 and #3 bearing housing& bearing upper half
Take initial clearances for bearing #1,2,3 and their labyrinth seals clearances
Remove lower half 2nd & third stage nozzle segments
Lube oil supply line leak test near bearing connection
Remove turbine side load coupling bolts
Removal of intermediate coupling bolts
Remove thrust bearing loaded and unloaded
Remove compressor rotor
Removal of lower half IGVS from casing
Removal of upper half IGVS from casing
Cleaning of IGVS before inspection
NDT & inspect inlet guide vanes rack ring, segments spacer gears etc.
Remove turbine rotor
Removal of turbine blades
Inspect first, second and third stage turbine buckets installation
NDT test on the turbine rotor (especially dovetail) + compressor rotor
NDT test on the compressor rotor
Installation of new turbine blades
Remove lower half bearing 2 &3
Cleaning of turbine casing upper / lower halves and replacement of insulation
boxes of 2nd & 3rd stage if required.
Cleaning of compressor, wrapper and exhaust casings faces, holes, taping and
cleaning of bolts, pins etc
Inspect bearings, for any defects / NDT
Cleaning and inspection of first stage nozzle support ring.
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Cleaning and inspection/ adjustment of the compressor rotor.
Compressor stator upper half backlash repair by inserting shims
Compressor stator upper half inspection and filling protocol
Compressor stator lower half backlash repair by inserting shims
Compressor stator lower half inspection and filling protocol
Inspection / removal / cleaning of shrouds blocks (upper and lower halves)
Inspect first, second and third stage nozzles vanes and diaphragms.
Make first stage nozzle ellipticity check
Major Overhauling Of Steam Turbine
The following are the maintenance activities during major overhauling.
Acoustical package removal, turbine enclosure fan supply to be disconnected
and its removal
Cladding and insulation removal of control valves
Scaffolding to be erected around the HP casing (left side).
Removal of coupling safe guard
Opening of coupling bolts protection plates
Steam turbine/generator coupling bolts removal with the help of hydraulic
machine
Removal of generator bearing's turbine side and exciter side bearing's exciter
side oil deflector
Steam turbine/generator alignment checking
Stop valves removal
Control valves removal
Balancing check of casing
LP casing rupturing diaphragms removal
Hp loop pipe upper removal
Motor & turning gear removal
Inlet & outlet bearings pedestal cover removal
Thrust bearing clearance checking
Removal of exhaust bearing upper half liner
Exhaust bearing clearance checking
Disassembly of thrust bearing
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Rotor displacement checking
Opening of gland steam supply and return pipe flanges
Insertion of shims under lower HP casing left and right sides
Casing joint plane unscrew
Upper casing removal
Casing joint plane studs removal
1/2 upper diaphragms & sealing boxes removal
Radial clearances (l-r) and axial clearances checking
Bottom radial clearances checking
Rotor removal
1/2 lower diaphragms and sealing removal
Lower halves of inlet and exhaust bearings removal
Cleaning by sand blasting (gland sealing/diaphragms)
Rotor expertise (Mp testing)
Journal/thrust bearings expertise (ultrasonic and NDT)
Turning gear expertise
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Washing of GT-8
Introduction
Gas turbine performance is affected by the deposits on compressor and turbine blades
during operation. Due to this loss of power and fuel consumption may increases.
Compressor performance decreases due to reduced air flow, lower compressor
efficiency and lower compressor pressure ratio. It may be due to ingested air which
may contains dust, sand, hydrocarbons, fumes and salts. The deposits at turbine blades
occur as a result of type and treatment of fuel being burned. Therefore to increase the
efficiency of turbine, washing of gas turbine is required.
Washing
Washing of gas turbine is done with washing liquid to remove the deposits at turbine
blades and solid air particles from compressor blades. Washing is carried out
according to the OEM recommendation. Normally to increase the efficiency of gas
turbine, compressor and turbine blades washing is recommended.
Turbine Washing:
Turbine washing is carried out after every 250 EOH of machine at FO. If the
machine is running on gas then there is no need for carrying out the washing as the
gas is a clean fuel with negligible proportion of impurities in it.
Compressor Washing:
Compressor washing is carried out after every 1800-2200 EOH of gas turbine
running at FO. But in normal operation it is carried out after third or fourth Turbine
washing depending on the condition of the IGV’s.
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Detergent
For compressor washing detergent TURCO 5884 is used as a washing liquid. TURCO
5884 is concentrated liquid cleaner which is effective in removal of oil, salt and solid
deposits from compressor blades.
Properties
Ash free
Readily miscible with water
Typically very low in phenol, chloride and sulpher
Determination of Washing Liquid
Washing liquid is mixed with water at 80°C in the ratio of 1:4. The quantity of
washing liquid used normally is 100 liters in the washing liquid reservoir and
according to the ratio water is added up to 400 liters. Usually during compressor
washing 40-50 liters of the detergent is used.
Washing Requirements
Washing water is heated up to 80°C in the washing tank and the turbine wheel space
should be less than 150°C (difference of temperature between turbine and washing
liquid < 67°C, called spread). If the spread is greater than 67°C, then thermal stresses
will be caused in the turbine blades.
Atomizing air discharge valve located on atomizing air manifold in GT compartment
should close.
Booster air compressor breaker should rack out.
22
Major components of washing System
Washing Pump:
Washing pump is installed with the washing tank for pumping the water in the
washing nozzles. The specifications of pump are:
Type: Centrifugal Pump
Flow rate: 6 liter/sec
Power of motor: 12 KW
Rpm: 2900
Liquid Detergent Washing Pump:
The pump is installed with the washing tank for pumping the liquid detergent
in the washing nozzles. The specifications of pump are:
Type: Centrifugal Pump
Flow rate: 1.5 liter/sec
Rpm: 2900
Washing Tank
A tank with a capacity of 20 ton is used as a reservoir.
Arrangement of Nozzles
During turbine washing the water is sprayed onto the turbine blades trough the
nozzles provided for atomizing air. At the compressor side eight fixed nozzles are
provided for compressor washing.
Drainage
There are total 23 drains of water provided with a common header.
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PROCEDURE
Compressor Washing
The Gas turbine is desynchronized about six to eight hours prior to washing activity.
Washing speed of gas turbine is 18 %. For this purpose water is sprayed through eight
nozzles. The inlet guide vanes and inlet dampers are closed as the machine is on
turning gear, so if the rotor temperature does not drop then the crank start is given to
lower the rotor temperature.
Compressor washing is being started by using detergent TURCO 5884 by giving
washing start. Washing pump is started for 5 mints. After that liquid detergent
washing pump is started and washing is done by mixing of water and detergent. After
this again only water pump is started for five mints to remove the detergent from
compressor blades. Then give shut down command, both detergent and washing pump
will stop and machine will remain at stand still speed for 15 mints for soaking
purpose.
Now again give the washing start to machine and rinse only with water for 15 mint.
Then we have stopped the pump but machine remain at washing speed for turbine
blades washing.
Turbine Washing
Turbine washing is carried out in three steps;
1. First turbine blade washing for 25 min.
2. Soaking time of 45 min.
3. Second turbine blade washing for 25 min.
Machine is given the washing start bypassing the ignition. During washing the turbine
speed is nearly 580 rpm. The water is injected with the help of washing pump at about
6 liters/sec for 25 min.
Then the turbine is kept at zero rpm for giving a soaking time of 45 min so that the
deposited sulpher and other complex salts can be easily removed during second
turbine blade washing. Also the maintenance section can work during the standstill
position of the shaft. During this time period maintenance section can perform its
duty.
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Maintenance activities during soaking time
Inspection of compressor inlet and IGVs.
Inspection of turbine exhaust end after clearance report by the chemist.
Manual operation of compressor bleed valve.
Changing of lube oil of main fuel oil pump.
Change of in service HP filter with cleaned ones. HP filter #2 filter elements
were changed.
Inspection of air intake filter house.
Booster air compressor was replaced. Technician removed its coupling with
the help of puller and then put on at other booster compressor which was
installed.
After completion of all inspections and soaking time machine again started by
giving washing start for 25 mints only with water. At the end of completion of
washing GT put on turning gear.
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Condenser:
In thermal power plants, the primary purpose of a surface condenser is
to condense the exhaust steam from a steam turbine to obtain
maximum efficiency and also to convert the turbine exhaust steam into pure water so
that it may be reused in the steam generator or boiler as boiler feed water. This
condenser is just like a shell and tube heat exchanger. Water drops down and collects
in hot well from where water is extracted through condensate extraction pump and
discharged to the feed water tank.
Condenser view (General)
The condenser view which has been shown above is not a view of STG-12 condenser,
but the working principle is same. The steam turbine itself is a device to convert
the heat in steam to mechanical power. The difference between the heat of steam per
unit weight at the inlet to the turbine and the heat of steam per unit weight at the outlet
to the turbine represents the heat which is converted to mechanical power. Therefore,
the more the conversion of heat per pound or kilogram of steam to mechanical power
in the turbine, the better is its efficiency. By condensing the exhaust steam of a
turbine at a pressure below atmospheric pressure, the steam pressure drop between the
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inlet and exhaust of the turbine is increased, which increases the amount of heat
available for conversion to mechanical power. Most of the heat liberated due
to condensation of the exhaust steam is carried away by the cooling medium (water)
used by the surface condenser.
Main Functions of Condenser
Condensation of bled steam from the LP turbine.
Water reserve in the condenser hot well.
Normal and emergency make-up water in the circuit.
Collection of liquid drain returns.
Condenser Tubes Leakage
STG 12 condenser tubes were leaking. To attend this leakage STG-12 was on forced
outage.
Tubes Technical data
Number of tubes per condenser 12532
Tube size, outer dia * wall thickness (24 * 1) mm
Tubes Leakage Observation
Tubes leakage is observed through variation in the chemistry of demi water. In each
shift once a time sample is taken from condenser. Chemical section analyzes its ph
value and performs all other necessary tests. If its chemistry is disturbed then it is to
be thought that some condenser tubes are leaking.
Effect of Tubes Leakage
If tubes are leaking then cooling water will mix with condensate water. This mixture
of water will go into the feed water tank, HRSG and Steam turbine. This water will
corrode the HP, LP drum and tubes in HRSG.
Besides this it will also effect on steam turbine blades. There will be chance of
erosion and corrosion on steam turbine blades which will reduce the efficiency of
steam turbine.
Methods of Leakage Detection
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Here three methods are used for identification of leakage tubes.
1. Filling of condenser
2. Through candle flame
3. By applying polythene
Procedure
Today maintenance team used first method. First of all condenser was filled up with
demi water. Condenser manholes were opened. When condenser was fully filled up
with water then it was observed that water start to flow outside from some tubes.
All tubes were inspected one by one. The tube in which there was leakage, plugged
from one side with copper plug. Then water starts to flow on other side and was
inspected that which tubes leaking, same tube on other side was also plugged with
copper plug. At the end total six tubes were plugged. At the end all the tubes counted
which were plugged. Whenever tubes are plugged, it will be counted. Maximum 5 %
tubes of each tube bundle can be plugged. When condenser efficiency decreases and
maximum tubes are plugged then condenser is replaced with new one.
Condenser Tubes Plugged Status STG-12
East side top 14
East side bottom 142
West side top 24
West side bottom 150
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Cooling Tower
Cooling towers operate on the principle of removing heat from water to an air stream
by evaporating a small portion of water flow.
The induced draught cooling tower is manufactured with high quality material and
should retain their original performance for many years. Therefore high attention is
given for its maintenance.
Components of cooling tower
Each cooling tower consists of the following components
cold water basin
ventilation group
6 cells casing
In each cell, an interior equipment
Drift eliminator
Water distribution pipes
Filling system
Ventilation Group
Each ventilation group comprises of the following
1. fan
2. reducer
3. motor
4. transmission system
Fan
Each cell of tower is fitted with an axial flow fan type. The fan blades slope can be
adjusted when fan is stopped. The blades are made of fiberglass reinforced polyester.
They are statically balanced. The high efficiency propeller type designed and a tip
speed not exceeding 60 m/s assure a low operation noise and a minimum of vibration
effects.
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Gear box
The fans are driven via right angle double reduction gear boxes of the bevel spiral
pattern.
The gearboxes are mounted centrally within the fan case on a common structural steel
weldment and the fan hub is mounted directly upon the vertical low speed shaft.
Gear Box
Gear box replacement of cooling tower fan (11 CRF 302AF)
Cooling tower fan of unit 11 was tripped due to some reasons then it was requested to
maintenance section to cause of failure of cooling tower fan. Maintenance team
inspected that gears were rubbing with gear box body due to large play between
couplings. At the end it was decided to replace the gear box with refurbished one.
Procedure
Following steps are used for replacement of gear box.
Installation of scaffolding.
Lube oil was drained and level switch removed.
U-clamp bolts were removed.
Five blades of fan were removed one by one with the help of chain block.
Fan hub plate removed and put on side by keeping it up with overhead crane
and chain block.
Four bolts of gear box were replaced.
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Six bolts of flexible coupling (coupling spacer) were removed. Here coupling
membrane is used for flexibility.
Coupling Membrane
Small fan which is shaft driven is used for gear box cooling was also removed.
Then gear box was put outside with overhead crane.
Coupling was removed from old gear box with the help of puller and installed
at refurbished gear box.
Refurbished gear box was installed.
Clearance of coupling membrane checked with vernier caliper. It was same in
all directions.
Gear box oil filled. 50 liter is used.
Hub plate and blades were installed.
Two blades tips were damaged, instead of these refurbished blades were
installed.
Blade angle was corrected with degree set. Blade angle is 19.6
U-clamp bolts were tightened.
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Failure of CT fan
After completion of gear box replacement, CT fan was put into operation. As soon as
it was put into operation it was again tripped at high vibration. Reasons of failure may
be
Shafts misalignment
Blades angle
Bearing damage
But all these were correct. So it was decided to again install the two blades which
were replaced. After this problem was solved. It was occur due to unbalancing of
blades weights.
34
35
Booster Air Compressor
Booster air compressor is a compact, rotary lobe type axial flow compressor. The
meshing of two screw type rotors synchronized by timing gears provides controlled
compression of the air for maximum efficiency.
Operating Principle
Compression is effected by the main and gate rotors meshing enclosed in the housing.
The timing gears maintain close rotor clearance. The rotors do not touch each other,
the housing, or the bearing carrier. Although clearances are small, lubrication in the
compression chamber is not required, insuring oil free air delivery.
Main rotor Gate rotor
The compression cycle begins as the rotors unmesh at the inlet port. Air is drawn into
rotor cavities, trapped, and compressed by reducing cavities as rotation continues.
When proper compression is made, the cavities discharge port, completing the cycle.
The cycle occurs twice each revolution and is continuous.
36
Description
Two heavy duty angular contact ball bearing are used on each rotor shaft. Rotation is
counter clockwise viewing the drive shaft. The main rotor runs twice the speed of the
gate rotor.
Bearing housing Gear Pinion
Maintenance
Blower efficiency depends on the quality of maintenance.
Gears and gear end bearings are oil splash lubricated. Gear case oil level should be
daily checked. Change oil every 100 to 1000 hours of operation. Inlet end bearings are
grease lubricated. Regrease bearings every 250 hours of operation.
Common causes of blower failure
Poor air filter maintenance
Inadequate lubrication
Discharge pressure above blower rating
Blower speed below minimum rating
Blower speed too low for discharge pressure
Shims wear and tear
37
Repairing Procedure
Compressor was dismantled. All parts were removed one by one. It was observed that
gaskets were leak. Actually shims are used here according to manufacture design but
last time gaskets were used due to unavailability of shims. Now shims will be
installed. Repairing is still under process.
38
39
High Differential Pressure Problem
Today GT-6 was tripped due to high ∆P. Indication turbine inlet pressure drop was
appeared and machine put to normal shut down.
∆P is measured in Pascal.
1300 Pascal alarm
1800 Pascal normal shutdown
This differential pressure was increased due to foggy weather. In foggy weather due
to moisture, filters are choked. Due to presence of dust particles, moistures are mixed
with it and it becomes like a mud and filters are choked.
Remedy
To prevent from this situation prefilters are applied so that moistures may not go
inside filter house.
Prefilters trap the moistures contents. Thus filters are prevented from choking.
∆P of block II
Today ∆P of GT 5-8 was recoded as follows.
GT-5 725 Pa
GT-6 › 1800 Pa
GT-7 512 Pa
GT-8 500 Pa
It is to be thought that why this problem only at GT 6 while filters of remaining GT,s
were also replaced at the same time. It was because of more operation time than
others. It was operated about one month more than other.
After application of pre filters GT was given start. But at 60 % it was again on normal
shut down. After some time it was given two crank starts to dry the wet filters. Then
machine was again started but at 72 % it laid down on normal shutdown due to torque
40
converter limit switch problem. Indication torque converter drain valve trouble
appeared. Then instruments section adjusted its limit switch. Then GT was started.
Initially its ∆P increase up to 1650 Pa at 100 % speed and then it begin to decrease
when it was synchronized. It was observed that there was 100 Pa difference between
outer and inner gauges. At 20 MW it was 1350 Pa.
Next day normal operation was carried out. Weather condition was better. But in
night shift it was again normal shut down due to high ∆P.
In morning booster air compressor was modified. New line installed. It was given
start but machine take normal shut down at 98 %. Three time it was started but
pressure drop was high. Some prefilters were removed and instrument section
checked its manual cleaning. Machine was started. Initially differential pressure was
high so it was put on FSNL for 15 mints. After that gradually load was increased by
inspecting its ∆P. after that machine was put on temperature control. At temperature
control mode IGVs were modulated. By closing IGVs back pressure was increased
and thus differential pressure decreased. Load was increased and GT took maximum
load 92 MW.
41
42
Circulating Water Pump
It is a tubular casing pump with semi axial impeller. It is a single stage centrifugal
type pump. It has a propeller type impeller. This pump is used to circulate the water
from cooling tower to condenser where steam is condensed.
Pump construction
The main components of the pump are
Inlet Nozzle
Diffuser
Riser Pipes
Discharge Elbow
Pump Motor
Lantern
After having passed the inlet chamber and the inlet nozzle, the fluid pumped flows
through the impeller and diffuser to discharge nozzle of the discharge elbow.
43
Inlet chamber
Vertical tubular casing pumps are high specific speed pumps and this pump type
reacts immediately to irregularities and disturbances in the approach flow. Such
disturbances lead to premature wear of bearing due to unsteady running of the pump
(vibration, cavitations) and secondly they cause a drop of the pump out put and
efficiency.
In all cases it is important to take the necessary steps to prevent foreign matter from
entering the pump with the flow, because these particles normally destroy the guide
bearings, damage the impeller and possibly damage other components as well.
Shaft bearing
The shafting of the pump is supported in plain bearings. These bearings are flooded
by the fluid pump. Dry running for a limited amount of time (not more than one
minute), such as is often the case during start-up of the unit, does not damage the set.
Journal bearing
Oil lubricated thrust and journal bearings
The purpose of the bearing is to absorb the axial thrust produced by the pump while it
is running the parts and to provide the top guidance for the shaft in a radial sense. By
installing the pump in an upright position, the parts of the thrust and journal bearing s
can be fully submerged in an oil bath. The heat generated during operation is
eliminated by the cooler which is also submerged in the oil bath.
44
Bearing housing
General operating data
Operating parameters Normal operating Emergency operating
Medium pumped Cooling water
Medium temperature Approx 30 C
Density 996 kg/m
Flow 8360 m/h 11700 m/h
Head 17.2 m 13.25 m
Power 462 kw 498 kw
Speed 594 1/min
Direction of speed C.W from top
Power supply E-Motor (550 kw)
45
Pump problem
During normal operation it was observed that there was abnormal sound from pump.
After that pump tripped at high vibration. So job card was raised and informed to
mechanical section for inspection. After inspection it was decided to open the open
for its complete inspection.
Repairing procedure
After taken permit the pump was dismantled as follows.
First of all pump coupling was removed.
After removal of coupling eclectic motor was removed with the help of crane.
Over flow line was removed.
By removing the motor, bolts of motor stool and pump elbow were removed.
Pump outlet pipe bolts were tightened to give clearance for the removal of
pump elbow.
Pump elbow was removed by tilting the motor stool.
Then motor stool was removed with the help of crane and put it on side.
Bearing lantern was removed.
Then pump body was removed with the help of two cranes and shifted to
turbine hall.
Pump
Typical weights
Weight of the different components was noted as given below.
46
Component Weight (Manual) Weight (crane)
Motor 13.5 12.2
Motor stool 2.7 2.5
Pump 10.7 6
Water filling 3.7 -
Bearing lantern - 2
Inspection of pump
After dismantling pump inspection was carried out. It was observed that bell mouth
was ruptured. Bell mouth SS coating was damage. This coating is welded and bolted.
It was ruptured from welded joint and thus it created abnormal sound.
Shaft bearing was also damage due to which pump tripped at high vibration.
Remedy
After complete inspection it was decided to replace the bell mouth and shaft bearing.
Refurbished bell mouth was installed.
Bell mouth
Besides this impeller blades angles were misalign. Their angles were set manually.
Bolts were loosened then blades adjusted according to marking between A & B.
47
Impeller
Bearing Lantern
It consists of combined journal and thrust bearing. First of all its cooler was removed.
Here heat is exchange through finned tubes. Service water is used for cooling the lube
oil.
It’s cleaning and inspection was carried out.
Gland packing was removed and replaced with new 16 mm. five gland packing was
changed. Bearing upper plate was opened and thrust pads were removed. It was
inspected and all pads were found ok.
After complete inspection of the pump it was again installed. The reverse procedure
was adopted to install it. First of pump casing was put into the basin at inlet cone.
Bearing lantern was installed with the help of crane. Then motor stool but its bolts
were not fitted because elbow was to be placed there it was placed by tilting on one
side then elbow installed & motor stool bolts were tightened. Adjusting nut was
placed. Motor was places on motor stool. Alignment was carried out. Coupling was
installed. Pump was started but it again tripped. It was investigated and found limit
switch problem. Instrument section checked it pump came into operation.
48
49
Hydraulic Power System
Electro hydraulic power pack is designed to generate sufficient power to operate one
by pass and one boiler inlet isolator. All hydraulic components are totally enclosed in
a painted weather proof cabinet.
Power Pack Main Components
1. hydraulic reservoir
2. Motor/pump unit (PU1)
3. Motor/pump unit (PU2)
4. Motor/pump unit (PU3)
5. hydraulic Accumulator (emergency Pressure relief)
6. hydraulic Accumulator (pilot control)
7. Solenoid valve
8. Manifold 91(Boiler inlet isolator solenoid valves)
9. Manifold 92(Bypass isolator solenoid valves)
10. Manifold 93(Bypass isolators emergency pressure relief valves)
11. Pump unloader valve
12. hydraulic cylinders
13. filtration
Hydraulic Reservoir
The hydraulic fluid used in this system is fire-resistant, type
HOUGHTOSAFE 620.
Reservoir Capacity: 200 liter
Its replacement is on yearly basis.
A replaceable filter element is provided in the main fluid return line to the
reservoir.
50
A flexible pronal separator is incorporated into the reservoir venting system.
This maintains a physical barrier at the fluid/air interface so preventing
contamination of the fluid and deterioration of the reservoir lining.
Motor/Pump Unit (PU l)
Electric motor (10 kW & 1440 rpm)
Pump
Variable displacement pressure compensated in line axial piston pump.
Normal working pressure = 140 bar
This pump which only operates when normal movement of the blades is
required.
It also acts as a 'back-up' pump to the motor/pump unit (PU2) in the event of
its failure.
The output of motor/pump units (PU l) is monitored by the power unit
mounted pressure gauge (PG l).
51
Setting of PS-1 (21)
If this switch sense less then 20 bars for 03 sec then “PU-1 Failure” indication
appeared and system shifted to emergency relief mode for opening of BYD.
Motor/Pump Unit (PU 2)
Electric motor (3 kW & 1440 rpm)
Pump Type
Variable displacement pressure compensated in line axial piston
pump.
Normal working pressure = 140 bar
This unit runs continuously when the system is energized, its primary purpose
is to supply hydraulic fluid to charge and maintain the two main linked storage
accumulators (86) and (87).
Its secondary role is to maintain pressure into the hydraulic cylinders holding
the Boiler Inlet blades in either their fully open or fully closed position.
PU2 acts as a 'back-up' to motor/pump unit (PU l).
The output of this pump may be monitored visually by pressure gauge (PG2).
In the event of a pressure loss pressure switch (PS2) will energize the main
motor pump unit (PU l).
This pressure switch will also cause directional valve (30) to operate directing
the output from pump unit (PU l) into the main accumulator circuit ensuring
52
the availability of hydraulic stored energy in the event that emergency venting
is required.
If PU-1 already failed then “PU-2 failure” indication appeared & emergency
relief function starts.
Motor/pump unit (PU3)
Electric motor 1.5 kW & 1440 rpm with fixed displacement radial piston
pump.
Purpose of PU3 is to provide hydraulic pressure to the pilot circuit controlling
the six logic check element valves (56) to (61) via the solenoid valves (34) to
(39).
Output of PU-3 is monitored by PG-3 (20) HNY20CP011 locally & pressure
switches PS-4 (24) and PS-5 (140) used for remote signals.
Normal working pressure = 140bar
if pressure is ≥ 145 bar, PS-4 give the signal for de-energising the solenoid v/v
40 Loader / Un-loader v/v) which will start oil circulation back to reservoir till
sensing the pressure 125 bar and at 125 bar PS-4 give the signal for energising
the solenoid v/v 40 which will stop the circulation and again maintained the
system pressure up to 145 bar.
If system pressure could not rise above 125 bar even after energising the
solenoid v/v 40 then after 30 sec delay, PS-4 gives the alarm signal “Pressure
low” if said alarm / indication did not reset and also pressure further fall up to
90 bar another pressure switch # 40 PS-5) gives the trip signal of indication
“Control Fluid Pressure Low” which cause emergency opening of BYD
through emergency relief mode.
53
Pilot accumulator 88 stored hydraulic energy through this pump.
Hydraulic Accumulators (Emergency pressure relief)
Capacity of accumulator 37.5 L
The accumulator fluid pressure is displayed by pressure gauge (PG 4)
If the gas turbine internal duct pressure exceeding the predetermined safe
maximum level, limit switches on the main frame of the bypass isolator trigger
the release of the stored hydraulic fluid, causing the by pass blades to open
rapidly in a minimum time of 10 seconds.
Drain valves (74 and 75) enable the stored fluid to be drained safely back to
the reservoir for maintenance purposes.
The speed of the emergency venting operation can be regulated using a
combination of flow regulators.
54
Hydraulic Accumulators (Pilot control Circuit)
This accumulator has a capacity of 4 L.
To open the logic elements in the event of emergency venting.
In the event of power or PU 3 failure, this stored fluid causes the by pass
blades to go into the emergency mode.
Its pressure is displayed by pressure gauge (PG 3).
Pump Unloader Valve (40)
Pump unit (PU3) runs continuously charging the pilot control circuit accumulator
(88). At the pre-set charge pressure switch (PS4) is actuated, this causes the solenoid
(P) of valve (40) to de-energize allowing the pumped fluid to flow directly back to the
reservoir.
55
Hydraulic Cylinders
All of the cylinders are double acting tie-rod type of cylinders incorporating
cushioned end stops in both directions. Self-aligning bearings are fitted at both ends.
Provision is made for the attachment of banjo mounted counterbalance valves for hose
failure protection.
Filtration
The cleanliness of the hydraulic fluid is of paramount importance. All three-pressure
lines from the pumps and main manifold return line are filtered to 12 micron
absolute.
56
OPERATING MODES
Interlock System.
As an operating safety precaution, the Boiler Inlet and the By-Pass Isolators are
electrically interlocked to prevent the By-Pass blades from closing unless the Boiler
Inlet blades are open. Conversely the Boiler Inlet blades cannot be closed unless the
By-Pass blades are open.
Manual Operation
A hydraulic hand pump (101) is located within the main hydraulic power unit
enclosure. This allows movement of the Boiler Inlet or the By-Pass Isolator blades in
the event of a loss of electrical power, i.e. during commissioning or major
maintenance. A ball valve (124) allows the operator to select either the Boiler Inlet or
the By-Pass Isolators. As a safety precaution the shut-off valves are fitted with
electrical interlock to isolate the solenoid valves from the control circuit during
manual operation.
Hydraulic Pipe Failure
Pressure retention in the full-bore volumes of both sets of hydraulic cylinders is
critical. In the event of a pipe failure in the hydraulic circuit it is important to prevent
uncontrolled closing of the Bypass Isolator blades as this could cause serious damage
to the blade seals or to the Isolator main frame or the Flap To prevent this happening
each of the hydraulic cylinders for the Bypass Isolator are fitted with two pilot
operated counterbalance valves.(112,113.114 and 115) They function by allowing
fluid flow from the cylinder only when there is a pressure balance between both sides
of the cylinder. If a flexible hose fails then the controlling pressures become
imbalance and the valve shuts, locking the system in a fail-fixed condition.
57
In the case of the Boiler Inlet Isolators the cylinders have to maintain these closed
against the supporting pressure within the cylinders. To ensure these conditions, and
to prevent structural damage in the event of flexible hose failure, counterbalance
valves (130, 131 132 and 133) are fitted directly to the base of each hydraulic
cylinder.
58
Overload Protection
The pressure compensators of pump units (PU1) and (PU2) are set approximately at
110% of the maximum required for any operation. Should any situation arise where
an obstruction jams any blade, the generated torque imposed cannot rise above this
maximum value which is within the design safety factor for the isolators. Also, if the
situation arises where the blade is driven only on one side, again the torque imposed
on the blade is limited by the maximum hydraulic pressure to 110% of the output
from one cylinder.
Pump unit (PU3) is protected by a single relief valve (26) set a a value slightly
higher than the setting of pressure switch (PS4). Relief valves (28) and (29) protect
the system on the annulus side of the By-Pass cylinders, should any fault develop in
the main accumulator circuit Relief valve (27) protects the system controlling the
Boiler Inlet Isolator. In the closed position the Isolator blades must allow duct
pressures exceeding the specified maximum to force them open. In doing so a
situation of pressure intensification occurs as pressure is fed through the
counterbalance valve from the full bore side to the annulus side of the cylinders. The
individual relief valves in the full-bore line allow this excess fluid to drain to the
reservoir. The counterbalance valves attached to the base of the cylinders operating
the Boiler Inlet Isolator are fully compensated.
BY-PASS ISOLATOR
Closed, Pressure Relieving Position
The air barrier fan motor (BF1) is running and the shut off valve (FV1) is open.
Pump unit (PU1) is de-energized; Pump units (PU2) and (PU3) are running
continuously. Limit switches (LS1) and (LS3) are actuated by the By-Pass blades in
their closed position. Limit switches (LS8) and LS10) are actuated by the Boiler Inlet
blades in their open position. (N.B. the limit switches are actually doubled in quantity,
i.e. 2 x LS1, 2 x LS3, 2 x LS8, and 2 x LS10.)
The operation of the limit switches energize solenoid (J), (K), (1) and (M) of
valves (36) to (39) causing the pilot control pressure on logic elements (58) to ~ to
59
decay to zero. Both logic elements open allowing the hydraulic fluid stored in the
main accumulator (86) and (87) to flow via elements (59) and (60) directly to the
annulus area of cylinders (104) to (107). The blades are then held closed against the
duct pressure. The accumulator pressure is pre-set to balance the specified duct
pressure. The full-bore sides of the cylinders are vented via elements (58) and (61) to
reservoir.
The accumulators effectively act as liquid springs allowing the horizontally closed
blades to open and close according to fluctuations of the duct pressure. The action of
opening spills the excess pressure into the vent allowing the blades to settle again to
the closed position. A pre-set maximum angle of opening is set and controlled by two
limit switches (1S5) and 1S6). If either or both of the blades reach this maximum
angle, (10 degrees), these limit switches initiate the Emergency Pressure Relief mode,
60
61
Normal Opening/Closing
The main pump (PUl) is energized simultaneously with the operation of the opening
or closing control, which energizes the relevant directional valves.
The pump units (PU2) and (PU3) are running continuously. Solenoids (G) and (H) of
valves (34) and (35) are energized allowing normal operation of the blades. To open
the blades, solenoids (D) and (E) are energized operating valves (32) and (33). The
combined output from pumps (PUl) and (PU2) is split and directed through the
control valuing to the hydraulic cylinders.
Two identical stacks of valves control the independent operation of each blade. Each
stack consists of a double acting directional valve (32) and (33), a double acting pilot
operated check valve (42) and (43), a dual flow regulator (46) and (47), and a double
pilot operated counterbalance valve (54) and (55).
The double' acting pilot operated check valves (42) and (43) enable the blades to be
held in any intermediate position or fully open by de-energizing the relevant
directional valves.
The dual flow regulators (46) and (47) allow the speed of normal operation to be
controlled. The fluid flow is regulated in the 'meter in' mode, i.e. it is restricted into
the hydraulic cylinder circuit, but allowed to flow freely from it. This form of
regulation allows the double counterbalance valves (54) and (55) to maintain a
smooth and controlled motion of the blades.
As the cylinders extend thus opening the blades, fluid flows from the annulus side of
the cylinders back to tank via deceleration valves (102) and (103).
Note: These valves are incorporated principally to control the speed of opening as the
blades near their fully open position when operated in the emergency relief mode.
At the 10-degree position of opening, limit switches (1S5) and (1S6) will actuate.
These have no function in the normal mode of operation. In the fully open position
limit switches (1S2) and (1S4) are actuated. It is only in this position with these limit
switches operated that the Boiler Inlet Isolator can be closed.
62
Solenoids (D) and (E) remain energized enabling pump (PU2) to hold the blades
positively open. Solenoids (G) and (H) are continuously energized, maintaining logic
check elements in their closed condition. . Pump units (PU2) and (PU3) continue to
run.
63
Normal Closing:
The blades cannot be closed unless limit switches (1S8) and (1S10) are actuated. To
close the blades, solenoids (C) and (F) are energized operating directional valves (32)
and (33). The hydraulic fluid is then directed through the valves described in the
opening sequence above, but in the reverse direction. During normal closing, if the
duct pressure rises sufficiently the blades will be prevented from closing. The excess
fluid pressure generated will be relieved to reservoir by relief valves (28) and (29).
Pump units (PU1) and (PU3) continue to run.
64
Emergency Relief Mode
The emergency opening mode can be initiated at any time and is also
automatically selected if the electrical power fails. The by-pass Isolator blades are in
the normal closed pressure relief position Pump units (PU2) and (PU3) are running
and solenoids (G) and (H) are energized. As the duct pressure increases above pre-
determined levels the by-pass blades will rise to the 10-degree position. 1imit
switches (1S5) and (1S6) will be operated causing valve solenoids (G), (H), (J), (K),
(1) and (M) to de-energize. This allows logic check elements (56) and (57) to open,
and (58) to (61) to close. The effect is to direct the hydraulic fluid stored in the main
accumulators (86) and (87) to the full bore side of the cylinders (104) to (107) via
logic element (57). The annulus sides of the cylinders are vented to reservoir via the
deceleration valves (102) and (103) and logic element (56).
The blades will open rapidly, controlled initially by flow regulators (51) and
(52). At the 70-degree position cams on the blade stub shafts engage a pair of de-
celeration valves (102) and (103), these reduce the flow at a rate determined by the
cam characteristics. The time of operation is to be adjusted to give a minimum time of
4 seconds to the 70 degree position and 10 seconds to fully open.
Note: for normal operation the deceleration valve full flow setting is adjusted so as to
give control to flow regulators (51) and (52).
65
66
Shut Down or Electrical Power Failure
If the system is shut down or the power fails then all solenoids will de-
energize. In this state the system will revert to the fail safe emergency operating mode
and the by-pass isolator blades will open fully.
Opening the Blades with the hand pump
Open valves (136) and (137), close valves (79) and (80), (81) and (82).
Operate valve (124) to select the by-pass Isolator. Open valves (120) and (121), and
close valves (122) and (123) then operate the hand pump.
Closing the blades with the hand pump
Maintain valves (136) and (137), (79) and (80), (81) and (82) and (124) as
they are for opening. Open valves (122) and (123), and close valves (120) and (121),
67
then operate the hand pump. The operating speeds are controlled by the capacity of
the hand pump and by the setting of the various flow regulators in the system.
BOILER INLET ISOLATOR
Closed, Static Mode
The air barrier fan motor (BF2) is running and the shut-off valve (FV2) is open. To be
in the closed position The By-Pass Isolator blades must be fully open and operating
limit switches (152) and (154). The Boiler Inlet blades will be operating limit
switches (157) and 159), which will de-energize pump unit (PU1). Pump units (PU2)
and (PU3) will be running and solenoids (G) and (H) will be energized.
Solenoids (B) of directional valve (31) will still be energized even after the blades
have fully closed. The output from pump unit (PU2) is directed via check valve (70)
and the control valves to the full bore side of the cylinders (108) to (111) maintaining
the blades in the closed position.
68
The Boiler Inlet blades in this closed position are held shut against the duct pressure
by the continuing hydraulic pressure in the cylinders. This hydraulic pressure must be
regulated so as to hold the blades shut against a maximum of 350-mm H2O pressure
within the duct. If duct pressure increases beyond this figure then the blades must
open. The hydraulic pressure holding the flaps closed increases to a maximum at
which point a relief valve (27) allows excess pressure and fluid to escape to the tank.
Pressure compensated pilot operated counterbalance valves mounted directly to the
base of the cylinders allow them to retract thereby opening the blades.
69
Opening/Closing Mode
70
Pump units (PU2) and (PU3) and solenoids (G) and (H) are continually energized. To
open the Boiler Inlet Isolator, pump unit (PU1) and solenoid (A) of directional valve
(31) must be energized. Hydraulic fluid is then directed through the dual pilot
operated check valve, then divided and passed through flow regulators (44A) and
45B) to the annulus side of cylinders (108) to (111). The blades then open; by de-
energizing solenoids (A) or (B) of valve (31) the blades may be held in any
intermediate and the fully open position. To close the Boiler Inlet Isolator, limit
switches (152) and 154) must be actuated by the By-Pass blades in their fully open
position. Pump unit (PU1) and solenoid (B) of valve (31) are energized, directing the
pump output to the full bore side of the cylinders. When fully closed limit switches
(157) and (159) de-energize pump unit (PU1) allowing pump unit (PU2) to maintain
the blades in their closed state.
71
72
73
Opening the blades with the hand pump
To open the boiler Inlet blades open valves (134) and (135), operate valve
(124) to select the Boiler Inlet Isolator. Open valves (118) and (119), and close valves
(116) and (117) then operate the hand pump.
Closing the blades with the hand pump
Maintain valves (134), (135) and (124) as they are for opening. Open valves
(116) and (117), close valves (118) and (119) then operate the hand pump.
74
75
76
Atomizing Air System
The atomizing air system provides sufficient pressure in the air atomizing chamber of
the fuel nozzle body to maintain the ratio of atomizing air pressure to compressor
discharge pressure at approximately 1.3 or greater over the full operating range of the
turbine. Since the output of the main atomizing air compressor, driven by the
accessory gear, is low at turbine firing speed, a starting atomizing air compressor
provides a similar pressure ratio during the firing and warm-up period of the starting
cycle and during a portion of the accelerating cycle. Continuous blow-down to
atmosphere is also provided to clear the main gas turbine compressor of accumulated
dirt.
Major system components
Main atomizing air compressor
Starting atomizing air compressor
Atomizing air heat exchanger
Air filter
Operation
When liquid fuel oil is sprayed into the turbine combustors it forms large droplets as it
leaves the fuel nozzles. The droplets will not burn completely in the chambers and
many could go out of the exhaust stack in this state. A low pressure atomizing air
system is used to provide atomizing air through supplementary orifices in the fuel
nozzle which directs the air to impinge upon the fuel jet discharging from each
nozzle. This stream of atomizing air breaks the fuel jet up into a fine mist, permitting
ignition and combustion with significantly increased efficiency and a decrease of
combustion particles discharging through the exhaust into the atmosphere. It is
necessary, therefore, that the air atomizing system be operative from the time of
ignition firing through acceleration and through operation of the turbine.
Air taken from the atomizing air extraction manifold of the compressor discharge
casing passes through the air-to-water heat exchanger (cooler) HX1 to reduce the
77
temperature of the air sufficiently to maintain a uniform air inlet temperature to the
atomizing air compressor. The atomizing air cooler heat exchanger, located in the
turbine base under the inlet plenum, uses water from the turbine cooling water system
as the cooling medium to dissipate the heat.
CAUTION
Failure to clean or replace the atomizing air filter cartridges after an alarm has been
annunciated may result in damage to the filter cartridge and/or the main atomizing
air compressor and could result in insufficient pressure ratio to properly atomize the
liquid fuel.
Switch 26 AA-1 is an adjustable heat sensitive thermo-switch provided to sound an
alarm when the temperature of the air from the atomizing air pre-cooler entering the
main atomizing air compressor is excessive. When the atomizing air reaches the
temperature setting of this switch, the alarm is activated. Improper control of the
temperature may be due to failure of the sensor, the precooler or insufficient cooling
water flow. Continued operation above 135 °C should not be permitted for any
significant length of time since it may result in failure of the main atomizing air
compressor or in insufficient atomizing air to provide proper combustion. Atomizing
air temperature high alarm is at 105°C, and machine takes shut down command if
atomizing air temperature after cooler becomes 135°C.
Main Atomizing Air Compressor
Compressor discharge air, now cleaned and cooled reaches the main atomizing air
compressor. This is a single stage, flange mounted, centrifugal compressor driven by
an inboard shaft of the turbine accessory gear. It contains a single impeller mounted
on the pinion shaft of the integral input speed-increasing gear box driven directly by
the accessory gear. Output of the main compressor provides sufficient air for
atomizing and combustion when the turbine is at approximately 60 % (1800 rpm)
speed.
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Differential pressure switch 63 AD-1, located in a bypass around the compressor,
monitors the air pressure and indicates an alarm if the differential pressure across the
compressor drop to a level inadequate for proper atomization of the fuel. Air, now
identified as atomizing air, leaves the compressor and is piped to the atomizing air
manifold. This manifold has many (14) piping providing equal pressure distribution of
atomizing air to the 14 individual fuel nozzles.
Booster Air Compressor
When the turbine is first fired, the accessory gear is not rotating at full speed and the
main atomizing air compressor is not outputting sufficient air for proper fuel
atomization. During this period, the starting (booster) atomizing air compressor,
driven by an electric motor, 88AB is in operation supplying the necessary atomizing
air. The starting atomizing air compressor at this time has a high pressure ratio and is
discharging through the main atomizing air compressor which has a low pressure
ratio. The main atomizing air compressor pressure ratio increases with increasing
turbine speed and at approximately 60 % speed the flow demand of the main
atomizing air compressor approximates the maximum flow capability of the starting
atomizing air compressor.
The check valve in the air input line to the main compressor begins to open allowing
air to be supplied to the main compressor simultaneously from both the main air line
and the starting air compressor. The pressure ratio of the starting atomizing air
compressor decreases to one and it is shut down at approx. 70 % (2100 rpm) when
speed relay 14 HC pickup.
Now all of the air being supplied for atomizing purpose is directed to the atomizing
air main compressor. The starting air compressor is completely bypassed.
When GT is running on Gas
During gas fuel operation, shaft driven main atomizing air compressor is still running
but there is no need of air for fuel atomization. Therefore, air discharge from main
atomizing air compressor is bypassed back to its suction and it is given at cooler inlet.
For this purpose solenoid valve 20 AA opens and it give opening air to isolation valve
VA 18. In this way, air is bypassed and very less air goes to main atomizing air
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manifold. Similarly, solenoid valve 20PL-1 opens to open the isolation valve VA 19-1
and through this valve purge air is supplied for purging the fuel nozzles.
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