Maintenance Report

(December 15, 2009 to March 31, 2010)

Submitted To:

Mr. Mushtaq Ahmad

Principal Engineer (Mechanical)

Block-II

CONTENTS

Summary

4

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

1.8 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

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

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

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

Modifications

Some systems were modified for efficiency improvement. 1. New line was installed at booster air compressor 2. HRSG Isolation valve

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.

(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.

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.

3. Identify, evaluate, plan and assign / execute preventive & corrective maintenance jobs as per OEM recommendations.

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:

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

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

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.

 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

 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 cracknessand 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 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 cracknessand 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)

 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

 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.

 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

 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

 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)

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.

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.

Major components of washing System

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

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.

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.

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

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

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

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.

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

 Four bolts of gear box were replaced.

 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.

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.

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.

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

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.

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.

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.

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.

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

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)

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.

Weight of the different components was noted as given below.

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

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.

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.

 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

 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).

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.

 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 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

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.

 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.

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.

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.

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

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.

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

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,

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.

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.

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.

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

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.

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.

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.

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.

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.

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

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.

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.

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.