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Attock Gen Limited

Internship Report Intern Syed Arsalan Ahmed BE Mechatronics Engineering NUST

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Foreword This internship report is written to share my experience of working in a professional setup and to give a

formal report of the knowledge gained during the six weeks. Getting an internship at AGL was no doubt

an honour for me as I had the opportunity to witness the running of one of the most technically

advanced Combined Cycle Power Plant in the country. The experience was great because during the

study period one hardly gets a chance to witness application of theoretical knowledge but an internship

after graduation has provided me with a chance to get a steady knowledge about the implementing of

engineering concepts to practical systems and robust designing.

The internship although providing a good knowledge of all the processes of a power plant helped me

focus mainly on the Instrumentation and Automation as I was assigned in E&I Department. I must add

that being a mechatronics engineer and working on a power plant was a dream come true as I felt at

home at the all the sections of power plant.

I must also add that I am highly impressed with the level of professionalism and technical expertise of

the AGL staff. Their dedication to the work and the sense of responsibility has helped AGL to be a

reliable power provider to the country.

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Acknowledgements

First I would like to thank the AGL HR department for providing me with an opportunity to intern here. I

would also like to acknowledge the fact that government of Pakistan has showed its utmost negligence

in solving the energy crisis of the country thus giving chance to many private companies to establish

power plants providing young engineers such as myself with great learning opportunities.

I would like to acknowledge the support provided by the AGL technical team in helping me adjust in the

new environment and helping me in every possible way to learn. Especially Deputy Manager E&I Mr.

Iftikhar has trained the Management Trainees very well and developed a competent learning

environment which helped me as an intern.

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Table of Contents Foreword ................................................................................................................................................. i

Acknowledgements ................................................................................................................................. ii

Table of Contents ................................................................................................................................... iii

1. Introduction .................................................................................................................................... 1

Attock Group of Companies: ................................................................................................................ 1

Attock Gen Limited: ............................................................................................................................. 1

2. Plant Overview ................................................................................................................................ 2

1. Engine:......................................................................................................................................... 2

2. Turbine: ....................................................................................................................................... 3

3. Alternator: ................................................................................................................................... 3

3. AGL Systems .................................................................................................................................... 4

1. Fuel Oil System: ........................................................................................................................... 4

2. Lube Oil System: .......................................................................................................................... 5

3. Compressed Air System: .............................................................................................................. 6

3. Cooling Water System: ................................................................................................................. 7

4. Charge Air & Cooling System: ....................................................................................................... 8

5. HRSG System: .............................................................................................................................. 8

4. Electricity Generation System .......................................................................................................... 9

1. Generators:.................................................................................................................................. 9

2. Switch Gear Room: .................................................................................................................... 10

3. Black Start Unit: ......................................................................................................................... 10

4. Switch Yard: ............................................................................................................................... 10

5. Operation and Maintenance: ......................................................................................................... 11

Control Room: ................................................................................................................................... 11

Engine Safety: .................................................................................................................................... 11

24K Engine Maintenance: .................................................................................................................. 11

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1. Introduction

Attock Group of Companies:

Attock Refinery Limited (ARL) was incorporated as a Private Limited Company in November, 1978 to take

over the business of the Attock Oil Company Limited (AOC) relating to refining of crude oil and supplying

of refined petroleum products. It was subsequently converted into a Public Limited Company in June,

1979 and is listed on the three Stock Exchanges of the country. The Company is also registered with

Central Depository Company of Pakistan Limited (CDC).

Attock Gen Limited:

Attock Gen Limited is the first Independent Power Producer of Pakistan registered under the Power

Policy 2002 of the Government of Pakistan. It is owned by the famous Attock Group of Companies. The

gross capacity of AGL Power Plant is 165 MW while the dispatch capacity is 156 MW.

The plant is equipped with the latest engine technology of Wartsila, Finland. There are a total of Nine (9)

18V46 Diesel Generators and One (1) Steam Turbine from Peter Brotherhood, UK. The major fuel used is

Heavy Furnace Oil (HFO) while Light Furnace Oil (LFO) is also used to start and shut down the engine.

The power produced by AGL is fed to two areas of Rawalpindi – Bahria Town and REPCO.

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2. Plant Overview A crisp overview of the plant is given in the coming lines.

The AGL power plant is a combined cycle power plant with the gross production capacity of 165 MW.

The plant can run on both heavy and light furnace oil. The main constituents of the plant are:

1. Engine: The Engines installed at the plant are of the latest cutting edge technology made and installed by

Wärtsilä, a Finnish company with expertise in IC Engines. There are a total of nine 18V46 engines each

with a rated power of 17550 KW. The engines can run on both HFO and LFO providing flexibility on

operation but mostly it is run of HFO thus producing low cost electricity. The engine is equipped with a

turbocharger and a charge air cooler which boost up the engine efficiency. A few engine specifications

are given below.

Manufacturer Wärtsilä

Number of engines 9

Engine Type W18V46

Numbers of cylinders 18

Cylinder bore 460mm

Stroke 580mm

Speed 500 rpm

Rated Output 17.5 MW

Main Bearing Metal

Connected rod bearing Metal

Camshaft bearing Tri Metal

Exhaust valve type Nimonic

Rotation direction Clockwise

Weight 237,000 Kg

MEP 24 bar

Compression ratio 14 : 1

Compression Rings 2

Oil Scrapper Ring 1

Swept volume per cylinder 96 L

The engine operating parameters (load, rpm etc) are controlled by the Governor. The Governor control

on the engines has been provided by Woodward 723 and Woodward 502. These are the brain of the

engine and monitor the engine parameters in real time. The governor can also automatically trip the

engine if any anomalies are observed.

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2. Turbine: In order to improve the overall plant efficiency the plant is designed to recover the heat produced by

the combustion inside the engines, which would otherwise be a waste, and produce super heated steam

which runs the turbine; thus making the power plant a combined cycle power plant. The steam turbine

installed is an impulse type steam turbine. The main features of the turbine are given below.

Manufacturer Peter Brotherhood Ltd Inlet Pressure 15.0 Bar Inlet Temperature 357°C Exhaust Pressure 0.14 Bar Power Rating 15300 KW Turbine Speed 6048 rpm Alternator Speed 1500 rpm Turbine Trip Speed 6652-6955 rpm Turbine Critical Speed Band 1500-3000 rpm Turbine Rotation Anti Clockwise Staging 9 Rateau Steam Flow 18.3 Kg/s

3. Alternator: The alternators or generators installed on each engine are Synchronous type with brushless exciter

circuits. The generators have a feedback control provided by the Automatic Voltage Regulators. The AVR

controls the field excitation current by monitoring the output voltage and current thus providing real

time voltage and current regulations. The main alternator specifications are as follow.

Generator Type ABB AMG 1600SS12 DSE Poles 12 Windings Star(+ a neutral connection)

Output 20,588 KVA Power factor 0.80

Voltage 15kV Current 792 A

Frequency 50 Hz AVR ABB EA63-5 Excitation Voltage 109V DC

Excitation Current 10.3 A

Speed 500 rpm Cooling method Air cooled

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3. AGL Systems In this chapter the different systems operating within the plant are described in detail.

1. Fuel Oil System: The engines need a constant supply of fuel at a specific temperature and pressure. In normal operation

one engine can consume 3600 litres of fuel per hour. So in order for the smooth operation of the plant a

reliable system of providing fuel has been established. The engine can run on both light and heavy

furnace oil so the system comprises of the following two sub-systems.

Heavy Furnace Oil (HFO):

The HFO supplied by the ARL is used during the normal running of the plant but it needs to be filtered

before it can be injected into the engine. This is done in the Fuel Treatment room. Besides that the HFO

freezes at room temperature so a steam line also travels with the HFO pipeline to keep the fuel in liquid

state by heating the contents of the HFO pipe.

Light Furnace Oil (LFO):

As mentioned previously the HFO solidifies at low temperatures, so LFO is used while starting and

stopping the engine; normally the LFO is not used.

The HFO and LFO is required for the engine at all times so a storage facility in the form of tanks has been

made to keep the supply continuous.

The tank yard houses fuel tanks which are characterized as buffer and day tanks. The buffer tanks are

used to store the HFO which is being supplied from the Attock Refinery. There are two HFO buffer tanks

each with a capacity of 250,000 litres. The day tanks serve the purpose of supplying fuel to the engines.

The HFO day tanks and the LFO day tank have a capacity of 250,000 and 100,000 litres respectively.

The purpose of having separate tanks for HFO is that the HFO from the buffer tanks is first filtered and

then stored for use in day tanks.

The following instruments are mounted on these tanks for smooth operation of the fuel system.

1. Level switches (for starting and stopping the filling process)

2. Level Sensors with transmitters (for monitoring fuel levels at all times in the control room)

3. Analogue temperature sensors

4. Thermostatic valve (for regulating steam flow into the tanks for heating purposes)

The LFO from the LFO tank is directly sent to the engine hall but HFO from the buffer tanks first go to the

fuel treatment room.

Fuel Treatment Room

HFO Separator Unit:

The fuel treatment room houses five centrifugal separators which remove the solid particles from the

fuel and also regulate the remove and monitor the water content in the fuel. Each separator has the

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capacity to filter 10,600 litres of fuel per hour. The waste is collected in the sludge tank. The separator is

PLC controlled and monitors certain parameters with the help of sensors. The respective commands are

then issued to pneumatically controlled actuators. The separator unit comprises of the following items.

1. Separator (Alfa Laval)

2. Feeding pump

3. Analogue and digital pressure sensors

4. Temperature sensor (PT100)

5. 3-wayPneumatic Valve

6. Water transducer

HFO & LFO Feeder Unit:

In order to pump the fuel from the day tanks a feeder unit is unit is used. The feeder unit has two pumps

for feeding HFO and one pump for LFO, a total of three such stations for intermitted operation. The HFO

line also has filters for purifying the fuel. The feeder unit monitors the quality and amount of fuel in real

time. The pump motors have VFD control for adjusting the amount of fuel being fed to the engine hall.

The following parameters of the fuel are measured with the help of sensors.

1. Viscosity

2. Density

3. Flow rate

4. Temperature

5. All the control of the FT Room is automated and only supervised from the Control Room.

Booster Unit:

The main purpose of the booster unit is to increase the pressure of the fuel, but it also maintains the

fuel at optimum temperature by heating it in the heat exchangers, re-filtering it and cooling the unused

fuel sent back from the engine (amount of fuel used is decided by the governor).

The Feeder and Booster pumps have a capacity of 14,100 l/hr.

2. Lube Oil System: Lubrication serves as a main part of any mechanism with heavy loads. The lubrication serves many

purposes in an IC Engine. It reduces friction between the moving parts ensuring smooth operation and in

doing so also prevents the parts in contact from heating up. Thus the Lube Oil System forms the back

bone of the 18V46.The same lube oil is also used for lubricating the alternator bearings. The clean lube

oil is present in an enclosed channel in the sump of the engine. An engine driven pump helps the lube oil

to rise up to the crank shaft bearings from where it goes into the crank shaft, the big end bearing,

connecting road, the small end bearing and to the engine heads and other engine parts. In the end the

lube oil falls it the sump after lubricating the liner.

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Lube Oil Pumping Unit

Present in the Fuel treatment room and it pumps the lube oil to engine hall.

Lube Oil Tanks:

There are three lube oil tanks in the tank yard. A clean lube oil tank(55 m3), 2 Service Tanks (16 m3) and

1 Used Lube Oil Tank(16 m3).

Lube Oil Separator Units:

Centrifugal separators are installed behind each engine to remove water and solid impurities from the

lube oil. These separator units are just like the HFO separator units.

Lube Oil Cooler:

The LO Cooler regulates the LO temperature for optimum working.

Pre Lube Oil Pump

A pre lube oil pump is present to pump the lube oil at engine starting.

Oil Mist Detector:

An oil mist detector detects the mist in lube oil and then it is purified by oil mist separator.

The lube oil system has the following main instrumentation:

1. Level Switches

2. Level Sensors

3. Analogue Flow meter

4. Analogue and digital temperature sensors

5. Analogue and digital pressure sensors

6. PLC controlled 3-way AMOT Valve

3. Compressed Air System: The compressed air is of great importance in the working of the plant. The Compressed air serves two

main purposes.

1. The first purpose is to provide air at approximately 30 bars for the engine startups

2. The second use of compressed air is found in instruments operating on compressed air; such as

pneumatic valves or diaphragm pumps.

The system consists of two separate units for the purposes mentioned above:

Starting Air Compressor:

Make of compressor Sperre No of starting air unit compressors 6 Compressor capacity 108 m3/h Compressor pressure 30 bar Motor power 28 kW Motor make ABB

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Instrument Air Compressor:

Number of Units 2 Operating Pressure 7 bar Capacity 162 m3/h Power, Compressor Motor 22 kW Power, air dryer 1.25 kW Motor Make VEM

3. Cooling Water System: In order to cool the engine and air charged by the turbocharger a cooling water system is also present.

Apart form directly cooling the specific engine areas such as the engine heads the cooling water also is

used in cooling of the lube oil, and fuel oil. There is approximately 14,000 liters of water in circulation in

the cooling water system.

The water cooled by the radiators (LT) enters the engine hall and first passes through the heat

exchanger of the FO Cooler. It then goes to the charge air cooler (40⁰C) after gaining some (+70⁰C)

temperature it cools the LO then comes to the charge air cooler stage 2(80⁰C). This water now

converted to HT is sent into the engine heads to cool them and the HT out of the engine (85-90⁰C) is

sent to the radiators. The radiators cool the water to about 40⁰C and the whole cycle is repeated.

Following are the main portion of this system.

Radiators:

There are 4 radiators installed for cooling of a single engine. Each radiator is having 6 six cooling for

reducing the temperature of HT water. These fans have VFD control in the Swiych Gear Room.

HT Water Pre Heating Unit:

There is a pre heating unit for HT Water, which is used for pre heating of water at the start of engine to

make its temperature on the scale rated for staring of engine.

Expansion Vessel Tank:

This vessel is installed on roof near radiators. It is filled with water and completes the deficiency of

water that may occur due to heating n evaporating in the cooling system.

Maintenance Water Tank:

There are two maintenance water tanks in engine hall that contain water for maintenance purpose.

Chemical Dosing Unit:

This unit treats the water by adding some desired chemicals to make it useable.

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4. Charge Air & Cooling System: The air intake for combustion is required. In order to improve the volumetric efficiency of the engine the

air is compressed before being fed into the engine. The air is filtered through a lube oil filter and fine

filter; silencers are present to absorb the sound. This air is then passed thorough a compressor run by a

turbocharger. The air is compressed to about 3.2bar but its temperature is raised. In order to lower its

temperature the air is passed through charge air coolers and then it enters the charge air gallery from

where it is sucked in by the intake valves.

After the combustion of fuel and air in the engine the exhaust gasses are ejected out through exhaust

pipes. The exhaust pipes take it to the HRSG from where the gases go out of the stacks.

5. HRSG System: The Heat Recovery and Stem Generation System forms a very important part of the combined cycle

power plant. The Waste Heat of AGL HFO Engines is utilized by installing 9 No.s Vertical Water Tube

Boilers from Aalborg Industries. Each Boiler has a capacity of almost 8 Tonnes/Hour Steam Production.

They produce Saturated and Super-Heated Steam. Saturated Steam is used for plant’s own

consumption while Super-heated Steam is used to run the Steam Turbine.

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4. Electricity Generation System The electricity generation system comprises of the:

1. Generators

2. Switch Gear Room

3. Black Start Unit

4. Switch Yard

1. Generators: Each engine and the steam turbine has an alternator coupled to its shaft as a load. The generators are

synchronous type with exciter circuits mounted on the rotor. The Alternators are Brushless Excited

Synchronous Generators with the field current controlling the amount of output power and phase angle.

The AVR controls these parameters and works on the feedback principle monitoring the output voltage

and currents by first steeping them down to a suitable level using Current Transformers and Potential

Transformers. It then decides how much excitation current needs to be supplied to the exciter circuit.

The following diagram will give an idea of such a generator.

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NGR Panel:

The purpose of a neutral grounding resistor is to limit the ground fault current to a safe level so that all

the electrical equipment in the power system is protected. The resistor should be the only current path

between the neutral of power transformers or power generators and ground.

2. Switch Gear Room: There is a MV (medium voltage) room or switch gear room, where the generated voltage of generator

is fed. The purpose of the MV Room is to unite the output of all the generators to a common bus lines

which then go to the switch yard. Breakers for protection are also present here. From here the

generated voltage sent to Auxiliary Transformers and also to Switch Yard through Feeders.

3. Black Start Unit: The function of the black start unit is to enable a black-start of the power plant when there is no

power supply from the grid. The black start provides power for the auxiliaries(such as starting air

compressors, pre lubricating pump and battery charger etc), which are needed to be able to make

a black-start of the power plant. The black start unit is connected directly to the lo voltage switch

gear of the plant.

4. Switch Yard:

The MV busbar is fed to switch yard. Here it is stepped up to 132 kV from 15 kV by power transformers.

Switch yard consists of the following equipments:

1. 3 Power Transformers

2. A bus bars tie breaker

3. 2 outgoing feeders

4. Sf6 Circuit-breakers with common operating mechanism

5. Current Transformers for measuring and protection(mounted on Power Transformers)

6. Voltage Transformers

7. Lightning arrestors with counter(mounted on the Power Transformers)

8. Three pole rotary type dis-connector with manual operating mechanism

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5. Operation and Maintenance: The plant has two different teams working as operations and maintenance teams. The operations staff is

responsible for keeping the plant running and report any anomaly to maintenance department.

Control Room: The main and most important portion of the plant is the Control Room. All the plant activity, parameters

and systems are monitored through the control room. The automation of the plant is done with the help

of MODICON Quantum PLCs from Schneider Electric. The communication protocol used is HART. All the

parameters are displayed on computer screens and appropriate decisions are taken by the maintenance

staff according to any situation. The engine parameters can be adjusted by altering the governor

controls and power distribution can also be monitored.

Engine Safety: The plant has state of the art safety features embedded in the control systems. There are numerous

engine trips and alarms. To mention a few:

1. Oil Mist Detector

2. Liner Temperatures

3. Head Temperatures

4. Big end bearing Temperatures

5. Exhaust Gas Temperatures

6. Turbocharger Over speed trip

7. Engine RPM Trip

8. Turbine Over speed Trip

9. Boiler Pressure Trip

24K Engine Maintenance: During my stay I had the opportunity to witness the major engine maintenance of DG3. This helped me

to understand the engine working in detail and thus cleared my concepts. I saw the different stages of

the overhauling which was an experience in itself.

Apart from that there were some times when small maintenance was carried out which helped me learn

a great deal about the operation and maintenance inside a power plant.