A REPORT

ON

NFL

ABHINAV BABBER GIN/095319

PREPARED IN THE PARTIAL FULFILLMENT OF INDUSTRIAL TRAINING

ATNATIONAL FERTILIZERS Ltd., BATHINDA

Submitted to

SANT LONGOWAL INSTITUTEOF ENGINEERING & TECHNOLOGY

LONGOWAL, DISTT. SANGRUR

June-July 2010

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ACKNOWLEDGEMENT

I am very grateful to Dr. S.C Sharma (Head & Professor – Training & Placement

Department, and all other professors and lecturers of Electronic and communication

engineering department who guided me time to time by providing me desired guidance.

The industrial training in an industry / project site is an essential part of

curriculum for completion of B.E. degree. I am grateful to authorities at National

Fertilizers Limited, Bathinda for permitting me to undergo six months Industrial training

in their esteemed organization. During this training I have learnt a lot, for which I pay my

heartiest gratitude to the HRD Manager Mr. D.K. Bora and other staff members of

National Fertilizers Limited, Bathinda who helped me in all respects in fulfilling my

cherished desire of getting a successful Industrial training.

I am very thankful to Er. Nirlep singh(D.G.M –INST.), Er. B.B Grover (MGR),

Er. R.C Sharma (A.M), and all the supervisors and other officials for providing me

complete process details of their respective plants.

Abhinav Babber

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ABSTRACT

The training report on the working of National Fertilizers Limited, Bathinda

has been prepared in accordance with the requirement of scheme of three year B.E.

degree course in Instrumentation and control engineering being taught at Sant Longowal

Institute of Engineering & Technology.

In this course industrial training is an integral part of the curriculum and can

be undertaken in any reputed industry. I have done this training at National Fertilizers

Limited, Bathinda which is situated on Bathinda – Goniana road and is very well

connected with rail and road. It is very well known for its excellent performance over the

past years. I have studied whole plant with Captive Power Plant in detail.

It is pleasure to face the Industrial life that helped me to convert my

theoretical concepts into practical knowledge. During this training I came across many

emergency situations in the plant that surely explained me, actual industrial life.

Abhinav Babber

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Table of Contents

TOPIC PAGE NO.

INTRODUCTION 3 – 4

COMPANY PROFILE 5

UREA PLANT 6-10

STEAM GENERATION PLANT 11 - 13

CAPTIVE POWER PLANT 14 - 20

PROJECT STUDY 20 – 22

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INTRODUCTION

NFL is known in the industry for its work culture; value added human resources, safety,

environment, concern for ecology and its commitment to social upliftment.  All NFL

plants have been certified for ISO-9002 for conforming to international quality standards

and International Environmental Standard i.e. ISO-14001.   With the certification of

Corporate Office/Marketing operations under ISO-9001:2000, NFL has become the first

Fertilizer Company in the country to have its total business covered under ISO-9001

Certification. On 23rd August 1974, NFL was formed and registered to set up two modern

large capacity Nitrogenous Fertilizers plants.

NFL, Bathinda (Punjab)

NFL, Panipat (Haryana)

NFL was incorporated on 23 rd August 1974 in order to implement this project

contract were entered into with M/s " TOYO ENGINEERING CORPORATION " a well

known Japanese Engg. Company and Engg. India Ltd (EIL), a public sector and Engg.

Organization .This contract becomes effective on September 26, 1974 with a guaranteed

“Feed in “on the Bathinda Fertilizers project to implement within 36 months from the

zero date.

Due to the power requirements and some other factors, later on it was planned to

set up its own power house known as Captive Power Plant (CPP) with 2 turbo generators

of 15 MW each.

National Fertilizers Limited (N.F.L.) is the largest manufacturer of nitrogenous

fertilizers in the Northern India. It is presently operating four large fertilizers plants, two

of which are located at Nangal and Bathinda in the Punjab State, one at Panipat in

Haryana and one at Guna in M.P. While plants at Nangal, Bathinda and Panipat are fuel-

oil based, the one at Guna is gas-oil based. The overall installed capacity of NFL plants is

10.42 lakh MT per annum.

The old plant at Nangal was commissioned in 1961 followed by expansion which

was commissioned in 1978. Bathinda and Panipat plants were commissioned in 1979.

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Guna Plant which is the latest plant of NFL was commissioned in Dec, 1978 and is now

in full production.

NFL was incorporated on 23rd August, 1974 with two

manufacturing Units at Bathinda and Panipat. 

Subsequently, on the reorganization of Fertilizer group

of Companies in 1978,

The Nangal Unit of Fertilizer Corporation of India came

under the NFL fold. The Company expanded its

installed capacity in 1984 by installing and

commissioning of its Vijaipur gas based Plant in

Madhya Pradesh.       NFL Corporate office:

Noida

The Vijaipur Plant was a land mark achievement in project management in India.  The

plant was completed well within time and approved project cost.  In recognition of this

achievement, the project was awarded the First Prize in Excellence in Project

Management by Govt. of India.  Subsequently the Vijaipur plant doubled its capacity to

14.52 lakh MTs by commissioning Vijaipur Expansion Unit i.e. Vijaipur-II in 1997.  The

plant annual capacities have now been re-rated w.e.f. 1.4.2000 from 7.26 lakh MT of

Urea to 8.64 lakh MT for Vijaipur-I & Vijaipur-II Plants each. 

Three of the Units are strategically located in the high consumption areas of Punjab and

Haryana. The Company has an installed capacity of 35.49 lakh MTs of Nitrogenous

Fertilizers and has recorded an annual sales turnover of Rs.3, 474 crores during 2004-05.

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Strategically Located - Urea Plants

Leading Producer of Nitrogenous Fertilizers in the Country.

PRODUCTION

Capital Cost, Feed  Stock & Plants Capacity             

PlantsCapital Cost(Rs.Crore) Feed Stock

Existing  Capacity    MT/Year

(Lakh MT/Yr.)

Ammonia Urea CAN Bio-Fert.

Nangal-I 91.26Naptha

0.66 - 3.181 -

Nangal-II299.19

F.Oil/LSHS2.97 4.785** - -

7

Panipat338.41

F.Oil/LSHS2.97 5.115 - -

Bathinda349.41

F.Oil/LSHS2.97 5.115 - -

Vijaipur-I516.00

Natural Gas5.016* 8.646* - -

Vijaipur-II1071.00

Natural Gas5.016* 8.646* - -

Indore1.42 Strains - - - 100

Total2666.55 19.602 32.307 3.181 100

UREA PLANT

TYPES OF PROCESS CONVENTIONAL

MOLE RATIO

NH3:CO2 4:1

H20:CO2 0.54:1

%CONVERSION 70%

REACTION CONDITION:

PRESSURE:

CO2 250 kg/cm2

Carbamate 250 kg/cm2

Ammonia 250 kg/cm2

TEMPERATURE: 2000 C

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UREA PROCESS CLASSIFIED IN FOUR SECTION

1. Synthesis section.2. Decomposition section.3. Crystallization & Prilling section.4. Recovery section.

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PRESSURE MEASUREMENT

(PNEUMATIC SYSTEM)

For the measurement of pressure the single control loops method. The no. of component

used for this are:

Pressure gauge

Pressure transmitter

Pneumatic controller

Actuator

Positioner

Control valves

OPERATION

PRESSURE GAUGE measures the actual pressure in the pipeline.

PRESSURE TRANSMITTER takes actual pressure in its primary and secondary

part converts this pressure into 0.2 ~1.0 kg/cm2 signal.

A 1.4 kg/cm2 supply is providedto pneumatic controller.

Controller follows pressure transmitter signal and with set point value.

Controller gives output according to desired set point value and produces a output

signal of 0.2 ~ 1.0 kg/cm2.

Positioner accepts this signal and produces output signal i.e. given to the actuator.

Positioner acts according to controller signal.

Actuator diaphragm moves up & down according to positioner signal and control

valves moves accordingly.

In this way pressure in a pipeline is controlled.

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ACTUATOR

A fluid powered or electrically powered device that supplies and motion to a valve

closure member.

DIAPHRAGM

A flexible pressure responsive element that transmits force to the diaphragm plate and

actuator stem.

FORCE PLATE

The support plate which gives support to the diaphragm and exerts force uniformly.

CONTROL VALVE

A valve with actuator that automatically, fully or partially opens or closers that valve to a

position dictated by signals transmitted from controlling instruments can be called as

CONTROL VALVE.

The control valve is most important and widely used final element in auto control loop. A

control valve functions as a variable resistance in a pipeline. So by controlling the flow,

the valve indirectly controls the process variables that may be level, temperature, pressure

etc.

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VIBRATION MEASUREMENT

If the observed surface is rotating and rapidly changing the gap distance the RF envelope

is not constant amplitude but varies in direct proportion to the peak to peak movement of

the observed surface. This peak to peak movement of the observed surface causes the RF

envelope to be amplitude modulated.

VIBRATION AND AXIAL DISPLACEMENT

Transducer system is non contacting shaft vibration and relation position measurement

system. The system include a probe with an integral cable, extension cable and

proximate. The transducer system measurement the gap between the probe fit and an

absorbed metal surface and convert this distance to a proportional negative voltage.

The system measures both static and dynamic system probe tips are also each calibrated

to a specific probe type cable electrical length and temperature range. The scale factor is

200MV/mil(1mil=1/1000inch).

GAP MEASUREMENT

24 volts normally drive the proximator from an external source such as a power supply or

monitoring device. The proximator converts the DC drive voltage into an RF signal that

is applied to the probe through 95 ohm coaxial extension probe radiates the RF signal

into surrounding area as a magnetic field. If there is no conductive material within a

specified distance to intercept magnetic field. There is no power loss in RF signal the

output signal of proximator output terminals is max. 16volts. When a conductive material

approaches the probe tip, eddy current generated on the surfaces on the material resulting

power loss in RF signal. As a power loss is developed in RF signal, the output at

proximator output terminal is reduced proportionately. As the conserved conductive

surface come closer to the probe tab, the eddy currents on the surface of material

observed more power. When the gap reached specified minimum distance from the

conductive material surface. The material absorbs the total RF energy radiated by the

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probe. This is reflected as the maximum power loss the RF signal resulting a minimum

DC output signal at the proximator output terminal. The proximator measure the

magnetic of the RF envelopes and provide a DC output signal proportional to the packs

of envelopes. Thrust measurement and eccentricity measurement are the merely gap

measurement at the slow rate of change in the gap.

LEVEL MEASUREMENT

WHAT IS LEVEL?

The level may be expressed in term of pressure exerted over a datum level or in term of

the length of the liquid column.

WHY IT IS MEASURED?

To ensure that right amount of liquid/solid are added to the vessel at right time and for

safe operation.

WHY ITS MEASUREMENT IS IMPORTANT?

Level measurement is one of the important parameter in any process industry like our

fertilizer plant. The level has a significant effect on process quality, controllability,

process stability and optimization. Hence precise, accurate and reliable level

measurement is necessary. A wide variety of level measurement techniques are available

to meet the diverse level requirement of the process industry evolved over the years.

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STEAM GENERATION PLANT

Steam Generation plant is mainly installed for production of steam and then

distributed to various parts of the plant.

Here this section of plant installed in National Fertilizers Limited, Bathinda unit

produces and supplies steam at 100 Kg / cm2 pressure and nearly 480°C temperature to

Ammonia Plant.

In today’s world steam has gained importance in Industries. It may be used for

power processes and heating purposes as well.

BENEFITS OF STEAM

It is colorless, odourless and tasteless.

Very economical

Non-polluting

Can be used as heat exchanger.

It can be easily distributed to various sections of plant.

Steam is generated in Boilers (Water tube boilers mounted on common base fitted

with mountings and fittings) and then distributed to other parts of plants. For governing

the quantity of fuel to be burned and for maintaining the required pressure their are many

automatic fuel feeders, equipments and auxiliaries like pressure gauge etc.

In the Boilers used at National Fertilizers Limited (Bathinda unit); coal, oil natural

gas are used as a fuel for production of steam.

NFL , Bathinda is using steam for two purposes ; first and the main reason is for

running prime mover and other reason is to exchange heat in the processes taking place

their.

There are three boilers capable of producing steam at the rate of 150 Tonnes/hr

installed in CPP which were supplied and erected b BHEL. Generally two boilers are

enough to meet the requirements but third boiler is simultaneously running because if

steam load consumption increases then the third boiler plays its part in order to avoid any

faulty condition.

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FUELS USED:

Coal :

To obtain steam of desired Temperature and pressure, coal is burned to give major

source of heat.

Initially coal is stored at Coal Handling plant brought from coal sites. It is this

section of plant where coal is crushed by crushers in order to make small pieces of coal,

then after crushing it the coal pieces rare passed through heavy electromagnet where iron

is separated from coal if present. Coal is then sent to Bunkers from where it goes to

Grinding mill. Grinding mill is grinding coal into powder form.

Conveyor Belts are being used in the whole plant for transportation of Coal. The powder

form of coal is sent to the Boilers through pump as pump sucks the coal from grinding

mills and throws it into the boiler for combustion.

Fuel Oil :

As the Boilers are designed to work on both Coal as well as Fuel Oil so fuel oil can

also be pumped to Boiler for combustion.

Generally coal alone is not burnt Initially but Fuel Oil (LSHS) is mixed coal and then

sent to the furnace for combustion in order to get desired temperature .

WHY AND WHERE STEAM IS REQUIRED

As National Fertilizers Ltd, Bathinda unit has its own Steam Generation Plant

where steam is produced which is used for driving Turbo Compressors, Heating

Purposes, for various reactions taking place in the plant itself.

Steam is mainly consumed in the Ammonia Plant as nearly 6 to 7 tonne of steam is

required to produce 1 tonne of Ammonia. High Pressure Turbines are being used where

high pressure and temperature is to be maintained so SGP section plays a important role

for maintaining the said condition.

There are three boilers (VU-40 type supplied by M/S BHEL) of 150 tonne/hr

capacity .These boilers are Water Tube Boilers i.e. water is inside the tubes and hot air

surrounds it when coal is burnt, this makes the water in the tubes boil and steam

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formation takes place. In the beginning coal is burnt with fuel oil in order to get desired

temperature.

WATER AND STEAM SYSTEM

As the steam being used should be free from impurities like minerals, silica,

oxygen, Iron etc. in order to insure Safe and Efficient working of Steam turbines and

Boilers. For this purpose Raw Water is physically and chemically treated and finally

supplied to Steam Generation Plant from Ammonia plant. This water is called Boiler

Feed water which is further heated to 240º C by the flue Gases and taken to Steam Drum.

Steam Drum Acts as storage tank and also separates water from the steam at 315º C and

106 kg/cm2 pressure water then enters the Ring Header formed at on the bottom of

outside the furnace and rises by gravity through water wall tubes on the all the four sides,

taken heat from furnace and enters steam drum as a mixture of steam and water.

FLUE GAS SYSTEM

The products of combustion in the furnace consist of carbon-di-oxide, nitrogen,

ash, oxygen and sulphur-di-oxide. After leaving the furnace the heat

Of these gases called FLUE GASES, is utilized at various levels.

First the steam from steam drum is heated in two super heaters to get the required

temperatures of 4950C and then feed water in BANK TUBES is also heated and the gases

leave bank tubes at around 4970C next the heat is utilized to heat feed water in the

ECONOMIZER and gases are cooled down to 3200C. These gases are further cooled

down to 1500C in ROTARY AIR HEATER where the air is required for combustion and

conveying the coal is heated up. Temperature is not reduced further because at lower

temperature oxides of sulphur present in flue gases are converted to ACID which

damages the down stream equipments. These gases then pass through ELECTRO

STATIC PRECIPITATOR (ESP) where ash is removed.

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CAPTIVE POWER PLANT

INTRODUCTION:

National Fertilizers Limited has set a Captive Power Plant (CPP) at their complex

at BATHINDA, to ensure availability of stable, uninterrupted power and stream to the

Ammonia and Urea plant. This will minimize the tripping of the Fertilizer Plant due to

transit voltage dips and power cuts.

Since inception, Bathinda unit was drawing electric power from Punjab State

Electricity Board (P.S.E.B). Electricity is the main driving force after steam in the plant,

being used for moving auxiliary equipments. The unit requires 27MW of power/hr when

running at full load. There are two 15 MW turbo-generators to generate power. Under

normal running conditions of the plant and healthiness of the P.S.E.B. grid, we generally

run in synchronism with the grid merely drawing the power corresponding to the

minimum charges to be paid to state electricity board. In case of any disturbance in the

grid, our system gets isolated from the grid automatically. With both generators running,

we are able to feed power to the whole plant, thus production is not affected. In case only

one turbo generator is in line and grid cuts off, urea plant is cut off automatically to

balance the load with one generator. As soon as the grid becomes stable, the generators

are again synchronized with it. The power generation of each generator can be varied

with 2 MW to 15 MW maximum, provision exists to run the generator on 10 % extra load

continuously for one hour only.

Operation of C.P.P. is based upon microprocessor based computerized

instrumentation which allows automatic operation, start up, shut down of the whole or

part of the plant.

Latest instrumentation has been used in this plant. It allows controlling process

variables like flow, pressure, temperature, power factor, voltage, frequency, etc. There is

operator interface unit (IOU) Like a TV screen on which various parameters can be

17

displayed and controlled. It allows fully automatic start-up, shut-down of boiler, turbine

and other auxiliaries.

NEED FOR C.P.P:

It was thought to install a captive power plant in which electric power for our

requirement shall be generated in a COAL FIRED BOILER. The benefits envisaged

were:

1. Any disturbance in the PSEB grid used to trip the whole plant. Lot of money was

lost due to this as each re-startup costs around 40 to 50 lakhs rupees. Moreover,

frequent tripping’s had an ill effect on machines and equipments extending the re-

startup period.

2. Three boilers of 150Te/hr steam capacity were initially installed in SGP to keep 25

boilers running and one stand by as designed steam requirement was less than 300Te/hr.

but in actual operation steam requirement was more and all three boilers had to be run

and there was no breathing time for their maintenance. As new boiler was to be installed

for CPP, its capacity was so designed that it could export around 60Te of steam for

process requirement so that only 2 boilers of SGP would be run keeping the 3rd as stand

by.

With these points in mind CPP was installed. The functioning of CPP can be sub-

divided into parts:

BOILER AND ITS AUXILIARIES: For generation of high pressure superheated steam.

TURBO-GENERATOR AND ITS AUXILIARIES: To generate power, using steam from the boiler.

Operation of CPP is based upon microprocessor based computerized instrumentation

which allows automatic operation, start up, shut down of the whole or the part of the

plant.

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BOILER

The basic principle of this boiler is the same as discussed earlier for SGP boiler

that is formation of steam by heating boiler feed water inside furnace fired by coal and

heavy oil, utilization of heat of the gases and venting these gases at a safe height. Main

differences between the two boilers are:

SGP boiler is tangentially fired where as CPP boiler is front fired with 6 coal

burners and 6 oil gun fixed inside the coal housing.

SGP boiler can be loaded up to 30% load with oil firing only whereas CPP boiler

can be fully loaded with oil alone.

Height of combustible zone in CPP boiler is more and it has residence time of 1.5 sec

where SGP boiler has 1.0 sec.

Mills used for pulverizations of coal in SGP are negative pressure bowl mills whereas in

CPP ball tube mill are used which are positive pressure mills.

Due to more residence time and better pulverization the efficiency of CPP boiler is

about 4% higher.

Boiler feed water required for steam generation can be fully generated in CPP itself.

A part of the steam generated is exported for process use in ammonia plant and

rest is utilized for power generation in turbo generators as described below:

DESCRIPTION

MITSUI RILEY TYPE BOILER

Maximum evaporation 2, 30,000kg/hr

Design process for boiler 124 kg/cm2G

Steam temp at outlet 4950C

Heating surface 1250M2

POWER GENERATION:

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In C.P.P. two generators of 15MW capacity generate a voltage of 11KV which is

fed to the two transformers in the yard. The rating of the transformers is 31.5/25 KVA,

these two values depend upon the cooling which we provide, as here 25KVA capacity is

when cooling is oil natural air natural and 31.5KVA capacity is when cooling is oil

natural air forced. Both these transformers step up the voltage level to 132KV. From the

transformers the three phases pass through the lightning arrestors (LA). After this they

pass on to the isolator. After this the two lines pass on to the TRANSMISSION pole

called DOUBLE CIRCUIT TRANSMISSION. Then these lines go to the M.R.S. i.e.

main receiving station.

TURBINE:

The turbine used is supplied by M/S SGP of AUSTRIA. It is condensing cum

extraction turbine designed as single casing reaction turbine with single control stage and

high pressure (HP), mild pressure (MP) and low pressure (LP) reaction parts.

The turbine is fed with high pressure steam at 100kg from boiler and flows through

various control valves for normal and emergency operation. It gets high velocity through

the nozzle group and then passes over the impellers fixed on to the rotor and fixed

diffusers thus rotating the turbine. The enthalpy of steam is utilized in steps. Steam is also

extracted from various stages. HP1 at 10.4kg/cm2, HP2 at 8.1kg/cm2, feed water bleed at

4.3kg/cm2 and LP bleed at 0.9kg/cm2.

The exhaust steam from the turbine is condensed in a condenser maintained under

vacuum to extract maximum steam enthalpy. The output of the turbine depends on flow

of steam and heat difference that is on condition of steam at the main steam valve and the

pressure at the turbine outlet or condenser pressure. The turbine is connected to the

generator through speed reducing gears.

The exhaust steam is condensed in a condenser using cooling water. The resulting

condensate can be fed back to LP heater but is normally sent to the polishing water plant.

As shall be clear from the attached block diagram various bleeds from the turbine

are utilized for heating purpose. HP1 and HP2 are used for heating boiler feed water in

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HP1 and HP2 heaters. Feed water bleeds is used for heating the feed water tank and LP

bleed is used for heating the polish water make up to the feed water tank.

A lubrication system is also there to lubricate the various bearings of the turbine,

gears and generator. Normally the oil pump driven by the turbine shaft supplies oil but

auxiliary motor driven pumps are used for start up and during shutdown. A turning gear

has been provided for slow cooling of turbine rotor.

Latest instrumentation has been used in this plant. Bailey’s net work-90

microprocessor based instrumentation system is being used. The NETWORK 90

SYSTEM is a distributed process control system. Using a series of integrated control

nodes. The network 90 system allows controlling process variables like flow, pressure

and temperature according to a control configuration. There is operator interface unit

(OIU) like a TV screen on which various parameters can be displayed and controlled. It

allows fully automatic start-up/shut-down of boiler, turbine and other auxiliaries.

DESCRIPTION:-

Make Simmering Graz Panker, Austria

Type Multifunction (28 stages)

Capacity 65 T/H at 15 MW

RPM 6789 at 50 Hz

Critical speed 3200-3600 RPM

GENERATORS CPP is having two number turbo generators of capacity 15MW each. The

generators are type SAT three phase, 50Hz, 11kV, 984amps, at 0.8 power factor rating

supplied by M/S JEUMONT SCHNEIDER OF FRANCE. These are totally enclosed self

ventilated type with two lateral airs to water coolers for cooling. The alternators are able

to bear 10% overload for one hr with an increase in temp. of 100C while maintaining the

voltage as near as possible to the rated one. The excitation is compound and brush less

with exciter rotor and Rectifier Bridge mounted on the extended main shaft on non

driving end. The excitation is controlled automatically with automatic voltage regulator

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and a PLC controller. All protection relays installed for protection of generator are solid

state having high accuracy, quick response and low power consumption.

Under normal running conditions of the plant and healthiness of the PSEB grid, we

generally run in synchronism with the grid merely drawing the power corresponding to

minimum charges to be paid to state electricity board. In case of any disturbance in the

grid measured by higher low frequency, high rate of change of frequency, low voltage

etc. our system gets isolated from the grid automatically. With both generators running,

we are able to feed power to the whole plant, thus production is not affected.

UNINTERRUPTED POWER SUPPLY: -

The uninterruptible power supply system is connected between a critical load, such

as digital drives & automation, distributed digital process control system, telecom

equipment, programmable logic controller, mission critical applications, computer and its

three phase mains power supply under all rated load and input supply conditions.

The system offers the user with the following advantages: -

Increased power supply: -

The UPS has its own internal voltage and frequency regulator circuits which ensure

that its output is maintained within close tolerances independent of voltage and frequency

variations on the mains power lines.

REDUNDANT Vs NON REDUNDANT CONFIGURATIONS:-

In a non-redundant configuration the system is sized such that both UPS modules

are required to feed the potential load and if one of the two modules develops a fault or

for some reason shut down, the other module also automatically shuts down.

In such an event the load is transferred to an unprocessed bypass supply.

In a redundant module configuration the system is sized such that the potential load can

be provided by just one of the two modules. Under normal circumstances both modules

are operational and share the load current equally; but if one module develops a fault, or

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is shut down, the second module is able to take over the full load demand and continue to

provide it with processed, backed-up power.

7400 Module Design:-

The UPS basically operates as an AC- DC-AC converter. The first conversion

stage (from AC to DC) uses a 3 phase fully controlled silicon controlled rectifier (SCR)

bridge rectifier to convert the incoming mains supply into a regulated 432V DC bus bar.

The DC bus bar produced by the rectifier provides both battery charging power and

power to the inverter section-which is of a transistorized / IGBT based pulse width

modulation (PWM) design and provides the second conversion phase i.e. reconverting

the DC bus bar voltage back into an AC voltage waveform.

AMMONIA PLANT

Ammonia is the major constituent in the production of urea and separately in the

ammonia plant. This plant has production capacity of 900 M.T. of liquid ammonia per

day. We can easily divide the whole process into following different section and discuss.

Then separately according of function of these section:

1. AIR SEPARATION UNIT (A.S.U.)

2. SHELL GASSIFICATION AND CARBON RECOVERY

3. DE-SULPHURION (RECOVERY-1)

4. SHIFT CONVERTOR (CO SHIFT CONVERSION)

5. CARBIN DIOXIDE REMOVAL

6. NITROGEN WASH UNIT (N.W.U.)

7. AMMONIA SYNTHESIS SECTION

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1. AIR SEPARATION UNIT (A.S.U.)

Air has following composition:

Nitrogen 78.03%

Oxygen 20.93%

Argon 0.93%

Carbon 0.93%

It is provided for getting oxygen and nitrogen required for production of NH3 from air is

the first section from atmosphere and is pre-cooled. Then further cooled in air chiller.

Then moisture and dust etc. are removed by passing through alumunia molecular seves.

Final products i.e. N2 and O2 are obtained when air is rectified in the rectifying

column.

Product O2 is the first compressed and then led to reactors in shell gasification process.

For partial oxidation of food stock for producing raw gas is separated toH2, H2S and CO2,

CO2 is send to the urea plant, H2S is sent to sulphur recovery plant. On the other hand N2

and H2 are given to N.W.U. in the ratio of 1:3 to get pure synthesis gas to manufacture

NH3.

2. SHELL GASIFICATION AND CARBON RECOVERY

Lines of O2 feedback and stream led to the gasifier column where in the presence of high

temperature of the order 13500 C produce raw gas containing CO, H2S, HCN, heat is

generated in this unit. This heat is not washed but utilized to produce steam in the waste

boiler.

Some unburnt carbon is also present along with other gases in raw gas, as it can check the

line. It is removed by stages water wash and there is final scrubbing stage. HCN is also

removed in this stage.

3. DE-SULPHURISATION

Sulphur compound are removed in this section because otherwise these poison the

catalyst present in the next section. Methanol has a property of absorbing different gases

at different temp. Absorption process is carried out at low temp. and high pressure, H2O

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and COS are removed in the raw gas to only 0.1 PPM in this unit by absorbing with

MeOH. MeOH is regenerated by N2 by stripping and H2S is sent to sulphur recovery

plant.

4. SHIFT CONVERTOR

In this unit get CO2 and H2 from CO and steam at high temp. by passing the gas catalyst

as per the following reaction:

CO(g) +H2O(steam) ......... H2 + CO2

In this industrial method of producing H2 as per le chatlier principle for high

concentration of product excess is to be introduced and temp. should kept low and

reaction rate is high. So compromise is made and temp. is around 350-500 oC. Fe is used

as catalyst in reaction.

5. CO2 REMOVAL

In this unit we get a mixture of gas(H2, CO2) from shift conversion and CO2 is removed

from H2 by absorbing CO2 with methanol of low temp. This mixture of MeOH and CO2 is

stripped by N2 where CO2 is regenerated and send to UREA PLANT, in this unit we get

98% of H2 and send to N.W.U.

6. NITROGEN WASH UNIT (N.W.U.)

Even a little of CO still remains in raw gas after the shift convertor process. This is

removed in N.W.U. where liquid N2 is sprayed on raw gas of 98% H2 from the top of the

tank. Before leaving this section, purified H2 gas is mixed with N2 in the ratio 3:1 and

forms an admixture without reaction, it is called synthesis gas.

7. AMMONIA SYNTHESIS SECTION

The synthesis gas from N.W.U. is compressed from 37 kg/cm2 to 230 kg/cm2 in the

centrifugal type synthesis compressor. Then the gas enters the synthesis hot exchanger

with hot effluent gas from synthesis economizer. At the outlet of the compressor the gas

contains 16% ammonia.

N2 + 3H2 …………… 2NH3

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