Iffco Aonla, Ashish Lal

Ashish Lal, I.P.E. 09113009 IFFCO AONLA Page 1

INDIAN FARMERS FERTILIZERS

CO-OPERATIVE LIMITED

AONLA Unit (U.P.)

TRAINING REPORT

STEAM & POWER GENERATION PLANT

DURATION

15th June 2012 to 31th July 2012

Submitted to:

Training & Placement Section,

IFFCO AONLA UNIT, U.P.

Submitted by:

ASHISH LAL

09113009

Industrial & Production Engg.

B.Tech. (Final Year)

Dr. B.R. Ambedkar N.I.T. Jalandhar,

Punjab

8300/190/VT-52/12-13


ACKNOWLEDGEMENT

It is my great pleasure to express my sincere gratitude to Mr. D.

Kalia, DGM(TRG), IFFCO, Aonla Unit for his deep interest

profile inspiration, valuable advice during the entire course of

industrial training.

I am highly thankful to Mr. Rajeev Trehan, Centre of Trg. &

Placement, and Prof. R.K. Garg, Head, Centre of Trg. &

Placement, Dr. B.R. Ambedkar National Institute of Technology,

Jalandhar, Punjab for taking interest and guidance in my

endeavour to get opportunity to work at IFFCO.

I am also thankful to staff of IFFCO, Aonla for their help and

assistance during my training period.

ASHISH LAL

B.TECH.(FINAL YEAR)

INDUSTRIAL & PRODUCTION ENGG.

Dr. B.R. Ambedkar National Institute of Technology,

Jalandhar, Punjab


CONTENTS

Company Profile 4

Abstract 7

Urea 10

Introduction 13

Brief Description of S.G.P.G. (Steam & Power

Generation Plant) 15

Various parts of S.G.P.G.

Quality of steam 24

Condenser 27

Deaerator 29

Fuel System 30

Combustion Air System 35

Boiler make up water treatment plant 37

H.R.S.G. (Heat Recovery Steam Generation) 38

Gas turbine 40

Industrial Gas turbine 43

Conclusion 45

References 46


COMPANY PROFILE

IFFCO has 40,000 member cooperatives. IFFCO has been ranked#37 in

top companies in India in 2011 by Fortune India 500 list.

Indian Farmers Fertilizer Co-operative Limited (IFFCO) was registered on

November 3, 1967 as a Multi-unit Co-operative Society. On the enactment

of the Multistate Cooperative Societies act 1984 & 2002, the Society is

deemed to be registered as a Multistate Cooperative Society. The Society

is primarily engaged in production and distribution of fertilizers. The

byelaws of the Society provide a broad frame work for the activities of

IFFCO as a Cooperative Society.

IFFCO commissioned an ammonia - urea complex at Kalol and the

NPK/DAP plant at Kandla both in the state of Gujarat in 1975. Another

ammonia - urea complex was set up at Phulpur in the state of Uttar

Pradesh in 1981. The ammonia - urea unit at Aonla was commissioned in

1988.

In 1993, IFFCO had drawn up a major expansion programme of all the

four plants under overall aegis of IFFCO VISION 2000. The expansion

projects at Aonla, Kalol, Phulpur and Kandla have been completed on

schedule. Thus all the projects conceived as part of Vision 2000 have been

realized without time or cost overruns. All the production units of IFFCO

have established a reputation for excellence and quality. A new growth

path has been chalked out to realize newer dreams and greater heights

through Vision 2010.

which is presently under implementation. As part of the new vision,

IFFCO has acquired fertilizer unit at Paradeep in Orissa in September

2005.

IFFCO has made strategic investments in several joint ventures. Godavari

Fertilizers and Chemicals Ltd (GFCL) & Indian Potash Ltd (IPL) in India,

Industries Chimiques du Senegal (ICS) in Senegal and Oman India


Fertilizer Company (OMIFCO) in Oman are important fertilizer joint

ventures. Indo Egyptian Fertilizer Co (IEFC) in Egypt is under

implementation. As part of strategic diversification, IFFCO has entered

into several key sectors. IFFCO-Tokyo General Insurance Ltd (ITGI) is a

foray into general insurance sector. Through ITGI, IFFCO has formulated

new services of benefit to farmers. 'Sankat Haran Bima Yojana' provides

free insurance cover to farmers along with each bag of IFFCO fertilizer

purchased. To take the benefits of emerging concepts like agricultural

commodity trading, IFFCO has taken equity in National Commodity and

Derivative Exchange (NCDEX) and National Collateral Management

Services Ltd (NCMSL). IFFCO Chhattisgarh Power Ltd (ICPL) which is

under implementation is yet another foray to move into core area of

power. IFFCO is also behind several other companies with the sole

intention of benefitting farmers.

The distribution of IFFCO's fertilizer is undertaken through over 38155 co-

operative societies. The entire activities of Distribution, Sales and

Promotion are co-ordinate by Marketing Central Office (MKCO) at New

Delhi assisted by the Marketing offices in the field. In addition, essential

agro-inputs for crop production are made available to the farmers through

a chain of 158 Farmers Service Centre (FSC). IFFCO has promoted several

institutions and organizations to work for the welfare of farmers,

strengthening cooperative movement, improve Indian agriculture. Indian

Farm Forestry Development Cooperative Ltd (IFFDC), Cooperative Rural

Development Trust (CORDET), IFFCO Foundation, Kisan Sewa Trust

belong to this category. An ambitious project 'ICT Initiatives for Farmers

and Cooperatives' is launched to promote e-culture in rural India. IFFCO

obsessively nurtures its relations with farmers and undertakes a large

number of agricultural extension activities for their benefit every year.

At IFFCO, the thirst for ever improving the services to farmers and

member co-operatives is insatiable, commitment to quality is

insurmountable and harnessing of mother earths' bounty to drive hunger

away from India in an ecologically sustainable manner is the prime

mission. All that IFFCO cherishes in exchange is an everlasting smile on


the face of Indian Farmer who form the moving spirit behind this mission.

IFFCO, today, is a leading player in India's fertilizer industry and is

making substantial contribution to the efforts of Indian Government to

increase food grain production in the country.



For efficient and uninterrupted running of a fertilizer plant a reliable

source of power is very much essential. All the major rotating equipments

of Ammonia and Urea plant are driven by electrical motor. To meet the

demand of high pressure steam and dependable electrical power, the

steam and power generators have been installed. The steam generator of

Aonla unit will supply high pressure steam to process plants and Gas

turbine generators will meet the power requirement of the plant. There

are two Gas Turbine Generators (GTG), one Steam Generator (SG) and

two Heat Recovery Steam Generating units (HRSG).

The GTG have been designed to operate on natural gas (NG), high speed

diesel (HSD) or Naptha fuels.

The exhaust of GT at about 500 deg C is used in HRSG to generate steam

at high pressure.

Two HRSG units each having capacity to generate 80 T/hr at 116 atm and

515O C is manufactured by M/s Kawasaki heavy industries , Japan. HRSG is

a packed type boiler having bank tubes, a set of super heaters, De-super

heaters and economizer.

The SG unit is a water tube double drum, natural circulation, oil (low

sulphur high start, LSHS) or natural gas fired boiler manufactured by M/s

Mitsui Engg. Co. Japan.

The capacity of the SG unit is 150 tonns/hr of super heated steam at

apressure of 116 atm and temp 515 deg C. The SG is designed to use NG or

LSHS fuel for regular firing. For initial light up of the SG, HSD will be

used.

The SG is pressurized furnace with no induced F.D. fan. Two F.D. fans,

one turbine driven and other motor driven have been provided to supply

combustion air.

A direct spray type De-super heater has been provided between primary

and secondary super heater to control steam temperature.

Super heater is of convection type, counter flow, drainable, inverted U-


looped tubes with spiral fins. Super heater section is located in the highest

gas temp zone and materials are designed to satisfy the requirement of

opearation conditions. Super heater elements are bottom supported by

lower header holding plates.

The MD type boiler is provided with a steam drum and a water drum.

Both of the drum have a main hole on each end for maintenance and

inspection. The steam drum is equipped with sets of steam purifiers inside

to obtain the required steam purity.

The furnace has an ample volume to secure complete combustion of

specified fuel. The furnace walls are of welded longitudinal fin tubes

panels to form a completely gas tight enclosure. The furnace floor is

covered with a layer of refractory bricks so as to shield the tubes from

radiant heat to secure a good circulation of water.


IFFCO's Urea is not merely a source of 46% of nutrient nitrogen for crops, but it is an integral part of millions of farmers in India. A bag of IFFCO's urea is a constant source of confidence and is a trusted

companion for Indian farmer.

When farmers buy IFFCO's urea, they know that what they get is not just a product but a complete package of services, ably supported by a dedicated team of qualified personnel. More importantly, they are aware that it is their own urea, produced and supplied by a cooperative

society owned by themselves.


About Urea

Urea is the most important nitrogenous fertiliser in the country because

of its high N content (46%N). Besides its use in the crops, it is used as a

cattle feed supplement to replace a part of protein requirements. It has

also numerous industrial uses notably for production of plastics.

Specification of urea as per

Fertiliser Control Order

1. Moisture % by weight,

maximum 1.0

2. Total N % by weight (on dry

basis) minimum 46.0

3. Biuret % by weight, maximum 1.5

4. Particle size

90% of the material shall pass

through 2.8 mm IS sieve and not less

than 80% by weight shall be retained

on 1 mm IS sieve.


If urea is applied to bare soil surface significant quantities of ammonia may be lost by volatilisation because of its rapid hydrolysis to ammonium carbonate. The hydrolysis of urea can be altered by the use of several compound called urease inhibitors. These inhibitors inactivate the enzyme and thereby prevent the rapid hydrolysis of urea when it is added to soil. The rapid hydrolysis of urea in soils is also responsible for ammonia injury to seedlings if large quantities of this material placed with or too close to the seed. Proper placement of fertiliser urea with respect to seed can eliminate this difficulty.


INDIAN FARMERS FERILIZERS

COOPERATIVE LIMITED

INTRODUCTION

Iffco Aonla complex is one of the giant cooperative fetilizer

manufacturing industries in India.

The Iffco complex at Aonla consists of two Ammonia units of 1350 MT/day

capacity and two Urea units of 1100 MT/day each capacity with the

required offsite facilities.

For efficient and uninterrupted running of a fertilizer plant a reliable

source of power is very much essential. All the major rotating equipments

of Ammonia and Urea plant are driven by electrical motor. To meet the

demand of high pressure steam and dependable electrical power, the

steam and power generators have been installed. The steam generator of

Aonla unit will supply high pressure steam to process plants and Gas

turbine generators will meet the power requirement of the plant. There

are two Gas Turbine Generators (GTG), one Steam Generator (SG) and


two Heat Recovery Steam Generating units (HRSG). One GTG will be in

line while the other is stand by. The stand by unit can come on full load in

13 minutes.

The GTG, manufactured by M/S Hitachi limited, Japan has a capacity to

generate 25.280 MW at ISO base rating (means atmosphere temperature

15deg C & 60% humidity at sea level) or 18.320 MW power output at the

site conditions. The GTG have been designed to operate on natural gas

(NG), high speed diesel (HSD) or Naptha fuels. The exhaust of GT at

about 500 deg C will be used in HRSG to generate steam at high pressure.

There is a provision to by pass the GT exhaust in case it is not required

due to shut down of the respective HRSG. In this case exhaust will be

vented to atmosphere. Two HRSG units each having capacity to generate

80 T/hr at 116 atm and 515O C is manufactured by M/s Kawasaki heavy

industries , Japan. HRSG is a packed type boiler having bank tubes, a set

of super heaters, De-super heaters and economizer. The temp of exhaust

gas from GTG is increased by supplementary firing. The exhaust of GTG is

having sufficient quantity of excess air which is utilized for combustion of

supplement fuel and so no separate Forced draft (F.D.) fan has been

provided. For steam temp control, direct water spray type attemperator

has been provided between primary and secondary super heaters.

The SG unit is a water tube double drum, natural circulation, oil (low

sulphur high start, LSHS) or natural gas fired boiler manufactured by M/s

Mitsui Engg. Co. Japan. The capacity of the SG unit is 150 tonns/hr of

super heated steam at apressure of 116 atm and temp 515 deg C. The SG is

designed to use NG or LSHS fuel for regular firing. For initial light up of

the SG, HSD will be used. The SG is pressurized furnace with no induced

F.D. fan. Two F.D. fans, one turbine driven and other motor driven have

been provided to supply combustion air. A direct spray type De-super

heater has been provided between primary and secondary super heater to

control steam temperature.


GAS TURBINE GENERATOR (GTG) PRINCIPLE

The gas turbine like any other heat engine is a device of converting part of

fuel's chemical energy into useful available mechanical power.

It does this in the manner similarily in, many ways to the system used by

four stroke cycle reciprocating internal combustion engine. Air is drawn

into the compressor, usually through an air filter situated in a "Filter

house" to remove any harmful solid particle from the air stream. This air

is then compressed to a designed figure by a multi stage axial compressor.

The hot compressor air is then fed to the combustion system where it is

mixed with injected fuel. Here the fuel burns and add its energy to the air.

DETAILED DESCRIPTION OF STEAM

GENRATION

The Mitsui MD (middle to semi large industrial boiler) type steam

generator is of outdoor use, self standing natural circulation type. The

steam generator is designed to fire HSD, LSHS/FO, and NG with four set

of oil and gas combination burners

The steam generator comprises a water cooled furnace, a convection

bank, steam and water drum, headers for collecting and distributing water

and steam, primary and secondary super heater, framed, casing insulation

etc.


DRUM AND INTERNALS:

The MD type boiler is provided with a steam drum and a water drum.

Both of the drum have a main hole on each end for maintenance and

inspection. The steam drum is equipped with sets of steam purifiers inside

to obtain the required steam purity.

The steam drum is equipped with internal pipes for feed water, chemical

and continous blow-down as well as stream purifier. The internal pipes

are arranged so as to ensure good distribution of feed water and chemicals

in the drum and to collect relatively highly concentrated boiler water for

blow down. The nozzles for feed water and chemicals are of double pipe

type so as to reduce thermal stresses due to the temp differences.

Finally the steam passes through the scrubbers. This comprises a number

of corrugated metal plates. When the steam flows through it, any

remaining water particles are efficiently removed. This occurs due to

sharp change in the flow direction.

FURNACE:

The furnace has an ample volume to secure complete combustion of

specified fuel. The furnace walls are of welded longitudinal fin tubes

panels to form a completely gas tight enclosure. The furnace floor is

covered with a layer of refractory bricks so as to shield the tubes from

radiant heat to secure a good circulation of water. The front wall is

equipped with burner in two rows. The rear wall forms a partition wall

dividing the convection section from the furnace. The rear tubes form a

nose baffle to provide a superheater space at the upper part of the

furnace. The side walls are provided with lower and upper header which is

connected to water and steam drums with connection pipes. Sufficient

number of observation holes are provided on the front side walls to check

the firing conditon and for maintenance.


SUPER HEATER:

The super heater is provided with two stages of super heaters. In primary

and secondary super heater both of then are of convection and pendant

type. The primary super heater is located at the lower gas temp part while

the secondary is at the higher temp part. The steam flows, contour to gas

in the primary super heater and parallel in the secondary heat.

The super heater tubes are hung to super heater headers which are

mounted on the furnace header. Therefore, thermal, expansion of the

tubes are hung to the super heater headers which are mounted on the

furnace header. Therefore, thermal expansion of the tubes and headers is

free, which avoids excessive stresses.

Retractable soot blowers and access doors are provided between the

primary and secondary super heater for cleaning and maintenance.

DE-SUPER HEATER:

A de-super heater is also provided on the connecting pipe between the

primary and secondary super heaters to control the final steam pressure.

Feed water is sprayed in the steam flow through a spray nozzle which

reduces the steam temp. Immediately downstream of the nozzle, a

thermal sleeve is furnished so as to provide direct contact of sprayed

water to the connecting pipe wall.

ECONOMISER:

Economiser is furnished downstream the convection bank to recover

waste heat from flue gases.

The economiser comprises a number of spiral wound finned tubes, inlet

and outlet headers and sufficient frames and casing. It is supported by the


steel structure using slide shoes to cater with horizontal thermal

expansion.

Reciprocating type soot blower with multiple nozzles is furnished to

effectively clean the heating surfaces.

BOILER FEED WATER SYSTEM:

The requirement of water for the boiler is met from the water treatment

plant. In the water treatment plant, DM water temp is raised to 60 deg C

by passing it through return condensate cooler before sending to steam

generation plant. In deaerator dissolve gases O2 and CO2 are removed up

to less than 0.005 ppm by raising the wter temp to 126 deg C and stripping

at a pressure of 1.44 kg/cm sq. By steam in deaerator storage tank,

Cyclohexamine and Hydrazine are dosed to raise the pH of water to 8.5-

9.5 and further chemical treatment of the boiler water to remove the

remaining oxygen to nil.

Boiler feed water pump takes suction from deaerator. The pump discharge

at pressure of 162 kf/cm sq g and temp 126 deg C through economiser it

enters the boiler drum. There is boiler feed water preheater located

between pump discharge and economizer to raise the BFW temp from 126

deg C to 140 deg C in case the boiler is on LSHS firing. This rise in temp is

essential to avoid condensation of oxides of sulphur on coil surface and to

prevent corrosion.

The outlet of BFW preheater is divided into two branches, the small

branch leads to the De-super heaters of the SG and HRSG units to control

the steam temp and other leads water to SG and HRSG units through

respective economiser. In economiser, feed water utilises the waste heat

from the flue gases and temp of water raised to 190 to 310 deg C

respectively.


DEAERATING HEATER:

Deaerator is very important in the boiler feed water system. Its basic

function is to remove O2 and CO2 dissolved in water to a considerable

extent and store water for supplying to boiler feed pumps.

DEAERATOR:

The deaerator functions on heat and mass transfer process. In deaerator

the nozzles and trays have been provided, through which water is sprayed

and distribute into fine droplets to increase the surface area of the water.

The process removes the dissolved gases upto some extent. Then the

stream is mixed with water in mixed box named scrubber. This process

also removes the dissolved gases. By the above process, in water, O2

contents get reduced to 0.005 ppm.

STORAGE TANK:

This is for storing of the feed water which is deaerated. The storage tank is

designed to prevent subsequent penetration of oxygen during the feeding

water process after the necessary deaeration. The temp of the water is also

kept constant inside the storage tank by covering the tank with insulating

material.

COMBUSTION AIR SYSTEM:

The air required for the combustion of air in steam generator is meeting

by two centrifugal types forced draft fan (F.D. fan). One fan is driven by

electrical motor while other by steam turbine. During the startup of the

SG, motor driven fan is taken in service in case steam is not available to

driven fan is taken in service in case steam is not available to drive the


turbine.

The FD fan sucks the air from the atmosphere and discharge to the

furnace at a pressure of 90mm-500mm water gauge. The quantity of air is

controlled by the vane provided at the suction side of FD fan. Two air

heaters have been provided in the discharge duct of FD fans, which are

known as steam oil heater and gas air heater. These air heaters raise the

temp to 145 deg C.

DESCRIPTION OF HRSG:

GENERAL:

The boiler consists of and arranged in the same casing as follows:

Super heater

Evaporator with steam drum

Economiser

All tubes are spiral finned and are arranged in vertical rows with staggered

tube arrangement to horizontal gas flow. All tubes circuits originate from

inlet header and discharge to outlet header, and besides tubes and its

header and discharge to outlet header, and besides tubes and its header

are arranged so that all tube bank sections are fully drainable. Whole

boiler is supported with the bottom casing on the foundation.

STEAM DRUM:

Steam drum is of all welded construction, fabricated from carbon steel

material and equipped with steam purifier of baffle screen type in steam

drum and necessary nozzle and connections. The drum has been

mounted on above the boiler and is supported with down corner pipes.


EVAPORATOR:

Evaporator section is composed of several components which consist of

number of tube with spiral fin and each inlet and outlet header. Each

component is made up of water circulation circuits separately. Evaporator

elements are bottom supported by lower header holding plates.

WATER CIRCULATION SYSTEM:

The water circulation circuit consists of steam drum, down corner pipes,

down corner headers, supply pipes, steam generating tubes (evaporators)

and riser pipe. The basic system functions are as follows:

Sub cooled water in the steam drum is led to the down corner headers

through heated down corner pipes and is disrtributed to each evaporator

inlet header from down corner headers. The mixture of water and steam

generated by the heat absorption of evaporator flows from evaporator

outlet headers to steam drum through the riser pipes.

SUPER HEATER:

Super heater is of convection type, counter flow, drainable, inverted U-

looped tubes with spiral fins. Super heater section is located in the highest

gas temp zone and materials are designed to satisfy the requirement of

opearation conditions. Super heater elements are bottom supported by

lower header holding plates.

ECONOMISER:

Economiser is of counter flow, drainable, vertical tubes with spiral fines.


Economiser selection is composed of several components which consist of

number of tubes and inlet header (lower) and outlet header (upper).

These components are connected in series with several economiser tubes.

Air vent and drain valve is provided on the upper and lower header,

respectively. Economiser elements are bottom supported by lower header

holding plates.



The quality of steam for high pressure driven turbines is very much

essential to keep the equipment in proper running condition and achieve

the high efficiency. The quality of steam at Steam Generating Plant shall

be maintained as under:

pH 7.0 to 9.0

SiO2 0.02 ppm

Cond. 1.0 Micromhos/cm

Total dissolved

solids as Na 1.0 ppm

pH of steam is maintained to prevent corrosion of steam pipe line and

return condensate line. The Silica concentration in steam to lower value

prevents the Silica deposition on the turbine blades. If it is not controlled

in long run, this deposition of Silica on the tip of blades reduces efficiency

of the blades, increases back pressure, and at worst it makes the rotor

unbalanced and results in failure.

The analysis of steam for conductivity detects any carry over of salts from

steam drum due to some or other reason. These salts, when carried over

with steam, get deposited on the turbine blades and reduces the efficiency

of the machine.

The total dissolved solids in steam are to be maintained to lower value to

prevent any deposition in Super heater tubes and Turbine blades. The

deposition of solids in Super heater tubes reduces the heat transfer to

steam. This causes the overheating of the tube metal and finally failure of

the tube.


Steam System

The steam requirement for steam and power generation plant for their

auxiliaries and main consumer plant (Urea) are at different pressures and

temperatures.

The requirements are as under:

1. High pressure steam at 116 Atm and 515°C.

2. Medium pressure steam at 39 Atm and 478°C.

3. Medium pressure steam at 39 Atm and 400°C.

4. Low pressure steam at 4.5 Ata and 225°C.

High Pressure Steam (116 Atm and 515°C)

The high pressure steam is generated in Main Steam Generating unit and

Heat Recovery Steam Generating Units. The outlet of these units is

connected to a header, which is called High Pressure Steam Header. This

header supplies steam at 116 Atm and 515°C to Urea Plant and Auxiliaries

of Steam and power Generating Units through Pressure Reducing and De-

Superheating Station.

The requirement of Medium and Lower Pressure Steam is met through

Pressure Reducing and De-Superheating Stations (PRDS). For this

purpose two PRDS have been provided in Steam Generating Plant. In

PRDS, firstly the pressure is reduced through pressure Control Valve and

then boiler water is sprayed at controlled rate through the nozzles to

bring down the steam temperature at required value. The requirement of

steam for Urea Plant is met from High pressure Header. The High

Pressure Header is charged from Steam Generator and Heat Recovery

Steam Generator outlet.


Medium Pressure Steam (478°C)

The medium pressure steam at 478°C is required for Boiler Feed Pump

and F.D. drive turbines. This is achieved after reducing the high pressure

steam to 39 Atm pressure by pressure Reducing Station No.1.

Medium Pressure Steam (400°C)

The medium pressure steam at 400°C required for the following

equipment is drawn from Pressure Reducing Station No.1 and further de-

superheated to 400°C by De-Superheating station No. 1.

1. Boiler Feed Water Preheater 2. Atomising Steam Header 3. Soot blowing header for SG and HRSG soot blowers 4. Ammonia Plant Medium steam pressure header 5. Furnace oil bulk storage tank area. 6. Pressure reducing Station No. 2.

Low Pressure Steam (225°C)

The exhaust of Boiler Feed Pump drive turbines at 4.5 Atm and 459°C is

de-superheated to 225°C by De-Superheating Station No.2 and discharge

to L.P. Steam Header. In this header Blow Down tank vent steam and F.D.

or drive turbine exhaust steam is discharged. This Low Pressure Header

supply steam to the following:

1. Fuel Gas Superheater 2. HSD Heater 3. FO/LSHS Heater 4. Steam Air Heater 5. Header for DM Plant 6. Deaerator

The shortfall of steam in L.P. header is met through Pressure Reducing

Station No. 2 which draws steam from Medium Pressure Steam Header.


Diagram of a typical water-cooled surface condenser.

The surface condenser is a shell and tube heat exchanger in which cooling water is circulated through the tubes. The exhaust steam from the low pressure turbine enters the shell where it is cooled and converted to condensate (water) by flowing over the tubes as shown in the adjacent diagram. Such condensers use steam ejectors or rotary motor-driven exhausters for continuous removal of air and gases from the steam side to maintain vacuum.

For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressure in the condensing steam. Since the condenser temperature can almost always be kept significantly below 100 oC where the vapor pressure of water is much less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-condensible air into the closed loop must be prevented. Plants operating in hot climates may have to reduce output if their source of condenser cooling water becomes warmer; unfortunately this usually coincides with periods of high electrical demand for air conditioning.


The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through water from a river, lake or ocean.


Diagram of boiler feed water deaerator (with vertical, domed aeration section and

horizontal water storage section.

A steam generating boiler requires that the boiler feed water should be devoid of air and other dissolved gases, particularly corrosive ones, in order to avoid corrosion of the metal. Generally, power stations use a deaerator to provide for the removal of air and other dissolved gases from the boiler feedwater. A deaerator typically includes a vertical, domed deaeration section mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler

feedwater storage tank.

There are many different designs for a deaerator and the designs will vary from one manufacturer to another. The adjacent diagram depicts a typical conventional trayed deaerator. If operated properly, most deaerator manufacturers will guarantee that oxygen in the deaerated water will not exceed 7 ppb by weight (0.005 cm³/L).


The fuels used in Steam Generator & Heat Recovery Steam Generating

units are HSD, Furnace Oil/Low Sulphur Heavy Stock (FO/LSHS) and

Natural Gas.

The liquid fuels are stored in two Day Oil Tanks located near Steam

Generating Units The Day Oil Tanks have a storage capacity of 80 tons

and 175 tons of HSD and FO/LSHS respectively. The HSD in day tank will

be transferred directly from the oil tanker received from Indian Oil

Corporation and FO/LSHS will be transferred from Bulk Storage Tanks

located in Naphtha Storage Tanks area.

H.S.D.

H.S.D. is required for warming up guns while starting the steam

Generator from cold condition when steam is not available for heating

FO/LSHS. HSD has the advantage of being less viscous at ambient

temperatures, requires no heating and has low sulphur contents. The low

sulphur reduces the chances of low temperature corrosion in the Air

Heater area, which arises due to condensation of sulphur trioxide in the

flue gas in low temperature regions. Having negligible carbon residual,

HSD burns completely in a cold furnace and leaves no soot deposits on

the colder heat transfer surfaces.

Specification of H.S.D.

GCV K.cal/kg - 10000

H Hv K.cal/kg - 9500


Sulphur Wt% - 1.0 (Max)

Pour Point - 6 °C (max)

The HSD pump draws oil from day tank through strainer and delivers the

oil to Steam Generator. The oil pressure at pump discharge is controlled

at about 20 kg/cm2 through a pressure control valve automatically. The

outlet of the pressure control valve leads to day oil tank. The HSD flow at

20 kg/cm2 is controlled through a flow control valve to achieve the

required oil flow for the Furnace and thus pressure reduces to 6-10

kg/cm2

After flow control valve a Trip Valve has been provided which cut off the

HSD supply to furnace in unwanted condition. This trip va]ve operates

through a Signal received from Burner Management System. The HSD

line after Trip Valve gets divided into two branches and supply HSD only

two lower tier burners. Trip valves have been provided in each HSD

burner line. The HSD burner valve operates through a signal from Burner

Management System. The HSD oil in burner gets atomised automatically

due to high oil pressure and burns in the furnace.

L.P. Gas Ignitors

To ignite the HSD and F.O. burners, the L.P. Gas Igniters have been

provided with each burner. The L.P. gas stored in cylinders is led to

ignitors located near F.O./HSD burners. The L.P. Gas pressure in the line

is controlled through a self pressure control valve. The gas line is divided

into four branches, lead to each ignitor. In each gas ignitor line, a Trip

valve has been provided which cut off the gas supply when not required.

The signal to operate the Trip valve is received from Burner Management

System.


FO/LSHS

FO/LSHS is required for oil guns to generate steam, Preheating of this oil

is necessary to reduce the viscosity for easy transportation and better

atomisation.

Specification of F.O. and LSHS

F.O. LSHS

GCV K.Cal/kg 10,000 10,000

LHV K.Cal/kg 9,500 9,500

Sulphur Wt% 4.5 1.0

Pour point °C 37 72

Sp. Gravity at 15°C 0.95 0.93

Viscosity 170 Cst 23.87 Cst

at 50°C at 95°C

Furnace oil/LSHS from storage tank is led to the oil pump located near

day oil tanks at a temperature of 50°C to 6.0°C. This temperature is

achieved by using a steam coil heater located in the bottom of the oil

tank. The F0/LSHS oil passes through the oil strainer on the suction side

of the high pressure gear pump and gets pressurized to about 12 kg/cm2

required for atomization. The pressure control valve, connected to the

delivery side of the pump controls the oil header pressure automatically

and leads to the day tank. FO/LSHS from the delivery side of the pump


enters the oil heater where it is heated from pumping temperature to

about 110°C. The outlet temperature of this oil from the oil heater is

automatically maintained at a constant value by automatic temperature

regulating valve mounted on the steam supply line to the heater. The

temperature regulating valve controls the quantity of steam to heater to

maintain the heater outlet oil temperature. The flow of FD/LSHS at

110deg C is controlled through a flow control valve. The oil pressure after

flow control valve reduces to 6-8.5 kg/cm2. The flow control valve

operates through a signal fed from Automatic Combustion Control

System. After this flow control valve there is a Trip valve, which cut off the

oil supply to the furnace in unwanted conditions. This valve is operated

through a signal from Burner Management System. The main oil header

divided into four branches to supply Fuel oil to four branches. In each

burner oil line, one Trip Valve has been provided, which cut off the Fuel

oil supply to the individual burner, when required. This Trip valve

operates through a signal received from Burner Management System.

After this Trip valve oil flows to burner, where it gets automised with

medium pressure steam and burns in furnace.



The air is required for combustion of fuel in Steam Generating Unit. To

meet this requirement of air in Steam Generator two centrifugal type

forced Draft Fans (F.D. fan) have been provided. One fan is driven by

electrical motor while other by steam turbine. During the startup of the

SG, motor driven fan is taken in service in case steam is not available to

drive the turbine.

The F.D. fan sucks the air from atmosphere and discharge to the furnace

at a pressure of 90 mm- 550 mm water gauge. The quantity of air is

controlled by the vane provided at the suction side of the F.D. fan. Two air

heaters have been provided in the discharge duct of F.D. fans, which are

known as Steam Coil Heater and Gas Air Heater. These Air Heaters raise

the air temperature to 145°C. The hot air helps in proper combustion of

fuel.

The Forced Draft fans supply cold atmospheric air through Steam Air

Heater and Gas Air Heater to the furnace for combustion of fuel. The Gas

Air Heater takes up waste heat from the flue gas of Steam Generator and

adds it to the combustion air.

The Counter Current parallel flow of the gas and atmospheric air results

in good transfer of heat, thus bringing coldest metal elements in contact

with less hot flue gas. If metal temperature is too low, there is a chance of

condensation of corrosive gas on the elements of GAH and consequent

corrosion of the heating elements. Generally during cold season and low

load operating condition, such troubles are encountered. To prevent or

reduce chances of this type of corrosion, the inlet temperature of cold air

to Gas Air Heater is controlled by heating it in a steam air heater. The low


pressure steam is passed through the heating coils and F.D. fan discharge

air is allowed to flow over it. The steam gives up heat, gets condensed and

the condensate is drained through a trap. The cold atmospheric air at

about 20 to 40°C while passing over the steam coil picks up heat and gets

heated upto about 50°C.

Thus when air of 50°C is allowed at cold end of Gas Air Heater, there is no

condensation of corrosive gases and so chance of chemical corrosion is

reduced.


Since there is continuous withdrawal of steam and continuous return of condensate to the boiler, losses due to blow-down and leakages have to be made up for so as to maintain the desired water level in the boiler steam drum. For this, continuous make-up water is added to the boiler water system. The impurities in the raw water input to the plant generally consist of calcium and magnesium salts which impart hardness to the water. Hardness in the make-up water to the boiler will form deposits on the tube water surfaces which will lead to overheating and failure of the tubes. Thus, the salts have to be removed from the water and that is done by a water demineralising treatment plant (DM). A DM plant generally consists of cation, anion and mixed bed exchangers. The final water from this process consists essentially of hydrogen ions and hydroxide ions which is the chemical composition of pure water. The DM water, being very pure, becomes highly corrosive once it absorbs oxygen from the atmosphere because of its very high affinity for oxygen absorption.

The capacity of the DM plant is dictated by the type and quantity of salts in the raw water input. However, some storage is essential as the DM plant may be down for maintenance. For this purpose, a storage tank is installed from which DM water is continuously withdrawn for boiler make-up. The storage tank for DM water is made from materials not affected by corrosive water, such as PVC. The piping and valves are generally of stainless steel. Sometimes, a steam blanketing arrangement or stainless steel doughnut float is provided on top of the water in the tank to avoid contact with atmospheric air. DM water make-up is generally added at the steam space of the surface condenser (i.e., the vacuum side). This arrangement not only sprays the water but also DM water gets deaerated, with the dissolved gases being removed by the ejector of the condenser itself.


A heat recovery steam generator or HRSG is an energy recovery heat

exchanger that recovers heat from a hot gas stream. It produces steam

that can be used in a process (cogeneration) or used to drive a steam

turbine (combined cycle).

General usage

A common application for an HRSG is in a combined-cycle power station,

where hot exhaust from a gas turbine is fed to an HRSG to generate steam

which in turn drives a steam turbine. This combination produces

electricity more efficiently than either the gas turbine or steam turbine

alone. Another application for an HRSG is in diesel engine combined cycle

power plants, where hot exhaust from a diesel engine, as primary source

of energy, is fed to an HRSG to generate steam which in turn drives a

steam turbine. The HRSG is also an important component in cogeneration

plants. Cogeneration plants typically have a higher overall efficiency in

comparison to a combined cycle plant. This is due to the loss of energy

associated with the steam turbine.

HRSGs

HRSGs consist of four major components: the economizer, evaporator,

superheater and water preheater. The different components are put

together to meet the operating requirements of the unit.

Modular HRSGs can be categorized by a number of ways such as direction

of exhaust gases flow or number of pressure levels. Based on the flow of

exhaust gases, HRSGs are categorized into vertical and horizontal types.

In horizontal type HRSGs, exhaust gas flows horizontally over vertical

tubes whereas in vertical type HRSGs, exhaust gas flow vertically over

horizontal tubes. Based on pressure levels, HRSGs can be categorized into

single pressure and multi pressure. Single pressure HRSGs have only one

steam drum and steam is generated at single pressure level whereas multi

pressure HRSGs employ two (double pressure) or three (triple pressure)


steam drums. As such triple pressure HRSGs consist of three sections: an

LP (low pressure) section, a reheat/IP (intermediate pressure) section,

and an HP (high pressure) section. Each section has a steam drum and an

evaporator section where water is converted to steam. This steam then

passes through superheaters to raise the temperature and pressure past

the saturation point.


A gas turbine, also called a combustion turbine, is a type of internal

combustion engine. It has an upstream rotating compressor coupled to a

downstream turbine, and a combustion chamber in-between.

Energy is added to the gas stream in the combustor, where fuel is mixed

with air and ignited. In the high pressure environment of the combustor,

combustion of the fuel increases the temperature. The products of the

combustion are forced into the turbine section. There, the high velocity

and volume of the gas flow is directed through a nozzle over the turbine's

blades, spinning the turbine which powers the compressor and, for some

turbines, drives their mechanical output. The energy given up to the

turbine comes from the reduction in the temperature and pressure of the

exhaust gas.

Energy can be extracted in the form of shaft power, compressed air or

thrust or any combination of these and used to power aircraft, trains,

ships, generators, or even tanks.


Gases passing through an ideal gas turbine undergo three thermodynamic

processes. These are isentropic compression, isobaric (constant pressure)

combustion and isentropic expansion. Together these make up the

Brayton cycle.

In a practical gas turbine, gases are first accelerated in either a centrifugal

or axial compressor. These gases are then slowed using a diverging nozzle

known as a diffuser; these processes increase the pressure and

temperature of the flow. In an ideal system this is isentropic. However, in

practice energy is lost to heat, due to friction and turbulence. Gases then

pass from the diffuser to a combustion chamber, or similar device, where

heat is added. In an ideal system this occurs at constant pressure (isobaric

heat addition). As there is no change in pressure the specific volume of

the gases increases. In practical situations this process is usually

accompanied by a slight loss in pressure, due to friction. Finally, this

larger volume of gases is expanded and accelerated by nozzle guide vanes

before energy is extracted by a turbine. In an ideal system these are gases

expanded isentropically and leave the turbine at their original pressure. In

practice this process is not isentropic as energy is once again lost to

friction and turbulence.

If the device has been designed to power a shaft as with an industrial

generator or a turboprop, the exit pressure will be as close to the entry

pressure as possible. In practice it is necessary that some pressure remains

at the outlet in order to fully expel the exhaust gases. In the case of a jet

engine only enough pressure and energy is extracted from the flow to

drive the compressor and other components. The remaining high pressure

gases are accelerated to provide a jet that can, for example, be used to

propel an aircraft.

As with all cyclic heat engines, higher combustion temperatures can allow

for greater efficiencies. However, temperatures are limited by ability of

the steel, nickel, ceramic, or other materials that make up the engine to


withstand high temperatures and stresses. To combat this many turbines

feature complex blade cooling systems.

As a general rule, the smaller the engine the higher the rotation rate of

the shaft(s) must be to maintain tip speed. Blade tip speed determines the

maximum pressure ratios that can be obtained by the turbine and the

compressor. This in turn limits the maximum power and efficiency that

can be obtained by the engine. In order for tip speed to remain constant,

if the diameter of a rotor is reduced by half, the rotational speed must

double. For example large Jet engines operate around 10,000 rpm, while

micro turbines spin as fast as 500,000 rpm.

Mechanically, gas turbines can be considerably less complex than internal

combustion piston engines. Simple turbines might have one moving part:

the shaft/compressor/turbine/alternative-rotor assembly (see image

above), not counting the fuel system. However, the required precision

manufacturing for components and temperature resistant alloys necessary

for high efficiency often make the construction of a simple turbine more

complicated than piston engines.

More sophisticated turbines (such as those found in modern jet engines)

may have multiple shafts (spools), hundreds of turbine blades, movable

stator blades, and a vast system of complex piping, combustors and heat

exchangers.

Thrust bearings and journal bearings are a critical part of design.

Traditionally, they have been hydrodynamic oil bearings, or oil-cooled

ball bearings. These bearings are being surpassed by foil bearings, which

have been successfully used in micro turbines and auxiliary power units.


Model series 5000, Simple-cycle, Single-shaft, Heavy duty Gas Turbine with Diesel start

Industrial gas turbines differ from aeroderivative in that the frames,

bearings, and blading are of heavier construction. Industrial gas turbines

range in size from truck-mounted mobile plants to enormous, complex

systems. They can be particularly efficient—up to 60%—when waste heat

from the gas turbine is recovered by a heat recovery steam generator to

power a conventional steam turbine in a combined cycle configuration.

They can also be run in a cogeneration configuration: the exhaust is used

for space or water heating, or drives an absorption chiller for cooling or

refrigeration. Such engines require a dedicated enclosure, both to protect

the engine from the elements and the operators from the noise.

The construction process for gas turbines can take as little as several

weeks to a few months, compared to years for base load power plants.

Their other main advantage is the ability to be turned on and off within

minutes, supplying power during peak demand. Since single cycle (gas


turbine only) power plants are less efficient than combined cycle plants,

they are usually used as peaking power plants, which operate anywhere

from several hours per day to a few dozen hours per year, depending on

the electricity demand and the generating capacity of the region. In areas

with a shortage of base load and load following power plant capacity or

low fuel costs, a gas turbine power plant may regularly operate during

most hours of the day. A large single cycle gas turbine typically produces

100 to 400 megawatts of power and has 35–40% thermal efficiency.


The study of the Steam & Power Generation Plant at Iffco Aonla was an interactive as well as practical industrial experience. The production of power from the fuel, the heat recovery system, boiler configurations, turbine working, condenser working, and many more processes were made clear with the visual and practical analysis. Apart from the theoretical knowledge gained in the classroom, the industrial exposure was an opportunity to have real life shop-floor experience. I express my gratitude to Mr. D. Kalia, D.G.M.(Training), IFFCO AONLA for his beneficial guidance and, for sharing his precious practical experience in the field.

I am also very thankful to Rajeev Trehan sir, and Dr. R.K.Garg, for their

supervision and the opportunity provided to us.


Steam and Power Generation Plant (S.P.G.P.) Manual,

IFFCO Aonla, Technical Library.

www.wikipedia.com

www.iffcoaonla.com

Documents

Iffco Aonla, Ashish Lal