Analysis of Power Generation Plant at Pakistan Steel Mills

Pakistan Steel Mills

“Thermal Power Plant” Visit Report

Group Members:

Waleed Ahmed ME-071

Talha Fareed Khan ME-072

Abdul Rafay Khokar ME-073

Syed Wajahat Hassan ME-075

Danial Sohail ME-089

Syed Osaid ul Haq ME-102

Daniyal Iqbal Khan ME-103

Owais Ali ME-105

Syed Wajahat ME-106

Muhammad Hasan ME-108

Rafay Mustafa ` ME-124

Thermal Power Plant Pakistan Steel Mills

1 | P a g e

Preface / Acknowledgments

Relating theoretical knowledge with practical experience is important as it enhances concepts

and this is reason, why engineering students are advised to visit industries and relate their

theoretical knowledge with industrial practices.

Instructed by course instructor of “Steam generation and steam turbine” students had to visit any

industry with its own Power generation capability, in groups, and to present their learning in

form of reports. As a result we managed a visit to Pakistan Steel Mill, which has its own Power

generation plant with production capacity of 155 Mw.

This report presents a brief description of Russia made power generation plan implied by PSM’s

Thermal Power Plant. It briefly discuss every component in plant along with detailed description

of boiler and turbine, main components related to our course SGST, it also presents some

recommendations that according to our point of view, should be applied by PSM to their plant in

order to increase overall efficiency and to reduce damages occurring to boiler due to scale

formation in tubes.

All in all this report provides its reader an overview of Power generation and also gives an

insight to an engineering student about technologies of mid 70’s as Russia installed this power

generation plant in 1973.

This visit helped a lot to boost our knowledge about Steam Generation and Steam Turbine, but

this would be impossible without help Mr. Shamsi and Engr. Shakeel Ahmed, who organized

this visit for us and helped us throughout our visit. We also want to thank Mr. Izhar ul Hasan

(deputy manager) who illustrated and demonstrated every component of power cycle and onsite

made it easy for us to understand function of individual component.


2 | P a g e

Table of Content

S.no Contents

Pg. no

1. Thermal Power Plant - Pakistan Steel Mills

3

2. Power Generation Cycle 4

3. Water chemical treatment plant 5

4. Furnace Fuel 9

5. Boilers 10

6. Turbines 16

7. Turbo blower station 17

8. Recommendations 18

9. Source of information 20


3 | P a g e

Thermal Power Plant - Pakistan Steel Mills

When project of PSM was approved by Govt. of Pakistan in 1970’s it also included PSM’s own

Power generation Plant. This power generation project was included because consumption of

electricity at PSM was going to be too high that electricity from K.E grid would have cost a lot to

fulfill demands of PSM. This demand of electricity is due to high capacity blowers, compressors

and other plant equipment which fire up PSM’s furnaces, not only this but area occupied by PSM

is like a small city and all these power requirements are fulfilled by Thermal Power Plant at

Pakistan Steel Mill.

Another reason for installing a power plant was availability of fuel. PSM produces Blast Furnace

Gas, Coke Oven Gas and Coal Tar as by product of steel making process. All these by-products

can be used as fuels and burning these fuels to produce electricity reduces plant operating cost.

All these fuels have low market value because of its quality, but PSM’s power plant furnace is

capable of burning these fuels. In short PSM utilizes it’s by product to get electricity.

PSM’s Thermal Power Plant (TPP) has total electricity production capacity of 155 Mw. 4 Russia

made natural circulation water tube boilers produces steam to drive 4 turbines, three 55 Mw

turbines are used for electricity generation and fourth 60 Mw turbine is used to drive compressor

at Turbo Blower Station (TBS).

Water Chemical Treatment Plant WCTP provides de-mineralized water to boilers and residual

steam from turbines is supplied as process heating in different departments of PSM and some

amount is utilized to drive turbine in TBS.


4 | P a g e

Power Generation Cycle:

WCTP at TPP provides de-mineralized water to boilers, capacity of each boiler is 220 tons/hr,

and boiler provides super heated steam at a temperature of 560 oC.

Boiler utilizes 2 Forced draft and 2 Induced draft fans for supply and suction of fresh air and flue

gases respectively. Each boiler have 8 burners for burning fuel, it can burn 4 different kind of

fuels, but PSM mostly use Natural Gas for firing furnace because of its good Calorific value and

less cost.

From boiler steam is supplied to turbine for power production, turbine rotates and provides shaft

power and this shaft power is converted into electricity from generators, electricity from

generators is supplied to M.S.G.R where it is connected to K.E grid.

Turbines have extraction points for Feed water heater, which pre heats water entering boiler,

residual steam from turbine is supplied to TBS where another turbine is driven and its shaft

power is used to drive a compressor for blowing air into furnace. Rest of residual steam is

supplied to different departments in steel mill where it helps in processes like rolling, forging etc.

Some departments of steel mill also have small scale boilers therefore they use condensate from

TPP as feed water because of its de-mineralized nature.

Condensate from TBS and other departments of PSM reaches WCTP where it is again treated

completely because fewer precautions are taken during transfer of condensate and it has lost its

de-mineralized nature. From WCTP water is taken to boiler and cycle continues.


5 | P a g e

Water Chemical Treatment Plant (WCTP):

It is designed to meet the following demands;

De-mineralized water for steam generation purpose

Soft water for plant technological needs.

Steam condensate cleaning to treat the contaminated condensate received from different

shops (TPP & TBS).

Processes in Water Chemical Treatment Plant

(WCTP):

CLEARIFIER Lime

coagulated

storage

Mechanical

filter

Rear

Pump

Primary Cat-

ion

exchanger

Secondary

Cat-ion

Exchanger

Secondary

An-ion

Exchanger

Storage

Water

tank De

Carbonizer

Primary An-

ion

Exchanger


6 | P a g e

Stages of Water Treatment:

The process of water treatment may be divided into the following stages;

Cold process softening by liming followed by clarification added with coagulation to

remove mechanical and organic suspended particles

Mechanical filtration

Softening by ion-exchange to reduce hardness of water.

Demineralization to remove all dissolved salts from water by treating it in a series of cat-

ion and anion exchangers

Degasification (de-carbonization) to reduce the concentration of dissolved CO2 in water.

Raw Water Treatment Scheme at WCTP:

It consists of following steps;

Pre-heating Of Water:

Raw water is pumped to the WCTP by two lines up to the inlet of four raw water inlet booster

pumps. From here the water is pumped to the main building (TPP) where it is heated up to 36-40

C in raw water heaters.

Clarifier:

A pair of pipelines carries water to (TPP) and another pair carries it back to Clarifier at WCTP.

Here liming and coagulation is carried out simultaneously in order to remove magnesium and

calcium temporary hardness present in soluble form by converting them to less soluble

compounds. Hydrated Ca(OH)2 and coagulant ferrous sulphate (FeSO4.7H2O) are used for this

purpose.

The following are the reactions;

Ca(HCO3)2 + Ca(OH)2 = CaCO3 + H2O

Mg(HCO3)2 + Ca(OH)2 = MgCO3 + CaCO3 + H2O

MgCO3 + Ca(OH)2 = Mg(OH)2 + CaCO3


7 | P a g e

Mechanical Filter:

Now clarified water is pumped into the double chamber mechanical filter. Here all the suspended

materials are removed mechanically by passing the water through chamber of coal. After this

filtration water is divided in to two parts one is given to sodium-Anion exchanger and other is

given to Hydrogen-Cation exchanger.

Sodium Cat-ion Exchanger:

In sodium ion exchanger remaining calcium and magnesium cations that are hard to remove are

exchanged by sodium cations known as “sulforated coal” this is a Na-Cycle. At the exhaust of

ion exchange capacity the Na-cation exchangers are regenerated with a 3-6% solution of

common salt NaCL.

Primary Cat-ion Exchanger:

The second steam coming out of a mechanical filter is treated in hydrogen-cation exchanger .

Here the calcium, magnesium and sodium cations of water soluble salts are exchanged by

hydrogen-cation of H-carbon exchange material. Regeneration of H-carbon exchange material of

this stage is carried with 1.5-2.2% sulfuric acid solution.

Primary Anion Exchanger:

Acidic water of H-carbon exchanger led to primary anion-exchanger. This is the first step of

anion exchanger. Here the exchange of anions of strong acids (SO2,Cl2,NO3) takes place with

the OH- ions of exchange resin. At the end it is regenerated with 2-4% aqueous sodium

hydroxide NaOH.

H2SO4 + KOH = H2O + KSO4

HO + KOH = H20 + KCL

HNO3 + KOH = H20 + KNO3


8 | P a g e

De-carbonizer:

After this ion exchange two pipe lines take this water to decarbonizer units. Decarbonizer is

filled with 1 inch porcelain “rashing rings”, dumped into cylindrical shell in order to increase

water and air surface contact area to effect degasification. Carbonic acid H2CO3 formed during

H-Cation exchange is decomposed by spraying the water from the top.

H2CO3 = CO2(g) + H2O

Secondary Cat-ion Exchanger

Two decarbonizer water collecting tanks V=200m3 at the bottom of decarbonizer collect this

water. From these tanks it is pumped into 2nd stage H-cation exchanger. The H-Cation replaces

remaining traces of sodium as well as calcium and magnesium cations of different salts from

water with their H-Cation.

Secondary Anion Exchanger:

After the ion exchanger in secondary H-Cation exchanger the water enters a final stage of ions

removal called secondary anion exchanger. Here a strongly basic anion exchange resin AB-17

exchanges the ion of week acids H2CO3 & H2SiO3. The ion exchange resin of of secondary

cation exchanger is regenerated with 3.5-5.5% sulfuric acid and that of secondary anion

exchanger with a solution of 4-4.5% sodium hydroxide.


9 | P a g e

Fuels

Fuel is one of most important consideration when designing boilers because of day by day

increasing cost of fossil fuels. Special attention was given to this perspective when boilers of

thermal power plant at PSM were designed, boilers were designed in such a way that it doesn't

rely completely on fossil fuel but can also work with fuels obtained as by-product of steel-

making process. These boilers can burn Natural Gas, Blast Furnace Gas, Coke Oven Gas and

Coal Tar, where blast furnace gas and coke oven gas is by-product of different metallurgical

process at PSM.

Calorific value of above mentioned fuel is as follows:

Calorific value (Kcal/m3/hr) Name of gas

8400 Natural gas

880 Blast furnace gas

8900 Coal tar

4600 Coke oven gas

Calorific value while dealing fuels in boilers is important in determining flow rate of steam

exiting boiler, lower CV gives lower flow rates. Because of limited burning capacity of fuel in

furnace.

Given boiler gives following steam flow rates while burning different fuels:

While burning blast furnace gas: - 135 tons/h.

while burning natural gas :- 220 tons/h

Furthermore; availability of Coke oven gas and Blast furnace gas has decreased because of

decrease in production at PSM, only 10% of total capacity nowadays, therefore these fuels

individually does not fulfill demand of boiler and Coal Tar produces ash which needs to be

removed from time to time. Therefore boiler furnace works on mixture of coke and natural gases,

and mixture of coal tar and blast-furnace gas for better burning with better Net Calorific Value of

fuel along with fulfilling requirements of boiler.


10 | P a g e

Boiler

“Thermal Power Plant”

In order to fulfill power requirements of Pakistan Steel Mill, electricity generation plant was

setup with capacity of producing 165 Mw of power through three 55 Mw Steam Turbine

accompanied by 3 Russia made boilers for producing super-heated steam at a rate of 220 tons/

hour each. Not only electricity is generated but residual steam is utilized to run another turbine

which drives compressors directly in Turbo Blower Plant, and is also used as purified feed water

for boilers in different departments of Steel mill.

Boiler Type and Specification:

Boilers are high pressure water tube boilers with Natural Circulation, as mentioned in their

model number: TIM-159/CO, where CO denotes Natural Circulation of water inside boiler due

to pressure head.

Capacity 220 tons/hour

Steam Pressure 100 kgf / cm2

Super-heated steam temperature 540 oC

Total Heating area 19393 m2

Feed Water Pressure 160 kgf/ cm2

Boiler Structure:

Boilers basic structure is a ∩ shaped where one shaft is up-stream flue gas duct called Furnace

or Radiation Shaft, special arrangements are at roof of boiler for super-heated steam, and other is

downstream shaft call Convective Shaft with an exit for flue gases into air preheater at bottom of

shaft.


11 | P a g e

Schematic showing basic boiler components along with flow direction of water (green) and steam (red)


12 | P a g e

BOILER FURNACE:

Boilers furnace is versatile type furnace with ability to burn four different kinds of fuel through 8

burners located on radiation shaft different burners. These fuels include Natural Gas, Blast

Furnace Gas, Coke Oven Gas and Coal Tar. Not only individually using these fuels, furnace can

also work with mixture of coke and natural gases, and mixture of coal tar and blast-furnace gas

for better burning with better Net Calorific Value of fuel.

All eight burners are placed on up-stream radiation shaft in such a way that 4 burners are on one

side of shaft and other four on other side. As shown in following figure:

Burners located on upper side are designated to burn Natural Gas and Coal Tar while lower

burner use Blast furnace gas and Coke oven gas as fuel.

Amount of gas that can be burned by burners according to fuel used is as follows:

Fuel Burning Capacity Natural Gas 4000 m3/ hr.

Blast Furnace Gas 25000 m3/ hr.

Coke Oven Gas 3875 m3/ hr.

Coal Tar 1.2 ton/ hr.


13 | P a g e

Regenerative air heaters:

Burning large amount of fuel requires a large amount of air. Air is supplied to furnace through 2

Forced draft fans and is sucked into Regenerative Air heaters through 2 induced draft fans.

Each F.D fan forces fresh air at a rate of 60,000 m3 / hr. into R.A.H, where fresh air is heated

through flue gases exiting boiler. Flue gases exits boiler at a temperature ranging from 230-270

C and drops its temperature to 150 C in R.A.H, where as fresh air enter R.A.H. at 40 C and exits

R.A.H at 220 C.

Regenerative air heaters have two vertical columns. Fresh air from F.D fans travels in one

column and flue gases from boiler travels in other column. Air heater fan is placed in such a way

that it intersects the two columns. Air heater fan travels from one column to another column

without allowing two gases to mix into each other. Fan absorbs heat into its fins due to higher

temperature of flue and dissipates its energy into low temperature fresh air region. Speed of air

heating fan ranges from 2-3 rpm.

Feed Water Economizer:

Water before supplying to steam drum for evaporation cycle is heated to raise its temperature,

feed water economizer is placed at bottom of radiation shaft when flue gases have lost most of

their energy content and have less temperatures for producing super-heated steam, therefore that

energy is utilized in preheating water.

Lower Headers:

Below furnace of boiler are Header known as lower headers, here saturated water is collected

before sending it to water walls for heating, they acts as mud drum in boilers, TIM 159/CO has

14 lower headers in total with 4 located on wider side of boiler while rest are on other side of

boiler.

Distribution of risers in headers is as follows:

Header Location Number of headers in that

location

Numbers of tubes in each Header

Left 3 35

Right 3 35

Front 4 32 (2) and 38 (2)

Rear 4 32 (2) and 38 (2)


14 | P a g e

Upper Headers:

These are chambers at top of furnace where steam and water is collected from risers and water

walls, and steam is forwarded to Steam drum whereas water recirculates till it becomes steam.

There are 14 upper header in all positioned in same manner as lower header but number of down

comers is less than number of risers, water comes down to lower header through 44 tubes.

Steam Drum:

From upper header steam is directed to steam drum located above the radiation chamber. Here

steam is separated from carryover through cyclone separators and remaining water is brought

back to lower headers for recirculation. Steam pressure inside steam drum is 100 Kgf / cm2 (98

bars). Saturated steam from steam drum enters Ceiling Super heaters.

Ceiling Super Heater and Screen Super Heater

In ∩ shaped boiler, portion connecting ceiling of radiation shaft with ceiling of convective shaft

is covered with ceiling super heater. for further heating steam from ceiling super heating enters,

these are vertically hanging tubes located at horizontal shaft connecting radiation and convective

shafts.

De Super heaters

Superheated steam from Screen super heaters enters De Super Heater, it reduces/regulates

temperature of steam especially when boilers is working on partial load to avoid damages to

tubes and components.

Condenser: Function of condenser is to form condensate for de super-heaters.it is located outside but on the

top of boiler plant. It consist of cylindrical steel shell in which feed water tubes are passing

through, and is connected to boiler drum by two pipes through which steam is provided. Here

steam transfers its energy to feed water, it gets preheated, and steam condensates to liquid water

which is free from all impurities.

Suspension Super Heater:

Steam from De super heater enter Suspension super heater, these are horizontal pipes containing

steam for super heating, place in such an order that a only a little space is present in between

pipelines so that flue gases get forced over its surface and maximum heat transfer take place.

Suspension super heater gets its name from face that these tubes are suspended with help of

clamps in convection chamber.


15 | P a g e

There are two stages of suspension super heater:

● 1st stage Convective Super Heater or Inlet Packet

● 2nd stage Convective Super Heater or Outlet Packet

Steam Chest:

Super-heated steam from Suspension super heaters enters Steam chest, a cylindrical drum at top

of boiler. Steam chest is place where steam is temporarily stored before supplying to turbine for

power extraction.

Temperatures of Water and Steam at inlet and outlet of different

Boiler components:

COMPONENT INLEToC OUTLEToC

Suspension System 215 228

Condenser 228 271

Economizer 271 320

Ceiling super heater 320 350

Turning Chamber 350 360

Screen Super heater 360 485

Convective Suspended S.H

(Inlet Packet)

485 540

Convective Suspended S.H

(outlet Packet)

540 560


16 | P a g e

Turbines

“Thermal Power Plant”

The TPP operates on a Rankine Cycle. The plant has 3 steam turbines installed. Each turbine

consists of 28 stages, of which, 15 are impulse stages and 13 are reaction stages. 1st of every

turbine has Curtis blading that is double blades to withstand the impulse force exerted by

incoming high pressure superheated stem from boiler. Labyrinth seal is used as a Seal to seal the

turbines. A generator is installed after each turbine which converts the mechanical energy from

turbine in the form of rotary motion of shaft, into electricity

Turbine Specification

Two extraction 10-16 atm and 1.5 to 3 atm

Rated output 60 Mw

Speed 3000 rpm

Frequency 50 Hz

Steam Pressure = 85 – 95 Kg/cm2

Steam Temperature = 525 – 540 C

Cooling water flow rate (through Condenser) = 8000 m3/hr

Cooling water inlet temperature = 28C

Max steam flow at nominal conditions = 402 ton/hr

Turbine Efficiency

To increase overall efficiency of the power plant cycle, feed water heating is performed. Bled

steam from different stages is used for regeneration.

To maximize turbine efficiency, the steam is expanded, doing work, in a number of stages. These

stages are characterized by how the energy is extracted from them are known as either impulse o

reaction turbines. Most steam turbines use a mixture of the reaction and impulse designs: each

stage behaves as either one or the other, but the overall turbine uses both. Typically, higher

pressure sections are impulsive type and lower pressure stages are reaction type.


17 | P a g e

Turbo Blower Station “TBS”

Pakistan Steel is the largest steel making plant in Pakistan, with a production capacity of 1.1

million ton per annum of steel. Pakistan steel mill uses 2 blast furnaces to meet that requirement.

Blast furnace requires hot compressed air for melting iron and for that purpose a turbo blower

station was set up. A fraction of steam (process steam) is taken out the thermal power plant

turbine and fed into a thermal blower turbine which in turn drives a compressor providing

compressed air.

The compressor consists of 4 stages. Those are

Sucking air from the atmosphere and passing it through a mechanical filter

Compressed air goes into the cooler

Comes back from the cooler

Finally it is blown into the blast furnace.

The cooling water passes through the condenser to remove the heat generated by compressing

gas, at a rate of 8000m3/hr.

The inlet temperature of cooling water is around 28⁰C.

There are 3 blowers present at the turbo blower station, each compressing air up to 4 atm

absolute pressure. Their specification is listed below.

Specification of turbo blowers

There are 3 blowers present at the turbo blower station.

Each blower has 4 stages

The blowers are run by steam turbine operating at 29 atm pressure

Each blower has the capacity to produce 1600 Nm3/min to 2200 Nm3/min of air for the

blast furnace.

The turbine installed at TBS is Russian made (model no ∩T-60-90/13).The turbine has two

extraction points for steam at 10-16 atm pressure and1.5-3 atm and the rated power output is

60mw at 3000 rpm


18 | P a g e

Recommendation:

De-Mineralization of Feed Water:

In order to deliver pure de-mineralized water to boiler in Thermal Power Plant, WCTP has to

treat condensate steam every time it circulates because of mishandling of condensate in TPP,

TBS and other department of steel mill, which utilizes low quality steam discharge by Power

Plant, cause an overload on WCTP thus decreasing quality of water delivered by WCTP.

Currently WCTP delivers medium quality de-mineralized water to TPP, this medium quality

water is reducing boiler efficiency as well as causing damage to boiler tubes and turbine rotors.

Therefore Pakistan Steel Mill should update WCTP with modern technologies and should install

other plants too for handling such higher flow rates. Listed below are the processes that can be

used to produce de-mineralized water.

Reverse osmosis

De mineralization of water can be done on industrial scale by using the reverse osmosis

process. RO is similar to osmosis but the only difference is that a large pressure is applied to

make the flow of water against the osmotic pressure. To obtain highly demineralized water,

the process is carried out two times. RO is preferred for large scale purification.

Nanofilteration

Nanofilteration process can be used along with RO process to obtain high quality water.

Membranes of nanofilters are limited to nano sizes and further purification can be done RO.

Theses process have no heating cost and the separation takes place at room temperature. The

only disadvantage of this process is that the membranes have to be changed after a while and

they are not yet commercially available.

Distillation

The process of distillation can be used to remove impurities from the water. The process is

carried out by first heating water to its boiling point and collecting the steam in a separate

container. All the suspended impurities are left behind as the water evaporates. However to

obtain a high quality distilled water, the process is carried out twice because certain volatile

oil get mixed with the water droplets during the boiling process. This process is not usually

preferred due to high heating cost.


19 | P a g e

Effective Utilization of Feed Water: Thermal Power Plant discharge flue gases at 150 oC, thus wasting a lot of available energy, this

energy can be utilized for better efficiency and maximum utilization of resources, this energy can

be utilized in following ways:

● For distillation of KSWB water for obtaining pure feed water.

● For heating fuel used in furnaces in different department of Pakistan Steel Mill.

● For heating raw water in WCTP to optimize it for best chemical reactions.


20 | P a g e

Sources of Information:

Boiler Structure diagram by Russian engineer

PSM official website

Notes by Site engineer at TPP

Turbine handbook

Notes by engineer at WCTP

Engineering

Analysis of Power Generation Plant at Pakistan Steel Mills