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PROJECT REPORT FOR THE PARTIAL FULFILLMENT OF BACHELOR DEGREE IN MECHANICAL ENGINEERING A STUDY OF EVAPORATIVE COOLING SYSTEM AT VISAKHAPATNAM STEEL PLANT Under the guidance Of Mr. N.VENUGOPALA RAO, Mgr (M) MMSM Dept., VSP Submitted by: C.KARTHIK (8801045121)
Transcript
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PROJECT REPORT FOR THE PARTIAL FULFILLMENT OF BACHELOR DEGREE

IN MECHANICAL ENGINEERING

A STUDY OFEVAPORATIVE COOLING SYSTEM AT

VISAKHAPATNAM STEEL PLANT

Under the guidance

Of

Mr. N.VENUGOPALA RAO, Mgr (M)

MMSM Dept., VSP

Submitted by:

C.KARTHIK (8801045121)

ODANNA ERUMALLA (8866533689)

Training dated from 04/06/2012 to 16/06/2012

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VISAKHAPATNAM STEEL PLANT

RASHTRIYA ISPAT NIGAM LIMITED,

Certificate

This is to certify that the project report in industrial training for the partial fulfillment of Bachelor degree in Mechanical Engineering at SARDAR VALLABHBHAI NATIONAL INSTITUTE OF TECHNOLOGY entitled “A Study of EVAPORATIVE COOLING SYSTEM at Visakhapatnam Steel Plant “ is a bonifide record of

C. KARTHIK (8801045121)

ODANNA ERUMALLA (8866533689)

The results embodied in this project report have not been submitted to any other University or Institute for the award of any Degree or Diploma.

As a part of summer training at VSP, Visakhapatnam, this project is carried out with the objective of making the participant well versed in Evaporative Cooling System and its scope.

Under the guidance of

Mr. N.VENUGOPAL RAO, Mgr (M)

MMSM Dept. VSP

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ABSTRACT

This project report deals with the study of “Evaporative cooling system (ECS)”, in walking beam-reheating furnaces, primarily used at rolling mills in steel industries.

A keen study of the system was made in ‘Medium Merchant and Structural Mill (MMSM)’ at Visakhapatnam Steel Plant (VSP), the first integrated and most modernized steel plant in the country.

Evaporative Cooling System (ECS) forms an important component in cooling the skids ( the supports used for carrying blooms) in walking beam-reheating furnaces, ‘the most commonly used’ in rolling mills.

This project describes the basic principle and working of the system in detail with specifications. The troubles that may be encountered in various components of ECS like turbines, governors, pumps etc. along with their possible solutions have been dealt with. The merits and demerits of the system were also discussed.

Finally certain suggestions were also given which may make the system more economical.

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Contents:

1. Introduction to VSP

2. Medium Merchant and Structural Mill (MMSM)

3. Concept behind evaporative cooling system (ECS)

4. Components of ECS

5. Auxiliary units of ECS

6. Conclusion and suggestions

7. References

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CHAPTER

1INTRODUCTION

HIGHLIGHTS:

Introduction to Visakhapatnam Steel Plant (VSP)

Vision , Mission and Objectives

Major products of VSP

Major units in plant

Role of various departments in converting from ore to steel.

Ore to steel block diagram

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INTRODUCTION TO VISAKHAPATNAM STEEL PLANT (VSP):

Steel comprises one of the most important inputs in all Visakhapatnam steel plant, the first coastal based steel plant of India is located 16kms south west of city of destiny i.e. Visakhapatnam. Bestowed with modern technologies, VSP has an installed capacity of 3 million tones per annum of liquid steel and 2.656 million tonnes of saleable steel. At VSP there is emphasis on total automation, seamless integration and efficient up gradation, which result in wide range of long and structural products to meet stringent demands of discerning customers within India and abroad. VSP products meet exalting international quality standards such as JIS, DIN, and BIS, BS etc.

VSP has become the first integrated steel plant in the country to be certified to all the three international standards for quality (ISO-9001), for environment management (ISO-14001) and for occupational health and safety (OHSAS-18001).

VSP exports quality pig iron and steel products to Srilanka, Myanmar, Nepal, middle-East, USA and South East Asia (pig iron). Having a total manpower of about 16755 VSP has envisaged a labour productivity of not less than 262 tonnes per man year of liquid steel which is the best in the country and comparable with international levels.

VSP TECHONOLOGY: STATE-OF-THE-ART TECHNOLOGY:

7m tall coke oven batteries with coke dry quenching Biggest blast furnaces in the country

Bell – less top charging system in the blast furnace.

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100% slag granulation at the blast furnace cast house .

Suppressed combustion LD-gas recovery system .

100% continuous casting of liquid steel.

“TEMPCORE” & “STELMOR” cooling process in LMMM and WRM respectively.

Extensive waste heat recovery system . Comprehensive pollution control measures

VISION

To be a continuously growing world class company we shall

Harness our growth potential and sustain profitable growth. Deliver high quality and cost competitive products and be the first choice

of customers. Create an inspiring work environment to unleash the creative energy of

people. Achieve excellence in enterprise management. Be respected corporate citizen, ensure clean and green environment and

develop vibrant communities around

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MISSION

To attain 16 million ton liquid steel capacity through technological up-gradation, operational efficiency and expansion; to produce steel at international standards of cost and quality; and to meet the aspirations of the stakeholders.

OBJECTIVES

Expand plant capacity to 6.3Mt by 2011-12 with the mission to expand further in subsequent phases as per Corporate Plan

Revamping existing Blast Furnaces to make them energy efficient to contemporary levels and in the process increase their capacity by 1 Mt, thus total hot metal capacity to 7.5 Mt

Be amongst top five lowest cost liquid steel producers in the world Achieve higher levels of customer satisfaction Vibrant work culture in the organization Be proactive in conserving environment, maintaining high levels of safety

& addressing social concerns

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Major Units

Department Annual Capacity(‘000 T) Units(3.0 MT Stage)Coke Ovens 2,261 4 batteries,(3) of 67

Ovens &7Meters HeightSinter Plant 5,256 2 Sinter Machines of 312

SQ.Mtr grate area each

Blast FurnaCE 3,400 2 furnaces of 3200 Cu.Mtr. Volume each

Steel Melt Shop 3,000 3 LD Converters each of 133 Cu.mtr. volume and Six 4 strand bloom casters

LMMM 710 4 Strand finishing MillWRM 850 2 x 10 strand finishing

MillMMSM 850 6 Strand Finishing Mill

Main Products of VSP

Steel products By-Products

Angles Flats Nut Coke Granulatedslag

Billets Rounds Coke Dust Lime FinesChannels Re-Bars Coal Tar Ammonium

Sulphate Beams Wire-Bars Anthracene BenzeneSquares HP Naphthalene Toulene,

Xylene,

Wash Oil

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MAJOR DEPARTMENTS

Raw Material handling plant (RMHP)

The Raw Material Handling Plant (RMHP) receives the basic raw materials required for the Steel making process from various sources through railway wagons and by road. These are Stacked by stackers and reclaimed by reclaimers and distributed to various departments of VSP through conveyor system. The Iron Ore Fines, Iron Ore Lump, Sized Iron Ore, Limestone (BF&SMSgrades), Dolomite (BF & SMS grades), Sand, Quartzite and Manganese lumps are stacked at Ore& Flux Yard. The Imported Coking Coal (ICC), Medium Coking Coal (MCC), Boiler Coal (BC) are stacked in Coal Yard. Coke is sent directly to Blast Furnace after tippling from ore and flux wagon tipplers .

Raw Materials to the tune of 12-13 Million tons required for producing 3million Tones of Liquid Steel.

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These raw materials are sent to various departments as indicated below:

Sinter Plant: Iron Ore Fines, Lime stone (BF), Dolomite, Sand and LD slag. Blast Furnace : Sized Iron Ore, Limestone (BF)/ LD slag, Manganese

Lump, Quartzite and Coke. SMS: Dolomite (SMS), Sized Iron Ore, Dolo chips. CRMP: Limestone (SMS), Dolomite (SMS), Dolo chips. TPP: Crushed Boiler Coal. COCCP: Imported coking coal (ICC), Medium coking coal (MCC).

The Raw Material Handling Plant is divided into two sections Coal Handling Plant (CHP) and Ore Handling Plant (OHP).

Coke Ovens & Coal Chemical Plant

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Coking coal after selective crushing and proper blending is subjected to destructive distillation (heating in the absence of air) in the Coke Ovens. A Coke Oven After heating for nearly a period of 16-18 hours at a temperature of about 1100oC, coke is obtained and is used as a fuel as well as reducing agent in the Blast Furnace.

The Coke Ovens of VSP are engineering feats by themselves. They are the tallest ovens constructed in the country.

A Coke Oven comprise of two hollow chambers namely ‘coal chamber’ and ‘heating chamber’.In the heating chamber a gaseous fuel such as Blast Furnace Gas, Coke Oven Gas etc. is burnt.The heat so generated is conducted through the common wall to heat & carbonize the Coking Coal placed in the adjacent coal chamber.

Number of ovens built in series one after the other form a Coke Oven Battery.The Plant has 3 batteries of 7mtr. tall ovens with each battery consisting of 67 ovens.

Another feature is the dry cooling of coke carried out by the inert gas nitrogen thus,

reducing pollution considerably.

Besides a bio-chemical plant separately undertakes the treatment of effluents. By-products like benzene, toluene, xylene, napthalene, coal tar, creosote oil, pitch, ammonium sulphate and benzol products are also recovered from the coke ovens gas. VSP produces, among other by-products, pushkala a prime fertilizer based on ammonium sulphate.

Sinter plant

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Iron ore fines, coke breeze, limestone and dolomite along with recycled metallurgical wastes are converted into a hard and porous ferrous agglomerated ferrous material(mass) called ‘Sinter’ at the Sinter Plant, which forms 80% of iron bearing charge in the Blast Furnace.

Sinter is A BETTER FEED MATERIAL to Blast Furnace in comparison to Iron Ore lumps and its usage in Blast Furnaces help in increasing productivity, decreasing the coke rate & improving the quality of Hot Metal produced.

The Sinter Plant comprises of two sinter machines each having 312 square meters of grate area with a total production capacity of 5.256 million tonnes per annum.

Blast Furnace

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VSP has two Blast Furnaces named as “Godavari” & “Krishna” with an effective volume of 3200 cu.m, each of which are the largest in the country equipped with Paulworth Bell less top equipment with conveyor charging.

Blast Furnace is charged with coke, iron ore and sinter from the top and produces about 5000 tonnes of molten iron per day. Its novel circular cast house with four tap holes ensures continuous tapping of hot metal. The annual production capacity of these Blast Furnaces is 3.4 million tonnes of liquid iron.

Provision exists for granulation of 100% liquid slag at blast furnace cast house and utilization of blast furnace gas top pressure (1.5-2.0 atmospheric pressure) to generate 12 MW of power in each furnace by employing gas expansion turbines.

Steel Melt Shop and Continuous Casting:

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Steel Melting Shop is divided into two major sections.

CONVERTER SHOP :

Bulk Material Handing Section (BMHS) Mixer Shop Converter Bay Scrap Yard Slag Yard Ladle Preparation Bay

CONTINUOUS CASTING SHOP :

Tundish preparation Bay (TP Bay) Argon Rinsing Station (ARS) & IRUT & LF Continuous Casting Machines Gas Cutting Machines Bloom Storage Yard.

Three Top blown converters called as LD converters (or Basic Oxygen furnaces/Converters), each of 133 cu.m. Volume, produce a total of 2.7 million tones of liquid steel per annum.

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99.5% pure oxygen at 15-16 KSCG pressure is blown in the Converter through

Oxygen lance.It consists of three concentrically arranged steel tubes with connecting branches for Metal - Flexible - Hoses. Central pipe is for supplying oxygen, intermediate pipe is for incoming cooling water and outside pipe is for outgoing water. At lower part of lance there are 4 nos. Convergent - Divergent copper nozzles syrnetrically arranged at 17.50 to the lance axis.

Oxygen oxidizes the impurities present in the Hot Metal, which are fixed as slag

with basic fluxes such as lime.

Characterstics of converter is given below:

Capacity = 150 Tonne Effective Volume = 133 cum Converter specific volume = 0.886 Meter Cube per Tonne Height to Diameter Ratio = 1.36

Refractory for converter lining is MgO based e.g. Sea water Magnesia, Magnesia carbon, Tar, Bonded.Dolomite Bricks, Pitch Bonded Dolomite Bricks etc.

Different grades of steel of Superior quality can be made by this process by controlling the Oxygen blow or addition of various Ferro alloys or special additives such as FeSi, FeMn, SiMn, Coke Breeze, aluminium etc. in required quantities while liquid steel is being tapped from the converter into a steel ladle

This liquid steel thus produced is casted in six-4 strand bloom casters. A special feature in energy conservation is the collection of Converter gas to be used as a fuel in the plant.

The entire molten steel at VSP is continuously cast at the radial type continuous casting machines resulting in significant energy conservation and better quality steel. 100% Continuous casting on such a large scale has been conceived for the first time in India.

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The foremost important factor in the continuous casting is the copper mould which decides the efficiency of the process.

Copper is an ideal material for mould because it is having

i) good thermal conductivity. ii) mechanical strength must be retained at operating temperature 250 degree C. iii) recrystallization temperature above 300 degree C. iv) low friction coefficient and good resistant to wear. v) chemical immunity w.r.t. steel.

 

ROLLING MILLS

The cast blooms from continuous casting department are heated and rolled in the three high speed and fully automated rolling mills, designed to produce 2.656 million tones per annum of finished products from continuously cast blooms with a wide range products like Reinforcement bars, rounds, squares, flats, angles, channels, billets, wire rods etc.

The mills are : a. Light & Medium Merchant Mill (LMMM) b. Medium Merchant & structural Mill (MMSM) c. Wire Rod mill (WRM)

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Some of the Salient features of the mill are : a. High capacity and high speed. c. Double sided cooling beds of walking beam type. d. High capacity and high productive sawing lines. e. Automatic bundling machines. f. Computerization at the sequential process control and material tracking g. Adoption of closed circuit TV at furnaces. h. evaporative cooling system and waste heat recovery.

.

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CHAPTER

2MEDIUM MERCHANT AND STRUCTURAL MILL (MMSM)

HIGHLIGHTS:

MMSM:

Introduction to MMSM

Description of process in MMSM

Walking Beam Reheating Furnace:

Components of reheating furnace

Equipment specifications

Furnace construction features

Fixed and moving beams

Combustion systems

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INTRODUCTION :

In Medium Merchant and Structural Mills (MMSM) The blooms of size 250x250mm are heated to temperatures around 1200 c and rolled into different Categories of bars and structurals like rounds, squares, flats, angles, channels, HE and IPE beams by timely estimation of demand.

MAJOR FACILITIES:In order to meet the production requirements, the following major facilities are available in MMSM.

CHARGING GRID & FURNACE:- 3 charging grids.- 2 x 130 t/hr top and bottom fired walking beam furnaces with evaporative cooling system.

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MILL PROPER:

The mill train of MMSM consists of a total of 20 stands as follows:

Roughing train consists of 8 stands as

two high horizontal stands,

vertical standards

combination stands

Intermediate train has 6 mill stands as per details given below

high horizontal stands

combination stands

horizontal stands/2 universal stands

Finishing train consists of 6 stands namely

combination stands horizontal stands/4 universal stands

The important feature of this mill is that Universal beams (both parallel and wide flange) have been rolled first time in India using Universal stands. Parallel flange beams have advantage over conventional beams as per the same weight the section is stronger and stiffer due to greater moment of inertia and higher radius of gyration.

COOLING BEDS STRAIGHTENER & BATCHING: - 120 m long double sided rake type cooling bed. - 2 straightening machines, one in each line. - 2 collecting beds and batch transfer equipment. FINISHING AREA: - 2 cold saw lines each consisting of one stationary saw and two movable saws. - 2 x 24 m bundling machines and 2 x 24m and 2 x 12 m piling machines .

- Online refinishing line.

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The technical specifications of various products produced in the mill are as given Below:

CATEGORY SIZE(mm)

1. Bars

Rounds …… 42-45

50-75

Squares …… 40-65

Flats …… 100x10-20150x10-20

2. Structurals

Equal angles …… 75×75×6-1080×80×6-1090×90×6-12100×110×6-12110×110×6-12

Unequal angles …… 80×60×6-10

100×75×6-12

Channels …… 100×150125×65150×75175×75180×90

T-bars …… 100×100

Beams, HE type …… 96×100100×100114×120

Beam, IPE type …… 100×55120×64140×73160×82180×91

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The various grades of steel produced are as follows:

1. Bars - Mild steel- Medium carbon steel- Forging quality- Bright bar quality- Free cutting

2. Structurals - IS 226- IS 2062- IS 961- Lloyds Gr A

PROCESS DESCRIPTION:

The input material to the mill is continuous cast blooms of size 250x250mm. Two walking beam type furnaces are provided for reheating the blooms. For charging the furnace the blooms are loaded on the bloom charging grids in batches by magnet cranes. Blooms are visually inspected on the charging grids and weighed one by one on a weigh scale incorporated in the charging roller table, aligned in front of the furnace and charged into the walking beam furnace by a bloom charging device. The heated blooms from the furnace are discharged one by one onto the delivery roller table by bloom discharging device for feeding them to the first stand of roughing train. During transportation to the first roughing stand, the blooms are descaled on all 4 sides by a hydraulic descaler.

The mill train consists of continuous roughing, intermediate and finishing group of stands. Depending on the section being rolled the combined stands, provided on each of the continuous trains, are arranged in a horizontal or vertical position. In case of the rolling of beams suitable no. Of horizontal stands, provided in the continuous intermediate and finishing trains are replaced by universal stands.

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Generally the front ends of the bars are cut by shears installed before the intermediate train and finishing train. Front end cropping, dividing of finished bars into multiple sale lengths for cooling bed, emergency cutting and test piece sample cutting is done by the shear provided after the finishing group. Inline size measurement is done for rounds, squares, and flats on equipment provided after finishing group of stands.

Following the shear after the finishing train is a series of water boxes and roller tables complete with water spraying nozzles for controlled and rapid cooling of divided bars after which they are directed with the help of a diverter switch to the double sided cooling bed. The finishing of cooled bars is done on inline automatic finishing lines installed after each cooling bedside. This finishing lines is provided with facilities for straightening, cutting, inspecting, sorting according to surface quality and length, counting, piling, bundling, tying, weighing and tagging with embossed metallic tags.

EOT cranes having 20-tonnes capacity,10m crane rail height and fitted with Rotating rolling, spreader beam and magnet/slings is available for removing piled and bundled products to the storage area.

MMSM TECHNICAL DATA :

CAPACITY : 8,50,000 T/YEAR PRODUCTS : ANGLES, CHANNELS, BEAMS, FLATS, ROUNDS & SQUARES SP. FUEL CONSUMPTION : 340 X 1,000 KCAL/T SP. POWER CONSUMPTION : 93.92 KWH/T ROLLING RATE : 222 T/HOUR

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INTRODUCTION TO REHEATING FURNACE

Re-heating furnace is the equipment which is used to re-heat the already cast material which enables to allow the material for plastic deformation to get the desired shapes of the product.

Quantity of heat to be imparted to the charges :-

If the charges is to be heated in a furnace, heat must be first generated in the furnace. The heat must then be transferred to the material which is to be heated.

The heat that is to be imparted to the charge equals to the weight of charge times temperature rise times mean sp. Heat of charge.

i.e. H=mstm=weight at chargess=specific heat of charget=rise in temperature.

Transmission of heat to the surface of the charge :

In furnace heat is transferred by conduction, convection & radiation.Most of heat transfer to the charge takes place by radiation

i.e. radiation from walls and flames etc., about 90-95% of heat transfer takes place by radiation.

It is obvious that to transfer heat to the charge, the heat must be generated by burning of fuel . During this process furnace equipment like dampers, burners, and supporting skids, various valves and elements of cooling system are to be controlled and keep them in good operating conditions. Furnace atmosphere is to be strictly maintained.

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IMPORTANT COMPONENTS OF THE FURACE:

The reheating furnace includes the following components:

Furnace structural framework

Walking beam driving mechanism

Walking beam and fixed beams

Combustion air fan

Burners

Waste gas exhaust system

Refractory and insulation

Fuel system, evaporative cooling system, lubrication and hydraulic system

The specifications of the blooms being fed into the furnace are:

Blooms Size

Thickness 250mm

Width 250mm

Length 6000mm

Weight 2900kgs

EQUIPMENT SPECIFICATION:

The walking beam furnace is used for heating blooms of plane carbon steel, low alloy steel, free cutting steel, medium and high carbon steels from ambient to about 1200 ˚C . The furnace is charged in two rows for 6mts long blooms

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Type …… Top and bottom fired walking beam furnace

Number (total) …… Two

Nominal output …… 250T/hr

Charge temp at inlet …… Ambient

Charge temp at outlet …… 1200c

Temp. difference between

Surface and core (max.) …… 30c

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FURNACE CONSTRUCTION FEATURES:

The furnace is fabricated from steel plates adequately reinforced with structural steel members for the robust construction. Steel plates and steel members of heavy section are provided to support the hearth.

1. Charging and discharging doors:

The furnace is provided with charging and discharging doors of suitable dimensions. The doors fabricated from structural steel sections and lined with refractory materials. The doors are balanced by counterweights and operated through electric drives. The discharge doors are of water-cooled type. The door openings and door peripheries are fitted with heat resistant casting.

2. Side doors:

A sufficient number of side doors are arranged over the entire furnace length at the workload level. Arrangement for manual operation, locking in open position and wedged guides for ensuring proper tightness in closed position is provided. These doors and the opening periphery are made of heat resistant casting with refractory lining. Clean out doors at the furnace hearth level are also provided. For sealing the gaps at the bottom hearth around walking beam post, water

troughs made out of corrosion resistant steel plates of adequate thickness are provided.

Charging and discharging side front walls:

The charging and discharging side front are equipped with water-cooled Lintels that support the roof noses.

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COMBUSTION SYSTEMS:

1. Burner:

Adequate number of burners of suitable design to fire mixed gas in per heating, heating(top and bottom) and soaking zones (top and bottom) are provided.

2. Combustion air fan:

The furnace is provided with two nos. of combustion air fan, one in operation and one as a standby. The rated capacity of the fan is 30% higher than the volume of air required for maximum connected load of the burners considering 10% excess air.

3.Waste Gas Recovery System :

a. Chimney : products of combustion are exhausted from the preheating section of the furnace through underground flue channel leading to a chimney .

b. Dampers : Dampers for automatic pressure controlling the waste gas is made of heat resistant material to withstand the temperature of the waste gases.

c. Air and Gas recuperators : connection type multi tubular air and gas recuperator is provided in the gas flue channel. The unit is designed for preheating the inlet air to the burner manifold to a temperature of around 380c.

d. Dilution air fan : A centrifugal lower complete with accessories is provided for supplying cold air in the waste gas flue upstream of the recuperator to prevent the recuperator tubes from overheating.

e. Legging : The combustion air pipe and gas pie between the recuperators and the burners is lagged externally with insulating materials. Internally with refractory material depending on the diameter. The lagging is protected by galvanized sheet steel wrapping.

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4. Refractories and insulation:

a. The roof of the furnace is flat suspended type, which is built up with shaped roof hanger bricks made out of superheat duty firebricks. The roof hanger bricks are backed up with a layer of insulating matter. The roof brick hanger is made up of heat resistant steels.

b. The wall is lined with high alumina firebricks backed up with cold faced insulating bricks and insulating blocks.

c. The furnace hearth is lined with high alumina firebricks backed up with clod faced insulating bricks and insulating blocks.

d. The doors are lined with high temperature insulting castables.The waste gas flue upstream of the recuperator is lined with heat duty firebricks backed up with clod-faced insulating bricks. Down stream of the recuperator is line up with medium heat duty firebricks backed up with cold-faced insulating bricks. One ventilation course of red brick is provided between the refractory brick and concrete walls. Thickness of the refractory layers in the waste gas flue is so chosen that the maximum temperature on the flue concrete face doesn’t exceed150c.

e. The movable and stationary beams are lined with high alumina castables backed up by insulation materials.

The basic walking beam system consists out of a lifting and drive frame which work independent from each other. During the lift movement the lift frame will be lifted or lowered by means of rollers and an increasing slope beam. The movement forward and backward will be executed by the drive frame with rollers. The advantage of this system compared to the system with the eccentric drive is the variable pitch distance of the walking beam system. The sealing between the stationary and movement hearth is done using a water sealing unit.

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Audiovisual alarms:

Audio visual alarms are provided for abnormal conditions of the following parameters;

Over temperature of each zone of the furnace. Low furnace pressure High temperature of combustion air Over temperature of waste gas before recuperator High oxygen content of waste gas Low pressure of mixed gas supply Low pressure of cooling water supply

Safety interlocks:

Complete safety control equipment to protect the furnace in the case of mixed gas, combustion air, and cooling water and power failure is provided. In the event of any of these failures occurs or system does not have normal required pressure at the supply header, the safety shut off valve in the mixed gas line at inlet to the furnace will automatically shut off with the consequent audio visual alarms.

SALIENT FEATURES :

o Walking beam type reheating furnaceo 4 walking & 4 fixed skidso 130 T/Hr capacity (150 t/hr max)o Single or two row charging and dischargingo Top and bottom firedo Long flame and flat flame burnerso three heating zones, two soaking zones

zone-1 - 12 top heating flat flame burners zone-2 - 12 top heating flat flame burners zone-3 - 8 bottom heating long flame burners zone-4 - 18 top soaking flat flame burners zone-5 - 9 bottom soaking long flame burners.

o Evaporative cooling systems

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o Two steam turbines and one motor drive centrifugal pumpo In line air and gas recuperators for waste heat recovery

o Auto purging of zoneso Input of furnace heating material – blooms of 250*250mm cross

section and around 6 m longo Stack height 80 m (chimmne)o Fuel- mixed gas (BF+LD=CO) with 2000kcal/nm3 of calorific valueo Discharging temp. 1200 – 1240’co Duration 64 sec.

NORMAL OPERATING PARAMETERS :

Mixed gas pressure – 600mmwc Combustion air pressure – 900mmwc ECS drum pressure – 15bar Indirect cooling water pressure – 4.5bar Instrument air pressure – 4.5bar Drum level – 20 to 50mm Feed water pressure - >20bar Furnace pressure – 0.4 to 1.0mmwc Skid flow

Fixed o Post circuit – 19nm3/hro Skid circuit – 62nm3/hr

Movingo Post circuit – 52nm3/hro Skid circuit – 62nm3/hr

Hot air exhaust – 370*c Dilution temp. set point – 720*c Gas recuperator meatl temp. max – 430*c Air recuperator metal temp. max – 620*c

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WALKING BEAMS (SKIDS):

Operation:

Blooms are moved forward step by step, avoiding any friction or rubbing during its conveyance through the furnace. The blooms are gently lifted from the stationary beams, moved forward by walking beam and gently placed on stationary beams. Both walking and stationary beams are properly supported on vertical posts. The walking beam supporting posts are fastened to a movable frame which are equipped with rollers and permit the vertical and horizontal movement for the transfer of the blooms. The walking beams and stationary beams are fabricated out of seamless steam tubes.

Vertical and Horizontal Movements:

Vertical and horizontal movements of the beams are obtained through separate hydraulic cylinders. The operation of the cylinders ensures gradual startup and gradual stoppage during lifting and lowering and horizontal movement.

Charging and Discharging Equipment:

The blooms are conveyed and positioned in front of the furnace on roller table by electrical control. After positioning the blooms on the roller table, the blooms are transferred on the charging table by means of charging device in single row or in two rows. The blooms are discharged from the furnace separately from each row by means of discharging device. Two discharging devices are suitable for single row or two-row operation.

Hydraulic Power Pack Unit:

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A centrally located hydraulic power pack unit is provided for the furnace for operation of the various hydraulic cylinders for walking beam mechanism. The power pack unit consists of fluid tanks, pumps with drive and control, necessary solenoid valves, flow control valves, check valves, pressure relief valves, filters etc. One standby pump with drive unit is also provided.

Grease Lubrication System:

An automatically controlled centralized lubrication system is provided with necessary safety arrangement for lubrication of all moving parts.

Skids and Support Tube Cooling System:

Evaporative cooling system (ECS) is provided for cooling skids and support tubes. Steam generated is diverted to plant steam network. The evaporative cooling system comprises of separating drums, recirculation pumps, demineralised water, storage tanks, feed pumps with necessary pipes, valves,fittings,gadgets and necessary instrumentation.

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CHAPTER

3EVAPORATIVE COOLING SYSTEM (ECS):PRINCIPLE AND DESCRIPTION

HIGHLIGHTS:

Introduction

History and facts

Concept behind ECS

Working of ECS

Applications of ECS

Merits and Demerits of ECS compared to water cooled system

Main equipments in ECS

ECS circuit

Instrumentation and control system for ECS

General Design of ECS

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INTRODUCTION:

In evaporative cooling, also called steam or vapour cooling, the temperature of cooling water is allowed to reach a temperature of 100c. This method of cooling utilizes the high latent heat of water to obtain cooling with minimum of water the cooling circuit is such that the coolant is always liquid but the steam formed is flashed of in a separate vessel. The makeup water so form is sent back for cooling.

CONCEPT BEHIND ECS:

In evaporative cooling, hot water at boiling temperature is fed from a steam drum to the cooling components. Because of the heat energy to be absorbed by the cooling components, a part of the water is evaporated at almo9st constant temperature.

The steam/water mixture returning to the steam drum is separated into saturated steam and water. The steam is drawn from the drum and the water is available for recirculation. Consequently in evaporative cooling, at normally constant pressure in the seam drum, every point of the circuit has a constant temperature independent of the respective heat load.

On the other hand, in hot water cooling the heat energy to be absorbed by a cooling component is used to increase the temperature of the water flowing through it, In such circuits it must in any case be ensured that at every point of the cooling system the water has a lower temperature than the boiling temperature corresponding to the pressure. If this condition is not achieved, there will be local generation of steam, which can lead to damages.

Furthermore, hot water cooling requires guaranteed removal of the heat energy from the water circuit by means of a heat exchanger, In case of emergency the heat energy cannot be vented to atmosphere not even for short periods of time-as it would be possible with evaporative cooling.

Compared with other cooling systems the evaporative cooling has a further substantial advantage; to absorb and transfer much higher heat amounts.

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WORKING OF ECS :

The Major Components of ECS are the steam drum where hot water around 95 to 100 C exists in the drum along with the steam. The working pressure pf drum is around 13 to 15 bars thus acting as boiler.

This hot water is circulated to the furnace skids for cooling purpose through

recirculating centrifugal pumps. There are three such pumps in which one is electric motor driven and the other two are steam turbine driven. In case the power gets shut down unavoidable circumstances the steam turbine coupled with the pump starts automatically to circulate water to the skids.

Hot water after passing through the furnace skids(which is around 1200 C),the latent heat of vaporization by which it partially converts into steam and returns back to steam drum, where the steam and water gets separated . The amount of water converted into steam is compensated by the feed water supplied by DMDA (De-Mineralized, De-Aeration) plant through multistage centrifugal pumps. The steam produced in the system

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can be utilized by Supplying it to the steam network or to drive the steam turbine.

There are two pressure relief valves and an exhaust valve for relieving the

excess steam pressure, when the pressure in the steam drum exceeds permissible value(which is around 17 bar).There is a dosing drum connected with pipe network for maintaining a constant ph around 7.5 by adding chemicals periods sampling of drum water is done for regularly monitoring the specified standards of boiler water.

Forced circulation or natural circulation:

In forced circulation the circuit is maintained by recirculation pumps. Forced circulation can be used for all types of hot cooling. Natural circulation, however, is only possible in evaporative cooling, whereby the steam drum must always be installed above the cooling components.

In the down comers (between steam drum and cooling components) there is always water of a substantially higher specific weight than that of the steam/ water mixture in the risers (between cooling components and steam drum).

In this way sufficient lifting force is generated for maintaining the necessary water circulation.

APPLICATIONS OF COOLING SYSTEM :

In the following metallurgical furnaces ECS nowadays be successfully employed in the cooling components indicated below:

Pusher type and walking beam furnaces

Longitudinal skids Supporting tubes Cross overs Vertical supports Lintels Door frames

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Electric arc furnaces

Roofs and roof rings Walls panels and shell rings Doors and door frames Waste gas ducts(fixed and movable sections)

MERITS AND DEMERITS OF ECS COMPARED TO WATER COOLED SYSTEM:

Merits:

Scale formation is reduced in the pipeline as the water which flows through the ECS pipe line is De-Mineralized and De Aerated and also at a temperature of 90 to 100C

There is no requirement for replacing pipe lines for years since the water flowing through ECS pipe lines is free from all corrosion causing substances like dissolved oxygen salts of calcium and magnesium etc.

The steam that is generated along with the hot water after the cooling effect is used to run prime mo9vers like steam turbine.

Water requirement is less in ECS as hot water in the ECS system has higher heat absorbing capacity than water used in water-cooled system.

Since DMDA plant is integrated with in the ECS system of the rolling mill De Mineralized De Aerated water is available at an economical cost, this makes the ECS system of the plant efficient and economical.

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Demerits:

The initial set up cost for the ECS system is quite high when compared to the water-cooled system.

Utmost care has to be taken for the safety of the employees working near the system since the pressures involved are quite any imbalance can cause the system to explode. So safety measures are to be followed by conducting periodic inspection of the boiler.

The cost of pipe insulation is more in the case of the ECS system since a larger diameter pipe insulation has to be used when compared to the water cooled system to sustain the hot water and steam at high pressure.

MAIN EQUIPMENTS:

The evaporative cooling system is designed as a forced circulation hot cooling system to cool the pipes inside furnace.

The system consists mainly of the following parts:

Steam drum

Recirculating pumps

Inlet pipes

Inlet Swivel joint units

Cooling components

Outlet pipes

Outlet Swivel joint units

Steam takeoff pipe

Feed water supply pipes

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The (DIA.3a) shows the Evaporative Cooling system (ECS) circuit and the nomenclature of various pars given hence.

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INSTRUMENTATION AND CONTROL SYSTEM FOR ECS

1. Automatic controls:

Automatic steam control of each separator drum Three-element water level control of each separator drum By

controlling steam flow and feed water flow with drum level signal.

2. Measurements : recording of the following parameters for each separator drum

Steam pressure Drum water level Steam flow Feed water flow

Circulation water flow for each cooling circuit

3. Malfunctions: In case of any abnormal condition of the following parameters audiovisual are provided

Water level in steam drum too high(150mm above center line) Water level in steam drum too low (100-150mm below center

line). The furnace automatically trips at 250mm below centerline.

Steam drums pressure too high or low. Sudden fall out of recalculating pumps Single flow rate too low Feed water pressure too low.

4. Safety interlocks:

Complete safety control equipment to project each of the steam drums in the event of failure of feed water supply as well as for any other abnormalities is provided.

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CHAPTER

4COMPONENTS OF EVAPORATIVE COOLING SYSTEM

(ECS)

HIGHLIGHTS:

DMDA plant

Steam drum and its specifications

Turbine with woodward speed governor

Centrifugal pump

Swivel joint

Other components of ECS

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DMDA (De Mineralisation and De Aeration) PLANT:

The Demineralised and Deaerated water required by the Evaporative Cooling System (ECS) in rolling mills is supplied from DMDA plant. The plant also serves the needs of other departments like Thermal Power Plant (TPP), Coke ovens and Steel Melting Shop (SMS). The brief overview of plant working is as below:

RAW WATER ANALYSIS:

The required quality of feed water is:

PH 8 to 8.5Conductivity - 300 micro mho/cmTotal dissolved salts-150 to 200 ppm (mg/ l ton)Turbidity-10tol5NTU

DMDA Flow process chart

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Finally we obtain water of the following quality: PH value 7.5 to 8.0 Conductivity < 7 to 9 micro mho/cm Silica < 0.02 ppm Oxygen 0.007ppm. From here the water is pumped to the various units of the plant like TPP, Coke ovens, SMS and Rolling mills (MMSM, LMMM&WRM).

REQUIREMENT FOR FEED WATER AND BOILER WATER:

Feed water: General requirement - Clear and colourless PH value (at 25ºC) - 8.3 to 9.5 Total hardness - < 1mg/kg (as CaCo3) = 0.02 mval/kg Oil - < 0.5 mg/kg Oxygen - < 0.02 mg/kg CO2 (combined) - < 25 mg/kg CO2 (free) - undetectable Fe (total) - < 0.05 mg/kg Cu (total) - 0.01 mg/kg KMnO4 (consumption) - < 10 mg/kg Conductivity (at 20º C) - < 130 mg/kg (as NaCl) Cl- - < 10 mg/kg SiO2 - < 1 mg/kg

Boiler water

P value - < 90 mg/kg (as CO32-) = 3 mval/kg

SiO2 - <10 mg/kg PO4

3- - < 15 mg/kg Conductivity (at 20ºC) - < 1300 mg/kg Cl- - < 100 mg/kg

The continuous blow down is assumed as 10 %. If demineralised feed water is used, the continuous blow down may be zero.

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MAIN OPERATING DATA:

STEAM DRUM:

The steam drum is located at a longitudinal side of the furnace. Underneath the steam drum (approx. 10 m) are the recirculating pumps installed.

STEAM DRUM SPECIFICATIONS:

Working pressure - 15 to 17 bar Working temperature - 201 to 207ºC Volume - 12 m3

Dimensions - Ø 1600mm Length 6000mm Blow off flow rate - 1.3 m3/hr Saturated steam blow off rate - 13.2 T/ hr Effective pick up pressure - 17 bar Steam at drum inlet: Flow rate - 4.5 to 9 T/hr Temperature - 201 to 207ºC

Pressure in drum - 15 to 17 bar Available steam pressure - 12 to 15 bar

Feed water: Flow rate - 13m3/hr Temperature - 105ºC Pressure available - 23.5 bar

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TURBINE

Steam turbine:

Steam turbine is a single stage Impulse type machine, a cut-away view of a single stage turbine with woodward speed governors are shown in the figure following is a description of the major components that comprises a turbine .

Specification of a steam turbine:

Speed governor-TG-13Driven machine- centrifugal pumpNumber of stages-1,CurtisTurbines rotation – ccw as viewed from governor end

Power(kw)

SpeedTR/MIN

Inlet pressure(BAR ABS.)

INLET TEMP(˚C)

EXHAUSTPRESSURE(BAR ABS.)

GUARANTY 134 1470 15 300 atm

NORMAL 134 1470 9 180 atm

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1

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1– Governor Lever2 – Mechanical Shaft Governor3 – Steam end Bearing case4 – Sentinal Warning Valve5 -- Exhaust end bearing6 – Turbine shaft7 – Carbon packing rings8 – Steam chest9 – Steam chest drains10 – Steam strainer11 – Steam chest cover drains12 – Trip Lever13 – Oil Rings14 – Packing case Leak offs15 – Turbine wheels16 – Turbine case17 – Hand valves18 – Woodward UG or PG governor19 – Oil Lever Indicators20 – Over Speed cup21 -- Oil drains22 – Steam ring drain23 -- Casing drain24 – Thrust bearing25 – Main bearings26 – Coupling27 – Governor Adaptor housing28 – Hand speed changer29 – Woodward TG Governor

Casing Material : admission steam end: acier steel Exhaust end : Acier steel

Speed range : Min-1249 Max-1544

Inlet Valve : HP size 2.5” double steelEmergency overspeed trip setting: 1776rpmJournal Bearing : Steam end-0.17mm

0.22mm Exhaust end-0.22mm

Lubrication : Oil ring

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Centrifugal pump

Operating conditions :

o Liquid – boiler feed watero Pumping temp. – 201 to 207⁰co Specific gravity – 850 kg/m3o Vapour pressure – 17.96 baro Discharge pressure – 22.5 to 24 baro Suction pressure max – 16 to 18 baro Differential pressure – 5 or 6 baro Differential head – 77m

Performance :

Speed – 1460 rpmEfficiency – 78%Power – 111kwMax power – 125kwMax head – 87mMin constant flow – 100 m3/hr

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Swivel joint:

Introduction:

Since 1971 already, movable components for instance at walking beam furnaces no longer present any problem. The utilized swivel joints remain freely movable and require no lubrication. An appreciable advantage for operation safety and availability consists in

the fact that this type of joint cannot get jammed. The arrangement of the joints is adapted to the space conditions and –if

required- individual swivel joints can be re-placed during a scheduled furnace stop with no furnace temperature reduction. Swivel joints are made up of high grade steel and have an unlimited lifetime; only the replaceable sealing ring is subject to wear and tear and has to be replaced after several years’ operation, when deteriorated.

Swivel joints at walking beam furnaces are operating under a pressure of up to 55 bar g/270˚C.

Nowadays more than 1,500 swivel joints at walking beam furnaces are successfully in operation all over the world.

Description of the swivel joint units in ECS system:

swivel joint units are designed to provide moving skid systems with cooling water. These moving piping connections (fittings) allow feeding respectively removing of hot and pressurized water, steam and steam-water mixture.

The main parts of swivel joint are the ball nozzle that is pressed against the carbon seal ring against the helical spring. This initial pressing tights the swivel joint up between ball nozzle and carbon seal, when the cooling system is not under operating pressure. Under operating conditions the medium pressure raises the pressing of ball nozzle upon carbon seal thus enhancing the sealing effect.

The extra axial deviation of the ball nozzle against the swivel joint centerline is limited to 3.5˚ to avoid inadmissible edge pressure between ball nozzle and carbon seal ring. The middle swivel joint of a swivel joint unit is

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equipped with a roller and pivot guide. The pivot guide prevents any extra axial deviation of the ball nozzle against the centerline of the swivel joint assuring it’s genuine rotation relatively to the centerline of the swivel joint. The roller guide with the corresponding guide rail keeps the three swivel joints of a swivel joint unit in one moving plane and prevents the middle swivel joint from leaving this plane.

An elastic connection (weight compensation) between the upper fixing plate and the ‘S’ pipe serves as a weight relief for the upper swivel joint. The swivel joint acts as connection between a fixed and a moving joint. This joint has a rotation angle of 15 degrees. There are total 24 swivel joints connected in four joints.

Swivel joint units:

Horizontal movement - 400mm

Vertical movement - 200mm

Operating pressure (max) - 24.5 bar(gauge)

Operating temperature (max) -217˚C

SWIVEL JOINT PARTS:

1. MALE COUPLING(STAINLESS STEEL)

2. END COVER(STRL STEEL)

3. COLLER NUT(STRL STEEL)

4. COUPLING BODY(STAINLESS STEEL)

4a. SLEEVE (STRL STEEL)

5. GUIDE BUSH(STRL STEEL)

6. SPACER(STRL STEEL)

7. COMPRESSION SPRING( SPRING STEEL)

8. HEX HEAD BOLT(CARBON STEEL)

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DIAGRAM:

ARPEX COUPLING:

Arpex couplings are equally suitable for clockwise & anticlockwise rotation, also for reversing operation. In special design they can be installed vertically or inclined . The two coupling parts can be fitted to either of shaft ends to be connected . a gap remaining between mounted hub and shaft shoulder can be filled by a keyway or spacer bush. A sleeve of this type is not however essential for proper functioning of coupling. Arpex couplings will compensate deviations in relative positions of shaft to be connected. However, parallel offset &angular misalignment of shaft to be connected should be kept as small as possible. Alignment must be carried out in two perpendicular planes. An acceptable alignment can be obtained using a straight edge. More accurate alignment can be got by using a dial indicator.

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ORIFICEMETER:

Orifice meter is used in controlling the amount of cooling water in the skids and posts circuit. Mounting the flow rate of water. So this orifice meter aids the instrumentation to know whether a particular flow rate of water is maintained or not ,otherwise the instrumentation controls will take care of the required flow rate.

STEAM TRAP:

Steam traps; pass steam and condensate through a strainer before entering the trap. A circular baffle keeps the entering steam and condensate from impinging on the cylinder or on the disk. The impulse type of steam trap is dependent on the principle that hot water under pressure tends to flash into steam when the pressure is reduced. The only moving part in the steam trap is the disk. A flange near the top of the disk acts as an Impulse Steam Trap piston. The working surface above the flange is larger than the working surface below the flange.

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SUGGESTIONS AND CONCLUSIONS

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References:

Stein Hurtey Manuals

M.N. Dastur Report on MMSM

Training Manual, VSP.

Steam Tables

Manuals of pipes and joints.


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