blast furnace

AUTOMATION OF THE BLAST FURNACEAUTOMATION OF THE BLAST FURNACEThe Khwarzimic Science Society

2000 The Khwarzimic Science SocietyCentre of Excellence in Solid State Physics

Punjab University | Quaid-e-Azam Campus | Lahore 54590 | Pakistan [email protected] | http://www.khwarzimic.org | Ph (0) 92 42 5864185 | Fx (0) 92 42 5864534

Sabih D KhanMember KSS and Member Advertisement CommitteeFeb 23 2000http://khwarzimic.org/docs/blast_furnace.pdf

Title:Title:

Process and Control of BF Process(Computer Integrated Extraction)

Outlines:

• Introduction.• Electronic Sensors and Control.

Sensors1. Composition Analysis.

Optical Emission.X-Ray methods-energy

dispersed.Atomic absorption.Fusion analysis of gases.Plasma Method.Ion-selective electrode.Mass spectroscopy.Neutron Activation.

2. Sizing and Screening.3. Temperature Measurement.

(i). Optical Pyrometer.(ii). Thermal / IR Camera

System.(iii). Thermo-couples.(iv). Semi-conductor

Temperature Sensors.(v). Thermisters and RTD's.

4. Pressure Measurement.(i). Strain gages and Load cells.(ii). Linear Variable Differential

Transformer.(iii). Potentiometers.

5. Misc. Sensors.(i). Height of burden in stack.(ii). Gas flow meters.

Control Devices.1. Effectors / Actuators.

(i). Mechanical.(ii). Pneumetic.(iii). Hydraulic.

2. Robotic Manipulators.3. Automated / Semi-Automated Ground

Vehicles.4. Interfacing Devices.

Computers.1. Main Computers.

(i). Microsoft's Windows Family.(ii). MacOS.(iii). Unix.(iv). Linux.(v). Solaris.

2. Micro-controllers.(i). Microprocessor.(ii). Program Memory.(iii). Data Memory.(iv). Registers.(v). Parallel Ports.(vi). Serial Port.(vii). Interupt.(viii). Timer Counters.

3. Local Area Network.4. PLC Network.

• Pakistan Steel Mill Automation.1. Raw Material Preparation Plant.

(i). Reception and Storage Facility.(ii). Crushing and screening plant.(iii). Sintering Plant.

2. Coke Oven and By-Product Plant.3. Ironmaking Plant.4. Steelmaking Plant.5. Steel Forming Plant.

• Conclusion.• Refernces.

Introduction:

The electronic and computer revolution lead tothe automation of many mission critical manufacturingprocesses, which resulted in better quality managementand close specification control along with a considerabledecrease in the cost per piece of the product. This alsolead to solve the problem of worker strikes which werequite common in the first world countries due to verystrong worker unions. The automation also saved manylives by replacing humans in many harmfulenvironments. The first era of the automation evolutionwas the use of remotely human operated robots andmachines which enabled humans to control the factoryby sitting in the control room. The next era was theComputer Integrated Manufacturing (CIM) and ComputerAided Manufacturing which allowed the machines tomanufacture the required product from drawings and theonly staff required was/is maintainace staff anddesigners. The new era is named as flexiblemanufacturing which is an extension of CIM/CAM but thedifference is that many different products can be madefrom the same machinery at the same time, thusreducing the cost per part to ground.




In these papers an approach to CIM is used andI named it Computer Integrated Extraction (CIE).Currently, the blast furnace at Karachi Steel Mill isalready automated but the system lacks completecomputer integration and still requires operators withMetallurgy and Computer experience. My aim in thesepapers is to propose some guide lines which can beused in blast furnace to run it on auto-pilot orautonomous computer only system, which will no longerbe dependent upon operator skill. Currently, the furnaceruns on three shifts on 24-hours continous cycle and it isover employed. The proposed system might help downsize the un-necessary staff and may help to makeKarachi Steel Mill profitable.

Electronic Sensors and Control:

The main variables in the blast furnace whichneed to be sensed by the master computer forcomprehensive sensing and control are:

1. Composition.2. Sizing or Screening.3. Temperature.4. Pressure.5. Voltage. (only in Electrical Generators)6. Ampere. (only in Electrical Generators)7. Misc. Variables and Sensing.

Next are the electro-mechnical devices toenable complete control of master computer, thesedevices may come in the following categories:

1. Effectors / Acuators to replace humans inoperations, like openning and closing of doors in Cokeovens, controling double bell charging system, etc.

2. Robotic Manupulators to replace human arms inoperations like picking samples, tranfering materialsfrom Automated Ground Vehicles, carrying molten metalin ladle, etc.

3. Automated / Semi-Automated Ground Vehicle totransport mterials and products from one processtoanother, like carrying sintered charge from sinter plant toblast furnace charging mechanism.

4. Interfacing Devices to integrate existing controldevices with computer, like integration of oxygen valve inthe converter process.

Next is the computer related machines to controlthe whole operations, this includes:

1. Personal and Mainframe Computers, which maybe divided as:

(a). Master Control Computers.(b). Terminals for Data Entry and Remote

Process Control.(c). Dedicated computers like Controller of

Spectrometer and Industrial Screens.(d). Microcontrollers for programable logic

control of equipment like thermocouples, pressure transducers, etc.

2. LAN Based high speed computer network.3. Microcontroller-PLC (Programable LogicControl) network for Microcontroller integration withmain computers.4. Interface Cards and Circuits for the integration ofexisting machine controls and sensors with maincomputers.

Sensors

1. Composition Analysis:

Composition analysis is one of the main missioncritical variables to guarantee troubleless BF Operationand Product Composition. In a typical steel product froma BF operation the main critical elements are:

1. Carbon. (Fe3C, Solid Solution, Free Form)2. Sulphur. (MnS, FeS, etc.)3. Phosphorus. (Free Form, etc.)4. Manganese. (Free Form, MnS)5. Silicon. (Solid Solution, Free Form, Oxide)

And some other important elements are:

1. Chromium.2. Molybdenum.3. Nickel.4. Aluminum.5. Titanium.6. As.7. Bismuth.8. Cobolt.9. Copper.10. Nitrogen.11. Niobium.12. Vanadium.13. Lead.14. Rare Earth Metals.15. Antimony.16. Zirconium.17. Oxygen.18. Hydrogen.




Some typical products and stages which arenecessary to analize are:

___________________________________________________________________________

Materials Elements requiredAnalysis Time

___________________________________________________________________________ProductsCarbon Steels

Liquid C, P, S, Si, Mn, O, H, NLess than a minuteSolid1-5 minutes (Max)

Alloy SteelsLiquid C, P, S, Si, Mn, Mo, Ni, Cr, O, HLess than a minuteSolid1-5 minutes (Max)

Special SteelsLiquid C, P, S, Si, Mn, Mo, Ni, Cr, O,

H, Less than a minuteSolid Co, N, Pb, V, Sb, As, Bi1-5 minutes (Max)

SlagsSolid Fe2O3, Fe, SiO2, MnO, CaO,

Al2O3, In some steel plantsMgO

less than minute; Normally

1-5 minutes.Ores

Solid Fe, Si, Mn, Ca, Al4-10 minutes (used to pay(granular)mine owners and ore vendors)

Also to check on blending

plant operation.Coke

Solid C, S, O, H2O, N2, etc.Depends upon technique

Pig Iron(hot metal)

Liquid P, S, Mn, Al, Si, C1-5 minutes

RefractoriesBrittle Al, Mg (as oxides)5-10 minutesSolid Si, Ca, etc.

SintersHard, Brittle Fe, P, S, Mn, Al, Si, CaO, C1-5 minutesSolid

Ferro AlloysHard, Brittle Fe, Mn, Ni, Co1-5 minutesSolid Cr

PollutantsUsually NH4OH, As, Cyanides (CN),

Fluorides 1-5 minutesliquids (F), CO

GaseousBlast Furnace

Off-take CO, CO2, etc.10 secondsIn-Take O2, CO2, H2O Vapours, etc.(vital fo safety)

Steel ConvertorInput gase O2Output gases CO, CO2, FeO, etc.

___________________________________________________________________________

One of the main applications of intermediate-stage analysis is to diagnose the faults in steelmakingpractice via slag analysis. Much information can bededuced from this source, a typical analysis being asfollows:

FexOy 17-18%CaO 43%SiO2 14%P2O5 1.1-1.5%S 0.1%MgO 10%Al2O3 6%

Here if the iron oxide content is low then overr-oxidation is present, due to faulty charge calculations orincorrect hot metal analysis. A high FexOy indicatespossibly faulty lance practice. The lime and silica levelsare affected by flux addition practice, which may befaulty. The P2O5 level is sensitive to either:

1. High Temperature at turn down.2. Low state of oidation of slag, i.e. high

turndown carbon.3. Low slag iron (<14%), low CaO level in

slag or badly fluxed slag.




Sulphur levels are also critical indications of practice inoxygen steel making. The ratio between sulphur in slagto sulphur in steel should be between 5 and 8. If it is high8-15 then the extra sulphur in the slag must be traced. Ifit is low then poor fluxing is indicated , with high blast-furnace slag carry-over as an alternative explanation.

Instruments used in the analysis are:

___________________________________________________________________________

Method of Analysis Materials to be Automation Method

analyzed___________________________________________________________________________

Optical Emission (a). Crude SteelStand-alone computer integrated with

(b). Products main network.

X-Ray Fluorescence (a). SlagsStand-alone computer integrated with

(b). Sintersmain network.

Inert Gas Fusion SteelsTerminal attached to the main network.

Plasma Method LiquidsStand-alone computer integrated with

main network.

Ion-selective electrods LiquidsStand-alone computer

integrated with main network.

Mass Spectrometry Off-take gasesStand-alone computer integrated with

main network.

Neutron activation solid steelStand-alone computer integrated with

main network.

Hight Temp. Combustion S and C in SteelStand-alone computer

integrated with main network.___________________________________________________________________________

A brief desciption of the methods is:

• Optical Emission:

A spark or arc is struck to a solid sample. Thelight emitted is then wavelengthdispersed by a gratinginto spectral lines whose intensities ae compared withthose frrom a reference sample. The intensity of radiantemission at selected wavelengths is measured by anarray of photomultiplierr tubes. Signal outputs arecompared to percentage composition using computer.The computer will be connected to the Master Computerby a LAN (Local Area Networrk) through which it willsend the percentage composition to the MasterComputer.

• X-ray methods-energy dispersed:

This technique is the same as the wavelengthdispersed x-ray method except that the emittedfluorescent radiation is detected by dopedsemiconductor whose output is proportional to thewavelength (energy) of the X-ray. Again, composition isderived by comparison with standard sample andcalculated on computer, which will send the pecentagecomposition to the Master Computer by LAN.

• Atomic absorption:

The sample in liquid form is passed into a flame,where atomic species are formed. Radiation from anarrow band source is passed through the flame whereradiation, characteristic of the element to be determined,is absorbed. Measurement of the absorption coefficientof the flame determines the concentation of the element.The calculated percentage composition calculated by anattached computer, is sent to main computer by LAN.

• Fusion analysis of gases:

In this basic method of the detemination ofoxygen in steels, the solid sample is fused in a graphitecrucible either under vacuum or in argon atmosphere.Oxides present in the sample are reduced to formcarbon monoxide which is measured typically by infrra-red absorption. Nitrides present in the sample aredecomposed during the fusion process. N2 is usuallymeasured by a volumetric process after removal of COand H2. Hydrogen can also be determined typically byits thermal conductivity afte the gases have beenextracted from the liquid sample. Palladium is used toisolate hydrogen from the extracted gas mixture. Thisprocess is rather difficult to integrate with the maincomputer network. However this can be done by using aterminal to the main network.




• Plasma Method:

The liquid is first nebulized and then passed intoan inductively coupled plasma. Then in these methodsthe vapour of a liquid to be analyzed, or a gas, passesthrrough a coil in which a radio-frequency field iscreated, so exciting emission spectra characteristic ofthe vapour or gas. The composition of the gas (orvapour) is then easily found using a conventionalspectrometer attached with a computer. The data is thensent to Master Computer by LAN.

• Ion-selective electrodes:

It has been found that simple electrochemicalcells can be formed in ions in solution can be deteminedwithout, in many cases, interference from other ions. Asimple emf measurement gives a result in terms of ionconcentation, which can be converted into percentagecomposition and sent to master computer.

• Mass Spectroscopy:

A gas can easily be analyzed by ionizing itsconstituents and passing the ions through a magneticfield. As the radius of the path followed by the ions is afuction of their mass, slits can be placed to isolate theions of interest. This method is particularly useful for theanalysis of waste gases from the furnaces for CO, CO2,N2 and H2. The result calculated by the attachedcomputer is sent to master computer by LAN.

• Neutron Activation:

In this elegant technique, neutron bombardmentof a solid sample produces an unstable isotope, whichdecays, emitting gamma rays. Counting the resultinggamma rays results in a determination of the element inquestion provided that only the right energy gamma raysproduced by inelastic scatteing of the incident neutrrons.

Neutron activation has been used for thedetemination of oxygen, with the prompt gamma mehodbeing usefull for Si determination. However, neutronactivation has made little or no impact on the steelindustry despite intense effort in the 1960s.

2. Sizing and screening:

Sizing and screening is required at raw materialinput and sinter plant to let the desired sized particlespass and reject the remaining. This can simply beachieved by using industrial screens, which start fromsmall diameter screens to large diameter screens inmany steps, electronic weighing machines permanently

manufactured at the bottom of each screen can be usedto measure the weight retained in each screen and thisdata may be digitized and put to an attached computer,which will feed the data to the master computer by LAN.The attached computer besides sending the weightsretained, can also be used to control robotic arms tospread the particles uniformly on the screens and toremove particles from the screen. The robotic arms canalso be replaced by mechanical counterparts for cost-reduction.

3. Temperature Measurement:

Temperature is the main mission critical variableespecially in blast furnace, which should be measured atall costs. The temperature in the blast furnace givesfollowing information:

1. Combustion: The extent of combustion ofcoke and oxygen in air can be directly known bylooking at the temperature of the blast furnace.

2. Reactions and Processes: The temperature,especially the temperature distribution of the entireblast furnace gives an idea of the extent of reactions andprocesses occuring in the furnace.

3. Condition of Refractory Bricks: Thecondition of the refractory bricks can be judged fromthe comparison of the temperature of outer shell andinternal temperature.

Numerous devices can be used to determine thetemperature of various stages in steel making, some ofthe most common methods are:

(i). Optical Pyrometer:

The temperature results in the emission ofradiations of special wavelengths, an optical pyrometeris device used to measure the intensity of these specialradiations by semiconductor photo sensors and displaythem as the temperature on the display. The are usuallygun shaped devices and can be used to measure thedesired temperature without any contact with the hotmaterial. Special Computer integrated opticalpyrometers are also comming into market which can beplaced on fixed positions and digitized to connect with acomputer. However, they are mostly used as portableunits to inspect the temperature.

(ii). Thermal / IR Camera Systems:

Thermal / IR Cameras measuring light usually in3 to 8 micrometer wavelength by a thermally stablecooled Camera Array. It measures the near infra-red




light emitted from hot objects by black-body radiation.These cameras usually contains built in computers orexternal portable computers to make temperaturedistribution diagrams in real time and also provide pointtemperatures at selected points without any physicalcontact. Thermal Graphs or thermograms are usuallyobtained from these cameras. The are also used todetect the thermal gaps in the furnace due to possiblewear-off or damage of the furnace linning. This is veryexpensive equipment, extremely useful and is used inthe inspection of the furnace for refractory damages andis quite commonly employed during the errection of thefurnace by manufacturer..

(iii). Thermo-couples:

Thermo-couples are formed by joining twodissimilar metallic wires and measuring the emf in thewires by keeping one joint at reference temperature andthe other at temperature to be measured. They are themost widely used temperature measurement tools inmetallurgy, due to their easy operation, high accuracy,high temperature stability and rugged use.

Depending upon the metals used, the developedvoltage increases between 7 and 75 micro-volt for eachdegree celcius increase in temperature. J-Thermocouplea junction between iron and constantan is uesd tomeasure between -184 to 760 degree celcius. And C.A.Junction of Platinum and its alloy and 13% Rodium hasa usefull range of 0 to 1600 degree celcius.

In Cold Junction Compensation, a referencejunction made of the same metals must be connected inseries with the junction being used to makemeasurement. The reference junction is connected inthe reverse direction from the measuring junction. This isdone so that the output connecting wires are bothconstantan. The thermocouples are formed byconnecting these wires to the copper wires going to theamplifier will then cancel out. The input voltage to theamplifier will be the difference between the voltagesacross the two thermocouples. If we simply amplify thisvoltage, however, there is a problem if the temperatureof both thermocouples is changing. The problem is that itis impossible to tell that which thermocouple caused achange in output voltage.

As a solution an electronic circuit is used tocompensate for changes in temperature of the referencejunction. AD590 shown here produces a currentproportional to its temperature. The AD590 is attached tothe reference thermocouple so that they are both at thesame temperature. The current from the AD590, whenpassed through the resister network, produces a voltagewhich compensates for changes in the reference

thermocouple with temperature. The signal to theamplifier then is proportional only in changes in thesensor thermocouple.

Another problem is that the voltage does notchange linearly with temperature change. This can becorrected with analog circuitary which changes gain ofthe amplifier according to the value of the signal.However, in digital application correction can easily bedone using a lookup table in ROM or Program Memoryof the Microcontroller and an analog to digital converterto convert the analog value to the digital one. The digitalvalue is then used as a pointerr to a ROM location whichcontains the correct temperature for that reading.

(iv). Semiconductor Temperature Sensors:

Semiconductor sensors like National's LM35 canbe used to measure lower temperatures in the range of -55 to 150 degree celcius. The voltage increases by10mV for each degree celcius rise in temperature. Theanalog to digital converter usually of operationalamplifiers and the output of LM35 is adjusted to 0V for 0degree celcius. But due to their lower temperaturemeasuring capability they are not employed inmetallurgy.

(v). Thermister and RTDs:

Resistance Temperature Detectors andthermisters are also commonly used temperaturesensors. RTD's have capability to measure in the rangeof -250 to 850 degree celcius. These RTD's andThermisters can be encapsulated in refractory bricks dueto their low cost. These bricks may be used to line theothermost layer of the furnace to give precise readings.The resistance is converted into voltage change anddigitized by analog to digital converter.

The Thermocouples or RTD's may be connectedto microcontrollers (Like AT89C5X) via A/D converters ordirectly with microcontrollers with builtin A/D Converters.The microcontrollers will be connected to the servermicrocontroller by two wires TXD and RXD besides twopower wires. The Server Microcontroller will beconnected with an external computer connected toMaster Computer by LAN. The data from eachmicrocontroller can be accessed by addressing eachmicrocontroller seperately, thus exploiting serial interruptfeature of Atmel 8051- Architecture.

3. Pressure Measurement:

Pressure measurement of off-take gases, blastgases and internal blast furnace pressure is veryimportant variable.




(i). Strain Gages and Load Cells:

A strain gage is a small resistor whose valuechanges whens its length is changed. It may be made ofthin wire, thin foil or semi-conductor material. These areused to convert mechanical pressure guages alreadyinstalled in the Off-Take Gas Processing Plant intoanalog electronic signals, whcih in turn are converted todigtal signals by analog to digital converter andintegrated with microcontroller.

(ii). Linear Variable Differential Transformers:

In this method the core of the transformer ismoveable and the change in the voltage of secondarycoil is exploited to measure the temperature. A fixedvoltage of known value and 20Khz frequency is fed atprimary coil as AC Excitation Signal. The secondarycoils are actually two coils and opposite ends of eachare connected with each other, while the remaining twoare used as output. The output voltage is converted intodigital signal by special AC interface digitizer and is fedto microcontroller.

(iii). Potentiometers:

Potentiometers can be used with pressureguages to give a reading of pressure in a linear changein resistance, which can be converted into digital signalby analog to digital converter and fed to microcontroller.

5. Misc. Sensors:

Varius other sensors can be used in SteelMaking to detect various variables which are importantfor complete automation are used. Some of them are:

(i). Height of Burden in Stack:

Height of burden in stack is an important factorand can be detected by a variety of methods. One of themost easly and low cost method is the use of laser beamto detect the height. The laser may enter the stack froma quatz window on one side and leave the stack to bedetected from another quartz window on the oppositeside. A pulsing laser of UV band may be employed toprevent it from being interfered by the light produced bythe heat in the stack. More than one laser beams can beprovided at different heights to enable the computers todetect exact height.

Another alternative which is less affected by thepresence of dust particles is the use of ultra-soundinstead of laser. An ultra-sound transducer will send asignal from its diaphram on the top of the stack and

below the double bell loading system and receive thesound waves after being reflected by burden surface andby noting the time taken to return the sound waves willyeild in the exact burden height. The only disadvantageis to make an ultra-sound system stable enough tooperate at 200 to 600 degree celcius.

An indirect way, however, is to look at thethermal profile of the blast furnace as detected by thearrays of temperature sensors. The specific heat of theburden is greater than that of the atmosphere above itand at the surface of the burden there is a rapiddecrease in temperature in the thermal profile. Thismethod still requires atleast one laser sensor atmaximum possible height of the burden which it may beharmful, to provide an additional safety as there may befalse readings by thermal profile.

(ii). Gas flow detectors:

The velocity of the in-take gas or hot blast is animportant factor and may be measured by theintroduction of a small turbine connected to a small lowpower generator just before tuyers. The voltagegenerated by the generator may be converted into digitaldata by analog to digital converter and fed tomicrocontroller or computer.

Control Devices

1. Effetors / Actuators:

Effectors or Actuators provide translatory motionand may be used in Blast Furnace operations like inopening and closing of bells in double bell chargingsystem, Tilting Steel Converter, etc. There are numerousways to make effectors / actuators, some of the commonones are:

(i). Mechanical Actuators:

Mechanical actuators are very common in robotsand many industries where robots are being employed inone way or the other. They may be a threaded shaftconnected to a high speed motor and shaft being fixed ina nut like arrangement. The nut arrangement will movein translatory motion on the rotatory motion of the shaft.A stepper motor may be used to drive the shaft toprovide accurate control of the actuator length. Yetanother alternative used in most of the CNC Machines isthe servo control, in which a linear potentiometerconnected with the nut to detect its location on the shaft,will be driving the servo circuit and the servo circuit willprovide an accurate control of the motor according to theinput signal provided by the microcontroller.




(ii). Pneumetic Actuators:

In pneumetic actuators air or gas is pumped intothe actuator by a pump. Thee system can be understoodby visualizing the actuator as an injection syring as usedin medicine. When air is pumped into it from the openingthe piston will move upward, thus making translatorymotion and when it is removed the piston will movedownwad. This mechanism can also be contolled by aservo control circuit and linear potentiometer.

(iii). Hydrolic Actuators:

This is same as pneumetic actuator, but the onlydifference is the use of water or oils instead of air formoving the piston. It is used for more heavy jobs wherevery powerfull force is required like in the tilting of steelconverter.

2. Robotic Manupulators:

Robotic Manupulators are an essential part ofautomation installation, they required to replace humanarms and perform much more powerfull and heavy jobslike transferring run-of-mine from thee conveyor belts tothe crushers and grinders, lifting and moving crucible ofmolten metal, etc. The design and type of manupulatorin automation is job specific and may require manybooks to cover this subject, however a brief overview ofsome of the commonly used devices to drive and senseis given below:

(i). Motors:

Motors are used to provide rotatory motion invarious parts of the manipulator and drive other deviceslike Actuators, Pneumetic and Hydraulic Pumps, etc.There are different types of motors used dependingupon their usage. High speed motors are used in mobileunits to move robots and manipulators, etc. Steppermotors usually coupled with rotation sensors are widelyused in operations where precise motion is required, butin modern automation applications they are largelyreplaced with servo motors which have built in sensorsto guarantee its precise motion. A servo motor consistsof a motor usually geared and coupled with a feedbackpotentiometer, which controls the oscillations of a squarewave oscillator. A comparator compares the oscillationsof this local oscillator and the control signal feededexternally, if the frequency of both signals is not same itwill continue the motor to rotate untill both signalsmatches each other. Thus a precise position can beobtained by feeding an appropriate input pulse.

Servo Motors and Stepper motors both can beintegrated with a microcontroller. To integrate a steppermotor simply connect four digital output of themicrocontroller to the stepper motor through an opengate buffer as stepper motor requires large amount ofcurrent. In case of stepper motor a single digital output isconnected to the servo motor, but this output andmicrocontroller should be fast enough to give pulsesinstead of static logic signals.

(ii). Actuators:

Actuators are used to provide translationalmotion and are usually of mechanical, peumetic andhydraulic type, depending upon the application andprecision.

(iii). Sensors:

Sensors are the fundemental parts of all themanipulators and robots. They may range from simplepotentiometers to fibre-optic pads. Simple potentiometerare usually used to detect the rotaional or translationalposition of the part. Pressure transducers and micro-switches are used in hand to detect the firm grasp of thehand on the job. Optical and Magnetic Tachometers areused to measure the speed of the rotation. In opticaltachometer a beam is allowed to pass through a hole ina gear and each revolution results in passing of a beamof light to the photo sensors, which gives the speed bycounting the number of beams per second. Opticalbeams are also used to detect precise position of therotation in some advanced applications. Fibre-opticpads, which usually have a built in micro-computer areused to detect the bends, etc. in the manipulators, actingjust like skin, but there use in robotics is very limited dueto their high cost.

3. Automated / Semi-Automated GroundVehicle:

Autmated Ground Vehicles may be used totransport raw material, products and samples from onesection of the steel mill ro another. They usually consistsof mobile units, sensors and autonomous computers. Insteel mills the most common AGV's are the one thatmove on tracks or optical, magnetic or electric stripswhich are build on the floor of the mill. I personallyrecommend optical strips due to the ease of thereplacement and low cost. In most cases a differentcolor (which maye be fluorescent) is painted on the floorwhich acts as a guideline for the mobile unit of AGVwhich optical detection circuits. At reletively low costinstallations, semi-automated ground vehicles are also




found which are controlled externally by human beingssitting in a control room.

4. Interfacing Devices:

Various interfacing cards and circuits are usedto integrate manually controlled equipment. Theseinterfacing circuits usually require analog to digitalconverters and digital to analog converters. Operationalamplifiers are used as ADCs and DACs and now thereare some specialized micro-controllers which have builtin ADCs and DACs and can be used to connect theseanalog devices to digital network. To connect digitalequipment with computers micro-controllers or parallelports are used. Micro-controllers connect to thesedevices by their parallel ports and connect to thePersonel Computer with serial ports. Intel's 8255A is aprogrammable parallel port which can be used to in ISA-Slot Cards to integerate digital devices with PersonelComputer. Similarly, Intel's 8251 is used to connectdigital equipments on serial outputs to personelcomputer, normally used serial protocol in most of theindustrial equipment is RS-232.

Computers:

1. Main Computers:

The Main computers may be Mac Machines,Unix Workstations, IBM Compatible PersonnelComputers or Main Frames, depending upon theinvestment of the installation and application. In mostcases IBM Compatible Computers or to be moreaccurate Intel Microchips based computers are low cost,easy to use and more up-to-date. But some specialapplications might require some properties which areonly found on Mac Machines, Unix Workstations or MainFrames. The selection of an appropriate operatingsystem also varies from one installation to another. Abrief review of some of the commonly found operatingsystems in automation applications is as follows:

(i). Microsoft's Windows Family:

Microsoft's Windows Family includes Windows95-98 (a combination of DOS Kernel and Windows GUI),Windows NT (Windows New Technology Kernel) andWindows 2000 (an upgrade of both Windows 98 andWindows NT). These operating systems especiallyWindows 95-98 are easy to use, user friendly andgraphical environments, which from the performanceview point is a drawback as too many system resourcesare wasted on graphics but very little is usefully appliedto control automation equipment. However, they arealways prefered by end users and are used as terminal

to inspect or view what is happening in the AutomationConputers.

Windows NT and Windows 2000 on the otherhand is bit more usefull as it serves as a server of anetwork of computers and at the same time is userfriendly and reletively easy to operate. But its eye popinggraphics are also a threat to its lower performance fromthe hardware point of view. But it is being prefered bymany industrialists in their automation project asWindows NT operators are easy to find and can be puton reletively lower wages. Also the upgrade of thesystem is inexpensive and can be done without evenhiring a team of software designes. Softwaredevelopment is also inexpensive on Microsoft basedoperating systems due to their wide spread availablility.

(ii). MacOS:

MacOS is another graphical windows basedoperating system which runs only on Macintoshcomputers. The common networking protocol is theappletalk. The system is very efficient in terms ofgraphics use as in most models there is seperatehardware to deal with the graphics and thus comparitivilymore powerful resources can be provided to theautomation equipment. However, its software developersare very hard to find and also its cost and upgrade is abig threat to its use in automation. However, it is mostlyused where virtual reality and 3D graphics are required.

(iii). Unix:

Unix unlike Windows and MacOS is 128-bitoperating system and most of the work can beperformed on non-graphic interface which allows betterperformance from the hardware point of view. The onlyhurdle is its cost, availability and upgrading cost. Thesoftware developers are also not hard to find but inMicrosoft dominated countries like Pakistan, India theyare bit hard to find and costly. However, the stability ofthe Unix machines persues industrialists to choose thisfor their automation needs. In some examples the UnixSystems are running from many years without shuttingdown, Internet is the best example which is about 80-90% of Unix Servers.

(iv). Linux:

Linux is a unix clone developed and distributedfree for mostly Intel based computers. It is very muchlike Unix, but the good point about it is that its sourcecode is freely available and it can be customized to anautomation process thus ranking it far above the otheroperating systems in industry. It is highly stable, just likeUnix, the main hurdle which may be found is the higher




cost of the development of a customized kernel and lackof user friendly environment. But this all is changing withthe introduction of RedHat, Debian, BeOS and othercommercial clones which makes it easy to customizeand user friendly. X Window a windows based GUIsoftware can be run on linux to make it GUI just likeMacOS and Microsoft Windows.

(v). Solaris:

Solaris is introduced by Sun Microsomputersand has been it commercial trade mark ever since. InPakistan its use by PAKNET an internet division of PTCLhave given an example of its high stability andresistance to intense traffice without any failure. It isusually a non-graphical OS which allows it to providebetter power to automation process. Very recently it wasannounced by Sun Microcomputers that its source codeis open for industry to be used and customized. Thisopenned new frontiers for its use in Automation.

2. Micro-controller:

Micro-controller is perhaps the most importantdevice which actually made automation possible. Inmosr micro-controllers the microprocessor, RAM, ROM,Parallel Ports and Serial Ports are all incorporated on asingle microchip, thus enabling it to be used inautomation very easily. Texas Instrument's is usingIntel's 8051-family microprocessors with built in ROM,RAM, Parallel Ports, Serial Ports and even Analog toDigital Converters, a specialized microchip can be foundfrom its long list to suite the requirement. However, itslack of availability and reletively higher cost in Pakistanis a threat towards its use. Another company Atmel hasintroduced it micro-controller line includingAT89C51(costs around Rs.125/-) , AT89C52 (costsaround Rs.250/-) and AT89C55 (costs around Rs.450/-).All these contain 12MHz to 24MHz 8051Microprocessor, Flash memory (electronicallyprogramable) instead of conventional ROM, limitedRAM, Parallel Ports usually four, Serial Ports, Interruptand Timer Counter. AT89CX051 is with built in analog todigital converter, thus requiring minimum circuitary inanalog interfacing. However, AT89CX051 is notavailable in our local market, but can easily be importedfrom international market at very low cost. Some devicesused in Atmel microchips are reviewed as follows:

(i). Microprocessor:

Each of the Atmel Micro-controllers use Intel's8051-Familt Microprocessor which can be operated atfrequencies 12MHz to upto 24MHz, which are quitesufficient for automation applications. The 8051-Assembly language is vey much like 8086-Assembly

which is taught in many Universities, but lot more easier.Some common difference are:

1. OUT, INP and MOV statements are merged intoa single MOV statement, which may be used to addressmemory, ports and registers very easily.2. Single pins of the parallel ports can be easilyaddressed with going into the trouble of extracting themfrom bytes.3. There are various statements to provide nibbleor bit operations which are quite common in automation.

4. The name of the registers is also different.

(ii). Program Memory:

The program memory is stored on an on-chipflash EEPROM which can be erased and reprogrammedvery easily and is highly stable to guarantee itscontinous use for many years in automation. InAT89C51 it is 4 kilo bytes, in AT89C52 it is 8K and soon.

(iii). Data Memory:

The RAM is bit lower only 128-256 bytes, but itis enough for most of the automation requirements. It isfaster than conventional RAMs and external RAM ofupto 1 Mega Byte can be easily added, but at thesacrifice of two parallel ports.

(iv). Registers:

Registers are fast dynamic memory usuallycontained in a microprocessor to provide faster access.Just like 8086 and newer microprocessors, Atmel chipecontain registers named:

A-Accumulator(ACC)R0-8 bit General Purpose RegisterR1-8 bit General Purpose RegisterR2-8 bit General Purpose RegisterR3-8 bit General Purpose RegisterR4-8 bit General Purpose RegisterR5-8 bit General Purpose RegisterR6-8 bit General Purpose RegisterR7-8 bit General Purpose RegisterDPTR-16 bit RegisterP0-8 bit Parallel PortP1-8 bit Parallel PortP2-8 bit Parallel PortP3-8 bit Parallel PortSP-8 bit Serial PortT0-16 bit TimerT1-16 bit Timerand others.




(v). Parallel Port:

There are four parallel ports namely P0, P1, P2and P3 with registers, which can be used as input aswell as output. Each bit can be individually addressedand set as both input or output and thus provides ease inprogramming. The parallel ports may be used to controlrobot manipulators, thermocouples, pressuretransducers, motors, actuators, etc.

(vi). Serial Port:

There is one serial port provided in port 3 whichcan be used as serial port as well as parallel port. Thetwo connections RxD and TxD allows the use of only twowires to communicate between two micro-controllers.There are different modes of serial port and atmultiprocessor communication mode it can used tocommunicate between more than one micro-controllersusing Client-Server Model, and each micro-controllercan be addressed. The serial port is provided with aninterrupt which is used to inform the processor about thearrival of data, this can also be disabled it data polling isrequired.

(vii). Interupt:

There are five to six interupts provide in thesystem which include two external interupts, one serial,and two to three timer counter interupts. An interupt isused to stop the processor function temporarily thanperform a specific function like receiving serial.

(viii). Timer Counter:

Two to three timer counters are provided toenable micro-controller to count frequencies. These maybe used in applications like frequency counting, baudrate determination for serial ports, etc.

3. Local Area Network:

Local Area Network is used to connect thedifferent computers in various departments with a centralserver. A typical network consists of a Server usuallyrunning Windows NT or Windows 2000, ClientComputers running Windows 95-2000 or Windows NT,Network Hub, Network Cards usually Ethernet card. TheClient and Server Computers with Ethernet or LAN Cardinstalled in ISA or PCI Slots are connected to NetworkHub (central exchange or switcher) by unshieldedtwisted cable, usually of three pairs. Common protocolslike TCP/IP, IPX/SPX and NetBIOU can be used tocommunicate between the computers. The remote usersfrom any where in the World can be connected by

telephone line on the server and can access the entirenetwork.

4. PLC Network:

A PLC Network can be established in varioussections of automation by simply connected RxD andTxD wires of each micro-controller. One micro-controlleris usually assigned as Server or Host micro-controllerand may be used to pass tockens to the client micro-controllers and act as a bridge between the network andthe external computer. High Speed TTL Buffers may beused to amplify the signal in large networks and idealy128 micro-controllers can be linked like this.

Pakistan Steel Mill Automation:

All the above devices can be integrated to fullyautomate Pakistan Steel Mill at Karachi. Although it isautomated already and a LAN network already existsthere, but it still require various operators and workers.What my target is to give some ideas about how toautomate it fully and run it without operators at nighttime, which will result in the lower expenses as less staffis required and at the same time higher quality aseverything is computer controlled and no human skill iseffective on the final product.

1. Raw Materials Preparation Plant:

The plant is intended for receiving, storing andpreparing raw materials for iron and steel making plantsand Refractories Production. The materials to be storedand processed are:

Raw Material Job to be DoneUsage

___________________________________________________________________________Iron Ore Stored andProcessed Fe SourceManganese Ore Stored and Processed

Steel AdditiveLime Stone Stored and Processed

FuxingDolomite Stored and Processed

CalcinationTar-bonded Dolomite Stored and Processed

RefractoriesBauxite and Fluorspar Stored and Processed

Steel AdditiveRefractory Clays Stored and Processed

RefractoriesCoke Stored

Fuel




Other Additives Stored and ProcessedSteel Additives

___________________________________________________________________________

The various sections of this department are:

(i). Reception and Storage Facility:

Reception and Storage Facility may be manualor automatic by using Automated Ground Vehicles,CCTV Cameras for record, Manipulators for loading andunloading. The raw material after unloading from theships on the sea ports by robot manipulators may be puton already existing conveyor belts and transfered to theplant. Here the robot manipulators unload it from theconveyor belt and transfer them to the storage area inbins carried by Automated Ground Vehicles. Onrequirement the bins are carried to cruching plant andreturned for temporary storage.

(ii). Crushing and Screening Plant:

Upon requirement the raw material is carriedhere for crushing by AGVs and unloaded from bins byrobot manipulators. After crushing the crushed materialis passed through screens and collected again in thebins which are carried to storage area or the sinteringplant.

(iii). Sintering Plant:

Raw material and Coke fines (from coke and by-product plant) in the bins brought by AGVs is unloadedand entered in the sinter plant which is running under thecontrol of a computer, manipulators, actuators andmotors and is sensed by thermocouples, computerizedscreens, etc. After sintering, crushing and screening thesintered charge is collected in bins and sent to the ironmaking plant. Sinter samples are taken to labs forcomposition analysis.

2. Coke Oven and By-Product Plant:

The coke is carried from the storage area byAGV's in bins. After reaching here coke is unloaded frombins and put in coke oven. After oven it is dry quenchedby the aid of robot manipulators with external parts ofhigh temperature resistant material. The cold quenchedcoke is then blended with coal and collected in bins andtransported to storage area for temporary storage byAGV's. The by-product plant can be automated on thesimilar basis. Time to time samples of coke and by-products are collected from munipulators and screensand transported to Labs for composition analysis.

3. Iron Making Plant:

The sintered charge and coke are brought inbins by AGVs and are unloaded in skips by manipulatorsand fed to the blast furnace.The Double bell loadingsystem is already automated by actuators. Thethermocouples installed in the ports and RTD(Resistance Themal Detectors) incapsulated in outer ormiddle layer of refractory bricks are connected withmicrocontroller via analog to digital converters, and inmicro-controller program memory there are lookuptables to convert readings into absolute centigradetemperature which can be fed to the attached computer.The pressure sensors, gas flow meters and othersconnected in gas treatment section are also integrated tothe computer by numerous micro-controllers. The hot-blast stoves are controlled by micro-controllers withdigtal to analog converters and a temperature can bemaintained from the computer. The pressure andtemperature of the furnace and gas storage vessels isstrinctly monitored by more than two computers to allowproper functioning.

The hot material from metal notch is poured intoa ladle controlled by an already existing manipulator inthe Hot-Metal Relining Shop. Slag is seperated by usingexisting techniques and some manual technique may beautomated by interfacing circuits and devices aspreviously discussed. The hot metal ladle is thentransfered to the steel making plant by mobilemanipulators. Samples of pig iron are carried to lab byusing existing automation techniques.

4. Steelmaking Plant:

The hot metal in the ladle is poured into largesteel converters and oxygen gas is blown. Samples ofoxygen are carried to labs by small pipes and pumps forcomposition analysis. The off-take gases from the top ofthe converter are analyzed for FeO and CO2 by using asmall on-floor gas mass spectroscope. Numerous RTDsare encpsulated in outer layer bricks of the converter toallow temperature measurement. After complete oxygenblowing the molten steel is poured into ladles whichcarry it to continous casting plant.

5. Steel Forming Plant:

This plant contains continous casting equipmentwhich converts molten steel into continous long billets byrapid quenching with water. The temperature of thecontinous casting plant is sensed by thermocouples andthe process is controlled by various manipulators.Samples of molten steel are take at specific intervals totransfer to labs for composition analysis.




The final billets are cold and hot rolled, cut andstored in product storage area temporarily andtransported out of the Mill by human driven trucks andlong vehicles. All the billet handling in the plant is doneby very strong hydraulically driven robot manipulators.

Conclusion:

Well to put in a nut shell, the iron and steelmaking plant can be put on a complete automation withhelp from local engineers in quite less investment.According to my suggestion the process should becarried out gradually by automating one section at a timeand after completion all the sections are automated bycentral computer. The proper automation depends uponthe skills of the team of software developers. Both thehardware and software engineers should be atleastgraduate or diploma holders in Metallurgy to fullyunderstand the processes and automate themaccordingly. Industrial Automation of MetallurgicalIndustries is a new field and is very prospective one.Indian Universities are giving a lot of emphasis on theirmetallurgists to take interests in computing andautomation. Some of the Pakistan Industries are beingautomated by Indian Metallurgists.

References:

• An Introduction to Modern Steel Making (3rdEdition, Khanna Publishers 1998)

by Dr. R. H. Tupkary and V. R. Tupkary

• Control and Analysis in Iron and Steelmaking(Butterworth Scientific Ltd., 1983)

by R. V. Williams

• Microcontroller Data Book (AtmelCorporation., 1995)

by Atmel Engineers

• Detailed Project Report of Paksitan Steel Mill(Pipri Site) (1973)

by Unknown Authors

• Computers in Manufacturing (McGraw Hill.,1983)

by the Editors of American Machinist

• Microprocessors and Interfacing (McGrawHill)

by Douglas V. Hall

• The Manufacture of Iron and Steelby Unknown Author

• The Blast Furnaceby Unknown Author

• Machine Visionby Unknown Author

• Flexible Manufacturingby Unknown Author

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blast furnace

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