Project 2

AUTOMATION OF GAS CLEANING PLANT IN BLAST FURNACE A PROJECT REPORT Submitted by

ERSHAD.C.H

Reg NO:91304107004

RAJA.T

Reg NO:91304107016

RAJASHRIRAM.V

Reg NO:91304107017

in partial fulfillment for the award of the degree of

BACHELOR OF ENGINEERING IN ELECTRONICS AND INSTRUMENTATION ENGINEERING RVS COLLEGE OF ENGINEERING AND TECHNOLOGY DINDIGUL

ANNAUNIVERSITY:CHENNAI 600 025 APRIL-2008

AUTOMATION OF GAS CLEANING PLANT IN BLAST FURNACE A PROJECT REPORT Submitted by

ERSHAD.C.H

Reg NO:91304107004

RAJA.T

Reg NO:91304107016

RAJASHRIRAM.V

Reg NO:91304107017

in partial fulfillment for the award of the degree of

BACHELOR OF ENGINEERING IN ELECTRONICS AND INSTRUMENTATION ENGINEERING RVS COLLEGE OF ENGINEERING AND TECHNOLOGY DINDIGUL

ANNAUNIVERSITY: CHENNAI 600 025 APRIL-2008

ANNAUNIVERSITY: CHENNAI- 600 025

BONAFIDE CERTIFICATE

Certified that this project report “AUTOMATION OF GAS CLEANING PLANT IN BLAST FURNACE” is the bonafide work of ERSHAD.C H RAJA.T RAJASHRIRAM.V who carried out the project work under my supervision.

SIGNATURE SIGNATURE Mr.R.GANESAN

Mr.M.VADIVEL

HEAD OF THE DEPARTMENT

SUPERVISOR

EIE Department, RVS Nagar, RVS CET, Dindigul-5.

Lecturer, EIE Department, RVS Nagar, RVS CET, Dindigul-5.

Submitted to the Viva-Voce Examination held on_________________.

Internal Examiner

External Examiner ii

ACKNOWLEDGEMENT We express our profound thanks to our Principal Prof. Dr. C.G.RAVICHANDRAN M.E.,Ph.D., RVS College of Engineering and Technology, for his kind cooperation in all aspects of our project work. We are deeply obliged to Mr. R.GANESAN M.E.,(Ph.D), Head of the Department, Department of Electronics And Instrumentation, for the generous help and sustained interest throughout the period of project. We express our deep sense of gratitude to our internal guide Mr. M.VADIVEL, B.E., for his enthusiastic encouragement and continuous support which helped us in finishing this project. We are also grateful to Mr. RAVINDRA HEGDE, Senior Manager, Electrical Department, JINDAL SOUTH WEST (SOUTHERN IRON AND STEEL COMPANY LIMITED, Mettur) for guiding us to complete our project successfully. We extend our cordial thanks to all the staff members of the Department of Electronics and Instrumentation Engineering of our college for their continuous support and help throughout the course of the project

iii

ABSTRACT The objective of our project is “CLEANING THE BLAST FURNACE GAS FROM DUST PARTICLES and automating the process using PROGRAMMABLE LOGIC CONTROLLER”. The blast furnace is using very hot gases for melting the ore. After the heating process the hot air at the outlet of the blast furnace is called as the blast furnace gas or BF gas. This BF gas is mixture of several gases like CO2, CO, N2, O2, Hydrocarbons and dust. In order to recycle the BF gas for running another blast furnace or for running a power plant the BF gas should be separated from dust. For cleaning the BF gas from dust the ‘GAS CLEANING PLANT’ is needed. The PLC used here is SIEMENS SEMATIC S7 300. Continuous controller is used on S7 300 PLC to control technical processes with continuous input and output variables. There are four separate processes involving six sequence of operations. Three of them can be done in ON/OFF mode , then the rest of them can be done in continuous mode. iv

TABLE OF CONTENTS CHAPTER NO.

1

TITLE

PAGE NO.

ABSTRACT

iv

LIST OF TABLE

ix

LIST OF FIGURES

x

LIST OF ABBREVIATIONS

xii

Introduction

1

1.1 Objective

1

1.2 Major blocks in GCP

1

1.2.1 Block diagram

2

1.3 Overview of GCP processes

2

1.4 Role of PLC

3

1.5 How the objective of the project 2

is satisfied

4

Project description

5

2.1 Operation

5

2.2 P&I diagram

7

2.2.1 P&I instrument details

8

2.3 Description of individual blocks

10

2.3.1 Dust catcher

10

2.3.2 Quenching

11

2.3.3 Venturi scrubbers

14

2.3.4 Cyclonic separator

15

2.3.5 Seal pot

16

2.4 Measuring instrument details 2.4.1 Temperature measurement vi

18 18

2.4.1.1 Equipment details

18

2.4.1.2 Resistance thermometers

19

2.4.1.4 Thermocouple

24

2.4.2 Pressure sensors

27

2.4.2.1 Equipment details

27

2.4.2.2 Bourdon tube

28

2.4.2.3 Diaphragm

30

2.4.3 Flow meter

31

2.4.3.1 Equipment details

31

2.4.3.2 Orifice plate

33

2.4.4 Position sensors

35

2.4.4.1 Inductive sensor

35

2.4.4.2 LVDT

36

2.4.4.3 Hall effect sensor

39

2.4.5 Transmitter details 2.5 Valve details

42 44

2.5.1 Gate valves

44

2.5.2 Isolation valves

45

2.5.2.1 Ball valves

46

2.5.2.2 Butterfly valves

47

2.6 Actuator details

48

2.7 Programming instruments

55

2.7.1 PLC details

55

2.7.2 Siemens S7 300 PLC

59

2.7.3 PID Controller

63

2.8 Software details vii

66

3

2.8.1 Sequence of operation

66

2.8.2 Program

68

2.9 Advantages of GCP

70

3.1Conclusion

71

APPENDIX

72

REFERENCES

75

viii

LIST OF TABLE TABLE NO

DESCRIPTION

PAGE NO

1

P&I diagram symbols

8

2

P&I diagram control room signals

9

3

Temperature Transmitter details

18

4

Location of temperature transmitters

19

5

Temperature sensor details

19

6

Location of temperature sensors

19

7

Pressure gauge details (water line)

27

8

Location of pressure gauge (water line)

27

9

Pressure gauge details (gas line)

27

10

Location of pressure gauge (gas line)

27

11

Orifice plate details (water)

31

12

Location of orifice plate (water)

31

13

Orifice plate details (Gas)

32

14

Pressure/Flow/Differential pressure transmitter details

15

42

Location of pressure/flow/differential pressure transmitters:

43

16

S7 Modules

61

17

Arrangement of modules

61

18

Components of S7 PLC

62

ix

LIST OF FIGURES FIGURE NO

DESCRIPTION

PAGE NO

1.1

Block diagram

2

2.1

P&I diagram

7

2.2

Dust catcher

10

2.3

Quencher

12

2.4

Venturi scrubber

14

2.5

Cyclonic separator

15

2.6

Seal pot

17

2.7

RTD

21

2.7

RTD wire connection

22

2.9

Thermo couple

24

2.10

Membrane type manometer

29

2.11

Indicator slide with card and dial

29

2.12

Mechanical slide with Bourdon tube

29

2.13

Diaphragm

30

2.14

Flat-plate, Sharp-edge orifice

33

2.15

Orifice plate

33

2.16

Inductive sensor

35

2.17

LVDT

36

2.18

Working of LVDT

38

2.19

Hall effect sensor

40

2.20

Hall effect sensor

41

2.21

Gate valve

44

2.22

T and L type ball valves

46

2.23

Industrial electric actuator

48

x

2.24

Electric multi-turn actuator on gate valve

49

2.25

Electric part turn actuator on butterfly valve

50

2.26

PLC

55

2.27

Block of PLC

57

2.28

S7 Modules

59

2.29

S7 Module arrangements

60

2.30

Block diagram of PID Controller

64

2.31

PLC Program

68

xi

LIST OF ABBREVIATIONS ABBREVIATIONS

EXPANSIONS

PAGE

GCP

Gas Cleaning Plant

1

BF

Blast Furnace

1

P&I

Process and Instrumentation

8

RTD

Resistance Temperature Detectors

19

LVDT

Linear Variable Differential Transformer

36

PLC

Programmable Logic Controller

55

PID

Proportional Integral Derivative Controller

63

xii

CHAPTER 1 1. INTRODUCTION The blast furnace is using very hot gases for melting the ore. After the heating process the hot air at the outlet of the blast furnace is called as the blast furnace gas or BF gas. This BF gas is mixture of several gases like CO2, CO, N2, O2, Hydrocarbons and dust. 1.1.

OBJECTIVE:

Why GCP is used in Steel plants? In order to recycle the BF gas for running another blast furnace or for running a power plant the BF gas should be separated from dust. For cleaning the BF gas from dust the ‘Gas cleaning plant’ is needed. The BF gas coming out of the blast furnace is in the temperature range of 15000C.When it is directly exposed to the atmosphere it gives rise to serious thermal pollution. The BF gas consists of a lot of dust particles which may also cause environmental problems. The problems and hazards due to the direct exposure of BF gas to the atmosphere can be minimized to a great extend by means of GCP. 1.2. MAJOR BLOCKS IN GCP: The GCP will perform its operation using the following functional blocks: (1).Dust Catcher (2).Quencher (3).Venturies (4).Cyclonic Separator (5).Seal pot 1

1.2.1. BLOCK DIAGRAM:

Fig 1.1 Block Diagram 1.3.

OVERVIEW OF GCP PROCESSES: The dust catcher consists of a container in which there is a

suddenly bent tube. Due to the suddenly bent tube the velocity becomes zero. When the velocity becomes zero the macro dust particles looses its velocity and gets collected at the bottom of the dust catcher. It can be removed periodically. The quencher collects the BF gas from the dust catcher and sprays water over it. Due to the sudden cooling using water as quenching agent some amount of dust particles gets collected from the BF gas. The outlet of the quencher is in the form of sludge. It can be removed using seal pot periodically. 2

Two venturies are used in the GCP. These venturies are supplied with water and the BF gas. The water is sprayed over the BF gas so that some amount of dust in BF gas gets eliminated in the form of sludge. The cyclonic separator is having fan which can be rotated with high speed. Water is passed through it. This will eliminate the remaining dust particles in the form of sludge. The seal pot is used for removing the sludge from the quencher, venturi1 and cyclonic separator. The gate valve at the bottom of the seal pot should be opened manually for every two hours to remove the sludge collected in it. The sludge will be removed partially every time. The space in the removed area should be filled with water in order to control the leakage of hazardous BF gas. 1.4.

ROLE OF PLC: The various signals collected from the sensors and transmitters are sent

to the PLC using two wire 4-20mA transmission lines. The PLC can be programmed logically for the automatic operation of the GCP. There are three set of digital sequence of operations that can be programmed by using the Siemens S7 300 PLC. There are another three controlling operations which can be done through PID controllers. According to the inputs and outputs, the PLC may switch the controllers. The signals from temperature, pressure and flow transmitters which can also be fed to the PLC so that monitoring processes can be done in the control room. 3

1.5.

How the objective of the project is satisfied: There are various digitally operated valves and pumps at various

stages of gas cleaning process that can be directly operated by logically programming the PLC. The analog controllers can be used to open and close the septum valves and also it can be used for adjusting the venturi throat according to the pressure ranges. By doing these processes the objective of the project can be achieved using the GCP.

4

CHAPTER 2 2. PROJECT DESCRIPTION 2.1. OPERATION: The gas generated in the blast furnace is taken to dust catcher, where coarse suspended particles are separated out from gas. The semi clean gas, i.e., the gas with finer suspended particles, from the dust catcher is then passed through quencher and two venturi scrubbers positioned in series. The first stage venturi is to be operated by manual control from remote and local push buttons. The second stage venturi is having automatic control to ensure set pressure drop across two venturies. Both the venturies possesses electromechanical actuator for adjustment of throat opening to keep the dust loading of 5mg/Nm3 in the final gas. Since outlet gas from second venturi contains lot of moisture, the gas is taken in the cyclonic separator for removal of moisture. Clean gas is then taken finally to the blast stove. Adequate quantity of water is sprayed in quencher and venturi scrubbers. Seal pots with sufficient dip length are provided at the bottom of the quencher, venturi and cyclonic separator to prevent gas leakage. Septum valve is provided to regulate/ maintain BF top pressure over a wide range of flow. The range of BF top pressure to be maintained also varies from 0 to 1.5 kg/cm2. 5

The pressure on down stream side is normally 800 to 1000mmWC. Considering this it can be seen that the control range is very wide. The septum valve is specially designed to operate in this wide range, at the same time giving good controllability. Septum valve is the combination of four number of specially designed butterfly valve. The contaminated water from quencher and venturi scrubbers is continuously removed for continuous operation without malfunctioning. The operation of GCP is explained in the P&I diagram shown in the next page in the figure2.1.

6

2.2. P&I DIAGRAM:

7

2.2.1 P&I INSTRUMENT DETAILS: Table 1 P&I Diagram symbols: Symbol

Name of the Instrument Gate valve(GV) Isolation valve(IV) Water pipe line Signal line(4-20mA) Display/Control on PLC system Diaphragm seal Field instrument Non return valve(NRV) Electrical line Digital signal Control signal

8

Table 2 P&I Diagram control signals: Tag name Level Flow Temperature Pressure Position Differential

First affix L F T P Z DP

Second affix

Pressure Alarm High Low Transmitter Indicator Totalizer Element Controller Manual

HC

loader Electrical

EA

Third affix

A H L T I Q E C

Actuator

9

2.3. DESCRIPTION OF INDIVIDUAL BLOCKS The general description of individual blocks is explained in the following: 2.3.1. DUST CATCHER: The dust catcher is the instrument used to separate macro particles from air or a gas. The dust catcher here used is dry type dust catcher.

Fig2.2 Dust catcher This is the first step used in Gas cleaning plant (refer to fig-1).The blast furnace gas at the outlet of blast furnace will contain large amount of dust particles. The dusts in the BF gas are at various sizes. The GCP will have dust catcher at its front to remove large sized dusts. The dust catching process will have BF gas with higher pressure at its inlet. And so it will travel with higher velocity. 10

The dust catcher is constructed such that the narrow pipe consisting of the BF gas is opened to an enlarged vessel. This in turn will suddenly decrease the pressure of the BF gas (i.e. pressure=0).When the pressure is zero; it will also make the velocity to zero. When the velocity=0 the macro dust particles combined with BF gas will loose its grip and fell to the bottom of the dust catcher. The BF gas without macro dust particles can be removed through

the

outlet

provided

on

the

side of

the

dust

catcher.

The macro dust particles are let to be collected at the bottom of dust catcher. It can be removed through a hole provided at the bottom periodically using the conveyor belt.The outlet of the Dust catcher is the BF gas without macro dust particles. 2.3.2. QUENCHING: Quenching refers to the rapid cooling process. But in GCP the quenching process is used to remove the micro dust particle from BF gas. The quenching is the first process in wet GCP. The process consists of a large container in which the BF gas is opened after passing the dust catcher. It consists of a sprayer supplied with water. An outlet is provided at the middle portion of the side wall of quencher to remove BF gas after completion of quenching process. During the process, BF gas is allowed to pass from the top inside the quencher. If the gases entering the scrubber are too hot, some liquid droplets may evaporate before they have a chance to contact dust in the exhaust stream, and others may evaporate after contact, causing captured particles to become re-entrained. 11

Fig2.3 Quencher Water is supplied to the sprayer continuously. The BF gas is sprayed with water. When water is sprayed with very high velocity, it will pick of many micro dust particles mixed with BF gas. The moderately cleaned BF gas is then sent out through the outlet provided for that. The smaller dusts react with water to form slag. The slag is removed through the outlet provided at the bottom. Slag should be removed periodically using seal pot, without letting the Bf gas to pass out. In some cases, quenching can actually save money. Cooling the gases reduces the temperature and, therefore, the volume of gases, permitting the use of less expensive construction materials and a smaller scrubber vessel and fan. 12

A quenching system can be as simple as spraying liquid into the duct just preceding the main scrubbing vessel, or it can be a separate chamber (or tower) with its own spray system identical to a spray tower. Quenchers are designed using the same principles as scrubbers. Increasing the gas-liquid contact in them increases their operational efficiency. Small liquid droplets cool the exhaust stream more quickly than large droplets because they evaporate more easily. Therefore, less liquid is required. However, in most scrubbing systems, approximately one-and-ahalf to two and- a-half times the theoretical evaporation demand is required to ensure proper cooling. Evaporation also depends on time; it does not occur instantaneously. Quenching with re-circulated scrubber liquor could potentially reduce overall scrubber performance, since recycled liquid usually contains a high level of suspended and dissolved solids. As the liquid droplets evaporate, these solids could become re-entrained in the exhaust gas stream. To help reduce this problem, clean makeup water can be added directly to the quench system rather than adding all makeup water to a common sump. Thus Quencher is helping the GCP to remove partially micro dust particles from the BF gas.

13

2.3.3. VENTURI SCRUBBERS: Venturi Scrubber is a compact scrubber. It comprises of convergent inlet section, constricted throat followed by divergent outlet section.

Fig2.4 Venturi Scrubber The scrubbing liquid is fed into the inlet section tangentially through a number of pipes & ensures that entire surface area of section is flooded with scrubbing liquid. The dust laden gas enters the scrubber vertically from top & immediately hits the film of scrubbing water where some separation takes place. The Gas then enters the venturi throat which has annular shape. This ensures that the highest possible volume of water is taken up by gas, which becomes saturated in this area. 14

At the narrowest cross section of throat there is a sharp tear off edge where because of sudden change in gas speed the scrubbing water is atomized into tiny droplets. Because of high relative speed between the gas / dust mixture & the droplets the dust particles strike the droplets at high speed & are entrained by them. 2.3.4. CYCLONIC SEPARATOR: Cyclonic separation is a method of removing particulates from an air stream, without the use of filters, through vortex, separation. Rotational effects and gravity are used to separate mixtures of solids and fluids.

Fig2.5 Cyclonic Separator 15

A high speed rotating air-flow is established within a cylindrical or conical container called a cyclone. Air flows in a spiral pattern, beginning at the top (wide end) of the cyclone and ending at the bottom (narrow) end before exiting the cyclone in a straight stream through the center of the cyclone and out the top. Larger (denser) particles in the rotating air stream have too much inertia to follow the tight curve of the air stream and strike the outside wall, falling then to the bottom of the cyclone where they can be removed. In a conical system, as the rotating air-flow moves towards the narrow end of the cyclone the rotational radius of the air stream is reduced, separating smaller and smaller particles from the air stream. The cyclone geometry, together with air flow rate, defines the cut point of the cyclone. This is the size of particle that will be removed from the air stream with a 50% efficiency. Particles larger than the cut point will be removed with a greater efficiency and smaller particles with a lower efficiency. 2.3.5. SEAL POT: The seal pot is an instrument used to remove the slag from the GCP. The instrument consists of inlet tube, outlet tube, collection cylinder, water inlet tube and a manual gate valve. The sprayed water quencher, venturi, cyclonic separator reacts with the micro dust particles of BF gas forming slag. This slag formed should be removed periodically for continuous operation of GCP. It can be removed manually or logically programmed using the gate valve.

16

Fig2.6 Seal Pot The sprayed water quencher, venturi, cyclonic separator reacts with the micro dust particles of BF gas forming slag. This slag formed should be removed periodically for continuous operation of GCP. It can be removed manually or logically programmed using the gate valve. There is a problem when completely removing slag from seal pot. When it is fully removed the CO gas will escape along with it. So it should be partially removed and filling the free space left with water for precautionary operation. The Gate valve must be opened every 2 hours and a half the amount of collected slag should be removed by filling the remaining space with water. Thus Seal pot doing a special work in GCP. 17

2.4.

MEASURING INSTRUMENT DETAILS: The instruments used for measuring temperature, pressure, flow and

position

that are used for various measuring, sensing, controlling and

monitoring purposes are detailed in the following. 2.4.1. TEMPERATURE MEASUREMENT: In GCP the instruments used for temperature measurement are thermocouple and RTD. 2.4.1.1. EQUIPMENT DETAILS: Table 3 Temperature Transmitter details: Type

Analog Electronics Microprocessor based SMART system Power supply 12-20VDC Input RTD Pt100 Operating Temperature 50˚C Accuracy + 0.2% of span Output 4-20mA DC Ambient Temperature limit 60˚C Relative Humidity 95% Indicator Digital Case material Cast Aluminium Electrical safety Safe Electrical connection 1/2inch NPT(f) Cold junction compensation No Burn out protection Yes

18

Table 4 Location of Temperature Transmitters: TT101 0-400˚C Quencher inlet Gas line TT102 0-200˚C 1st Venturi outlet Gas line TT103 0-200˚C GCP outlet Gas line Table 5 Temperature Sensor details: Element Platinum-Nickel Type Simplex Lead wire Silver Insulation Mineral insulated Sensor length 550mm Extension length 75mm Shape Tapered Electrical 3wire & 1/2inch NPT connection Table 6 Location of Temperature Sensor: TE101 0-400˚C Quencher inlet Gas line TE102 0-200˚C First Venturi inlet TE103 0-200˚C GCP outlet Gas line

2.4.1.2. RESISTANCE THERMOMETERS: Resistance thermometers, also called resistance temperature detectors (RTDs), are temperature sensors that exploit the predictable change in electrical resistance of some materials with changing temperature. As they are almost invariably made of platinum, they are often called platinum resistance

thermometers.

They

are

slowly

replacing

thermocouples in many industrial applications below 600 °C.

19

the

use

of

There are two broad categories, "film" and "wire-wound" types. •

Film thermometers have a layer of platinum on a substrate; the layer may be extremely thin, perhaps 1 micrometer. Advantages of this type are relatively low cost and fast response. Such devices have improved in performance although the different expansion rates of the substrate and platinum give "strain gauge" effects and stability problems.

•

Wire-wound thermometers can have greater accuracy, especially for wide temperature ranges. The coil diameter provides a compromise between mechanical stability and allowing expansion of the wire to minimize strain and consequential drift.

How do resistance thermometers work? Resistance thermometers are constructed in a number of forms and offer greater stability, accuracy and repeatability in some cases than thermocouples. While thermocouples use the Seebeck effect to generate a voltage, resistance thermometers use electrical resistance and require a small power source to operate. The resistance ideally varies linearly with temperature. Resistance thermometers are usually made using platinum, because of its linear resistance-temperature relationship and its chemical inertness. The platinum detecting wire needs to be kept free of contamination to remain stable. A platinum wire or film is supported on a former in such a way that it gets minimal differential expansion or other strains from its former, yet is reasonably resistant to vibration. RTD assemblies made from iron or copper are also used in some applications. 20

Resistance Thermometers: Resistance thermometer elements are available in a number of forms. The most common are:Wire wound in a ceramic insulator - wire spiral within sealed ceramic cylinder, works with temperatures to 850 °C •

Wire encapsulated in glass - wire around glass core with glass fused homogenously around, resists vibration, more protection to the detecting wire but smaller usable range

•

Thin film - platinum film on ceramic substrate, small and inexpensive to mass produce, fast response to temperature change

Resistance thermometer construction

Fig2.7 RTD These elements nearly always require insulated leads attached. At low temperatures PVC, silicon rubber or PTFE insulators are common to 250°C. Above this, glass fibre or ceramic are used. The measuring point and usually most of the leads require a housing or protection sleeve. This is often a metal alloy which is inert to a particular process. Often more consideration goes in to selecting and designing protection sheaths than sensors as this is the layer that must withstand chemical or physical attack and offer convenient process attachment points.

21

Resistance thermometer wiring configurations

Fig2.8 RTD Wire connection The simplest resistance thermometer configuration uses two wires. It is only used when high accuracy is not required as the resistance of the connecting wires is always included with that of the sensor leading to errors in the signal. Using this configuration you will be able to use 100 metres of cable. This applies equally to balanced bridge and fixed bridge system. Temperature to resistance equation The relation between temperature and resistance is given by the CallendarVan Dusen equation,

Here, RT is the resistance at temperature T, R0 is the resistance at 0 °C, and the constants (for an alpha=0.00385 platinum RTD) are

22

Since the B and C coefficients are relatively small, the resistance changes almost linearly with the temperature. Advantages of platinum resistance thermometers: •

High accuracy

•

Low drift

•

Wide operating range

•

Suitability for precision applications

Limitations: •

RTDs in industrial applications are rarely used above 660 °C. At temperatures above 660 °C it becomes increasingly difficult to prevent the platinum from becoming contaminated by impurities from the metal sheath of the thermometer. This is why laboratory standard thermometers replace the metal sheath with a glass construction. At very low temperatures, say below -270 °C (or 3 K), due to the fact that there are very few phonons, the resistance of a RTD is mainly determined by impurities and boundary scattering and thus basically independent of temperature. As a result, the sensitivity of the RTD is essentially zero and therefore not useful.

•

Compared to thermistors, platinum RTDs are less sensitive to small temperature changes and have a slower response time. However, thermistors have a smaller temperature range and stability.

23

2.4.1.3. THERMOCOUPLE:

Fig2.9 Thermocouple Thermocouple plugged to a multimeter displaying room temperature in °C. In electronics and in electrical engineering, thermocouples are a widely used type of temperature sensor and can also be used as a means to convert thermal potential difference into electric potential difference. They are cheap and interchangeable, have standard connectors, and can measure a wide range of temperatures. The main limitation is accuracy; system errors of less than one degree Celsius (°C) can be difficult to achieve. Principle of operation In 1821, the physicist Thomas Johann Seebeck discovered that when any conductor (such as a metal) is subjected to a thermal gradient, it will generate a voltage. This is now known as the thermoelectric effect or Seebeck effect. Any attempt to measure this voltage necessarily involves connecting another conductor to the "hot" end. This additional conductor will then also experience the temperature gradient, and develop a voltage of its own which will oppose the original. 24

Fortunately, the magnitude of the effect depends on the metal in use. Using a dissimilar metal to complete the circuit creates a circuit in which the two legs generate different voltages, leaving a small difference voltage available for measurement. That difference increases with temperature, and can typically be between one and seventy microvolts per degree Celsius (µV/°C) for the modern range of available metal combinations. Certain combinations have become popular as industry standards, driven by cost, availability, convenience, melting point, chemical properties, stability, and output. This coupling of two metals gives the thermocouple its name. It is important to note that thermocouples measure the temperature difference between two points, not absolute temperature. In traditional applications, one of the junctions the cold junction was maintained at a known (reference) temperature, while the other end was attached to a probe. Having available a known temperature cold junction, while useful for laboratory calibrations, is simply not convenient for most directly connected indicating and control instruments. They incorporate into their circuits an artificial cold junction using some other thermally sensitive device, such as a thermistor or diode, to measure the temperature of the input connections at the instrument, with special care being taken to minimize any temperature gradient between terminals. Hence, the voltage from a known cold junction can be simulated, and the appropriate correction applied. This is known as cold junction compensation. Additionally, a device can perform cold junction compensation by computation. It can translate device voltages to temperatures by either of two methods. It can use values from look-up tables or approximate using polynomial interpolation. 25

A thermocouple can produce current, which means it can be used to drive some processes directly, without the need for extra circuitry and power sources. For example, the power from a thermocouple can activate a valve when a temperature difference arises. The electric power generated by a thermocouple is a conversion of the heat energy that one must continuously supply to the hot side of the thermocouple to maintain the electric potential. The flow of heat is necessary because the current flowing through the thermocouple tends to cause the hot side to cool down and the cold side to heat up (the Peltier effect). Thermocouples can be connected in series with each other to form a thermopile, where all the hot junctions are exposed to the higher temperature and all the cold junctions to a lower temperature. Thus, the voltages of the individual thermocouple add up, which allows for a larger voltage and increased power.

26

2.4.2. PRESSURE SENSORS: In GCP Pressure sensors like Bourdon tube and Diaphragms are used. They are listed below: 2.4.2.1. EQUIPMENT DETAILS: Table 7 Pressure gauge details (water line): Sensing element Process

Bourdon tube 1/2inch NPT M

connection Accuracy

+1.0% of span

Table 8 Location of pressure gauge (water line): PI105 0-5Kg/cm² Quencher inlet water line PI106 0-5Kg/cm² 1st Venturi inlet Water line PI107 0-5Kg/cm² Separator inlet water line Table 9 Pressure gauge details (gas line): Sensing element Diaphragm Process Flanged (40NB ANSI) connection Accuracy +1.6%of PI101 0-12000mmWC Inletspan of GCP

Table 10 Location of pressure gauge (gas line):

PI102 0-12000mmWC Inlet of 2nd Venturi PI103 0-10000mmWC Inlet of septum valve PI104 0-1000mmWC Outlet of GCP

27

2.4.2.2. BOURDON TUBE:

Fig2.10 Membrane-type manometer A Bourdon gauge uses a coiled tube which as it expands due to pressure increase causes a rotation of an arm connected to the tube. A combination pressure and vacuum gauge (case and viewing glass removed)

Fig2.11 Indicator Side with card and Fig2.12 Mechanical Side with Bourdon dial

tube

28

In 1849 the Bourdon tube pressure gauge was patented in France by Eugene Bourdon. The pressure sensing element is a closed coiled tube connected to the chamber or pipe in which pressure is to be sensed. As the gauge pressure increases the tube will tend to uncoil, while a reduced gauge pressure will cause the tube to coil more tightly. This motion is transferred through a linkage to a gear train connected to an indicating needle. The needle is presented in front of a card face inscribed with the pressure indications associated with particular needle deflections. In a barometer, the Bourdon tube is sealed at both ends and the absolute pressure of the ambient atmosphere is sensed. Differential Bourdon gauges use two Bourdon tubes and a mechanical linkage that compares the readings. In the following pictures the transparent cover face has been removed and the mechanism removed from the case. This particular gauge is a combination vacuum and pressure gauge used for automotive diagnosis: •

the left side of the face, used for measuring manifold vacuum, is calibrated in centimeters of mercury on its inner scale and inches of mercury on its outer scale.

•

the right portion of the face is used to measure fuel pump pressure and is calibrated in fractions of 1 kgf/cm² on its inner scale and pounds per square inch on its outer scale.

29

2.4.2.3. DIAPHRAGM:

Fig2.13 Diaphragm A pile of pressure capsules with corrugated diaphragms in an aneroid barograph. A second type of aneroid gauge uses the deflection of a flexible membrane that separates regions of different pressure. The amount of deflection is repeatable for known pressures so the pressure can be determined using by calibration. The deformation of a thin diaphragm is dependent on the difference in pressure between its two faces. The reference face can be open to atmosphere to measure gauge pressure, open to a second port to measure differential pressure, or can be sealed against a vacuum or other fixed reference pressure to measure absolute pressure. The deformation can be measured using mechanical, optical or capacitive techniques. Ceramic and metallic diaphragms are used. Useful range: above 10-2 torr (roughly 1 Pa) For absolute measurements, welded pressure capsules with diaphragms on either side are often used. Shape: • • • •

Flat corrugated flattened tube capsule 30

2.4.3. FLOW METER: In GCP the only flow meter used is Orifice meter. 2.4.3.1. EQUIPMENT DETAILS: Table 11 Orifice plate details (water): Application Line size Fluid Fluid state Temperature Upstream pressure Viscosity Drain hole Pressure taps

Scrubbing water to gas 150NB Scrubbing water Re-circulated water with12% coal Iron Oxide dust 55˚C 3Kg/cm² ˜0.6 1/2inch NPT with plug 1inch NPTF

Table 12 Location of orifice plate (water): Pressur Range Location Flow Normal Line ID/ e 100NB

0-60m³/hr

150NB

Water line 0-130m³/hr 1st Venturi inlet 0-125m³/hr

4.5mm 155.4mm/

200NB

Water line 0-150m³/hr Separator inlet

4.85mm 206.3mm/

Quencher inlet

Water line

0-50m³/hr

0-140m³/hr

Thickness 105.3mm/

6.35mm

31

Table 13 Orifice Plate details (Gas): Application Gas cleaning plant outlet Dust size 1400mm,ID 1mm Thick plate Fluid Blast furnace gas with minute moisture & dust Gas composition CO:16.15% N2:55.19% CO2:56.70% H2O+HC:1.24% Flow max/min 108000Nm³/hr,104000Nm³/hr Temperature 45˚C Specific gravity 0.96 Upstream pressure 800mmWC at 104000Nm³/hr Orifice plate Concentric type Thickness 6.35mm Drain hole 1/2inch NPT Pressure taps 1 inch NPT, On-Duct Calibration Range 108000m³/hr Location GCP Outlet

32

2.4.3.2. ORIFICE PLATE:

Fig2.14 Flat-plate, sharp-edge orifice An orifice plate is a device used to measure the rate of fluid flow. It uses the same principle as a Venturi nozzle, namely Bernoulli’s principle which says that there is a relationship between the pressure of the fluid and the velocity of the fluid. When the velocity increases, the pressure decreases and vice versa.

Fig2.15

33

An orifice plate is basically a thin plate with a hole in the middle. It is usually placed in a pipe in which fluid flows. As fluid flows through the pipe, it has a certain velocity and a certain pressure. When the fluid reaches the orifice plate, with the hole in the middle, the fluid is forced to converge to go through the small hole; the point of maximum convergence actually occurs shortly downstream of the physical orifice, at the so-called vena contracta point (see drawing to the right). As it does so, the velocity and the pressure changes. Beyond the vena contracta, the fluid expands and the velocity and pressure change once again. By measuring the difference in fluid pressure between the normal pipe section and at the vena contracta, the volumetric and mass flow rates can be obtained from Bernoulli's equation.

34

2.4.4. POSITION SENSORS: 2.4.4.1. Inductive sensor

Fig2.16 Inductive sensor An inductive sensor is an electronic proximity sensor, which detects metallic objects without touching them. The sensor consists of an induction loop. Electric current generates a magnetic field, which collapses generating a current that falls asymptotically toward zero from its initial level when the input electricity ceases. The inductance of the loop changes according to the material inside it and since metals are much more effective inductors than other materials the presence of metal increases the current flowing through the loop. This change can be detected by sensing circuitry, which can signal to some other device whenever metal is detected.Common applications of inductive sensors include metal detectors, traffic lights, car washes, and a host of automated industrial processes. Because the sensor does not require physical contact it is particularly useful for applications where access presents challenges or where dirt is prevalent. The sensing range is rarely greater than 6cm, however, and it has no directionality. 35

2.4.4.2. Linear variable differential transformer

Fig2.17 LVDT Cut away view of an LVDT. Current is driven through the primary coil at A, causing an induction current to be generated through the secondary coils at B. L:inear variable differential transformer (LVDT) is a type of electrical transformer used for measuring linear displacement. The transformer has three solenoid coils placed end-to-end around a tube. The centre coil is the primary, and the two outer coils are the secondary. A cylindrical ferromagnetic core, attached to the object whose position is to be measured, slides along the axis of the tube. An alternating current is driven through the primary, causing a voltage to be induced in each secondary proportional to its mutual inductance with the primary. The frequency is usually in the range 1 to 10 kHz. As the core moves, these mutual inductances change, causing the voltages induced in the secondary to change. The coils are connected in reverse series, so that the output voltage is the difference (hence "differential") between the two secondary voltages. 36

When the core is in its central position, equidistant between the two secondary, equal but opposite voltages are induced in these two coils, so the output voltage is zero. When the core is displaced in one direction, the voltage in one coil increases as the other decreases, causing the output voltage to increase from zero to a maximum. This voltage is in phase with the primary voltage. When the core moves in the other direction, the output voltage also increases from zero to a maximum, but its phase is opposite to that of the primary. The magnitude of the output voltage is proportional to the distance moved by the core (up to its limit of travel), which is why the device is described as "linear". The phase of the voltage indicates the direction of the displacement. Because the sliding core does not touch the inside of the tube, it can move without friction, making the LVDT a highly reliable device. The absence of any sliding or rotating contacts allows the LVDT to be completely sealed against the environment. LVDTs are commonly used for position feedback in servomechanisms, and for automated measurement in machine tools and many other industrial and scientific applications LVDT Working Principle The LVDT, Linear Variable Differential Transformer is a well established transducer design which has been used throughout many decades for the accurate measurement of displacement and within closed loops for the control of positioning. In its simplest form, the design consists of a cylindrical array of primary and secondary windings with a separate cylindrical core which passes through the centre. 37

Fig2.18 Working of LVDT The LVDT, Linear Variable Differential Transformer is a well established transducer design which has been used throughout many decades for the accurate measurement of displacement and within closed loops for the control of positioning. In its simplest form, the design consists of a cylindrical array of a primary and secondary windings with a separate cylindrical core which passes through the centre. (Fig A)The primary windings (P) are energized with a constant amplitude A.C. supply at a frequency of 1 to 10 kHz. This produces an alternating magnetic field in the centre of the transducer which induces a signal into the secondary windings (S & S) depending on the position of the core. 38

Movement of the core within this area causes the secondary signal to change (Fig B). As the two secondary windings are positioned and connected in a set arrangement (push-pull mode), when the core is positioned at the centre, a zero signal is derived. Movement of the core from this point in either direction causes the signal to increase (Fig C). As the windings are wound in a particular precise manner, the signal output has a linear relationship with the actual mechanical movement of the core. The secondary output signal is then processed by a phase-sensitive demodulator which is switched at the same frequency as the primary energizing supply. This results in a final output which, after rectification and filtering, gives D.C. or 4-20mA output proportional to the core movement and also indicates its direction, positive or negative from the central zero point (Fig D). The distinct advantage of using an LVDT displacement transducer is that the moving core does not make contact with other electrical components of the assembly, as with resistive types, as so offers high reliability and long life. Further, the core can be so aligned that an air gap exists around it, ideal for applications where minimum mechanical friction is required. The LVDT design lends itself for easy modification to fulfill a whole range of different applications in both research & industry. 2.4.4.3. Hall Effect sensor A Hall Effect sensor is a transducer that varies its output voltage in response to changes in magnetic field. Hall sensors are used for proximity switching, positioning, speed detection, and current sensing applications. In its simplest form, the sensor operates as an analogue transducer, directly returning a voltage. With a known magnetic field, its distance from the Hall plate can be determined.

39

Using groups of sensors, the relative position of the magnet can be deduced.

Fig2.19 Hall effect sensor The magnetic piston (1) in this pneumatic cylinder will cause the Hall effect sensors (2 and 3) mounted on its outer wall to activate when it is fully retracted or extended. A Hall Effect sensor is a transducer that varies its output voltage in response to changes in magnetic field. Hall sensors are used for proximity switching, positioning, speed detection, and current sensing applications. In its simplest form, the sensor operates as an analogue transducer, directly returning a voltage. With a known magnetic field, its distance from the Hall plate can be determined. Using groups of sensors, the relative position of the magnet can be deduced. Electricity carried through a conductor will produce a magnetic field that varies with current, and a Hall sensor can be used to measure the current without interrupting the circuit. 40

Typically, the sensor is integrated with a wound core or permanent magnet that surrounds the conductor to be measured. Frequently, a Hall sensor is combined with circuitry that allows the device to act in a digital (on/off) mode, and may be called a switch in this configuration. Commonly seen in industrial applications such as the pictured pneumatic cylinder, they are also used in consumer equipment; for example some computer printers use them to detect missing paper and open covers. When high reliability is required, they are used in keyboards. Fig2.20

Fig2.20 Hall effect sensor Hall sensors are commonly used to time the speed of wheels and shafts, such as for internal combustion engine ignition timing or tachometers. They are used in Brushless DC electric motors to detect the position of the permanent magnet. In the pictured wheel carrying two equally spaced magnets, the voltage from the sensor will peak twice for each revolution. This arrangement is commonly used to regulate the speed of disc drives.

41

2.4.5. TRANSMITTER DETAILS: Table 14 Pressure/Flow/Differential Pressure Transmitter details: Application For pressure, flow & differential pressure at Inlet or outlet Duty Continuous Humidity 45˚C(max) 99%RH(max) Accuracy 0.1% of FSD Over pressure range 150% of rated pressure Instrument connection 1/2inchNPTF Process fluid Mini Blast Furnace outlet gas Composition: CO2=16.15% N2=55.19% CO=26.70% H2O+HC=1.24% Gas is 100% saturated Yes Maximum flow 108000Nm³/Hr Maximum pressure 12000mmWC Dust Granulometer 10-250,80% Dust content 15gm/Nm³ Power supply 240V DC,2 wire from PLC Output 4-20mA

42

Table 15 Location of pressure/flow/differential pressure transmitters: PT101 Diaphragm seal Quencher inlet 0-12000mmWC PT102

pressure transmitter Diaphragm seal

Secondary Venturi

0-12000mmWC

PT103

pressure transmitter Diaphragm seal

inlet Septum valve inlet

0-10000mmWC

PT104

pressure transmitter Diaphragm seal

GCP outlet

0-2000mmWC

Across Quencher

0-12000mmWC

pressure transmitter DPT101 Diaphragm seal Differential pressure transmitter DPT102 Diaphragm seal

FT101 FT102 FT103 FT104

inlet & Separator outlet Across 1st Venturi

0-12000mmWC

Differential pressure

inlet & outlet

transmitter Water flow transmitter

Quencher inlet

0-50m³/hr

Water flow transmitter

water line 1st Venturi inlet

0-125m³/hr

Water flow transmitter

water line Separator inlet

0-140³/hr

Gas flow transmitter

water line GCP outlet gas line 0-125m³/hr

43

2.5.

VALVE DETAILS: The GCP is using gate valves and isolation valves for the regulation of

BF gas moving inside pipelines. 2.5.1. GATE VALVES:

Fig2.21 Gate valve A Gate Valve, or Sluice Valve, as it is sometimes known, is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid. The distinct feature of a gate valve is the sealing surfaces between the gate and seats are planar. The gate faces can form a wedge shape or they can be parallel. Gate valves are sometimes used for regulating flow, but many are not suited for that purpose, having been designed to be fully opened or closed. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low friction loss. Gate valves are characterized as having either a rising or a non rising stem. Rising stems provide a visual indication of valve position. Non rising stems are used where vertical space is limited or underground. Bonnets provide leak proof closure for the valve body. Gate valves may have a screw-in, union, or bolted bonnet. Screw-in bonnet is the simplest, offering a durable, pressure-tight seal. Union bonnet is suitable for applications requiring frequent inspection and cleaning. It also gives the body added strength. Bolted bonnet is used for larger valves and higher pressure applications. 44

Another type of bonnet construction in a gate valve is pressure seal bonnet. This construction is adopted for valves for high pressure service, typically in excess of 15 Mpa (2250 psi). The unique feature about the pressure seal bonnet is that the body - bonnet joints seals improves as the internal pressure in the valve increases, compared to other constructions where the increase in internal pressure tends to create leaks in the bodybonnet joint. Gate valves normally have flanged ends which are drilled according to pipeline compatible flange dimensional standards. Cast iron, cast carbon steel, gun metal, stainless steel, alloy steels, and forged steels are different materials from which gate valves are constructed. Maintenance To avoid failure, it is a very good practice to use the valve three or four times a year. From its normal position of nearly full-open: wind it fully closed, then fully open, then half a turn closed. Make sure the system that the pipes are connected to doesn't require water flow whilst you do this. 2.5.2. ISOLATION VALVES: A valve intended for use only in the closed or fully open position. Isolation valves are used for diverting process media, facilitating maintenance, equipment removal and Isolation valves are a key component in any fluid system as they are used to stop the flow of fluid into a particular area of the system. They are also sometimes used to manually control the flow of the fluid.

45

Ball valves and butterfly valves are the two most important rotary valves or Isolation Valves associated with steam applications. 2.5.2.1. Ball Valves: A ball valve is a valve that opens by turning a handle attached to a ball inside the valve. The ball has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends of the valve, and flow is blocked. The handle position lets you "see" the valve's position. Ball valves are durable and usually work to achieve perfect shutoff even after years of disuse. They are therefore an excellent choice for shutoff applications (and are often preferred to globe valves and gate valves for this purpose). They do not offer the fine control that may be necessary in throttling applications but are sometimes used for this purpose. The body of ball valves may be made of metal, ceramic, or plastic. The ball may be chrome plated to make it more durable

Fig2.22 T and L Type ball valves 46

2.5.2.2. Butterfly Valve: A butterfly valve is a type of flow control device, typically used to regulate a fluid flowing through a section of pipe. The valve is similar in operation to a ball valve. A flat circular plate is positioned in the center of the pipe. The plate has a rod through it connected to an actuator on the outside of the valve. Rotating the actuator turns the plate either parallel or perpendicular to the flow. Unlike a ball valve, the plate is always present within the flow, therefore a pressure drop is always induced in the flow regardless of valve position. A butterfly valve is from a family of valves called quarter-turn valves. The "butterfly" is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the process fluid. The valve may also be opened incrementally to regulate flow. There are different kinds of butterfly valves, each adapted for different pressures and different usage. The resilient butterfly valve, which uses the flexibility of rubber, has the lowest pressure rating. The high performance butterfly valve, used in slightly higher-pressure systems, features a slight offset in the way the disc is positioned, which increases the valve's sealing ability and decreases its tendency to wear. The valve best suited for highpressure systems is the tricentric butterfly valve, which makes use of a metal seat, and is therefore able to withstand a greater amount of pressure. 47

2.6.

ACTUATOR DETAILS: Actuators are used for the automation of industrial valves and can be

found in all kinds of technical process plants: they are used in wastewater treatment plants, power plants and even refineries. This is where they play a major part in automating process control. The valves to be automated vary both in design and dimension. The diameters of the valves range from a few inches to a few metres. Depending on their type of supply, the actuators may be classified as pneumatic, hydraulic and electric actuators.

Fig2.23 Industrial Electric Actuator

48

Classification of the actuators according to their movement Travel means the distance of the closing element within the valve has to cover to completely open or close that valve. Typical closing elements include butterfly, globe or gate valve discs. These three closing elements stand for the three basic movements required for covering the travel. The butterfly valve disc is operated by a 90° swivel movement from end position OPEN to CLOSED, the globe valve disc is operated by a rather short linear movement (stroke) while the gate valve disc movement covers the full diameter of the valve. Each movement type requires a specific actuator type.

Fig2.24 Electric multi-turn actuator on a gate valve Multi-turn actuators

Multi-turn actuators are required for the automation of multi-turn valves. One of the major representatives of this type is the gate valve. The basic requirements on multi-turn actuators are described as follows:

49

"A multi-turn actuator is an actuator which transmits to the valve a torque for at least one full revolution. It is capable of withstanding thrust."A valve stem is mounted to the gate valve disc. The multi-turn actuator moves the gate valve disc from OPEN to CLOSED and vice versa via a stem nut. To cover the complete valve travel, the so-called valve stroke, the actuator has to perform – depending on the valve – a few or several hundred rotations. Due to their design, the stroke of electric actuators, contrary to that of their pneumatic counterparts, has no limits. Therefore, gate valves are exclusively automated by means of electric multi-turn actuators. The multi-turn actuator has to be able to withstand the weight of the gate valve disc by means of the valve attachment, the interface to the valve. This is expressed in the second sentence of the definition. Gate valves may have a diameter of approx. 4 inches to several meters. The torque requirement for multi-turn solutions ranges from approx. 10 N m to 30,000 N m.

Fig2.25Electric part-turn actuator on a butterfly valve 50

Part-turn actuators

Part-turn actuators are required for the automation of part-turn valves. Major representatives of this type are butterfly valves and ball valves. The basic requirements on part-turn actuators are described as follows: "A part-turn actuator is an actuator which transmits a torque to the valve for less than one full revolution. It need not be capable of withstanding thrust." Less than one full revolution usually means a swivel movement of 90°; however, there are some valve types requiring a different swing angle, such as two-way valves. The closing elements in part-turn actuators are always supported by the valve housing, i.e. the weight of the closing element does not act upon the part-turn actuator. This is expressed in the second sentence of the definition. Part-turn valves diameters range from a few inches to several meters. The torque requirement for operating the closing element has a comparable range from approximately 10 N m to several 100,000 N m. Electric actuators are unrivalled for large-diameter valves with high torque requirements. Linear actuators

Currently there is no international standard describing linear actuators or linear thrust units. A typical representative of the valves to be automated is the control valve. Just like the plug in the bathtub is pressed into the drain, the plug is pressed into the plug seat by a stroke movement. 51

The pressure of the medium acts upon the plug while the thrust unit has to provide the same amount of thrust to be able to hold and move the plug against this pressure. Most of the linear actuators used are pneumatic diaphragm actuators. They are characterized by a simple design principle and are therefore cost-effective. A compressed air supply is a prerequisite for their use. In case this is not possible, the use of thrust units is recommended which can easily be supplied with power. Motor Robust asynchronous 3-phase AC motors are mostly used as electric motors, for some applications also 1-phase AC or DC motors are used. The motors are specially adapted for valve automation requirements. Due to their design, they provide higher torques from standstill than comparable conventional motors. This feature is required to be able to unseat sticky valves. Electric actuators are used under extreme ambient conditions. Fan motors do not provide sufficient enclosure protection and can therefore not be used. Actuators can generally not be used for continuous operation since the motors have to cool down after a certain operating time. This suits the application since valves are not continuously operated. Limit and torque sensors

The limit switching measures the travel and signals when an end position has been reached, the torque switching measures the torque present in the valve. When exceeding a set limit, this is signaled in the same way.Actuators are often equipped with a remote position transmitter which indicates the valve position as continuous current or voltage signal. 52

Gearing

Often a worm gearing is used to reduce the high output speed of the electric motor. This enables a high reduction ratio within the gear stage, leading to a low efficiency which is desired for the actuators. The gearing is therefore self-locking i.e. it prevents accidental and undesired changes of the valve position by acting upon the valve’s closing element. This is of major importance for multi-turn actuators which are axially loaded with the weight of the gate valve disc. Valve attachment

The valve attachment consists of two elements. First: The flange used to firmly connect the actuator to the counterpart on the valve side. The higher the torque to be transmitted, the larger the flange required. Second: The output drive type used to transmit the torque or the thrust from the actuator to the valve shaft. Just like there is a multitude of valves there is also a multitude of valve attachments. Manual operation

In their basic version most electric actuators are equipped with a hand wheel for operating the actuators during commissioning or power failure. The hand wheel does not move during motor operation.

53

Actuator controls Both actuator signals and operation commands of the DCS are processed within the actuator controls. This task can in principle be assumed by external controls, e.g. a PLC. Modern actuators include integral controls which process signals locally without any delay. The controls also include the switchgear required to control the electric motor. This can either be reversing contactors or thyristors which, being an electric component, are not subject to mechanic wear. Controls use the switchgear to switch the electric motor on or off depending on the signals or commands present. Another task of the actuator controls is to provide the DCS with feedback signals, e.g. when reaching a valve end position. Electrical connection

The supply cables of the motor and the signal cables for transmitting the commands to the actuator and sending feedback signals on the actuator status are connected to the electrical connection. The electrical connection is ideally designed as plug/socket connector. For maintenance purposes, the wiring can easily be disconnected and reconnected.

54

2.7.

PROGRAMMING INSTRUMENTS: The GCP can be programmed digitally using PLC. Here the PLC used is

Siemens S7 300. Three operations of GCP can be done using PID. The details about PLC and PID controller are shown in the following. 2.7.1. PLC DETAILS: A programmable logic controller (PLC) or programmable controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result. Features

Fig2.26 PLC 55

Control panel with PLC (grey elements in the center). The unit consists of separate elements, from left to right; power supply, controller, relay units for in- and output. The main difference from other computers is that PLCs are armored for severe condition (dust, moisture, heat, cold, etc) and have the facility for extensive input/output (I/O) arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems. Some even use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays or solenoids, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a computer network that plugs into the PLC. PLCs were invented as replacements for automated systems that would use hundreds or thousands of relays, cam timers, and drum sequencers. Often, a single PLC can be programmed to replace thousands of relays. Programmable controllers were initially adopted by the automotive manufacturing industry, where software revision replaced the re-wiring of hard-wired control panels when production models changed. Many of the earliest PLCs expressed all decision making logic in simple ladder logic which appeared similar to electrical schematic diagrams. The electricians were quite able to trace out circuit problems with schematic diagrams using ladder logic. This program notation was chosen to reduce training demands for the existing technicians. Other early PLCs used a form of instruction list programming, based on a stack-based logic solver. 56

The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and networking. The data handling, storage, processing power and communication capabilities of some modern PLCs are approximately equivalent to desktop computers. PLC-like programming combined with remote I/O hardware, allow a general-purpose desktop computer to overlap some PLCs in certain applications.

Fig2.27 Block of PLC

57

How the PLC operates The PLC is a purpose-built machine control computer designed to read digital and analog inputs from various sensors, execute a user defined logic program, and write the resulting digital and analog output values to various end effectors. Scan cycle Exact details vary between manufacturers, but most PLCs follow a 'scan-cycle' format. Overhead Overhead includes testing I/O module integrity, verifying the user program logic hasn't changed, that the computer itself hasn't locked up (via a watchdog timer), and any necessary communications. Communications may include traffic over the PLC programmer port, remote I/O racks, and other external devices such as HMIs (Human Machine Interfaces). Input scan A 'snapshot' of the digital and analog values present at the input cards is saved to an input memory table. Logic execution The user program is scanned element by element, then rung by rung until the end of the program, and resulting values written to an output memory table.

58

Output scan Values from the resulting output memory table are written to the output modules. Once the output scan is complete the process repeats itself until the PLC is powered down. The time it takes to complete a scan cycle is, appropriately enough, the "scan cycle time", and ranges from hundreds of milliseconds (on older PLCs, and/or PLCs with very complex programs) to only a few milliseconds on newer PLCs, and/or PLCs executing short, simple 2.7.2. SIEMENS S7 300 PLC: S7 Modules: An S7-300 consists of several modules. The following diagram illustrates a possible configuration:

Fig2.28 S7 Modules

59

Table 16 S7 Modules:

Module Arrangements:

Fig2.29 S7 Module arrangements Table 17 Arrangement of modules:

60

Table 18 Components of S7 PLC

61

62

2.7.3. PID CONTROLLER: A proportional–integral–derivative controller (PID controller) is a generic control loop feedback mechanism widely used in industrial control systems. A PID controller attempts to correct the error between a measured process variable and a desired set point by calculating and then outputting a corrective action that can adjust the process accordingly. The PID controller calculation involves three separate parameters; the Proportional, the Integral and Derivative values. The Proportional value determines the reaction to the current error, the Integral determines the reaction based on the sum of recent errors and the Derivative determines the reaction to the rate at which the error has been changing. The weighted sum of these three actions is used to adjust the process via a control element such as the position of a control valve or the power supply of a heating element.By "tuning" the three constants in the PID controller algorithm the PID can provide control action designed for specific process requirements. The response of the controller can be described in terms of the responsiveness of the controller to an error, the degree to which the controller overshoots the setpoint and the degree of system oscillation. Note that the use of the PID algorithm for control does not guarantee optimal control of the system. Some applications may require using only one or two modes to provide the appropriate system control. This is achieved by setting the gain of undesired control outputs to zero. A PID controller will be called a PI, PD, P or I controller in the absence of the respective control actions. PI controllers are particularly common, since derivative action is very sensitive to measurement noise, and the absence of an integral value prevents the system from reaching its target value due to the control action. 63

Fig2.30 Block diagram of PID controller The PID control scheme is named after its three correcting terms, whose sum constitutes the manipulated variable (MV). Hence:

where Pout, Iout, and Dout are the contributions to the output from the PID controller from each of the three terms, as defined below Proportional term

The proportional term makes a change to the output that is proportional to the current error value. The proportional response can be adjusted by multiplying the error by a constant Kp, called the proportional gain.

Where • • • •

Pout: Proportional output Kp: Proportional Gain, a tuning parameter e: Error = SP − PV t: Time or instantaneous time (the present) 64

Integral term

Where • • • •

Iout: Integral output Ki: Integral Gain, a tuning parameter e: Error = SP − PV τ: Time in the past contributing to the integral response

Derivative term

Where • • • •

Dout: Derivative output Kd: Derivative Gain, a tuning parameter e: Error = SP − PV t: Time or instantaneous time (the present)

Output of PID controller: The output from the three terms, the proportional, the integral and the derivative terms are summed to calculate the output of the PID controller. Defining u(t) as the controller output, the final form of the PID algorithm is:

65

2.8. SOFTWARE PROGRAMMING DETAILS: 2.8.1. SEQUENCE OF OPERATIONS: Operations done in Quencher & Venturi inlet and Seal pot: 1. After passing dust catcher the hot gas was sensed by temperature sensor or flow sensor. By sensing it the water pump is operated so that water is sprayed inside the quencher. 2. The gas from quencher is again sensed by the temperature sensor or flow sensor and water pump is operated according to it. 3. The seal pot is used to seal the CO leakage while releasing slag. When two Position sensors are ON, the outlet valve should be open. When two sensors are OFF, Pump should be operated. Operations done by PID controller: 4.Venturi1 inlet and outlet pressure difference is measured using DPT1.Using that signal the Venturi throat is adjusted to control the pressure in the pipe. This can be done by PID controller. 5. Venturi2 throat is adjusted by using the DPT2 signal. This can be done by PID controller. 6. Septum valve contains 4 butterfly valves. Of that 3 valves are operated from the central control panel using PLC and electrical actuator for ON/OFF duty. The remaining 1 valve is used for regulating purpose. It is also operated by PLC and electrical actuator.All the butterfly valves of the septum valve are provided with 2 wire position transmitter to provide continuous feedback of individual butterfly valve to PLC/Control panel When the set pressure is beyond the range of regulating valve, the valve is fully open (60 to 70ºopen) or fully closed (0º). 66

The end limit switches of the valve will operated in this condition and give signal/indication that the set pressure is beyond range if regulating valve. In such case the ON/OFF valves are required to operated to bring the set pressure with in the range of regulating valve. If the regulating valve is fully closed & still BF top pressure is less than desired/set top pressure, 2/3 ON/OFF valves are required to be closed partially till the desired/set top pressure is achieved and regulating valve position is between 30º and 35º to have control range open both upper & lower side. Similarly if BF top pressure is more then valve is fully open(60 to 70ºopen), 2 or 3ON/OFF valves are required to be open gradually till the desired/set BF top pressure is achieved & regulating valve position is between 30 to 35º to have control range on upper & lower side.

67

2.8.2. PROGRAM:

68

69

2.9. ADVANTAGES OF GCP: • The GCP controls air pollution caused by dust from the BF gas in the atmosphere. • It reduces the temperature at the BF gas that are unused there by reducing the global warming. • The process in which the CO gas is recycled, makes the blast furnace to work at high efficiency.

70

CHAPTER 3 3.1.

CONCLUSION:

Summary of work done: The BF gas was directly exposed to the atmosphere in previously. It will cause severe effects to the environment. To overcome this, Gas cleaning plant is used to clear the dust in the BF gas and also it reduces the temperature of the wasted BF gas. The GCP can be operated automatically using Siemens S7 300 PLC. The gas can be collected from the blast furnace and treated with water for more than three times automatically to achieve the goal of the project. Suggestion of future work: The project should be extended such that even a small amount of CO gas should not be sent to the atmosphere by using the gas analyzers.

71

APPENDIX IMPLEMENTATION OF LOGIC GATES IN LADDER DIAGRAM OR logic

The lamp will come on if either contact A or contact B is actuated, because all it takes for the lamp to be energized is to have at least one path for current from wire L1 to wire 1. A simple OR logic function, implemented with nothing more than contacts and a lamp. AND logic: The AND logic functions can be mimicked by wiring the two contacts in series instead of parallel:

Now, the lamp energizes only if contact A and contact B are simultaneously actuated. A path exists for current from wire L1 to the lamp (wire 2) if and only if both switch contacts are closed. 72

NOT Logic: The logical inversion, or NOT, function can be performed on a contact input simply by using a normally-closed contact instead of a normally-open contact:

Now, the lamp energizes if the contact is not actuated, and de-energizes when the contact is actuated. A pattern quickly reveals itself when ladder circuits are compared with their logic gate counterparts: • • •

Parallel contacts are equivalent to an OR gate. Series contacts are equivalent to an AND gate. Normally-closed contacts are equivalent to a NOT gate (inverter).

73

The following are the functions of combinational circuits NAND Logic:

NOR Logic:

Exclusive OR Gate:

74

REFERENCES:

1. Bolton, W. (2005) ‘Mechatronics’, Pearson Education, Ltd, pp 460-482. 2. Jain, R.K. (1999) ‘Mechanical and Industrial Measurements’, Khanna Publishers, New Delhi.

3. Patranabis, D. (1996) ‘Principles of Industrial Instrumentation’, Tata McGraw Hill Publishing Company Ltd.

4. Sawhney, A.K. (2004) ‘A course in Electrical & Electronic Measurement and Instrumentation’, Dhanpat Rai and Co (P) Ltd. 5. Stephanopoulis, G. (1990) ‘Chemical Process Control’, Prentice Hall of India, New Delhi, 6. www.wikipedia.com.html

75