29-08-2014, 03:31 PM
ACKNOWLEDGEMENT I express my sincere thanks to ‘Ion Exchange (India) Limited’ for providing me the opportunity to get help and instructions about water treatment plant (WTP). I would also like to acknowledge the efforts of Er. OMPRAKASH YADAV and Er. MRIGENDRA SINGH providing me the necessary documents and instructions essential for me to complete this work. I would also like to thanks Mr. SATNAM SINGH MATHARU and Er. AKSHAY AGNIHOTRI for their efforts from CTIEMT shahpur Jalandhar’ much needed moral support and encouragement is provided on numerous occasions by my whole family and friends. And finally, I would like to thank the GOD for his kind blessing to complete this work successfully. Without blessing, it was impossible to complete this work.
Brief Profile of The Company/Industry And Project
ION EXCHANGE (INDIA) LIMITED
Ion Exchange India pioneered water treatment in India and is today the country's premier company in water and environment management, with a strong international presence. Formed in 1964, as a subsidiary of the Company of UK, we became a wholly Indian company in 1985 when divested their holding.
Over 4 decades of experience
In its 40 years of experience, the company has provided installations for diverse industries in India and abroad, from nuclear and thermal power, fertilizer and refinery, to automobile, electronics and textile. The company has an in-depth understanding and knowledge of the Indian market as well as of the cultural patterns prevailing particularly in South East Asia, Africa and the Middle East.
· More than 35,000 plants in India and abroad - packaged, pre-engineered and custom built.
· Over 400 major installations at thermal and nuclear power stations, fertilizer factories, refineries, petrochemical and other industries.
· Over US$30 million worth projects in India on global tender basis and many projects abroad.
· Exports of equipment, ion exchange resins, membranes and water treatment chemicals to Japan, South East Asia, USA, Europe, Africa, Egypt, Middle East, Russia, Bangladesh, Nepal.
Water Treatment Plant(WTP) orWater Treatment Works
A water treatment plant(WTP) orwater treatment worksis an industrial structure designed to removebiologicalorchemical wasteproducts fromwater, thereby permitting the treated water to be used for other purposes. Functions of wastewater treatment plants include:
· Agricultural wastewater treatment– treatment and disposal of liquidanimal waste,pesticideresidues etc. fromagriculture.
· Sewage treatment– treatment and disposal ofhuman waste, and otherhousehold wasteliquid fromtoilets,baths,showers,kitchens, andsinks.
· Industrial wastewater treatment– the treatment of wet wastes frommanufacturingindustry and commerce includingmining,quarryingandheavy industries.
Detailed Report of the Project/Work Carried Out In the Industry
FLOW TRANSMITTER
Flow can be measured in a variety of ways.
Variable Area Meter
Thevariable area (VA) meter, also commonly called aRota meter, consists of a tapered tube, typically made of glass, with a float inside that is pushed up by fluid flow and pulled down by gravity. As flow rate increases, greater viscous and pressure forces on the float cause it to rise until it becomes stationary at a location in the tube that is wide enough for the forces to balance. Floats are made in many different shapes, with spheres and spherical ellipses being the most common. Some are designed to spin visibly in the fluid stream to aid the user in determining whether the float is stuck or not. Rota meters are available for a wide range of liquids but are most commonly used with water or air. They can be made to reliably measure flow down to 1% accuracy.
Electromagnetic Flow Meters
Working principal of flow meter
The principle of operation for the magnetic flowmeter is based on the Faraday’s Law of Electromagnetic Induction.
An electrical current (I) is applied to a coil package inside the flowmeter. As a result, a magnetic field (B) is created across the metering pipe.
When a conductive liquid flows through the magnetic field, a small voltage (u) is induced. This voltage is proportional to the velocity of the flow and is accurately measured by two stainless steel electrodes mounted opposite each other inside the metering pipe. The two electrodes are connected to an advanced electronic input circuitry which processes the signal and in turn feeds it to the microprocessor inside the electronics module. The microprocessor then calculates the volumetric flow and controls the various outputs on the terminal board
TEMPERATURE TRANSMITTER
Resistance Temperature Detectors:
Resistance temperature detectors, popularly known asRTDs, are one of the conventional types of temperature sensors. Their working is based upon the “physical principle of the positive temperature coefficient of electrical resistance of metals, which means that as the temperature of a material increases, its electrical resistance will also increase in the direct proportion. In other words, RTDs have a property according to which their electrical resistance varies as a function of temperature.
Resistance temperature detectors are basically wire wound and thin film devices. Materials used for construction of RTDs mainly include:
§ Platinum: It is the most popular material amongst all and give very accurate results
§ Nickel
§ Copper
§ Balco (nickel & iron alloy)
§ Tungsten
However, the last two materials mentioned in the above list are rarely used.
A typical RTD design is shown in the figure below:
Following are the key points associated with resistance temperature detectors:
§ RTDs are basically active devices which need an electrical signal to generate a voltage drop across the sensor. This voltage drop is then determined with the help of a calibrated read-out device.
§ Due to lead wires which are usually employed to connect the RTD to readout device, errors can take place in temperature measurement results. Particularly in remote temperature measurement locations where longer lead wires are used, chances of errors are more frequent.
§ Unlikethermocouples, resistance temperature detectors operate in quite small temperature domain. Their temperature span ranges from about -200 °C to a maximum temperature of around 650 to 700 °C.
§ Although, Copper and Nickel are the cheapest materials, they are considered unsuitable for construction of RTDs because of non-linearity problems (in case of Nickel) and wire oxidation problems (in case of Copper).
§ The most suitable material for accurate temperature measurements is considered to be Platinum, since its temperature Coefficient of Resistance is nearly linear for its pure form.
Advantages
§ RTDs prove to be most accurate temperature sensors. They provide very accurate measurements even over comparatively narrow temperature spans.
§ They also give excellent stability and repeatability. They tend to provide stable output for longer periods of time.
§ RTDs provide immunization against electrical noise.
§ RTDs are very simple to recalibrate.
Disadvantages
§ Their overall temperature range is very small.
§ Their application involves high initial cost.
§ They are not rugged enough to be used in high vibration environments.
PH TRANSMITTER
PH transmitters, commonly called analyzers, provide electrical outputs that are proportional to potential of hydrogen (pH) inputs. The pH scale is used to express the acidity or alkalinity of a solution by measuring the concentration of hydrogen ions in the solution.
The pH of a solution can change with temperature, due to the effect of temperature pH sensitive glass in contact with the solution, which develops a potential (voltage) proportional to the pH of the solution. The reference electrode is designed to maintain a constant potential at any given temperature, and serves to complete the pH measuring circuit within the solution. It provides a known reference potential for the pH electrode. The difference in the potentials of the pH and reference electrodes provides a millivolt signal proportional to pH.
Effects on the Glass PH-Electrode
A glass pH electrode consists of an inert glass tube with a pH sensitive glass tip, either hemispherical (bulb) or flat in shape, blown onto it. The tip contains a fill solution with a known pH, and it is the influence of this solution on the inside of the glass tip versus the influence of the process solution on the outside that gives rise to its millivolt potential.
· Extremely high or low temperatures can alternatively boil the fill solution or freeze it, causing the electrode tip to break or crack
Effects on Reference Electrodes
The common reference electrode used in pH measurements consists of a silver wire coated with silver chloride in a fill solution of potassium chloride. The purpose of the potassium chloride is to maintain a reproducible concentration of silver ions in the fill solution, which in turn, results in a reproducible potential (voltage) on the silver-silver chloride wire. For the reference electrode to maintain a reproducible potential, the fill solution must remain relatively uncontaminated by certain components in the process solution. At the same time, the reference electrode must be in electrical contact with the pH electrode through the process solution. A porous liquid junction of ceramic, wood, or plastic, which allows ions to pass between the fill solution and the process, typically does this. This passage of ions between the reference electrode and the process is necessary to maintain electrical contact, but also creates the potential for contamination of the reference fill solution by components in the process solution.
The mechanism of reference poisoning is a conversion of the reference from a silver-silver chloride based electrode to an electrode based on different silver compound. The ions, which typically cause this form less soluble salt with silver than does chloride. These ions include bromide, iodide, and sulfide ions. When these ions enter the fill solution, they form insoluble precipitates with the silver ions in the fill solution. But there is no initial effect on the potential of the reference, because the silver ions lost to precipitation are replenished by silver ions dissolving off the silver chloride coating of the silver wire. It is not until the silver chloride coating is completely lost that a large change in the potential (and temperature behavior) of the reference occurs. At this point, the reference electrode must be replaced. Poisoning can also occur by reducing agent (bisulfite) or complexing agents (ammonia), which reduce the concentration of silver ion in the fill solution by reducing it to silver metal or complexing it. To counter this effect, multiple junction reference electrodes are used, which consist of two or more liquid junctions and fill solutions to slow the progress of the poisoning ions. Gelling of the reference fill solution is also used to prevent the transport of poisoning ions by convection. New approach is the use of a reference with a long tortuous path to the silver-silver chloride wire, along with gelling of the fill solution.
PH Transmitters Work
The device includes a pH sensor, which uses electrodes or wires to test the solution's pH, and a controller which processes the raw signal from the pH sensor and delivers it to the transmitter. In this way, a pH transmitter is able to convert the pH of a solution into an electrical signal. A pH transmitter differs from a pH meter because it has a communication interface which can transmit data to a control system or computer.
LEVEL MEASURING TRANSMITTER
Ultrasonic Level Measurement
Ultrasonic level measurementdevices basically employ sound waves for detection of liquid level. They usually work over the frequency range between 20 kHz to 200 kHz.
In this design, the level sensor is located at the top of the tank in such a way that it sends out the sound waves in the form of bursts in downward direction to the fluid in the tank under level measurement. As soon as the directed sound waves hits the surface of the fluid, sound echoes gets reflected and returned back to the sensor. The time taken by the sound wave to return back is directly proportional to the distance between the piezoelectric sensor and the material in the tank. This time duration is measured by the sensor which is then further used to calculate the level of liquid in the tank. In general, the medium over the fluid’s surface is air. However, one can employ a blanket of nitrogen or any other vapor also.
Key features of ultrasonic level measurement devices are listed below:
§ The speed of sound waves traveling via the medium which is normally air is prone to get affected by changes in the working temperature. In order to compensate for these changes in temperature and resulting changes in sound wave speed, the level measurement system must include a temperature sensing device. This will help in correct distance calculations and hence accurate level detection results.
§ In cases where heavy foam is found on the surface of the process fluid, the use of ultrasonic level measurement techniques are usually avoided since this foam work as a sound absorbent. Consequently, the sound wave will get scattered resulting in non reception of the exact signal by the sensor. This will cause improper functioning of the measurement system.
§ Good level measurement requires that the reflected echo from the fluid surface returns back in a straight line to the sensor. Besides, it calls for proper installation of ultrasonic transmitter over the tank. The transmitter should be mounted in such a way that the inner composition of the vessel or tank doesn’t get in the way of the signal.
Advantages
§ They do not make any contact with the process fluid under level detection.
§ They consist of fixed components only hence require less maintenance
§ They are usually mounted at the top of the vessel due to which they are less likely to offer leakage problems as compared to entirely wetted means.
Disadvantages
Ultrasonic level measurement technique cannot be suitably applied in all fields
· Materials like powders etc.
· Heavy vapors
· Surface turmoil
· Foam
· Ambient noise and temperature
Radar Type Level Transmitters
Radar technologyis mainly put into use for detection of level in continuous level measurement applications. Radar level transmitters provide non contact type of level measurement in case of liquids in a metal tank.
Aradar level detectorbasically includes:
§ A transmitter with an inbuilt solid-state oscillator
§ A radar antenna
§ A receiver along with a signal processor and an operator interface
The operation of all radar level detectors involves sending microwave beams emitted by a sensor to the surface of liquid in a tank. The electromagnetic waves after hitting the fluids surface returns back to the sensor which is mounted at the top of the tank or vessel. The time taken by the signal to return back i.e.time of flight(TOF)is then determined to measure the level of fluid in the tank.
Types of Radar Level Measurement Systems
Radar level measurement technology has been primarily classified into following two systems:
1. Noninvasive or Non-contact Systems
2. Invasive or Contact Systems
Noninvasive Systems
Non-invasive systems of measurement are basically known as thethrough-air radar systems. Two types of noninvasive systems exist. One is thefrequency-modulated continuous wavei.e.FMCW technologyand the other one isPulsed radar technology.
FMCW systems
“From an electronic module on top of the tank, a sensor oscillator sends down a linear frequency sweep, at a fixed bandwidth and sweep time. The reflected radar signal is delayed in proportion to the distance to the level surface. Its frequency is different from that of the transmitted signal, and the two signals blend into a new frequency proportional to distance.” This new frequency can then be used for accurate determination of fluid level. The major benefit of employingFMCWtechnique for level measurement in a tank is that the signals transmitted are frequency modulated i.e. FM instead of amplitude modulated i.e. AM signals. Now, the major part of noise in a tank falls in the AM range which does not influence the FM signals. Hence, FMCW happens to be the only system which can be suitably used for meeting high accuracy requirements oftank gauging.
Pulsed radar systems
They are also referred to aspulsed time-of-flightsystems. Their working principle is very much likeultrasonic level transmitters. “Pulsed Wave systems emit a microwave burst towards the process material. This burst is reflected by the surface of the material and detected by the same sensor which now acts as a receiver. Level is inferred from the time of flight (transmission to reception) of the microwave signal. The power range of pulse radar systems is very less as compared to FMCW systems. Hence, their performance gets largely influenced by tank obstructions and materials having low dielectric constants and foams.
Antenna Designs
Radar antennas employed for noninvasive measurement systems are available in following two major designs:
1. Parabolic dish antenna
2. Cone antenna
The figure below shows the schematic diagram of aparabolic dish antennawhich has the tendency to transmit the signals over a larger area and thecone antennawhich usually restrict the signals in a very narrow region.
One can select among above two antenna designs depending upon the application requirements and considering various factors like tank obstructions, presence of vapors or foam, surface turbulence and other physical properties of the liquid being measured. Size of the radar antenna also matters in deciding its suitability for a particular application. If the diameter of the antenna is small, there will be higher beam divergence as well as greater risk of undesirable wave reflections from tank obstructions. However, the probability of directed wave going back to the sensor is greater in case of small antennas. Also, the alignment of sensor is not very significant in small size antennas. On the other hand antennas having larger diameters tend to produce a more focused and strong signal since they cause smaller beam divergence. Besides, they are useful in eliminating noise disturbances emerging from flat and horizontal metallic surfaces. On the negative side, large antennas are more susceptible to multiple reflections from surface turbulence, tank obstructions and sloping surfaces. In some applications, the antennas installed at the top of the tank are totally sealed and isolated for protection purpose.
Invasive Systems
The invasive method used for liquid level measurement is calledGuided-wave radari.e.GWRmethod. In this method, a cable or rod is employed which act as a wave guide and directs the microwave from the sensor to the surface of material in the tank and then straight to its bottom. “The basis for GWR istime-domain reflectometry (TDR), which has been used for years to locate breaks in long lengths of cable that are underground or in building walls. A TDR generator develops more than 200,000 pulses of electromagnetic energy that travel down the waveguide and back
The dielectric constant of the process material will cause variation in impedance and reflects the wave back to the radar. Time taken by the pulses to go down and reflect back is determined to measure level of the fluid. In this method, the degradation of the signal in use is very less since the waveguide offers extremely efficient course for signal travel. Hence, level measurement in case of materials having very low dielectric constant can be done effectively. Also in this invasive measurement method, pulses are directed via a guide; hence factors like surface turbulence, foams, vapors or tank obstructions do not influence the measurement. GWR method is capable of working with different specific gravities and material coatings. However, there is always a danger that the probe or rod used as a waveguide may get impaired by the agitator blade or corrosiveness of the fluid under measurement. A typical guided wave radar system is shown in the figure below.
Guided Wave Radar v/s Through-air Radar
To overcome the measurement problems faced by through-air radar systems, guided wave radar systems are generally employed since they offer following advantages over through-air radar systems:
§ “Guided wave radar is 20 × more efficient than through-air radar because the guide provides a more focused energy path.”
§ In GWR method, various antenna designs and configurations make it possible to determine level of fluids having dielectric constant less than 1.4.
§ Also, these systems can be mounted in both vertical and horizontal positions depending upon the application.
§ These systems offer and efficient and clear path for signal travel.
§ The performance of GWR systems is not disturbed by vapors, foams, high temperature or pressure conditions.
§ These systems can operate in vacuum too without requiring any recalibration.
§ Beam divergence issues and false echoes resulting from tank walls and obstructions are not present in these guided wave radar systems.
Advantages
§ Radar level measurement technique offer extremely accurate and reliable detection of level in storage tanks and process vessels.
§ The performance of radar level transmitters remains unaffected by heavy vapors and mostly all other physical properties of the fluid under level measurement (except dielectric constant of the liquid).
Disadvantages
§ Major disadvantage associated with radar level detectors is their high cost.
§ Besides, these systems are not capable of detecting level between interfaces.
§ Also their pressure ratings are very restricted.
§ In case of pulse radar, one usually faces problem in getting accurate measurement results if the fluid being measured is very near to the radar antenna. Since, in that case the time taken by the signal to travel between sensor and process material will be very fast i.e. not adequate for accurate determination of level.
§ These devices work well with light layer of dirt and dust only. In situations where the layer of dust or foam gets substantial, they cease to detect the fluid level. Therefore, in dirty applications the radar level detectors gets replaced by ultrasonic level detectors.
PANEL
PLC and PAC Systems panels
The control systems are built around special devices, designed to operate industrial machines, and processes. We call these devices programmable logic controllers (PLC) and programmable automation controllers (PAC).
PLCS were introduced in the early 1970s. The term “PAC”, was developed to differentiate those older systems from today’s much more powerful, and flexible devices.
PLCS were designed to control machinery where, PACS can be used for machine control, process, motion control, and other applications.
There are five basic components in a PLC system:
• The PLC Processor or controller
• I/O (Input /Output) modules
• Chassis or backplane
• Power supply
• Programming software that runs in a PC
In addition to these 5, most PLCs also have:
• A network interface
v Let’s look at each in more detail.
Processor, Controller, or CPU
CPU of PLC performs the following works:
• Stores the control program and data in its memory
• Reads the status of connected input devices
• Executes the control program
• Commands connected outputs to change state based on program execution, For example: Turn a light on, start a fan, adjust a speed, or temperature
It comes in various physical forms
I/O Modules
It provides physically connection to field devices
• Input modules convert electrical signals coming in from input field devices such as pushbuttons to electrical signals that the PLC can understand.
• Output modules take information coming from the PLC and convert it to electrical signals the output field devices can understand, such as a motor starter, or a hydraulic solenoid valve
Input Modules
· Input modules interface directly to devices such as switches and temperature sensors.
· Input modules convert many different types of electrical signals such as 120VAC, 24VDC, or 4-20mA, to signals which the controller can understand.
· Input modules convert real world voltage and currents to signals the PLC can understand. Since there are different types of input devices, there is a wide variety of input modules available, including both digital and analog modules.
Discrete V/S Analog Modules
• Discrete modules use only a single bit to represent the state of the device. For example, a switch is either open or closed. Therefore, the bit is either a 0 (switch is open) or a 1 (switch is closed). Discrete modules are also known as Digital modules.
• Analog modules use words to represent the state of a device. An analog signal represents a value. For example, the temperature could be 5, 9, 20, 100, etc degrees. Analog modules use a value, such as 52, rather than a 0 or 1 to represent the state of the device.
Discrete Modules
· Devices that are either on or off, such as a pushbutton, get wired to discrete modules. Discrete modules come in a variety of types, such as 24VDC or 120VAC.
· Since it takes only 1 bit to represent the state of a device, a 16 point discrete module only requires 16 bits of memory in the controller to store the states of all the points on the module.
Analog Modules
· Devices that have a number associated with them, such as a temperature sensor, get wired to analog modules. Analog modules come in a variety of types, such as 4 to 20 mA or 0 to 10 VDC. You can buy analog modules that allow you to connect anywhere from 2 to 16 devices.
· Since it takes 1 word to represent a number, a 16 point analog module requires 16 words of memory in the controller to store the value of all the numbers on the module. Each word in a PLC takes 16 or 32 bits (depending on the PLC), therefore it takes 16 or 32 times the amount of PLC memory to store analog points vs. digital points.
Output Modules
· Output modules interface directly to devices such as motor starters and lights
· Output modules take digital signals from the PLC and convert them to electrical signals such as 24VDC and 4 mA that field devices can understand
Output modules take a signal from a PLC and convert it to a signal that a field device needs to operate. Since there are different types of output devices, there is a wide variety of output cards available, including both digital and analog cards.
Chassis/Backplane
All PLCs need some method of communicating between the controller, I/O and communications modules. Here are three ways used to accomplish this communications between the various components that make up the PLC system. Modules are installed in the same chassis as the PLC and Communicate over the chassis backplane
• Modules are designed to “plug” into each other. The interconnecting plugs form a backplane. There is no chassis
• Modules are built into the PLC. The modules come together in one physical block. The backplane in this case is transparent to the user.
Below is an example of a backplane in a chassis based system. You can see the backplane in the area where the modules are not inserted. The modules have connectors that plug into the black connectors on the backplane. All of the connectors on the backplane are connected together electrically.
Great flexibility in choice of modules.
• Modules can be easily installed or removed without affecting other modules
• Great flexibility in choice of modules. In some cases modules cannot be removed without “breaking the chain” and affecting all modules downstream.
• Low cost solution but limited flexibility. Generally used in smaller, simpler systems.
Programming Software
Software that runs on a PC is required to configure and program PLCs.
• Different products may require different programming software
• Software allows programs to be written in several different languages
Network Interface
Most PLCs have the ability to communicate with other devices. These devices include computers running programming software, or collecting data about the manufacturing process, a terminal that lets an operator enter commands into the PLC, or I/O that is located in a remote location from the PLC. The PLC will communicate to the other devices through a network interface.
Power Supply
A power supply is needed to provide power to the PLC. Power supplies come in various forms:
• Power supply modules that fit into one of the slots in a chassis
• External power supplies that mount to the outside of a chassis
• Stand alone power supplies that connect to the PLC or I/O through a power cable
• Embedded power supplies that come as part of the PLC block.
The PLC system is the center of a control system, but it is not the entire control system. There are several other key pieces that must be added to a PLC system to make a complete control system. Examples are:
• Operator terminals
• Networks
• Distributed I/O devices (I/O that is in a different location then the PLC)
Variable Frequency Drive (VFD) Panel
Variable frequency drive (VFD) usage has increased dramatically in HVAC applications. The VFDs are now commonly applied to air handlers, pumps, chillers and tower fans. A better understanding of VFDs will lead to improved application and selection of both equipment and HVAC systems.
Common VFD Terms
There are several terms used to describe devices that control speed. While the acronyms are often used interchangeably, the terms have different meanings.
Variable Frequency Drive (VFD)
This device uses power electronics to vary the frequency of input power to the motor, thereby controlling motor speed.
Variable Speed Drive (VSD)
This more generic term applies to devices that control the speed of either the motor or the equipment driven by the motor (fan, pump, compressor, etc.). This device can be either electronic or mechanical.
Adjustable Speed Drive (ASD)
Again, a more generic term applying to both mechanical and electrical means of controlling speed.