INSTRUMENTATION IN PROCESS PLANTS Instrumentation and process control systems plays a vital role in monitoring and controlling critical parameters for safe and efficient operation of plants part icularly in Powerplant industries. In Rain CII the different process parameters involved in calcination&powerplants are Temperature, Pressure, Flow, Level, Vibr ation, Speed, pH and conductivity. The different sensors and transmitters measur e all these parameters. Some of the parameters are used for indication only and some are used for indication and controlling purpose. PRESSURE The pressure sensors using in Calcination&Powerplants are manometers, pressure g auges and pressure transmitters. The pressure gauges may Borden tube type (for medium pressure), Bellow type (low pressure) or Diaphragm type (from few mmWC to several atm). All these gauges ar e used only for local indication. The pressure transmitters are used for indication and control purpose. All trans mitters works on the principle that the change in the capacitance due to change in area between a fixed electrode and two diaphragms causes current which in pro portional to the pressure of the system under test. Units Conversions : Kg/cm2, bar, mmWC, mm HG, psi, or Pascal. : 1Kg/cm2 = 10000mmWC. = (10000/13.6)mmHG = 15psi. = 100kpa. Pressure fundamentals: Pressure is a force applied to or distributed over a surface. The pressure(P)of a force(F)distributed over an area(A) is defined as: P=F/A Consider the following arrangement whereby multiples of equal weights compress a volume of air with in a cylindrical container. Not only weights exert a force. a column of liquid or gas stacks up and produces a down ward push. The height of the stack likewise represents the strenght of the downward force and is called the head pressure.the units of head are normally len gth but represent a force applied over a unit area.Traditionally, the downward p ush of this column of water was expressed as: 5 inches water gauge(or)water column Abbreviation-5 W.G. or 5W.C. Manometers: 1.the U-tube manometer is the eldest to manufacture and most widely used type. Measurements are taken from the topmost point of the curved surface(meniscus) of Hg and the lowest point of H20. 2.The well manometer amplifies the smaller level movement in the larger reservoi r by using a narrower scaled tube. This increases sensitivity of measurement in the ratio of the areas of the tubes. Using manometers to measure differential pressure: Differential head type flowmeters are the most economical of all the flow-rate d evices.They perform well with both liquids and gassed great deal of data and exp erience are available to support their position. Then major limitations are diff iculty in reading low flow rates,a suare-root relationship in read out, and mobi lity to cope with certain types of fluids(e.g:slurries) Some of these difficulties can be evercome by other types of flowmeters,such as the magnetic flowmeters. as the pie are shows,the effect of the measured pressur e is to increase the height of a column of material above its equilibrium state.

The difference in pressure between the process and reference is proportional to the height of the fluid supported. At the new equilibrium state: Pressure at A = Pressure at B High pressure + (h1+h)=low pressure (h1-h)d1+2hd High pressure-low pressure (h1-h)d1+2hd-(h1+h)d1 Differential Pressure=2hd-2hd1 Note: d is fill fluid; d1 is process fluid DIFFERENTIAL PRESSURE = 2h(d-d1) The important point to note is that the differential pressure is not only rel ated to the height difference between the columns (2h) but also the difference i n densities between the fill and process fluids (d-d1). If this letter point is not taken into account, significant errors can arise. Manometer measurements are reliant upon the weight of the fill fluid and as such are gravity dependent. Corrections for local gravity can be important. Glossary of Measurable Pressure Absolute Pressure: Measured above total vacum or zero absolute. Zero absolute re presents total lack of pressure. Atmospheric Pressure: The pressure exerted by the earths atmosphere. Atmospheric pressure at sea level is 14.696psia. The value of atmospheric pressure decreases with increasing altitude. Barometric Pressure: Same as atmospheric pressure. Differential Pressure: The difference in magnitude between some pressure value a nd same reference pressure. In a sense, absolute pressure could be considered as a differential pressure with total vacuum or Zero absolute as the reference. Li kewise, gauge pressure (defined below) could be considered similarly with atmosp heric pressure as the reference. Gauge Pressure: The pressure above atmospheric. Represents positive difference b etween measured pressure and existing atmospheric pressure. Can be converted to absolute by adding actual atmospheric pressure value. Hydrostatic Pressure: The pressure below a liquid surface exerted by the liquid above. Line Pressure: Force per unit area exerted on the surface of the pipe by a fluid Flowing parallel to a pipe wall. Static Pressure: Same as line pressure. Vacuum: Pressure below atmospheric. Working Pressure: Same as line pressure. Dynamic Pressure: Pressure exerted by a flowing material parallel to the directi on of such flow. Compound Pressure: A measurement from a base reference points that is neither th e atmosphere nor total vacuum.

General principles of Measurement The measurement of pressure is considered the basic process variable in that it is utilised for measurement of flow (difference of the pressure). Level (head or back pressure) and even temperature (fluid pressure in a filled thermal system) . All pressure measurement systems consist of two basic parts: a primary element , which is in contact, directly or indirectly, with the pressure medium and inte racts with pressure changes: and a secondary element, which translates this inte raction into appropriate values for use in indication, recording and /or control ling. Secondary elements A) Mechanical Transduces The most useful application of this principal are: 1) Bellows

A metallic bellows is a series of circular parts so formed of joined that they c an be expanded axially by pressure. To the extent it is desirable to limit their travel a range spring is employed so that the bellows work against it. The prac tical limitations of material selection usually limit the bellows to measurement s from. 5 to 70 psi. By increasing the diameter of the bellows force, pressure a s low as 06 psi (400pa) can be measured. 2) Bourbon Tubes

The original patent (1852, France) described it as a curved or twisted tubes who se cress section bent circular. The application of internal pressure causes the tube to unwind, or straighten out. The movement of the free end is transmitted t o a pointer or other indicating element. Phosphor Bronze, beryllium copper, stee l, chrome alloy and stainless steels are commonly used. Indeed, they are the most widely used types of pressure gauge. The pressure gauges can be filled with oil to limit the damage causes by vibrati on.

3).Metallic Diaphragms Gauge employing diaphragms give better and more positive indication that the Bou rbon types of gauge for low pressure range (below 15 psi). The principle employed simply requires that the deformed middle section of the d iaphragm push against and deference pointer on a scale. The aneroid barometer is an example of just such a system.

4).Force Balance Force balance pressure transmitters are closed loop feedback device in a force b alance ATM pressure displaces an element. The amount of displacement is detected and the element is returned to a Null or zero displacement position by a restor ing force, which can be pneumatic. Force balance type transmitters have been around for a long time and are fam

iliar to many users. They are rugged and work well with high pressure. But, they are big and can be sensitive to vibration and temperature. In the situation above, a force-balance principle is employed to generate a pneuma tic signal proportional to the diaphragm deformation. As the force bar is deflected towards the nozzle, back pressure in the nozzle is communicated to the output signal and the feedback bellows. These bellows bring the force bar to a new equilibrium position. B) Electronic Transducers The common pressure measurement techniques are strain gauge, force balance, vari able reluctance, capacitance, vibration wire, and solid state. Stain Gauge: Stain Gauge exhibits a change in electrical resistance that is prop ortional to a deformation that occurs when they are stretched. Thus, strain gaug e elements can be used to convert mechanical displacement caused by pressure int o an electronic signal, strain gauge pressure sensors are classified by the mate rial used for the strain gauge element and the method used to mount it to a mech anical element (diaphragm or beam) that will be deformed under pressure. In most instances, variable resistive stain gauge elements are configured into a wheats tone bridge. The circuit will also include other resistors to provide adjustment capability and temperature compensation. A strain gauge is accurate but not linear. They are inherently temperature sensi tive and required compensation. In addition, some mechanical method must be incl uded in the over all sensing element to provide overpressure protection. Accuracy of strain gauge based transmitters can vary from 0.1% to 1.0%fs, depend ing upon the amount of temperature compensation and other circuitry built into t hem. Obviously, then, price is a function of accuracy. Variable reluctance: Variable reluctance transmitters operate on the principle o f a moveable element changing position within a magnetic field. As a result, ind uctance changes to produce an output voltage that is proportional to the pressur e applied to the movable element. The transmitters are small and accurate, but t hey have complicated circuitry and mechanical overpressure protection is require d. Variable capacitance: Variable capacitance transmitters operate by having one pl ate of a capacitor moved when a pressure is applied. The movement changes the ca pacitance signal in proportion to the applied pressure. Capacitance based transm itters are accurate and small in size and weight. They are simple reliable and r emain stable over a wide temperature range. These are still the most widely used method of measuring differential pressure. The important member of the variable capacitance family is the differential capa citance transducer shown below. Different pressure applied to the external diaphragms compress silicon oil along ceramic channels, which in turn deform the capacitor plates (up to 1mm maximum) differently relative to the sensing diaphragm. The error inherent in the separa te capacitance measurement are negated when the difference is taken electronical ly. The rigid insulation is glass. The potential damage to external diaphragms due to overpressure is significant r educed by the moulded face of the sensor body. The diaphragm is simply pushed ba ck into this moulding and its own shape thereby reinforced.

Vibrating wire: Vibrating wire devices rely on an applied pressure to change the frequency of a vibration wire. The change in frequency is proportional to the a pplied pressure. Transmitters using this measurement method are very accurate, b ut the sensor tends to be complicated and its operation pressure range is limite d. Solid state: Solid state pressure sensors are usually made of a single silicon c rystal and measure a change in resistance or capacitance a pressure is applied. As pressure is applied, the diaphragm distorts Capacitive sensors detect the dis tortion directly and resistive sensor detect the resulting strain in the diaphra gm. Resistive sensors typically have four resistors in the diaphragm, connected as a whetstone bridge. The resistors are formed by diffusion or ion implantation inside the silicon, or deposited in a thin film on top of the silicon. Single crystal silicon is an excellent material for sensor because it exhibits a lmost no hysteresis and its electrical properties can be controlled with semicon ductor processing. ADVANTAGES/DISADVANTAGES OR PRESSURE SENSING METHODS Technique Stain Gauge ure Sensitive ressure Accurate Force Balance ive Familiar Safe in hazardous areas Large Complex Temperature Sens itive Variable Reluctance Differential Capacitance Sensitive Small Accurate Small Vary Rugged Accurate Simple Sensor Vibrating Wire Range Vibration Sensit ive Considerations for Mounting Transmitters Accurate Complex Limited Pressure Complex Static Pressure Vibration Sensit Advantages Simple Circuitry Small Disadvantages Temperat Mechanical Overp

Pressure tapin

gs

Differential pre ssure tapings The following points may prove useful in ensuring the best possible conditions f or accurate and low maintenance operation. Keep corrosive or hot process material away from the transmitter. Avoid sediment deposit in the impulse piping. Balance the liquid head on both legs of the impulse piping. Keep impulse piping as short as possible. Avoid ambient temperature gradients and fluctuations.

For liquid flow measurement, tap the side of the line to avoid sediment deposits . Mount the transmitter beside or below the taps so gases will vent into the pro cess line. Taps should be made to the side of the line for transmitters having side vent/dr ains. For liquid service, the side vent/drain should be mounted upward to allow venting of gases. For gas service, it should be mounted down to allow draining o f any accumulated liquid. Slope piping at least 3cm in 30cm up toward the process connection for l iquid and steam service. Slope piping at least 3cm in 30cm down towards the process connections for gas s ervice. Avoid high points in liquid lines and low points in gas lines. Keep both impulse legs at the same temperature. Use impulse piping of sufficient diameter to avoid friction effects. Vent gas from liquid piping legs.

Fill both piping legs to the same level when using sealing fluid, Avoid purging through the transmitter. Make the purge connection close t o the process taps and purge through equal lengths or the same size pipe.

Calibration of Smart Pressure Transmitter Before Calibration : Clean the Transmitter properly Note down the Calibration Range of the Transmitter Form History Card. Pressure Source Selection :

tor. essure r.

If Pressure is less than or equal to 1 Kg/cm2 use Manometer or Pressure Calibra If Pressure is Greater than 1 Kg/cm2 and Less Than or equal to 20 Kg/cm2 use Pr Calibrator or Dead Weight Tester or Comparison Tester If Pressure is Greater Than 20 Kg/cm2 Use Dead weight Tester or Comparison Teste

Calibration method :

Keep The Transmitter vertically then Connect 24 volts DC power supply ( alon g with 250 Ohms Resistor ) and SFC to the pressure transmitter as per the following circuit diagram. 250Ohms + +

_

_

Connect the transmitter Pressure Tapping to the Pressure Source, with proper fittings and tighten it fully. Switch On the 24 v DC power supply and SFC.

Apply required pressures to the transmitter (with out any leaks) as mentioned in the Calibration Report and note down the corresponding % out put Readings of SFC in Before calibration column of Calibration report. Open the relief valve of Pressure source and allow it to stabilize. Then check whether SFC reads zero % out put. If necessary correct LRV with the help of SFC ( Press LRV then Correct Then Enter ). Apply required pressure to the transmitter for Span calibration and stabili ze the applied pressure. Then check whether the SFC reads 100% out put. If necessary correct URV with the help of SFC ( Press URV then Correct Then Enter ). Repeat instructions 2.5 to 2.7 One or Two times for fine calibration.

After Zero and Span calibration, check for linearity by applying different pre ssures as mentioned in the Calibration Report and Note down the corresponding r eadings in the after Calibration Column.

Calibration set up for Analog pressureTransmitter Before Calibration : Clean the Transmitter properly Note down the Calibration Range of the Transmitter Form History Card. Calibration method : Keep The Transmitter vertically then Connect 24volts DC power supply and Mi lliammeter to the pressure transmitter as per the following circuit diagram. Connect the transmitter High Pressure Tapping to the Manometer / Pressure calib rator as per requirement, with proper fittings and tighten it fully . Switch On the 24 V DC Power Supply and Multimeter.

Apply required different pressures to the transmitter ( with out any leaks ) as mentioned in the Calibration Report and note down the corresponding Milli amps o ut put Readings in Before Calibration column of Calibration Report. Open the relief valve of pressure calibrator / Manometer and allow it to stabil ize. Then check whether the Milliammeter reads 4mA DC. If necessary adjust it for 4 ma. Apply require pressure to the transmitter HP side for Span calibration and s tabilize the applied pressure. Then check whether the milli ammeter reads 20mA D C. If necessary adjust it for 20 ma. Repeat instructions 2.5 to 2.6 One or Two times for Fine Calibration.

After Zero and Span calibration, check for linearity by applying different pre ssures as mentioned in the Calibration Report and Note down the corresponding r eadings in the after Calibration Column. .

TEMPERATRE Temperature is a very important parameter in process industry. The tempe rature sensors used in Calcination&Powerplants are Thermocouples, RTDs and Tempe rature gauges. Thermocouples are the temperature sensors works on the principle of See b ack effect. There are different types of thermocouples such as J, K, R, S, E type thermocouples to measure the temperature. But in Ammonia & Urea plants only K typ e and R type thermocouples are under use. K type thermocouple is used in both plants . R type thermocouple is used in Primary reformer of Ammonia plant where the tempe rature to be measure in around 745Deg. C. K type thermocouple can be used to measu re 0 1200 Deg. C range of temperature and the metals used are Chromel (+), and A lumel (-) R Type thermocouple can be used to measure 0-1482 Deg.C range of tempera ture and the metals (or materials of construction) used ate plat. 13% Rhodium (+ ) and Platinum (-). All these thermocouples are having two wires and can be used for both indication and control purpose. Thermocouples are used for high temper

ature and are measured in mV. RTDs (Resistance Temperature Detectors) are the temperature sensors, whi ch works on the principle that when there is a change in the temperature of a su bstance the resistance of the substance wills also changes. RTDs are used for in dication and control purpose. All the RTDs are having there lead wires and are u sed in both the plants. RTDs are used for low temperature measurements and are m easured in Ohms. All the temperature gauges are of bimetallic type (helical type). These type gauges works on principle of coefficient thermal expansion. These temperatu re gauges are used only for local indication. Units of temperature: Deg. C or Deg. F. CONVERTION FORMULAS: C = 5/9 (F - 32) F = 9/5 (C)+32 K = 273 +C R = 460 +F BIMETALLIC THERMOMETERS: The bimetallic thermometer is based on two simple principles. Fi rst that metals change in volumes in response to a change in temperature and, se condly, the coefficient of change is different for all metals. If two dissimilar metal strips are bonded together and then heated the resultant strip will tend to bend in the direction of metal with the lower coefficient of expansion. The d egree of deflection is proportional to the change in temperature. Since the amount of movement is typically rather small it is amp lified by using a long strip of material would into a helix or a spiral. One end of spiral is immersed in the medium to be measured and the other end is attache d to a pointer. The bimetallic thermometer may be rugged enough to actuate a rec order pen. The bimetallic thermometer offers the advantage of being much more re sistant to breakage than the glass thermometer. It is however, subject to change in calibration if handled roughly and the overall accuracy is not as good as th e glass thermometer. FILLED THERMAL ELEMENTS: The filled thermal element consists of a bulb connected to a sma ll-bore capillary, which is connected to an appropriate indicating device. The s ystem acts as a transducer that converts pressure at nearly constant volume to a mechanical movement, which in turn is converted to temperature by use of approp riate indicating scale. The entire mechanism is gas tight and filled with gas or liquid under pressure The fluid or gas inside the device expands and contracts with a change in temperature causing a spiral bourdon gauge to move. The response time and accuracy provided by thermal element are sufficient for many industrial-moni toring applications. Since the unit is self-contained and needs low power it is naturally explosion proof. On the down side the bulbs are usually much larger th en of a thermocouple or RTD. Also repair must typically be done at the manufactu rers facility. Thermocouple:

A Thermocouple is a thermoelectric temperature-measuring device. Welding, solder ing or merely pressing two dissimilar metals together in series to produce a the rmal electromotive force (E) forms it. When the junctions are at different tempe ratures. The measuring, or hot, junction is inserted into the medium where the t emperature is to be measured. The reference, or cold, junction is the open end t hat is the open end that is normally connected to the measuring instruments termi nals. The magnitude of this voltage (E) depends on the pair of materials A+B, and diff erence between the hot and cold junctions. T1 and T2. There fore, temperature ca n be read directly by using a sensitive calibrated electromotive force (EMF) dev ice.

Advantages: Moderate accuracy. Widest range (0-2000F). Rugged Remote and versatile mounting Moderately stable Moderate cost Disadvantages: Low output signal Calibration changed by contamination Electrical interference can be a problem Calibration is nonlinear over normal spans Higher installation costs(extension wires) RESISTANCE TEMPERATURE DETECTOR: RTD Types: Most RTDs fall into one of two types: immersion or surface mounted. In each case the element and its enclosure are designed for specific measurement applications and conditions. Immersion RTDs As the name suggest, immersion RTDs are meant to allow a sensing element to be i mmersed in a media to measure its temperature Various treaded to flange-mounted fittings are available to support such installation. The primary components of a n immersion RTDs are: Sensing element Protective sheath or shield Threaded and/or flange mount Housing(or head) Electrical connector Immersion Lengths: Many sensing elements require at least 4 cm of immersion in the fluid being meas ured to obtain minimal measurement error. The maximum immersion length can be al most any value nowever as the length increases the vibration and flow rate capab ilities of the sensor decreases. The diagram indicated the way in which immersio n length is measured. Almost any immersion length is possible lengths are common ly specified in 1cm increments.

Surface mounted RTDs:

In a number of applications, surface mounting of the sensing devices is the most efficient and/or convenient installation method. Be aware that for surface meas urement, conduction such as sensor insulation and lead wire conduction should be investigated to ensure an accurate measurement. Surface measurement is only as stable as the temperature at the surface. Variable such as weather the surface is insulated or uninsulated, can also affe ct temperature measurements. In general, the goal is to maximize heat conduction to the sensing element from the measured surface and to minimize conduction and convection of heat to the element from other sources. Advantages High accuracy, greatest over wide span. Relatively narrow spans, (10F) can be measured. Reproducibility not affected by temperature change. Short-term reproducibility is better than that of thermocouples. Compensation not necessary. Handle suppressed ranges. Relatively small sizes. Disadvantages More expensive. Limited above 1500F. Less rugged. Self-heating may be a problem. Vibration can affect wire wound types. Radiation pyrometer: Radiation pyrometers inter temperature by collecting the thermal radiati on from an object and focusing it on a sensor. The sensor or detector is typical ly a photon detector. which produces an output as the radiant energy striking it release electrical charges. The advantage of the radiation pyrometer method is that they produce a stable no n contact output signal. This is of particular usefulness when working with very high process temperatures where conventional sensing elements would have very s hort life spans. They are also useful in applications where the temperature of a continuously moving sheet of material must be monitored. Radiation pyrometers c an be very susceptible to ambient temperature fluctuations and often require spe cial installation or water cooling to maintain a constant ambient. Calibration of Resistance / ma transmitter (PT-100, RTD)

Type of equipment: Two wire analog Temperature transmitter RTD input. Before Calibration : Clean the Transmitter properly Note down the Range of the Transmitter from History card. :

Calibration Procedure

Connect 24volts DC power supply, Millimeter and Resistance Source to the Trans mitter as per the following circuit diagram. Switch on the 24v supply. Apply Resistance ( As Per Standard Temperature Chart ) corresponding to differe nt Temperatures as per requirement in Calibration Report and note down the corre sponding out put ma readings in the Before Calibration column of the Calibration S heet

I/p + Rh supply O/p Ma + + Ohms 24V DC

Apply Resistance Corresponding to 0C and Check for 4 ma output in the Millimeter display. If necessary adjust zero potentiometer.

Apply Resistance Corresponding to span range and Check for 20 ma output in the Millimeter. If necessary adjust span potentiometer. Repeat the Steps 2.2 to 2.3 One or Two for Fine Calibration.

As per Calibration Chart requirement Apply Resistance corresponding to different Temperatures and Note down the Corresponding Millimeter readings in After Calib ration column of the Calibration Report. Calibration for RTD (PT-100) Smart Temperature Transmitter (Make: Rosemount) Calibration Method: Connect 24volts DC power supply, Decade resistance box and HART Communicator to the transmitter as per the following circuit diagram. For three wire RTDs, short terminals 2 and 3. + + Ohms 24V DC supply ou tput Resistance ma

250 ohm

Switch-on the power supply and HART Communicator. Feed 100 ohms Resistance to the transmitter by Decade Resistance Box and check H ART Communicator reads 4mA output. . If not Trim the transmitter by using HART C ommunicator as below mentioned.

Select Diagnostics and Service mode Then Select Calibration option Then Select Sensor Trim Then Select Lower Sensor Trim and Press Enter Key.

Span Calibration: Apply Corresponding Resistance of Upper Range Value Temperature of the transmitt er for Span calibration with the help of Decade Resistance Box. the Then check whether the HART Communicator reads 20 milli Amps output. If not Trim transmitter by using HART Communicator as below mentioned Select Diagnostics and Service mode Then Select Calibration option Then Select Sensor Trim Then Select Upper Sensor Trim and Press Enter Key.

After fine calibration, check for linearity by applying different Resistance val ues with the help of Decade Resistance Box and note the error if any. Repeat instructions as above for the fine calibration and note the error if any. Calibration for mV / ma transmitter ( Thermocouple Input )

Type of equipment: Two wire analog Temperature transmitter thermocouple input. Before Calibration : Clean the Transmitter properly Note down the Type of the Thermocouple and Range of the Transmitter tory Card. Calibration Procedure : from His

Connect 24volts DC power supply, Millimeter and Millville source to the conve rter as per the following circuit diagram.

+ + mV source supply + mV ma

+ 24V DC

- Ma

Apply Milli volts ( As Per Standard Temperature Chart ) corresponding to differ ent Temperatures as per requirement in Calibration Report and note down the corr esponding out put ma readings in the Before Calibration column of the Calibration Sheet. Apply Milli volts Corresponding to 0C and Check for 4 ma output in the Millimete r display. If necessary adjust zero potentiometer. Apply the Milli volt Corresponding to span range and Check for 20 ma output in the Millimeter. If necessary adjust span potentiometer. Repeat the Steps 2.2 to 2.3 One or Two for Fine Calibration.

As per Calibration Chart requirement Apply Millie volts corresponding to differe nt Temperatures and Note down the Corresponding Millimeter readings in After Ca libration column of the Calibration Report. FLOW: Measuring fluid flow is one of the most important aspects of process control. In fact,it may well be the most frequently measured process variable. Flow is generally measured inferentially by measuring velocity through a known a rea. with this indirect method, the flow measured is the volume flow rate, Qv .s tated in its simplest terms: Qv = A V In this equation, A is the cross sectional area of the pipe and V is the fluid v elocity. A reliable flow indication is dependent upon the correct measurement of A and V. if for example, air bubbles are present in the fluid, the area term A of the equa tion would be artificially high. Likewise, if the velocity is measured as a poin t velocity at the center of the pipe, and it is used as the velocity term V of the equation, a greater Qv than actual would be calculated because V must reflect t he average velocity of the flow as it passes a cross section of the pipe. The different flow sensors used in Calcination & Powerplants are i) Flow transmitters using Orifice plates. ii) Magnetic Flow meter (KHRONE) which works on the principle of Faradays law of electromagnetic induction; is using in Urea plant. iii) Turbine flow meter (Bop & Reuther) is using in Urea plant. iv) Rotameters used in both the plants (Only one Rotameter is using in Ammon ia plant). v) Annubar is using in Ammonia plant. vi) Pitot Tube vii) Ultrasonic Flow meter All the above flow sensors are used for indication and control purpose. Unites cu m/Lr., Lrs/m in., mm WC, Gallon/m in, M3/hr. Differential pressure flowmeters: Head meters are most common type of meter used to measure fluid flow rates. They measure fluid flow indirectly by creating and measuring a differential pressure by means of an obstruction to the fluid flow. Using well-established conversion coefficients which depend on the type of head meter used and the diameter of th e pipe, a measurement of the differential pressure may be translated in to a vol ume rate. Orifice plates: A concentric, sharp-edged orifice plate is the simplest and least expensive of t he head meters. acting as a primary device, the orifice plate constricts the flo

w of a fluid to produce a differential pressure across the plate. The result is a high pressure upstream and a low pressure down stream that is proportional to the square of the flow velocity. An orifice plate usually produces a greater ove rall pressure loss than other primary devices. A practical advantage of this dev ice is that cost does not increase significantly with pipe size. the four types of orifice plates are shown below. Flow nozzle: Flow nozzles may be thought of as a variation on the venturi tube. The nozzle op ening is an elliptical restriction in the flow but with no outlet area for press ure recovery. pressure taps are located approximately pipe diameter downstream a nd 1pipe diameter upstream. The flow nozzle is a high velocity flowmeter used wh ere turbulence is high such as in steam flow at high temperatures. the pressure drop of a flow nozzle falls between that of the venturi tube and the orifice pla te (30% to 95%).

Pitot tubes: In general a pitot tube for indicating flow consists of two hollow tubes that se nse the pressure at different places within the pipe. These tubes can be mounted separately in the pipe or installed together in one casing as a single device. One tube measures the stagnation or impact pressure at a point in the flow. The other tube measures only the static pressure, usually at the wall of the pipe. T he differential pressure sensed through the Pitot tube is proportional to the sq uare of the velocity. Installing Pitot tubes involves determining the location o f maximum velocity with pipe traverses. Though a Pitot tube may be calibrated to measure fluid flow to 1/2%, changing velocity profiles may cause significant er rors. This is one reason Pitot tubes are primarily used to measured gases since the change in the flow velocity from average to centre is not a serious draw bac k. Pitot tubes have found limited applications in industrial markets because the y can easily become plugged with foreign material in the fluid. Their accuracy i s dependent on the velocity profile and they develop a very low differential pre ssure, which is difficult to measure. Annubar: The annubars principle of operation is similar to that of a standard Pitot tube w ithout the inaccuracy of single-point or the requirement of traversing and avera ging. The Annubar averages the flow via multiple upstream and downstream sensor ports and provides a differential pressure proportional to the flow rate. The sensor is a multiple tube, rigid structure that provides dual-averaging cham bers with a diamond-shaped cross section. The diamond shape establishes a fixed separation point of the fluid from the sen sor. This eliminates any shift in the low-pressure signal that would cause a cor responding loss of flow measurement accuracy. An Annubar can provide accurate measurement within 1% in all sizes. It will maintain its accuracy over an extremely long period of time. The diamond shaped flow coefficient remains stable over the long term and is unaffected by wear, dirt or grease build up.

Advantages/disadvantages of differential pressure flowmeters Advantages: Low cost Easily installed and/or replaced

No moving parts Suitable for most gases and liquids Available in a wide range of sizes and models Limitations: Square root head/flow relation ship High permanent pressure losses Low accuracy Flow range limited to 4:1 Accuracy affected by wear and/or damage of the flow primary element with corrosi ve fluids Variable area flowmeter: Variable area flowmeters (Rota meters) are typically made from a tapered glass t ube that is positioned vertically in the fluid flow. A float that is the same si ze as the base of the glass tube rides upward in relation to the amount of flow. Because the tube is larger in diameter at the top of glass than at the bottom. The float resides at the point where the differential pressure between the uppe r and lower surfaces balances the weight of the float. In most Rotameters applic ation, the flow rate is read directly from a scale inscribed on the glass; in so me cases an automatic sensing device is used to sense the level of the float and trasmit a flow signal. These these transmitting rotameters are often made from st ainless steel or other materials for various fluid applications and higher press ures.

LEVEL The following are the devices used to measure the level in both the Calc ination&Power plants. i) D. P. Transmitter ii) Level controller is used for indication and control purpose iii) Hydrostep which is based on the resistivity of the two substances (water and steam) that can be used for local indication only. This is used in Ammonia plant. iv) Capacitive type v) Radioactive type vi) Purge type vii) 3-Element Controller (Boiler Level Controller) Level gauges used only for local indication. Unit : % MESUREMENTS OF LEVEL: DIRECT METHODS Sight Glass The steam boilers and similar applications, a simple device for enabling th e level with in the boiler to be determined is the sight glass. It consists of a tube of toughened glass connected at both ends through asbestos packed unions a nd valves into the boiler, in which the water level is required. If the diameter of the bore of the tube is not small enough to introduced errors due to capalir ity the liquid will stand at the same level in the boiler and tube. The two valv es are provided so the steam may be shut of in case of breakage of the sight gla ss. The smaller valve at the bottom is provided for blowing out the gauge for cl eaning purposes.

FLOAT ACTUATED MECHANISMS The following diagrams illustrate different float types and indicators. Float operated gauge level indicator indicated liquid level in cone or flat roof UN-pressurized tanks. Recommended for use on tanks storing water, flue water, c hemicals other liquid products where operations do not require extreme accuracy cable pipe entry should be near an existing roof man hole or an inspection cover . The measurement of liquid level of medium and high pressure storage vessels presence unique problems which are not encounter with standard atmospheric or l ow pressure vessels. Butane and propane, for e.g., must be stored under pressure to comprise them into there liquid state. The indicating gauge shown here uses perforated tape. As long s tension is maintained, accuracys of 3mm over full range can be achieved, Cam operated limit switches can be incorporated too.

Capacitive Probes A Capacitive probe works in most liquids (and solids), as it relies upon th e dielectric constant of the liquid to operate. As the liquid rises in the space between two electrodes, which are in effect the two plates of a capacitor, the variation in capacitance can be monitored and set to alarm. The nature of the li quid must be considered. If it is non-conductive then with the vessel wall as th e second plate. The primary electrode or the first plate only should be insulate d from the vessel. However, if the liquid is conductive, the primary electrode m ust be fully insulated from the vessel and the liquid, usually via a coating of some sort. In this case, the liquid itself acts as the second plate of the capac itor, with the insulation of the primary electrode acting as the dielectric. Pro blems often arise from in correct in installation, build up of conductive coatin gs, damage to insulation and false signals caused by foams. For some organic based oils such as hydraulic fluid, the low dielectric con stant means that the probe sensitivity has to be increased, which can also lead to false alarms. To over come some of the problems mentioned above, a RF (radio frequency) c apacitance system is available the radio frequency excites the two electrodes, o ne of which may again be the vessel wall of appropriate. An electronic control b ox monitors the capacitance caused by the level of the liquid between the probes and the resistance caused by any coating, the later being measured and then eli minated by the electronics. Pressure Operated Level Gauging Bottom Mounted Transmitter

In open vessels the pressure transmitter mounted near the bottom of the tan k will measure the pressure corresponding to the height of the fluid above it. The connection is made to the high-pressure side of the transmitter. The lo w-pressure side is vented to atmosphere. If zero point of the desired level rang

e is above the transmitter, zero suppression of the range must be made. This adj ustment is limited to 500 percent of the span on the 1151 DP and 500 percent of the span on the 1151 GP. Example Let X = vertical distance between the minimum and maximum measurable levels Equal to 500 inches. Y = vertical distance between the transmitter datum line and the minimum m easurable level equal to 100 inches SG = specific gravity of the fluid equal to 0.9 H = maximum head pressure to be measured in inches of water. E = head pressure produced by y expressed in inches of water. Range = e to e + h, h = (X). (SG) = 450 inches WG, Then e = (y).(SG) = 90 inches WG, Range = 90 to 540 inches WG, Top Mounted Transmitter

A bubblier system using a top mounted pressure transmitter can be used in open ves sels. This system consists of an air supply, a pressure regulator, a constant fl ow meter, a pressure transmitter and tube extending down into the vessel. Air is bubbled through the tube at a constant flow rate the pressure required to maintain flow is determined by the vertical height of the liquid above the tube opening times the specific gravity. Examples Let X = Vertical distance between the minimum and maximum measurements levels eq ual to 100 inches. SG = Specific gravity of the fluid = 1.1 H = Maximum head pressure to be measured in inches of water. Range = zero to h Then h = (X).(SG)=100 inches WG Range = 0 to 110 inches WG CLOSED VESSELS In closed vessels the pressure above the liquid will affect the pressure measur ed at the bottom. The pressure at the bottom of the vessel is equal to the heigh t of the liquid multiplied by the specific gravity of the liquid plus the vessel pressure.

To measure true level, the vessel pressure must be subtracted from the meas urement. This is accomplished by making a pressure tap at the top of the vessel and connecting this to the low side of a differential pressure transmitter. Vess el pressure is now equally applied to both high and low sides of the transmitter . The resulting differential pressure is proportional to liquid heights multipli ed by specific gravity. DRY LEG If the gas above the liquid does not condense, the piping for the low side of th e transmitter will remain empty. Calculations for determining the range will be the same as those shown for open vessel bottom mounted transmitter. WET LEG If the gas above the liquid condenses, the piping for low side of the transmitte r will slowly fill up with liquid. To eliminate this potential error the pipe is purposely filled with a convenient reference fluid. The reference fluid will exert a head pressure on the low side of the transmitte r, and zero elevation of the range must be made. Example (wet leg) Let X = vertical distance between the minimum and maximum measurable levels equa l 500 inches Y = Vertical distance between the transmitter datum; line and the minimum measurable level equal 50 inches Z = Vertical distance between the top of the liquid in the wet leg and the transmitter datum line level 600 inches. SG1 = Specific gravity of the fluid equal 1.0 SG2 = Specific gravity of the fluid in the wet leg equal 1.1 H = Maximum head pressure to be measured in inches of water E = head pressure produced by y expressed in inches of water S = Head pressure produced by z expressed in inches of water Range = e s to h + e s Then h = (X) (SG1) = 500 inches WG E = (Y)(SG1) = 50 inches WG S = (z) (SG2) = 660 inches WG Range = -610 to 110 inches WG THE APPLICATION OF DIAPHARGM SEALS TO ELECTRONIC PRESSURE TRANSMITTER: The measurement of process pressure and differential pressure is not always a si mple procedure. For reasons of temperature, corrosive attack, clogging, sanitati on, or non-contamination, transmitters often cannot be allowed to come in to dir ect contact with the process fluid. When such conditions exist. Diaphragm seals

frequently are installed to solve the problem. If not properly applied, however the seals may cause additional problems. While the addition of a diaphragm seal does not affect transmitter accuracy directly, factors such as capillary length, mounting position and fill fluid introduce variables that inter with each other . The interaction between capillary and filled fluid manifests itself in temperatu re effects and time response the temperature effects are a function of the fille d fluid coefficient of expansion, fill fluid volume and diaphragm stiffness. As the fill fluid undergoes a temperature change it expands or the contracts the re sulting volume change flexes the diaphragm. This flexure increases or decreases the pressure in the seal and capillary system and is seen by transmitter as an o utput shift disregarding diaphragm stiffness, it can be set that for any given s ystem, the longer the capillary, the greater fill volume and the greater tempera ture effect. It follows logically that to minimize the effects of the temperatur e capillary length should be kept as short s possible.

Nucleonic Gauging The system operate on simple, non contacting, nuclear principle: gamma radiation will penetrate any material, but is absorbed in proportion to the amount of mas s it penetrate. A small gamma radiation source is safely housed in a shielded holder mounted out side the process vessel. When the shutter mechanism is opened, a collimated radi ation beam is emitted. This gamma energy penetrates vessel walls, spans across t he entire width of the vessel and is received by a detector also extremely mount ed directly opposite the portion of the radiation beam. The detector senses the radiation change and produces a signal used to indicate an alarm, operate a reco rder or perform various control functions. Because all system components are external to the process, measurement is truly. Non contacting the systems are therefore not affected by product temperature, pre ssure, corrosiveness, abrasiveness, or viscosity or by vessel size, shape of con struction, installation does not require wall modifications or down time, and ma intenance is minimal.

VIBRATION Vibration is process parameter used in ammonia plant. There are two type of vibr ation sensors used to measure vibration namely axial Displacement sensors and An gular vibration sensors. To measure the vibration of a body a vibration pickup c oil is placed near the vibrating body. SPEED Speed parameter is measured by digital tachometer. This parameter can be observed in T.G Area. ANALYZERS Analyzers are the instruments that are used to measure the concentration of the sample in a sample in a given mixture. These instruments can give thee q ualitative and quantitative information of the sample under test. The different

analyzers used in Rain CII Carbon India Limited are i) pH Analyzers ii) Conductivity Analyzers iii) Infrared Analyzers iv) Thermal conductivity Analyzers v) Oxygen Analyzers vi) Flue Gas Analyzers SWITCHES

Switch is a switching device and not a measuring instrument. The scale is provid ed primary for guidance to assist setting. All types of switch are used to trip and alarm purposes. Some of the switches are connected to the DCS panel for alar m indication and some are connected to the shutdown system for tripping the plan t. There is Pressure, Temperature, Level and Flow switches &belt conveyor safety switches are used in calcination&power Plants. TRANSMITTERS A transmitter may be described as a device used in a control system, whi ch senses and control a process variable (i.e. temperature, pressure level, and flow. Etc.) to an electrical signal which is proportional to the value of the se nsed variable. The electrical output is frequently at 0-20ma or 4-12mA. Transmit ting transducers are devices that convert the measured variable into a transmitt able signal, either pneumatic or electrical. By taking the advantage of microprocessor technology, a lot of transmitt er manufactures come our which a new generation of transmitters which allow digi tal communication, they are called smart Transmitters. Two basic types of Smart Tr ansmitters are currently available. The first system replaces the analog signal by a digitized 4ma or 20mA signal at the baud rate of 200 using the frequency fo r data communication. The second uses high frequency superimposed on the analog 4-20mA signal for data communication. Calibration in measuring range, Zero point correction, disturbance monitoring and remote diagnostics are possible using sm art Transmitters in conjunction with a process system or specific portable progr ammer called communicator.