Report on control panes and applications

8/4/2019 Report on control panes and applications

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1.PLANT PROFILENagarjuna Fertilizers and Chemicals Limited (NFCL) the flag ship of Nagarjuna group is

established in 1984. It is the first gas-based fertilizer plant in south India. The plant is based on

the latest fertilizer technology from M\S Snam Progetti, Italy for urea process with an installed

capacity of 1500 Mt/day for each unit. The ammonia process is based on technology from M\s

Haldor Tapsoe, Denmark with an installed capacity of 9000 MT/day per each unit.

The feed stock for unit-1 is Na and feed stock for unit-2 is MG/Naphtha or mix of Na

(Godavari Krishna basin through GAIL) and Naphtha (from HPCL, Vizag). Fuel for entire

complex is on natural gas. The current consumption of NG is 2.15 million standard cubic meters

per day. The water requirement of 6.0 million gallons/day is received from samalkot summer

reservoir through two pipelines.

The construction of the unit-1 was started in 1988 and the commercial production

commenced from august 1, 1988. The construction of unit-2 was started in 1995 and the

commercial production commenced from March 19, 1998. Presently the total average production

is about 4,600 MT or urea per day. The total cost of the emitting complex is Rs.2156 crores.

The entire plant is dividing as process plant-1, process plant -2 and offsites. The process plant-1

consists of NG based on ammonia and urea production units. The process plant-2 consists of theNaphtha based ammonia and urea based production units. The off sites include water treatment

plants, de-mineralization plants, cooling water, inert gas plants stream and power generation

plants, ammonia storages, bagging plant, urea silos etc. the stream and power generation plants

include auxiliary boilers and cogeneration gas turbine plants, GT-A and GT-B supplied by M/S

Miurgopigone inc and GT-C by Thormmaren internation bv, Netherlands.


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2. AMMONIA PROCESS DESCRIPTION

The methodology adopted by the NFCL for manufacture of ammonia is based on steam

reforming natural gas is used as feed stock for plant-1, whereas Naphtha for plant-2. About 85%

of world ammonia production is based on steam reforming concept. Both ammonia plants are

based on Haldor Topsoes low energy steam reformation technology. It consists of a

conventional front end with desulphurization, primary reforming, and secondary reforming, high

and low temperature shift conversions, CO2 removal by Giammarco-ventricle pottasium

carbonate solution of methanation. The synthesis loop consists of Topsoes S -200 radial flow

converter.

NFCL is the first plant to utilize 2s/3s CR. Ni-Nb alloy for the primary reformer tubes at

the grass root level, thereby enabling thinner reformer tubes and lower finance duty, which has

resulted in lower skin temperature and increased overall furnance efficiency. For conbustion air

pre heating in the primary reformer, waste heat recovery section, a finned plate type heat

exchanger is used instead of a Liungstrom type heater where there can be a possibility of leakage

of combustion air into flue gas. Low heat Giammarco- Vetrocoke (GV) process is adopted for

CO2 removal. Heat recovery by the Dm water heating in GV section is 0.4Gcal/Mt NH 3. The use

of S-200 converter which results in higher conversion per pass and lower pressure drop, leads to

considerable energy saving, Haldor- Topsoes low pressure synthesis loop of 140kg/cm

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in theconventional plants. Installation of purge gas recovery(PGRU) at the grass root level has helped

in low energy consumption in the primary reformer. Hydrogen recovery in the PGRU is more the

90%.

2.1 NATURAL GAS SUPPLY:

76% of the total natural gas is supplied to the NH 3 plant, 12% to the gas turbine and 12%

to the auxiliary boiler it is supplied from the off sire gas metering station at a pressure of

44kg/cm2. It is received directly from in NH3 plant at 40kg/cm

2. It is received directly from in

NH3 plant at 40kg/cm2. Fuel gas is received through separate header and it is used for burner.

Natural gas is used as

Feed stock


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Fuel Power consumption and steam generation plant.

Ammonia is manufactured by the following steps:

2.2 PRE DESULPHURISATION:

This operation involves removing the dissolved gases and sulphur compounds present in

the Naphtha. Dissolved gases like O2 can act as poison for the catalyst in the hydro generator

reactor, which is present in own steam. Naphtha is passed through a dearator to remove the

dissolved gases, natural gas being used as the stripping medium. Naphtha is used both as feed

and fuel. The requirement for fuel is taken from the outlet of the de aerator. Hydrogen sulphide

& organic sulphur compounds present in the Naphtha acts as strong catalyst poisons. The

remaining for fuel is taken from the outlet of the de aerator hydrogen sulphide & organic sulphur

compounds present in the Naphtha as strong catalysts poisons. The remaining stripped Naphtha

containing about 1000ppm of sulphur is the sent to the Hydro generator reactor in which

hydrogenation of organic sulphur compound takes place to give hydrogensulphide. The reactor is

filled with Nickel Molybdenum catalyst, which catalyst the hydrogenetion of organic sulphur

compounds to H2S.

RSH + H2 RH + H2S

H2S produced in the rector & that already present in the feed is then removed in H2S

absorbers. Each absorber containing one bed of ZNO catalyst to absorb the sulphur. The sulphur

removal in ZNO bed takes as follows

ZNO + H2S ZNS + H2O

ZNO + COS ZNS + CO2

2.3 FINAL DESULPHURISATION:

The purpose of desulphurisation is to receive the remaining hydrogen sulphide & organic

sulphur compounds present in the Naphtha, which are strong catalyst reactor. The process gas

after desulphurisation is sent to reforming.


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2.4 REFORMING SECTION:

The reforming process and the design of the reformer are based on the reaction between methane

and higher hydrocarbon present in the Natural gas with stream there by generating CO, hydrogen

and CO2. CatalystNi based catalyst is used inlet temperature 769.

CH4 + H2O CO2 + 3H2

CO + H2O CO2 + H2

2.4.1PRIMARY REFORMER:The primary reforming of natural gas is done ina Topsoe series side fired furnace. Pre heated

hot desulphurised natural gas and recycle gas mixture is combined with Hs steam and distributed

through hair pins tubes into Vcle reformer tubes filled with Ni catalyst. The tubes are placed

inside the side fired furnace are absorbed in the tubes by radiation from a number of wall burners

to the tubes.

In case of fired furnace, the reformer outlet temperature increases gradually from the top

towards the bottom. The tube kin temperature along the length of the tube can be controlled is

side fired furnace. Here potential for C formation cab be better controlled.

The primary reformer contains 190 tubes in two parallel sections and each section is

divided into 5 rows. The furnace operates with side firing of fuel gas on both sides of each row

of tubes to develop a process gap temperature of about 769 at the catalyst tube outlet.

There are 360 side fired wall burners arranged in 6 rows and each row having 15 burners.

These are LP radon type burner and are arranged construction. Offsite is used as fuel for burners.

CH4 + 2H2O CO2 + 4H2 + heat

CH4 + H2O CO + 3H2 + heat

CO2 + H2 CO + H2O + heat

Reaction starts at 500for the higher hydro carbon and 600

for the methane.


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CARBON FORMATION: Here C may be formed partly outside and partly inside thecatalyst. C deposits outside the particles will increase the pressure drop over the catalyst

bed add deposits inside the particles will reduce their activity and their mechanical

strength. It the catalyst is poisoned carbon formation may also occur due to low stream

carbon ratio. It the catalyst is sufficiently reduced.

STEAM/CARBON RATIO: It is the most economical when the ratio is 3:3:1. Howeverif the ratio is increased equilibrium shift towards right with a neat effect of decreased

Methane and CO2 and increase in CO and H2

PRESSURE: Though higher pressure will drive the reaction in the undesired direction, ifother factors remaining same reaction are performed under high pressure to save the

synthesis gas compression cost. This will also help to recover the heat by 6 B.F.W

preheating.

2.4.2 SECONDARY REFORMER:

In the secondary reformer the heat is supplied by combustion of plant of the gas achieved

by mixing air into the gas. The gas then passes down the Ni catalyst bed where the reaction is

completed with simultaneous cooling of the gas is 943CO2 is completely in the process. Process

air also supply the N2 and reduce the methane content of the process gas to a lower level order to

keep the inert gases low.

2H2 + O2 2H2Oheat

CH4 + 2O2 CO2 + 2H2Oheat

In the catalyst bed CH4 forming reaction takes place.

CH4 + 2H2O CO + 2H2 + heat

CO2 + H2 CO + H2O + heat

For heat recovery, reformed gas is passed through the tube side of a refractory lined waste heat

boiler.


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2.4.3 CO CONVERSION: CO present in the reformed gas is converted to CO2 in 2 shift

converters. The following reaction takes place in the shift converter:

CO + H2O CO + H2O

As the reaction results on temperature increase, the outlet gas will be at an unfavourable

equilibrium if heat is not removed before the conversion is completed. The shift reaction

increases the amount of H2 in the process gas.

2.4.4 CATALYST:Cu promoted iron oxide is used. Catalyst must be activated by reducing

it from Fe2O3 and Fe3O3. Above 400 catalyst activity will be decreased shift converter heat is

removed by W.H.B, B.F.W & trim heater.

2.5 CO2 REMOVAL SECTION (G.V section):

The unit provides gas free of CO2 for the production of ammonia & necessary CO2 for

urea production. In this unit, CO2 in the process gas is absorbed by the GV solution in an

absorber. Stripping of the absorbed CO2 is done in two regenerators and CO2 stripped is

supplied.

The chemistry involved in the removal of CO2 is chemisorptions and is as follows

CO2 + H2O HCO3 + H (1)

H2CO3 + KCO3 + H 2KHCO3 (2)

K2CO3 + CO2 + H2O 2KHCO3 (3)

The reaction rate of (3) depends on the reaction rate of (2). Reaction rate of (1) is slow

and the activator activates this reaction by quickly introducing the gases of CO 2 in the liquid

phase.

2.5.1 CO2 REGENERATOR: In the regeneration section (1) is removed by application of

heat and pressure reduction.

HIGH PRESSURE REGENERATOR: CO2 rich GV solution enters into the highpressure regenerator which is cooling under 1.04g steam is flowing counter currently to


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the rich solution and stripped off the CO2 coming out from the top. The excess steam

which is introduced into the regenerator.

LOW PRESSURE REGENERATOR: Low pressure regenerator is working under0.1(Kg/cm

2) rich solutions are introduces here from the high pressure section. No

external heat is supplied CO2 removal from the regenerator section is cooled in DM water

pre heater thus the vapour present with it is condensed. CO 2 gets from the low pressure

section CO2 coming from the high pressure section.

4CO + Ni Ni(CO)4

High Ar and CH4 concentration reduces the partial pressure of N2 and H2 therebyreducing the conversion rate. Therefore a constant purge of gas from the loop is

maintained to keep the inert level in the converter inlet at about 8%.

H2/N2 ratio in the makeup gas and in the synthesis loop must be close to the 3:1. I themakeup ratio is 2.78:1, after the addition of H2 from the purge gas it becomes 3. When

the ratio is decreased to 2.5 reaction rate will increase but circulating synthesis gas will

be heavier. Therefore a pressure drop will generate which will decrease separator

efficiency. Hence the ratio must be constant.

Reaction temperature of the synthesis gas is 252 and is heated in a inter bed exchangerby the hot gas coming out from the first bed. Before entering the first bed it is mixed with

the cold shot. This help to maintain temperature is increased to 520 - 530 . Before

entering the second bed the temp is decreased by the cold shot. The temperature in each

catalyst bed should not be below 360 otherwise the reaction will quickly extinguish itself

again temp should not be over 530

The capacity of the synthesis loop with regard to ammonia production rises withincreasing circulation rate. The NH3 production per cubic meter of circulation gas is

proportional to the temperature difference between converter exit and inlet.

The synthesis loop is designed for a maximum pressure of 115(Kg/cm2)g under designproduction rate, design inert level, design gas composition it can operate at a pressure of

142(Kg/cm2)g. actual pressure is dependent on

Process condition


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Inert level Production rate Catalyst rate NH3 concentration at the inlet.

The loop pressure will increase with increase in makeup gas flow to the loop. Decreasing the inert level and the circulation activity. Increasing the NH3 concentration at the inlet. By changing H2/N2 ratio away from the optimum.

2.5.2 CATALYST:

Catalyst is pre reduces and stabilized. Stabilization involves skin oxidation of the catalyst

where it takes 2% wt of the O2. Above 100

this pre reduced catalyst will react with air &

spontaneously heat up. It is activated by Iron oxide to Iron.

Actual process condition Temperature of the catalyst bed CATALYST POISON: Mainly the compound and compounds have catalyst activity

increases by loop pressure and circulation rate and decreasing inert level only 25% N 2

and H2 react to form NH3 rest to be recycled gas coming out from the convector.

2.5.3 REFRIGERATION SECTION:

The refrigeration sections used to liquefy gases NH3 and consist of a compressor, an

accumulator and number of chillers. Evaporator vapor from the makeup gas chiller and first NH3

chiller and from the flash vassal is compresses by the refrigeration compressor.

2.5.4 AMMONIA ABSORPTION:

Ammonia produced in the ammonia synthesis converter separated from the unrelated gas

mixture in the ammonia separator. Due to high pressure and low temperature and loop gases is

dissolved into NH3 to certain extent. The vapour from the top of the vessel is sent for

refrigeration.


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2.5.5 PURE GAS RECOVERY SECTION:

In order to maintain the inert convention in the synthesis loop at a constant value a

continuous purge is taken from the cold heat exchanger H2 from the cold heat exchanger. H2

from these inert is recovered and thus maintaining the N2:H2 ratio at 1:3.

2.6AMMONIA STORAGE TANKS

During normal operation Ammonia produced in the ammonia plant goes directly for Urea

manufacture. In case of Urea plant stoppage or running at low load, in order to avoid stoppage or

reduction of Ammonia plant load. Two Ammonia storage tanks of 5000Mt capacity are provided

where liquid Ammonia can be stored.

The storage tank is double wall double integrity type to ensure utmost safety. By double

integrity it is meant that the outer tank is also made of the same material as the inner tank and is

equally strong. In case the inner tank is very equally strong. In case inner tank leaks the outer

tank will be able to contain the ammonia. Due to heat ingress from ambient air and flashing of

product liquid Ammonia entering the tank from the Ammonia plant, Vapour will be generated in

the storage tank which are compressed, cooled, condensed and sent back to the Ammonia storage

tanks for Urea plant it is pumped by Ammonia storage pumps.

Emergency power is provided for the refrigeration system. Sufficient precaution and

provisions have been made incorporated to protect the storage tank from under and over

pressure.


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3. UREA PROCESS AND PLANT DESCRIPTION

Urea is produced by synthesis form liquid ammonia and gaseous CO2. In the reactor ER-101 the

ammonia and CO2 react to form ammonia carbonate, a portion of which dehydrates to form urea

and water. The reactions are:

2NH3 + CO2 NH2COONH4

NH2COONH4 NH2CONH2 + H2O

In the synthesis conditions the first reactions occur rapidly and is completed, the second reaction

occurs slowly.

The liquid ammonia coming directly is collected in ammonia receiving tank EV-101 from

the liquid ammonia receiver, the ammonia is pumped to the high pressure section of the plant.

Two pumps are used to do this. The first pump, the ammonia booster pump increases the

pressure of the ammonia to the second pump, the high pressure ammonia feed pump. The high

pressure ammonia feed pump is a reciprocating pump. Urea purification in the medium, low and

pre-vacuum pressure recoveries.

3.1 UREA PURIFICATION:

It is pointed out that the exchanger where urea purification are called decomposers in this

apparatus the residual carbonate decomposition takes place.

3.1.1 First Stage Purification and Recovery Stage at 18ksca:

The solution with a low residual CO2 content, leaving the bottom of the stripper is expanded at

the pressure of 18ksca and enters the medium pressure decomposed EE-102

The equipment is divided into two phases:

Separator EMV-02 where the released flash gases are removed before the salon enters thetube bundle.

Comparison section where the residual carbonate is decomposed and the required heat issupplied by means of M.P steam and M.P condensate flowing out from the stripper


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3.1.2 Second Purification and Recovery Stage At 4.5ksca:

This is divided into two parts

Top Separator Decomposition section

The liquid phase with the remaining inert gases is sent to the carbonate solution vesses from here

the carbonate solution is recycled back to the vaccum pre concentrator by means of the

centrifugal pump. The inert gases washed in the low pressure inert washing towers are collected

to vent stack practically free from ammonia.

3.1.3 Third Purification And Recovery Stage At 0.35ksca:

The gas leaving the preconcentrator top is routed to the vaccum unit where condensation

takes place. The Urea solution collected at the bottom pre contractor holder is sent to the vaccum

section by pumps.

3.2 UREA CONCENTRATION SETION: In order to prill urea, to concentrate the urea

solution up to 99.8% weight, a vaccum concentration section in two stages is provided for this.

3.3 UREA PRILLING:

The melted urea leaving the second vaccum holder is sent to the prilling bucket by means

of a centrifugal pump. The urea coming out of the bucket in the form of drop falls along the

prilling tower and encounters a cold air flow which causes its solidfications. The solid pills

falling to the bottom of the prilling tower are set into the conveyor.

3.4 PROCESS WATER TREATMENT: The condensed vapors from the first andsecond vaccum system, containing urea, ammonia and carbondioxide are collected in the process

condensate tank. In the tank the carbonate drain collected in the tank are fes by means pump.

3.5 FLUSHING NETWORKS: Three Flushing networks have been provided in the plant

operating at the following pressures


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HP flushingp-176ksc MP flushingp-22ksc LP flushing -p-9ksc

3.6 DE-DUSTING SYSTEM: The Urea melt coming out of the bucket in the form of

droplets add while falling inside the pill tower a counter current flow of cold air which causes

solidification. Hot air leaving prill tower top consist of fine urea dust and free-ammonia. In order

to prevent pollution caused during the process of prilling, deducting system has been

incorporated at prill tower top. The system also recovers urea, which is recycled back into the

system.


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4.BAGGING PLANT

BAGGING means pre-weighting the UREA in an automatic machine, dumping the pre-weighted

Urea material in an empty material and stitching the side bag. 8 Bagging streams are available

here. Any stream can be taken on line to the loading program.

Each Stream Has The Following Equipments:

Bunker Electromagnetic Vibrators Electromagnetic Bagging Machines with two independent units. Wooden Slat Conveyor Stitching Machine Bag Turner Stream of Conveyors and bag diverters for handling the stitched bags. Lorry loading Wagon loading


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5.POWER PLANTThe plant consists of mainly:

Boilers

Gas Turbines Stream Turbines GAIL

5.1 BOILERS:The auxillary boiler manufactured by Mitsui engineering and ship building

company limited, Japan is a pressurized furnance, natural circulation, two drum, three pass out

door, self standing, multiple fuel, front fired, bottom support unit.

5.1.1Water Drum And Stream Drum With Internals:

Boiler has a drum which support the stream during through 904 no. of bank tubes. Bank tube ends are inserted in steam drum and water drum are expanded and seal welded. Lower drum rests on its legs. One end of the lower drum is bolted tightly on foundation and is free to expand or

contract.

The other end rests on sliding pad and is free to expand or contract. About half the bank tubes act as a down corners. Preheated feed water from economizer is received in steam drum and a feed pipe placed

below normal water. Distributes through 73 numbers and 17mm diameter holes.

5.1.2 Boiler Bank Tubes:

The nest of the tubes connecting water and steam drum is called boiler bank tubes. They are 904 in number. The tube ends have been inserted in holes and expanded in the

drums.

The expanded tube forms a perfect sealing against drum plates and also the grooves.


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Further sealing is obtained by seal wedding the tubes to the drum.5.1.3 Further Wall Tubes:

The furnace has an ample volume to secure complete combustion of fuels. Furnace walls are made from tubes. The space between the tubes are covered by fins. The fins are welded to tubes thus forming totally gas tight furnance walls. Furnace wall tube receiver water from the lower drum and these tubes exceeds to make

the front wall.

5.1.4 Super Heater:

Two super heater both of pendant type, non-drainable have been provided. Both super heater are conventional type. Primary super heater is located near the bank of

tubes and secondary super heater is located at the exit of furnace.

Super heater are hung from super headers which are mounted on furnace side headers. Thermal expansion of super heater is vertical downward allowing free expansion.

5.1.5 De-Super Heater:

To have control over the super heater outlet steam temperature a de super heater has beenprovided between two super heaters.

Feed water trapped upstream of feed water control value is sprayed into steam at the endof primary super heater. This spray is done through super heater nozzle.

To prevent quenching a thermal sleeve is provided. Spray water will require from50%MCR to 110%MCR.

5.2 GAS TURBINES:

Gas turbine is a machine which works like a car engine fuel energy into mechanical

energy. By heating up compressed air and expanding it in a set of nozzels, and output shift will

drive a generator or a compressor.


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The compressed air is produced in the machine itself by an axial or a radial flow

compressor. The compressed air is heated up by fire. The fuel can be heavy oil, diesel oil,

kerosene or natural gas or combustion of gas and liquid fuel. The hot compresses air (~1200 c)

posses an amount of energy which will partly be transformed into velocity in the nozzles. The

high velocity air will now change direction in the gas turbine buckets, heating a force that will

rotate the turbine wheel. The process can be repeated in a second or even in a third wheel.

5.3 APPLICATION:

5.3.1 GENERATOR DRIVE: The biggest gas turbine by Thomason international is the so

called MS 900 IF of generator electric, USA design. This machine can produce about 220Mw.

This power can be compared with the total output of 5000 middle class cars or 3766600 lamp

bulbs of 60W each.

5.3.2 COMPRESSOR DRIVE: In the refiners in the chemical plant and th other industries the

gas turbines is a well known6 driver for process compressor. These are normally of the

centrifugal type. They consume a lot of power due to the very large volume flows are handled.

The combination gas turbine compressor is very compacting reliable. In the process, the

compressor inlet volume flow might be controlled in speed controlled processes we will find

the shaft gas turbine. In these machine we can control the speed of the output shaft by varying

the nozzels.

5.3.3 PROPULSION OF AIRCRAFT AND SHIPS: The well known boring 747 dc airbus

and fohher air planes are propelled by gas turbines. The fuel used is kerosene. Modern jet

engines are equipped with a front fan which delivers 80% of total thrust. The other 20% is

generated by the force of the accelerated exhaust gas. In ships, naval ships make use of there

relatively small, high power match to develop high cruising speeds. Gas turbines used for jet

engines can be modified for stationary use.


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6.OFFSITES6.1 PRE TREATMENT:

The water from samalkot reservoir being surface water has impurities that are not suitable

for industrial process and human consumption. The water after treatment is safe for use in

process and for human consumption. The salient unit processes that are involved within the

scope of treatment are

Pre-chlorination of raw water in stilling chamber Coagulation with chemicals in flash mixer Flocculation and clarification in Clariflocculator Filtration in rapid gravity filter Post chlorination of filtered water for drinking water purpose.

6.1.1 Pre-chlorination:

Pre-chlorination is the application of chlorine to raw water prior to any unit treatment

process. The point of application as well as the dosage is determined by the objectives viz.

control of bacterial growth in raw water, prevention of mud ball formation and slime promotionin filters, reduction of taste and colour and minimizing the post chlorinisation dosage when

dealing with heavy polluted water.

6.1.2 Coagulation with Chemicals in Flash Mixer:

Very fine suspended particles and colloidal donor settle by simple gravitational

sedimentations and a special treatment is necessary to remove them from suspension. Chemical

coagulation is an important process applied extensively in water treatment practice. The effect

produced by addition of a chemical to a colloidal dispersion, resulting in particle destabilization

that eventually changes into readily settle able solids is called coagulation. The commonly used

cost effective, coagulation in water treatment is aluminium sulphate commonly as alum with a

chemical formula AL2(SO4)3 18H2O


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For a coagulant to act efficiently, it is necessary that there is sufficient alkanety, in the

neutral water, when the alkanity is found to be less than required for complete neutralization of

coagulant. Alkanity is imparted by addition of sodium carbonate solution and it reacts with alum.

6.1.3 Clariflocculator:

The object of clariflocculator is to form distinct settle able flocs during flocculation and their

removal by gravitational setting in the clarifying zone. The cleared water overflows leaving

behind the settle able solids.

The clariflocculator is a circular tank with flocculation zone in the centre for flocculation

and the outer being the clarifying zone for sedimentation. The raw water entering clariflocculator

discharges at the top of the flocculation zone through the central opening provided in the central

shaft. The water entering the flocculation zone is to subject to slow agitation by the paddles

provided.

6.1.4 Filter Beds:

The object of this unit to remove the residual suspended impurities from clarified water. The

filtering media consists of sand and gravel of desired size and quality. The clarified water

containing the residual suspended matter passes down the filter during which the solids are

retained on the top of the filter media. Filters water is used for back washing the filters the waterbeing drawn from the wash water tank located on the top of the filter house.

6.2 DM PLANT:

Water is main responsible for the formation of deposits on the water side heating surfaces

of boiler units and since these deposits posses low thermal conductivity they cause overheating

of tubes, thereby reducing the strength of the metal. Of much importance to the elimination of

the above mentioned problems is suitable treatment of water. Such water treatment of water

includes ion exchange method. Ion exchanger removes unwanted ions from raw water by

transferring them to a solid material called an ion exchange. This operation is cyclic chemical

process and the complete cycle usually includes back washing, regeneration and rinsing.


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The plant consists of

Filtered water supply system Activated carbon filters Strong acidic cation exchanger Degasser towers Degassed water storage and pumping system WBA units, SBA units, Mixed beds

6.2.1Filtered Water Supply System: After removing the turbidity in PTP, water is supplied to

the DM plant by means of 4 filtered water pumps.

6.2.2 Activated Carbon Filters: The filtered water from common discharge having residual

chlorine is passed through activated carbon filers to remove any organic matter present and

residual chlorine which effects the SAC resin.

6.2.3Strong Acidic Cation Exchanger: The dechlorinated water from activated carbon filters

enters the cation exchanger were cations such as Ca, Na etc are taken up by the cation resin and

converted into corresponding mineral acids.

6.2.4Degassed Tower: De cationsed water from the cation exchanger which contains free CO2

or carbonic acid flows down a packed tower against a counter current flow of low pressure air

supplied by a monitories air blower from bottom of the tower, CO 2 is stripped from water by

scrubbing action of air and carried out through the vent.

6.2.6 Weak Base Anion Exchanger: The degasser water containing anion like sulphates,

nitrates, chlorides and silica enter water weak base anion exchanger either after completion.

6.2.7 Strong Base Anion Exchanger: The water devoid of strong anions like chlorides,

sulphates and nitrates containing only residual chloride and residual CO2 and silica is passed

through SBA exchanger for complete removal of anions.

6.2.8 Filter Beds: The water free from almost all tons containing residual CO2 and silica is

passed through mixed bed unit called polishing unit, which contains both cation and anion resins


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in mixed water. The outlet from this unit is demenaralised water containing silica less than 0.01

ppm, PH 7.0

6.3EFFLUENT TREATMENT PLANT

The water scheme essentially involves removal of oil and Clariflocculator sludge. PH correction

and dilution so as to make the treated effluent water fit for aquatic life and plants.

6.3.1Oil Separator: The oil bearing effluent from process plant and offsites is collected in oil

separation pit. The disc oil separator is a floating device supported by 3 numbers of floats which

in turn are firmly secured to the two sliding guides provided in the oil separation pit. The

principle behind disc oil separator is based on the adhesion of oil, to the lateral surface of

metallic discs arranged perpendicular and partially submerged in respect to the surface of oil and

routing in respect to the horizontal axis.

6.3.2 Removal of Sludge: Sludge thickener is provided to increase the solid concentration of

Clariflocculator sludge. It is a circular sedimentation tank. The sludge is received at the central

chute. The settled sludge is with drawn to the thickened sludge pit by gravity. The effluent

overflows to circular peripheral launder and conveyed to collection sump or equalization pond

directly.

6.3.3 Ph Correction: The ammonia and urea bearing effluents from the respective plant off-spec

process condensate from urea and ammonia plant, acidic regeneration effluent from DM plant.

HCL acid is added to bring down the PH to the range 7 to 8. When the PH of the mixed effluent

is stabilized, it is pumped to equalization pond by effluent recirculation transfer pump.

6.4 COOLING TOWERS:

Most industrial process need cooling medium for efficient and proper operation. Water is the

most effective cooling medium and

It is readily available in plenty. It is easily handled. It can carry large amount of heat per unit volume.


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It does not expand or compress significantly with in normally encountered temperatureranges. It does not decompose.

The system using water as coolant are called as cooling water systems. They

control temperature and pressure by transferring heat from hot process fluid into the cooling

water which carries the unwanted heat away. There are 3 basic cooling water systems. The

choice of the right cooling water system depend on various factors such as type of process fluid

being cooled, nature of the process, availabilty and the cost of water characterstics of water and

environmental considerations.

6.5 INERT GAS PLANT

The plant is designed to produce gaseous and liquid nitrogen with a high level of purity,

oxygen content of the order of less than 1ppm by volume by volume. The process adopted here is

seperation of air into nitrogen and waste gas rich in O2. The compressed air is cooled, liquified

and then distilled there by a portion of nitrogen content of the air is seperated as pure nitrogen.

The waste gas is expanded through an expanded to produce refrigeration necessary for the

operation of the plant.

6.5.1 Equipment associated with warm ends for purification of air

MAIN AIR COMPRESSOR: The screw compressor consists of two stages, namely oneL.P and one H.P and it is provided as a source of feed air to the plant.

CHILLER: The chiller unit is intended for lowering the feed air temp from 49 to 12with the help of a closed loop refrigeneration system, thereby removing the bulk of the

moisture content from it before passing it on molecular sieve bed.

MOLECULAR SIEVE ADSORBER: The molecular sieve adsorbers are mainlyintended for drying and removal of cantaminants like CO2 and hydro carboons like

Acetylene, Propylene etc.., by employing solid granular dessicant.

6.5.2 The Main Equipments Are:

COLD BOX: As the name implies, cold box consists of equipment associated withcryogenic process such as main heat exchanger, HP column and re-boiler/condensor


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vessel valves, control valves and expander. During operation of plant pure N 2 gas is fed

into Cold box to prevent O2 rich in atmosphere which may develop due to leaks.

EXPANDER: The cryogenic centripetal expands is employed as a cold producer. Thewaste gas is generated in the re boiler is the motive force for spinning the expander.

STORAGE TANKS: Two number of sorage are provided for storing N2 in the state ofliquid.

VAPORIZER: Two numbers of ambient vaporizers are installed because of enormoussurface area to which it is exposed and aided by start type arrangement of the tube LIN is

instantly to become GAN.


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7.DCS and PLC7.1 MAJOR TYPES OF INDUSTRIAL CONTROL SYSTEMS:

Industrial control system or ICS comprise of different types of control systems that are

currently in operation in various industries. These control systems include PLC, SCADA and

DCS and various others:

7.1.1 PLC:

They are based on the Boolean logic operations whereas some models use timers and some have

continuous control. These devices are computer based and are used to control various process

and equipments within a facility. PLCs control the components in the DCS and SCADA systems

but they are primary components in smaller control configurations.

7.1.2 DCS:Distributed Control Systems consists of decentralized elements and all the processes are

controlled by these elements. Human interaction is minimized so the labor costs and injuries can

be reduced.

7.1.3 EMBEDDED CONTROL:

In this control system, small components are attached to the industrial computer system with the

help of a network and control is exercised.

7.1.4 SCADA:

Supervisory Control And Data Acquisition refers to a centralized system and this system is

composed of various subsystems like Remote Telemetry Units, Human Machine Interface,

Programmable Logic Controller or PLC and Communications.


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7.2 PROGRAMMABLE LOGIC CONTROLLER

A programmable logic controller (PLC) or programmable controller is a digital computer used

for automation of electromechanical processes, such as control of machinery on factory assembly

lines, amusement rides, or lighting fixtures. PLCs are used in many industries and machines.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 hard real time system since output

results must be produced in response to input conditions within a bounded time, otherwise

unintended operation will result. These PLCs were programmed in "ladder logic", which strongly

resembles a schematic diagram of relay 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. Early PLCs, up to the mid-1980s, were

programmed using proprietary programming panels or special-purpose programming terminals,

which often had dedicated function keys representing the various logical elements of PLC

programs. Programs were stored on cassette tape cartridges.

Facilities for printing and documentation were very minimal due to lack of memory capacity.

The very oldest PLCs used non-volatile magnetic core memory. More recently, PLCs areprogrammed using application software on personal computers. The computer is connected to

the PLC through Ethernet, RS-232, RS-485 or RS-422 cabling. The programming software

allows entry and editing of the ladder-style logic. Generally the software provides functions for

debugging and troubleshooting the PLC software.

7.2.1 COMPONENTS OF PLC:

CENTRAL PROCESSING UNIT:The CPU used is a standard CPU present in many other microprocessor controlled

systems. The choice of the CPU depends on the process to be controlled. Generally 8 or

16 bit CPUs fulfilling the requirement adequately.


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MEMORY UNIT:Memory in a PLC system is divided into the program memory which is usually stored in

EPROM/ROM, and the operating memory. The RAM memory is necessary for the

operation of the program and the temporary storage of input and output data. Typical

memory sizes of PLC systems are around 1kb for small PLCs, few kb for medium sizes

and greater than 10-20 kb for larger PLC depending on the requirements. Many PLC

would support easy memory upgrades.

INPUT/ OUTPUT UNIT:Input/Output units are the interfaces between the internal PLC systems and the external

processes to be monitored and controlled. Since the PLC is a logic based device with a

typical operating voltage of 5 volts and the external processes usually demand higher

powers and currents, the I/O modules are optically or otherwise isolated. The typical I/O

operating voltages are 5V - 240 V dc (or ac) and currents from 0.1A up to several

amperes. The I/O modules are designed in this way to minimize or eliminate the need for

any intermediate circuitry between the PLC and the process to be controlled.

7.2.2 PROGRAMMING UNIT:

Programming units are essential components of the PLC systems. Since they are used only in the

development/testing stage of a PLC program, they are not permanently attached to the PLC. The

program in a ladder diagram or other form can be designed and usually tested before

downloading to the PLC. The Programming unit can be a dedicated device or a personal

computer. It allows the graphical display of the program (ladder diagram). The unit, once

connected to the PLC can download the program and allows for the real time monitoring of its

operation to assist debugging. Once the program is found to operate as required the

Programming Unit is disconnected from the PLC which continues the operation.


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Fig 1: programming unit of plc

7.2.3 PLC OPERATION STEPS:

Input Scan: Scans the state of the Inputs Program Scan: Executes the program logic Output Scan: Energize/de-energize the outputs Housekeeping

7.2.4 TRADITIONAL PLC APPLICATIONS:

In automated system, PLC controller is usually the central part of a process control

system. To run more complex processes it is possible to connect more PLC controllers to a

central computer.

7.2.5 DISADVANTAGES OF PLC CONTROL:

Too much work required in connecting wires. Difficulty with changes or replacements. Difficulty in finding errors; requiring skillful work force. When a problem occurs, hold-up time is indefinite, usually long.


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7.2.6 ADVANTAGES OF PLC CONTROL:

Rugged and designed to withstand vibrations, temperature, humidity, and noise. Have interfacing for inputs and outputs already inside the controller. Easily programmed and have an easily understood programming langauge.

7.3 DISTRIBUTED CONTROL SYSTEM:

A distributed control system (DCS) refers to a control system usually of a manufacturing system,

process or any kind of dynamic system, in which the controller elements are not central in

location (like the brain) but are distributed throughout the system with each component sub-

system controlled by one or more controllers. The entire system of controllers is connected by

networks for communication and monitoring.

Fig.2: Distributed control System

A DCS typically uses custom designed processors as controllers and uses both proprietary

interconnections and communications protocol for communication. Input and output modules

form component parts of the DCS. The processor receives information from input modules and

sends information to output modules. The input modules receive information from input

instruments in the process (a.k.a. field) and transmit instructions to the output instruments in the

field. Computer buses or electrical buses connect the processor and modules through multiplexer

or demultiplexers. Buses also connect the distributed controllers with the central controller and

finally to the Human-Machine Interface (HMI) or control consoles. See Process Automation

System. Elements of a distributed control system may directly connect to physical equipment


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such as switches, pumps and valves or may work through an intermediate system such as a

SCADA system.

7.4 HISTORY:

Early minicomputers were used in the control of industrial processes since the beginning of the

1960s. The IBM 1800, for example, was an early computer that had input/output hardware to

gather process signals in a plant for conversion from field contact levels (for digital points) and

analog signals to the digital domain.

Fig.3: working block diagram of DCS

The first industrial control computer system was built 1959 at the Texaco Port Arthur, Texas,

refinery with an RW-300 of the Ramo-Wooldridge Company

The DCS was introduced in 1975. Both Honeywell and Japanese electrical engineering firm

Yokogawa introduced their own independently produced DCSs at roughly the same time, with

the TDC 2000 and CENTU systems, respectively. US-based Bristol also introduced their UCS

3000 universal controller in 1975.

Digital communication between distributed controllers, workstations and other computing

elements (peer to peer access) was one of the primary advantages of the DCS. Attention was

duly focused on the networks, which provided the all-important lines of communication that, for

process applications, had to incorporate specific functions such as determinism and redundancy


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7.5 COMPONENTS OF DCS:

DCS System consists minimum of the following components:

Field Control station (FCS): It consists of input/output modules, CPU andcommunication bus.

Operator station: It is basically human interface machine with monitor, the operatorman can view the process in the plant and check if any alarm is presents and he can

change any setting, print reports etc.

Engineering station: It is used to configure all input & output and drawing and anythings required to be monitored on Operator station monitor.

Information management system: This component maintain a continues and completetrack record of every function done by the operator every command performed and can

be viewed as history.

Controller Subsystems: Provides continuous and or discontinuous monitoring andcontrol of the process.

7.6 APPLICATIONS:

Distributed Control Systems (DCSs) are dedicated systems used to control manufacturing

processes that are continuous or batch-oriented, such as oil refining, petrochemicals, central

station power generation, fertilizers, pharmaceuticals, food & beverage manufacturing, cement

production, steelmaking, and papermaking. DCSs are connected to sensors and actuators and use

set point control to control the flow of material through the plant. The most common example is

a set point control loop consisting of a pressure sensor, controller, and control valve. Pressure or

flow measurements are transmitted to the controller, usually through the aid of a signal

conditioning Input/output (I/O) device.

When the measured variable reaches a certain point, the controller instructs a valve or actuation

device to open or close until the fluidic flow process reaches the desired setpoint. Large oil

refineries have many thousands of I/O points and employ very large DCSs.


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Processes are not limited to fluidic flow through pipes, however, and can also include things like

paper machines and their associated quality controls (Quality Control System QCS), variable

speed drives and motor control centers, cement kilns, mining operations, ore processing

facilities, and many others.A typical DCS consists of functionally and/or geographically

distributed digital controllers capable of executing from 1 to 256 or more regulatory control

loops in one control box.

The input/output devices (I/O) can be integral with the controller or located remotely via a field

network. Todays controllers have extensive computational capabilities and, in addition to

proportional, integral, and derivative (PID) control, can generally perform logic and sequential

control.

Modern DCSs support also neural networks and fuzzy application. DCSs may employ one or

several workstations and can be configured at the workstation or by an off-line personal

computer. Local communication is handled by a control network with transmission over twisted

pair, coaxial, or fiber optic cable. A server and/or applications processor may be included in the

system for extra computational, data collection, and reporting capability.

7.7 ADVANTAGES:

The computer can record and store a very large amount of data The data can be displayed in any way the user requires Thousands of sensors over a wide area can be connected to the system The operator can incorporate real data simulations into the system Many types of data can be collected from the RTUs The data can be viewed from anywhere, not just on site.

7.8 DISADVANTAGES:

Different operating skills are required, such as system analysts and programmer With thousands of sensors there is still a lot of wire to deal with.


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7.9 DIFFERENCES BETWEEN DCS AND PLC:

The differences between DCS and PLC are: DCS (Distributed Control System) is a CONTROL

SYSTEM that works using several controllers and coordinates the work of all these controllers.

Each controller is handling a separate plant. This controller is referred to the PLC.

The PLC (Programmable Logic Controller) is a CONTROLLER which can be re-program back.

If the PLC is only a stand-alone and not combined with other PLCs, it is called as DDC. It means

PLC is a sub system of a large system called DCS.

DCS is not a large PLC. Because system architecture of DCS and PLC are different. DCS is not PLCs that integrated into one large system. "Controller" in the PLC is more

intended as a "Logic Controller", while Controller in the DCS is more intended as a

"Process Controller".

Both DCS and PLC is a configurable and reconfigurable.
http://program-plc.blogspot.com/http://program-plc.blogspot.com/


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8.MEASUREMENT OF TEMPERATURE

8.1 INTRODUCTION:

Temperature is arguably the one physical variable in science to which man is most

sensitive. Websters defines temperature as the degree of hotness or coldness measured on

a definite scale. It is sometimes more convient to think of temperature as the level of

thermal energy. It is similar to voltage as a measure of electrical energy. Temperature is

the driving force for heat flow much the way voltage is the driving force for the flow

of electricity.

8.2 PRIMARY AND SECONDARY THEROMOMETERS:

Thermometers can be divided into two separate groups according to the level of

knowledge about the physical basis of the underlying thermodynamic laws and quantities. For

primary thermometers the measured property of matter is known so well that temperature

can be calculated without any unknown quantities. Examples of these are thermometers

based on the equation of state of a gas, on the velocity of sound in a gas, on the thermal

noise of an electrical resistor, on blackbody radiation, and on the angular anisotropy of

gamma ray emission of certain radioactive nuclei in a magnetic field. Primary thermometers

are relatively complex.

Secondary thermometers are most widely used because of their convenience. Also,

they are often much more sensitive than primary ones. For secondary thermometers knowledge

of the measured property is not sufficient to allow direct calculation of temperature. They

have to be calibrated against a primary thermometer at least at one temperature or at a

number of fixed temperatures. Such fixed points, for example, triple points and

superconducting transitions, occur reproducibly at the same temperature.

8.3 CALIBRATION:

Thermometers can be calibrated either by comparing them with other

calibrated thermometers or by checking them against known fixed points on the


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temperature scale. The best known of these fixed points are the melting and boiling

points of pure water.

The traditional method of putting a scale on a liquid-in-glass or liquid-in-metal

thermometer was in three in stages:

Immerse the sensing portion in a stirred mixture of pure ice and water at 1Standard atmosphere and mark the point indicated when it had come to

thermal equilibrium.

Immerse the sensing portion in a steam bath at 1 Standard atmosphere andagain mark the point indicated.

Divide the distance between these marks into equal portions according to thetemperature scale being used.

Other fixed points were used in the past are the body temperature (of a healthy

adult male) which was originally used by Fahrenheit as his upper fixed point (96

F (36 C) to be a number divisible by 12) and the lowest temperature given by a mixture

of salt and ice, which was originally the definition of 0 F (18 C).As body temperature

varies, the Fahrenheit scale was later changed to use an upper fixed point of boiling

water at 212 F (100 C).

These have now been replaced by the defining points in the International

Temperature Scale of 1990, though in practice the melting point of water is more

commonly used than its triple point, the latter being more difficult to manage and thus

restricted to critical standard measurement. Now a days manufacturers will often use a

thermostat bath or solid block where the temperature is held constant relative to a

calibrated thermometer. Other thermometers to be calibrated are put into the same bath or

block and allowed to come to equilibrium, then the scale marked, or any deviation from

the instrument scale recorded .For many modern devices calibration will be stating some

value to be used in processing an electronic signal to convert it to a temperature.


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8.3.1 SELECTING A CALIBRATION SYSTEM:

Before selecting equipment for a calibration system, it is important to have a clear

idea of what results are expected. The object should provide the greatest return on

investment by selecting the equipment which will satisfy the need. The following points

should be considered.

Size and type of devices to be calibrated. Total number of frequency of calibrations. Temperature range. Accuracy requirements.

Speed and convenience of changing temperature.

Speed and convenience of measuring bath temperature.

8.4 THERMOCOUPLE:

A thermocouple is a thermo-electric temperature-measuring device .It is formed by

welding, soldering, or merely pressing two dissimilar metals together in series to produce

a thermal electromotive force(E), when the junctions are at different temperatures.

8.4.1 THEORY OF THERMOCOUPLES:

Any junction of dissimilar metals will produce an electric potential related to

temperature. Thermocouples for practical measurement of temperature are junctions of

specific alloys which have a predictable and repeatable relationship between temperature

and voltage. Different alloys are used for different temperature ranges. Properties such as

resistance to corrosion may also be important when choosing a type of thermocouple.

Where the measurement point is far from the measuring instrument, the intermediate

connection can be made by extension wires which are less costly than the materials used

to make the sensor.


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8.4.2 Different Thermocouple Types:

A thermocouple is available in different combinations of metals or calibrations.

The four most common calibrations are J, K, T and E. There are high temperature calibrations R,

S, C and GB. Each calibration has a different temperature range and environment, althoughthe maximum temperature varies with the diameter of the wire used in thermocouple.

Although the thermocouple calibration dictates the temperature range, the maximum range

is also limited by the diameter of the thermocouple wire.

8.4.3 How to Choose a Thermocouple Type?

Because a thermocouple measures in wide temperature ranges and can be relatively

rugged, thermocouples are very often used in industry. The following criteria are used in

selecting a thermocouple:

Temperature range Chemical resistance of the thermocouple or sheath material Abrasion and vibration resistance Installation requirements

Fig.4: practical circuit of thermocouple
http://en.wikipedia.org/wiki/File:Thermocouple_circuit.svg


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This phenomenon of generating EMFs is governed by the Peltier, Thomson and

Setback effects each producing EMFs in the thermoelectric circuit.

The Peltier and Thomson effects are heat-transport effects associated with electric

current. They describe the interchange between thermal and electric energy.

8.4.4 BIMETALLIC THERMOMETERS:

The bimetallic thermometer is based on two simple principles. First that metals change

in volume in response to a change in temperature and, secondly, the coefficient of change

is different for all metals strips are bonded together and then heated the resultant strip to

bend in the direction of the metal with the lower coefficient of expansion. The degree of

deflection is proportional to the change in temperature.

Since the amount of movement is typically rather small it is amplified by using a

long strip of material wound into a helix or a spiral. One end of the spiral is immersed

in the medium to be measured and the other end is attached to a pointer. The bimetallic

thermometer may be rugged to actuate a recorder pen. The bimetallic thermometer offers

the advantage of being much more resistant to breakage than the glass thermometer. It is

however, subject is not as the glass thermometer.

8.5 FILLED THERMAL ELEMENTS:The filled thermal element consists of a bulb connected to a small capillary,

which is connected to an appropriate indicating device. The system acts as a transducer,

which in turn is converted to temperature by use of an appropriate 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 are

provided by the filled thermal element are sufficient for many industrial-monitoring

applications. Since the unit is self-contained and needs no power it is naturally explosion

proof. On the down side the bulbs are usually much larger than that of a thermocouple

or RTD. Also repair must typically be done at the manufacturers facility.


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8.6 QUARTZ CRYSTAL THERMOMETERS:

Measurement of temperature deviations in the 103

to 106C range has been made,

using a specially designed 5Mc quartz crystal unit. The crystal unit consists of a 5 Ycut

crystal plate in a glass bulb. The oscillator is a Piercetype transistor circuit similar to

those presently in use in ground station frequency standards. The crystal units have a

temperaturefrequency coefficient of approximately 80 parts per 106C. The crystal Q is of

the order of 3 million, and the oscillator has a short time stability of 3 pp 1010

, giving a

temperature sensitivity of 3.8106

C for periods of the order of 10 sec. To measure

temperature deviations of a few micro degrees requires the ability to measure frequency

deviations of a few parts in 1010

. However, to measure temperature deviations of a few

tenths of a milli degree, it is necessary only to measure frequency deviations of a few

parts in 108.

8.7 RADIATION PYROMETRY:

Radiation pyrometers infer temperature by collecting the thermal radiation from an

object and focusing it on a sensor. The sensor or detector is typically a photon detector,

which produces an output as the radiant energy striking it releases electrical charges.

The advantage of the radiation pyrometery method is that they produce a stable

non-contact output signal. This is of particular usefulness when working with very highprocess temperatures where conventional sensing elements would have very short life

spans. They are also useful in applications where the temperature of a continuously

moving sheet of material must be monitored. Radiation pyrometers can be very

susceptible to ambient temperature fluctuations and often require special installation or

water-cooling to maintain a constant ambient.

8.8 THERMISTORS:

Thermistor is a type of resistor whose resistance varies significantly with

temperature, more than in standard resistors. The word is a portmanteau of thermal and

resistor. Thermistors are widely used as inrush current limiters, temperature sensors, self-

resetting over current protectors, and self-regulating heating elements.


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Thermistors differ from resistance temperature detectors(RTD) in that the material

used in a thermistor is generally a ceramic or polmer, while RTDs use pure metals. The

temperature response is also different. RTDs are useful over larger temperature ranges, while

thermistors typically achieve a higher precision within a limited temperature range.

Thermistor symbol

Assuming, as a first approximation that the relationship between resistance and

temperature is linear, then:

R kT

Where

R = change in resistance

T= change in temperature

k= first-order temperature coefficient of resistance

Thermistors can be classified into two types, depending on the sign of k. If k is

positive, the resistance increases with increasing temperature, and the device is called apositive temperature coefficient(PTC) Thermistor or posistor. If k is negative, the

resistance decreases with increasing temperature, and the device is called a negative

temperature coefficient(NTC) thermistor. Resistors that are not Thermistor are designed to

have a k as close to zero as possible so that their resistance remains nearly constant

over a wide temperature range.

Instead of the temperature coefficient k, sometimes the temperature coefficient of

resistance (alpha) or T is used. It is defined as


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8.9 RESISTANCE TEMPERATURE DETECTORS:

The same year that Seebeck made his discovery, Sir Humphrey Davy announced

that the resistivity of metals showed marked temperature dependence. In 1871 Sir

William Siemens suggested the use of platinum in a resistance thermometer.

Resistance thermometers also called resistance detectors or resistive thermal

devices 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(PRTs). They are slowly

replacing the use of thermocouples in many industrial applications below 600 C, due to

higher accuracy and repeatability.

Rt =Ro[1+(t-to)]

Where:

Rt= resistance of temperature T

Ro= resistance of standard temperature To

= temperature coefficient ofresistance

Nickel offers the best sensitivity or change in resistance for a change in

temperature. Because platinum is a noble metal, it offers the greatest stability and largest

temperature range of the RTD metals. Its good linearity combined with the high

repeatability and stability make platinum the most widely used metal for RTDs.

To achieve an accurate R vs T curve and equation over the wide temperature

range can be a complex procedure, the equation must contain variables that will account

for variations in nominal resistance as specific temperature as well variations due to the

effect of strain and impurities. For example the Calender-Van Dusen equation is

commonly used in industry to define the R vs T relationship for platinum between 183C

and +630C.


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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.

8.9.1 IMMERSION RTDS:

As the name suggests, immersion RTDs are meant to allow a sensing element to be

immersed in media to measure its temperature. Various threaded to flange-mounted

fittings area available to support such installation. The primary components of an

immersion RTD are:

Sensing element Protective sheath or shield Threaded or flange mount Housing Electrical connector

8.9.2 SURFACE-MOUNTED RTDS:

In a number of applications surface mounting of the sensing device is

the most efficient or convenient installation method. Be aware that for surface

measurement , conditions such as sensor insulation and lead wire conduction should be

investigated to ensure an accurate measurement.

8.9.3 PLATINUM RTD:

It is also known as PtRTD, platinum RTDs are typically the most linear, stable,

repeatable, and accurate of all RTDs.Platinum wire was choosen by OMEGA because it

best meets the need of precision thermometry.

8.9.4 THIN FILM RTD:

Thin film RTDs are made up of a thin layer of a base metal embedded into a

ceramic substrate and trimmed to produce the desired resistance value. OMEGA RTDs


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are made by depositing platinum as a film on a substrate and then capsulating both. This

method allows for the production of small, fast response, accurate sensors. Thin film

elements conform to the European curve.

8.10 SENSING ELEMENTS:

The heart of an RTD is the sensing element. The most basic configuration for an

RTD sensing element suitable for practical application. The small diameter wire element

is wound in a baffler manner onto a cylindrical mandrel, usually made of ceramic. Lead

wires run axially through the mandrel and are connected to the element wire. The

mandrel assembly is usually covered with a coating or glaze to protect the element wire.

RTD sensing element design considers several factors that affect accuracy. For example,

in RTDs the sensing element materials should have thermal expansion properties as similar

to platinum as possible.

8.11 SIGNALLING CONDITION NECESSARY FOR TEMPERATURE

MEASUREMENTS:

To make accurate and reliable temperature measurements, signal conditioning is required. In

designing the right measurements system for your temperature sensor, you should consider,

8.11.1 AMPLIFICATION:

Output signals from temperature sensors are typically in the millivolt range, so you

should amplify the signal and take care to prevent noise in your measurement system.

Choose a gain that optimizes the input limits of the analog-to-digital converter (ADC) in

your hardware. To improve the noise performance of your system, you can amplify the

low-level voltages near the signal source or measurement point.

8.11.2 ISOLATION:

Thermocouples being mounted on or soldered directly to a conductive material,

such as steel or water, introduce another source of noise. This configuration makes

thermocouples particularly susceptible to common-mode voltage and ground loops. Isolation


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helps to prevent ground loops and can dramatically improve the rejection of common-

mode voltage. With conductive material that has a large common-mode voltage, isolation

is required because non isolated amplifiers cannot measure signals with large common-

mode voltages.

8.11.3 FILTERING:

Lowpass filters are commonly used to effectively eliminate high-frequency noise in

temperature measurements. For example, lowpass filters are useful for removing the 60 Hz

power line noise that is prevalent in many laboratory and plant settings.

8.11.4 EXCITATION:

Because resistance temperature detectors (RTDs) and thermistors are resistive

devices, you must supply them with an excitation current and then read the voltage across

their terminals. If extra heat cannot be dissipated, heating caused by the excitation current

can raise the temperature of the sensing element above that of the ambient temperature.

Self-heating actually changes the resistance of the RTD or thermistor, causing error in the

measurement. You can minimize the effects of self-heating by supplying lower excitation

current.

8.11.5 ACCURACY AND RESOLUTION:

In selecting the right sensor and data acquisition hardware, you must know the

accuracy and resolution requirements for your application. Though filtering and

amplification can dramatically improve the accuracy of thermocouple measurements, RTDs

and thermistors are known to yield more accurate readings. In addition to sensor

considerations, you should match the required accuracy and resolution for your application

to the data acquisition and signal conditioning hardware that you select.


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9.MEASUREMENT OF PRESSUREGravity dependent and independent units of force and pressure are given. The concepts of

liquid head, static pressure and various other pressure definitions are intorduced. Important

manometer types are surveyed and the essential principles of operations are explained.

9.1 SECONDARY ELEMENTS:

Bellows, metallic diaphram, force-balance, bourdon spring are compared to modern

electronic versions. The important principles of pressure transmitter selection are outlined and

reinforced by the space study, calibration of transmitters is out lined.

9.2 MANOMETERS:

The U tube is the easiest to manufacture and most widely used type. Measurements aretaken from the topmost point of the curved surface(meniscus) of hg and the lowest point

of H2O

The well manometer amplifies the smaller level moment in the larger reservoir by using anarrower scaled tube. This increases sensitivity of measurements in the ratio of the areas

of the tubes.

In the inclined manometer, the inclined leg further amplifies the small level fluctuationsof larger well by the sine of the angle of inclination. The narrower tube can be

parabolically curved to extract the square root and rear flow rate directly. Often dyed oil

issued in these devices and detergent is added to reduce frictional effects with the glass.

The instrument is supplied with the quoted specific gravity of the oil is used.

The mercury float manometer uses metallic displaces, which floats in mercury. Thepointer, passes through the gland and indicate against the scale.

The bell type manometer is used expensively in industry to measure low pressure, with arange of generally from 2-20cm of water. With proper design to minimize friction this

gauge can be made responsive to the smallest pressure variations normally encountered in

industry, except for those measurements which might be termed high vaccum.


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Figure 6

With the design of bell type instrument, most of the bell will be out of liquid when the

differential pressure is zero. Increasing the differential will then force the bell down against the

action of spring and the lower pressure. Whether the pressure forces the bell ups and down is of

no concern is studying the characterstics of this type of instrument.

9.3 RING BALANCE TYPE:

This type of instrument is frequently used for the measurement of low differential

pressure of the order of a few inches of water gauge. The essential portion of this instrument

consists of a hollow ring of circular section, partitioned at its upper part and partially filled with a

liquid in order to form two pressure measuring chambers. The body of the ring is supported at its

centre by knife edging resting on a bearing surface, or by roller bearing or ball bearings. The

force which operates the instrument is due to the difference between the pressures on the two

sides of the partition. This ring will therefore rotate in a counterclockwise direction.


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Figure 7

9.4 MEASURING DIFFERENTIAL PRESSURE:

Differential head type flow meters are the most economical of all the flow rates devices.

They perform well with both liquids and gases. A great deal of data and experience are available

to support their position. Their major limitations are difficulty in reading low flow rates, a square

root relationship in read out and inability to cope with certain types of fluids. Some difficulties

can overcome by other types of flow meters, such as the magnetic flow meter. As the picture

shows, the effect of the measured pressure is to increase the height of a column of material above

its equilibrium state. The difference in the pressure between process and reference is proportional

to the height of the fluid supported.

9.5 MEASURABLE PRESSURES:

Absolute Pressures Atmospheric Pressure Barometric Pressure Differential Pressure


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Gauge Pressure Hydrostatic Pressure Static Pressure Vaccum Working Pressure Dynamic Pressure Compound Pressure

9.6 GENERAL PRINCIPLE OF MEASUREMENT:

The measurement of pressure is considered the basic process variable in that it is utilized

for measurement of flow and even temperature. All pressures measurement systems consist of

two basic parts, a primary element which is contact, directly or indirectly with the pressure

medium and interacts with pressure changes and a secondary element which translates this

interaction into appropriate values for use in indicating, recording and/or controlling.

9.7 MECHANICAL TRANSDUCERS:

9.7.1 BELLOWS: A metallic bellows is a series of circular parts so firmed or joined that

they can 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 practical limitations of material

selection usually limit the bellows to measurements from 0.5 to 70psi by increasing the diameter

of the bellows force, pressures as low as 0.06psi can be measured.

9.7.2 BOURDON TUBES: The original patent described it as a curved or twisted tube

whose cross section isnt circular. The application of internal pressure causes the tube to un wind

or straighten out. The movement of the free end is transmitted to a pointer or other indicatingelement. Phosphor bronze, beryllium copper, steel, chrome alloy and stainless steel are

commonly used. Indeed they are the most widely used type of pressure gauge. The pressure

gauge can be filled with oil to limit the damage caused by variation.


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9.7.3 METTALIC DIAPHRAGM: Gauges employing diaphragm give a better and more

positive indication than the bourdon type of gauge for low pressure ranges. The principle

employed simply requires that the deformed middle section of the diaphragm push against and

deflect a pointer on a scale. The aneroid barometer is an example of such a system

9.7.4 FORCE BALANCE: Force balance pressure transmitters are closed loop feedback

devices. In a force balance unit, pressure displays an element. The amount of displacement is

detected and the element is returned to null or zero displacement position by restoring force

which can be pneumatic.

Force balance type transmitters have been around for a long time and are familiar to

many users. They are rugged and work well with high pressures. But they are big and can be

sensitive to vibration and temperature. In a situation above a force balance principle is employed

to generate a pneumatic signal proportional to the diaphragm deformation 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.


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10. MEASUREMENT OF LEVEL

In many industrial processes it is very important to know the level of liquid in a tank or

vessel. The need for an instrument to indicate this probably arose with the invention of the steam

engine. It is essential to know the level of the water in the boiler while it is in use and under

pressure but it is impossible to view it directly. Industrial methods of determining level can be

divided into two groups.

Level measurement is one of the oldest measurements. The measurement of industrial process

level parameters is of great importance in the industrial field. The level of liquids may affect

both the pressure and the rate of flow in and out of the tank or vessel, hence the quality may be

effected. In this, we will be discussing about different methods of level measurement.

In the first group, the level if the liquid is measured directly by means of a hook type level

indicator, a sight glass, or float-actuated mechanism. In the second group, use is made of the

fact that the pressure due to a column, but only upon the depth and density. Thus, if the pressure

due to the column of liquid doesnt depend on the cross sectional area of the column, but not

only on the depth and the density. Thus, if the pressure due to a column of liquid of known

density is known density is measured, then its depth may be calculated. The pressure may be

measured directly, by balancing it against a mercury column.

It may be measured by means of a gauge using some form of diaphragm of elastic pressure

element, or some form of gas or liquid purge system is used when a fluid pressure equal to that

of a column of liquid has to be measured in this second group may be included weighing tubes

and buoyancy types.

Methods of Liquid Level Measurement:

Generally there are two methods used in industries for measuring liquid level. There are:

direct methods indirect method


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DIRECT METHOD:

This is simplest method of measuring liquid level. In this method, the level of the liquid is

measured directly by means of following level indicators:

hook type level indicator sight glass float type

10.1HOOK TYPE LEVEL INDICATOR:

When the level of liquid in an open tank is measured directly on a scale,it is sometimes difficult

to read the level accurately because of parallax error. In this case a hook type of level indicator is

used.

10.1.1 Construction:

Hook type level indicator consists of a wire of corrosion resisting alloy about in diameter, bent

into u shape with longer than the other, as shown. The shorter arm is pointed with a 60 degrees

taper, while the longer one is attached to a slider having a vernier scale, which moves over the

main scale and indicates the level.

Fig 8: Hook-type level indicator


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10.1.2 Working:

Here the hook is pushed below the surface of the liquid whose level is to be measured and

gradually increased until the point is just about to break through the surface. It is then clamped,

and the level is read on the scale. This principle is further used in measuring point nanometer inwhich the measuring point consists of steel point fixed upwards underneath the water surface. an

eye piece is fixed to view this point at 45 degrees under the water so that in addition to the point

being seen, the image of the point by total internal reflection is also seen, as shown in the figure.

Now, the water level is adjusted until the tip of the image touches tip of the point and the level is

read on the scale. Since the point is always under water, the trouble due to the surface tension,

when the point is above the water, is not experienced.

10.2 SIGHT GLASS:

This is also called as gauge glass. This is another method of liquid level measurement. It is used

for continuous indication of liquid level within the tank or vessel.

10.2.1 Construction and working:

A sight glass instrument consists of a graduated tube of toughened glass which is

connected to the interior of the tank at the bottom in which the water level is required. This

figure shows a simple sight glass for open tank in which the liquid level in the sight glass

matches the level of liquid in the tank. As the level of liquid in the tank rises and falls, the level

in the sight glass also rises and falls accordingly. Thus by measuring the level in the sight glass,

level of liquid in the tank is measured. In the sight glass, it is not necessary to use the same liquid

as in the tank. Any other desired liquid also can be used.

Fig 9: Sight glass for an open task


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When it is desired to measure a liquid level with the liquid under the pressure or vaccum

,the sight glass must be connected to the tank at the top as well as at the bottom ,otherwise the

pressure difference between the tank and the sight glass would cause false reading.

in this case, the glass tube is enclosed in a protective housing ,and two valves areprovided for isolating the gauge from the tank in the case of breakage of the sight glass .the

smaller valve at the bottom is provided for blowing out the gauge for cleaning purposes. In the

figure it shows a high pressure sight glass in which measurement is made by reading the

position of the liquid level on the calibrated scale. This is type of sight glass in high pressure

tanks is used with appropriate safety precautions. The glass tube must have a small inside

diameter and the thick wall.

Fig 10: High Pressure sight glass

10.2.2 Advantages:

Direct reading is possible. Glassless designs are available in numerous materials for corrision resistance.

10.2.3 Disadvantages:

It is read only where the tank is located, which is not always convenient. Accuracy and readability depend on the cleanliness of the glass and fluid.


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10.3 Float type level indicator:

Float operated level indicator is used to measure liquid levels in a tank in which a float rests on

the surface of liquid and follows the changing level of the liquid. The movement of the float is

transmitted to a transmitted to a pointer through a suitable mechanism which indicates the levelon a calibrated scale. Various types of floats are used such as hollow metal spheres, Cylindrical -

-shaped floats and disc shaped floats.

10.3.1 Construction and working:

This figure shows the simplest form of float operated mechanism for the continuous

liquid level measurement. In this case, the movement of the float is transmitted to the pointer by

stainless steel or phosphor-bronze flexible cable wound around a pulley, and pointer indicates

liquid level in the tank. The float is made of corrosion resisting material and rests on liquid level

surface between two girds to avoid error due to turbulence. With this type of instrument liquid

level from 1/2ft to 60 ft can be easily measured.

Fig 11 : Float operated liquid level indicator

With the float operated of mechanism, the liquid level can be transmitted to a distant place using

a hydraulic transmission system, as shown in the figure.


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10.3.2 Advantages:

It is possible to read the liquid levels in the tank from the ground level even if the tank iskept empty below the round level.

It cost is low and has reliable designs.

It operates over a large temperature range.10.3.3 Disadvantages:

They are normally limited to moderate

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