zinc report
TRANSCRIPT
COLLEGE OF TECHNOLOGY & ENGINEERING UDAIPUR
M A HA R A N A P R A TA P U N I V E R S I TY O F A G R I C U L T U R E & T E C H N O L O G Y , (R A j.)
A
Training
Report
at
Hindustan Zinc Ltd., Debari
Duration: 1th June to 30th June 2010
Submitted To: Submitted By:Dr. Navneet Agrawal Dinesh kumar salvi Training Incharge III year ECE
D E P A R T M E N T O F E L E C T R O N I C S & C O M M U N I C A T I O N E N G I N E E R I N G
Acknowledgement
Main aim of this practical training is to get practical knowledge about the working of an industry and use of modern engineering in it. Training makes us to know how the knowledge from book is applied to practical life. During my schedule in H.Z.L., Debari, I got an opportunity to know about the working condition in plant and got more knowledge about my branch of study.
Behind completion of this training, some persons played a key role directly or indirectly.
So I would like to thank those persons without whose contribution this work proves too much for me.
I express my deep regards and gratitude to honorable “Mr.Navneet Agrawal”
Head of Training and Placement Department for suggesting the advice, keen interest, and constant boost up, invaluable guidance.
I am grateful to “Mr.B.P.Kant” working at HZL, Debari. for giving me guidance,
kind support and mental preparation for training report. I am thankful and grateful to “Mr.P.K.JAIN” Sr.Manager (HRDC) at H.Z.L., Debari
(RAJ.) for giving me chance of training at their prestigious industry, which will be helpful in my progress toward bright future.
I am also helpful to the executive staff, technical and non-technical staff of H.Z.L. for
extending their kind support, information and practical knowledge during my four-week practical training at their unit H.Z.L., Debari, Udaipur.
Dinesh kumar salvi
III year ECE
Preface
Practical training is a way to implement theoretical knowledge to practical use. To become a successful engineer it is necessary to have a sound practical knowledge because it is the only way by which one can acquire proficiency & skill to work successfully in different industries. It is proven fact that bookish knowledge is not sufficient because things are not as ideal in practical field as they should be.
Hindustan Zinc Ltd. is one of the best examples to understand the production process & productivity in particular of Zinc.
It is a matter of great pleasure that our college authorities have recommended a practical training of 30 days to supplement our theoretical knowledge acquired in the college.
This report is an attempt made to study the overall production system & related action of Zinc Smelter, Debari a unit a HZL. It is engaged in the production of high grade Zinc metal & other byproducts viz. Cd, Sulphuric acid etc. since 1968 adopting hydro metallurgical technology. Dinesh kumar salvi
III year ECE
INDEX
S.NO. TOPIC PG. NO.
1. Introduction 5
Safety department 9
Roster plant 11
Acid plant 15
Leaching & Purification plant 17
Residue Treatment plant 20
Zinc dust plant 20
Zinc Electrolysis & Melting 21
Central Workshop 22
2. STUDY OF LEVEL RADAR TRANSMITTER 23
RADAR 25
APPLICATION OF RADAR 28
MEASURING PRINCIPLE 34
ADVANTAGES AND DISADVANTAGES 42
CONCLUSION 43
BIBLIOGRAPHY 44
IntroductionHindustan Zinc Limited (HZL):
One of the India’s leading Zinc Producers and exceptional in its extent of this technological
complete with vertical integration IN other non-ferrous metals.
HZL was incorporation on 10th February 1968 as a public sector company after the take
over of the Erstwhile Metal Corporation of India. It was expanded on December 1976 and later on
April 1985. The foundation stone of this company is being kept by Shri Manu Bhai Shah Minister
of Industry on 26 June 1962.
HZL operations are broad lend based & its activities range from exploration, mining & are
processing to smelting and refining of Pb, Zn, Cd, Co, Cu & other precious metals. It also produces
sulphuric acid and rock phosphate.
Total plant area is 200.3 Hectare of HZL, Debari. Total Zinc production of Hindustan Zinc
is 73206Tonnes per Annum and major suppliers of HZL are Finland, Sweden and Germany.
1.Overview
Name & Location : Debari Zinc Smelter,
Village Debari ,
Udaipur (Rajasthan)
Age : Feb.1968 (40 years)
Expanded Dec.,1976
April 1985 & Dec.2000
Process : Hydrometallurgy
Covered Area (Ha) : 22.65
Total Plant Area (Ha) : 126
Zinc Smelter Debari is hydrometallurgical smelter producing high grade Zinc metal and other by
products like Cd and Sulphuric Acid since 1968.
1. Operating Capacity:
Zn : 80,000MT
Acid : 130,000MT
Cd : 250MT
Zinc dust : 360MT
2. Work force: 876 Nos.
Central Workshop Managerial & Engineering Staff : 84 Nos
Supervisory & Technical Staff : 58 Nos.
Labour : 729 Nos.
(a) Skilled : 154Nos.
(b) Semi-Skilled : 555Nos.
(c) Unskilled : 250Nos.
3. Raw Material Supplies:-
(a) Zawar Mines
(b) Agucha Mines
(c) Rajpura Dariba Mines
4. Product Buyers:-
(a) Tata
(b) Bhel
(c) Steel Companies
5. Steps of process:-
(6) Maximum Power Demand: - 38-40MW
(7) Process Collaborators:-
1. Krebs Penorrova, France:-
Leaching, Purification, Electrolysis
Mining
Roasting
Leaching
Electrolysis
Melting
Zinc Ingots
2. Lurgi, GMBH, and Germany:-
Roaster and gas clearing
3. Auto Kumpu, Finland:-
RTP, Wartsila Plant
4. I.S.C., ALLOY, U.K.:-
Zinc dust plant, Allen Power Plant
2. Properties of Zinc (metallic) at 293K :
1. Density : 7140Kg./m3
2. Melting Point : 693K
3. Specific Latent Heat of Fusion : 10 J/ Kg
4. Specific heat capacity : 385 J/Kg/K
5. Linear expansivity : 31/K
6. Thermal conductivity : 111 W/m/k
7. Electric Sensitivity : 5.9 ohm –meter
8. Temp. Coefficient of resistance : 40/k
9. Tensile Strength : 150 Mpa
10. Elongation : 50%
11. Young’ modulus : 110 Gpa
12. Passion’s Ratio : 0.25
3. Applications of Zinc:
Galvanizing: It is one of the best forms of protection against corrosion, used extensively in
building, construction, infrastructure, household appliances, automobiles, steel furniture, etc.
Zinc Oxide: Most widely used zinc compound, zinc oxide is used in the vulcanization of rubber,
as well as in ceramics, paints, animal feed and pharmaceuticals, and many other products and
processes. A special grade of zinc oxide has long been used in photocopiers.
Zinc Die Castings: Zinc is an ideal material for die casting and is extensively used in hardware,
electrical equipments, automotive and electronic components.
Rolled Zinc: Zinc sheet is used extensively in the building industry for roofing, flashing and
weathering applications. Zinc sheet is also used in graphic art to make plates and blocks, as well as
battery callots and coinage.
Alloys: Zinc is extensively used in making alloys such as brass, an alloy of copper & zinc.
4. Safety Department:
Safety is a degree of control over hazards. Workers working in the factory are exposed to all sorts
of dangers so some personal protective equipment are available to protect them head to toe such as-
1. Ear Muff
2. Dust Mask
3. Face Shield
4. Gas Mask
5. Gloves
6. Goggles
7. Helmets
8. Leg Guard
9. Respirators
10. Rubber Apron
11. Rubber Gum Boots
12. Safety Ball
13. Safety shoes
Factorizing the entire operation to safe sequence efficiency in carefully performing the work. For
the welfare of group in which the worker attached, you and your own protection of job. Accidents
are caused due to following reasons
1. Unsafe Condition
2. Unsafe Act
Unsafe Condition: Such condition includes leaking gases & unprotects able machines, not
furnace, professional hazard, occupational diseases prevailing in the industry.
Unsafe act: These accidents happen due to laziness and negligence of the rules while he is on duty.
General Rules and Safety
1. Be alert on work & do it in attention.
2. Working place path should be clean.
3. Always use safety belt while climbing up ladders.
4. Take help from skilled worker to start machine.
5. Waste dirt should not be scattered in Narrow Street.
6. Scattered thing stored in proper place.
7. Before eating meal, wash hands & clean nail.
8. While working in hot place put on asbestos gloves.
9. Don't store guiding wheel at moisturized place, don't use them at higher than rated speed.
10. Don’t pass beyond the chain block or come when heavy loading is being done.
5. Zinc smelting steps in Various plant:
5.1) ROASTER PLANT
This is the first department, where the treatment of zinc is being done. Zinc sulphide is carried on
conveyer belts to the furnace. Here zinc-sulphide is converted into zinc oxide or calcine. SO 2 is a
by product of the process which is further used for obtaining H2SO4 in the Acid Plant. SO2 is
harmful so it is recovered by the quenching tower, PGCT, WGT.
Procedure-
Zinc concentrate handling system consists of two Phases i.e. phase 1 and phase 2.
PHASE I- Concentrate comes from ZM and RAM.
These concentrate are Transported by trucks and dumpers from mines and all unloaded on surface
grizzly of under ground hopes. Series of belt conveyors Transfer the concentrate from under
ground hopper to blend storage yard. Unloading on different heaps is done with the help of triple
conveyor. The storage yard is divided into parts for ZM, RDM and RAM.
To avoid wind losses water is sprayed through sprayer or manually by using Hose pipes. This also
to maintain required moisture in concentrates. The water spraying is done manually whenever
needed.
PHASE 2-
Activities of phase 2 are as follows- Zinc Concentrates of different mines from storage yard are
charged in the underground hoppers (104A and 104B) in the required ratio with the help of Terex..
Mixing ratio is decided by availability of concentrate from different units. The criterion of mixing
is marinating Zinc and Sulphur Content min. 50% and 28% respectively. Also feed back from
reaching and electrolysis about cathode sheet quantity is taken into consideration. Zinc dross (from
Zinc melting section is also added along with concentrates in very little quantity.
The mixture of different concentrate (called blend) is transported to bins of Roaster- 1 and II and
with the help of series of belt conveyors and a vibrating screen which allows only under size
material to go bins.
Oversize materials is ground in a hammer Mill and charged back to 104 A and 104 B hoppers. An
electro magnet is provided on one of the Conveyors to attract and separate iron pieces, if any going
to bins. Water is also sprayed on 107 & 108 belt Conveyors to increase moisture is blend feed.
Minimum 8% moisture is maintained in blend feed. Sample is drawn from extraction belt and is
analyzed for moisture twice in a shift.
All operation of starting the conveyors is done by an operator deputed at control room of blend
yard.Zinc blend is taken from the blend bin through extraction belt to rotary table feeder and high
speed feed machine. Then blend is fed to fluidized bed roaster through furnace feed hole. Zinc
blend is roaster to produce Calcine and sulpher dioxide gas.
2Zns+3O2 2Zno+ 2So2+ heat
Air for roasting of Zinc blend supplied through roaster air blower continuously to roaster furnace
through nozzles. Calcine form furnace comes out through over flow, under flow, boiler, cyclones
and hot gas precipitator which is sent to reaching plant through screw conveyors is air cooled and
other conveyors are water cooled for cooling of calcine.
Hot gases with fine calcine particles coming from roaster furnace pass waste heat boiler in which
hot gases are cooled, and steam is produced by circulation of DM water in boiler tube bundles.
Extraction Belt
Rotary Table
Feed Machine
Roaster Furnace
Water heater boiler
Cyclone
HGP
Gas Scrubber
Star Cooler
Wet Esp. /EF I &II Stage
Hg. Removal Tower
Feed Bin
ID Fan
Calcine
Calcine
Calcine
Calcine
Air Blower
Sodium Silicate
Water is also circulated in furnace cooling coil installed in furnace hearth to maintain the desired
bed temperature.
Gases leaving waste heat boiler are passed through cyclone to remove the calcine particles and then
passed through hot gas precipitator to remove the fine particles of calcine by the application of
electric field.
Gases leaving the hot gas precipitator are passed through scrubbing tower to cool down. In
scrubbing tower spraying of water is done from top and gases entre from the bottom. Dust free
gases from the scrubbing tower are passed through star cooled for further cooling. The gases
leaving from star
cooler are passed
though electro filter
to remove the
miss completely.
Sodium silicate
dosing: - Sodium
silicate dosing is
done in scrubber
circulating
water to remove
fluoride from So2
bearing gases as per
following
reaction –
Na2 SiO3 + 6HF Na2
SiF6 + 3H2O
The dosing
system consists of a
sodium silicate
storage tank, dilution
tank, pump tank
and dosing pump (2Nos.). Dilute solution of 5% strength is prepared in dilution tank and dosing
sate is decided as per fluoride content in concentrate as per instruction of day Mgr (p)/ Mgr (p).
5.2) BOILER CIRCUIT
Boiler circuit is use to generate the steam using the heat which is dissipated from Roaster plant.
In Boiler, dematerialized water is use. This dematerialized water is supplied from DM. Plant.
Feeding of water in boiler is control and supplied by an electric/ turbo feed pump. Circulation of
boiler water is done by electric/turbo circulation pump through roaster furnace coil, boiler bundles
and bundles of guide pipe.
Block Diagram of Roaster and Gas Cleaning Plant
Figure: Block diagram of Roaster Plant
Excess steam in exported to leaching plant. In case of power failure or any emergency turbo
feed/turbo circulation pump may be run with the help of generated steam to feed the water in boiler
drum and water can be circulated in cooling coils and boiler bundles. In boiler water following
values are maintained.
Chemical i.e. sodium sulphite, trisodium phosphate caustic soda are prepared and injected in
Derator discharge through I dosing pump.
5.3) ACID PLANT:
Production of sulphuric acid in acid plant 1 and 2 is done.
Sulphuric acid thus produced is stored in acid storage tank labeled as A, B and C product sulphuric
acid is stored in acid storage tank D&E.
The acid is supplied to the leaching plant or in tanks A, B, C of acid plant No.2 through a transfer
pump of capacity 1000MT, 1000MT and 1500MT respectively. Finally gases are discharged
through chimney to atmosphere.
Standard Minimum Maximum
Ph 10.5 8.0 13.0
Alkalinity 200ppm - 500ppm
Hardness Nil - Nil
Chloride Nil - 50ppm
Sulphite 10ppm 5ppm -
Phosphate 20ppm 10ppm -
SO2 Bearing Gases
Drying Tower
SO2 Blower
Heat exchanger
I II Converter
IV III
Heat exchanger
Final absorption tower
Stack
Heat exchanger
IPAT
Acid storage tank
Figure: Block diagram of acid plant
Minimum 97% acid concentration is maintained in acid storage tanks. Acid of supply tank A, B &
C is analyzed and analysis is recorded in register No. ZSD/R&A/Reg.07. If any how the acid
concentration is found below 97% in any supply tanks, this acid is recycled back to acid circulation
tank to build up the concentration to 97% min. or raise the concentration by mixing with fresh
product acid of higher concentration or alternatively this acid is used for internal consumption in
leaching, RTP or DM plant
Pre-Heater:- The preheater is to generate flue gases heating the catalyst mass up to 365oc (min),
when starting the plant after shut down. Hot air is obtained by burning LDO with air in combustion
chamber of preheater.
LDO is supplied to the burner, where combustion takes place and air is heated. The air for
atomization and combustion is provided by combustion blower. Air for dilution is provided by
dilution blower. The hot air is passed through the tube of heat exchanger whereas the sulphur
dioxide bearing gases passes on shall side and get heated. The fuel gas is vented to atmosphere
through the stack.
5.4) LEACHING & PURIFICATION PLANT
Leaching is selective dissolution of ore minerals/oxides, alkalis or solution of other reagent
according to condition adjusted in a manner to leave max gangue in soluble residue. Calcine come
in hopper with the help of bucket elevator. From hopper calcine is coming to roller conveyor
through a rotatry valve. By adjusting speed of rotatry valve calcine rate can be increased or
decreased. The calcine if in excess can be stored in silos. The average rate of calcine consumption
is 11 MT/ hr., whereas rate of solution supplied is 90m3/hr. This corresponds to 140-150 MT of
Zinc ingots.
The department consists of following sections:
1. Neutral leaching
2. acid Leaching
3. Purification
4. Residual treatment plant
5. cadmium plant
NEUTRAL LEACHING:
The iron leached from fine particles of ZnO.Fe2O3 will be precipitated as hydroxides in neutral
medium according to equation.
Fe2(SO4)3+3ZnO+3H2O → 2Fe(OH)3+3ZnSO4
The Zn in calcine is present as:
ZnO - 81 to 83% ZnSO4 – 6 to 7 %
ZnS - 1 to 2% ZnOFe2O3 – 10%
In first stage of neutral leaching solution will be slightly acidic& PH is 2.8 to 3.2.So main equation:
MeO+ H2SO4 → MeSO4+H2O
Where Me→ Zn, Cu, Ni, Co, Mg, Pd.
The PH solution discharged after completion of leaching is 4.5 & at that PH acidity is negligible.
ACID LEACHING:
This is carried in carriers having capacity of 45 m3.The underflow from neutral leaching
containing dissolved ZnO & ZnO.Fe2CO3 is leached with spent electrolyte to PH of 2.8. Alternate
carriers are provided with heating coil through which steam is passed. Reaction time is 5 hr. most
soluble oxide go into solution. The overflow containing 30-40 GPL of Zn is sent to neutral
leaching. Underflow is pumped to two drum filters.
PURIFICATION:
Purification of Zinc sulphate is necessary as certain elements even if amounting to milligrams per
liter may cause:-
1. Hydrogen evolution and dissolution of Zinc by reducing impurities Fe++, Co, Ni, As etc.
2. Zinc is electro positive to ordinary metal like copper, iron, cadmium etc. therefore during
electrolysis these elements coil tends to deposit along with zinc, affecting the purity of the
final product and current efficient.
Principle:
Keeping temperature to 80 to 85 degree C, the clear overflow from the natural thickener is fed into
the purification stage. The purpose of this stage is to remove base metal impurities like copper,
cadmium, nickel etc. which are harmful to electrolysis of zinc. All these elements are removed by
precipitation with the help of Zinc dust. Zinc being placed higher then all the elements in the
electromechanical series of elements, displaces them from solution of sulphates as per the
following reaction:
Zn + MnSO4 ZnSO4 + Mppt
LeachingCalcine
Joaosite
Neutralization
Thickning
Acid leaching
Residual Treatment
Jarosite filteration
Purification
Purified neutralSolution
Cd recovery
Zerosite cake to ETP
Cd Pencil
U/F
O/f
U/F
U/F
Thickening
Figure: Process flow chart of Leaching plant
Also addition of antimony tratarte and copper sulphate speed up the rate of reaction to ensure
complete removal of impurities.
5.5) RESIDUE TREATMENT PLANT
The Zinc ferrite ZnO. Fe2O3 in the acid thickness under flow gets leached in the conversion and
simultaneously the leached iron is precipitated as Zerosite. Here the section is carried out in there
lead or brick line rectors of 300 meter cube capacity each, at a temperature of 95 to 100C. Some
amount of MnO2 is also added to take care of reducing impurities. In this operation Zinc ferrite is
precipitated as complex known as Zerosite.
The Zerosite slurry from this reaction is settled in the DORR with county current decantation.
Zerosite from the last thickener continues repulped and filtered again to recover water soluble Zinc.
The cake is subsequently repulped and pumped in ETP where it is neutralized to8ph and discarded
into lagoon . The over low from the DORR contains 80-100 GPL iron is send to neutral leaching.
5.6) ZINC DUST PLANT
The use of Zinc dust is for internal consumption, use in purification process to remove CuSO4,
CdSO4, CoSO4, NiSO4 in leaching plant.
The reaction follows as-
Zn + MeSO4→ ZnSO4 + Me↓
Due to higher electropositive element, the process of Zn dust involves the following:
1. Zn melting
2. Zn vaporization
3. Condensation
4. Production Technology
For Zn vaporization a voltage of 1000-11000C is created with the help of two electrodes, one at top
& other at base. It is filled with molten Zn.
For condensation N2 gas is being used. The N2 gas & five particles of Zn dust is being passed N2
gas is passed containing five particles of Zn dust.
The Zn dust is get at bottom. The body of condenser is made up of mild steel. The separate Zn dust
cyclone is being used. Again to separate Zn dust from N2 gas it is passed through a bag filter.
Production rate is about 6- 6.5MT/day. The pressure of N2 gas is about 600 cubic feet. The
consumption to produce 1 MT Zn dust is about 825 – 850 KW/hr.
5.7) ZINC ELECTROLYSIS & MELTING:
Electrolysis of ZnSO4 solution takes place in electrolysis cells with Al as cathode & Pb as anode.
The reaction can be represented as
ZnSO4→ Zn2+ + SO42-
SO4 + H2O→ H2SO4 + ½O2
Zn ions migrate towards the cathode and get deposited in form of sheets whereas O2 is given off at
anode. As SO2 ions, this results in formation of Sulphuric Acid. The oxygen is liberated oxides the
manganese sulphate in solution to MnO2 which deposit on the anode surface as anode mud which
is then cleaned out periodically.
5.8) SOLUTION COOLING & STORAGE
Neutral electrolyte form purification shall be available at 60 – 700C as hot purification process had
adopted for expansion the neutral solution is fed direct to atmospheric coolers where direct solution
is cooled to 850C. Two coolers have been provided for the purpose of which one would stand by.
The HZL has adopted “HAMON 50 BELEO” Belgion design for atmospheric coolers which are
being used in nos. of other plants in the world.
ZnSO4 solution that has to be cooled is taken through main feeder & it is distributed through
reinforced polyester pipes on which is stainless steel 316 spraying nozzles are fixed. Above this,
drift eliminated are arranged in two layers in form of layers of PVC waves. These waves,
assembled in panes are easily removable through top of coolers. The cooler is fitted with forced
draught fan fitted with FRP blades. The fan stock is also made up from FRP & stainless steel
grating provides protection to fan inlet. The fan is driven pulley & belt by two speed motors. These
coolers are used to reduce the temperature from 420C to 350C.
Electrolysis takes place in lead lines concrete cells which are connected electricity by means of Cu
bus bars in series parallel system for flow of current in existing cell house. The cells are arranged
in 40 rows. Each row has 6 cells with 27 Al cathode and 28 lead anodes. After expansion, each cell
will have its own feed system & its own independent discharge of electrolytes.
6. Central Workshop:
The Zinc smelter, Debari has a central workshop for securing & repairing of different mechanical
equipments such as pumps, fans, mechanical conveyors, hoists etc. The central workshop consists
of following shops:
1. Machine shop
2. Welding shop
3. Smiting shop
4. Wood shop
6.1) MACHINE SHOP :-
Machine shop is the biggest shop in all shops it consists of various machines. They are-
1. lathe machine
2. Drilling machine3. Slottering machine4. Shaper machine5. Punching machine
STUDY OF LEVEL RADAR TRANSMITTER
LEVEL SENSOR:
Level sensors detect the level of substances that flow, including liquids, slurries, granular
materials, and powders. Fluids and fluidized solids flow to become essentially level in their
containers (or other physical boundaries) because of gravity whereas most bulk solids pile
at an angle of repose to a peak. The substance to be measured can be inside a container or
can be in its natural form (e.g. a river or a lake). The level measurement can be either
continuous or point values. Continuous level sensors measure level within a specified range
and determine the exact amount of substance in a certain place, while point-level sensors
only indicate whether the substance is above or below the sensing point. Generally the
latter detect levels that are excessively high or low.
There are many physical and application variables that affect the selection of the optimal
level monitoring method for industrial and commercial processes. The selection criteria
include the physical: phase (liquid, solid or slurry), temperature, pressure or vacuum,
chemistry, dielectric constant of medium, density (specific gravity) of medium, agitation
(action), acoustical or electrical noise, vibration, mechanical shock, tank or bin size and
shape. Also important are the application constraints: price, accuracy, appearance, response
rate, ease of calibration or programming, physical size and mounting of the instrument,
monitoring or control of continuous or discrete (point) levels.
TRANSMITTER
A transmitter can be a separate piece of electronic equipment, or an electrical circuit within
another electronic device. A transmitter and receiver combined in one unit is called a
transceiver.
Fig.Antenna tower of Crystal Palace transmitter, London
The term transmitter is often abbreviated "XMTR" or "TX" in technical documents. The
purpose of most transmitters is radio communication of information over a distance. The
information is provided to the transmitter in the form of an electronic signal, such as an
audio (sound) signal from a microphone, a video (TV) signal from a TV camera, or in
wireless networking devices a digital signal from a computer. The transmitter combines the
information signal to be carried with the radio frequency signal which generates the radio
waves, which is often called the carrier. This process is called modulation. The information
can be added to the carrier in several different ways, in different types of transmitter. In an
amplitude modulation (AM) transmitter, the information is added to the radio signal by
varying its amplitude (strength). In a frequency modulation (FM) transmitter, it is added by
varying the radio signal's frequency slightly. Many other types of modulation are used.
RADAR
Radar is an object-detection system which uses electromagnetic waves—specifically radio
waves—to determine the range, altitude, direction, or speed of both moving and fixed
objects such as aircraft, ships, spacecraft, guided missiles, motor vehicles, weather
formations, and terrain. The radar dish, or antenna, transmits pulses of radio waves or
microwaves which bounce off any object in their path. The object returns a tiny part of the
wave's energy to a dish or antenna which is usually located at the same site as the
transmitter.
Fig. long-range radar
A long-range radar antenna, known as ALTAIR, used to detect and track space objects in
conjunction with ABM testing at the Ronald Reagan Test Site on Kwajalein Atoll.
Fig.Israeli military radar
Israeli military radar is typical of the type of radar used for air traffic control. The antenna
rotates at a steady rate, sweeping the local airspace with a narrow vertical fan-shaped beam,
to detect aircraft at all altitudes.
This Melbourne base Primary and secondary radar is used for air traffic control and
terminal area intrusion detection by local domestic aircraft.
APPLICATIONS OF RADAR
Fig. Commercial marine radar antenna
Commercial Marine Radar Antenna The rotating antenna radiates a vertical fan-shaped
beam. The information provided by radar includes the bearing and range (and therefore
position) of the object from the radar scanner. It is thus used in many different fields where
the need for such positioning is crucial. The first use of radar was for military purposes: to
locate air, ground and sea targets. This evolved in the civilian field into applications for
aircraft, ships, and roads.
In aviation, aircraft are equipped with radar devices that warn of obstacles in or
approaching their path and give accurate altitude readings. They can land in fog at airports
equipped with radar-assisted ground-controlled approach (GCA) systems, in which the
plane's flight is observed on radar screens while operators radio landing directions to the
pilot.
Marine radars are used to measure the bearing and distance of ships to prevent collision
with other ships, to navigate and to fix their position at sea when within range of shore or
other fixed references such as islands, buoys, and lightships. In port or in harbour, vessel
traffic service radar systems are used to monitor and regulate ship movements in busy
waters. Police forces use radar guns to monitor vehicle speeds on the roads.
Meteorologists use radar to monitor precipitation. It has become the primary tool for short-
term weather forecasting and to watch for severe weather such as thunderstorms, tornadoes,
winter storms, precipitation types, etc. Geologists use specialised ground-penetrating radars
to map the composition of the Earth's crust.
PRINCIPLES OF RADAR
A radar system has a transmitter that emits radio waves called radar signals in
predetermined directions. When these come into contact with an object they are usually
reflected and/or scattered in many directions. Radar signals are reflected especially well by
materials of considerable electrical conductivity—especially by most metals, by seawater,
by wet land, and by wetlands. Some of these make the use of radar altimeters possible. The
radar signals that are reflected back towards the transmitter are the desirable ones that make
radar work. If the object is moving either closer or farther away, there is a slight change in
the frequency of the radio waves, due to the Doppler effect.
Radar receivers are usually, but not always, in the same location as the transmitter.
Although the reflected radar signals captured by the receiving antenna are usually very
weak, these signals can be strengthened by the electronic amplifiers that all radar sets
contain. More sophisticated methods of signal processing are also nearly always used in
order to recover useful radar signals.
The weak absorption of radio waves by the medium through which it passes is what enables
radar sets to detect objects at relatively-long ranges—ranges at which other electromagnetic
wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly
attenuated. Such things as fog, clouds, rain, falling snow, and sleet that block visible light
are usually transparent to radio waves. Certain, specific radio frequencies that are absorbed
or scattered by water vapor, raindrops, or atmospheric gases (especially oxygen) are
avoided in designing radars except when detection of these is intended.
Finally, radar relies on its own transmissions, rather than light from the Sun or the Moon, or
from electromagnetic waves emitted by the objects themselves, such as infrared
wavelengths (heat). This process of directing artificial radio waves towards objects is called
illumination, regardless of the fact that radio waves are completely invisible to the human
eye or cameras.
RADAR SIGNAL PROCESSING
Distance measurement
Transit time
Pulse radar: The round-trip time for the radar pulse to get to the target and return is
measured. The distance is proportional to this time.
Fig. Continuous wave (CW) radar
One way to measure the distance to an object is to transmit a short pulse of radio signal
(electromagnetic radiation), and measure the time it takes for the reflection to return. The
distance is one-half the product of the round trip time (because the signal has to travel to
the target and then back to the receiver) and the speed of the signal. Since radio waves
travel at the speed of light (186,000 miles per second or 300,000,000 meters per second),
accurate distance measurement requires high-performance electronics.
In most cases, the receiver does not detect the return while the signal is being transmitted.
Through the use of a device called a duplexer, the radar switches between transmitting and
receiving at a predetermined rate. The minimum range is calculated by measuring the
length of the pulse multiplied by the speed of light, divided by two. In order to detect closer
targets one must use a shorter pulse length.
A similar effect imposes a maximum range as well. If the return from the target comes in
when the next pulse is being sent out, once again the receiver cannot tell the difference. In
order to maximize range, longer times between pulses should be used, referred to as a pulse
repetition time (PRT), or its reciprocal, pulse repetition frequency (PRF).These two effects
tend to be at odds with each other, and it is not easy to combine both good short range and
good long range in a single radar. This is because the short pulses needed for a good
minimum range broadcast have less total energy, making the returns much smaller and the
target harder to detect. This could be offset by using more pulses, but this would shorten the
maximum range again. So each radar uses a particular type of signal. Long-range radars
tend to use long pulses with long delays between them, and short range radars use smaller
pulses with less time between them. This pattern of pulses and pauses is known as the pulse
repetition frequency (or PRF), and is one of the main ways to characterize a radar. As
electronics have improved many radars now can change their PRF thereby changing their
range. The newest radars fire 2 pulses during one cell, one for short range 10 km / 6 miles
and a separate signal for longer ranges 100 km /60 miles.
The distance resolution and the characteristics of the received signal as compared to noise
depends heavily on the shape of the pulse. The pulse is often modulated to achieve better
performance using a technique known as pulse compression.
Distance may also be measured as a function of time. The radar mile is the amount of time
it takes for a radar pulse to travel one nautical mile, reflect off a target, and return to the
radar antenna. Since a nautical mile is defined as exactly 1,852 meters, then dividing this
distance by the speed of light (exactly 299,792,458 meters per second), and then
multiplying the result by 2 (round trip = twice the distance), yields a result of
approximately 12.36 microseconds in duration.
RADAR COMPONENTS
A transmitter that generates the radio signal with an oscillator such as a klystron or a
magnetron and controls its duration by a modulator.
A waveguide that links the transmitter and the antenna.
A duplexer that serves as a switch between the antenna and the transmitter or the
receiver for the signal when the antenna is used in both situations.
A receiver. Knowing the shape of the desired received signal (a pulse), an optimal
receiver can be designed using a matched filter.
An electronic section that controls all those devices and the antenna to perform the
radar scan ordered by a software.
A link to end users.
RADAR LEVEL TRANSMITTERS
INTRODUCTION
Radar technology is mainly put into use for detection of level in continuous level
measurement applications. Radar level transmitters provide non contact type of level
measurement in case of liquids in a metal tank. They make use of EM i.e. electromagnetic
waves usually in the microwave X-band range which is near about 10 GHz. Hence, they
can be also known as microwave level measurement devices. However there are some
differences between radar and microwave types. They are:
1. Power levels in case of radar systems are about 0.01 mW/cm2 whereas in case of
microwave systems, these levels range from 0.1 to 5 mW/cm2.
2. Microwaves can work at higher energy levels; hence they are competent enough to
endure extra coating as compared to radar level detectors.
A radar level detector basically includes:
A transmitter with an inbuilt solid-state oscillator
A radar antenna
A receiver along with a signal processor and an operator interface
The operation of all radar level detectors involves sending microwave beams emitted by a
sensor to the surface of liquid in a tank. The electromagnetic waves after hitting the fluids
surface returns back to the sensor which is mounted at the top of the tank or vessel. The
time taken by the signal to return back i.e. time of flight (TOF) is then determined to
measure the level of fluid in the tank.
MEASURING PRINCIPLE
Frequency Modulated Continuous Wave (FMCW)
A radar signal is emitted via an antenna, reflected on the product surface and received after
a time t. The radar principle used is FMCW (Frequency Modulated Continuous Wave). The
FMCW-radar transmits a high frequency signal whose frequency increases linearly during
the measurement phase (called the frequency sweep).
The signal is emitted, reflected on the measuring surface and received with a time delay, t.
Delay time, t=2d/c, where d is the distance to the product surface and c is the speed of light
in the gas above the product. For further signal processing the difference Δf is calculated
from the actual transmit frequency and the receive frequency.
The difference is directly proportional to the distance. A large frequency difference
corresponds to a large distance and vice versa. The frequency difference Δf is transformed
via a Fourier transformation (FFT) into a frequency spectrum and then the distance is
calculated from the spectrum. The level results from the difference between tank height and
measuring
TYPES OF RADAR LEVEL MEASUREMENT
SYSTEMS
Radar level measurement technology has been primarily classified into following two
systems:
1. Noninvasive or Non-contact Systems
2. Invasive or Contact Systems
NONINVASIVE SYSTEMS (THROUGH AIR)
Two types of noninvasive systems exist. One is the frequency-modulated continuous
wave i.e. FMCW technology and the other one is Pulsed radar technology.
FMCW systems
“From an electronic module on top of the tank, a sensor oscillator sends down a linear
frequency sweep, at a fixed bandwidth and sweep time. The reflected radar signal is
delayed in proportion to the distance to the level surface. Its frequency is different from that
of the transmitted signal, and the two signals blend into a new frequency proportional to
distance. This new frequency can then be used for accurate determination of fluid level.
The major benefit of employing FMCW technique for level measurement in a tank is that
the signals transmitted are frequency modulated i.e. FM instead of amplitude modulated i.e.
AM signals. Now, the major part of noise in a tank falls in the AM range which does
not influence the FM signals. Hence, FMCW happens to be the only system which can be
suitably used for meeting high accuracy requirements of tank gauging.
Pulsed radar systems
They are also referred to as pulsed time-of-flight systems. Their working principle is very
much like ultrasonic level transmitters. “Pulsed Wave systems emit a microwave burst
towards the process material. This burst is reflected by the surface of the material and
detected by the same sensor which now acts as a receiver. Level is inferred from the time of
flight (transmission to reception) of the microwave signal.”[2] The power range of pulse
radar systems is very less as compared to FMCW systems. Hence, their performance gets
largely influenced by tank obstructions and materials having low dielectric constants and
foams.
Antenna Designs
Radar antennas employed for noninvasive measurement systems are available in following
two major designs:
1. Parabolic dish antenna
2. Cone antenna
The figure below shows the schematic diagram of a parabolic dish antenna which has the
tendency to transmit the signals over a larger area and the cone antenna which
Usually restrict the signals in a very narrow region.
One can select among above two antenna designs depending upon the application
requirements and considering various factors like tank obstructions, presence of vapors or
foam, surface turbulence and other physical properties of the liquid being measured.
Size of the radar antenna also matters in deciding its suitability for a particular application.
If the diameter of the antenna is small, there will be higher beam divergence as well as
greater risk of undesirable wave reflections from tank obstructions. However, the
probability of directed wave going back to the sensor is greater in case of small antennas.
Also, the alignment of sensor is not very significant in small size antennas.
On the other hand antennas having larger diameters tend to produce a more focused and
strong signal since they cause smaller beam divergence. Besides, they are useful in
eliminating noise disturbances emerging from flat and horizontal metallic surfaces.
In some applications, the antennas installed at the top of the tank are totally sealed and
isolated for protection purpose.
Through-air Radar Systems
Non-invasive systems of measurement are basically known as the through-air radar
systems. They usually employ a horn antenna or a rod antenna for sending microwave
beams onto the surface of the liquid being measured. These antennas mounted at the top of
the tank then receive the reflected microwave signal back from the fluid surface. A timing
circuit is incorporated in the systems which measures the time of flight and hence the
distance between the antenna and the fluid level is determined.
These systems can pose measurement problems if the dielectric constant of the fluid being
measured is very low. “The reason is that the amount of reflected energy at microwave
(radar) frequencies is dependent on the dielectric constant i.e. εr of the fluid, and if εr is low,
most of the radar's energy enters or passes through. Water ( εr = 80) produces an excellent
reflection at the change or discontinuity in εr.”[4]
Besides, this radar level measurement technique faces the same beam divergence issues
which affects ultrasonic level transmitters. Moreover, issues like internal piping, antenna
deposits, and manifold wave reflections from tank coatings and obstructions may lead to
inaccurate results. In order to get rid of these errors, advanced algorithms employing fuzzy
logic should be integrated with these radar transmitters. However, these arrangements
would make the transmitter setup very complicated.
INVASIVE SYSTEMS (GUIDED WAVE)
The invasive method used for liquid level measurement is called Guided-wave radar i.e.
GWR method. In this method, a cable or rod is employed which act as a wave guide and
directs the microwave from the sensor to the surface of material in the tank and then
straight to its bottom.
“The basis for GWR is time-domain reflectometry (TDR), which has been used for years to
locate breaks in long lengths of cable that are underground or in building walls. A TDR
generator develops more than 200,000 pulses of electromagnetic energy that travel down
the waveguide and back.
The dielectric constant of the process material will cause variation in impedance and
reflects the wave back to the radar. Time taken by the pulses to go down and reflect back is
determined to measure level of the fluid.
In this method, the degradation of the signal in use is very less since the waveguide offers
extremely efficient course for signal travel. Hence, level measurement in case of materials
having very low dielectric constant can be done effectively. Also in this invasive
measurement method, pulses are directed via a guide; hence factors like surface turbulence,
foams, vapors or tank obstructions do not influence the measurement.
GWR method is capable of working with different specific gravities and material coatings.
However, there is always a danger that the probe or rod used as a waveguide may get
impaired by the agitator blade or corrosiveness of the fluid under measurement. A typical
guided wave radar system is shown in the figure below.
Fig : Guide wave Radar System
GUIDED WAVE RADAR V/S THROUGH-AIR
RADAR
To overcome the measurement problems faced by through-air radar systems, guided wave
radar systems are generally employed since they offer following advantages over through-
air radar systems:
As with through-air radar, a change from a lower to a higher εr causes the reflection.
Guided wave radar is 20 × more efficient than through-air radar because the guide
provides a more focused energy path.
In GWR method, various antenna designs and configurations make it possible to
determine level of fluids having dielectric constant less than 1.4.
Also, these systems can be mounted in both vertical and horizontal positions
depending upon the application.
These systems offer and efficient and clear path for signal travel.
The performance of GWR systems is not disturbed by vapors, foams, high
temperature or pressure conditions.
These systems can operate in vacuum too without requiring any recalibration.
Beam divergence issues and false echoes resulting from tank walls and obstructions
are not present in these guided wave radar systems.
ADVANTAGES
Major advantages of radar level detectors include:
Radar level measurement technique offer extremely accurate and reliable detection
of level in storage tanks and process vessels.
The performance of radar level transmitters remains unaffected by heavy vapors and
mostly all other physical properties of the fluid under level measurement (except
dielectric constant of the liquid).
DISADVANTAGES
Radar level measurement systems incorporate following drawbacks:
Major disadvantage associated with radar level detectors is their high cost.
Besides, these systems are not capable of detecting level between interfaces.
Also their pressure ratings are very restricted.
In case of pulse radar, one usually faces problem in getting accurate measurement
results if the fluid being measured is very near to the radar antenna. Since, in that
case the time taken by the signal to travel between sensor and process material will
be very fast i.e. not adequate for accurate determination of level.
These devices work well with light layer of dirt and dust only. In situations where
the layer of dust or foam gets substantial, they cease to detect the fluid level.
Therefore, in dirty applications the radar level detectors gets replaced by ultrasonic
level detectors.
CONCLUSION
The 30 days training stint at HZL proved to be a fruitful and learning experience as it
provided an opportunity for me to work in a rapidly developing organization striving for
excellence in its operations and services.
The Project team, with whom I worked in my time spent here, not only cleared my basic
knowledge but also explained the systematic and efficient manner in which they carry out
their day to day operations for achieving customer satisfaction. The hierarchy at HZL
insures that there is accountability and transparency in the system and the projects
undertaken are completed on or before time.
BIBLIOGRAPHY
1. Technical references provided by company
2. www.emursonprocess.com
3. www.babbiltlevel.com
Day to day notes
Spacing instrument-“fly ash level detection”.
Deter-“float level sensor”.
Sensor magazine-Article on level
Mega level measuremwnt article
END