Solutions from KROHNE - Mineral Processing - Alumina
• Electromagnetic Flowmeters
• Variable Area Flowmeters
• Radar Level Transmitters
Mineral Processing – Alumina
Aluminum is a light, durable, conductive, corrosion resistant metal with strong affinity for oxygen. This has made it a
widely used material in aerospace, construction, marine industries as well as domestic applications.
Aluminum occurs naturally as the mineral bauxite (primarily mixture of Al2O33H2O, Fe2O3 and SiO2) and is purified in
following process.
Manufacturing Process
Bauxite is crushed and washed to remove water soluble impurities. Remaining material is dissolved in Sodium
Hydroxide and heated, where Alumina (in the form of Al2O3) is selectively dissolved. Through series of filtration and
evaporation insoluble materials are removed resulting in Al2O3 + Water. Later this mixture is heated at an elevated
temperature of 1000°C to produce Alumina powder.
The picture below shows a typical flow chart of Alumina production
Bauxite
Crushing
Grinding
Heater
Predesilication
Flash
cooling
Digester
vessels
Blow off
Precipitation +
classification
Lime
1ststage filtration
Fine seed filters +
product deliquoring
HID
Security
Filtration / Diaster
Filters
2nd stage
filtration
Calcination
Settler / HRD
Mud
Washing
Water
Electricity
Red mud
Evaporation
Turbine
Process material
Steam
Condensate
Strong Liquor
2
Boiler
Spent Liquor
Pregnant liquor
Seed slurry
Mineral Processing – Alumina
Fact: 4 tons of Bauxite is required to produce 2 tons of Alumina
Even though the mining of bauxite is relatively simple, it is the process of transforming bauxite into aluminum that is complex.
This complex process involves accurate measurement and control of flow/level of many process fluids and slurries.
Following are the major sections of an alumina plant:
1.
3.
5.
7.
Bauxite Grinding
Digestion and Dilution
Security Filtration
Calcination
2.
4.
6.
8.
Pre-desilication
Settler Washer
Precipitation and Classification
Evaporation and Utility
Bauxite Grinding
Alumina extraction starts with this section where the bauxite is crushed to produce uniformly sized material. This material is then
mixed with Caustic / Mother liquor at high temperature and pressure. The output from this section is Bauxite Slurry and Red Mud.
Accurate measurement of Bauxite slurry is very important as this decides the plant output and efficiency of entire system.
Bauxite slurry is abrasive in nature and KROHNE electromagnetic flowmeter IFS 4000 is the best choice for flow measurement due
to its advantages like maintenance free construction, negligible pressure loss etc. Mother liquor flow measurement is equally
important and again the best choice is the electromagnetic flowmeter model IFS 4000. Radar level transmitter is required to
measure the height of the bauxite ore as well as bauxite slurry and Optiwave 7300 from KROHNE is the most reliable choice for
the toughest level measurement tasks.
Pre-desilication
Red mud, resulting from Bauxite grinding section, contains un-dissolved bauxite, sodium aluminate, silicon and traces of iron and
titanium. This mixture gradually settles at the bottom of the tank and is then removed. Even though Red Mud is a waste material,
it is important to measure it's volume as it determines the quality of the ore. To measure the red mud flow, KROHNE
electromagnetic flowmeter model IFS 4000 is the best choice.
Digestion and Dilution
Bauxite slurry is pumped into closed digester vessels where chemical reaction to dissolve alumina takes place. Here slurry is
heated to about 80-145ºC, based on the type of process and ore quality. Caustic Soda is added to dissolve aluminum in the
slurry. Un-dissolved particles are removed in the form of water. Digestion takes place at around 50 psi pressure in closed vessels
and results in Sodium Aluminate solution. As this process takes place in high pressure and high temperature, slurry is pumped in
to series of flash tanks to reduce pressure and temperature before it is transferred in to Settler tanks.
To measure the flow of slurry as well as caustic, electromagnetic flowmeter model IFS 4000 is the best solution. Flowmeters
selected should be able to withstand the high temperature and pressure in this area besides abrasion and corrosion. Level radars
on the digester tanks indicate and record the level of caustic and slurry in the digester and settler tanks.
Settler Washer
Settling is achieved primarily by gravity, although some chemicals are added to aid the process. The impurities in the slurry like
sand, iron and other trace elements that do not dissolve will eventually settle down.
The liquor at the top of the tank is directed through series of filters. After washing, Alumina and Caustic is recovered and
remaining red mud is pumped in to large storage tanks where it is dried by evaporation.
Flocculent Dosing: It is a small system/process in Alumina manufacturing. Chemicals are dosed into the Settler Washer to
increase the molecular weight of slurry particles so as to have better settling of slurry particles. This increases the quantity of
sodium aluminate content in the slurry.
In this system, accurate dosing of the chemicals is achieved using electromagnetic flowmeters IFS 4000.
Security Filtration: This liquor still contains tiny and fine suspended crystals and these needs to be removed. Specially designed
filters are used to remove all impurities. The material caught by the filters, known as filter cake, is washed to recover alumina and
caustic soda. The filtered liquor, sodium aluminate solution, is then cooled and pumped into Precipitators.
Accurate flow of slurry and liquor into and out of the Settler Washer needs to be measured along with level of the slurry in the
tanks to control the process.
Lime is added during the process and magnetic flowmeters are needed to measure flow of lime slurry.
KROHNE electromagnetic flowmeter model IFS 4000 and level radar Optiwave 7300C are used for accurate measurement of
flow and level.
3
Mineral Processing – Alumina
Precipitation
This section is series of many tall tanks, called precipitator. The clear Sodium Aluminate solution from the Settler is pumped into
the precipitators. Fine particles of alumina called “seed crystals” are added to start the precipitation of pure alumina particles /
Hydrate Slurry as the liquor cools. Alumina crystals begin to grow around the seeds and then settle to the bottom of the tank
where they are removed and transferred into thickening tanks. Finally it is filtered again for “Seeds” and then transferred into
calcinations section.
Hydrate slurry, Seed Slurry and water flow measurement is critical to control the process.
Seeds, seed slurry, that are added as catalysts also need to be measured to check and control the process efficiency.
Calcination
Calcination is a heating process to remove water from aluminum hydrate to get Anhydrous alumina.
Calciner is brick lined kiln which is gas fired at around 1100 °C. Aluminum particles are suspended above a screen by hot air and
calcined. The result of this section is white powder and this powder is pure Alumina. The caustic soda from aluminum hydrate is
reused again.
Measurement and control of flow of Hydrate slurry is very important and needs to be measured accurately. Electromagnetic
flowmeters are the best used to measure flow of hydrate slurry.
Fact: 2 tons of alumina is required to produce 1 ton of Aluminum.
Evaporation
During manufacturing process, heavy amount of caustic is used. In order to reduce the wastage, used caustic obtained from various
sections / processes is collected and recycled through evaporation section.
Alumina powder, which is the final product, obtained from the calciner is stored in silos before being processed in the smelter plants
to produce aluminum.
Measurement of level of alumina powder is very critical as this fine powder has a very low dielectric constant and powder tends to
deposit on the antenna of the radar thereby making measurement more critical. Radar selected for this application has to be
accurate and should be able to measure the level of very low die-electric powders.
KROHNE level radar make Optiwave 6300 with unique design of “drop antenna” is best choice for difficult level measurement.
Solutions from KROHNE - Flow and Level expert
KROHNE is an international leader for the development and production of innovative and reliable process measuring
instruments. With strong presence of over eight decades, KROHNE offers the following products for Alumina sector.
1. Electromagnetic flowmeters
2. Variable Area flowmeters
3. Radar Level transmitters
Solutions for difficult flow measurement
KROHNE has unique expertise in the field of field of flow measurement. We not only show our know-how in standard
applications, but also in applications demanding tailor-made solutions. As the founder and global market leader of
Electromagnetic flowmeter technology for process measuring technology, we have been trusted partners who offer innovative
solutions to our customers for more about six decades.
For reproducibility of the measured value, it is not only the transmitter that is decisive. The stability of the primary head under
temperature and pressure stresses also plays an important role. In order to obtain reliable measurement even for the most critical
media, electrode construction and the process connection must also be taken into consideration.
Probably electromagnetic flowmeters are the only flow measuring instruments to cover a wide range of applications ranging
from simple water, aggressive chemicals to paste, pulp and slurries.
4
Mineral Processing – Alumina
Product highlights
•? Reliable flow measuring instrument, largely independent of the flow profile.
•? The highest degree of application certainty even in the case of rapidly changing media, pH, large amount of solids and
pulsating flow.
•? Only flow measuring instrument to measure media with slurry/solid content.
•? Obstruction-less flow path, maintenance free and very low pressure loss.
•? Abrasion and corrosion resistant liner to suit all applications.
•? All KROHNE flowmeters are wet calibrated in direct volume comparison – the most accurate calibration method by far.
•? High pressure and high temperature designs available.
Technical Specifications
Sizes
DN 10 …. DN 3000 / 3/8” ….. 120”
Process connection
ASME (150# / 300# / 600#), DIN (PN 10 / PN 16 / PN 40), IS
Measurement range
-12 … 12m/s
Power supply
110 / 220 VAC, 24 VDC
Output
mA, Pulse, Status
Communication
HART, Foundation fieldbus, Profibus PA / DP
Accuracy
± 0.3% of m.v, higher accuracy available on request
Repeatability
± 0.1% of m.v
Permissible gas content
≤　5% by volume
Permissible solid content
≤　70% by volume
Electrical conductivity
≥　5µS/cm for process fluids and 20µS/cm for water
Protection class
Flow sensor: IP 67, IP 68 (optional)
Signal converter: IP 65, IP 67
Signal converter enclosure
Die cast Aluminum, SS 304 / SS 316 optionally
5
Mineral Processing – Alumina
Variable Area Flowmeters
Since 1921, the name of KROHNE has not only stood for innovative and reliable process measuring technology solutions, but also
exact, reliable and long lasting variable area measuring technology.
VA Meters are one of the proven and most popular flow measuring devices used to measure flow of clean liquids and gases.
Simple and robust construction with transmitter and switches are available optionally for measurement and controlling.
Product highlights
•
Reliable and proven flow measuring instrument, for liquids and gases even without external power supply.
•? High application certainty even for very small amounts of flow.
•? Low maintenance, simple installation and start-up.
•? Modular transmitter and switching assembly.
•
Excellent long term stability.
•
PTFE lined flow section / measuring cone available for corrosive applications.
•? High pressure and high temperature designs available.
•? New designs with LC display and many more features.
Technical Specifications
6
Sizes
DN 15 …. DN 100 / 1/2” ….. 4”
Process connection
ASME (150# / 300# / 600#), DIN (PN 10 / PN 16 / PN 40 / PN100), JIS
Measurement range
10 …. 120000 lph for liquids and 0.7 …. 2800m³/hr for gases
Turn-down ratio
10:1 , Optionally 100:1
Measuring part
SS 316, Hastelloy C4, Titanium, Monell, Ceramic / PTFE lined
Power supply
24 VDC
Output
mA, switching
Communication
HART, Foundation fieldbus, Profibus PA / DP
Accuracy
Class 1.6
Repeatability
± 0.1% of m.v
Display
Angular
Protection class
Flow sensor: IP 67
Display enclosure material
Die cast Aluminum, SS 304 / SS 316 optionally
Mineral Processing – Alumina
Solutions for difficult level measurement
KROHNE has unique expertise in the field of level measurement technology. In 1989, KROHNE introduced the first process radar
device and became the pioneer of using radar level measuring technology in process technology. In 1995, KROHNE also became
the forerunner in the field of radar devices on the TDR (Time Domain Reflectometry) principle, using guided microwaves. With
these TDR radars, interface of level of two immiscible liquids can be measured.
KROHNE offers non-contact level radars based on FMCW (Frequency Modulated Continuous Wave) technology for applications
with high agitations and chemically corrosive environment.
For simpler liquid level measuring applications, KROHNE offers ultrasonic level transmitters.
KROHNE introduced a new unique design of “Drop Antenna” for level measurement of solids and powders in very dusty
atmospheres.
Product highlights
•? Reliable radars for very complex applications involving agitators, surfaces with foams / uneven surfaces and solids or
powders with highest degree of accuracy.
•? Wizard driven and touch screen programming with empty spectrum and tank bottom following for tanks with high
agitations.
•? Measuring range up to 100m
•? Higher signal dynamics and greater bandwidth (24 GHz) for better accuracy and reliable process control.
•? Suitable for temperatures up to 1700 °C and pressure up to 1000 Bar.
•? Lowest dead band of 50mm only.
•? High standard accuracy of ± 1mm.
•? Optional antenna purging, cooling and heating facility.
•? Transducer can be removed and rotated under tank working conditions.
•? Display in various difficult languages including Chinese, Japanese and Russian.
•? Ultrasonic level transmitters for both sumps and water / wastewater basins.
•? Non-contact flow measurement and detection in open channels.
Technical Specifications
Application range
Level measurement of Solids, Powders, Slurry and liquids
Measuring range
80m, optionally 100m
Die-electric constant
Material of construction
≥　1.5
Antenna: SS316L, Hastelloy C, PTFE, PP
Housing: Die cast Aluminum, optionally SS 316L
Flanges: SS 316L, optionally with PTFE / PP flange plate
Temperature
-40 … 200 Deg C
Pressure
-1 … 40 Bar
Process connection
Flange version: 1 ½” … 8” in 150 lbs / 300 lbs
Threaded version: 1 ½” BSP / NPT
Power supply
Output
Display
14 … 30 VDC
4-20mA,HART, Optionally second output 4-20mA, HART Foundation fieldbus /
Profibus PA/DP
Touch screen LCD display, 9 lines, 160 x 160 pixels
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KROHNE Marshall Pvt. Ltd.
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Industrial Estate,
'H' Block, Pimpri,
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Tel.: 91(0)20 - 27442020
Fax: 91(0)20 - 27442040
E-mail: [email protected]
Mineral Processing – Alumina
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Doc#CIG/0211/13/V1.R0
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