Energy Alternatives India, CHENNAI

Dec’ 2014

CENTRIFUGE Overview of Centrifuge

Nitesh Dattaram Kamerkar

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CENTRIFUGE

ENERGY ALTERNATIVES INDIA(EAI), CHENNAI

THEORY OF CENTRIFUGATION :-

When a solid-liquid suspension is rotated in a cylindrical container (bowl) the

suspension is subject to a centrifugal force in the radial direction.

Centrifugation is a process by which solid particles are sedimented and

separated from a liquid using centrifugal force as a driving force.

Depending on the rotational speed and distance from the axis of rotation, the

centrifugal force can be many times greater than the force of gravity, allowing

even very small particles or particles slightly denser than the fluid to settle.

Centrifugation:Any object moving in a circle at a steady angular velocity is

subject to an outward directed force(F). The magnitude of this force depends on

the angular velocity in radians (ω), and the radius of rotation (r).

F= gravitational force and also referred to as the relative centrifugal force(RCF)

Sedimentation of a molecule influenced by

a. Properties of the molecules (Size, shape, density)

b. Properties of the solvent, or the gradient material(density,viscosity,

temperature)

c. Interactions between the solute molecules and the solventgradient

molecule

-As the rotor spins, centrifugal force is applied to each molecule in the sample:

Centrifugal force= Mω2r

M= Mass(molecular weight),

ω=angular velocity(radians/sec),

r= distance from the axis of the rotation

In Centrifuge the effective gravitational forcemay increase on a test tube so as to cause the

precipitate ("pellet") to gather on the bottom of the tube. The remaining solution is called the

"supernate" or "supernatant liquid". The supernatant liquid is then either quickly decanted from the

tube without disturbing the precipitate, or withdrawn with a Pasteur pipette.

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CENTRIFUGE

ENERGY ALTERNATIVES INDIA(EAI), CHENNAI

TYPES OF CENTRIFUGATION :-

Preparative :

Used to separate organelles and molecules

Can handle larger liquid volumes

No optical read-out

Separation methods used in preparative ultracentrifugation:

1. Differential Centrifugation- pelleting,

2. Density Gradient Centrifugation

I. Differential Centrifugation

Based on the size of the particles.

Used for simple pelleting, for the separation of sub cellular organelles and

macromolecules.

First sample must be homogenized.

Sedimentation depends on mass, shape and partial specific volume of a

macromolecule, as well assolvent density, rotor size, rate of rotation.

Usually uses a fixed angle rotor.

II. Density gradient Centrifugation

Method to purify subcellular organelles andmacromolecules.

Density gradients generated by placing layer after layer ofgradient media.

Density gradient centrifugation classified into two: a. Rate-Zonal

Use of continuous density gradient of solvent such assucrose.

Density increases towards the bottom of the tube.

Sample layered on the topmolecules form discrete bands after

centrifugation.

Separation based on size of the molecules.

For Example: -Swinging bucket rotors.

b. Isopycnic

Based on the density of the molecules

The word "isopycnic" means "equal density".

Mix gradient material with the sample molecule (CsCl)

Molecules move to the position where their density is sameas the

gradient material (isopycnic position).

Inorder to generate a gradient, we select a CsClconcentration that

will give a range of densities that includesthe range of molecules that

have to be separated.

- used for the separation of DNA.

- Swinging bucket or fixed angle rotor.

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CENTRIFUGE

ENERGY ALTERNATIVES INDIA(EAI), CHENNAI

Analytical :

Uses small size samples.

Built-in optical system.

Uses relatively pure sample.

CENTRIFUGE :-

Centrifuges are sedimentation devices in which suspended solids are separated from

a liquid under the action of centrifugal forces generated by spinning the internal

bowl of thecentrifuge.

The resulting settling velocities of the solidscan be significantly higher than those

generated by gravity forces.

Centrifuges can be thought of assedimentation vessels operating under high

“gravitational” forces.

Decanter centrifuges provide a highly versatile and reliable option for a large variety

of separationprocesses. They are commonly used for the following applications:

- The separation of solid-liquid suspensions (two-phase separation),

- The separation of solid-liquid-liquid suspensions (three-phase separation),

- The thickening or dewatering of separated solids,

- The clarification of a liquid phase or liquid phases,

- The sizing of solids,

- The sorting of solids.

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CENTRIFUGE

ENERGY ALTERNATIVES INDIA(EAI), CHENNAI

CLASSIFICATION OF CENTRIFUGE :-

ACCORDING TO SPEED –

Desktop clinical centrifuges: below 3000rpm

High speed centrifuges : 20,000 to 25,000rpm

The Ultracentrifuge :75,000rpm

a. Drive and speed control

b. Temperature control

c. Vacuum System

d. Rotors

ACCORDING TO ROTOR ORIENTATION –

Swinging bucket rotors

Fixed angle

Vertical

ACCORDING TO INTENDED USES –

Ultracentrifuges

o These are optimized for spinning a rotor at very high speeds and are popular

in the fields of molecular biology, biochemistry and polymer science. This type

may include preparative or analytical, fixed-angle or swing head varieties.

Haematocrit centrifuges

o These are used to measure the percentage of red blood cells in whole blood.

Gas centrifuges

o Gas Centrifuge is a device that performs isotope separation of gases.

o A prominent use of gas centrifuges is for the separation of uranium- 235 from

uranium- 238. The separation of uranium requires the material in gaseous

form; uranium hexafluoride (UF6) is used for uranium enrichment.

o Including Zippe-type centrifuges.

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CENTRIFUGE

ENERGY ALTERNATIVES INDIA(EAI), CHENNAI

Approximate Estimated Separative Power of Selected Gas Centrifuges1

VARIOUS CENTRIFUGE

MODELS

LENGTH (M) WALL SPEED (m/s) SEPARATIVE

POWER (SWU/yr)

Zippe 0.30 360 0.886

P1 2.00 350 5.580

IR-1 2.00 330 4.930

IR-2m 1.25 480 6.563

TC-10 type 3.20 500 18.23

ACCORDING TO THEIR CONSTRUCTION –

Solid bowl centrifuges (decanters)

Basket centrifuges

- Perforated basket centrifuges

- Imperforated basket centrifuges

Disk bowl centrifuges

INDUSTRIAL CENTRIFUGES ACCORDING TO THE TYPE OF SEPARATION OF THE

HIGH DENSITY FRACTION FROM LOW DENSITY ONE –

Screen Centrifuges

o Screen/scroll centrifuges

o Pusher centrifuges

o Peeler centrifuges

o Decanter centrifuges

o Solid Bowl centrifuges

o Conical plate centrifuges

1 Institute for Science & International Security Report (ISIS),

www.isis-online.org

SWU:- "Separative work" – the amount of separation done by an enrichment process – is a

function of the concentrations of the feedstock, the enriched output, and the depleted

tailings; and is expressed in units which are so calculated as to be proportional to the total input

(energy / machine operation time) and to the mass processed. Separative work is not energy.

The same amount of separative work will require different amounts of energy depending on the

efficiency of the separation technology. Separative work is measured in Separative work units

SWU, kg SW, or kg UTA (from the German Urantrennarbeit – literally uranium separation work)

1 SWU = 1 kg SW = 1 kg UTA

Source: -http://en.wikipedia.org/wiki/Enriched_uranium

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CENTRIFUGE

ENERGY ALTERNATIVES INDIA(EAI), CHENNAI

PROCESS FUNCTION OF CENTRIFUGE :-

1. Separation (solid/liquid, solid/liquid/liquid and solid/solid/liquid

separation)

Centrifugation can be used for solid-liquid separation provided the solids are

heavier than the liquid. Centrifuge can also be used to separate a heavy phase,

and two lighter liquid phases, with one of the lighter phases being lighter than the

other. As discussed, solids can be lighter than liquid and separation is by flotation

of the dispersed solid phase.

2. Clarification- minimal solids in liquid product

Centrifuge can be used to clarify the discharged separated lighter liquid phase.

The objective is to minimize the discrete suspended solids in the light continuous

phase. Usually, only fine submicron biosolids are left uncaptured by

centrifugation and they escape with the discharged light phase.

3. Classification -sort by size and density

Centrifuge is used to classify solids of different sizes. One of the several possible

applications is to classify crystals of different size range, with the finer

submicron sizes leaving with the light phase and retaining only the larger sizes in

the separated heavy phase. Either of the separated solids can be the product. For

example, the larger crystals can be the product crystals while the finer crystals are

returned to the crystallizer to grow to larger crystals. Another similar application

is to classify smaller size cell debris in the light liquid phase from the heavier

products after homogenizing cells.

4. Degritting- remove oversized and foreign particles

Degritting is similar to classification where unwanted particles, larger or denser,

are rejected in the sediment, with product (smaller or less dense) overflowing in

the lighter liquid phase. Another situation is where smaller unwanted particles are

rejected in the light liquid phase, and valuable heavier solids are settled with the

heavier phase.

5. Thickening or concentration- remove liquid, concentrate solids

Centrifuge is frequently used to concentrate the solid phase by sedimentation and

compaction, removing the excess liquid phase in the overflow or centrate. This

reduces the volume of the product in downstream processing.

6. Separation and repulping - remove impurities by washing or diluting

With a concentrated suspension containing contaminants such as salts and ions, it

is diluted and washed so that the contaminants are dissolved in the wash liquid.

Subsequently, the suspension is sent for centrifugation to remove the spent wash

liquid with dissolved contaminants or finely suspended

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CENTRIFUGE

ENERGY ALTERNATIVES INDIA(EAI), CHENNAI

SIGNIFICANT APPLICATIONS OFCENTRIFUGES :-

Isolating suspensions

Simple centrifuges are used in chemistry, biology, and biochemistry for isolating and

separating suspensions. They vary widely in speed and capacity. They usually comprise a

rotor containing two, four, six, or many more numbered wells within which the samples,

contained in centrifuge tubes, may be placed.

Isotope separation

Other centrifuges, the first being the Zippe-type centrifuge, separate isotopes, and these

kinds of centrifuges are in use in nuclear power and nuclear weapon programs.

Gas centrifuges are used in uranium enrichment.

The heavier isotope of uranium (uranium-238) in the uranium hexafluoride gas tends to

concentrate at the walls of the centrifuge as it spins, while the desired uranium-

235 isotope is extracted and concentrated with a scoop selectively placed inside the

centrifuge. It takes many thousands of centrifugations to enrich uranium enough for use

in a nuclear reactor (around 3.5% enrichment), and many thousands more to enrich it

to weapons-grade (above 90% enrichment) for use in nuclear weapons.

Aeronautics and astronautics

The 20 G centrifuge at the NASA Ames Research Center

Human centrifuges are exceptionally large centrifuges that test the reactions and

tolerance of pilots and astronauts to acceleration above those experienced in the

Earth's gravity.

The US Air Force at Holloman Air Force Base, New Mexico operates a human centrifuge.

The centrifuge at Holloman AFB is operated by the aerospace physiology department for

the purpose of training and evaluating prospective fighter pilots for high-g flight in Air

Force fighter aircraft.

The use of large centrifuges to simulate a feeling of gravity has been proposed for future

long-duration space missions. Exposure to this simulated gravity would prevent or reduce

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CENTRIFUGE

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the bone decalcification and muscle atrophy that affect individuals exposed to long

periods of freefall.

The first centrifuges used for human research were used by Erasmus Darwin, the

grandfather of Charles Darwin. The first largescale human centrifuge designed for

Aeronautical training was created in Germany in 1933.

Geotechnical centrifuge modeling

Geotechnical centrifuge modeling is used for physical testing of models involving soils.

Centrifuge acceleration is applied to scale models to scale the gravitational

acceleration and enable prototype scale stresses to be obtained in scale models.

Problems such as building and bridge foundations, earth dams, tunnels, and slope

stability, including effects such as blast loading and earthquake shaking.

Commercial applications

Sugar centrifugal machines, to separating sugar crystals from the crystallized syrup,

or mother liquor.

Centrifuges with a batch weight of up to 2,200 kg per charge are used in the sugar

industry to separate the sugar crystals from the mother liquor.

Standalone centrifuges for drying (hand-washed) clothes – usually with a water outlet.

Washing machines

Centrifuges are used in the attraction Mission: SPACE, located at Epcot in Walt Disney

World, which propels riders using a combination of a centrifuge and a motion

simulator to simulate the feeling of going into space.

In soil mechanics, centrifuges utilize centrifugal acceleration to match soil stresses in a

scale model to those found in reality.

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CENTRIFUGE

ENERGY ALTERNATIVES INDIA(EAI), CHENNAI

Large industrial centrifuges are commonly used in water and wastewater treatment to

dry sludges. The resulting dry product is often termedcake, and the water leaving a

centrifuge after most of the solids have been removed is called centrate.

Large industrial centrifuges are also used in the oil industry to remove solids from

the drilling fluid.

Disc-stack centrifuges used by some companies in Oil Sands industry to separate small

amounts of water and solids from bitumen.

Centrifuges are used to separate cream (remove fat) from milk.

LIMITATIONS OFCENTRIFUGE

Limitations of the centrifuge include high capital and operational costs as they

are energy-intensive. In addition, the maintenance costs and number of incidents of

breakdown are higher than with static separators due to the moving parts.

Another limitation is the narrow range for optimum performance with variable conditions

like feed acceleration, positioning of the interface and solid discharge method. In

addition, sealing materials, especially the dynamic sealing materials, must be carefully

chosen to be chemically and thermally resistant.; therefore, a much more extensive

design and optimization program is required than with the static separators; therefore, a

much more extensive design and optimization program is required than with the static

separators.

The actual achieved separative power of gas centrifuge will be always lower than its

theoretical separative power reflecting additional inefficiencies in the centrifuges when

running as individual machines and in cascades.For example, The IR-1 centrifuge

achieves an average separative power in cascades of less than one SWU/year,

significantly less than its theoretical maximum separative power of 4.9 SWU/year.

Although its value when run individually is greater, it is still far below the theoretical value.

It also experiences a relatively high breakage rate, which accounts for much of the

additional reduction of its separative power when run in production cascades.

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CENTRIFUGE

ENERGY ALTERNATIVES INDIA(EAI), CHENNAI

INNOVATIONS

There’s a downside to the medical equipment donations that find their way to Sub-

Saharan Africa: Many of the devices never get used. The World Health

Organizationestimates up to 70 percent of all donations end up in what’s referred to as a

“medical device graveyard.” Much of the equipment it is too complex, requires non-

existent infrastructure or can’t be repaired once broken.

With this in mind, Jack Albert Trew designed the Spokefuge, a manual centrifuge

powered by a spinning bike wheel. Trew, a designer from the United Kingdom, knew he

needed to make use of readily accessible equipment (the wheel) and it should use

no electricity. “From the very start I wanted the product to be a simple and hassle free

alternative for blood diagnosis,” he says. “I had no intention of creating a more complex

and frustrating task that people would not want to do.”

Jack Albert Trew designed a low-tech centrifuge that's powered by a spinning bike

wheel2

To use it, people prick a finger and collect a sample that fits into a standard capillary

tube. This tube is then inserted into the Spokefuge’s rubber sleeve, which creates an air-

tight seal. The sleeve is slipped inside the swinging arm attachment that clips onto the

bike spokes and spins for about 10 minutes, the amount of time it takes to sufficiently

separate a sample at speeds of more than 750 rpm. The resulting sample, once

separated, can be compared to a microhematocrit chart.

2http://www.wired.com/2014/12/clever-bike-powered-centrifuge-developing-countries/#slide-id-1671949

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CENTRIFUGE

ENERGY ALTERNATIVES INDIA(EAI), CHENNAI

INVERTING FILTER3

For the most difficult filtering materials, the Inverting Filter Centrifuge should be

considered. The Inverting Filter does not leave a residual heel, as peelers do, allowing

you to perform a Thin Cake Operation that may be required for the most difficult filtering

products. In addition, the Inverting Filter can be fitted with the unique Pressure-Added

Centrifugation System (PAC) which allows the use of gas pressure as an additional driving

force to dry the cake inside the centrifuge beyond what spinning alone can do. This can

increase production by shortening the overall cycle time.

3http://www.heinkelusa.com/

Pressure Added

Centrifugation System

(PAC) can increase

production by shortening

the overall cycle time. It

also can reduce the load in

a downstream dryer or

eliminate the need for one

completely, thereby saving

on both capital and

operational costs.

1300 mm diameter Inverting FilterCentrifuge in the open position

PRESSURE ADDED

CENTRIFUGATION (PAC) SYSTEM

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CENTRIFUGE

ENERGY ALTERNATIVES INDIA(EAI), CHENNAI