Armfield Engineering Education

FOOD TECHNOLOGY

FT29 Batch Solvent Extraction and Desolventising Unit - Issue 3

The Armfield Solvent Extraction Unit is a floor standing, batch process suitable for both teaching and research. Capable of carrying out a variety of solid/liquid extractions, it is particularly suitable for 'leaching' edible oils from oil-bearing seeds and desolventising both the extracted solids and the miscella.

Order Specification |
Process Capabilities |
Description |
Technical Specification

Modes of operation |
Requirements |
Shipping Specification and Dimensions

Ordering Specification

A floor standing batch solvent extraction unit designed to allow instruction and research into the principle of solid-liquid extraction. The main process vessels and the support framework are constructed in stainless steel, other materials in contact with the process fluid include borosilicate glass, PTFE and PVDF.

Extractor vessel total volume is 100 litres which allows a solids working capacity of 25kg (based on a density of 560kg/m 3 ).

Miscella collecting tank/still is 30 litres capacity.

Extractor and miscella vessels have a facility for direct as well as indirect steam addition.

Vapours from the extractor and miscella vessels are condensed in a solvent condenser which employs a coil of heat transfer area 2.5m 2 through which cooling water is circulated. Cooling water flow rate can be varied from 0 - 22 litres per minute using a variable area flow meter.

Condensate enters a solvent water separator tank where solvent and water are separated under gravity so that solvent can be re-used. Capacity of the solvent storage section is 16 litres.

Water condensate is collected in a waste water tank of 15 litres capacity.

A PTFE diaphragm vacuum pump allows operation at reduced pressure to 100mbar.

Modes of operation include:-

• extraction by recirculating miscella
• extraction by washing with clean solvent
• desolventising of extracted material
• desolventising miscella.

All electrical equipment used is to the appropriate flameproof standard. All major process vessels are designed in accordance with the appropriate pressure vessel standards.

A comprehensive instruction manual is supplied which details installation and commissioning procedures as well as suggested operational procedures.

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Process Capabilities

> operation of small scale version of the industrial process
> effect of degree of pretreatment of solid material on extraction efficiency
> effect of solvent type
> effect of solvent percolation rate
> effect of process temperature and pressure
> effect of extraction time and drain time
> method and degree of solvent recovery.

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Description

All vessels, pipes, valves and fittings in contact with process materials are constructed in stainless steel with the exception of the solvent condenser which is borosilicate glass. The support framework is also stainless steel.

Inspecting the interior of
the extractor vessle

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The extractor/desolventiser is a cylindrical vessel having a hinged lid used for charging the extrac-tion material. The base of the vessel is inclined slightly towards a door for discharging the extracted and desolventised meal. Material is supported above the base by a perforated plate covered with a fine woven mesh which allows solvent to drain through to the miscella tank whilst retaining the solids.

The vessel base is equipped with a steam chest to administer indirect steam for process heating. Direct steam is injected at a variable rate through a distribution pipe positioned above the mesh. A similar distribution pipe positioned near the top of the vessel allows solvent to be sprayed uniformly onto the bed of material.

The miscella tank, positioned directly below the extractor to collect the draining liquid, is also a cylindrical vessel incorporating a steam chest as its base. This vessel also incorporates a direct steam distribution pipe through which steam can be metered at a variable rate.

Vapour from either or both of these vessels, produced in the desolventising process, is directed by ducting to the solvent condenser. This is an inclined cylindrical glass tube containing a double coil through which cooling water is circulated.

Condensate (usually a mixture of solvent and water) drains into the solvent water separator tank which is designed to allow thorough separation of the solvent and water by a gravity process.

(Note: Only hexane or solvents having a similar specific gravity can be effectively separated in this tank).

Solvent reclaimed from this vessel can then be recirculated by the solvent pump at a regulated rate through a variable area flow meter. Excess water overflows to a waste water tank from where it can be disposed of on completion of the process.

Operation at reduced system pressures are achieved by a PTFE diaphragm type vacuum pump. The outlet of this pump is piped through a flame arrester to a suitable ventilation point.

Schematic diagram
of the FT29

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Each vessel is equipped with suitable level/sight glasses so that the processes can be observed and monitored. Pressure and temperature gauges are supplied where necessary as are adequate sampling and drain valves.

Hexane is the most widely used solvent in the extraction process and, due to the inflammable nature of this product, electrical equipment has been kept to a minimum. Where electrical equipment must be used, it is specified to the appropriate standards for safety.

The main processing vessels have been designed in accordance with the appropriate code of practice for welded pressure vessels.

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Modes of Operation

Extraction by recirculating miscella This involves priming the miscella tank with clean solvent then pumping the solvent to the extractor where it percolates through the material bed and drains as miscella back into the tank for recirculation.

Extraction by washing with clean solvent

As miscella is formed, steam admitted to the miscella tank base causes solvent to evaporate. The vapour is condensed in the solvent condenser and returns to the separator tank from which it is pumped back to the extractor.

Desolventising extracted material

When the extraction is complete, the static hold-up of solvent remaining in the material must be removed and this is achieved using a combination of direct and indirect steam and vacuum. The solvent vapourises and is condensed along with the direct steam and the condensate. The mixture of solvent and water is separated in the solvent water separator tank. When the extracted material is free of solvent it is discharged through the door at the base of the extractor.

Desolventising miscella

Miscella is a mixture of the solvent and oil from the extraction material which accumulates in the miscella tank during the process. The solvent and oil are separated in a similar method as for material desolventising using a combination of direct and indirect steam and vacuum.

A higher level of vacuum is required than for material desolventising in order to produce solvent-free oil.

Within each mode of operation, many operating parameters such as process temperature, solvent temperature, solvent flow rate, direct steam flow rate and system pressure can be adjusted to allow a high degree of experimentation.

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Technical Specification

In order to allow a high degree of experimentation a variety of liquid solvents may be used which are often inflammable. The unit is therefore intended for installation in an area designated as safe. Relevant local regulations regarding the operation of this type of equipment must be observed.

Flameproof electrical equipment has been specified to be compatible with most common solvents. Electrostatic bonding has been incorporated and it is important to make sure the framework is adequately earthed when installed.

Extraction, miscella, solvent separation and waste water vessels are designed in accordance with the BS5500 code for pressure vessels.

Extractor vessel:

Volume: 100 litres
Batch capacity: 25kg based on density of 560kg/m3
Direct steam: 0 - 7 kg/hr
Indirect steam: 0 - 3.5 bar

Miscella tank:

Volume: 30 litres
Minimum extract: 2 litres
Direct steam: 0 - 4kg/hr
Indirect steam: 0 - 3.5 bar

Solvent condenser:

Condensing capacity: 2.5kW
Condensing area: 2.5m2
Cooling medium: water
Cooling water flow range: 0 - 22 lpm

Solvent water separator tank:

Volume of separator 16 litres section:

Volume of solvent 16 litres store section:

Waste water tank:

Total volume: 15 litres

Vacuum pump:

Type: Double PTFE diaphragm
Drive: Flameproof a.c. motor
Operating pressure: 100mbar (max).

Solvent pump:

Type: Gear
Drive: flameproof a.c. motor
Solvent flow range 0-8 lpm.

SOME EXAMPLES OF EXTRACTIONS POSSIBLE USING FT29
Extraction material	Extract	Solvent
Oilseeds/presscakes	Edible oil	Hexane
Tree bark	Tannin	Water
Solanium (a grass)	Steroid	Dil. sulphuric acid
Pyrethrum flower	Insecticide	Hexane
Tea leaves	Tea	Water
Wheat germ	Oil	Hexane
Rice bran	Oil	Hexane
Poppy stalks	Morphine	Water
Flowers/fruits	Essential oils	Hexane
Liquorice roots	Liquorice juice	Water