Flash point is the minimum temperature at which a liquid gives off vapour in sufficient concentration to form an ignitable mixture with the air near the liquid's surface. It is an indicator of the liquid's susceptibility to ignition.
Flash point is generally determined by heating liquid in test equipment and measuring the temperature at which a flash is obtained when a small flame is introduced in the vapour zone above the liquid's surface.
In most vegetable oils, flashpoint typically occurs at around 315°C.
At fire point, accumulated breakdown products are capable of supporting a flame on their own. i.e. vapours from the oil can catch on fire rather explosively, and the fire is self-sustaining at this point. In vegetable oils, this typically occurs at 375°C.
Given that most crude edible oils are transported and shipped over vast distances, the flash point is a key criteria to determine potential fire and explosion hazards. Flash point analysis is used to identify this crude oil deficiency and prevent an accidental fire or explosion in an environment that isn't necessarily explosion-proof. Most trading standards automatically reject crude vegetable oil shipments with a flashpoint below 121°C.
In the solvent extraction process, the flash point of oils tend to be lower because of the solvent residue that remains in the oil. With an effective distillation system, this residue can be brought down to negligible quantities.
The distillation system of an extraction plant provides the means for evaporating and stripping the solvent from the oil. Oil after distillation has a flashpoint of at least 121°C and preferably 150°C or more.
During solvent extraction, miscella (oil-rich extract) containing 20–30% oil recovered from flaked or expanded meats is sent to the distillation section that includes evaporators and an oil stripper. The oil content exiting the first-stage evaporator is 65–70%. It is heated with vapours from the desolventizing toaster. In the second-stage evaporator, the oil content is 90–95%. An oil stripper uses steam-injection vapour, high heat, and high vacuum to reduce the solvent down to less than 0.2% in the oil. The oil temperature in the stripper must not exceed 115°C to ensure the oil is not scorched and the colour remains light.
The evaporated solvent is recycled back to the extractor. The oil is then sent to a vacuum dryer to remove any residual stripping steam condensate, following which it is immediately cooled before being placed in storage.
Flash point determination is an easy method to ensure your solvent-evaporation equipment is operating as it should.
A higher flashpoint means lower hexane residue. For the purpose of this assessment let's assume the flash point of miscella is the same as for hexane, though in reality its flash point is likely to be higher (only applicable for oils recovered by solvent extraction). Hexane free oils have high flash points, which may vary slightly dependent on the degree of purity. They are extremely unlikely to form flammable (explosive) atmospheres unless heated significantly above ambient temperature.
Flash point data Crude extraction oil > 121 °C and preferably > 150°C Refined oil usually > 285°C (related to process conditions)
If the flash point readings during the assessment are high it means your distillation system is not functioning as it should. You need to check vacuum settings, whether the plant is achieving optimal temperature parameters, and if the levels in the stripping columns.
High hexane levels in the oil also mean higher hexane losses. An efficient distillation system ensure maximum hexane residue removal from both cake and oil and saves money.
Kumar's Solvent Extraction plants are custom designed specifically to the type of feed, with highly efficient distillation systems, that achieve a flashpoint of 150°C or more.
Kumar guarantees flash point of 150°C for all our solvent extraction plants. This can be brought up to with 150°C with an optimised refinery process.
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