Deodorization systems

How it works

How deodorization of oil works

Deodorization is a steam-distillation process to remove free fatty acids and volatile components present in crude edible oil at this stage of processing. These unwanted substances negatively affect the odour, flavour, colour and stability of the final product. To strip these substances from the oil, steam is passed through the oil at very low pressure, relatively high temperature and high-vacuum conditions.

Deaeration

Before heating the oil, air must be removed under vacuum (deaeration) to prevent oxidation, thereby protecting product quality. After leaving the deaerator, the oil is regeneratively heated in a special heat exchanger, the economizer, by the hot oil leaving the deodorization column. This ensures that as much heat as possible is recovered from the hot oil. The oil then proceeds to a final heater where it is brought to the exact temperature required for deodorization, normally using high-pressure steam.

Pre-stripping and retention

When the oil has reached the designated temperature, in range of 220-260°C depending on the processed oil, it is fed to the deodorization column, the main component used for deodorizing edible fats and oils. The column can consist of a stripping section and a retention section. When the oil passes through the stripping section, it is exposed to a combination of vacuum and steam that removes volatiles – including free fatty acids (FFAs) – that have a higher vapour pressure than the oil itself. If present, these volatile impurities affect the flavour, odour and stability of edible oils.

The oil is then held in a retention section for a certain amount of time for thermal treatment – known as heat bleaching – that removes undesirable pigments and ensures the stability of the final product. The length of time the oil is kept in the retention section depends upon the desired product specifications.

Post-stripping and GE stripping

The oil is fed under vacuum to the post-stripping section where, as a thin film, it is exposed to a combination of vacuum and steam that removes volatiles, including compounds of thermal degradation generated during retention at high temperatures. The treated oil is then cooled.  

At temperatures below 200°C, the formation of glycidyl esters (GEs) is limited and therefore GE cam be stripped without formation from cooled quench oil. A specially designed column filled with structured packing, or GE stripper, effectively removes GEs to levels below 0.5 ppm in size by promoting contact between steam and oil under vacuum conditions. However, to be effective, this method calls for immediate cooling after GE stripping.  

Condensing removed impurities

The volatile impurities removed from the oil are condensed in a scrubber unit, using recirculated and cooled distillate. The scrubber is either placed on top of the stripping section or built as a separate vessel.

Cooling

Finally, cooling the oil occurs in two stages: (1) in the economizer to the specified final temperature, and (2) in the process of polish filtration before being transferred to subsequent processes, storage or packaging.