Two processes have been developed for the refining of edible oils and fats, i.e. physical and chemical refining; the decision which process to use depends on the types and qualities of the crude oil to be processed. The names physical and chemical refining come from the process technology used to remove the free fatty acids (FFA) those are responsible for the oil acidity. Physical refining is a process making use of the lower boiling point of the FFA compared to the boiling point of the triglyceride oil. In chemical or alkaline refining, an alkali is used to neutralize the FFA. Chemical refining is the traditional method used in past centuries. The main purpose of chemical refining is to saponify the FFA by an alkaline solution and dilute the resulting soaps in a water phase. These soaps are removed by separators. For small-scale batch processes static separation is used but for continuous processing and large-scale processes, centrifugal separation is used. The neutral oils are subsequently bleached and deodorized. This chemical refining can be used for reliably refining virtually all crude oils, including oils of low quality, with the exception of castor oil.

The aim of HUM Refining is to remove the objectionable co-constituents in the oil with the least possible damage to the glycerides and minimal loss of desirable constituents.

It is a sequence of several of the following processes:

❚ HUM Degumming (HDGM), to remove phospholipids or gums from the crude oil.
❚ HUM Neutralizing (HNTR), to remove of free fatty acids, residual phospholipids in degummed oils or all the phospholipids in the crude oils are also removed as insoluble hydrates
❚ HUM Bleaching (HBLC), to remove pigments, metal and soaps from the crude oil.
❚ HUM Winterizing (HWNT), to remove of high temperature melting components present in small quantities.
❚ HUM Deodorizing (HDEO), to remove volatile compounds (mainly ketones and aldehydes) contributing to oil taste and odor, total free fatty acids in physical refining and the residual free fatty acids from neutralized bleached oils.

HUM Degumming (HDGM)

Crude oil obtained by HUM Oil pressing (HPRS) or HUM Extraction (HEXT) of oilseeds will throw a deposit of so-called gums on storage. The chemical nature of these gums has been difficult to determine. They contain nitrogen and sugar and can start fermenting so they were at one stage thought to consist of glycolipids and proteins. Now it is known that these gums consist mainly of phosphatides but also contain entrained oil and meal particles. They are formed when the oil absorbs water that causes some of the phosphatides to become hydrated and thereby oil-insoluble. Accordingly, hydrating the gums and removing the hydrated gums from the oil before storing the oil can prevent the formation of a gum deposit. This processing is carried out by HUM Degumming.

HUM Winterizing (HWNT)

This step, also called dewaxing, is only applied when the oil is not clear at room temperature because of the presence of waxes or saturated triacylglycerol’s. It is important to note that these compounds do not affect negatively the oil performance or functionality, but the appearance of the oil is not acceptable to consumers. Thus, the objective of this step is the removal of high temperature melting components present in small quantities. The crystallization process normally used consists of cooling the oil down gradually to temperatures of 4 to 8ºC in a maturing tank. After increasing the crystal size at this temperature for 24 h, the solids are separated by centrifugation at max 20ºC. This treatment ensures excellent clarity of oils when stored at either room or refrigeration temperatures.

HUM Deodorizing (HDEO)

Deodorization of fats and oils normally consists of steam distillation at elevated temperature under reduced pressure, although nitrogen has also been used. The purpose of this step is to remove volatile compounds (mainly ketones and aldehydes) contributing to oil taste and odor, total free fatty acids in physical refining and the residual free fatty acids from neutralized bleached oils. The deodorization conditions also contribute to the removal of contaminants (light PAH, pesticides, etc.) and to the reduction of color of the oil due to the breakdown of the remaining carotenes at high temperature. The efficiency of deodorization is a function of pressure (max 3 mbar,g), temperature (230 to 260ºC), residence time (0.5 to 3 h) and volume of stripping gas (1 to 3%). However, differences in the deodorization equipment used also have a major impact on efficiency. After the deodorization, the oil is cooled and addition of citric acid (100 mg/kg of 20% citric acid) is recommended to chelate metal traces and increase its stability during storage.

HUM Deodorizing (HDEO) will meet semi-continuous or continuous multi-level column requirements in deodorized way, whether it is after a conventional chemical refinery system or a de-acidifier, which is the main function of a modern physical refinery plant. Election of continuous deodorization will be appropriate for the product changes occurring once or twice a week; if product change is performed more frequently, semi-continuous deodorization will be appropriate.

The advantage of PLC controlled process is that it makes possible change of feeding oil of different type without interrupting the normal deodorization operation, with the possible lowest product mixture ratio. The start signal at the automatic controlled process of the plant is the pumping in of the raw oil. Every independent oil tribute is introduced to deodorization step by step following the steps as follows: degassing, heating with heat exchanger of heater, final heating with high pressure steam, deodorization, cooling with the heat exchanger of heater and cooling with indirect cooling liquid. Oil is processed passing through different deodorization layers before it is cooled by internal heat transfer at the last step where citric acid is added to steam in the scraper column.

Deodorization, which is the last step of refining process, is a distillation process, using steam as carrier, in order to remove unwanted odor and taste from the degummed or neutralized oil for the purpose of producing high quality oil or tallow.

It will meet all your semi-continuous or continuous multi-level column requirements in deodorized way, whether it is after a conventional chemical refinery system or a de-acidifier, which is the main function of a modern physical refinery plant. Election of continuous deodorization will be appropriate for the product changes occurring once or twice a week; if product change is performed more frequently, semi-continuous deodorization will be appropriate.

HUM MULTI-LEVEL DEODORIZATION COLUMN

Semi-continuous deodorization and de-acidification process principle

Amount of tribute must absolutely be defined before degummed and bleached oil is fed to deodorization unit. Determination of the definite amount of tribute can be done by weighing in a feeding tank on loading cells or by the volume of the degassing tank on deodorization.

The start signal at the automatic controlled process of the plant is the pumping in of the raw oil. Every independent oil tribute is introduced to deodorization step by step following the steps as follows: degassing, heating with heat exchanger of heater, final heating with high pressure steam, deodorization, cooling with the heat exchanger of heater and cooling with indirect cooling liquid.

The advantage of PLC controlled process is that it makes possible change of feeding oil of different type without interrupting the normal deodorization operation, with the possible lowest product mixture ratio.

General edible oils and tallow are deodorized in temperatures varying between 230-260°C and about 3 mbar pressure.

Continuous deodorization and de-acidification process principle with scraper column

The degummed and bleached oil is first pre-heated via heat transfer in the heating system made of hot deodorized oil. Then it is brought to final process temperature by indirect high pressure steam heating.

For the de-acidification of higher free fat acids, remaining time in scraper column at higher scraper temperatures is with lower temperature (heat change in the middle is optional).

Oil is processed passing through different deodorization layers before it is cooled by internal heat transfer at the last step where citric acid is added to steam in the scraper column,

General edible oils and tallow are deodorized in temperatures varying between 230-260°C and about 3-5 mbar pressure.

STRIKING POINTS

❚ High vacuum at each tray of deodorizer
❚ Heating of oil to deodorization temperature under vacuum
❚ Internal heat change at deodorization
❚ Internal heat exchange at deodorization under vacuum with the help of single or double heaters at semi-continuous process.
❚ Heat exchange between cold bleached oil and hot deodorized oil under vacuum at continuous process
❚ Processing of edible oil appropriately for such reasons as short stay of the oil containing high free oil acid under high temperatures at scraper column at continuous process.
❚ Excessive limitation of the air entering to deodorization
❚ Citric acid dosage that makes compounds with heavy metals in the oil in order to reduce the ratio of the oxidation of deodorized oil.
❚ Low pollution of each tribute during product change at semi-continuous process.
❚ Low increase rate of trans-isomers during deodorization at low temperatures
❚ High quality of deodorized oil for such reasons as low increase ratio of trans-isomers in case the oil, which is scraped under high temperatures, and which contains high free fat acid has an additional scraper column.
❚ Deodorization by the circulation systems with high efficiency heat exchange and mammoth pump
❚ No time and product loss for frequent product changes at semi-continuous process
❚ Heat recovery between incoming and outgoing oil at continuous process.
❚ Low oil levels at the levels of deodorization at continuous process
❚ High plant efficiency for such reasons as decreased steam consumption during processing of the oil containing high free fat acid with the inclusion of an additional scraper at continuous process.
❚ Free fat acids are concentrated in a steam scraper and thus waste water is minimized.
❚ De-acidification, as a continuous process integrated with a physical refinery plant does not produce waste as soapstock as in chemical refinery. This means less investment and operational cost.