Bleaching in food industry

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1. OBJECTIVE


The objective of bleaching is to remove pigments, metals, e.g. nickel or iron from other oil refinery process; residual soaps and phospholipids from the oil or fat (BAT in the Food, Drink and Milk Industries, June 2005).


2. FIELD OF APPLICATION


Bleaching is applied in the refining of edible oils and fats and also in fruit and vegetable canning. (BAT in the Food, Drink and Milk Industries, June 2005).


3. DESCRIPTION OF TECHNIQUES, METHODS AND EQUIPMENT


Edible oils and fats are mixed with bleaching earth that has an affinity for adsorbing the above mentioned undesirable compounds. The oil is mixed under vacuum conditions with 0.1-3% of bleaching earth. This is a clay mineral, such as bentonite or montmorillonite, that has been activated by thermal and/or acidic or other treatments. These earths, sometimes mixed with small amounts of activated carbon, have a very high adsorbing capacity. After bleaching for 30-90min the oil is separated from the bleaching earth using filters. The spent earth contains high amounts of oil, up to 30%. A steam stripping process can recover a part of the oil or fat. Used bleaching earth can be added to the meal in integrated installations. The bleached oil is further treated in other refinery processes. The equipment used for bleaching consists of mixing vessels, vacuum generators and filters (BAT in the Food, Drink and Milk Industries, June 2005).


4. COMPETITIVE TECHNOLOGIES AND ENERGY SAVING POTENTIALS


a) Changes in the process
  • Re-use of waste steam: (BAT in the Food, Drink and Milk Industries, June 2005)
During the bleaching process, oil and bleaching earth are heated by steam up to temperatures 130°C. Steam is also needed for the oil recovery from the spent bleaching earth. Re-use of waste steam from other stages of the refining process can reduce the energy consumption.
  • Energy production from spent bleaching earth: (BAT in the Food, Drink and Milk Industries, June 2005)
The spent bleaching earth contains 20-40% fat. This makes the waste prone to spontaneous combustion or valuable material for bio-gas production.


b) Changes in the energy distribution system
No information is available.


c) Changes in the heat supply system
No information is available.


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