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PRE TREATMENT AND BLEACHING
The feed oil is heated to 65-70°C in the Economiser by outgoing deodorized oil followed by feed heater (during start up). Concentrated phosphoric acid (0.05 - 0.10%) is injected by the Acid Metering Pump and intensively mixed with the oil in the Acid Mixer before entering the Conditioning Reactor. The oil is discharged into the slurry mixer above the Bleacher. The Pre-treated oil is pumped in to the Bleacher vessel which is kept under vacuum, and heated up to Bleaching temperature under continuous mechanical agitation. The calculated quantity of bleaching earth is charged to Bleacher under oil level in order to avoid earth entry to the bleaching vacuum system. The earth adsorbs any residual gums and soap as well as trace metals, color bodies and other polar impurities. The Bleacher has mechanical agitator operates under vacuum to ensure complete moisture and air removal. The dried oil-earth mixture is discharged to the Filters with the help of pump, where the spent earth is removed.
Filter Management: The standard bleaching system is based on the use of two filters of which one is on line while the other is being cleaned and prepared for the next cycle. When a filter has reached its maximum capacity, as indicated by high feed pressure, it is taken off line for cleaning and replaced by the other filter.
The cleaning procedure begins by first pressurizing the filter with steam to expel residual oil into the Recovered Oil Tank and dry the spent filter cake. The oil recovered from the filter cake is collected in the tank and can usually be recycled to the Bleacher. After drying, a bottom discharge valve on the filter is opened and the leaves pneumatically vibrated so that the spent cake is dislodged and discharged via a hopper. The filter is then closed and readied for the next batch. Before going on line again it can be pre-coated with filter aid and/or bleaching earth in order to seal the filter leaves and minimize clogging. The adsorbents are mixed with bleached oil in the Precoat/Heel Tank and applied to the leaves by circulation with the Precoat Pump. When not using filter aid or “off-line” pre-coat, the empty clean filter is filled and put on line while the other filter is still in operation. The filtrate from the clean filter is recycled back to the Bleacher until the filter is pre-coated with bleaching earth and the oil is clear. After this the full flow is switched to the new filter.