Bleaching & filtration
is carefully designed to allow processing of low quality feedstocks. Filters can be aligned to allow evacuation of spent bleaching earth by redler transport system to central point. Spent cake cooler can be added for safety.
In general, the first stage of the pre-treatment is done in the ‘degumming section’. Here a large part of contaminants is removed from the raw material blend, but the oil after degumming still needs additional cleaning steps to finally meet the stringent specifications for contaminants before the HVO units. As a second cleaning step the degummed oil can be bleached with solid absorbents (bleaching clays, silica, filter aids...) to reduce mostly the P and metals content of the feedstocks to acceptable levels.
For ‘good’ quality feedstocks (most vegetable oils, UCO, PFAD, etc) the sequence of these two cleaning steps is sufficient to reach the required purity of the feedstock blends, as specified by the HVO technology providers. However, for some low quality feedstocks (low grade animal fats, low quality UCO, fatty acid oils etc...) some additional pre-treatment steps still might be added as an option.
How does it work?
The oil blend coming from the degumming section, is first again pre-treated with some citric acid solution with high shear mixing, to allow better removal of residual P and metals.
Then the solid absorbents (bleaching earth, filter aid, silica...) are dosed in the oil stream. Especially for large plants, the dosing systems can be fully automated with silo’s for the absorbents, pneumatic conveying systems and precise dosing units. Then the oil will be contacted with the absorbent(s) during a well defined time in the bleacher (‘bleaching’).
From the bleacher the oil is then pumped to the vertical hermetical filters for removal of the contaminants together with the absorbents by filtration. The spent filter cakes are collected under the filters and need to be disposed. Also this system can be fully automated with cake coolers and conveyor systems, to minimize human intervention in the process to a minimum. After final polishing filtration and cooling, the oil is then ready to go to the HVO production units.
