BLEACHING EARTHS
“Counter Current” Bleach Process (by B+B)
blocked, cleaning becomes necessary which, in turn, causes an interruption in flow. Most bleaching clays will act as a body feed and are made with excellent filtration characteristics. In bleaching, the amount of bleaching clay and filter aid used is an important cost factor. The amount of oil in the filter cake is also important as any oil in the cake will be synonymous with additional loss. Because filtration takes place via the cake built on the screen, cake drying is an important step as drying which takes place for too long or at too high a temperature will bake the cake on the screen.
FRESH CLAY BLEACHED FILTERED OIL
VACUUM BLEACHER
CONVENTIONAL LEAF FILTER
CAKE BACK TO MEAL PROCESS
Tri-Clear ® Double bleach ® or Combi-Clean ® Process Figure 5: Counter Current bleaching process (with pre-filtration and or silica purification) REDUCED CLAY SILICA
120-130°C
H2O (OIL)
BLEACHED CLEAN OIL
REFINED OIL
SILICA BLEACHER
90°C
VACUUM BLEACHER STAND-BY
Bleaching Filtration
70°C
(pre-coated application)
90°C VACUUM DRYER
CAKE BACK TO MEAL PROCESS24 x 110 Dutch Weave
Filter Screen Wire thickness 0.26 – 0.36 mm Figure 6: Tri-Clear, Combiclean process or DoublePass bleaching • Retention approx. 120 microns nominal •
Bleaching Filtration
Bleaching filtration (with standard carbon or fine clays, (pre-coated application) pre-treated with silica and pre-coated application) 24x110 Dutch Weave Filter Screen Wire thickness 0.26-0.36 mm PZ80 (Strong) Panzer Weave Filter Screen • Wire thickness Retention approximately 120 microns nominal 0.2 – 0.4 mm
Pre-coat Filter Screen •
Retention approx. 80 microns nominal
Bleaching filtration Mesh (Plain Weave) Filter Screen (with standard carbon on fine 60 clays, pre-treated with silica and pre-coated applicati on • Wire thickness 0.19 mm PZ280 (strong) Panzer Weave Filter Screen • Retention approx. 200-240 microns nominal Wire thickness 0.2-0.4mm Retention approximately 80 microns nominal Pre-coat filter screen 60 mesh (Plain Weave) Filter Screen Wire thickness 0.19mm Retention approximately 200-240 microns nominal Figure 7: Filtration screens fine as to go through the filter screen, nor too big as to block the screen. When the application requires a continuous dosage of filter aid during the entire cycle, this is called body feed. 24 OFI – JUNE 2022
Bleaching earths filtration June 2022.indd 5
The body feed will keep the cake open and will give enough porosity so that the maximum quantity of suspended solids can be retained before the septum becomes blocked. When the septum is
Source: PMI-Tech (Europe) BV
BLEACHER
Automation options
The processing industry has been looking for more efficient options to filter or clean bleached oil for many years. Increased capacities and increased number of filters has resulted in bigger units to provide more filter area per filter, less operator involvement, and more automation. Filter areas in vertical tank and vertical leaf filters have increased from 50m2 to 125m2 per unit. Horizontal tank filters are available at 225m2 per filter but require a much larger footprint and create housekeeping problems when opened for cleaning. Pressure leaf filters are discontinuous and need to be taken off-line to be cleaned, whereas a continuous process requires more than two filters, requiring more and better automation as there is no time to open filters for visual inspection. Cake discharge has always been a point of concern as it was not always known if the filter cake had left the filter after the vibration cycle, with cake accumulation potentially resulting in damaged filter leaves. The solution is the use of load cells that measure the weight of the empty filter tank. If the cake is not fully discharged, the filter will not be able 36 to go back on-line. The selected and chosen screen is also an important part of successful filter performance.
Source: PMI-Tech (Europe) BV
OPTIONAL SILICA BLEACH
Source: PMI-Tech (Europe) BV
FILTERED OIL
RPP PULSE FILTER
Filtration trends
Filtration is heading towards bigger capacities with multiple filters in service, which will demand more automation and better utilisation of installations. Waste management is also becoming increasingly important and special attention should be paid to spent clay and carbon; and the disposal of consumables such as filter bags and cartridges. This 38 will require the implementation of special screens and cake discharge systems to improve cake discharge in bleached oil. ● Rick Veldkamp is the European sales manager of PMI-Tech (Europe), Netherlands 37
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13/06/2022 15:13:23
