Rotary pressure filters are extensively utilized in the sugar industry to filter carbonated liquor, a solution consisting of sugar and lime that has undergone carbonation to eliminate impurities. These filters are known for their ability to conduct both pressure filtration and cake washing within a single unit.
A rotary pressure filter comprises a cylindrical drum that rotates at a gradual pace either horizontally or vertically. The drum is partitioned into multiple sections, each equipped with its individual filter medium, commonly made of cloth, and designated process zone. The drum is enclosed within a pressure vessel, which contains the feed slurry, wash liquid, and filtrate. Rotary pressure filter involves several key steps for proper filtration-
Distribution: Carbonated liquor, containing a mixture of sugar crystals and molasses, is evenly distributed onto a filter medium (typically a cloth) that covers a rotating drum. The drum is divided into compartments, each filled with the filter medium.
Filtration: As the drum rotates, the carbonated liquor passes through the filter medium, allowing the liquid to flow while the sugar crystals and impurities form a layer of filter cake on the surface. The filter medium captures and retains the solids while permitting the passage of the liquid.
Washing: Following the initial filtration, the filter cake undergoes a washing process to eliminate any remaining molasses or impurities. Water or a specialized washing solution is sprayed onto the filter cake, dissolving and removing undesired substances.
Drying: Once the washing is complete, the filter cake goes through a drying phase to eliminate any excess moisture. This can be accomplished by applying heat or utilizing a vacuum to extract the remaining moisture from the filter cake.
Discharge: Finally, the dried filter cake is discharged from the rotary pressure filter, while the filtrate (filtered liquid) is collected for further processing.
The rotary pressure filter is specifically employed in sugar refineries for filtering carbonated liquor due to several advantages:
Continuous Operation: The system allows for uninterrupted operation, ensuring a consistent flow of filtered liquor. This is particularly important in sugar refineries that require a continuous production process.
Efficient Separation: The rotary pressure filter effectively separates sugar crystals from molasses and other impurities. This capability plays a crucial role in producing high-quality sugar by removing unwanted substances. It can handle high solid concentrations and viscosities, which are typical for carbonated liquor. And it has low filtration rates and low residual moisture, which improves the efficiency and quality of sugar production.
Washing Capability: It can perform multiple cake treatments in a single unit, which reduces the need for additional equipment and space. The filter cake can be thoroughly washed to eliminate residual molasses and impurities, resulting in a clean and refined product.
Drying Capability: They operate in a closed and gas-tight manner, which prevents air ingress and product oxidation. The drying process within the rotary pressure filter helps achieve the desired moisture content in the filter cake, ensuring optimal sugar quality.
Overall, the rotary pressure filter provides a reliable and efficient solution for the filtration of carbonated liquor in the sugar refinery, contributing to the production of superior-quality sugar products.
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