Filter Cake Washing Method

Filter Cake Washing Method

Filter presses are often used for solid-liquid separation in the industrial field, forming filtrate and filter cake. Some filter presses are equipped with a filter cake washing system, which can clean the filter cake. This article will introduce you to filter cake washing and filter cake washing methods.

What is Washing Cake?

The operation process of displacing the mother liquor from the filter cake with washing water is called filter cake washing. In this case, the mother liquor usually needs to be collected, or the mother liquor is toxic and needs to be cleaned.

The washing process of the filter cake is more complicated than the filtration process because washing not only involves the flow of washing water and mother liquor in the pores of the filter cake but is also accompanied by phenomena such as liquid replacement, mixing, and diffusion. Therefore, the washing of filter cake is a very complex process with many influencing factors. In addition, the mother liquor between the particles is constantly replaced by washing water per unit time, which will cause the diluted concentration of the washing liquid between the particles to drop even lower. Therefore, under the premise of the same amount of washing water, multiple washings of the filter cake will make the washing rate higher, and the filter cake washing will be completed more thoroughly.

Why is Washing of Filter Cake Required?

• Remove impurities present in the filter cake to purify the filter cake and improve the purity of the filter cake;
• Recover valuable filtrate retained in the filter cake to increase filtrate recovery rate;
• The mother liquor is toxic. Use washing liquid to dissolve harmful impurities in the filter cake.

3 Filter Cake Washing Methods

Displacement Washing: This method involves passing the washing liquid through the filter cake in a single direction. It’s efficient in removing soluble impurities as the washing liquid displaces the mother liquor in the cake. The effectiveness of displacement washing depends on the cake’s uniformity and the washing liquid’s flow rate.

Dilution Washing:  Dilution washing: In dilution washing, the filter cake is re-slurried, and the filtering and washing are repeated. This method is more thorough than displacement washing but requires more cleaning fluid. It’s particularly useful when the cake is less permeable or when the impurities are more challenging to remove.

Countercurrent washing: This advanced method involves multiple washing stages, in which the freshest washing liquid contacts the cleanest filter cake, and then the discharged liquid can be used as the washing liquid for another stage, and the liquid discharged again is used as the washing liquid for the final stage. What is discharged later can be used as mother liquor.

Conclusion

Each of these methods has its advantages and applications depending on the nature of the filter cake, the types of impurities remaining, and the desired purity level of the final product. The choice of washing method should be based on the understanding of the filtration process and the properties of the filter cake.