Learn What Filter Type and Size Is Best With Filtration Testing
By performing filter tests, we can determine the filterability of a slurry and determine the size of filter needed. These tests can also help decide if you need a horizontal belt filter, drum filter, or some other type of filter. The filtration tests can determine the optimum solids concentration and/or filtrate clarity that can be achieved.
Filtration testing includes filter cloth determination, filter cake solids or moisture determination, filtrate clarity, and cake wash efficiency, when needed. Filtration testing can also determine the best filter type or treatment for a particular slurry.
Drum filters, horizontal belt filters, disc filters, and other filter types use vacuum pressure to improve the filtration rate and liquid extraction beyond gravity filtration alone. Most filtration testing in the WesTech lab is under vacuum. This allows us to control the vacuum level, compare the performance of different cloths, and determine other parameters needed to size a filter.
The filter leaf is a base with channels that allows a filter cloth to be well supported and provides quick removal of liquid through the filter cloth while under vacuum.
We test various filter cloths based on particle size analysis of the slurry solids. We then compare the results of the tests and choose the filter that gives the best combination of filtration rate, cake discharge, durability, and filtrate clarity.
Cake washing can remove the mother liquor from a filter cake. We use filter cake wash testing to determine the volume of wash water needed to accomplish this goal.
Filtration testing produces filter cakes that form from the solids portion of slurries. We then determine the moisture and solids content of the filter cakes.
During filter testing, a vacuum filter flask collects the filtrate. We measure the solids content of the filtrate and report this as the expected filtrate clarity from a full-scale filter.
The solids in some slurries may be too small and diffuse to form a cake by regular vacuum filtration. In these cases, a bed of material, or precoat, can be built up on the filter cloth to catch the solids and keep them from passing through the filter cloth with the liquid. With each complete cycle, a blade removes a thin portion of the precoat, taking the solids with it and leaving a clean precoat for the next filtration cycle.
Diatomaceous earth and perlite are the common materials used in precoat bed formation. We test various grades of these materials, based on particle size analyses of the slurries. We then compare the ability of the materials to stop the solids on the surface and minimize or prohibit penetration of the solids into the precoat bed. We then compare the form time, cake formation, and filtrate clarity of the sample with the different precoat materials and choose the one best suited for the slurry.
Because a portion of the precoat bed is removed with the solids cake each revolution, the precoat bed will eventually be consumed. The precoat bed consumption rate is calculated and reported to determine how long the filter may run before the precoat bed needs to be renewed.
Another driving force used in filtration is compression – forcing the liquid out by squeezing the slurry in some manner. We have a benchtop filter press that uses plates of varying thicknesses to test this type of filtration. With an air compressor providing the driving force, an air diaphragm pump pushes the slurry into a chamber that has filter cloths on both ends. We use the data generated during testing to size a filter press for the specific slurry submitted.
Lab testing helps determine chemical pretreatment, percent recycle, float layer solids concentration, and subnatant clarity.
Our jar testing helps determine chemical pretreatment for coagulation, flocculation, metals removal, and more.
We provide guidance on equipment decisions related to thickening and clarification.