FILTRATION PROCESS- The Basics of Solid/Liquid Separation
This section is intended to conceptualize filtration in general as well as give some guidance on what type of filtration you are looking for. Simply put, a fully automated, self-cleaning, constant pressure and throughput filter does not exist. Each of our models offers an optimum solution to specific aspects of filtration, while sacrificing others. Any vendor who claims otherwise has failed to filter their spin.
The first step to solving any filtration problem is determining the square feet of filter area and cubic feet of cake capacity that are required to achieve a specified throughput. To begin to approximate an answer, compare your situation to clean water, which flows through the typical filter at a rate of one gallon per square foot per minute. Provide and conceptualize with scale-able data. The viscosity of your product will play an important part in determining filter area as well. If you are filtering honey, for example, you may need a larger filter area to get the desired throughput than if you are filtering whiskey. All of our filter models accommodate different cartridges to adjust to your specific needs: for example, our 33" Diameter Horizontal Plate Filter can have the same size pressure vessel with 42 filter plates (for more filter area and lower solids) or only 17 plates (with a greater cake capacity). The same logic is applied to our vertical plate filters by increasing or decreasing spacing between the filter plates.
Particle Size & Percentage of Solids
Determining your processes level of filtration is an important step in determining the type of filter and media you need. Find the particle size of the solids you are attempting to filter and the particle size distribution. If your particle size is above 75 microns you may be able to use a wire mesh or sieve-type media. If your particle size is 3-75 you may be looking at filter paper. Less than 3 microns you will be looking at using a filter cake composed of diatomaceous earth or a membrane filter. Determining the percentage of solids in your slurry is also essential in selecting a filter type. Larger percentages of solids will change the spacing between filter plates (also known as filter leaves) and possibly even the type of filter and consumables (DE, Activated Carbon, etc).
The temperature of your slurry will play a large part in determining the type of filter, material of construction and selecting filter media. Higher temperature applications may require a jacket on the filter, require a specific gasket type and limit your filter media options.
Horizontal Or Vertical
In addition to filtration surface area, we need to decide whether your optimum solution requires horizontal or vertical filter plates. Factors that could influence this decision include automation requirements, economics of first cost and filter media, ergonomics, space restraints, flow rate, cake thickness and more.
Generally, but not always, our vertical plate MCRO's are used for high flow industrial applications or when automation is required. Vertical filters are often used with limited floor space or when automation is required. Horizontal plate filters are often used as an industry standard due to their lower first cost and ongoing economics of use, ease of use and versatility.
Whether you call it a pressure filter, leaf filter, vertical pressure filter, vertical pressure leaf filter, horizontal filter or horizontal leaf filter a general description of Sparkler®’s configurations follow:
Horizontal Plate Filters (HPF) have a horizontal plate configuration with a vertical shell
Vertical Filters (VF) have vertical filter plates with a vertical shell
MCRO filters have vertical filter plates with a horizontal shell
Nutsche filters have a single horizontal plate or basket in a vertical shell
We have constructed filter vessels from Carbon Steel, all varieties of Stainless Steel, Hastelloy, Titanium, Monel, Copper, Iron, Nickel and unique combinations for wetted and non-wetted components. Again, material matters only in the context of your problem. We have fabricated filter plates from all of the above materials and Polypropylene. Chemical compatibility, temperature and acidity are some things to consider when selecting the material of construction for your pressure filter.
Every filter may be outfitted with a heat/coolant jacket to decrease product viscosity, drying and other process aspects related to temperature control. Depending on design and material, temperature may range from 20F to 3500F. Every vessel may be piped and flanged to accommodate any installation requirement. Sight glasses, base type, cover mechanism and additional ports are all things to consider when determining the design of your pressure filter.
Most models use air, nitrogen, or some other pressurized gas to force end cycle filtrate through the system, assuring maximum batch filtration and economic return. If filter aid precoat and body feed are used, the end-cycle discharge phase dries accumulated cake, see Dry Cake Discharge. This result makes the manual cleaning of horizontal plate filters more user friendly and enables vibratory dry cake discharge of vertical plate models. In many of our models a Wet-Cake Discharge is the most efficient method and consists of manual or automatic "washing" the filter plate clean.
Filter Media is a section all on its own, see the about section on filter media for additional information. Back in the day, Sparkler Filters® were touted for their capacity to use virtually every filter media in existence. Indeed, media was regarded as so critical to the process the company adopted a sort of Swiss Army Knife attitude towards its products; since each model worked well with the five major media used at the time, it should be considered as five filters in one. Nothing has changed. Our horizontal plate filters have been built to accommodate every media currently available, including every paper, cloth, membrane, screen, and every filter aid, including diatomaceous earth, activated carbon, cellulose, Perlite and Dicolite.
Filter Cake in general terms is the sum of cake solids captured within a filter. These cake solids can be relatively wet, relatively dry, packed, loosely packed, porous, nonporous, dense, sparse, thick, thin, heterogeneous, homogenous and all these variants are based on the characteristics of the accumulated solids and process conditions.
In many applications and specifically when a precoat is used, the initial barrier, membrane or septum is the lattice or structure that we build cake solids. During primary filtration the cake solids build, increasing efficiency and depth. The depth of the cake solids also increases resistance to flow.
When the filter cake is the product, sometimes a wash step and/or a drying step is added. Air can be used to blowdown and/or blowback liquid. End of cycle steps to change characteristics of captured solids are based on desired cake discharge and desired output.
Body feed is when additional porous material is added to product before or during filtration to counteract and reduce the resistance created by the solids to be filtered. In instances where we capture and remove a sticky, tacking and compressible solids body feed is added at some ratio to maintain porosity and void fraction within cake solids extended run time and increasing cake thickness.
Thie brief article just touches the surface of industrial liquid filtration. Proper filtration can be a difficult and technically challenging subject. With this general information in mind, our L-1000 lab filter and other rental units are available for scale able testing. We recommend conducting experiments if your filter application is challenging and you do not have reliable data, for the purpose of determining how much your application varies from our reference standard of water, whose characteristics are one gallon per minute per square foot; flux rate of 1 gpm/ft2. Together we can zero in on a solution that will remove variability from your filtration process. If you would like assistance on selecting the right filter for your specific application, please contact us or fill out a application data sheet here.