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29
Jun
2021

What is a Lenticular Filter and How Do They Work?

Posted: 06/29/2021
Updated: 07/06/2021
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This definitive guide will cover the basics of lenticular filters, how they function, what benefits they provide and the many ways in which they can be customized.

What is a Lenticular Filter?

A lenticular filter is a type of filter cartridge that utilizes a wide surface area and the use of depth filtration to maximize retention of solid contaminants.

cartridge cross-section
Cross-Section of a Lenticular Filter
filter cell cutaway
Cutaway of a Lenticular Cell

The main characteristic that makes lenticular filters unique is their accordion-like structure, which is designed to maximize surface area.

Lenticular filters are made of a series of stacked discs or "cells" attached to a central core.

Each cell is comprised of a rigid polypropylene center support screen sandwiched between two round discs of depth media which are then secured together on the outer edge via a thermally bonded polypropylene band. The completed cell is then thermally bonded to the center core to prevent product bypass. The channel-like structure of the cell interior is designed to direct the flow of liquid toward the central core.

The Importance of Surface Area

In filtration, "surface area" or “effective filtration area” refers to the total area of the filter that is capable of processing fluid. Surface area is the key determining factor for flow rate, or how quickly fluid moves through the filter.

The more surface area a filter has, the quicker it can process fluid. This makes lenticular filters ideal for applications that require processing large volumes of fluid with heavy solids content.

The number of cells a lenticular filter has and the space between each cell directly affect the filter's total surface area.

How Does a Lenticular Filter Work?

Just like most cartridge filters, lenticular filters flow from the outside in. Here’s how it works:

filter flow diagram
Lenticular Filter Flow Diagram

First, the unfiltered liquid is pushed into the filter housing through the housing's inlet pipe. This is achieved by applying positive pressure to the feeding vessel using either a pump or compressed air. As the liquid flows into the housing, it surrounds the filter and envelops each cell. The pressure forces the liquid into the filter media of the cells.

As the fluid moves through the depth media, it follows what is known as a "tortuous path", meaning it takes a non-linear route. The numerous twists and turns the fluid must take depletes the energy of the particles in the fluid, causing them to become "trapped" within the media.

Unlike standard membrane filters where contaminants are trapped on the surface alone, depth media captures contaminants throughout the entire volume of the media.

Finally, the filtered fluid reaches the center of the cell, where it is channeled into the filter core and down through the outlet pipe of the filter housing.

What are the Benefits of Lenticular Filtration?

Lenticular filtration is not the only means of removing heavy solids over a broad surface area. For example, a filter press can be used to achieve the same goal. There are, however, several advantages of lenticular filtration that make it a desirable alternative to plate and frame filters.

Of course, the degree of benefit will be different for each application, and not all applications will benefit from using lenticular filters over a filter press.

High Flow Rate

One of the main advantages of lenticular filtration is a high flow rate due to the increased surface area. This allows large batches of product to be processed in a short period of time, which leads to a quicker return on investment.

Easy Filter Changeout & Maintenance

Lenticular filters have a modular design that allows them to be replaced easily and quickly. This results in less downtime spent changing out filters.

Additionally, this design makes lenticulars fully CIP (clean in place) capable.

Increased Scalability

Another benefit of the modular design of lenticular filters is ease of scalability. Lenticular housings are designed to scale vertically, so you can increase your capacity by adding filter elements to your existing housing. Lenticular housings are made to accommodate up to 4 cartridges and can be built in the vertical or horizontal orientation depending on your needs.

Small Footprint

Vertical scaling also means that a lenticular housing offers a very small footprint regardless of how many filters it holds. A 4-stack lenticular housing has the same footprint as a 1-stack lenticular housing. Additionally, most lenticular housings are built with mountable legs, allowing them to be fitted with casters or mounted on a skid for mobility.

Low Startup Costs

The cost of filter presses varies greatly and can easily reach the $100,000 range. For those starting out on a budget, the $1,000 - $3,000 cost of a lenticular housing is much easier to manage.

Fully Closed Loop – No Leaks

Lenticular filter housings are completely closed loop. Product can be processed start-to-finish without ever being open to atmosphere. This is particularly useful for applications that deal with hazardous or volatile liquids.

Applications for Lenticular Filtration

Lenticular filtration is most beneficial for applications where the fluid being processed is heavily saturated with solids.

The applications best suited for lenticular filtration include:

Can You Reuse a Lenticular Filter?

Lenticular filters can be reused with limited effectiveness if properly stored between runs. Proper storage for lenticular filters will vary depending on the application and the chemical composition of the fluid being filtered.

To find out what storage methods are best suited for your application, visit our Contact Us page and speak with a filtration specialist.

Due to the nature of depth media, cleaning a lenticular filter for reuse can be a challenge. Because depth media retains particles throughout its entire volume, cleaning the surface of the cells provides only a marginal increase in filter life.

The life of the filter can also be extended by running a cleaning solvent through the filter such as ethanol, but even this produces diminishing returns with each use. Eventually, the filter will need to be replaced.

When Should You Replace a Lenticular Filter?

The right time to replace a lenticular filter depends on the type of lenticular and what it is being used for. The process for determining when to change out your filter will be different depending on whether the filter is being used to remove solids or to remove color.

When Removing Solids

For lenticulars used to remove solids or waxes, it's generally best to replace the filter when the differential pressure reaches around 25 psi.

Differential Pressure

Differential pressure is the difference between the inlet pressure and outlet pressure. As the filter starts to load up with solids, the pressure of the fluid entering the housing at the inlet (the dirty side) will increase while the pressure of the fluid exiting the housing at the outlet (the clean side) will decrease. Finding the difference between these two pressures will help you determine when it's time to replace the filter.

When Removing Color

When using carbon lenticulars to remove color, the only way to know when to change the filter is to observe the color of the end product. This can be done inline by using a sight glass fitting on the outlet pipe of the lenticular housing. When the color of the fluid exiting the housing returns to the original green color of the fluid entering the housing, it's time to change the filter.

Can You Backwash a Lenticular Filter?

A lenticular filter can only be backwashed if it was built to allow backwashing. This usually involves covering the lenticular cells with a protective layer of scrim or netting to prevent filter shock due to flow reversal during the backwashing process.

Although the life of your filter can be extended by backwashing, the amount of life recovered will be limited by how much particulate is captured beneath the surface of the media. The features that make depth media effective at capturing particles also make it difficult to release those particles when backwashing.

Carbon lenticular filters will not benefit from backwashing as the spent carbon cannot be recovered using this process.

Warning

Reversing the flow of liquid on a lenticular without this protective layer can damage or outright destroy the filter.

top view of filter destroyed by backflow
Top view of a lenticular filter damaged by backflow
filter blowout due to backflow
Side view of a lenticular filter damaged by backflow

Types of Lenticular Filters

Not all lenticular filters are created equal. To find the right filter to fit your needs, you will first need to be aware of the options available.

Warning

Do not try to mix different types of lenticulars in the same housing! A common misconception about stacking lenticular filters is that the flow of liquid moves from one filter to the next. This is not the case! Liquid is processed by all cartridges in the housing simultaneously, not in stages. It’s best to think of the stacked cartridges as one single filter, just with more surface area.

Double O-Ring vs. Flat Gasket

Lenticular filters are available in two different end configurations: Double O-Ring and Flat Gasket. Each configuration requires a different type of housing, so figuring out which type suits your needs best should be the first thing you do.

Flat Gasket

flat gasket lenticular filter
Lenticular Filter - 12 Inch - Flat Gasket

Flat Gasket (also known as "double open end") is most common in the beverage and botanical extract industries. They are designed to be used with a center post that goes through the filter core to hold it in place.

A spring at the top of the center post applies pressure to the filter, pressing the gaskets against the metal surface of the housing to form a seal. The height of the center post must match the number of filters used in the housing, so scaling up requires the purchase of a new center post as well as a new dome for the housing.

Pros
  • More readily available on the market
  • More compact and easier to store.
  • Compatible housings are generally less expensive.
Cons
  • Flat surface seal is prone to bypass.
  • Requires the use of a center post and additional parts.
  • Scaling up is more expensive.

Double O-Ring

double o-ring lenticular filter
Lenticular Filter - 12 Inch - Double O-Ring

Double O-Ring lenticulars do not require the use of a center post. They have a male and female end and are designed to plug into each other when stacking. The tabs of the male end are aligned with the grooves of the female end and locked into place.

A positive seal is formed when the two o-rings on the male end of the filter are pressed against the inner wall of the female end. This dual o-ring design virtually eliminates the potential for bypass. A major benefit of the plug-in design is that scaling up only requires a new housing dome as there is no center post to deal with.

Pros
  • Dual O-Rings virtually eliminate bypass
  • Less spare parts to deal with
  • Scaling up is easier and less expensive
Cons
  • Less market availability
  • Cartridges can be difficult to remove or install if o-rings are not lubricated
  • Compatible housings tend to cost more

Filter Aids

The depth media in a lenticular filter is commonly joined with some type of filter aid to increase efficiency. A filter aid is a powdered substance that is either added to the solution being filtered or incorporated into the filter media itself. Lenticular filters can be embedded with filter aids to avoid the hassle of dealing with loose powders.

The two most common filter aids used in lenticular filters are Diatomaceous Earth and Activated Carbon.

Diatomaceous Earth

microscopic view of a diatom
A diatom viewed through an electron microscope.

Diatomaceous earth (DE) is a white, chalky powder made up of tiny silica structures known as diatoms. It is a powerful filter aid for removing solids due to the porosity of the diatoms. The diatoms are composed of a honeycomb structure of variously sized pores. This allows it to capture minuscule molecules such as bacteria and some viruses.

When incorporated into depth media, the diatomaceous earth forms a "porous cake" that strains particulate out of the liquid that passes through it. This results in effective removal of ultra-fine particles without affecting flow rate. Another advantage of diatomaceous earth as a filter aid is that it does not affect the odor or color of the filtrate.

Activated Carbon

activated carbon lenticular filter
Carbon Lenticular Filter

Activated carbon is extremely effective at removing unwanted color and odor in botanical extracts. The murky, green color of crude extract is caused by plant dyes such as chlorophyll which are byproducts of the extraction process. Activated carbon binds to the chlorophyll molecules, removing them from the solution.

The result of treating crude extract with activated carbon is a clear liquid with a light gold color. Carbon lenticulars provide an efficient way to remove color and odor without having to deal with the hassle of loose carbon powders.

Micron Rating

The micron rating of a filter refers to the size of the particles it's built to remove. For reference, the smallest micron size visible to the human eye is around 40 - 60.

Lenticular filters can be customized with micron ratings as low as 0.25 (bacterial scale). The best micron rating for your needs will depend on your application and what you're looking to filter.

To find out what micron rating is best suited for your application, visit our Contact Us page and speak with a filtration specialist.

Cartridge Diameter

There are two sizes available for lenticular filters: 12-inch and 16-inch. A 16-inch lenticular offers more than twice the surface area of the standard 12-inch version. This means that two 16-inch lenticulars can process more than twice as much product as two 12-inch lenticulars.

While this may tempt you to start using the 16-inch version right away, the availability of 16-inch housings and cartridges is much lower than that of the 12-inch version. Still, if you find yourself in a situation where a 3-stack 12-inch lenticular setup isn't sufficient, consider switching over to the 16-inch version.

Gasket Material

Lenticular filters use gaskets (o-rings) to create a seal. The material of these gaskets can be customized to fit your application's needs. Due to the varying compatibility of elastomers and chemicals, it's best to choose a gasket material that is the most compatible with the chemical composition of the liquid you are filtering.

If you are unsure of which gasket material is compatible with your application, take a look at this Chemical Compatibility Database by Cole-Parmer.

Is Lenticular Filtration Right for Me?

By now you should have a good idea of what lenticular filters are and how they work. You're probably wondering how lenticular filtration fits into your application, or whether it fits at all.

First, ask yourself the following questions:

  • Is the fluid you’re filtering heavily loaded with solids or waxes?
  • Do you have limited space for equipment in your facility?
  • Do you need to process large batches over a short period of time?
  • Is the product you’re filtering vulnerable to oxidation?
  • Are you dealing with volatile solvents or liquids that require adherence to strict regulatory standards?

If you answered one or more of those questions "yes", then it’s highly likely that you will benefit from lenticular filtration.

Our Work in Lenticular Filtration

For years CLEAR Solutions has assisted professionals across numerous industries with equipment installation, standard operating procedures and troubleshooting.

In that time, we’ve helped our users mitigate various issues and roadblocks related to filtration. If our knowledge and experience can help you avoid an expensive mistake, why not take advantage of it?

We represent manufacturers of the highest quality and best performing lenticular filters on the market. This includes the company that invented the lenticular filter, ErtelAlsop!

But that's not all we provide. With over 30 years of application experience and a vast network of industry experts and engineers, we not only provide you with the equipment to get the job done, but the knowledge to get the job done well.

Where Can You Buy Lenticular Filters?

If you know what you're looking for and need something fast, we offer several options for lenticular filters and housings that can be purchased directly through our Online Store. These filters have been customized to fit the numerous application needs.

If you still aren't sure if lenticular filtration is right for you or if you're looking to speak to a filtration specialist to help you build a customized solution, we're happy to help. You can fill out our contact form, or reach out to us directly by phone (949) 429-8922 or email info@clearsolutionscorp.com