How To Extend the Life of Your Final Filters and Lower Costs
In every process, the final filter is critical in assuring that your filtrate meets expectations and requirements. It is typically the most expensive filter as well. The useful life span of a final filter will determine your replacement schedule and impact your filtration costs.
But what if it were possible to prolong the life of your final filters, improve process efficiency, and lower filtration costs? By implementing an effective Prefiltration strategy, this can be achieved.
Since 1998, we have been supporting process teams by providing effective business and technical filtration solutions that achieve our customers' goals. Critical Process Filtration is a mid-sized filter manufacturer that has designed and shipped millions of filters to numerous companies producing pharmaceuticals, food, chemicals, electronics, medical supplies, and more.
We have compiled the most commonly asked questions and situations that most filtration operations experience. Today, we'll explore Prefiltration and its effects on process efficiency and costs.
Whether your process is removing high particle loads, clarifying your product to improve aesthetics, or sterilizing a product by removing bacteria, your filters may become blocked more quickly, leading to troublesome mid-process filter replacements. To mitigate this, a larger filter area can be utilized from the beginning, or prefilters can be introduced. The role of prefilters is to handle a portion of the particle load, thus reducing the burden on the final filter and extending its lifespan.
In some cases, a specific filter and liquid combination may not achieve the desired throughput, or the flow rate may not be sufficient to meet time constraints. In such situations, utilizing prefilters can help rectify the issue. The appropriate selection of prefilters can be determined through flow decay measurements.
The implementation of prefilters not only enhances the Effective Filtration Area (EFA) of the system but may also improve filter efficiency.
A dual filter system is more adept at capturing smaller particles that could pass through a single filter.
To lower filtration expenses, the common approach is to purchase fewer filters or seek more competitive pricing. However, implementing a prefiltration strategy offers an alternative solution. Given the high cost of your current filters, let's examine how the addition of more filters can ultimately lead to cost savings over time. Below is an example with straightforward yet realistic cost estimates (actual costs vary by vendor).
Your filters foul before completing a batch
Although your final product adheres to all specifications, indicating that the filters are functioning correctly, the fouling of filter membrane pores by contaminants during batch processing necessitates a mid-process shutdown to replace the filters. This results in increased processing times and potential product loss when the filter housings are emptied and refilled. For sterilizing applications, this could disrupt your sterile process, requiring a thorough cleaning of the system before resuming operations.
One potential solution would be to increase the size of your filter system and install more of the same filters currently in use. A more effective approach might involve installing cost-effective prefilters to extend the life of your more expensive final filters. The prefilter could take the load off the final filter, and with proper selection and sizing, you could facilitate the processing of an entire batch.
How can increasing the number of filters lead to cost savings?
Assuming that two sets of filters are needed for a batch, using double the current filters would enable the entire batch to be filtered, but wouldn’t result in cost savings (other than the inherent cost associated with process interruptions). However, if a more affordable prefilter is installed before the final filter, this setup could potentially process the entire batch without the need for additional expensive final filters.
Reducing costs with a single prefilter
For instance, if your current filters are priced at $100 each and the process requires two filters per batch, the total filter cost per batch is $200. This remains consistent whether you replace filters during the process or use both simultaneously to process the entire batch without interruption. However, incorporating a $50 prefilter in place of the 2nd final filter allows processing the entire batch, resulting in a reduced filter cost per batch of $150, which represents a 25% savings, while still avoiding the need for interrupting the process.
By handling a portion of the load, the prefilter reduces the flow decay rate of the final filter, thus enhancing overall throughput. Additionally, by lowering the challenge posed by larger particles to the final filter, it preserves the smaller pores that might otherwise be blocked, potentially boosting the filter's efficiency for adsorptive captures.
Changing prefilters instead of the final filter can be a cost-effective solution
If interrupting the process to replace filters does not lead to significant issues, installing prefilters could result in savings. In the previous example, two final filters are needed to process a batch. However, it may be possible to identify a prefilter that will adequately protect the final filter so that it will not only handle a full batch but may be able to filter multiple batches, even if the prefilter needs to be replaced during the process.
Cost reductions achieved through the reuse of final filters
The final filter, priced at $100, along with a $50 prefilter setup, and the operation begins. The prefilter needs to be replaced during the batch process, while the final filter remains effective. If two prefilters are necessary for this batch, the overall filter expense amounts to $200 ($100 for the final filter and 2 x $50 for the prefilters). At this point, it may not appear that any savings are realized.
However, if the prefilters enable the final filter to process multiple batches, the savings become significant. What previously cost $200 a batch now costs $100 for subsequent batches (2 x $50 prefilters with the final filter still in operation). This results in 50% savings, and the more batches the final filter can process, the lower your costs will be. Certain applications are subject to regulatory restrictions regarding the reuse of final filters.
To determine the flow-limiting impacts of the particle load and the best approach for your application, it is important to measure the flow decay. This initial flow decay assessment can be conducted for the proposed processing filter to determine if the chosen (final) filter can achieve sufficient flow rates, retention, and throughput. A similar analysis, after utilizing a prefilter, demonstrates the prefilter's effect on the decay rate. By comparing the flow decay curves, one can observe the beneficial impact of using the prefilter. The goal of a prefilter is to adjust the flow decay curve to allow for acceptable throughput over a reasonable time frame (see Fig. 1). Evaluating various prefilters enables a comparison of their relative efficiencies. If needed, multiple prefilters can be employed alongside the final membrane to create the complete filter assembly.
For each filter or combination of filters, the volume of liquid that passes through is plotted against time. This allows for comparisons to be made, ultimately leading to the identification of the optimal prefilter-filter pairing.
Completing this series of preliminary flow decay assessments, which are designed to progressively and realistically meet production needs, will yield precise data that will guide the selection of suitable prefilter and final filter combinations in the correct ratio of their filter areas.
Figure 1. Flow Decay
What should I do if I lack room for additional filters?
Consider replacing your existing final filter with one that has an integral pre-filter built in. This is accomplished by layering the prefilter over the final filter during manufacturing, which protects the final filter without requiring additional housing. Utilizing this type of device can extend the life of the filter to handle a full batch, resulting in potential cost savings.
Implementing a cost-saving solution through an integrated prefilter
The $100 filters currently used require two final filters per batch ($200). By replacing them with a single filter that has a built-in prefilter layer (at a modest price increase per filter - $125 each), the batch cost is reduced by $75. This change lowers the overall filter expense per batch from $200 to $125, representing a 37% reduction, while also eliminating the need to interrupt the process for a filter change (see Fig. 2).
Figure 2. Filter with a Built-in Prefilter Layer
Total throughput, which measures the overall volume of filtrate that can be processed before the filter element becomes clogged, is arguably the most critical performance metric in various applications, particularly in media filtration. It is directly related to the filter's surface area, the size of the system, and the combinations of prefilters used. If your filter is not optimized for total throughput or if an unsuitable pre- and final filter combination is selected, the impact on the overall filtration costs can be significant. A filter that seems less expensive may lead to higher filtration expenses. Improved flow rates of the filter result in a lower required Effective Filtration Area (EFA), thereby decreasing the cost per liter.
Are you interested in maximizing the effectiveness of your final filters through prefiltration?
Savings are realized not through discounts, but by optimizing the process steps within the application and all related parameters. The improvement in the predictive performance reduces the need to overestimate the membrane area required for large-scale operations, which can subsequently lower the costs associated with large-scale processes and boost confidence in process development efforts.
Now that we have examined how installing prefilters can result in lower overall filtration costs, Critical Process Filtration is ready to assess your existing filtration process and provide recommendations to optimize the performance and cost of your system. Although the cost savings illustrated in the previous examples may appear minimal, it's important to consider systems that utilize multiple filters simultaneously; these savings can accumulate significantly based on the number of filters in operation.
Our knowledgeable Applications and Process Support team at Critical Process Filtration is equipped to conduct any necessary testing to determine the most suitable filters for your application and will support you through the validation process as needed. For more information on incorporating prefilters and reducing your filtration costs, contact us here.
