Liquid filters get a reboot

Engineering tackles flow capacity, operating life and researchers have worked to address liquid filtration challenges such as throughput volume, integrity, and the availability of replacement filters.

By Colter Marcks, Donaldson Company August 9, 2018
The global beverage industry is undergoing a growth boom. A recent forecast predicts that combined sales of alcoholic and non-alcoholic beverages will grow 3% a year, reaching $1.9 trillion by 2021. Key drivers are growing urbanization, changing lifestyles, and disposable income. The bonanza puts heavy production demands on the processors of bottled water, carbonated drinks, juices, coffee and tea, beer, wine, and spirits. 
As beverage processors function at top speed, they’re requiring more from system components in terms of speed, performance, and cost of operation. One area ripe for improvement has been liquid filtration. Traditional technology—generally melt-blown polypropylene media inside a linear cage—has changed very little over the past three decades. Filtration is critical to removing dirt, debris, and bacteria from ingredient water, concentrates, flavorings, and other liquids; yet the harsh conditions of processing and sterilizing have historically worn out filters quickly and raised concerns about integrity. To solve this challenge, a team of 40 materials scientists and engineers collaborated with major beer and soft drink brands on two years of development and testing. The user-manufacturer group tackled three historic liquid filtration challenges: 
  • Throughput volume
  • Integrity and lifecycle
  • Availability of replacement filters.
In 2016, full-scale manufacturing got underway in a clean-room facility in Haan, Germany. The result of the venture is a complete reset of the media, cage structure, and production process in liquid filtration. These elements now are available commercially. Here is how the engineering team addressed longstanding liquid filtration challenges with new technology.
Throughput volume 
A filter unable to keep up with high-volume flow causes pressure loss, which slows production and wastes energy. How well a filter handles a high flow rate is driven primarily by the volume of media in the cartridge, along with the media’s pore size and length. Because the industry standard for liquid filter vessels is to use cartridges of 2.75 in. diameter with length increments of 10 in., there has been a limited ability to increase media volume within this defined physical space. 
To solve this space problem, materials scientists on the project chose a unique polyethersulfone (PES) media with asymmetric, tapered pores. The pores graduate in diameter to a microscopic size at the clean side of the process, providing the optimal cutoff range necessary for liquid sterilization while minimizing restriction to flow. 
In addition, the development team was able to pack 20% more of this new material into a standard 2.75 in. diameter cartridge, in part through redesigning the cage structure. Using a rhombus pattern, every pleat in the filter has equal exposure along the filter length, opening up 10% more free space than previous configurations. This extra space optimizes flow, reduces pressure drop, and creates more consistent loading characteristics.
Together these changes make the new elements capable of processing more fluid without increasing assembly size or pumping pressure, which translates to energy savings and increased production. 
Integrity and lifecycle 
Filter media is a delicate, precision material, so the cage around it needs to resist collapse. Structural failure is a risk in food and beverage plants that process highly viscous fluids, use high operating temperatures, or practice steam sterilization, all which tend to soften filter cages over time and through repeated use. (Steam exposure often occurs in non-ideal process design, as well.) Any cage twisting during filter replacement also can change the shape of the PES membrane and reduce its effectiveness 
For these reasons, cage strength was a key goal in the engineering project. The same structure that created greater flow space—triangulations similar to bridge supports—was confirmed to deliver greater stability as well. This support cage resists deformation and stands up better to pressure differential during high volumes of fluid processing. The result is improved food safety, lifecycle, and overall cost savings.
Filter replacement 
The third challenge for liquid processors has been enduring long wait times for compatible filter parts. Processing applications vary so widely that thousands of unique components exist in various lengths, media, micron ratings, elastomer types, and end connections. Waiting for a supplier to manufacturer and ship a one-off part can cost weeks of downtime.
To address this problem, engineers working on the new filter technology developed single-flow manufacturing. Components in each 10 in. element module, including a specific length or end-cap style, can be quickly custom-manufactured one at a time with a choice of media. 
Colter Marcks is in the engineering manager for Donaldson Company’s Process Filtration Division.