Retrofitting in amino acid production: BHS supplies rotary pressure filters for the dietary supplement industry

September 2018

The reference at a glance


New process for manufacturing amino acid


Rotary pressure filter RPF A12

Operating site

Rotary pressure filter of type RPF A12




Filtration of the L-threonine crystals


Replacing horizontal automatic filter presses with rotary pressure filters

L-threonine is an essential amino acid in both the animal and human diet and is produced on an industrial scale across the world. An American manufacturer of dietary supplements was using outdated horizontal automated filter presses to filter L-threonine crystals. BHS-Sonthofen tested its different filter systems for use in this challenging filter application, and, together with the customer, decided on rotary pressure filters as a high-performance alternative that also optimally suits the existing production process.

L-threonine has to be added to humans’ and animals’ diets. A lack of it can lead to developmental and growth disorders, weakening of the immune system and other problems. Industrially manufactured L-threonine is used in livestock production in particular, because grain-based animal feed does not provide animals with their recommended dietary allowance of this amino acid. L-threonine is also used in human medicine to treat digestive disorders, deficiency symptoms, organically induced deficiencies and for parenteral nutrition.

Customer’s procedure was outdated

The American dietary supplement manufacturer used horizontal automated filter presses to separate L-threonine crystals from the diluted mother liquor in batch production. These filters, however, posed a number of issues. Low reliability, short maintenance intervals, expensive spare parts (particularly for the filter cloth) and time-intensive manual cleaning caused production delays. The filter cake was also pressed out under high pressure, which led to increased grain particle breakage in the delicate crystals and consequent product losses. Furthermore, the multi-day maintenance phase required every six to eight weeks meant that another filter had to be available to fill in during the other unit’s downtimes.

The manufacturer therefore needed a modern and more efficient filter system that could also be used in the existing production process. The customer defined its key data: filtration of 2,500 kg L-threonine crystals per hour at a purity of over 98.5%, a residual moisture of less than 20% and freshwater consumption of less than 0.12 liters per liter of suspension. The company then contacted BHS-Sonthofen with this request.

Two filter types facing off against one another

To find the optimal solution for the filtration application, Garrett Bergquist, Project Engineer for Filtration Technology at BHS-Sonthofen in Charlotte, North Carolina, opted for a series of laboratory experiments with different filter types and parameters: “We carried out vacuum and pressure experiments as well as single-stage and multi-stage washing, with and without an intermediate dehumidification process for different washing agent ratios and cake thicknesses.

These kinds of extensive laboratory tests are essential in determining the most efficient procedure possible.” In the next step, multi-week endurance testing was carried out for the most promising approaches. This testing is important as it enables the identification of any long-term issues that may arise under real-life conditions. For example, testers can track the condition of the filter cloth.

“We narrowed it down to two solutions: A rotary pressure filter with single-stage counterflow washing and an intermediate dehumidification process, and a belt filter with two-stage counterflow washing and an intermediate dehumidification process,” says Bergquist, summarizing the endurance tests. “Both filter systems are very suitable for the job – in particular, their ‘gentle’ handling of the solid makes both the belt and the rotary pressure filter suitable for delicate products such as nutritional supplements.” At this point, it was time to carefully examine the special application and all peripheral operating parameters to give the customer the best possible recommendation.

Retrofitting from BHS-Sonthofen

The rotary pressure filter came out on top, even though the belt filter delivered minutely better purity at slightly lower water consumption and is successfully used by BHS for this kind of application across the world. Here is where BHS-Sonthofen’s high level of expertise in comprehensive process optimization came into play. “Even if the figures for product quality and resource efficiency speak in favor of the belt filter, in this case, the rotary pressure filter was the better choice,” says Bergquist. “It delivers lower residual moisture, and this is important for the subsequent process step in the dryer.” The currently installed dryer would have been overburdened by residual moisture of up to 25 percent from the belt filter. In contrast, the rotary pressure filter reduces residual moisture to less than 19 percent. Very much in line with the retrofitting concept, the customer was able to continue to use the remainder of their existing system without a problem when the new filter was installed.

The new filter, a BHS Rotary Pressure Filter of type RPF A 12 with a 2.88 m² filter surface, replaces two automatic filter presses with a filter surface of approx. 6 m² each. This doesn’t just save space – maintenance work was reduced to just one tenth of the previous time. With a machine availability of over 96 percent, the customer made significant strides in improving efficiency in L-threonine filtration without having to adjust or reconfigure the entire process chain, all thanks to the support of BHS-Sonthofen.