The Agitated Nutsche Filter Dryer (ANFD) technology have been broadly used in commercial manufacturing of advanced drugs around the world for the past 20 years. From the outside, the technology seems to have remained the same throughout the years, but looking closer equipment designer such as Powder Systems Limited (PSL) have refined these pressured filter dryers to make them the “work horses” of pharmaceutical plant.


  •  Filtration

Filtering in a pressured nutsche filter dryer is becoming the most common type of equipment for Active Pharmaceutical Ingredient (API) manufacturing as it combines filtering and drying with excellent containment.

By continuously working closely with drug manufacturers, the filtration experts of PSL developed an ultimate filtration process refining process details such as high welding quality of the filter mesh onto the support ring, special filter plate design to ensure optimal drainability but also innovative filtration rings and meshes to offer side, bottom and also basket filtration capabilities.


  • Washing

Once the solid and liquid are separated by applying gas pressure (usually nitrogen), it is important to remove the residual filtrate and wash out any impurities.  In order to improve the efficiency of the filtration and washing, the agitator is used to smooth out any cracks or preferential channels that have formed in the product cake.

The type of agitator is key for an efficient washing process. PSL one-piece agitator has alternating teeth on each arm (typically two) which forces the product back and forth across the surface creating a differential velocity mixing.


  • Drying

Once the product has been filtered and washed, the product is ready to be dried, or the product can be discharged as a wet cake or re-slurry. The heat transfer area of the dryer is one of the most important factors in product drying. The heat transfer area can be divided into 3 basic parts: the filter base, the vessel sidewall and dished-top, and the heated agitator.

PSL’s Filter Dryer provide optimum heat transfer firstly through a direct heating of the filter base. Some filters have a few centimeter gap of air between the heated base and the filter media. This air gap will isolate the heat from directly heating the product and usually only accounts for 5% of the heat transfer.  With PSL’s ANFD, the product has a direct base heating, where the filter media sits directly on the heated base, and can supply up to 25% of the heat transfer.

The agitator is, by far, the most active heat transfer surface of the dryer, accounting for more than 50% of the heat used for drying. Filter Dryers’ agitator of PSL have been designed to supply a maximum of heat transfer with heating fluid running through the shaft and arms. The PSL agitator is a totally sealed one piece component, to prevent leakage of heat transfer fluid into the process as shown on the image below.

Finally the sidewalls that are in direct contact with the cake make up for the other 25 to 40% of the heat transfer. In order to eliminate any condensation of the evaporated solvent from dripping back into the product during drying, the rest of the vessel wall and dished-top need to be heated.


  • Discharging

There is various ways to discharge the product from an ANFD vessel. The most common method, especially with large scale filters, is through an automated discharge plug using the agitator to offload the powder into a container. However, this method does not provide a full product recovery and can cause cleaning difficulties.

PSL pioneered discharging method, called the Direct Heel Recovery system, has proven to be the most efficient for high yield productivity. The offloading glovebox isolator manufactured and integrated by PSL provides high containment down to nanogram levels, thus protecting the operator, product and environment during the discharging operation. Through the ergonomically designed high containment isolator, the operator can rake out all the remaining heel for a full product recovery under safe conditions.

For even higher containment requirement, PSL is the only manufacturer in the world to provide the ground breaking FilterBox: a Filter Dryer fully integrated in a high containment isolator.


  • Sterile application

To meet the increasing demand from the biopharmaceutical market, PSL developed a unique aseptic design to provide sterile filtration and drying. The filters have CIP (Clean-In-Place) and SIP (Steam-In-Place) capabilities and are built to meet the strict manufacturing requirements necessary for aseptic processes. PSL’s filter dryers utilise gas lift-off mechanical seals and a unique tilting offloading design avoiding the use of large footprint and capital expenditure of VHP isolators. The rotating vessel allows a maximal product recovery of almost 100%, while maintaining the sterility envelop.


  • Technology transfer

Lab scale filter dryer technology has not always been available for accurate scaling up studies. During laboratories studies and R&D product development, chemists need to work on similar technology to evaluate and determine the parameters discussed above. Traditional filtration and drying methods usually found in laboratories are Buchner filtration, centrifuge and oven drier.

These technologies cannot be transferred successfully onto commercial production scale. Therefore, PSL launched a smaller agitated nutsche filter dryer to provide same technology for less than 200 grams batch of final product. These Lab Nutsche Filter Dryer called GFD® can be found in glass for complete process visibility or stainless steel for higher pressure requirement as shown in Image 4. The GFD range performs the same filtration under vacuum and pressure, washing and re-slurry capabilities, and thermal drying through a heating jacket.


For more information on PSL Filter Dryer products range, please contact us here or +44 (0) 151 448 7700