Pharmaceutical Agitated Screw Feeder with Agitated Hopper
Ajax Equipment has designed and manufactured a hopper and screw feeder for leading powder processing equipment supplier. In addition to clean-in-place and steam sterilisation-in-place, the equipment meets the combined requirements of ATEX and the Pressure Equipment Directive (PED).
Ajax's approach was to treat the hopper and screw feeder as a single construction from which, in this case, powder is fed to a jet mill for further processing. Independent testing of a variety of milled and un-milled powders for their wall friction, bridging and bulk density characteristics indicated that agitation of the powder produced the best material condition for handling. Drawing on its expertise in powder handling, Ajax Equipment also interpreted the flow characteristics of the material to design an agitator to sweep close to the walls of the hopper, eliminating the risk of bridging, and ensuring smooth, reliable powder flow to give stable in-feed to the mill.
Using the powder handling analysis data, Ajax was able to overcome the poor flow characteristics of the powder to ensure a reliable and controlled feed from the agitator via the screw to the client's milling machine. The screw feeder meters pharmaceutical powder out of the hopper at a variable rate of between 20 to 100 Kg / hour.
Screw Feeder Design
It uses a state-of-the-art volumetric screw feeder with a stepped shaft and variable pitch, to pick up material progressively from the full length of the agitated hopper outlet, to provide a consistent feed rate to the mill. The agitator and screw feeder drives are controlled by separate invertors to maximise co-ordination between agitation and screw feed for optimum powder discharge.
SIP and CIP
To meet the stringent demands of steam-sterilisation in place, both the hopper and screw feeder are cleaned by steam at 1.5 bar at 128OC. The equipment is also designed to operate at a maximum operating temperature of 140 OC and withstand an internal pressure of 4 bar, as well as able to sustain a full vacuum.
All parts of the hopper and screw feeder are constructed of 316L stainless steel with internal surfaces mechanically polished and then electro polished to a finish of 0.3 microns. The hopper has a jacketed construction for insulation ensuring minimal heat loss to maintain temperature during the steam sterilisation procedure. To meet hygienic processing requirements, all internal surfaces are crack and crevice free. In addition all joints feature a modified 'O' ring flange joint profile which was specifically engineered by Ajax. This joint arrangement uses a combination of FDA compliant aseptic seals in PTFE, and silicone and encapsulated FEP for all access points and joints.
ATEX rating for manufacturing equipment is commonplace. However in this case it is the vessel's internal zone, which demands ATEX compliance with the equipment itself being positioned in a safe area. The hopper's internal pressurised processing atmosphere is classed as hazardous and rated ATEX Zone 21 to a maximum surface temperature of 160oC. This meant careful consideration of the mechanical features such as clearances between rotating parts and relative velocities.
Validation of Clean-ability
During the pre-commissioning stage the hopper and feeder assembly was exposed to acid and alkali reagents and cleaned with pharmaceutical quality water. The unit was then stripped down and swab tested to validate the cleanliness of the hopper and feeder after cleaning. After this the vessel is then used for a number of manufacturing campaigns using many different APIs without disassembly for cleaning between campaigns.
To assist with the validation, Ajax Equipment used a triclover clamp fitting at the top of the agitator's ceramic coated shaft with PTFE lip seals and o-ring seal assembly. This allows the agitator to be dismantled without removing the drive shaft. Similarly the screw feeder contains a bespoke seal assembly such that the auger can be removed without disturbing the seals. The seals in both the hopper and feeder are fulfilling an important role in both preserving the pressure during cleaning as well as eliminating the risk of leaks.