Mixing and Granulation - GEA Pharma Systems

ContinuousImprovementSafety•Improved safety for integrated granulationand drying suitesExtensive safety testing confirms pressureenhancement effects and identifies safe designlimits for integrated systems GEA Pharma Systemsin conjunction with the FSA, the safety specialistcentre in Germany, have carried out an extensive testprogramme involving over 100 test explosions. Thisresearch has shown conclusively that should anexplosion occur during the transfer operation in anintegrated system where a granulator is connecteddirectly to a fluid bed dryer without an explosionisolation valve, the secondary explosion pressures inthe granulator can be significantly higher than inthe fluid bed. These tests have enabled GEA PharmaSystems to gain full EC type approval for a range ofpressure shock resistant integrated systems and 16-bar pressure shock resistant high shear granulators.Safety when using organic solventsThe tests were carried out with hybrid mixtures thatbehave in the same way as pharmaceutical productscontaining organic solvents and showed that thefinal explosion pressure in the granulator isdependent on the volumes of the two vessels andthat the length and diameter of the interconnectingduct is critical in ensuring that the pressure remainswithin safe limits.The tests showed that where the fluid bed isdesigned in accordance with VDI 2263 part 5 (i.e.:for a 10-bar explosion pressure, which the standardconsiders to be adequate for all pharmaceuticalpowders and organic solvent combinations), thenthe granulator must be able to withstand an overpressure of at least 16 bar to provide a range oftransfer duct configurations which are both practicaland safe.Where the fluid bed is required to handle materialswith explosion pressures greater than 10 bar (e.g.:metal powders) - and hence is designed outside ofthe VDI standard - or where the configuration of theinterconnecting duct is outside the safe designparameters, then either the granulator must bedesigned to a higher pressure shock resistance or ahygienic fast acting valve, or some other form ofprotection, is essential. The test program showedthat the pressure enhancement effects are caused bythe difference in the propagation speed between thepressure wave and the flame front. The worst casesare when the pressure in the granulator is able torise significantly before the flame can reach it andignite the pre-compressed material. For the range oftransfer duct configurations to be used with the 16-bar granulator design, the presence of bends andobstructions such as mills was not seen to affect theincrease in pressure.For plant processing powders, or mixtures that arenot flammable at the time of transfer between thegranulator and the fluid bed, then the risk ofexplosion is eliminated and hence a wider range oftransfer duct designs can be used safely. Thisextensive research program has significantlyadvanced the state of the art in safety technology forpharmaceutical plants and confirms GEA PharmaSystems’ commitment to introducing newproducts which are based on soundresearch and developmentusing solid process knowhow and understanding.13