Improved safety for integrated granulation and drying suites
Extensive safety testing confirms pressure enhancement effects and
identifies safe design limits for integrated systems. GEA Pharma Systems in
conjunction with the FSA, the safety specialist centre in Germany, have carried
out an extensive test programme involving over 100 test explosions. This
research has shown conclusively that should an explosion occur during the
transfer operation in an integrated system where a granulator is connected
directly to a fluid bed dryer without an explosion isolation valve, the
secondary explosion pressures in the granulator can be significantly higher
than in the fluid bed. These tests have enabled GEA Pharma Systems to gain
full EC type approval for a range of pressure shock resistant integrated
systems and
16-bar pressure shock resistant high shear granulators.
Safety when using organic solvents
The tests were
carried out with hybrid mixtures that behave in the same way as pharmaceutical
products containing organic solvents and showed that the final explosion
pressure in the granulator is dependent on the volumes of the two vessels and
that the length and diameter of the interconnecting duct is critical in
ensuring that the pressure remains within safe limits.
The tests showed that where the fluid bed is designed in accordance
with VDI 2263 part 5 (i.e.: for a 10-bar explosion pressure, which the standard
considers to be adequate for all pharmaceutical powders and organic solvent
combinations), then the granulator must be able to withstand an over pressure
of at least 16 bar to provide a range of transfer duct configurations which are
both practical and safe. Where the fluid bed is required to handle materials
with explosion pressures greater than 10 bar (e.g.: metal powders) - and hence
is designed outside of the VDI standard - or where the configuration of the
interconnecting duct is outside the safe design parameters, then either the
granulator must be designed to a higher pressure shock resistance or a hygienic
fast acting valve, or some other form of protection, is essential.
The test program showed that the pressure enhancement effects are
caused by the difference in the propagation speed between the pressure wave and
the flame front. The worst cases are when the pressure in the granulator is
able to rise significantly before the flame can reach it and ignite the
pre-compressed material. For the range of transfer duct configurations to be
used with the 16-bar granulator design, the presence of bends and obstructions
such as mills was not seen to affect the increase in pressure. For plant
processing powders, or mixtures that are not flammable at the time of transfer
between the granulator and the fluid bed, then the risk of explosion is
eliminated and hence a wider range of transfer duct designs can be used
safely.
This extensive research program has significantly advanced the state of the
art in safety technology for pharmaceutical plants and confirms GEA Pharma Systems
Systems’ commitment to introducing new products which are based on sound
research and development using solid process know how and understanding.