8/2/2019 Vacuum Conveying Article
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PHARMACEUTICAL ENGINEERING
A gentle methodVacuum conveying systems for
pharmaceuticaloperations
Sharon Nowak
Vacuum conveying for tabletting operations offers special
advantagesfor material transfer including cleaner, dust free and
contained operationwith minimal product exposure. It also offers a
gentle method to move alarge volume of bulks especially in areas
with height limitations, wheregravity discharge from a large bin or
tote may not be an option. Finally, theoption to use either dense
or dilute phase vacuum transfer offers
much more versatility in powder transfer.
Bulk transfer by pneumatic vacuum con-veying has become one of
the more popularmeans of transport for a wide variety
ofpharmaceutical, nutraceutical and foodmaterials. The gentle use
of vacuum ineither dilute or dense phase ensures thatthe powder or
granulate remains withinthe process, as opposed to leaks or
lossesthat are often results of positive pressuretransfer systems.
The use of either dense ordilute phase vacuum can be applied to
awide variety of tablet operations includingthe loading of
blenders, sifters, mills, cap-sule fillers, tablet presses and even
finishedtablet and capsule handling without da-mage to the finished
product. Dilute phase
conveying should be used with materialswhere segregation or
attrition in the con-veying line is not a concern. Comparativegas
or air velocities in a 3 pipe for dilutephase can range from 15 up
to 35 m/s. Inmost applications the gas is air, however, inthe
pharmaceutical industry, nitrogen isalso widely used due to its
inerting capabil-ities as well as the natural purity of the
gas.
Without segregation
In dense phase operations, a reduced gasvelocity range of 0.04
to only 9 m/s is uti-lised. The lower gas velocity means the
force exerted on the conveyed powder orgranulate is much
gentler. This gentle ac-tion also reduces the segregation
issuesoften experienced with the more aggressivedilute phase
operation. It should be noted,however, that there are limitations
to dense
phase conveying. These limitations includeconveying distances in
excess of 3.6 m ver-tical and 4.6 m horizontal, and
conveyingmaterials which are cohesive, hygroscopic,or so coarse in
particle size that they willnot readily form slugs.By definition,
dense phase means a higherproduct to gas ratio, or a smaller amount
ofgas is used to move a large quantity of pro-duct. The less the
gas requirement, the lessthe power consumed by the exhauster
orvacuum pump. Typically material is pickedup from the outlet of a
specialty hopper,
which creates a pressure differential andallows slugs of product
to form. In addi-tion, the hopper also includes a type ofmakeup air
inlet, which aids in the formingof the slugs as they travel and
pulsethrough the conveying line. The com-bination of the relatively
low air velocityand an expanded line size result in a type
ofsiphon-like effect for conveying to the va-cuum receiver, with
less resultant attritionand segregation.
Vacuum receiver
Regardless of the type of conveying tech-nique used (dilute or
dense), the material isdelivered directly to a vacuum
receiver,which allows for the break of the vacuum
P-Series receiver in mirror finish
8/2/2019 Vacuum Conveying Article
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Concentration
andSeparation
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GW28e/05
cpp 040
cpp 3/2007 63
and the release of the material from the gasstream. This
receiver includes a reverse jetfilter, which is pulsed when the
vacuum breaks to allow for cleaning of the filtermedia. The outlet
of the receiver includes avalve, either flap type or butterfly.
This
valve is sequenced to open after the va-cuum breaks and the
filter has been pulsed,thus delivering product to the processbelow.
K-Tron Premier PCSs line of pneu-matic receivers offers a wide
variety offilter options dependent upon the appli-cation. For the
pharmaceutical industry,special PTFE coated wide pleat
membranefilters with stainless steel end caps are util-ized to
ensure maximum filter efficiencyand optimal cleaning capability.
The Pre-mier PCS line of vacuum receivers offers aneasy-to-clean
design for ease of operation
and maintenance. All flanges are affixedwith means of sanitary
triclover typeclamps, thus resulting in disassembly with-out tools.
All system components are de-signed to ensure the optimum in
powderhandling specific to the process require-ments. Specialised
options in wash-in-place designs, swing out filter heads forheight
restrictions and HEPA filtration areall available depending upon
the appli-
cation and process. All pneumatic sol-utions, including the
product pickup op-
tion, are engineered with operator and pro-duct safety, superior
ergonomic design andease of maintenance in mind.The conveying of
filled capsules or tabletsrequires special modifications to the
pneu-matic receiver in order to avoid any dam-age to the product.
Due to the individualparticle density of filled capsules or
tablets,and their overall higher mass, a lower over-all velocity of
the individual tablet results.
In other words, a small granulate weighingmuch less will move a
lot faster in equival-ent gas velocities than a tablet the size of
anaspirin. In order to balance the higherrequired gas velocities,
the inlet to the re-ceiver is tangential and expanded, to allow
for a natural deceleration of the product be-fore it enters the
receiver. In addition, thereceiver is often lined with a soft
foodgrade rubber liner to avoid any productdegredation which may
occur after impactto a standard stainless steel receiver.Vacuum
conveying, via dense or dilutephase, is the logical choice for
efficient bulktransfer. It offers a gentle method to move alarge
volume of material especially in areaswith height limitations,
where gravity dis-charge from a large bin or tote may not bean
option. Finally, the option to use either
dense or dilute phase vacuum transferoffers much more
versatility in powdertransfer. Both individual ingredients aswell
as powder blends can be conveyedwithout worry of segregation or
attritionon the product.
cpp 455
Special lined receiver and expanded inlet fortablet/capsule
conveying
