MANUFACTURING
How to Double your Blending Capacity
whilst Reducing the Number of Blenders
Summary
Tumbling is the most widely used way of dry powder blending
in the oral solid dosage (OSD) manufacturing environment.
The aim of this article is to demonstrate how IBC blenders, when
compared with other methods of dry powder blending, can
significantly increase your blending capacity and reduce your
manufacturing costs.
Batch size selection criterion is challenged - can we get closer to
a ‘batch to order’ philosophy?
Inline sampling is scrutinised - is it now unnecessary and overly
expensive?
And finally attention is paid to the actual transfer of the batch
from the blender to the next process. How does an IBC container
ensure that the uniformity of the carefully blended batch is not
‘lost in transition’?
Introduction
The Different Types of Blenders
All dry blend operations rely on three basic blending
mechanisms:
1. Convection – the overall transfer of lots from one place
to another, forced by a rotating mixing element usually
(ribbon blenders, conical screw blenders etc.)
2. Diffusion – a redistribution of particles, a relative change
of place in the blend (tumble blending)
3. Shear – the actual forced movement over slip planes
(plough shear blenders etc.)
V-Blender Stationary
later. Of course, unlike stationary blenders, there is a limitation
in batch size as the IBC needs to remain a transportable size,
using a pallet truck. Modern IBC blenders are available up to
3500 litres in volume, effectively holding a batch of 1200-1400
kg.
Apart from widely used high shear blending for wet granulation,
the third type is not often used in solid dosage manufacturing,
because of granules’ degradation effects. In OSD manufacturing
environments, most of the blenders used are tumble blenders,
either ‘stationary’ (V-cone, hexagonal, double cone etc.) or
‘mobile’ (IBC or drum blenders). The main reason for this is
that these blenders are quicker and easier to clean thanks to
the absence of mixing elements. They therefore also present less
contamination risk.
Mobile or Stationary
What is an IBC Blender?
Intermediate bulk container (or IBC) blenders basically consist
of two parts. One is the blending chamber, which is the IBC
itself, and the other part is the drive mechanism which picks up
and rotates the IBC. This separation of chamber and mechanism
is the most important difference between mobile shell and
stationary shell blenders. It has striking benefits in terms of
overall blending capacity and operational costs, as we will see
70 INTERNATIONAL PHARMACEUTICAL INDUSTRY
IBC-Blender (Mobile)
Stationary blenders can be used for larger volumes, however
in practice, due to height limitations, sensible capacities do not
usually go above 4000 litres gross volume.
Winter 2013 Volume 5 Issue 4
MANUFACTURING
What Drives the Requirement for Larger Batch Volumes?
Regulatory bodies require specic sampling methods and
quantities to analyse and validate that a blend is uniform.
The cost of such sampling is significant and it makes sense to
increase the batch size in order to reduce the ‘QC cost per kg’.
On the other hand, with quality by design (QbD) efforts and
strict control over the raw material properties, the need for blend
sampling could become a thing of the past, or at least be done
randomly and as a parallel action while the batch moves further
downstream. PAT methods such as the use of NIR spectroscopy
might replace blend sampling altogether, and sometimes it does
already. Still, apart from regulations, individual companies
can also have their own mandatory procedures which make
sampling definitely not yet extinct.
Besides a reduced sampling cost, there is another reason
for looking at larger batches. This is a direct consequence of a
basic flaw of stationary blenders: the need to clean the blender
at product change. In practice, the time it takes to clean a
blender (and to validate the cleaning) is less than proportional
with its size. Twice the size does not mean twice the time. Or,
in other words, the relative cleaning cost reduces with the size
of the batch.
a huge benefit reflected in considerable overall equipment
effectiveness. There is little or no ‘waiting’.
It is important to realise that this is only true for fully
contained IBCs. Basic butterfly valve containers do not fall into
this category, unless they are cleaned prior to receiving the
blend (as during a previous discharge the ‘outside’ facing of
the valve has been in contact with product).
IBCs using cone valve systems or split butterfly valve
technology provide for the containment that is required to avoid
blender room cleaning.
If a batch cannot be released unless Quality Control gives the
green light, then IBC blending is again the better option. You
can remove the IBC, move it to quarantine and continue using
the blender for the next batch.
However, there is also the blending room itself to clean.
With a bigger stationary blender, the room will need to be
proportionally higher. Because of the larger footprint of the
room itself, the ‘extra square metres to clean’ are more than
proportional unfortunately.
Finally, it makes sense to collect multiple ‘lots’ from one wet
granulator into one larger IBC or have it vacuum transferred into
one larger stationary blender. This means namely less making
and breaking of the connection underneath the dried granulesmill and therefore less contamination of the blender room.
Concluding, we can say however that batch size selection
around powder blending is largely influenced by cost following
geometrical limitations, sampling requirements and cleaning.
Not particularly value-adding reasons, not particularly ‘lean’…
Because of this, IBC blending is a very interesting alternative
as you will see below. The batch flexibility brings ‘batching to
order’ a bit closer.
What are the Benefits of Modern IBC Blending?
To summarise:
• IBC blenders do not have to be cleaned, not even at product
change
• IBC blenders are loaded and unloaded very quickly
(placement or removal of the IBC)
• One blender can take multiple IBC sizes, therefore the
blending ‘chamber’ can match the ordered batch size
• Modern IBC blenders can nowadays also process large
batches (up to 1400 kg)
• Sampling can be done ‘off line’, not affecting the availability
of the machine.
Cleaning of the IBC blender is limited to the cleaning of the
IBC, which is done off-line in a separate washing area. The
blender room also does not require cleaning, all-in-all providing
72 INTERNATIONAL PHARMACEUTICAL INDUSTRY
Stationary Blender Flow Diagram
IBC Blender FlowDiagram
If stationary blenders are used, the batch remains in the
blender, awaiting QC release, and this puts the machine out of
action for quite a while and reduces the OEE significantly.
The following simple calculation demonstrates the difference
between IBC and stationary blenders in a more quantitative way.
We compare here the two machines both homogenising 1200
kg of collected lots. The IBC blender loading and unloading is
simply a matter of placing and removing the IBC of course. For
the stationary blender, we choose loading it with a full batch
IBC of 1200 kg. To avoid a large unrealistic stack-up height,
the loading is done via a vacuum system. This requires either
a controlled transfer to the vacuum pick-up system (cone valve
technology can do that) or opening up the IBC and manually
manoeuvring a pneumatic lance to get the product out. The
latter of course is not preferred for contamination and operator
cost reasons.
The unloading of the stationary blender is assumed by
gravity, straight into a full batch container. We have to bring
in an element of cleaning. We have assumed it is required
after five batches and we estimate it takes three hours for the
stationary blender, including cleaning the room. This means an
average of 36 minutes per run.
Winter 2013 Volume 5 Issue 4
MANUFACTURING
In this scenario, the overall blending capacity of an IBC blender
isBlender Calculation Table more than three times that of the stationary blender!
IBC Blending Minutes Stationary Blending Minutes Loading time 5 Loading Time (including removal time of vacuum receiver) 30 Blending time 15 Blending time 15 Unloading time 5 Unloading 5 Cleaning time average N/A Cleaning time average 36 Total cycle time 25 Total cycle time 86 Overall blending capacity 2,880 kg/h Overall blending capacity 837 kg/h What does this mean? From a capital investment point of view,
a single IBC blender situated in a relatively small room produces
the same number of blends per time as three stationary blenders
with consequently three cleanrooms. Although an individual
IBC blender is normally more expensive than a similar sized
stationary blender, the total investment to achieve a certain
blending capacity is often lower. It also means less operator
intervention, so reduced running costs.
How do you Accommodate Multi-stage Blending?
The concept of fully contained IBC blending is challenged when
multi-stage blending is required. It would not be a good idea to
open up the IBC inside the blender room, because that activity
would contaminate the room and cleaning at product change
is the unfortunate consequence. An approach could be to bring
the IBC back to the dispensing area to receive the addition.
This of course is not possible with a stationary blender where
dust exposure is present during any docking or undocking
procedure.
For adding a lubricant (a stearate for example), a better
solution is on its way. Matcon have designed a lubricant
addition system which is being tested at present. It will allow the
addition to be loaded into the IBC without the need to open it.
This way, even lubricant addition will not cause the room to
be cleaned or the IBC to be transported back and forth to the
dispensary. This further adds to the ‘lean’ approach of OSD
manufacturing.
How do you Prevent Segregation During Transfer?
Sampling protocols and tools do get a lot of attention in order
Stationary Blender segregation during discharge
to avoid ‘disturbing’ the batch and to ensure the samples form
a representative image of the batch as a whole. Yet the actual
transfer of the batch to the next process step is where the batch
is ‘very disturbed’. That changes things considerably and the
batch is in danger of losing its required degree of homogeneity.
The material has to flow out by gravity and possible rolling
effects present a segregation risk that cannot be ignored. This
happens typically when a batch discharge shows a funnel
74 INTERNATIONAL PHARMACEUTICAL INDUSTRY
rather than a mass flow discharge pattern.
This is even more important for direct compression products.
The blends here do not necessarily have a very uniform particle
size distribution, which further increases the particle separation
risks.
The solution is cone valve IBC blending. A cone valve IBC
is known to discharge powders without rolling effects, by
‘holding back’ the batch in the centre and promoting the flow
from the sides of the IBC. In other words, ‘mass flow’ rather
than ‘funnel flow’. This way, the blend uniformity is maintained
during transfer of the batch into the tablet press, the sachet filler,
capsule line or roller compactor.
Concluding
Cone valve IBC blenders have striking benefits over both
stationary blenders as well as traditional butterfly valve based
IBC tumblers:
•
•
•
•
•
A much higher overall blending throughput replacing 2-3
stationary blenders
Ability to blend up to 1400 kg
No cleaning – reduced operational cost and high OEE
No segregation (cone valve technology)
Optional contained lubricant addition system
Yes,
it’s
perfectly
possible to reduce the
number of blenders whilst
doubling your blending
throughput.
If you would like more
information
regarding
how an IBC blender could
improve the capabilities of
your manufacturing line,
please feel free to contact
me, without obligation, on
the details shown.
By providing us with information regarding batch sizes,
cleaning time and current blenders used, it will enable us to
advise you more accurately regarding the benefits and financial
rewards of introducing IBC blenders into your production line.
Wim Spook (BSc Engineering) is a
professional powder handling specialist
with extensive experience working in
hygiene business environments for many
years. He joined Matcon Ltd in 1997 as
Sales Manager for Holland and Belgium,
focusing on the food and pharmaceutical
industries.
In
2009,
he
became
Pharmaceutical Business Development
Director of Matcon Ltd UK.
Email: wspook@idexcorp.com
Winter 2013 Volume 5 Issue 4