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Journey
to global standards
The
import of hi-tech process plant and machinery is imperative till
the time exact equivalents are developed by the Indian capital machinery
industry. This shall help processors to upgrade their pharma products
to world-class standards says G A Nair
Continued
from last week
 Before
the mills are discussed, one has to appreciate the functions of
the classifier which ultimately is the outlet for the products and
therefore is responsible for accurate control of the required fine
powders.
In an Air Classifier, the particles to be classified are dispersed
in air (see figure 3) as in the Turboplex ATP Classifier, where
the particle stream is transported through the classifier wheel
via a blower. The classifier wheel is rotating with a Frequency
Converter, variable speed drive. The particles are subject to two
forces. First the drag force of the air flow trying to pull them
through the wheel. Second, there is the opposing centrifugal force
pushing the particles away from the classifier. By adjusting the
classifier wheel and the air flow, a very precise control over the
top cut micron size of the powder is possible, by using such high
quality classifiers.
Here again, sizes from 100 to 1000 are available, some of them with
a multihead design, a special development of Alpine, whereby more
than one classifier wheel (upto 6) can be mounted on the chamber,
increasing the production in direct proportion.
Since A to Z materials in powder form are classified, many of them
with high hardness and some of them very abrasive, the state-of-the-art
in classifier wheel design incorporates the appropriate choice of
materials of construction, ranging from mild steel to ceramics,
single piece CNC machined/moulded construction, with sophisticated
bearing design for speeds ranging from 1200 to 12000 rpm and even
an ingenious purging system to ensure that the coarse and the fine
powders do not mix, and the powder does not enter the bearings.
Some of these features are the result of failure of conventional
classifiers in critical applications and one to one problem solving
R&D work done by Alpine with top chemical and pharmaceutical
companies in Europe.
Turboplex handles a variety of applications, e.g, dyes, pigments,
powder coatings, toners, pharmaceuticals, food stuffs, mineral powders,
abrasives, ceramic and metal powders.
Spiral jet mills
 Spiral
jet mills have a simple design without moving parts. The microniser
comprises (figure 4) of a flat cylindrical grinding chamber, an
injector for product and an air injector. The air (gas) entering
at a high speed through the tangential nozzles rotate the feed material
which particles colliding and reducing in size.
There is a classifying effect from the spiral flow, in a free vortex
with fine particles leaving the mill by the drag force of the air
and large particles held back by mass force (centrifugal effect).
Considerable improvements have been made over the last three decades
to give special features particularly for the pharmaceutical industry.
For example, the special features of pharma design 100 AS from Alpine
are:
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Lack of dead spaces
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Mill body and cover in monobloc design
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O-ring seals in aspetically machined grooves
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Variety of sealing materials available to meet all possible requirements
eg: silicon, EPDM white, FDA quality, Viton
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Material of construction: 1.4404 (AISI 316 L)
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Surface finish Ra less than 0.8 microns
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No threads in product contacted parts
-
Component weight under 10 kg
Variety of different equipment available; nozzle rings with different
nozzle diameter and angles; adjustable fines outlet; New PTFE line
machine available for extremely difficult; sticky products; ceramic
lined machine available for abrasive products (eg cosmetic industry)
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Scale up guaranteed
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Typical range of capacity: 0.5 to 5kg/hour
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Grinding air/gas volume 35-45 cubic meters/hour
Limitations of spiral jet
mills
However
there are limitations to the spiral jet mills which led the way
for the development are perfection of the AFG jet mills (fluidised
bed opposed jet mills).
Some of the several limitations of spiral jet mills are:
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Method of product injection limits feed size, over-sized feed
causing blockage
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Blockage in feed with over size result in fluctuation in feed
rates and in turn in the PSD (particle size distribution)
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Risk of build-up and scaling in the mill chamber, reducing output
efficiency
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Difficulty to mill sticky substances, eg: steroids
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Lack of control of PSD
Fluidised bed opposed jet mill
 Fluidised
bed opposed jet mill (figure 5) uses compressed air moving at supersonic
speed through opposed nozzles, fluidising the material, drawing
the particles from the fluidised bed, accelerating them to impact
against each other and breaking down to fines. A fountain-like flow
forms around the focal point of the jets. Fine materials are carried
upwards to the rotating air classifier, with coarser particles being
retained in the bed and reground, the whole action taking place
towards the middle of the cylindrical chamber, with the minimum
of material to metal contact.
The AFG mill has been developed and perfected over last two decades
eliminating the limitations of the spiral jet mill. There is no
limitation on the feed size, no build up and scaling, hardness upto
10 mohs is handled, no heating and no contamination.
Above all, the AFG milling process controls the PSD of the product
to better accuracy than any other micronising system.
Variations of AFG in pharma design for pharma, food application
with CIP/SIP and explosion containment, serve these industries.
The design, engineering, and plant layout concepts are approved
by FDA and adhere to GMP directives, based chemical industry standards,
Hoffmann Roche standards, Ciba Giegy standards and tailor-made customer
requirements.
Operational advantages achieved are reliable calibration, qualification
and validation, reproducibility, saving cleaning agents, savings
through shorter down times and user-friendly dismantling/refitting.
Applications of AFG include ceramics, abrasives, rare-earths, fluorescent
pigments, toners in any form and colour, pesticides, mineral powders,
and pharmaceutical powders. In toners, the AFG holds a 70 per cent
marketshare covering UK, USA, Japan and India also.
Developments in ultrafine dry grinding field have reduced the end
fineness to below 10 microns. Super fine powders upto 80 per cent
below two microns through a dry agitated ball mill has been a break-through
in technology with high system reliability and optimum energy utilisation.
The combination has resulted in an extremely cost effective operation
as is possible in the Alpine ATR mill (figure 6).
Products like aluminium oxide, alumina hydrate, titanium dioxide
and a variety of hard materials can be processed from raw material
to superfine powders, without iron pick up, discolouration, with
the minimum size and weight of the equipment and lower costs.
Beyond 5 microns upto even 0.2 microns dry grinding becomes progressively
difficult and impossible. Hence wet micronisation technology developed
with recirculation type agitated ball mills of different designs.
The wet milling had inherent
problems like heating,
discolouration,
high wear and tear, big consumption of grinding media and generally
high energy bills. A lot of improvements have been done by the manufacturers
of wet grinding systems in Germany, which have resulted in energy
efficient mills like Discoplex Agitator Ball mill (ADP) (see figure
7) from Alpine, suitable for high throughputs, highly viscous suspensions,
minimum grinding pearls/cooling water consumption and operator safety
features. These mills are used for minerals, pesticides, herbicides,
fungicides, paints and inks, polymer emulsions and tailor-made for
other ultra fine powders. The wet product can be dried to get the
powders.
 All
through the last many years of development, the basis of an eventual
performance guarantee for a milling/classifying systems has been
through sample tests. However, large companies like Alpine have
installed virtually the entire range of mills and classifiers in
a test centre, to conduct production scale test, if desired in the
presence of the customers. Thus today it is possible for an Indian
pharmaceutical company to conduct a test of an NDDS (novel drug
delivery system) drug in quantities of one to two kg through a pharma
design mill, at one end of the range, and another company manufacturing
aluminium oxide powders in India can conduct a test on a 1t/hr production
scale AFG also in the same test centre. This is the state-of-the-art
in proof of performance before the investment decision.
The evolution of ultra fine dry/wet grinding systems resulted in
matching performance from laboratory scale mills and classifiers
as also particle size analysis equipment.
Compact and highly versatile multi processing systems as available
from Alpine incorporating a fluidised bed opposed jet mill, a classifier
impact mill and a classifier separately, all fitting into the same
housing, with integrated accessories like pressure filter and control
system all mounted on the same table, virtually becomes a test laboratory
in itself capable of handling A to Z powders of harness upto 10
mohs in explosion proof design.
Laboratory scale classifiers like 100 MZR for harder materials and
50 ATP can handle powders 97 per cent less than 2-120 microns range
in quantities upto two kg. Such laboratory equipment are used even
as pilot plants for market analysis of new powders in small batches.
 The
particle size analysis of dry powders upto 10 microns earlier done
through the popular A 200 LS model from Alpine, after successful
operation over several years and feedback from over 30,000 locations
worldwide, including several in India, have helped in the further
development and incorporation of features like automatic measurement,
printout, interface with PC and certification etc. in the new model
200 LS-N (See figure 8) supplied with high precision and durable
sieves, in sizes 10 microns-4000 microns.
For measurement below 10 microns the popular Laser Analysers are
used, like Malvern, who in association with Alpine offer an Online
Analysing System also.
Conclusions
To conclude, like the automobile industry where, though they claim
even 70 per cent indigenisation in the beginning itself, around
30 per cent is the hi-tech computer controlled, mpfi engines, the
special components of the transmission, steering and suspension
that make the difference between the Santro and the Ambassador or
the Opel and the Premier. The process industries in India also should
accept the fact that those who invented and spent millions to perfect
a world-class machine would like to keep the core, high-tech portion
within their scope of supply, whereas the lesser components and
accessories can be localised and cost saved. The 70 per cent level
will take some more time in this field, but 50 per cent is possible
in many cases. Towards this even the writer, working between Alpine
in Germany and Indian process industries have made big strides in
local sourcing to reduce landed costs.
 What
the new government could do through CII and CAPEXIL in the meanwhile,
is to identify the real hi-tech process plant and machinery, which
need to be imported and reconsider the customs tariff and procedures
to simplify the import of such systems till such time exact equivalents
are developed by our own enterprising capital machinery industry.
Such support from the government will help processors to upgrade
their chemical/pharma/food products to world-class standards for
exports and better profit margins.
The author G A Nair is managing director of Impetus Incorporated,
Chennai
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