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Pump and Valve Selection
For ultrapure processing
The global market for the purification of air, gases and liquids in
high-technology industries has grown from less than $0.5 billion in the
early 1980s, to more than $13 billion in 2002, and is on track for
double-digit growth through 2007, according to some market analysts. The
manufacture of electronic components, active pharmaceutical ingredients
and fragile biological compounds, and demanding requirements for ultrapure
water, all require the utmost in cleanliness during process operations.
Production of pharmaceuticals and biotechnology-derived products for human
consumption is being retooled to meet increasingly strict regulatory
standards for purity. One of the latest initiatives of U.S. Food and Drug
Administration is the development of guidelines for sterile drugs that are
produced by aseptic processing. According to a draft concept published in
September 2002, there are basic differences between conventional “terminal
sterilization” methods, and “aseptic processing”, which involves more
variables. Terminal sterilization usually involves filling and sealing
product containers under the conditions of a high-quality environment; in
most cases, the product, container and closure have acceptably low rates
of biological contaminants, but they can not be considered to be sterile.
In aseptic processing, however, the drug product, container and closure
are subjected to separate sterilization processes, and are then brought
together. Because no further processing is used to sterilize the product
once it is in its final container, it is critical that containers be
filled and sealed in an environment of extremely high quality and
sterility.
The current Good Manufacturing Practices (cGMP), set FDA, and similar
global standards set by the International Organization for Standardization
(ISO), will continue to guide the design of high-purity equipment.
Suppliers of sanitary and high-purity equipment must meet these guidelines
as they strive to make product and design improvements that ensure maximum
cleanliness, process flexibility and system compatability.
Clean-in-plaiesce capabilit
Increasingly, clean-in-place (CIP) is the technology that
distinguishes conventional chemical process equipment from that used for
sanitary or ultrapure manufacturing. CIP equipment can be cleaned and
sterilized automatically in place, and is designed so that no dismantling
or disassembling of the system is required. Originally designed for
applications in the food and dairy industry, CIP systems are now mandated
by many companies in the pharmaceutical, biotechnology and semiconductor
sectors. CIP is typically achieved by pumping a cleaning solution through
a piping network, so that it flows across all internal equipment surfaces.
In addition, spray devices are used to clean vessels, reactors and other
process equipment. In addition to eliminating the need to dismantle and
reassemble system components every time cleaning is required between
batches, CIP capabilities allow the system operator to carefully control
cleanliness. For example, automated CIP systems monitor and control
parameters, reduce operator exposure to products, and permit the use of
cleaners that may be more aggressive than those used when operator
intervention is required. While CIP components and systems often are more
expensive than conventional alternatives, for many high-purity process
operators, there is no choice but to use CIP, to meet their challenging
requirements for product and process cleanliness.
Building in process flexibility
Multi-functional equipment designs that incorporate several unit
operations in a single system are making steady inroads for the production
and handling of delicate, temperature-sensitive processes. Some systems,
for example, combine drying operations with other operations, such as
filtration and mixing.
In general, the trend in drying is away from convection drying systems
that use direct heat, and toward conduction drying, whereby heat is
applied indirectly. An increasing popular choice for indirect heating is
vacuum drying. That’s because it allows products to be gently dried in
less time and at lower temperatures. High-purity processors are also
leaning toward vacuum dryers that conserve energy and allow solvents to be
recovered for reuse.
For example, vacuum-operated conical mixer dryers from Krauss-Maffei
Kunststofftechnik GmbH are equipped with a bottom-drive mixing screw that
simultaneously mixes and homogenizes product while it is being dried. Most
of the product moisture or mother liquid is removed during batch
centrifugation, which precedes the drying step.
Meanwhile, by combining filtration and drying, filter-dryer systems
separate solids from liquids, and discharge them as free-flowing powders.
One direct benefit of such a systems is this: Because separation and
drying occur inside of a single, sealed vessel, product purity and process
containment can be maximized.
Microwaves can reduce drying time by as much as 50% for certain products.
In recent years, the dominance of mechanically sealed high-purity mixers
has been challenged by the introduction of products using magnetically
coupled agitators, which have the advantage of hermetic sealing. Such
systems use no rotary seals, which reduces maintenance requirements, and
eliminate the need for packings or lubrication, both of which can
introduce impurities during system operation.
As these designes have evolved, some of the problems associated with the
earliest generation of magnetically coupled mixers have been eliminated.
For example, one shortcoming of conventional magnetically coupled mixers
is their cleanability, due to the restricted flow of cleaning fluids
through the small openings in the outer rotor head.
To meet the validation requirements for CIP capabilities, some magnetic
mixer models are equipped with an open mixer head that can be completely
flushed. One particular enhancement for improved cleanability in
magnetic-drive mixers comes from Lightnin through its Hyper-Flow bearings.
Compared with traditional sleeve bearings, Hyper-Flow bearings have fewer
contact points, so they result in reduced particulate generation,
permitting easier and more thorough cleaning.
Ensuring purity during fluid flow
High-purity tubing must carry sensitive product feed streams into a
plant, protect feedstock purity between reactors and vessels at various
processing steps during manufacture, and deliver uncontaminated finished
product for packaging and shipping.
Contamination control is a constant challenge as high-purity fluids are
transported through process plants, for even deionized, ultrapure water
systems will support microbial biofilms with significant cell densities
after only a few weeks of service. The problem is further complicated by
small inner diameters of some tubing, which make such tubing difficult to
clean. Increasingly, it is essential that tubing material used for
ultrapure or pristine processing operations be able to withstand cleaning
and sterilization using CIP and steam-in-place (SIP) protocols.
In pharmaceutical applications, for example, variations in flow or poorly
planned piping slopes or bends can create either stagnant areas where
contaminants can concentrate, or areas of turbulence, which can strip
biofilm buildup from tubing walls and carry it into large production
vessels. Especially for chip fabrication, tubing systems must be carefully
designed to prevent turbulence while transporting caustic or hazardous
liquids under extremely high temperatures and pressures.
Installed tubing material must also be readily repairable or easily
replaceable, in the event that a section break or changes in the
manufacturing process require that a feed stream or process line be
rerouted. Adding to these challenges, tubing material used for ultrapure
processes must be compatible with tubing materials used elsewhere in the
plant, to allow for cost-effective modification of process systems.
Plastics are often specified for critical fluid-handling applications for
the tubing that is used to transport chemicals and water for semiconductor
fabrication and rinsing. For application that may involve exposure to
corrosive process chemicals and cleaning fluids, fluoropolymers offer the
best overall performance. Some, such as perfluoroalkoxy (PFA) and
polytrafluoroethylene (PTFE) are fully fluorinated; others, including
polyvinylidine fluoride (PVDF) and ethylene chlorotrifluoroethylene (ECTFE),
are only partially fluorinated.
Pump selection
Most critical to the design and specification of pumps for high-purity
applications is cleanability. The most popular styles of pump for
high-purity applications are centrifugal pumps and positive-displacement
pumps, which are easy-draining, and fit well into CIP operations. Other
pump types, such as diaphragm pumps and liquid-ring pumps, are typically
specified for viscous or otherwise difficult fluids, but such designes
have configurations that make them more difficult to clean.
Centrifugal pumps are widely specified for high-purity applications,
thanks to their simplicity, comparatively low cost and easy cleanability.
Product is moved through the pump by the spinning action of an impeller.
As the liquid is pushed from the impeller’s center to its outer diameter,
it absorbs energy from the impeller action. This energy is then used to
force the liquid out of the pump.
Positive-displacement pumps, such as peristaltic or rotary-lobe styles,
are commonly applied for high-viscosity or shear-sensitive products.
During operation, positive-displacement pumps displace liquid by creating
a space between the pumping elements and trapping the liquid in the space.
The rotation of the pumping elements then reduces the size of the space
and moves the liquid out of the pump.
While plastic pumps have been around for some time, a newcomer in the
high-purity plastic pump sector is the nonmetallic, magnetically coupled
pump. Such nonmetallic pumps can be operated at the low flowrates that is
often needed for pumping fluids used for refrigeration, pharmaceutical
processing and semiconductor fabrication.
Valve selection
When it comes to selecting valves for ultrapure processes,
cleanability is a critical aspect to be considered. The first step is to
select valves with an easy-to-clean design — one that inherently limits
the accumulation of contaminants. In the pharmaceutical industry, for
instance, the diaphragm valve is often preferred for process fluid because
it has no crevices or recesses to harbor contaminants. Internal surfaces
are smooth and gently curved for easy cleaning. There are no sharp corners
that are difficult to wash out, and there are no seams in which materials
can collect.
Meanwhile, depending on the application, other types of high-purity or
sanitary valves can also be used. These include pinch, ball check,
full-port plug and full-port ball valves. Compared with diaphragm valves,
ball valves can save on piping, valves, fittings, pump requirements and
maintenance.<<
Trend Report courtesy of Dechema
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