Vacuum Pumps
‘Plug and pump’
vacuum systems in chemical
and pharmaceutical processes
Bob Campbell
Leading chemical processors around the world are driving a new trend for vacuum to be seen as a ‘utility’;
highly reliable, flexible, and available on demand in a ‘plug and pump’ system that requires minimum set-up
and maintenance, is cost-effective to run and environmentally sound. When processors are specifying a new
vacuum system, cost-of-ownership and environmental impact are key issues.
Recent advances in dry vacuum pump technology meet this challenge head on. New designs offer high
reliability effluent-free pumping, high levels of controllability and long service intervals, even in the most difficult of harsh chemical processing applications.
This article discusses the recent evolution of dry vacuum pump technology for the chemical and pharmaceutical processing industries with particular regard to energy usage, environmental impact, carbon footprint, cost of ownership and safety. It looks at the very latest in chemical pump technology - the new advanced discrete variable pitch tapered-screw technology – and uses a case study example to highlight process and cost benefits in specific chemical and pharmaceutical applications.
Bob Campbell is the Market Sector Manager
for the Process Industry with Edwards Vacuum
where he has held several different roles
including Product Manager, Marketing and
Business Development since first joining
Edwards in 1999. Bob earned a B.S. in
Mechanical Engineering Technology from Old
Dominion University in 1989. Before joining
with Edwards, he worked for several major vacuum pump
manufacturers, accumulating experience applications engineering,
marketing, systems engineering, system assembly and service
operations.
Introduction
A
lthough the vacuum system represents
an apparently small part of any chemical or pharmaceutical processing
plant, its role is highly significant from product quality, consistency and yield to the costefficiency of the process. Selecting the right
vacuum pump system offers engineers an opportunity to reduce the energy usage, environmental impact and carbon footprint of the process. At the same time it makes productivity
and/or quality improve.
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Table: Cost of Ownership Dry pumps vs steam ejectors
Cost of Steam Ejector System vs Dry Vacuum Pumps – 3 Year Operation
of processes, including
distillation, evaporation,
crystallization, drying,
solvent recovery, deodorization, filtration and for
house or general vacuum
duties. The technology is
well established around
the world as an efficient,
reliable option for demanding chemical processing industry applications.
The key advantage of
all dry pumps, including
roots, claw and screw
technologies, is that they
do not use water or oil
for sealing or lubrication
of the vacuum stages.
This removes the risk of
process contamination,
and also eliminates the
need to dispose of effluent associated with the
‘wet’ technologies such
as steam ejectors and liquid ring pumps (LRPs).
Hence emissions are reduced.
Reducing emissions and running costs
with dry vacuum pump technology
Dry vacuum pumps are used to pump some of the
most aggressive and problematic gases in a broad range
Dry pumps are energy efficient and the reduced
power consumption results in lower carbon footprint and environmental impact. A dry vacuum
pump costs up to 90% less to run than its steam
ejector equivalent. When compared to an LRP system, the running cost of a dry pump can be significantly cheaper.
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Dry pumps are energy efficient and the reduced power consumption results in lower carbon footprint and environmental impact. A dry
vacuum pump costs up
to 90% less to run than
its steam ejector equivalent (see Table). Similarly, compared to an LRP system, the running cost of a dry pump
can be significantly cheaper.
Dry pumps offer the best thermal efficiency of any process vacuum-producing system. Not only does the dry
system use significantly less energy when it is running
but, unlike a steam ejector, it can be switched off between
cycles so that it uses no energy at all when it is not required. Inverters can also be used to minimise the power
usage when in standby mode.
It is true that for many standard applications, the capital cost of a dry pump may be higher than, for example,
an equivalent oil-sealed or cast iron liquid ring vacuum
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pump. However when the cost of the total installed package and the running costs are taken into account, dry
vacuum systems can be considerably more cost-effective
(refer Fig).
A good example of this is provided by an agrochemical manufacturer based in Andhra Pradesh, who
switched from multi-stage steam ejectors to dry vacuum
pumps. In a 12-month trial project significant savings
were realised as a result of reduced energy consumption,
and it was found that almost all of the valuable uncontaminated speciality chemicals could be recovered at the
exhaust for reuse in the process. The results were so impressive that the customer ordered a further 12 systems,
and has now replaced all its steam ejector systems with
dry vacuum pumps.
Innovation in dry pumping technology
Advanced discrete variable pitch tapered-screw technology requires minimum set-up and maintenance, is
cost-effective to run and environmentally sound. It is developed to meet demands for high reliability, highly flexible ‘vacuum on demand’ from the chemical sector.
This latest generation pump technology is used to
minimise their environmental impact. It provides all the
advantages of dry pumps, with low energy usage and utility costs, deep and flexible vacuum down to 10-3 mbar,
no contamination of the process stream or cooling water
and no effluent generation.
The technology has excellent liquids and solids handling capability to cope with process upsets. It can continuously pump up to one litre of liquid per minute and
up to 25 litre slugs without stopping, making it robust
and reliable even in harsh processing environments.
Dry pumping technology has excellent liquid
handling capability, continuously pumping up to
one litre of liquid per minute and up to 25 litre
slugs without stopping, making it robust and reliable even in severe processing environments.
Advanced companies in the pharmaceutical and fine
chemicals sector were early adopters of dry vacuum
pumping technology since the first pumps were installed
in the late eighties. The sector has been quick to recognise
the clear advantages of dry pumps over traditional wet
technologies in most applications, including higher reliability and flexibility, better cost of ownership and lower
environmental impact.
One such early adopter of dry vacuum pumping is an
Italian manufacturer of active pharmaceutical ingredients
(APIs). The company standardised on dry pumps and
has about 50 vacuum pumps installed for reactor service
and distillation applications and a further 20 pumps
(approx) for drying applications.
Like other leading chemical processors around the
world this Italian API manufacturer was very interested
in the new ‘plug and pump’ technology because of its
ease of installation, integral control, very low noise level
and low maintenance requirements. This company has
been testing a new advanced screw technology pump for
almost a year now, and on the basis of the trial results,
has already bought two more.
High performance
Dry pumps have very similar performance characteristics to oil-sealed
Operating cost of Steam Ejector vs Dry Vacuum Pump - 3 year operation
pumps, typically
90,00,000
covering the pres80,00,000
sure range 1000 to 1
mbar
at near con70,00,000
stant volumetric effi60,00,000
ciency
with ultimate
50,00,000
pressures of 10 -1 to
40,00,000
10-2 mbar. Their oper30,00,000
Steam ejector
ating range can be
20,00,000
extended with the
Dry pump
10.00,000
addition of booster
stages.
0
0
6
18
24
36
12
30
The latest evoluMonths
tion in dry pump
Fig. Initial cost paid back within 8.5 months, savings thereafter of over Rs 20 lacs per year
technology offers
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manufacturers who are still using liquid-sealed pumps
the opportunity to ‘leap-frog’ to the benefits of a plug and
pump system.
This is exactly what a major international manufacturer of high quality flavours and fine ingredients did
when they replaced all their LRPs and oil-sealed ejectors
with latest dry pump technology. Five months on, the new
pumps continue to operate with no problems even under
harsh conditions.
Operating under very harsh conditions
One of the problems with existing dry pump technologies is that chemicals can become compacted and solidify
during the pump cool-down phase, causing a pump seizure. This was the case for a major global manufacturer
of specialty chemicals operating dry vacuum pumps and
mechanical boosters on an evaporation process that includes a phenol condenser, a receiver and a knock-out pot
ahead of the vacuum equipment.
Case study
The manufacturer had experienced major downtime
and maintenance costs due to phenol (melting point 41oC)
solidifying in the pump when it stopped or cooled down,
thus cold seizing the vacuum pumps.
Traces of triphenyl phosphate (melting point 48-510C)
were also causing problems. Another problematic chemical handled by the pump is phosphorous oxychloride.
The pumps suffered from irregular liquid slugging
caused by the problems with draining of the knock-out
pot.
The manufacturer and supplier evolved operating and
recovery strategies to minimise the amount of pump seizures and damage. However, the maintenance costs were
still high as the liquid slugging and subsequent cold seizures could not be completely eliminated without expensive pipework changes.
As one of the toughest vacuum pump applications in
the world, this company was keen to trial the latest generation of tapered, discrete variable pitch screw technology – the CXS chemical pump. The new pump design in-
corporates superior liquids and solids handling capabilities to reduce the chances of cold seizures and any subsequent internal pump damage when restarting. The new
pump has been running for several months without any
stoppages caused by liquid slugs or any restart damage
and with no maintenance costs. The customer is very satisfied with the pump’s performance.
Safety
Dry pumps are designed to pump flammable materials safely because they are contact-free pumping mechanisms with no ignition sources in normal operation.
Two ignition sources are generally considered with
dry pumps: spark ignition and auto-ignition (ignition by
temperature alone). Auto-ignition is simple enough to
deal with by running the pump in a pre-tested configuration which avoids auto-ignition. However, spark ignition can never be ruled out entirely in a fault condition,
no matter how rare. You must therefore implement a suitable protection strategy when pumping explosive gases.
The European ATEX directive requires process operators to undertake a risk analysis of the whole process, and
to identify protection strategies to mitigate the risks. We
regularly advise customers all over the world on these issues and, in areas where an explosion threat is identified, can provide guidelines on avoiding, eliminating,
containing and limiting the effects of an explosion, to
ATEX and other standards.
Conclusion
The global chemical industry has a history of driving
development in all areas of process equipment, not least
that of vacuum systems. When processors are specifying
a new vacuum system, cost-of-ownership and environmental impact are now key issues. The latest discrete, variable pitch tapered-screw dry pump technology offers
chemical processors high reliability effluent-free pumping, high levels of controllability and long service intervals, even in the most harsh chemical processing applications.
However, spark ignition can never be ruled
out entirely in a fault condition, no matter how
rare. You must therefore implement a suitable
protection strategy when pumping explosive
gases.
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Chemical Industry Digest. July 2012