che_october-2024 - 40
risk factor of the oxygen concentration. In contrast, a
continuous-flow purge system is indirect and relies on
pressure-sensor setpoints. As long as the overpressure
on the seals or housing is maintained, no oxygen from
the environment can penetrate the system and the oxygen
concentration is held below the critical level. This is
done with flowmeters and pressure gages.
However, since continuous-flow systems rely on presFIGURE
6. Differential pressures are maintained with an overpressure sealing
and monitoring system
sure sensor setpoints, applications using lower differential
pressures may be susceptible to erroneous system
shutdowns. In these cases, oxygen sensors may provide
more sensitive monitoring of this danger zone.
Both methods ensure safe operation if they are properly
planned, installed and maintained. Unfortunately, the
weak point with an oxygen sensor is the sensor itself,
which requires programmable logic controller (PLC) programming,
calibration, periodic replacement and maintenance.
Overall, continuous-flow purging offers better net
positive usability when compared with oxygen monitoring.
Safe and efficient separation
FIGURE 7. Internal oxygen concentrations can be managed in two ways: with
oxygen sensors and with a continuous-flow purge system
Using an inert gas to form a tightly sealed or purged centrifuge
is an excellent solution for a variety of applications,
including explosion protection in the chemical, pharmaceutical,
petrochemical or biodiesel industries; and environmental
protection from hazardous materials, such as
those generated during tar cleaning.
Once commissioned, a leak-tightness test schedule
should be created and performed regularly to verify the
tightness of the purge unit. Routine maintenance and
testing points include threaded connections, manometers,
meters, flowmeters and hoses. Supply lines also
must be checked at regular intervals for damage, clogs
and tightness (Figure 8).
Centrifuges are extremely efficient, with higher
FIGURE 8. Routine maintenance and testing points include threaded connections,
manometers, meters, flowmeters and hoses
to the atmosphere. This is only possible if the pressure at
the seal face is higher than the pressure in the decanter
housing (>0.290 psi) and the outside atmosphere. The
differential pressure (0.725-1.45 psi) between the housing
and the gas feed point is monitored and controlled.
Seals are pressurized to keeping oxygen from entering
the system.
Managing O2 concentrations
Internal oxygen concentrations can be managed in two
ways: with oxygen sensors and with a continuous-flow
purge system (Figure 7). Oxygen sensors monitor the
oxygen concentration inside the centrifuge housing.
An advantage to using these sensors is the continuous
monitoring they offer, especially if the differential pressure
between the internal housing and the atmosphere is less
than 0.290 psi.
Oxygen sensors provide direct information about the
40
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
OCTOBER 2024
throughput than filters or presses and they operate continuously,
instead of in batches as with filters or presses.
It is possible to separate two phases, three phases or a
very light emulsion with a purged centrifuge. Many systems
are also fully automated, which reduces operator
involvement overseeing the machine.
n
Edited by Scott Jenkins
References
1. Green, D. and Southard, M., " Perry's Chemical Engineers' Handbook, " 9th ed., McGraw-Hill Professional
Publishing, 2018.
2. National Fire Protection Association (NFPA) Standards Council, National Electric Code NFPA 70, 2023
edition, nfpa.org.
Acknowlegements
All images in this article appear courtesy of Flottweg Separation Technology Inc.
Author
Lee Betkowski has been the biotech, chemical, pharmaceutical
(BCP) industry manager for Flottweg Separation Technology
Inc. (10700 Toebben Drive, Independence, KY 41051; Email:
lbetkowski@flottweg.net) for 13 years. Prior to joining Flottweg,
he worked for Krauss Maffei (pusher, peeler centrifuges, dryers),
Rosenmund (filter dryers) and De Dietrich (glass-lined steel
equipment). Betkowski has nearly 30 years of experience in the
biotechnology, chemical and pharmaceutical industries, working
predominantly with centrifuge products and technology.
http://www.nfpa.org
http://WWW.CHEMENGONLINE.COM
che_october-2024
Table of Contents for the Digital Edition of che_october-2024
che_october-2024 - Intro
che_october-2024 - Cover1
che_october-2024 - Cover2
che_october-2024 - 1
che_october-2024 - 2
che_october-2024 - 3
che_october-2024 - 4
che_october-2024 - 5
che_october-2024 - 6
che_october-2024 - 7
che_october-2024 - 8
che_october-2024 - 9
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che_october-2024 - 11
che_october-2024 - 12
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