Chemical Engineering June 2010 - 48

Sealing Special Advertising Section
Sealing systems cut pumping energy costs
Common installation arrangements for mechanical seals may use more energy than
the motor driving the pump, but careful choice of seal support systems can cut costs
F
or pump energy efficiency improvements, look to sealing systems;
that's the message from the Fluid Sealing Assn. (FSA;
www.fluidsealing.com) and the European Sealing Assn. (ESA;
www.europeansealing.com).
A mechanical seal is an energy-efficient device in itself, but the
same is not always true of the support systems used to control the
operating environment around the seal. FSA research shows that
in many applications, thermal energy lost by the seal flush system
exceeds the power required to run the pump to which the seal is
fitted. As a result, the energy savings that can be achieved from
better seal support systems are often far higher than those possible
through fitting variable-speed drives or re-sizing pumps.
Recent developments in mechanical seal technology and materials
have focused on producing seals that can operate without
additional support systems, even in challenging applications.
Older seal designs, however, often require a supply of liquid
- either once-through or recirculated - to remove heat and prevent
contaminants in the process fluid from damaging the seal.
Some of the simpler seal support systems, notably Cool
External Flush (API Plan 32) and Cooled Recirculation (API
Plan 21), operate by diluting and/or cooling the pumped fluid.
As Figure 1 shows, the resulting heat loss can easily be greater
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48 ChemiCal engineering www.Che.Com JUne 2010
7.6 l/min (2 gpm) kerosene
flush at 38°C (100°F)
351 W (1,200 BTU/hr)
= frictional power consumed
by seal
47 kW (160,000 BTU/
hr) = power required
to replace heat lost
through dilution of the
pumped fluid
Figure 1: The 47 kW of heat lost from this seal flush could
represent more energy than the pump motor consumes
than the power required to drive the pump. This wastes energy
and reduces the available capacity of plant cooling and heating
systems.
Figure 2 shows that API Plans 32 and 21 between them account
for more than one-third of seal support systems operating at temperatures
above 200°C (400°F). The FSA obtained this information
from a survey of 28,000 seal applications.
Figure 2 also shows that some alternative seal support systems
use considerably less energy than the wasteful Plans 32
and 21. Plan 23, for instance, is a high-temperature arrangement
similar to Plan 21 in that the seal is supplied with liquid that has
passed through an external cooler. Whereas in Plan 21 the source
of this liquid is the discharge side of the pump, via a flow control
orifice, in Plan 23 a pumping ring in the seal chamber does the job
with much lower energy consumption. Arrangements using a barrier
gas (Plan 74) or a seal that can handle the duty without recirculation
(Plan 2) have virtually zero energy requirement.
The study of the
energy used by seal
support systems
falls under the
umbrella of Sealing
Systems Matter, a
project by the FSA
and the ESA to help
users of sealing
devices and systems
use less energy,
contain emissions,
improve safety, and
increase equipment
reliability by optimizing
sealing systems.
An important
part of the initiative
is a focus on lifecycle
costs, rather
than the initial costs
which have traditionally
dominated
seal selection. ■
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Figure 2: Some of the most commonly
used seal support designs (top) are also
some of the most energy-hungry (above)
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http://www.fluidsealing.com http://www.europeansealing.com http://www.procoproducts.com http://adlinks.che.com/29251-16 http://www.Che.Com
Chemical Engineering June 2010

Table of Contents for the Digital Edition of Chemical Engineering June 2010
