Efficiency Through Indirect Measures

If Not Considered and Monitored, Indirect Factors Can Directly Impact the True Efficiency of the Product-Transfer Process

Introduction
Typically, the amount of product pumped per unit of
energy used would be considered a very direct measure
of efficiency. However, operators tasked with optimizing
energy savings and reducing costs must also consider
broader and possibly indirect energy consumption. This
white paper explores how pump design can affect three
indirect efficiency areas:
n Use of seal coolant (water) with the associated energy
consumed to supply and then treat.
n Pump design that affects efficiency of product recovery.
n Pump design that reduces product loss and
consequential energy use to treat this waste.
These indirect factors often result in what can be termed
“energy creep.” Energy creep occurs when indirect efficiency
issues are not monitored and unintended waste occurs.
To begin, the fluids for mechanical seal flush fluid are
not free.
While seal cooling or flush only applies to a subset of
pump applications, it serves as a good example of an
indirect efficiency issue for those analyzing the total energy
footprint of pump selection. Frequent applications can be
found in the food, beverage and pharmaceutical industries
where transferring sweeteners that tend to crystallize on
seal faces can cause premature seal failure. (See Figure 1
showing transfer line from sweetener storage.) Traditionally,
the common solution to this has been to use advanced
seals (most of which are not permitted or adaptable for
hygienic applications) or using mechanical seals with water
or other fluid flush.
However, seal water usage on pumps is a classic case in
which energy creep can occur. It is typical over time that
the volume of seal water is increased to be safe. In fact,
some experts in the industry noted that they typically see
up to 10 times the necessary amount of water actually
needed for seal flush. Ultimately, the ideal would be to
avoid needing seal flushing at all.

Benefits of Eccentric Disc Design
Negating the use of seal water altogether can help to avoid
this cost (and possible creep). The solution is to use pumps
that have totally sealed pumping chambers and do not
require seal flush. Diaphragm and magnetic-drive pumps
may be familiar options. However, new to the field are
eccentric movement pumps that better fit some applications
that are not suitable for the former pump styles.
Most processors realize that water is becoming a valuable
(and increasingly expensive) natural resource. Water is a
visible expense as the county, city or other sources that
provide it are passing onto the processor the costs to supply
and then treat the water. If the processor treats the water,
he can determine the energy usage and costs for this. For
an example, a processor who handles sweeteners in the
confectionary industry has calculated that his plant’s total
cost for water used in flushing seals was more than $10,000
per year/per pump.
In another case, a processor that makes sauces in the
Southeast United States was faced with a permit cost of
more than $400,000 if additional water was to be used in
the plant. The reason is if water is used over and above the
limit, the county must expand its water-treatment capacity.
The project was canceled because of this reason. Whether it
is a per-pump water use cost or permit cost, new options
to negate the use of water means less energy used to
supply and treat the water, as well as other costs that may
be incurred.
The eccentric movement or eccentric disc design for
sealing pumps is an alternative to the magnetic drive or
diaphragm, no-flush options. The eccentric movement
sealed pumps do not use mechanical seals and, therefore,
seal flushing is not needed. Compared to magnetic drives,
the eccentric movement designs can also be configured
in a hygienic/sanitary design, employed in semi-abrasive
applications, and at the same time avoid heat build.
The eccentric movement pump is one of the few nonpulsing
positives displacement pumps that negates the
use of dynamic seals. In most cases, this pump is driven
by standard rotating drives. This drives the shaft within
the pump with a coupling. However, unlike most pumps,
the shaft is machined on different planes so that the drive
end of the shaft is on a different plane than the tip that is
driving the pumping mechanism (See Figure 2 — Mouvex
C-Series pump cutaway).
Attached to the shaft are bearings and both are enclosed by
a hermetically sealed metal bellow or rubber boot. As the
shaft rotates, the metal bellows or rubber boot (See Figure
3 — Mouvex S Series pump boot and exploded view) does
not rotate thanks to the bearings. Instead, it flexes in an
eccentric motion. This flexing is very minor and within
the elastic range of the stainless steel so that preventive
maintenance (PM) inspection is recommended at 150
million duty cycles, meaning for some applications a PM of
every 5 years is more than adequate.
The actual pumping mechanism is similar to the peristaltic
effect of hose pumps, but this pump does not use hoses, so
it does not fall victim to any of the possible issues associated
with them. The disc of the pump is driven by the eccentric
movement of the shaft, which produces a peristaltic effect
on a channeled cylinder. Product flows in an inner and
outer pumping chamber, producing fully complementary
flows. The pump, therefore, does not produce pulsation.
Since this pump does not depend on clearances for
operation and, in fact, takes up clearance that could be
generated by wear, the pump has no measurable slip.
With no mechanical seal, there are no surfaces on which
products, such as corn syrup, liquid sugar, glucose or any
number of difficult-to-seal fluids can crystallize, adhere, and
subsequently damage the seal. Therefore, with no dynamic
seal the need for flush water to remove these products
is eliminated.
Why Discard What You Already Pumped?
The eccentric movement pump concept goes beyond
resolving broader efficiency issues from just a water or
seal-flush use perspective. During the production cycle of
a traditional pumping system, startup and shutdown are
highly inefficient because:

n The pumping system is not stabilized, so the product
being pumped is not to specification and must be
re-worked or treated for waste.
n For most pumps, once the inlet tank is empty and the
pump loses prime, the discharge line remains full of
product and also becomes a loss.
It is clear that pumping a product and then not using it is
a very inefficient use of resources. Disposing or treating this
unsuitable fluid further adds to this inefficiency.
Efficiencies When Starting A Process
Since it has essentially no slip, the eccentric movement
technology is able to produce a stabilized and usable
product flow much earlier in the startup process. This
compares with pump styles that have slip and require
a control system to adjust and compensate. As a field
application example, companies that use spray-drying
processes find this to be the case in their operations.
Typically, processes of this nature begin on water for
calibration and stabilization. The water is then replaced
with actual product. However, a process upset occurs when
this change occurs. The degree to which a pump has no slip
and can maintain constant flow during the transition is
related to how the process retains stability and product
losses are minimized during transition. In the case of spray
driers, much like shower heads, if flow changes the spray
pattern changes, rendering differences in the product and
possible rejection.

Efficiencies When Ending A Pumping
Process
On completion of a process, the residual product left in
the pump discharge line also represents an opportunity for
cost savings by improving product recovery and reducing
treatment needs for lost product.
In another field application example, a company that
produces coffee extract was able to recover an additional
400 pounds of product at the end of each run because
even after the feed tank was empty, the pump continued
to effectively pump air, thus helping purge the line.
Pumps that are able to run dry and continue to generate
air pressure on the discharge to purge the product out of
the discharge line are considered to produce a compressor
effect. The pumps that employ the eccentric movement
principle such as the Mouvex® pump, produce this
compressor effect. When considering the effect of efficiency,
recovering 400 pounds per run meant:
n Resources did not need to be used in treating it as
waste.
n All the resources to produce it were not lost.
n Resources would not be used to reproduce the lost
coffee extract.
The additional indirect efficiency issue was that coffee
extract was very aggressive on mechanical seals and
required advanced seals or water flush. Mouvex eccentric
movement technology, with its seal-less design, also helped
in this application because resources were not expended for
seal water.
Putting It All Together
While it is important to consider the direct efficiency
parameters of a pump, such as the amount of product
pumped per unit energy consumed, considerations should
include the indirect efficiency consequences of pump
technology selection. The issues of periphery services to
the pump—such as seal water, or consequences of the
pump design, such as the amount of product loss and waste
treatment costs—all combine to create the true efficiency of
the product-transfer process.
Wallace Wittkoff is the Hygienic Director for Dover
Corporation’s Pump Solutions Group (PSG™). He can be reached
at (502) 905-9169 or Wallace.wittkoff@PumpSG.com. PSG is
comprised of six leading pump companies—Wilden®, Blackmer®,
Griswold™, Neptune™, Almatec® and Mouvex®. You can find
more information on Mouvex at www.mouvex.com and PSG at
www.pumpsg.com.