POWER February 2011 - 20

to accept solid flinger discs or at least a
lubricant application method other than
slinger rings. Also, slinger rings can become
dislodged when the equipment is
transported from a factory or shop to an
installation site and become lodged between
shaft and ring locator pin or some
other housing component.
When a pump does require an overhaul,
systematic upgrading is practiced by best-ofclass
companies on every pump that enters
their repair shop. Bearing protector seals are
among the first upgrade components. However,
some widely used bearing protector
seals have a dynamic O-ring located directly
across from a sharp-edged groove (Figure
3, top left). Under certain operating conditions,
this O-ring will abrade, and elastomer
flakes will contaminate the lubricant, possibly
causing " black oil. " Others use V-rings
for unitizing rotor and stator into a single
package (Figure 3, top right), but these then
tend to induce frictional drag. More recent
designs (Figure 3, bottom image) manage to
avoid such risks, and upgrading to the leastrisk
bearing protector seal makes much sense
to the reliability-focused.
Systematic upgrading of BFW and other
important process pumps also includes
retrofitting only the very best constant
level lubricators. This implies that reliability-driven
facilities would use pressurebalanced
models that typically cost $30 to
$50 more than the traditional nonbalanced
models found on most process pumps.
True reliability-focused purchasers have
justifiable concerns with traditional and
failure-prone means of lubricant delivery.
Communicate with a pump manufacturer
when vulnerabilities of certain pump designs
are discovered. On their part, operators
must use rigorous checklists that lead
to better installation procedures, verification
of adequacy before start-up, and adequacy
while running and when doing root
cause failure analysis. Reliability improvements
are a shared obligation that cannot
be disregarded by either party.
-Contributed by Heinz P. Bloch
(hpbloch@mchsi.com), machinery reliability
consultant and author of 18 books
on practical machinery management,
maintenance, and repair.
Designing Large
Package Boilers
Five natural gas-fired, shop-assembled
integrated boilers capable of generating
426,000 lb/h of saturated steam at
550 psig were recently commissioned in
Canada (Figure 4). These package boilers
were different from the typical D-type
boilers in two major respects. First, the
20
4. New packaged boiler design. Cleaver-Brooks has designed a high-efficiency, lowNOx
elevated drum package boiler that generates 426,000 lb/h of steam at 550 psig and that
minimizes field erection time. Courtesy: Cleaver-Brooks Engineered Boiler Division
design used an elevated drum with external
downcomers and risers, which helped
to increase the furnace and convection
bank dimensions while maintaining the
ability to ship the units. In addition, a
glycol-based closed-loop heat-recovery
system consisting of three finned tube
heat exchangers was incorporated to improve
boiler efficiency by about 2.3% and
to increase the air temperature to the
forced draft fan in severe winter conditions,
when -30F to -40F is likely to be
the ambient temperature.
The five package boilers, engineered by
Cleaver-Brooks Engineered Boiler Systems
(Nebraska Boiler and Natcom Burner divisions),
are now in commercial operation
and have successfully met the contract performance
guarantees in terms of emissions,
capacity, ramp rates, and efficiency.
Unique Boiler Design
Designing large package boilers rated at
over 400,000 lb/h steam production is
a challenge because of shipping limitations
within the U.S. and Canada. Fielderected
boilers, on the other hand, are
very expensive and take more time for
commissioning. Minimizing field assembly
time is crucial to cutting costs and
shortening the construction schedule
on such large projects.
This project began with a customer requirement
for a typical Nebraska D-Series
package boiler rated at 355,000 lb/h of
550 psig saturated steam, with 230F feedwww.powermag.com
Table
1. Boiler design and geometrical
data. Source: Cleaver-Brooks
Engineered Boiler Division
Design parameter
Steam generation at 120% load (lb/h)
Steam pressure (psig)
Feedwater temperature (F)
Boiler max duty (mmBtu/h, HHV)
Burner duty (mmBtu/h, HHV)
Boiler exit gas temperature (F)
Efficiency (%, HHV)
Furnace length (ft)
Furnace width (ft)
Furnace height (ft)
Furnace projected area (ft2)
Furnace volume (ft3)
Area heat release rate (Btu/ft2h)
Volumetric heat release rate (Btu/ft3h)
Average heat flux (Btu/ft2h)
Convection surface (ft2)
Economizer surface (ft2)
Air heater 1 (ft2)
Air heater 2 (ft2)
Scavenger (ft2)
Value
426,000
550
230
429
499
212
86
44
10
16
2,361
6,400
177,000
66,000
47,000
11,860
39,900
7,466
22,400
30,000
water temperature, and with 20% overfire
capability. In addition, the flue gas exit
temperature was not to exceed 215F.
The package boiler assembly consisted
of the furnace and convection bank as a
POWER | February 2011
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POWER February 2011

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