POWER March 2014 - 54

operations & Maintenance
Ljungström rotary regenerative APHs (Figure
2). Each brush seal consists of thousands of
filaments that form a high-integrity seal and
provide a high degree of abrasion resistance,
flex life, and bend recovery not possible with
rigid strip seals (Figure 3). Each bristle is independent
and flexible, allowing deflection to
conform to any irregularities and gap variations
and recover to its original position.
The inherent elasticity of the brush design dissipates
stress under deformation, reducing drag
and wear. In addition, within the dense barrier
of thousands of filaments is an independent and
flexible membrane designed for deflection that
conforms to any irregularities and gap variations
and recovers to its original position to ensure that
a tight seal is maintained (Figure 4).
855 PM 55Chevy 042213_Layout 1 4/21/13 9:42 PM Page 1
Quantifiable Benefits
Air preheater leakage can account for significant
increases in parasitic power draw from the boiler
fans, and this translates into lost net revenue.
Consider a typical 500-MW coal-fired
unit configured with two APHs originally
designed for 10% APH leakage. The unit
has combined 8,595 kW installed fan power
consisting of two primary, two secondary,
and two induced draft fans (excluding the air
quality control system). Referring to the fan
curves, we find that when the APH leakage
increases 10%, the fan power requirements
increase 13% (1.12 MW). Table 1 suggests
the simple payback for installing brush seals
that return the APH leakage to design values
can be a matter of days.
There are other significant benefits to using
brush seals that aren't included in Table
1. For example, reducing air leakage on a sustained
basis results in lower flue gas velocities
and, therefore, reduces the pressure losses in
downstream air quality control systems, and
results in a corresponding reduction in fan
load. For plants with electrostatic precipitators,
increased velocities attributable to APH
leakage may result in higher dust emissions
at the stack. For plants with fabric filters, the
higher air-to-cloth ratios due to APH leakage
can affect the frequency of bag cleaning and
possibly shorten bag life.
1955 Chevy 150/210
855 Series
Low NPSHa on your vacuum receiver got
you down? Fail to resume pumping as
suction levels resume? You need Carver
Pump 855 Series muscle!
Carver 855 Series are designed for use on
TYPICAL
RECEIVER
TANK
OVERHEAD
DRIVE
MOUNTS
DIRECTLY
TO TANK
FLANGE
vacuum receivers operating with up to 26 " Hg
vacuum. Flange mounted directly to the vacuum
receiver tank eliminates suction piping/NPSH
problems. Whether operating at a trickle or full flow,
specially designed impellers allow pumping to resume even
after periods of interrupted flow.
Capacities range to 600 GPM depending on discharge head
and speed of operation. Available in 6 sizes ranging from
1 " - 4 " , standard materials of construction include All Iron,
CD4MCu and Rubber Lined. The 855
Series features an overhead v-belt drive
arrangement as standard, with options for
either close coupled or frame mounted
drives. Packing is standard in the stuffing
box with mechanical seals as an option,
and don't forget to ask about our
Swing-Out design. Let us build
the muscle you need!
V-BELT
DRIVE
ASSEMBLY
Carver
Series 855
Field Performance Results
In June 2007, the Hardin Generating Station,
owned by Bicent Power (Hardin, Mont.), contracted
with Sealeze, a unit of Jason Inc., to
supply its axial and radial stainless steel brush
seals for both the hot and cold ends of the 119MW
Unit 1 Ljungström APH. The plant has
an average availability of nearly 97%.
Inspection of the brush seals in 2008
showed them to be in very good condition.
Some splaying of the brush was evident on
the cold end due to sootblower blasts of 205C
steam. To prevent direct sootblower impingement,
the brush seals mounted in the path of
sootblower blasts have been redesigned to
incorporate an angled orientation and an in4.
Membrane seal. The adaptive brush
design is built around a malleable alloy foil
membrane nestled within brush filaments
to provide a 70% to 80% reduction in leakage
without sacrificing overall seal flexibility.
Source: Sealeze
Creating Value.
Carver Pump Company
2415 Park Avenue
Muscatine, IA 52761
563.263.3410
Fax: 563.262.0510
www.carverpump.com
CIRCLE 21 ON READER SERVICE CARD
52
www.powermag.com
POWER | March 2014
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POWER March 2014

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