CCI DRAG
100DLC for Boiler Feedwater Control Applications
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sDemanding Feedwater Control Requirements
High Reliability
Faster Plant Start-up
Improve Plant Efciency
Eliminate Erosion and Cavitation
Reduce Required Hardware
Reduce Maintenance Costs
Figure 1: Typical Start-up Pressures
Figure 2: Cv requirements at various plant loads. Both represent same 2x2x1 CCPP conguration.Also note that the units for P are psi.
It is critical within power plant operations in drum boilers (or ow in
once-through boilers); the level of feedwater is within required limits.
Considering drum type boilers, if the drum level is too high or too low,
the plant may be forced to trip. Drum or boiler level control is crucial
at plant start-up, when the pressure differential between the Boiler
Feed Pump (BFP) and boiler is very high and control is difcult. Boiler
Feedwater Control Valves must achieve a smooth start-up and maintain
required drum level for safe, reliable and efcient plant operation. The
high pressure differential at start-up/low-load, and sensitive control
requirement, requires a high-performance severe service control valve.
Feedwater Control Valve Requirements
During Start-up and Low-load Operation
Operate at high pressure differentials of up to 240 bar (3500 psid) (Drum Boilers), without damaging the trim components, and
maintaining good control (Figure 1)
Smooth and quick transition from start-up to normal operation
Consistent and reliable operation
Tight shut-off to prevent leaks and subsequent valve erosion
During Normal Operation
A valve with a high capacity is required at normal operation to minimize frictional losses in the system to minimize Boiler feed
Pump power requirements (Figure 1).
During Load Change (assuming xed speed boiler feed pump)
Load changes are often experienced and this will result in a lower steam pressure and drum pressure, but feedwater pressure will remain
similar, resulting in a higher pressure differential. Figure 2 shows that
the P, and so Cv requirements, at full load on a 2 x 2 x1 Combined
Cycle Power Plant (CCPP) are signicantly different depending on
whether one GT (Gas Turbine) or two GTs are in operation, and
so the control valve used must be able to meet a wide range of Cv
requirements to provide full exibility to the plant.
With once through boilers there can be similar issues, particularly at
start-up when Boiler regulator valve is used before the main variable
speed pumps (usually steam turbine driven) go into operation.
Consequences of Feedwater Control Valve Problems
Cavitation/ashing: Insufcient pressure reducing stages will cause high velocity ows, leading to valve/trim damage owing to
cavitation/ashing
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Plant Load 1GT Operating 2 GT Operating
Cv P (psi) Cv P (psi)
9% 2.0 2750 2.0 2750
14% 3.0 2740 3.0 2700
18% 4.0 2675 4.1 2575
36% 8.4 2430 8.8 2230
55% 13.4 2160 14.6 1810
73% 19.7 1780 22.6 1350
82% 23.8 1545 29.2 1025
91% 29.3 1260 42.4 600
100% 38.1 900 114.4 100
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Figure 3; Combined feedwater control valve conguration instead of two
Smooth increases providesquick, stable start-up
Severe fluctuationsincrease plant-trip potential
Figure 4: Before and after DRAG combined solution was installed at a CCPP
Lost production: Poor control at low ows can lead to plant trips and/or an extended start-up process
High maintenance costs: Frequent replacement and repair of valve components adds to maintenance costs
Symptoms of Feedwater Control Valve Problems
Erosion damage: Caused by:
- Insufcient number of trim stages, creating excessive trim
velocities
- Poor seat design and insufcient seat force
Plug or stem breakage: Typically caused by high trim velocities, and subsequent trim vibration and fatigue failure
Vibration and noise: Caused by cavitation and excessive internal velocities
DRAG Reduces Costs and Improves Performance
CCI is able to offer a one valve solution with the 100DLC DRAG valve,
which meets both the high and low Cv requirements as an alternative to
the two valve system (Figure 3). This conguration is only possible due
to DRAG high rangeability trim providing excellent controllability at
all ows, from start-up through to normal operation. There are distinct
benets to the combined solution:
The change is eliminated providing a quick, smooth start-up
At start-up and increasing from low-load conditions, the transition
from the start-up to main valve is difcult to control and maintain
stability. At this stage in the process, plant trip is at risk and
undesirable as there will be penalties incurred owing to increased
maintenance, lost generating revenue and fuel costs. Considering
two valve solution, to avoid a plant trip, start-up is done gradually
owing to limitations at the feedwater control valve system, and
this can signicantly extend the start-up time. Extended start-up
times translate into lost revenues, and penalties (many government
environmental control bodies may apply penalties to a utility when
the start-up times exceed certain limits and may also require more
frequent maintenance of Gas Turbine as a result of trips)
Using a combined valve, the transition is eliminated and the
limitation of pressure drop across the main valve is eliminated
resulting in a smoother, quicker start-up. Figure 4 shows a clear
example of this for an 815MW Combined Cycle Power Plant (CCPP)
in the U.S. The plant now consistently achieves a 60-90 minute
3Feedwater Control Valve Solutions
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Table 1: System Components/Savings
System Components Your Savings
2 x Start-up line isolation valve
2 x Tee (e.g. 10 SCH160)
2 x Elbow (e.g. 3 SCH160)
Pipework (e.g. 10ft)
4 x large welds (e.g. 24hrs)
12 x small welds (e.g. 24hrs)
Start-up control valve
Control loop
Total Capital Cost
Figure 6: Web of problems caused by applying the wrong Boiler Feedwater Control Valve
Lost production
Noise & Vibration
Lagging/ silencing required
High maintenance costs
Trim & body wear
Insufficient Staging and leaks at shutoff
Cavitation or
flashing
High
velocities
Poor control
faster start-up and enjoys the fastest dispatch in its region and eet.
The smoothing of the transition also provides peace-of-mind that the
likelihood of a costly plant-trip has been minimized.
Maintenance costs are reduced
With the two valve solution, there is the potential risk of transferring
from the start-up to the main valve too soon. This exposes the main
valve to differential pressures it is not designed for, causing costly
damage. For the 815MW CCPP, this problem resulted in the trim-
sets requiring replacement on at least a yearly basis, contributing
signicantly to maintenance costs.
Using the two valve solution, the start-up valve was not able to
withstand the severe and erratic conditions of start-up, and for the
815MW CCPP this meant regular additional maintenance costs.
The plant has not experienced any of its original problems since
the Combined DRAG valves have been installed, providing them
with signicant maintenance cost savings and improved plant
performance.
Capital costs of additional hardware are reduced
By eliminating one valve from the system, associated hardware is
eliminated, providing cost savings in the system purchased (and
associated maintenance costs).
CCI estimates for a Feedwater Control System on a 500MW 2x2x1
Combined Cycle Power Plant, the hardware savings could amount
to at least $20,000 per unit with two units per Plant. Heres what
CCI have identied savings sources; ll in the table (Table 1) to see
what yours would be.
Severe Service Applications for CCI DRAG 100DLC
The CCI DRAG 100DLC are not solely used for Drum Level Control
of Combined Cycle Power plants, but can be equally applied to the
following applications:
Drum Level Control of conventional fossil red plants (Combined and start-up)
Start-up Feedwater Regulator valve on large sub critical and supercritical Boilers
Boiler Circulation Valves, used on supercritical once-through boilers to maintain minimum ow through the boilers.
4 More than a Feedwater Control Valve
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Figure 7: Multiple pressure reducing stages eliminates erosion
DRAG Combined Solution Controls Fluid Velocity
CCI has designed DRAG to operate within the ISA Guide, Control
Valves, Practical Guides for Measurements and Control, to provide
suf cient velocity control.
P
Fluid Velocity
vs. Stages of
Pressure Drop
Recommended
Velocity
Recommended
Stages
Bar psi4 Stages Multi-stage
Stagesm/s ft/s m/s ft/s
130 1885 54 177 30 98 16
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Service ConditionsVelocity (H2O)
m/s ft/s
Continuous service single phase uids 30 100
Cavitating & multi-phase uid outlet 23 75
High trim exit velocities are commonly responsible for erosion damage
in control valves (erosion increases to the power of 2 to 4 with velocity
increase).
The Velocity Control DRAG trim eliminates problems with trim erosion
by limiting the trims uid exit velocities and corresponding kinetic energy.
Figure 7 illustrates an analogy of how multiple pressure stages can
control this kinetic energy, eliminating erosion, vibration and noise.
With one pressure stage, the water ows over the edge of the dam with
high energy, resulting in erosion. With numerous steps to ow over in
the stepped dam, the water has much less energy as it reaches the base,
eliminating erosion.
By eliminating this destructive energy source, positioners, air sets and
other actuator components will not be as susceptible to damage or
calibration shift. Piping will also no longer be subject to fatigue failure
from valve-induced vibration.
Eliminate Cavitation with DRAG Combined Solution
The DRAG trim forces the ow to travel through paths of turns
(Figure 8). Each turn causes a pressure loss to the uid (Figure 9), and
so the pressure gradually reduces over the turns. This series of multiple
Figure 9: Each turn in the DRAG trim provides a pressure drop
Figure 8: CCI 100DLC multi-path, multi-stage trim designs are characterized to provide optimal valve performance at all ow conditions.
Control erosion by controlling velocity!
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Figure 12: Characterized Equal Percentage disk stack
pressure drops allows the pressure to reduce without falling below the
vapor pressure (Figure 10) and so avoids cavitation (Figure 11). As
cavitation is destructive to the valve and trim, the DRAG multistage
pressure drop provides a clear benet in terms of performance, and
maintenance costs.
Accurate Control and Reliable Operation at all Flow Conditions with the CCI DRAG Disk Stack
DRAG disk stacks can be customized to provide the required Cv
throughout the valve stroke; this is done by conguring disks of varying
numbers of turns within the stack (Figure 12). The DRAG control
valve disk stack features an equal percentage characteristics. These trim
characteristics provide very ne ow control. The disk stacks use disks
with more pressure letdown stages near the seat end of the trim (up to 20
stages or more), and fewer stages near the full-open end of the trim. This
provides critical protection of the seat ring while allowing superior ow
control throughout stroke of the valve. Independent and isolated ow
paths are utilized to eliminate short circuits between the ow paths.
Reliable Long Term Shutoff
The DRAG control valve uses a hard seat, which resists trash cutting,
and a very high seat loading to provide reliable and repeatable long-
term shutoff for very high pressure differentials. The actuator is sized
to provide a minimum seat ring loading of 500lbf per circumferential
inch (9 kg/mm) as recommended by ISA. The DRAG velocity control
trim design owing to control of velocity and high seat force for shut-off
protects the seat ring and plug surfaces from cutting or pitting due to
erosion.
Custom Design Meets Plants Needs
As well as 100DLC standard DRAG valve, CCI also provides custom
DRAG valves. Options such as anged ends, expanded butt-weld ends,
high temperatures seals, and forged body is available. CCI can also
provide a 2 valve solution (see Figure 3) if required. Please contact your
CCI representative for further details on non-standard options.
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% Flow1009080706050403020100
0 10 20 30 40 50 60 70 80 90 100
% Stroke
Modified Linear
Linear
Modified Equal %
Figure 11: Insufcient stages can lead to cavitation
P1
V1
Pv
Pvc
inlet velocity
Vvc
Vvc
Vvc
inlet pressure
Pvc
V2 outlet velocity
Pvccavitation bubbles form here
vapor pressure
P2 outlet pressurebubbles collapse, cavitation occurs
P1
V1
Pv
inlet velocity
pressure
V2 outlet velocity
P2 outlet pressure
vapor pressure
Figure 10: The DRAG staging stops erosion and cavitation.
DRAG 100 DLC - proled to maximize feedwater control performance
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Valve Performance Characteristics (% Cv vs. % Stroke)
Multiple Cv Trims Throughout Disk Stack
Allows characterized design for optimum control throughout start-up and normal
operation conditions.
7
Equal Percentage Modied Equal Percentage
Multi-Stage DRAG Disk Stack Technology
Limits uid velocities, controls vibration and erosion. Multiple Cv trims throughout disk stack
Class V Shut-off
A metal seat is standard, with a 500 PLI (9 kg/mm) loading force to achieve tight shut-off.
Disk Stack Labyrinth Grooves
This section of the disk stack has no ow passages; in their place labyrinth grooves break up clearance ow, preventing
seat ring damage.
Stem Packing
Multiple Teon packing design with graphite guide spacer for low packing
friction and long term leak free service. Graphite packing available for higher
temperature feedwater (after economizer).
High Integrity Balance Seal
The spring energized Teon balance seal is specially packaged in a split gland design for easy assembly and long service life. Other seal designs are available to meet high-temperature requirements.
DRAG 100 DLC features
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Benets DRAG 100DLC Competition
1 Provides the Valve Doctor Solution. CCI works with
plant operators to improve plant performance, reliability
and output.
2 Prevents Cavitation Damage. CCI works to ISA guidelines to ensure solutions prevent potential for cavitation.
3 Eliminates Erosion Damage. By controlling uid
velocities, erosion is eliminated.
4 Noise Eliminated. Noise eliminated through velocity
control, eliminating need and cost for lagging/silencing.
5 Stops Costly Maintenance Cycles. CCI valves are
designed and sized to provide longer intervals between
maintenance and allows easy access to all components.
6 Assists Quick Start-up. CCI valves are designed to handle
the severe start-up conditions to provide good control and
avoid plant-trips at start-up.
7 Avoids Plant Shutdowns. Valves are designed and sized
to handle severe conditions and provide excellent control.
8 Further Assists Quick Start-up. Combined valve provides
smooth, quick start-up.
9 Efcient Start-up. Stable start-up avoids plant-trips.
10 Ownership Cost of Additional Equipment Eliminated.
Additional instrumentation and hardware not required,
eliminating signicant associated costs.
Use this check list to evaluate the benets of CCIs DRAG 100DLC valve
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1500 ANSI 2500 ANSI
Globe AngleHeight Weight
Globe AngleHeight WeightTrim
Size Buttweld A B C Buttweld A B C
2.0 Use 2500 ANSIUse 2500
ANSI13.00
(330 mm)50
(1270 mm)400 lbs (180 kg)
3, 4 22.75 (578 mm) 13.00 (330 mm)
50 (2030 mm)
450 lbs (200 kg)
6 24.00 (610 mm)
2.5 or
3.0
4, 6 21.50 (546 mm) 13.75 (330 mm)
65 (1650 mm)
800 lbs (360 kg)
4, 6 26.50 (673 mm) 17.88 (454 mm)
65 (1650 mm)
1100 lbs (500 kg)
8 25.50 (648 mm) 829.25
(743 mm)
4.06, 8 27.75 (705 mm) 16.25
(413 mm)65
(1650 mm)1000 lbs (450 kg)
6, 8 36.00 (914 mm) 20.00 (508 mm)
65 (1650 mm)
2000 lbs (900 kg)
10 33.00 (838 mm) 1038.50
(978 mm)
5.0 8, 10 42.50(1080 mm)
Contact CCI for these
options
54 (1370 mm)
2500 lbs(1150 kg) 8, 10
42.50(1080 mm)
Contact CCI for these
options
54 (1370 mm)
2500 lbs(1150 kg)
6.0 10, 12, 1450.00
(1270 mm)74
(1880 mm)5000 lbs(2300 kg)
10, 12, 14
50.00(1270 mm)
74 (1880 mm)
5000 lbs(2300 kg)
7.0 10, 12, 1450.00
(1270 mm)74
(1880 mm)5000 lbs(2300 kg)
10, 12, 14
50.00(1270 mm)
74 (1880 mm)
5000 lbs(2300 kg)
9.0 12, 14, 1663.40
(1610 mm)76
(1920 mm)7500 lbs(3400 kg)
12, 14, 16
63.40(1610 mm)
76 (1920 mm)
7500 lbs(3400 kg)
Specications shown are for the 100DLC DRAG valve; the standard 100D DRAG valve offered. Other 100D DRAG valves are available where this specication is not suitable.
9Technical Specications
DRAG is a registered trademark of CCI.2006 CCI 560 12/06/06
Throughout the world, companies rely on CCI to solve their severe service control valve problems. CCI has provided custom solutions for these and other industry applications for nearly half a century.
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