CCI DRAG®

100DLC for Boiler Feedwater Control Applications

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sDemanding Feedwater Control Requirements

■ High Reliability

■ Faster Plant Start-up

■ Improve Plant Efficiency

■ 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 configuration.Also note that the units for ΔP are psi.

It is critical within power plant operations in drum boilers (or flow 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 difficult. Boiler

Feedwater Control Valves must achieve a smooth start-up and maintain

required drum level for safe, reliable and efficient 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 fixed 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 ΔP, and so Cv requirements, at full load on a 2 x 2 x1 Combined

Cycle Power Plant (CCPP) are significantly different depending on

whether one GT (Gas Turbine) or two GT’s are in operation, and

so the control valve used must be able to meet a wide range of Cv

requirements to provide full flexibility 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/flashing: Insufficient pressure reducing stages will

cause high velocity flows, leading to valve/trim damage owing to

cavitation/flashing

2

Plant Load

1GT Operating 2 GT Operating

Cv ΔP (psi) Cv ΔP (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 configuration instead of two

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Smooth increases providesquick, stable start-up

Severe fluctuationsincrease plant-trip potential

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Figure 4: Before and after DRAG® combined solution was installed at a CCPP

Lost production: Poor control at low flows 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:

- Insufficient number of trim stages, creating excessive trim

velocities

- Poor seat design and insufficient 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 configuration is only possible due

to DRAG® high rangeability trim providing excellent controllability at

all flows, from start-up through to normal operation. There are distinct

benefits 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 difficult 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 significantly 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 fleet.

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

significantly 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 significant 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. Here’s what

CCI have identified savings sources; fill 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 fired 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 flow 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

suffi cient velocity control.

ΔP

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

5

Service ConditionsVelocity (H2O)

m/s ft/s

Continuous service single phase fl uids 30 100

Cavitating & multi-phase fl 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 trim’s fl 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 fl ows over the edge of the dam with

high energy, resulting in erosion. With numerous steps to fl 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 fl ow to travel through paths of turns

(Figure 8). Each turn causes a pressure loss to the fl 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 fl 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 benefit 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 configuring 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 fine flow 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 flow

control throughout stroke of the valve. Independent and isolated flow

paths are utilized to eliminate short circuits between the flow 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 flanged 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.

6

% Flow1009080706050403020100

0 10 20 30 40 50 60 70 80 90 100

% Stroke

Modified Linear

Linear

Modified Equal %

Figure 11: Insufficient 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 - profiled 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 Modified Equal Percentage

Multi-Stage DRAG® Disk Stack Technology

Limits fluid 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 flow passages; in their place labyrinth grooves break up clearance flow, preventing

seat ring damage.

Stem Packing

Multiple Teflon 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 Teflon 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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Benefits 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 fluid

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 Efficient Start-up. Stable start-up avoids plant-trips.

10 Ownership Cost of Additional Equipment Eliminated.

Additional instrumentation and hardware not required,

eliminating significant associated costs.

Use this check list to evaluate the benefits of CCI’s DRAG™ 100DLC valve

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1500 ANSI 2500 ANSI

Globe Angle

Height Weight

Globe Angle

Height 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)8”

29.25” (743 mm)

4.0”

6”, 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)10”

38.50” (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”,

14”50.00”

(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”,

14”50.00”

(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”,

16”63.40”

(1610 mm)76”

(1920 mm)7500 lbs(3400 kg)

12”, 14”, 16”

63.40”(1610 mm)

76” (1920 mm)

7500 lbs(3400 kg)

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Specifications shown are for the 100DLC DRAG® valve; the standard 100D DRAG® valve offered. Other 100D DRAG® valves are available where this specification is not suitable.

9Technical Specifications

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.

CCI AustraliaPhone: 61 2 9918 409421 Catalina CrescentAvalon, NSW 2107Australia

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Phone: 43 1 869 27 40Fax: 43 1 865 36 03Lembockgasse 63/1AT-1233 ViennaAustria

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Contact us at:info@ccivalve.com

Visit us online for sales and service locations at: www.ccivalve.com

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Phone: 41 52 264 95 00Fax: 41 52 264 95 01lm Link 11, P.O. Box 65 8404, WinterthurSwitzerland

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