7/28/2019 205 Drag Valves for Boiler Feedpump Recirculation
1/6
BDRAG VALVES FOR
BOILER FEEDPUMP
RECIRCULATION
7/28/2019 205 Drag Valves for Boiler Feedpump Recirculation
2/6
INTRODUCTIONIn a power plant the boiler water is circulated in a closed loop by
a feedpump driven either by an electrical motor or a steam turbine.The pump takes the water from the deaerator or high pressureheaters and boosts the pressure as high as 5500 psi (387kg/cmz) insupercritical, once-thru boilers. These pumps require a certain mini-mum amount of flow to avoid overheating and cavitation problems.In order to protect the pump when the boiler feed flow require-ment is less than the minimum permissible flow through the feed-pump, a recirculation system is used to return a portion of the high
pressure flow back to the condenser or deaerator and from there tothe pump. See Figure 1 for a system schematic.
Figure 1- Schematic of typical once-thru,universal pressure, steam-generating plant,showing location of boiler feedpump recircu-lation valve.
DEAERATOR
SUPERHEATER
ECONOMIZER
-P TURBINE
L-P TURBINE
FiGGGil I I ( ) CONDENSER
HEATER PUMP 9 9w;g;TERDEMINERALIZER
Figure 2 - A CC I DRAG@ valve of globeconfiguration is shown located near pumpdischarge with flow to deaerator. An angleCC I DRAG valve is also available, should
piping configuration dictate. Systems dis-charging to the condenser normally useangle valves.
Figure 3 - Actuator control schematicshown is for 3-15 psi modulation signal, withincreasing signal tending to close valve.The actuator is fitted with a spring for failopen on loss of air signal. A snap-actingrelay is provided to ensure the valve isseated at maximum signal. The snap-acting relay is set as shown so the valvemodulates between 10% and 100% open.
SIGNAL INLET HIGH SELECTOR RELAY
POSITIONER
SNAP ACTING RELAY
(10% OFF SEAT)
REGULATOR
SET Q 5 PSI OVER CLOSEDPOSITION SIGNAL
ACT&ORSUPPLY INLET
80 PSI MIN / 150 PSI MAX
V
ACTUATOR
(FAIL OPEN)
7/28/2019 205 Drag Valves for Boiler Feedpump Recirculation
3/6
-A--JANGLE VALVE
AC7UATOR
A I R SUPPLY
T
GLOBE VALVE
TABLE 1
Face to Face/CL Actuator Dia.
Data listed is for comparison only. Actual numbers will vary based on flow conditions and other application requirements.
For P z 4100 PSI, a larger actuator may be required.
7/28/2019 205 Drag Valves for Boiler Feedpump Recirculation
4/6
CC1 DRAG VALVE FOR BOILER FEEDPUMPRECIRCULATION
Valve rating: ANSI Class 2500
Maximum allowable
working pressure: 6200 psig at -40 to +450F
Hydrostatic test: 9375 psig
Seat test: 6200 psig
MSS-SP 61 Class Leakage
cItem1
18
19
20
21
22
23
24
25
26
27
28b
29
3oc
31
Description Material/Component
Body
Seat Ring Gasket
Seat Ring
Disk Stack
Guide Bushing
Balance Seal
Plug Assembly
Bonnet/Pressure Bleed
Metal Seal
Bonnet Flange
Bonnet Stud
Bonnet Nut
Packing Spacer
Packing
Packing Follower
Actuator
Yoke
Positioner, Pneumatic
Limit Switches (not shown)
Packing Stud
Yoke Clamp
Packing Flange
Stem Connector
Stem Connector Bolting
Filter Regulator
Filter Regulator (not shown)
High Pressure Select Relay
I/P Transducer
Solenoid Valve
Snap Acting Relay
Actuator Fittings/Tubing
Modulating
Std Opt
On-Off
Std Opt
400 Series SS
TFE & 300 Series SS
400 Series SS/17-4 PH
X X
X X
X X
Notes:
a Recommended spare parts.
b Required for applications where the modulation signal is 4-20 mA.
c The snap acting relay is used to prevent the valve from throttling less than 10% off the seatThe snap acting relay assures 100% actuator loading in the closed position.
7/28/2019 205 Drag Valves for Boiler Feedpump Recirculation
5/6
O P E R A T I O N
Ideally the recirculation system would meter the flow in re-
sponse to the pumps requirements. This indicates the need for a
modulating control valve, which normally would be closed, but
opens automatically on turbine trip. The valve would need to
handle water with thermodynamic conditions at the inlet of 2500-
5500 psi (175-387kg/cm2) pressure and 300-500F (141-246C)
temperature and, at the outlet, saturation conditions in the range
of 1 IO-240F (41- 109 C) with corresponding pressures of- 12 psigto 10 psig. Thus, during modulation of full flow conditions, the
valve must handle high pressure drop and substantial flashing yet
manage to minimize erosion, cavitation, and noise problems.
When shut, the pressure could build as high as 5500 psig
(387kg/cm2) and the valve be expected to hold drop-tight against
leakage. Should the valve leak, even the smallest amount of flashing
steam and water mixture would cut the seating surface like a rough
wire and in a short while the shutoff function of the valve would be
lost. Excessive leakage cuts into the efficiency of the plant both
through direct energy loss, and because the boiler cannot be fed the
full rated flow. In the extreme case, a shut down of an entire power
plant may be necessitated because of a single leaking valve.
Clearly, there is a need for a Boiler Feedwater Pump Re-
circulation Valve that will:
1. Break down water pressure from 5500 psi (387kg/cm2) to
atmospheric or vacuum pressure and simultaneously neutralize
the effects of-trim erosion due to flashing;
-cavitation; and,
-mechanical vibration and noise.
2. Remain leak tight for long periods of time.
3. Modulate automatically and open in case of failure of power to
the valve operator.
A NEW CCI DRAG@ VALVE HAS BEEN DESIGNED
T O M E E T T H E S E S T R I N G E N T R E Q U I R E M E N T S
Information required for sizing procedure:
l Maximum flow rate
l Maximum pressure drop
l Pressure drop at maximum flow rate
l Vapor pressure of fluid (Figure 4)
l Specific gravity at flowing temperature or water temperature
(Figure 5)
l Inlet pressure and outlet pressure
Figure 4 TEMPERATURE (F)
Determine:
Cv = flow coefficient based on pressure drop at Qmax
Qmin = minimum controllable flow (GPM))
Procedure:
where: Po= FFP,, &ax = Flow (GPM)P, = Inlet Pressure
The above equations require the flow rate be in gallons per
minute (GPM) and the nressure be in pounds per sauare inch (psi).
1.0
k.80-70000 200 300 400 500
WATER TEMPERATURE - FFigure 5
These valves are designed for critical pressure steam plants, with
pump discharge pressures of 2500 to 5500 psi (175 to 387kg/cm2)
and fluid temperatures of 300 to 500F (141 to 246C). Thepatented CC I D R A G disk stack in these valves has a special, com-
plex pattern disk specifically designed for this service. The only
consideration required for sizing is to determine Cv required or flow
required in GPM. Select the valve from Table 1 which meets or
exceeds the required Cv or flow.
For end connections, refer to Buttweld Ends, Figures 6 thru 9.
P R E S S U R I Z E D S E A T P L U G
The pressurized seat plug design is a special form of the balanced
plug that is balanced during modulation, but unbalanced when
shut off.
While the unbalanced and balanced plugs may be applied in
either over-the-plug (flow-to-close) or under-the-plug (flow-to-open)
configurations, the pressurized seat plug is applied only in aflow-to-close configuration When the valve is completely shut off,
the balance hole is closed by the valve stem.
When the valve is shut, a tiny bleed path through the bonnet let
pressure build up on top of the valve plug, creating very high seat
loading for superior shutoff with a metal-seated valve. This seat
loading is in addition to the actuator loading applied to the seat.
Once the stem is lifted to uncover the balancing hole, the main
valve plug can be opened as easily as any other balanced plug
configuration. This feature provides superior shutoff (MSS-SP-61).
7/28/2019 205 Drag Valves for Boiler Feedpump Recirculation
6/6
Buttweld Ends ANSI B 16.25
6"
31
f/-R .25
.03
tAD-4
GURE 6
tlao _i $DlA*.O3
IIA
F I G URE 7i--_1.0+ f
120
6" 160 8&9
xxs
100
120
8" 140 9
xxs
160
F I G URE 8
F I G URE 9
_ . _ _ . . . ?.Note: Special weld ends are available. Include a sketch ot desiredweld end with the order.
Control Components Inc.We Solve Control Valve Problems.
22591 Avenida Empresa l Rancho Santa Margarita l California 92688 USA
Tel.: (714) 858,1877 Fax: (714) 858-1878
Sales & Service Offices Throughout The World.MC-BFR-3195