ANDERSON The Complete Blanketing and Safety … the Complete Blanketing and Safety Valve System including: • Pad and de-pad valves and regulators • Pressure/vacuum vents and low
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Anderson Greenwood is a world leaderin tank protection and blanketing.Anderson Greenwood has theexperience and products to meetalmost all blanketing and safety reliefdevice needs. Furthermore, we canprovide the Complete Blanketing andSafety Valve System including:• Pad and de-pad valves and
regulators• Pressure/vacuum vents and low
pressure pilot operated valves• Emergency vents and valves• Flame and detonation flame
arresters
Because of the interactions between pad (blanketing) valves, de-pad (outbreathing) valves, relief devices andflame arresters, each piece ofequipment should be considered when specifying the blanketing system.Because of these interactions betweencomponents in the system, it makessense to rely on one company to helpspecify and provide all of the productsthat make-up the complete pressurecontrol system.
In fact, with many applications, it ispossible to combine the functions of the de-pad valve and the pressure reliefvalves, thus minimizing the number ofvalves and tank connections. Moreover,Anderson Greenwood can provide pad, de-pad, flame arrestment andpressure/vacuum relief in a single tankpenetration.
Anderson Greenwood Tank and Equipment Blanketing Systems
Anderson Greenwood is either a trademark or registered trademark of Tyco International Services AG or itsaffiliates in the United States and/or other countries. All other brand names, product names, or trademarksbelong to their respective holders.
What is Blanketing or Padding?Blanketing is a process used tomaintain a gas blanket or pad in thevapor space of a pressure-tight liquidstorage vessel. Gas blanketing is used to:• Prevent Evaporation• Reduce Fugitive Emissions• Reduce or Eliminate Combustion Potential
• Reduce Corrosion• Prevent Contamination or Oxidation• Provide make-up when the pressuredrops in the tank
Tank Blanketing normally involves theuse of a valve or regulator to control the input of the pad gas, normally aninert gas such as nitrogen. When thepressure drops in the tank, the pad orblanketing valve will open and feed gas
and pressure into the vessel, thuslimiting the minimum pressure in thetank. This drop in pressure is normallycaused by pump out or thermalcooling. In the event of pressure rise in the tank due to heat input or pump in, the de-pad or vent valve will openand vent pressure or pad gas from thetank. Traditionally, this function wasperformed by a conservation vent orbreather valve. Today, because of theneed to collect the gas coming off thetop of the tank and to prevent thepressure from increasing to a pointwhere the vent valves will leak toatmosphere, a de-pad valve is set toopen at a point below the vent valves.The de-pad valve, because it normallydischarges to a closed system, must be balanced against back pressure.
The Complete SystemAnderson Greenwood combines theuse of a pilot operated blanketing valveand a pilot operated de-pad valve toprovide a simple, reliable, and accuratesystem. Furthermore, by utilizing amodulating de-pad or vent valve, youcan eliminate the need for traditionalweight loaded, unbalanced vent valves.This will reduce project costs,maintenance costs, conserve blanketgas and will further protect theenvironment.
Emergency Vent Blanket Gas
BV-1 BlanketPad Valve
Flame Arrester
Vacuum Breaker
Pilot OperatedBlanket De-pad Valve
To VaporRecovery
Unit
(Not required if the pilot valve and vacuumbreaker are sized per API 2000)
DetonationFlame
Arresters
Pressure and Vacuum Vent
Flame Arrester
To VaporRecovery
Unit
Pilot Operated BlanketDe-pad Valve
Vacuum Breaker
Emergency Vent
Flame Arrester
Flame Arrester
BV-1 BlanketPad Valve
Pressure and Vacuum Vent (Not required if the pilot valve and vacuumbreaker are sized per API 2000)
Blanket GasDetonationFlameArresters
Anderson Greenwood Tank and Equipment Blanketing Systems
Installation FlexibilityDepending on your systems needs, theAnderson Greenwood system has theflexibility to be installed so that the padvalve, de-pad valve and vacuumbreaker can be installed on a singlenozzle or multiple nozzles. Additionally,Anderson Greenwood can provideinternal sensing in the same tankconnection.
Blanketing Valve Features and Benefits• Lower Installation Costs – Single unit system reduces labor andmaterial costs.
• Simplicity of Setting Blanket Pressure – One unit to calibrate in lieu of conventional multi-unitsystems.
• Reduced Maintenance Costs – Topentry provides access to all internalparts without removal from the line.
• Optimum Performance – Reducessupply gas pressure from 200 psig [13.8 barg] to 1/2" wc [1.2 mbarg] inone stage.
The conventional method (Figure 1)employs as many as four regulators toreduce high supply pressure to lowblanket pressures, while the AndersonGreenwood system (Figure 2) is the firstvalve that requires only one unit toachieve reduction from 200 psig [13.8 barg] to low blanketing pressures.
The Type Y1 Pilot is used with the mainvalve to form a pressure reducing valvecapable of regulating tank pressures from 1/2" wc [1.2 mbarg] to 6 psig [0.41 barg]. The pilot will open when the sensed pressure falls below the setpressure. As the pilot opens, the mainvalve dome pressure decreases, andflow through the main valve occurs.When the downstream pressure issatisfied, the sensed pressure acting onthe sense plate will overcome thespring force to close the pilot, the mainvalve dome pressure increases, and themain valve closes.
RA OperationFor small flow requirements, the pilotcan be used by itself as a direct springtank blanketing valve. When used thisway, it is designated a Type RA. Theonly difference in construction is thelocation of the sense and inlet ports.The sensed pressure acting against the spring force will determine howmuch, if any, the pilot is to open.
Y1 OperationUpstream pressure enters the main body and acts upward against the mainvalve diaphragm. Due to a smallunbalanced dome area, the effectivearea above the diaphragm is slightlylarger than below. Shut-off will occurwhen the dome pressure is equal to theinlet pressure. The sleeve/diaphragmretainer assembly is lightly springloaded to provide initial closing forcewhen there is no pressure differentialacross the diaphragm.
The Type Y1 Pilot controls domepressure in response to tank pressure. A reduction in dome pressure allows thesleeve to move upward off the main seat,permitting flow through the valve. Theamount of lift depends on the pressurereduction in the dome. The greater thisreduction, the greater the flow. When thedownstream pressure is satisfied, thesensed pressure acting on the pilotsense plate will overcome the springforce to close the pilot, which in turncloses the valve. No system fluid isvented to the atmosphere.
BV-1 OperationThe diaphragm and sleeve are replacedby a piston in the main valve for morerugged construction. As with the Y1Valve, the pilot controls dome pressure.A reduction in dome pressure allows the piston to move horizontally off theseat, permitting flow through the valve.Maximum flow is controlled by the cageorifices.
Performance CharacteristicsSet pressure is defined as the point atwhich the valve begins to flow. As thedemand for flow increases, the tankpressure must drop in order for thevalve to respond, since a differentialpressure is required to create thenecessary forces to operate the valve.
This drop in tank pressure is called “droop.” When the valve is 100 percentopen, the tank pressure must increase for the valve to respond and close. The difference between start to open andclose is called deadband. For the Type Y1 blanketing valve, thisdeadband is 1" wc [2.5 mbarg] at thelowest set pressure. For the Type BV-1blanketing valve, this “deadband” is 3/4" wc [1.9 mbarg] at the lowest setpressure. Lockup, the rise above setpressure for total closure, is less than0.1" wc [0.25 mbarg].
Elastomer SelectionIt is important to specify an elastomer that is compatible with both the supply gas and the product being stored in the tank. Vapors will enter the valvefrom the discharge port and sense line.The BV-1 comes standard withFluorosilicone and Viton® seat and seals and Teflon® diaphragm. The RAand Y1 valves come standard withBUNA-N soft goods. The BV-1 isavailable with an internal purge whichsweeps a small flow rate of blanket gasback through the sense port and tankconnection.
NACE TrimPilot and main valve trims are available for sour gas service in accordance withthe latest edition of NACE MR0175.
GOX/LOXThe BV-1 model can be cleaned forGOX and LOX applications.
Pressure Vacuum Vent
Figure 1
1 2
3
4
Conventional Method
Anderson Greenwood Method
Lower Installation CostTo VaporRecovey
Figure 2
3
1 24
Pressure Vacuum Vent
Lower Installation CostTo VaporRecovery
Anderson Greenwood Tank and Equipment Blanketing Systems
When sizing for tank blanketing, it is imperative to consider both:
a. blanketing gas replacement for liquidloss during pump-out, and
b. the condensation/contraction of tankvapors during atmospheric thermalcooling.
Required amount of blanketing gas andcorrect size of valve must bedetermined on the basis that bothconditions could occur simultaneously.
The maximum flow rate through theblanketing valve will determine the sizeof relief valve. If a flow rate less thanthat listed in Table C is required,restricted nozzles are available to limitthe flow to 70, 50, 30 or 10 percent ofthe 100 percent rated capacity. Use ofrestricted nozzles, where applicable,will minimize the size of safety reliefvalve required. The BV-1 is alsoavailable with a 110 percent piston forincreased capacity.
To Size a Blanketing Valve1. Determine the gas flow rate due topump-out (from Table A, page 11).
2. Determine the gas flow rate due toatmospheric thermal cooling (fromTable B, page 12).
3. Add the requirements of 1 and 2 and select valve size based on aircapacity (from Table C, pages 13 and 14).
Excerpt From API 20001
For tanks with a capacity of 20,000 bblor more, the requirements for thevacuum condition are very close to thetheoretically computed value of 2 SCFHof air, per square foot of total shell androof area.
For tanks with a capacity of less than20,000 bbl, the requirements for the vacuum condition have been based on 1 SCFH of air, for each barrel of tankcapacity. This is substantially equivalentto a mean rate of vapor spacetemperature change of 100°F [38°C]per hour. (See Table B, page 12)
Note: 1. API 2000, Section 2.4 Table 2.
English Units
V = 907 C2CvP1X
–––– GT
Metric Units
V = 263 C2CvP1X
–––– GT
Gas Formula
Cv Valve Sizing Coefficients
Valve Size Nozzle Size Cv
RA: 1/2" [15 mm] No Options 0.385
BV-1: 1" [25 mm] 110% 14.5
BV-1: 1" [25 mm] 100% 13.2
BV-1: 1" [25 mm] 70% 9.2
BV-1: 1" [25 mm] 50% 6.6
BV-1: 1" [25 mm] 30% 4.0
BV-1: 1" [25 mm] 20% 2.6
BV-1: 1" [25 mm] 10% 1.3
BV-1: 1" [25 mm] 5% 0.7
Y1: 1" [25 mm] 100% 10.0
Y1: 1" [25 mm] 70% 7.0
Y1: 1" [25 mm] 50% 5.0
Y1: 1" [25 mm] 30% 3.0
Y1: 2" [50 mm] 100% 43.6
Y1: 2" [50 mm] 70% 30.5
Y1: 2" [50 mm] 50% 21.8
Y1: 2" [50 mm] 30% 13.1
Y1: 2" [50 mm] 10% 4.4
Nomenclature
Symbol Description English Units Metric Units
V Required capacity SCFM Nm3/hr
C2 Correction factor for specific heat ratio – –
CV Valve sizing coefficient – –
P1 Set pressure psig barg
X 0.66 for P1 ≤47.7 psia 3.288 bara0.69 for P1 >
G Specific gravity – –
T Relieving temperature °R (°F + 460) °K (°C + 273)
Values C2 and G
Gas C2 G
Air 1.00 1.00
Natural Gas 0.98 0.60
Nitrogen 1.00 0.97
Anderson Greenwood Tank and Equipment Blanketing Systems
InletPressure Outlet Type RA, 1/2" BV-1, 1" Y1, 1" Y1, 2"(psig) Press. Natural Gas Nitrogen Air Natural Gas Nitrogen Air Natural Gas Nitrogen Air Natural Gas Nitrogen Air
InletPressure Outlet Type RA, 1/2" [15 mm] BV-1, 1" [25 mm] Y1, 1" [25 mm] Y1, 2" [50 mm] (barg) Press. Natural Gas Nitrogen Air Natural Gas Nitrogen Air Natural Gas Nitrogen Air Natural Gas Nitrogen Air
C – CS (RA and Y1 only)S – 316 SSN – CS/NACE (All SS in BV-1, RA models)
Main Valve Trim Material
1 – Standard trim2 – 316 SS trim (RA, BV-1 standard)
Seat, Seal, and Diaphragm Material
B – BUNA-N (RA, Y1 standard)V – Viton®E – EPRX – Other (specify)F – Fluorosilicone with PTFE pilot diaphragm (standard for BV-1 model only)
Set Pressure Range
1 – 1/2" wc to 1.4" wc [1.2 to 3.5 mbarg] 6 – 0.6 psig to 1.4 psig [41 to 97 mbarg]2 – 1.2" wc to 4" wc [3.0 to 10.0 mbarg] 7 – 1.3 psig to 3.1 psig [90 to 215 mbarg]3 – 3.5" wc to 10" wc [8.7 to 25 mbarg] 8 – 2.3 psig to 3.5 psig [160 to 240 mbarg]4 – 8" wc to 18" wc [20 to 45 mbarg] 9 – 3.0 psig to 6.0 psig [0.2 to 0.41 mbarg]5 – 15" wc to 29" wc [37 to 72 mbarg]
Options
Y – Pilot filter (available Y1 only)N – No optionsE – External Purge MeterP – Internal Purge (available BV-1 only)S – Sense Line Control GaugeT – System Pressure GaugeD – Both - Sense Line Gauge and Tank Pressure Gauge
For special requirements contact your sales representative.Note:1. RA is always 100 percent.
Anderson Greenwood Tank and Equipment Blanketing Systems
Tyco Flow Control (TFC) provides the information herein in good faith but makes no representation as to its comprehensiveness or accuracy. This data sheet is intended only as a guide to TFC products and services. Individuals using this data sheet must exercise their independent judgment in evaluating product selection and determining product appropriateness for their particular purpose and system requirements. TFC MAKES NO REPRESENTATIONS OR WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE WITH RESPECT TO THE INFORMATION SET FORTH HEREIN OR THE PRODUCT(S) TO WHICH THE INFORMATION REFERS. ACCORDINGLY, TFC WILL NOT BE RESPONSIBLE FOR DAMAGES (OF ANY KIND OR NATURE, INCLUDING INCIDENTAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES) RESULTING FROM THE USE OF OR RELIANCE UPON THIS INFORMATION. Patents and Patents Pending in the U.S. and foreign countries. Tyco reserves the right to change product designs and specifications without notice. All registered trademarks are the property of their respective owners. Printed in the USA.