Boiler Condensate Return Basicscleaverbrooks.com/reference-center/resource-library... · 3 T T. T....
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Boiler Condensate Return Basics Presented by Steve Connor February 24, 2016
Transcript of Boiler Condensate Return Basicscleaverbrooks.com/reference-center/resource-library... · 3 T T. T....
Boiler Condensate Return Basics
Presented by Steve ConnorFebruary 24, 2016
What We Are Covering Today?
• Brief review of the total steam system• Why a proper condensate return system is so important• Condensate return and affect on the property’s operation• What compromises the optimum condensate return system• The corrective actions• Delivering condensate back to the boiler room• The choices for holding and treating this condensate.• Summary• Q/A
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T
T
T
T
SteamCondensate
H P Cond ReturnVent
D A TankD A Tank
Feed PumpBoiler
Strainer
Trap Trap
Trap TrapTT
TT
DA Tank
TT
TT
TTT
HP SteamPRV 15 psig
250 F
LP Steam150 psig
366 F
Trap
LP Condensate Return
Cond Recovery& Pump
MotiveForce
Supply and Return System(s)
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Legend
Water inletTo drainTo drain
Total Boiler Room
4
Chemical feedWater softener
Feed system
5
T
T
T
T
T
SteamCondensate
H P Cond ReturnVent
D A TankD A Tank
Feed PumpBoiler
Strainer
Trap Trap
Trap TrapTT
TT
DA Tank
TT
TT
TTT
HP SteamPRV 15 psig
250 F
LP Steam150 psig
366 F
Trap
LP Condensate Return
Cond Recovery& Pump
MotiveForce
Supply and Return System(s)
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Legend
Reasons why condensate system is important
• Operating cost reduction• Reliability• Safety
Let’s first look at Efficiency & Cost of Operation
OK…
What is the cost of steam?
2011 Steam Rate ($15.00/1,000 lb)
Steam - Basic Concepts
2120 F.
2000 F.
1000 F.
320 F.
00 F.138 880
Latent Heatof Vaporization(or Latent Heat
of Condensation)
LatentHeat ofFusion
Btu per pound of water
SensibleHeat
SensibleHeat
3380 F.
Boiler operating at 100 psig and 200 OF feed water
1 lb water at 338O F
1 lb steam at 338O F
1 lb water at 200O F
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Saturated Steam Table
Pressure (psig) 0 10 80 100
Saturation Temp 212 239.5 323.9 337.9
Volume (ft3/lb) 26.4 16.46 4.66 3.89
Sensible Heat (btu/lb) 180 207.9 294.4 308.9
Latent Heat (btu/lb) 970 952.5 891.9 880.7
Total Heat (btu/lb) 1150 1160.4 1186.3 1189.4
Start @ 32 deg. F
10
FWT
30
Gauge Pressure - psig
40
70
80
60
140
100
150
110
50
130
90
160
170
180
120
190
200
212
220
227
230
29.0
29.3
30.1
30.4
29.8
32.1
30.9
32.4
31.2
29.6
31.8
30.6
32.7
33.0
33.4
31.5
33.8
34.1
34.5
34.8
35.0
35.2
29.0
29.2
30.0
30.3
29.8
32.0
30.8
32.4
31.2
29.5
31.7
30.6
32.7
33.0
33.3
31.4
33.7
34.0
34.4
34.7
34.9
35.0
28.8
29.1
29.9
30.1
29.6
31.8
30.6
32.1
30.9
29.3
31.5
30.4
32.4
32.7
33.0
31.2
33.4
33.7
34.2
34.4
34.7
34.8
28.7
29.0
29.8
30.0
29.5
31.7
30.6
32.0
30.8
29.2
31.4
30.3
32.4
32.6
33.0
32.2
33.3
33.6
34.1
34.3
34.5
34.7
28.6
29.4
29.7
29.1
31.4
30.2
31.6
30.5
28.9
31.1
30.0
31.9
32.3
32.6
30.8
32.9
33.2
33.5
33.0
34.2
34.4
34.5
28.4
29.2
29.5
28.9
31.1
30.0
31.4
30.3
28.7
30.8
29.8
31.7
32.0
32.3
30.6
32.6
32.9
33.2
33.6
33.9
34.1
34.2
28.3
29.1
29.4
28.8
31.0
29.9
31.3
30.2
28.6
30.7
29.6
31.6
31.9
32.2
30.4
32.5
32.8
33.1
33.5
33.8
34.0
34.1
28.2
29.0
29.3
28.8
30.9
29.8
31.2
30.1
28.5
30.6
29.6
31.5
31.8
32.1
30.3
32.4
32.7
33.0
33.4
33.7
33.9
34.0
28.2
28.9
29.2
28.7
30.8
29.7
31.1
30.0
28.4
30.5
29.5
31.4
31.7
32.0
30.2
32.3
32.6
32.9
33.3
33.5
33.8
33.9
28.1
28.8
29.1
28.6
30.7
29.6
31.0
29.8
28.3
30.4
29.3
31.2
31.5
31.8
30.0
32.2
32.5
32.8
33.2
33.4
33.7
33.8
28.0
28.8
29.0
28.5
30.6
29.5
30.9
29.8
28.2
30.3
29.2
31.2
31.4
31.7
30.0
32.1
32.4
32.7
33.1
33.3
33.6
33.7
28.0
28.7
29.0
28.5
30.6
29.5
30.8
29.8
28.2
30.3
29.2
31.2
31.4
31.7
30.0
32.0
32.4
32.6
33.0
33.3
33.5
33.6
27.9
28.7
28.9
28.4
30.5
29.4
30.8
29.7
28.2
30.2
29.2
31.1
31.4
31.7
30.0
32.0
32.3
32.6
33.0
33.2
33.5
33.6
27.9
28.6
28.9
28.4
30.5
29.4
30.8
29.7
28.2
30.2
29.2
31.1
31.4
31.6
30.0
32.0
32.3
32.6
33.0
33.2
33.4
33.5
27.9
28.6
28.9
28.4
30.4
29.4
30.8
29.7
28.2
30.2
29.1
31.0
31.3
31.6
29.9
31.9
32.2
32.6
32.9
33.1
33.4
33.5
27.9
28.6
28.8
28.3
30.4
29.3
30.7
29.6
28.1
30.1
29.1
31.0
31.3
31.6
29.9
31.9
32.2
32.5
32.9
33.1
33.3
33.4
27.9
28.6
28.8
28.3
30.4
29.3
30.7
29.6
28.1
30.1
29.1
30.9
31.2
31.5
29.8
31.8
32.1
32.4
32.8
33.1
33.3
33.4
0 2 10 15 20 40 50 60 80 100 120 140 150 160 180 200 22027.8
28.5
28.8
28.3
30.4
29.3
30.6
29.6
28.1
30.1
29.0
30.9
31.2
31.5
29.8
31.8
32.1
32.4
32.8
33.0
33.3
33.4
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Capacity At Operating Pressures vs. FWT
.
Energy Dollars at Risk
$DOWNTHE
DRAIN
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Every 10 degree drop in feed watertemperature equals a 1% drop in efficiency!
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Blowdown Heat Recovery Types
Blowdown Heat Recovery Unit• Proportional blowdown heat recovery system • Atmospheric feed or deaerator• Automatically controls TDS• Single or Multiple Boilers • Blowdown is cooled before discharge (Code compliance)
Condensate Recovery
Savings Derived from:
• Fuel savings• Chemicals• Water • Sewer costs
Bringing back condensate at higher pressures will result in even greater savings!
Reliability Issues
Shell & Tube
Plate & FramePressure Regulating Valve
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Jacketed Kettle
Split System
Condensate Back-up or “Stall”
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Constant Orifice Purge
Steam Pump Trap
Steam power pump
Vacuum breaker
Water leg
Vacuum breaker
Trap
NOTE: 2.3 feet of static head = 1 pound pressure
Air vent
Non Condensable Gas Corrosion
Courtesy:http://www.engineeringtoolbox.com/oxygen-steel-pipe-...
50 F
86 F
122 F
• Almost 2 times more corrosive at 122o F than at 86o F
• Dissolved oxygen is 10 times more corrosive than CO2
CO2O2
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Air and Corrosion
The Piping is Subject to Corrosion
Subcooled Condensate + CO2 Forms Carbonic Acid
( CO2 + H2O H2CO3 )
40% more corrosive when combined with dissolved O2!!
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Carbonic Acid Corrosion
Cause and EffectCO2 + H2O = H2CO3
• Created where condensate is not fully drained.
• Attacks pipe and coil material.
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Carbonic Acid attack
Cause and EffectCO2 + H2O = H2CO3
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Mechanical Chemical
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Most Economical Long-Term Approach
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Steam/Water Separator
Separation Mechanism
Cyclonic Type
• Cyclonic (centrifugal force)• Baffle (directional flow change)• Coalescence (trapping media) pad)
Secondary Steam Branch Line
In-line separator
28To condensate return line
Drip pockets & Steam Trap Set
Isolation valves
Check valve
strainertrap
Drip Pockets
Steam Trap
Drip Leg6-10”
BD and Venting
Locations:• Low Spots• End of Main Ahead of
Expansion Joints• Ahead of Valves,
Bends & Regulators
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Locate every 150 – 300 feet in a linear length of steam pipe
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Steam Main Size Drip Leg Diameter Drip leg Length4” 4” 12”6” 4” 12”8” 4” 12”10” 6” 18”12” 6” 18”14” 8” 24”16” 8” 24”18” 10” 30”20” 10” 30”24” 12” 36”
Suggested Sizing
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Moving condensate from source to boiler room
Motive force of steam pressure differential
Condensate Transfer Tanks
• Standard models 200°F or less
• 210°F floor mounted units w/ low NPSH pumps
• 212°F elevated units available, thereby increasing NPSH
Steam & Condensate Velocity
Typical Velocities in steam systems:Process Piping 6000 – 8000 fpm(70 – 90 MPH)LP Heating Systems
4000 – 6000 fpm
(45 – 70 MPH)Typical Velocities in Condensate return systemsLiquid 180 – 420 fpmBi-phase Approx. 3000-
7000 fpm
• Boiler operating pressure• Pounds of condensate• Pressure at trap inlet• Pressure in line• Condensate pipe diameter• Allowable pressure drop
Note: Pressure drop should not exceed 20% of boiler’s maximum operating pressure
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T
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SteamCondensate
Common Condensate Return
D A TankD A Tank
Feed PumpBoiler
Strainer
Trap Trap
Trap TrapTT
TT
DA Tank
TT
TT
TTT
HP Steam LP Steam150 psig
366 F
MotiveForce
Supply and Return System(s)
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Legend
Trap
Saturated Steam Table
Pressure (psig) 0 10 80 100
Saturation Temp 212 239.5 323.9 337.9
Volume (ft3/lb) 26.4 16.46 4.66 3.89
Sensible Heat (btu/lb) 180 207.9 294.4 308.9
Latent Heat (btu/lb) 970 952.5 891.9 880.7
Total Heat (btu/lb) 1150 1160.4 1186.3 1189.4
Start @ 32 deg. F
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.017
Steam & Condensate Velocity
Typical Velocities in steam systems:
Process Piping 6000 – 8000 fpm
(70 – 90 MPH)
LP Heating Systems 4000 – 6000 fpm
(45 – 70 MPH)
Preferred Velocities in Condensate return systems
Liquid 180 – 420 fpm
Bi-phase Approx. 3000 - 7000 fpm
Condensate Pipe sizing
• Boiler operating pressure• Pounds of condensate• Pressure at trap inlet• Pressure in line• Condensate pipe diameter• Allowable pressure drop
Condensate pipe sizing criteria
Example:• 2000#/HR• 7000 ft/min• ¼# drop• 150# inlet• Zero & 15# outlet
And what’s the Safety Issue with condensate?
EfficiencyReliabilityCaptureTransportation
Cause & Effect of Water Hammer
Three Types of Water Hammer:
Hydraulic
Thermal
Differential
Thermal water hammer
The steam condensing void is rapidly filled with water
Thermal
Thermal Imaging & diffusion of condensate lines
Diffuser
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Flash Tank
Flash Tank• Higher temperature drip traps• Vent to atmosphere• Use flash steam for LP use (non-modulating)• Preheat boiler feed water
Drip trap location
Steam User
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Calculating Flash Steam %
Formula: (hf1 – hf2 )/hfg2 = % Flash
HF1: Sensible Btu’s inHF2: Sensible Btu’s outHFG2: Latent Btu’s out
Example: User operating at 150 psig with discharge @ 15 psig…..
338 – 218 = 120/946 = 13% Flash Captured! . Btu’s SAVED!. Water & Sewer charges SAVED!. Chemicals SAVED!
T
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T
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H P Condensate Return
Cond. Pump
D A TankD A Tank
Feed PumpBoiler
Strainer
Trap Trap
Trap TrapTT
TT
TT
TT
TTT
HP SteamPRV
15 psig250 F
LP Steam175 psig366 F
TrapMotiveForce
Feed Tank or DA
HP Condensate Recovery
High Pressure Condensate Receiver
• Takes high pressure condensate directly from the user.
• No need to deaerate.• Pump directly into
boiler• Feed the HPR from
the DA
Holding the boiler’s feed water and protecting the system
HOT Condensate returned
DeaeratorBoiler Feed System
A vented receiver, wastes energy.
48
Pressurized receiver, saves energy.
Steam diffusing tube
Chemical Feed Tank
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• Phosphonates• Chelant (de-scaler)• Polymers• Sulfite• Non-sulfite scavengers• Amines (neutralizing or filming)
Mixing and Dispensing
Final Summary
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• The boiler is part of a total system including its piping supply and return network, and all the associated accessories supporting the total whole.
• Proper condensate line engineering impacts energy efficiency, production reliability, and safety
• Every 10 degree pickup in feedwater temperature = 1% fuel savings• Condensate is sensible energy which increases with increasing
operating pressures• Reliability is affected by system backup (Stall) and system corrosion• Condensate line water hammer is normally Thermal type• Flash recovery systems can mitigate problem and save energy• Recommended velocities in bi-phase condensate lines is 3000 – 7000
ft/min• As line pressure in bi-phase condensate increases the volume
decreases, reducing line size for same velocity. • Condensate line sizing involves knowing boiler pressure, trap inlet
pressure, pounds of condensate, common line pressure, desired velocity, and desired pressure drop
