Boiler Steam System Supply Basics
Presented by Steve Connor
November 18, 2015
What We Are Covering Today?
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The steam supply system; boiler is the heart
Piping is an extension of the boiler
Phase change and consequences or outcomes
Process steam is both low and high pressure
A closer look at the steam supply or arterial system
Accommodating piping expansion and radiant heat
loss
Steam velocities and affects
Air & corrosion considerations
Condensate collection and trapping
A close look at popular steam traps
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Total Boiler Room
To drain
To drain
Water inlet
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Steam - Basic Concepts
Boiler operating at 100 psig and 200 OF feed water
Sensible Latent Sensible
Heat
Heat
Heat of
Fusion
Latent Heat
of Vaporization
(or Latent Heat
of Condensation)
1 lb
steam at
338O F
3380 F.
2120 F.
2000 F.
1000 F.
320
F.
00 F.
1 lb
water at
338O F
Btu per pound of water
1 lb
water at
200O F
138
880
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Saturated Steam Table
Start @ 32 deg. F
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
0.017
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
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Devastation…
Others Affects Surrounding
Steam Volume Expansion
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Applications for Low and High Pressure Steam
Some low pressure process applications
• High pressure steam:
• Motive force
• Higher Temperatures
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Split System
Pressure Regulating Valve
Jacketed Kettle
Shell & Tube
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Plate & Frame
Understanding the Load
Where are the system demands and irregularities?
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Applications for Low and High-Pressure Steam
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Supply and Return System(s)
150 psig
366 F
LP Steam
HP Steam
Strainer PRV
T
T
Trap
Motive
Force
T
Trap
T
Trap
T
Trap
Trap
H P Cond Return
Vent
DA
D A Tank
Tank
Boiler
15 psig
250 F
Cond Recovery
& Pump
Feed Pump
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LP Condensate Return
Legend
Steam
Condensate
Expansion of the Piping System
328 Linear Feet of Pipe
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DF
338 DF
14” Expansion!!
9” Expansion!!
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Accommodating the Piping System
The expansion loop is a technique used
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Accommodating the Piping System
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Sliding joint
Less space
Needs guiding and anchoring
Otherwise failure
Gland packing maintenance
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Accommodating the Piping System
Expansion bellows
• No packing
• Need guiding and support
• Incorporate limit rods
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Accommodating the Piping System
Roller supports movement
in (2) directions
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Piping Insulation
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Piping Heat Loss (Btu/hr per foot)
That’s 155,700 Btu’s per hour in 100 feet or, 5 Horsepower Every Hour!!
*Temp
1/2
3/4
1
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71
86
103
121
139
166
192
220
251
285
68
85
104
125
146
171
199
233
266
304
343
82
104
127
152
176
206
243
284
326
372
425
1-1/4 1 1/2
2 2 1/2
3
4
6
Diff.
100
120
140
160
180
200
225
250
275
300
325
107
127
155
186
217
251
297
347
398
455
520
113
142
173
213
243
282
334
389
447
510
580
138
175
212
256
297
346
410
478
550
628
705
163
206
251
301
351
408
483
563
649
742
843
194 243
246 308
300 375
360 451
417 522
488 622
578 726
674 849
778 978
888 1140
1010 1240
337
427
521
626
725
850
1009
1180
1360
1557
1730
* Temperature difference between the steam temperature and the ambient temperature in degrees F
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Energy Lost Through Uninsulated Pipe
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6” Steam Pipe @ 100 psig (338
Deg. F)
Radiates approx. 1650
Btu/HR/Foot
Figure 500 feet of uninsulated
pipe
Equals 826,000 Btu/HR (25
BHP)
Production hours per year =
5000 HR’s
At $0.35 per therm for natural
gas = $14,455 WASTED!
Annual fuel bill is $500,000/YR
= 3%
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The Effects of Insulation on a Steam
Distribution Line: 300’ of 8” Line
at 70 Deg. F, 0 mph wind, 100 psig steam
Also the heat loss…
700
Bare Pipe
600
1" Cal Sil
500
1-1/2" Cal Sil
400
2" Cal Sil
300
200
100
0
Lb/Hr
Condesate
Formation
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Steam Velocity/Pressure Drop
Typical Velocities in steam systems:
Process Piping:
6000 – 12000 fpm (70-136 MPH)
LP Heating Systems:
4000 - 6000 fpm (45-70 MPH)
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Steam Velocity/Pressure Drop
High Steam Velocities cause:
• High Pressure Drop
• Erosion
• Noise
• Enhance water hammer
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Flow / Velocity / Pressure Drop
• Velocity is proportional to flow rate.
• Pressure Drop is proportional to the square of the
flow rate.
• Example: 2” Line, flow in lb/hr at 100 psig
Flow
1000 lb/hr
2000 lb/hr
3000 lb/hr
Velocity
2780 fpm
5560 fpm
8340 fpm
Pressure Drop
0.7 psi / 100 ft
2.7 psi / 100 ft
6.0 psi / 100 ft
DOUBLING THE FLOW INCREASES DP 4 TIMES!
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Flow / Velocity / Pressure Drop
Reducer
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Going to Schedule 80 Pipe
for Corrosion Reasons?
1000 lb/hr Flow at 100 psig
Pipe Size
Sch 40 ID
Velocity
fpm
Velocity
mph
Press Drop
psi / 100 ft
3/4”
1”
1-1/4”
17,580
10,830
6,250
190
120
70
87.0
25.0
6.0
1-1/2”
2”
4,600
2,780
50
30
2.7
0.7
Remember the velocity and Delta P relationship!
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Condensate Formation
The Piping is Constantly Being Filled With Water (Condensate)
Always occurs to some degree; especially at startup
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Condensate Formation
The Steam Piping is Subject to Water Hammer!
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Effects of Water Hammer
BANG!
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Effects of Water Hammer
New York City
Midtown Manhattan
July 18, 2007
“We thought it was another 9/11 terrorist attack!”
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Properly Sizing the Drip Pocket
Steam velocity @ 70 to 90 MPH
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Suggested Sizing
Steam Main Size
Drip Leg Diameter
Drip leg Length
4”
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”
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Drip Legs Allow a Space for
Condensate and Dirt to Collect, and
Direct the Condensate to the Steam Trap
Locations:
• Low Spots
• End of Main Ahead of
Expansion Joints
• Ahead of Valves,
Bends, Regulators
Drip Leg
6-10”
BD and Venting
Steam Trap
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What Traps Do
Trap Steam
Remove
Condensate
Remove Air
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Air and Corrosion
The Piping is Subject to Corrosion
( CO2 + H2O H2CO3 )
Subcooled Condensate + CO2
Forms Carbonic Acid
40% more corrosive when combined with dissolved O2!!
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Air and Corrosion
Cause and Effect
CO2 + H2O = H2CO3
– Created where condensate is not
fully drained.
– Attacks pipe and coil material.
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Partial Pressure
Chamber containing air and steam delivers only
the heat of the partial pressure of the steam,
not the total pressure.
Effects of air on steam
temperature
• Air entering system
exerts its own
pressure, added to
steam pressure =
Total Pressure
• The temperature of
the air/steam mix is
below that of pure
steam.
Steam chamber 100% steam
Total pressure 86 psig
Steam pressure 86 psig
Steam temperature 327.8O F
Steam chamber 90% steam and 10% air
Total pressure 86 psig
Steam pressure 76 psig (equivalent)
Steam temperature 320.8O F
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What Traps Do
Trap Steam
Remove
Condensate
Remove Air
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What Goes into Selecting a Trap?
L: Load (#/hr of steam)
A: Application (Dictates the type of trap used)
M: Mod\Constant Pressure
B: Back Pressure
S: Supply Pressure
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Trap Categories
Thermodynamic
Disc
• Steam (flash) -flow operates valve
Mechanical
• Use difference in density between
steam and condensate to operate
valve, or a float operates the valve.
F&T
IB
Thermostatic
• Sense temperature change to
operate valve
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Why Steam Traps Fail
1.
Dirt
2.
*Pressure increases & drops
3.
Air binding
4.
Wear
5.
Misapplication
6.
*Water hammer
7.
Oversizing
What are warning signs?
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Warning Signs
1.
2.
3.
4.
5.
6.
7.
Vertical steam plume
Condensate tank failure
PRV’s not holding required pressure
DA or Surge overpressure/temperature
Production slow down
Piping wear and leaks
Heat exchanger failure (H2CO3)
What’s the failed open trap cost?
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Cost of Steam Trap Leaks
Dollars/Year at 100 Psig
Equivalent
Orifice
Diameter
1/16”
1/8”
1/4”
1/2”
Lbs./Yr.
Steam
Loss
Steam Cost Per 1000 Lbs.
$5.00
$7.50
$10.00
115,630
462,545
1,848,389
7,393,432
$578
$2,313
$9,242
$36,967
$867
$3,469
$13,863
$55,451
$1,156
$4,625
$18,484
$73,934
Cost Multipliers For Other Steam Pressures:
16 Psig -. 26
200 Psig - 1.87
50 Psig - .56
300 Psig - 2.74
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150 Psig - 1.43
600 Psig - 5.35
Thermodynamic Disc
Has (2) Concentric Seating Rings:
• Inner: Separates the inlet from the outlet
(P1 from P3)
• Outer: Controls leakage of steam
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Disk Trap Flashing Steam
Operation
P2
1. Flow of condensate opens disc
2. “Bernoulli concept:” As flow
increases, pressure drops
P1
3. Flash occurs
4. Disc shuts
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P3
Disk Trap Closed
Trapping
Steam
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Thermodynamic Traps
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Modulation – Fair - Good
Back pressure – Poor
Dirt – Poor
Wear – Poor
Water Hammer – Good
Corrosion - Good
Air Removal - Fair - Good
Outdoor – Fair to poor
Maintenance - Good
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Mechanical Types
Air Vent Valve or thermostatic
valve
Linkage
Fixed
Pivot
Valve
Ball
Seat
Inverted
Bucket
Float &
Thermostatic
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Mechanical Types
Air Vent
Linkage
Fixed
Pivot
Valve
Ball
Seat
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Float &
Thermostatic
F&T Traps
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Modulation – Very Good
Back pressure – Good
Dirt – Poor
Wear – Good
Water Hammer – Poor
Corrosion - Poor
Air Removal – Excellent
Outside – Poor
Maintenance – Fair Good
Air Vent or
thermostatic
valve
Linkage
Fixed
Pivot
Valve
Ball
Seat
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Inverted Bucket Opening
Valve wide open
Purging condensate
and air
Air vent orifice
Valve body
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Inverted Bucket Filling
Valve tightly closed
Trapping Steam
Steam
Condensate
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Inverted Bucket
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Modulation – Fair – Good*
Back pressure – Good
Dirt – Poor
Wear – Good
Water Hammer – Good
Corrosion – Good
Air Removal – Fair to Poor
Outside – Poor
*Requires a prime for sealing
Maintenance – Fair to poor
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Thermostatic Trap, Balanced Pressure
Thermostatic element
Expansion closes
valve.
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Balanced Pressure
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Modulation – Good
Back pressure – Good
Dirt – Good
Wear – Good
Water Hammer – Poor
Corrosion - Poor
Air Removal – Excellent
Outside – Good
Maintenance – Good
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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.
As the operating pressure of the system increases, the pound of water
converted to steam reduces in its volumetric size.
Significant heat loss is attributable to uninsulated piping and it adds to
considerable condensate forming in the steam lines.
Adequately sized steam line drip pockets should be placed every 150 –
300 linear feet, at turns, rises and terminations.
Water hammer is nothing to fool with….Correct it!
As the piping system heats up, it expands and this expansion must be
accounted for.
Piping supports and expansion joints accommodate for this phenomenon
Velocity of steam doubles with flow, but the pressure drop is the square
of the flow.
Velocity is affected by mass flow through the pipe and its ID
Air is a real problem for steam systems: Partial pressure and corrosion
Traps need the proper differential to work
Their biggest culprit is dirt.
Every trap has a pro and con, and must be selected based on application
and the conditions of the system. 56
• Gregg Achtenhagen, P.E.
LEED AP DB &C
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Senior Manager, Packaged Boiler Systems
[email protected]
414.577.2707
www.cleaverbrooks.com
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