Condensate Return Systems
Spirax Sarco Inc. Presented by Greyling Carey
Typical Steam Circuit
Boiler
Feed Pump
Feed Tank
SPACE
HEATING
KETTLES
TANKS
Steam and Condensate
Striving for maximum efficiency
Boiler
Steam generation, distribution and utilization
Condensate removal, heat recovery and return
Process
Why Return Condensate?
• Condensate is an extremely valuable resource. Its high
heat content justifies returning it to the feedwater
system.
• Condensate has already been treated and thus water
treatment costs are lowered.
• The high cost of condensate disposal is avoided.
• Water charges are lowered because fresh water is not
continually being added to the boiler.
• Condensate Recovery Savings of up to 25%
www.SpiraxSarco.com
Driving Forces
Profitability Energy
Costs Safety
Reliability Productivity
Environment
CUSTOMER
Energy Costs – The Cost of
Steam
• Gas prices exceed $4.00 per million Btu's in
February 2012
• August 2003 average price is $9.80 $/MMBTU gas
average steam cost = $16.96/1000 lbs. of steam
• Boiler efficiency – 85% (Stack Losses)
• Boiler Blowdown 6%
• Water/Chemical Costs - $0.80/1000 lbs.
• Condensate Recovery – 90% of steam load
• National Average Steam Cost = $9.70/1000 lbs. of steam
Typical Condensate
Observations
Condensate Recovery saves:
• Water costs
• Preheating energy costs
• Chemical treatment costs
• Effluent costs
• Boiler Blowdown %
• Emissions
• Damage to infrastructure
• Safety incidents
(Just 10 gpm can save over
$50,000 per year)
Condensate Recovery Payback Analysis
Instructions:
Input data in white boxes where appropriate:
Do NOT input data in blue boxes:
Data
Condensate Load 5000 lbs/hr
Annual Hours of Operation 8760 Hours per year
Raw Water Cost 2 $ per 1000 galls
Sewage or Effluent Cost 1 $ per 1000 galls
Water Treatment Chemicals 2 $ per 1000 galls
Condensate Return Temperature 190 Deg. F
Make Up Water Temperature 60 Deg. F
Steam Cost 5.00 $ per 1000 lbs
Boiler Operating Pressure 150 psig
1196 hg (BTU/lb)
339 hf (BTU/lb)
Boiler Blowdown 5 %
Cost of Fuel 4.10 $ per million BTU
Boiler Efficiency 85% %
Additional Information
Maximum Temperature permitted in sewer 140 Deg. F
Is water being used to cool condensate No Yes or No
Savings
Energy savings in condensate 28,470 $/year
Make up Water & Treatment Chemical Savings 21,007 $/year
Sewage/Effluent Cost Savings 5,252 $/year
Raw Water (cooling) Cost Savings 0 $/year
Boiler Blowdown Savings 490 $/year
CO2 Emissions Reduction 386 Tons/year
TOTAL ANNUAL SAVINGS 55,219 $/year
Typical Issues Caused with Improper
Condensate Systems
• System Reliability
• Safety
• Operation Control
• Productivity
• Product Quality
• Economic
• Environmental
Waterhammer
Control
Corrosion
Erosion
Equipment damage
Personnel Safety
Maintenance costs
Problems Incurred From Stalled
Condensate Systems
What happens when a Condensate
System Stalls
The Heat Transfer Equipment & Piping
Infrastructure Damages:
(HX, AHU, Kettles, Cylinders,
Autoclaves, Sterilizers & etc.)
Banging
Knocking
Corroding
Leaking
Fouling
Annoying
When the System Stall
We Do What?
Condensate is now :
Being dumped to the pad or drain
Wasted ($$$$$$)
Arousing EPA interest
Causing safety concerns
Annoying noises or flash vapor
The Problems Begin?
• Engineering & Design
• Architect Drawings
• Contractors Installation
• System Being Expanded
• Operation of the System
• Maintenance PM’s
What if condensate cannot drain?
Condensate ‘backs up’
Results in:
• Cooling
• Output swings
• Waterhammer
• O2 & CO2 corrosion
• Thermal stresses
• Fouling
Condensate Drainage
Solutions
Drain the Condensate to the Sewer
Eliminate the Backpressure
Suffer in Silence?
Effective Condensate Drainage
and Return Systems
Three Types of Condensate Return
Systems
• Gravity Drain – Vented open system 0 pressure gravity drain
to the boiler house
• Differential Pressure– Condensate that’s being pushed back
to the boiler house by steam trap differential pressure
• Closed or Vented System – Being pumped by electrical or
mechanical pumps
Specific volume of steam - 3.89 ft³/lb. at 100psig
Specific volume of steam - 26.8 ft³/lb at Patm
Specific volume of condensate - 0.017 ft³/lb.
1600 times smaller
‘Creates’ steam flow from high to low pressure
Vacuum potential
Condensation & Steam Flow
Line Sizing
• How do we size condensate lines?
• Differential Pressure?
• Lbs/hr or liquid flow gpm?
• Velocity?
• Copy similar installation?
To Size a Condensate Line
1. Determine Condensate Load lbs/hr
2. Two Phase lbs/hr or Liquid GPM
3. Determine the Total Back-Pressures
(return line pressure, lift & frictional losses)
4. Calculate % Flash Steam at Flow Rate
than Size Condensate Line based on Flash Steam
5. Differential Pressure Available
6. Base Sizing on Velocity at load lbs/hr or GPM
(two phase maximum of 4,000 ft/min)
(liquid maximum of 360 ft/min)
Back Pressure In Condensate
Return Systems
Pressure at end of Main: DA tank
+Vertical Lift
+Frictional Resistance in Piping
= Back Pressure
Quantity of Flash Steam in Line
100 lb. Flash Steam
99.44% of Total Volume
900 lb. Condensate
0.56 % of Total Volume
5,000 lbs/hr Steam/Condensate Load
• STEAM LINE (maximum 6,000 ft/min)
• 100 psig steam line – 3”
• 50 psig steam line – 4”
• 15 psig steam line – 6”
• CONDENSATE LINE (maximum of 4,000 ft/min) two-phase
• 100 psig to 10 psig – 10.6% flash = 530 lb/hr requires a 3” line
• 100 psig to 5 psig – 11.8% flash = 590 lb/r requires a 4” line
• 100 psig to 0 psig – 13.3% flash = 665 lb/hr requires 5” line
Quantity of Flash Steam
1000 lb/h
60 PSIG
0 PSIG
Mass
Condensate 900lb/h
Flash Steam 100lb/h
Volume
Condensate 0.017ft3/h
Flash Steam 26.8 ft3/h
Sizing of Condensate Return Lines
What’s Flash Steam?
Steam created when hot condensate is
exposed to a lower pressure.
FLASH STEAM
FLASH STEAM occurs when hot condensate at highpressure is released to a lower pressure. At the lowerpressure, the heat content (SENSIBLE HEAT) of the water(hot condensate) cannot exist in that form. A portion of thewater ‘boils off’ and becomes FLASH STEAM
Flash Steam contains valuable BTU’s / lb. Of heat which canbe utilized for lower pressure applications.
Condensate Line, Flash Tank, and Vent Line Sizing
Ways to Move Condensate Back to the
Boiler Room
• Gravity Drain
• Strictly Pushing with Pressure
• Electric Centrifugal Pumps
• Mechanical Pumps
• Pump Traps (dedicated to one piece of steam
equipment)
Condensate Pumps
When the air handling unit is at full capacity, the
steam pressure will be at 10 psig or 240 F … the
condensate will flash …
Condensate Pumping
• Condensate Load (lb./h)
• Electric Pump Capacity (GPM)
or
• Pressure Powered Pump Capacity (lb./h)
Electric Centrifugal Pumps
• Simplex
• Duplex
• With NPSH
Electric Condensate Pumps
Flash Steam from Vent
2- Phase flow: Condensate & Flash Steam at 212 F
HOT Condensate
Cavitation
Cavitation causes:
• Vibration
• Mechanical seals to overheat and fail
• Pitting of the impeller
• Motor bearing failure
• Capacity reduction
• Condensate losses
• High operating & maintenance costs
Mechanical Pumps
• Simplex
• Duplex
• Triplex
• Quadplex
Pressure Powered Pump
Pump Trap
• Both Float Trap and Mechanical Pump all
in One Body
• Dedicated to one piece of equipment
• Can work under pressure to Full Vacuum
• Total Fully Closed Condensate System
The Automatic Pump Trap - for smaller applications
Filling
Condensate IN
OUT
Exhaust open
First stage trap
seat open
Stalling
Condensate IN
Exhaust open
2nd stage trap
seat open
Outlet check valve
closed - NO flow
High Level Trip
Steam valve
open
Condensate
pumped OUT
Check valve
open
Pumping
Steam in
Condensate
pumped out
Float dropping
Exhausting
Exhaust OPEN
Steam inlet
CLOSED
Condensate
Filling AGAIN
Condensate IN
OUT
Exhaust open
First stage trap
seat open
Steam at 240 F
Typical Run of Condensate Line?
Steam at 15
psig
P = 0 psig
66 F
Vacuum
Breaker
At 0 psig,
with a 12”
head, we can
guarantee ¼
psi dP
12”
Revised Installation Layout
12”
12”
12”
24”
Air Handling Unit needs to be at least 5 FEET above floor level
Condensate Line Connections
Correct Incorrect
Condensate Condensate
Condensate
Why We Return Condensate
• To Optimize Steam Systems and
Energy Dollars?
$$$$$$$
Questions?