Condensate Return Systems Spirax Sarco Inc. Presented by Greyling Carey
Typical Steam Circuit KETTLES
SPACE HEATING TANKS
Feed Tank Boiler Feed Pump
Steam and Condensate Striving for maximum efficiency Steam generation, distribution and utilization Boiler
Process
Condensate removal, heat recovery and return
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%
Driving Forces
CUSTOMER
Energy Costs
Profitability
Productivity
Reliability Environment
www.SpiraxSarco.com
Safety
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 Payback Analysis Instructions: Input data in white boxes where appropriate:
Condensate Recovery saves:
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 Make Up Water Temperature Steam Cost Boiler Operating Pressure
190
Deg. F
60
Deg. F
5.00 150
$ per 1000 lbs
hg (BTU/lb)
339
hf (BTU/lb)
5
%
Cost of Fuel
4.10
$ per million BTU
Boiler Efficiency
85%
%
Additional Information Maximum Temperature permitted in sewer Is water being used to cool condensate
140 No
Yes or No
Energy savings in condensate
28,470
$/year
Make up Water & Treatment Chemical Savings
21,007
$/year
5,252
$/year
0
$/year
Boiler Blowdown Savings
490
$/year
CO2 Emissions Reduction
386
Tons/year
Raw Water (cooling) Cost Savings
TOTAL ANNUAL SAVINGS
55,219
• Chemical treatment costs • Effluent costs • Boiler Blowdown %
Deg. F
Savings
Sewage/Effluent Cost Savings
• Preheating energy costs
psig
1196
Boiler Blowdown
• Water costs
$/year
• Emissions • Damage to infrastructure • Safety incidents
(Just 10 gpm can save over $50,000 per year)
Typical Issues Caused with Improper Condensate Systems • • • • • • •
System Reliability Safety Operation Control Productivity Product Quality Economic Environmental
Problems Incurred From Stalled Condensate Systems Waterhammer Control Corrosion Erosion Equipment damage Personnel Safety Maintenance costs
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
Condensate Drainage What if condensate cannot drain? Condensate ‘backs up’ Results in: • Cooling • Output swings • Waterhammer • O2 & CO2 corrosion • Thermal stresses • Fouling
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
Condensation & Steam Flow 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
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
Sizing of Condensate Return Lines Quantity of Flash Steam 1000 lb/h
Mass
60 PSIG
Volume
Condensate 900lb/h
Condensate 0.017ft3/h
Flash Steam 100lb/h
Flash Steam 26.8 ft3/h
0 PSIG
What’s Flash Steam?
Steam created when hot condensate is exposed to a lower pressure.
FLASH STEAM
FLASH STEAM occurs when hot condensate at high pressure is released to a lower pressure. At the lower pressure, the heat content (SENSIBLE HEAT) of the water (hot condensate) cannot exist in that form. A portion of the water ‘boils off’ and becomes FLASH STEAM Flash Steam contains valuable BTU’s / lb. Of heat which can be 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
Exhaust open Condensate IN OUT First stage trap seat open
Stalling
Exhaust open Condensate IN
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 Float dropping
Condensate pumped out
Exhausting Steam inlet CLOSED Exhaust OPEN
Condensate
Filling AGAIN
Exhaust open Condensate IN OUT First stage trap seat open
Steam at 240 F
Typical Run of Condensate Line?
Revised Installation Layout Steam at 15 psig
Vacuum Breaker
66 F At 0 psig, with a 12” head, we can guarantee ¼ psi dP
12”
P = 0 psig 12” 12” 12”
24”
Air Handling Unit needs to be at least 5 FEET above floor level
Condensate Line Connections
Condensate
Condensate
Condensate
Incorrect
Correct
Why We Return Condensate
• To Optimize Steam Systems and Energy Dollars?
$$$$$$$
Questions?