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?