Formulas - Calculating Condensate Loads

Warm Up Load ( Heating Loss ) This is the amount of condensate which forms at starting up a power plant to raise the temperature of the metal of pipes, fittings, etc. to the operating temperature without including the normal radiation loss. As far as calculating the condensation load during the warming up period the required time is extremely important for sizing steam traps. Less warm up time increases the necessary capacity per trap. Allowing more time for warm up permits the use of smaller traps in smaller quantity.

           W x (T-t) x Sp. Heat x 60
Q = —————————————
                            L x m

Where Q = Quantity of Condensate ( Lbs/hr )
W = Total weight of pipes in LBS
T = Saturation Steam Temp ( °F ) t = initial temp of pipe ( °F ) usually surrounding air temp
m = minutes to heat up system
L = Latent heat of steam ( BTU’s/Hr )

Normal Condensate Load ( Radiation Loss )

Once the system is heated up steam condenses due to normal radiation losses to the surrounding air. These losses depend of course on the size and length of the pipe, on the pressure of steam and its latent heat and mainly on the type and thickness of insulation. The equation from which a normal regulation load can be calculated is:

               F x HL ( T - t )
Q = ——————————
                         L

Where F = Length of Pipe (ft)
HL ( T – t ) = Heat loss/foot of pipe at the temperature differential between steam and air
L = Latent heat of steam ( BTU’s/Hr. )

Condensation Load for Sizing Steam Traps

The condensation load builds up from 0 to maximum at the point where the warming up load drops to 0. It is assumed, therefore, that the peak is achieved halfway through the warming up period. Therefore, for sizing of steam traps, we take the maximum amount of condensate during the warming up period plus half of the radiation load.

Qt= QW + .5QR

Where Qt = Total condensation load at peak (LBS/Hr)
QW = Condensation load during warm up (LBS/Hr)
QR = Condensation load due to normal radiation loss (LBS/Hr)

Condensate in LBS/Hr created in steam mains 1” to 24” and pressure of 600 to 2500 PSI based on the warm up period of 1 hour and 100 feet of pipe, and based on the above assumption is shown in tables.

For shorter or longer heating up time, multiply by 60/m where m is the warm up time in minutes.

Properties of Saturated Steam

Standard Dimensions for Schedule 40 Pipe

Examples:
Warm up loss
Ambient Temp = 70°F
Working Temp = 366°F (150psig)
Warm up time = 720 minutes
1000 feet of 10 inch Schedule 40 pipe weighs = 40483
Latent heat = 857

        40483 x (366-70) x .12 x 60
Q = —————————————
                        857 x 720

Q = 472 lbs/hr

 

Radiation loss

Ambient Temp = 70°F
Working Temp = 366°F (150psig)
Differential temp = 294°F
Differential multiplier = .98
1000 feet 10 inch Schedule 40 uninsulated pipe
Latent heat = 857

        1000 x 2600 ( .98 [factor for 296° diff] )
Q = ——————————
                    857

Q = 2973 lbs/hr

 

Sizing for steam traps

Qt= QW + .5QR

.5QR = 1486.5 + QW = 472 = 1958.5

 

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