Makeup Water Rate

UFC 3-240-13FN

25 May 2005

upstream of the deaerator. The amount, expressed as either volume or percentage, of

makeup water required in a boiler is affected by blowdown, steam leaks, consumption of

steam in process equipment, and loss of condensate by boiler system leakage. In a

"tight" boiler system, where steam is not lost in process equipment, about 5 to 10%

makeup is expected. Water balance is affected by condensate return; however, boilers

that lose considerable condensate due to losses of steam or condensate can approach

a requirement for 100% makeup, which is a very inefficient and costly condition. The

calculations below can be used for determining makeup water needs and condensate

return rates.

3-1.6.1

Makeup Water Rate. Makeup is the difference between the volume of

condensate return and the volume of feedwater.

EQUATION

M=FR

(9)

where

M = makeup, kg/s (lb/hr)

F = feedwater, kg/s (lb/hr)

R = condensate return, kg/s (lb/hr)

3-1.6.2

Condensate Return Rate. Since the returned condensate usually does

not contain any appreciable level of dissolved solids or conductivity, determination of

percent makeup is calculated using the equation:

EQUATION

%M =(1- Fmho / Mmho ) x 100%

(10)

where

%M= % makeup

Fmho= feedwater conductivity, micromhos

Mmho= makeup conductivity, micromhos

EXAMPLE 3-2:

a) Makeup water conductivity is 900 mhos for the boiler water in this

example. The percent makeup is calculated:

%M = (1- Fmho / Mmho ) x 100%

EQUATION

or (1-250 / 900) x 100%

(11)

%M = 72%

b) This means that the makeup water is 28% of the feedwater. The

condensate return percent is calculated:

EQUATION

%R = 100 - %M = 100 - 28 = 72%

(12)

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