UFC 3-240-13FN
25 May 2005
with other chemicals), and selecting the required chemical treatment (addition) scheme
to ensure proper water treatment. Selection factors are described in paragraph 3-3.
Blowdown discharge rates can be used to calculate the rate of chemical addition and
the amount of chemical required to replace that lost in the blowdown and to meet the
treatment objectives. In practice, chemical feed equipment is set up to deliver the
chemicals on a "proportional-feed-on-demand" basis. The operator must keep treatment
levels within prescribed control ranges by adjusting pumps and timers while controlling
COC within the system. Selection of the type and quantity of required chemical
treatment is an issue that involves both technical concerns and ancillary issues
pertaining to institutional concerns in the areas of procurement, contracts, and budgets.
This situation is described in Chapter 10.
Example 3-4 illustrates phosphate demand. Similar approaches could be used
for other treatment technologies. In the case of sulfite, the treatment requirement must
first satisfy the demand due to oxygen in the feedwater. Additional sulfite is fed to attain
a residual or excess amount in the boiler water to ensure adequate protection. The
second part of Example 3-4 takes into account that the treatment chemical formulation
is not composed of 100% active ingredients. Formulations are most often less than 50%
active and can be as little as 10% active chemical, with the balance of the formulation
usually being water.
EXAMPLE 3-4:
a) The boiler in Examples 3-1, 3-2, and 3-3 will be operated with a phosphate
level of 60 ppm (as PO4) in the boiler water. The blowdown has been
determined to be 0.26 kilogram per second (2105 pounds per hour). The
required phosphate addition on a daily basis must equal the phosphate
that is discharged with the blowdown water, plus that used up in
precipitating calcium phosphate. The amount of phosphate required to
replace that lost in blowdown is calculated by this method:
Phosphate loss = (B)(treatment ppm residual)/1,000,000
= 0.26 kg/s x (60 ppm)/1,000,000
= 0.000016 kg/s (0.13 lb/hr) or 1.38 kg/day
b) The treatment chemical selected is sodium hexametaphosphate (HMP)
containing 90.5% phosphate as PO4. This means there is 0.905 kilogram
(0.905 pound) of phosphate (PO4) per kilogram (pound) of chemical:
Chemical required = phosphate loss 0.905
= 1.38 0.905
= 1.52 kg/day (3.35 lb/day)
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