Figure 1-30.General laboratory equipment.
complete treatment of feedwater must be considered. The
ideal water for boilers does not form scale or deposits.
does not pit feedwater systems and boiler surfaces, and
does not generate appreciable CO2 in steam. However.
such raw makeup water is impossible to get in the natural
state from wells or surface sources. Does the advantage
of treatment make up for the cost of treatment?
Feedwater of 20- to 25-ppm hardness as calcium
carbonate (CaCO3) need not be treated externally to
reduce hardness if enough alkalinity is present to
precipitate the hardness in the boiler as CaCO3, or if
hardness reducers, such as phosphates, are introduced to
combine with and precipitate the hardness. Precipitation
of this hardness in a low- or medium-pressure boiler
generally does not cause wasteful blowdown. When the
mixture ofcondensate and makeup in a medium-pressure
steam plant has a hardness greater than 20 to 25 ppm as
CaCO3, the hardness should be reduced to a level of 0 to 2
ppm as CaCO3.
Feedwater of a hardness in excess of 2 ppm as
CaCO3 should be treated to bring it within the range of
0 to 2 ppm as CaCO3. This small remaining hardness
can be precipitated in the boiler by secondary
treatment and removed by continuous blowoff
The test for hardness, as presented here, uses the
calorimetric titration method. This test is based on
finding the total calcium and magnesium content of a
sample by titration with a sequestering agent in the
presence of an organic dye sensitive to calcium and
magnesium ions. The end point is a color change from
red to blue, which occurs when all the calcium and
magnesium ions are separated.
The following equipment is used for the hardness
One 25-ml buret, automatic, complete
One 210-ml casserole, porcelain
One 50-ml cylinder, graduated
One stirring rod, glass
The reagents for the test are as follows: