Page 295 - Boiler plant and distribution system optimization manual

280 Boiler Plant and Distribution System Optimization Manual

Table 15.1—Effect of inadequate or improper water conditioning.

Automatic control of the continuous blow- temperatures. Waters containing large amounts
down involves the use of a continuous conduc- of calcium and magnesium minerals are “hard
tivity monitor to activate the blowdown control to wash with.” The amount of hardness in nor-
valve. These units can maintain boiler water con- mal water may vary from several ppm to more
ductivity within close limits and thereby min- than 500 ppm. Because calcium and magnesium
imize excessive blowdown loss, which occurs compounds are relatively insoluble in water, they
with manual control. tend to precipitate out, causing scale and deposit
problems. The hardness of the water source is an
WATER HARDNESS important consideration in determining the suit-
Hardness in the boiler water indicates the ability of water for steam generation.
presence of relatively insoluble impurities. Impu- As mentioned earlier, this process of precipi-
rities may be classed as (a) dissolved solids, (b) tation will take place on the heat exchange surfac-
dissolved gasses and (c) suspended matter. Ac- es and is known as scale.
tually, in the heating and concentration of boiler
water, these impurities will precipitate even more CONDENSATE SYSTEM CORROSION
rapidly since they are even less soluble at high The most prevalent type of condensate sys-