1.
Phosphates are used in the chemical
treatment of boiler water to
A. decrease dissolved oxygen content
B. control alkalinity and neutralize
vanadium
C. neutralize the hamful effects of
hydrogen embrittlement
D. convert scale-forming salts to
relatively harmless sludges
The most critical period of main turbine
operation is during cold start-up, rather
than hot shutdown because
A. harmonic vibrations associated with
critical speed can easily be reached
during start-up
B. the danger of blade erosion damage
from dry steam impingement is
greater during start-up
C. differential expansion can result
from the temperature difference
between the rotor and rotor casing
D. lubricant film thickness during start-
up is considerably less than the
dimensions of gear surface
irregularities
Answer (1)
Phosphates are commonly added to boiler water to prevent the formation of hard scale by reacting with scale-forming salts (such as calcium salts) to form relatively harmless sludges, which can be removed by blowdown. This helps protect the boiler system from damage caused by scale buildup.---2. The most critical period of main turbine operation is during cold start-up, rather than hot shutdown because:Answer: C. differential expansion can result from the temperature difference between the rotor and rotor casing
