Questions

3.12 Controlling TDS in the Boiler Water

1 What is the effect of the TDS being too high ?
a) Energy used is reduced
b) Water carry over
c) The water level will fall and lockout will occur
d) Waste of energy
2 What is the effect of the TDS being too low ?
a) Energy lost through excessive blowdown
b) Energy saved through reduced blowdown
c) Turbulent water conditions and wet steam
d) Waste of feed treatment chemicals
3 A boiler exports steam at the rate of 5 000 kg / h. An unneutralised water sample has a conductivity of 400 µS / cm. The required TDS is 2 750 ppm. The feedwater has a TDS of 200 ppm. What should be the boiler blowdown rate ?
a) 407 kg / h
b) 372 kg / h
c) 358 kg / h
d) 392 kg / h
4 What is the advantage of an automatic blowdown system over a simple manual control ?
a) The valve prevents the passage of flash steam
b) It does not need calibration
c) The amount of blowdown is correct for all boiler operating conditions
d) It can be retrofitted to existing manual valves
5 Why is a sample cooler essential for taking a sample of boiler water ?
a) Accuracy of reading
b) To neutralise the sample
c) Because TDS readings cannot be taken from inside the boiler
d) It excludes flash steam from the readings
6 For the same steam output, why will a packaged shell boiler tolerate a higher TDS level than a high pressure water-tube boiler ?
a) Water treatment is simpler for a packaged boiler and is less able to control TDS formation
b) The larger water surface area in a packaged boiler results in a lower foaming rate per m²
c) There is a greater steam space above the water in a packaged boiler so more foaming is acceptable
d) There is a lower water content in a water-tube boiler and less space for bubbles