3rd Class Power Engineering - B1 - Part 2 Exam Questions And Answers 100% Pass
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Course
Power Engineering
Institution
Power Engineering
3rd Class Power Engineering - B1 - Part 2
Exam Questions And Answers 100% Pass
Why boil out refractory? - answerTo remove any oil, grease, or other contaminating materials
from the internal surfaces of the waterside of the boiler.
Steps to boil out refractory? - answerAdd the following for each...
3rd Class Power Engineering - B1 - Part 2
Exam Questions And Answers 100% Pass
Why boil out refractory? - answer✔To remove any oil, grease, or other contaminating materials
from the internal surfaces of the waterside of the boiler.
Steps to boil out refractory? - answer✔Add the following for each 45000L of boiler water
content:
- 18kg of trisodium phosphate
- 2.25 kg of caustic soda
- 2.25 kg of sodium silicate
- 22.5 kg of soda ash
Pumped as a solution with a chemical feed pump or through a steam drum manhole.
Raise pressure to 1/2 design working pressure.
Operate blow off valves for 2-4 hours to clear sludge and sediment.
Boil out is complete when samples from the blow off show that the water is clear.
Boiler layup: Dry storage - answer✔Preferable for boilers that are out of service for an
extended period of time or where freezing temperatures are expected.
Small flame is used to evaporate any water left.
Moisture content is measured until the content is water free.
A moisture absorbing material, such as silica gel, should be placed on trays to absorb any free
moisture in the air.
Manholes should then closed and all connections on the boiler should be tightly blanked.
If available use an inert gas to provide positive pressure at approx. 35kPa.
Warning signs posted noting that boiler is stored under N2 pressure.
Boiler layup: Wet Storage - answer✔Used for boiler placed in stand-by condition.
2 methods: Boiler completely filled or boiler partially filled.
Completely filled:
Clean, empty boiler is closed and filled with softened, deaerated feedwater.
While filling, chemicals are added to prevent corrosion including an oxygen scavenger and
alkalinity control. Excess of O2 scavenger should be maintained and PH should be kept at 10.0.
Partially filled:
Fill boiler to normal working level. Space above the water is filled with an inert gas (N2) at
35kPa. In this way water will not be exposed to O2 and corrosion will be prevented.
TBC - answer✔
Cause of boiler scale? - answer✔Primary cause is presence of undesirable minerals in the boiler
water. Calcium and magnesium are the most common. Others are iron, copper, aluminum and
silica.
Effects of boiler scale? - answer✔Scale restricts heat transfer, causing metal to overheat.
Scale traps water beneath it, encouraging corrosion.
Scale sloughs off and causes flow restrictions.
2 internal methods of controlling boiler scale? - answer✔Use phosphates to precipitate the
scale forming solids and remove via blowdown. Other method involves using chelates to react
with scale forming solids and prevents them from dropping out of the solution with boiler
water.
Keys to phosphate treatment? - answer✔Typically uses orthophosphates (monosodium,
disodium, trisodium phosphate).
Success depends on alkalinity remaining above 9.5 pH and preferably between 11 and 12 pH.
Phosphate reacts and forms to create impurities known as suspended solids.
Susp. solids are then removed via blowdown.
Keys to chelate treatment? - answer✔Uses weak organic acids called chelants to hold scale
forming impurities in solution. Most common are EDTA and NTA.
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