Marine Boilers and Steam Plant Exam 2 Set 2

What is the largest heat loss from a boiler?

Stack loss

What is the largest unavoidable loss in the Rankine cycle?

Condenser loss

What is the purpose of excess air in combustion?

Ensure complete combustion

What effect does excessive excess air have on boiler efficiency?

Reduces efficiency

What can high stack temperatures indicate?

Excess air dirty heating surfaces or poor heat transfer

What causes secondary combustion?

Fuel burns outside the furnace

What are symptoms of poor combustion?

White smoke sparks carbon monoxide poor atomization

What two variables are used by a 2-element feedwater regulator?

Drum level and feedwater flow

What should be done upon loss of pneumatic control air?

Shift to manual feedwater control

What is the main cause of foaming?

Oil contamination

What does a high boiler water level cause?

Carryover

Why is carryover undesirable?

Water enters steam system and damages equipment

What damage can wet steam cause in turbines?

Blade erosion

What do high chloride levels indicate?

Seawater contamination or condenser leak

What does increasing hardness indicate?

Contamination entering the system

What are the principal corrosive gases in boiler systems?

Oxygen and carbon dioxide

Why is alkalinity maintained in boiler water?

Reduce corrosion and neutralize acids

What are the goals of boiler water treatment?

Prevent scale prevent corrosion suspend impurities

What is the purpose of bottom blowdown?

Remove sludge and settled solids

When is bottom blowdown most effective?

At low load or reduced pressure

What is the purpose of surface blowdown?

Remove foam oil and concentrated surface water

What can insufficient blowdown lead to?

Scale foaming carryover and high dissolved solids

What is scale?

Hard deposits on heating surfaces

Why is scale dangerous?

Reduces heat transfer and overheats tubes

What is sludge?

Loose deposits that settle in low points

What is film boiling?

Steam blanket forms on heating surface

Why is film boiling dangerous?

Tube overheating due to poor heat transfer

What is the first action when low water is suspected?

Secure fuel immediately

What should be done after multiple tube failures?

Secure fires isolate boiler and relieve pressure

How should a disappearing water level in the gauge glass be treated?

As an emergency

What three elements are required for a furnace explosion?

Fuel oxygen and ignition source

Why is furnace purging performed?

Remove unburned fuel vapors before light off

What does furnace purging prevent?

Flarebacks and furnace explosions

Why does a boiler continue producing steam after fires are secured?

Stored heat remains in boiler

Before placing a boiler on the line its pressure should be?

Slightly above header pressure

What type of water is preferred for boiler washing?

Heated freshwater

What is a boil out used for?

Remove oil contamination

What commonly causes handhole leaks?

Bad gasket damaged seat or improper tightening

Why does nitrogen contribute to stack loss?

It absorbs heat and leaves with exhaust gases

What may a bright white flame indicate?

Excess air

What is the consequence of too much excess air?

Increased stack losses

What may increased oxygen scavenger demand indicate?

Poor deaeration

What condition can opposite chemistry trends in two boilers indicate?

Crossover leakage

What can surface blowdown be used for besides impurity control?

Lower high water level

What is the difference between scale and sludge?

Scale is hard deposit sludge is loose deposit

What reduces superheater temperature by reducing combustion intensity?

Lower forced draft pressure