Boiler Operations: Combustion, Water Treatment & Safety

What is the largest heat loss in most boilers?

Stack loss

Why does nitrogen contribute to heat loss?

It absorbs heat and carries heat out the stack

Why is excess air supplied to a boiler furnace?

To ensure complete combustion

What is a typical excess air value used in boilers?

About 20%

What happens if too much excess air is supplied?

Reduced efficiency and increased stack losses

What may a bright white flame indicate?

Excess air

What can a high stack temperature indicate?

Excess air dirty heating surfaces or poor heat transfer

What is secondary combustion?

Fuel burning outside the furnace

What are signs of poor combustion?

White smoke sparking flame ends CO production poor atomization

What is a boiler's turndown ratio?

Maximum firing rate divided by minimum stable firing rate

What variables does a 2-element feedwater regulator use?

Drum level and feedwater flow

What should be done if pneumatic control air is lost?

Shift to manual feedwater control

What should be investigated if feed tank level is dropping?

Inventory losses or leaks

What does a high boiler water level cause?

Carryover

What is carryover?

Boiler water carried with the steam

What boiler condition commonly causes foaming?

Oil contamination

Why is wet steam undesirable?

It causes turbine blade erosion

What do high chlorides 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

What does increasing oxygen scavenger demand suggest?

Poor deaeration or oxygen ingress

Why is alkalinity maintained in boiler water?

To reduce corrosion and neutralize acids

What are the goals of boiler water treatment?

Prevent scale prevent corrosion keep impurities suspended

What is the purpose of bottom blowdown?

Remove sludge and settled solids

When is bottom blowdown usually performed?

At low load or reduced pressure

What is the purpose of surface blowdown?

Remove foam oil and concentrated surface water

How can a high boiler water level be reduced quickly?

Surface blowdown

What can result from insufficient blowdown?

High dissolved solids foaming carryover and scale

What is scale?

Hard deposits on heating surfaces

Why is scale dangerous?

It reduces heat transfer and overheats tubes

What is sludge?

Loose deposits that settle in low areas

What is film boiling?

Formation of a steam blanket on the heating surface

Why is film boiling dangerous?

Heat transfer drops and tube metal overheats

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 disappearing water in a gauge glass be treated?

As an emergency until verified

What three things are required for a furnace explosion?

Fuel oxygen and an ignition source

What happens if one element of the explosion triangle is removed?

An explosion cannot occur

Why is furnace purging performed?

To remove unburned fuel vapors before light off

What does furnace purging prevent?

Flarebacks and furnace explosions

What is the largest unavoidable loss in the Rankine cycle?

Condenser loss

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

Stored heat remains in the boiler

Before cutting a boiler into the steam header boiler pressure should be?

Slightly above header pressure

What type of water is preferred for boiler washing?

Heated freshwater

In what direction should boiler cleaning proceed?

Following the gas flow path

What is a boil out used for?

Removing oil contamination

What are common causes of handhole leaks?

Bad gasket damaged seating surface or improper tightening

Purpose of a steam drum?

Separate steam from water

Purpose of a mud drum?

Collect sediment and sludge

Purpose of generating tubes?

Transfer heat to water and produce steam

Purpose of a superheater?

Raise steam temperature above saturation

Purpose of an economizer?

Preheat feedwater using stack gases

Purpose of an air heater?

Preheat combustion air

What three things are required for combustion?

Fuel oxygen and ignition

Incomplete combustion produces what gas?

Carbon monoxide

What is atomization?

Breaking fuel into fine droplets

Poor atomization results in what?

Smoky fires and poor combustion

Function of a forced draft fan?

Supply combustion air

Function of an induced draft fan?

Remove flue gases and maintain draft

What is saturated steam?

Steam at the boiling temperature for its pressure

What is superheated steam?

Steam heated above saturation temperature

What is latent heat?

Heat added during phase change without temperature change

What is sensible heat?

Heat that causes temperature increase

As pressure increases saturation temperature does what?

Increases

Purpose of a deaerator?

Remove dissolved gases

Main gases removed by a deaerator?

Oxygen and carbon dioxide

Purpose of a feedwater heater?

Improve efficiency by heating feedwater

Why is condensate reused?

Saves heat and treated water

Purpose of a feed pump?

Force water into the boiler

Most dangerous boiler casualty?

Low water condition

What can low water cause?

Tube overheating and failure

Tube bulging indicates what?

Overheating

Tube rupture indicates what?

Severe overheating or overpressure

Purpose of a safety valve?

Prevent excessive boiler pressure

When should a safety valve lift?

At set pressure

What should never be done to a safety valve?

Tamper with its setting

Safety valves are tested to verify what?

Proper lifting pressure