Fundamentals of Combustion

Question 1

Why is Sulfur undesirable?

Answer 1

1. Contains far less heat than hydrogen but requires the same amount of oxygen
2. Can cause corrosion on boilers
3. Gases (SO2 & SO3) are environmentally unfriendly

Question 2

What are the three combustible elements found in fuels?

Answer 2

Carbon, Hydrogen & Sulfur

Question 3

What type of fuel contains the largest proportion of ash? (coal, oil & gas)

Answer 3

Coal

Question 4

The fuel with the highest _____ content has the highest heating value

Answer 4

hydrogen

Question 5

List the following in ascending heat content gas, coal, oil & wood

Answer 5

1. Wood
2. Coal
3. Oil
4. Gas

Question 6

What is the composition of air?

Answer 6

23% O2 & 77% Nitrogen

Question 7

What does incomplete combustion result in?

Answer 7

unburnt carbon in the flue gas & formation of carbon monoxide

Question 8

Why is it necessary to provide more than the theoretical air?

Answer 8

to compensate for the imperfect mixing of molecules

Question 9

When CO is formed is the heat released greater or less than CO2?

Answer 9

Less

Question 10

What are the main constitutes in the flue gas?

Answer 10

CO2, H2O, SO2, O2 & N2

Question 11

What are the three Ts?

Answer 11

Time, Temperature & Turbulence

Question 12

What is OFA?

Answer 12

a portion of air injected at a higher point in the furnace to complete combustion

Question 13

Why is the fuel atomised?

Answer 13

Increased surface area and promote mixing

Question 14

In oil fired boilers what is the usual method of providing ignition?

Answer 14

start up burners with light distillate oil or natural gas. The ignition is started with an electric arc/spark

Question 15

What are the two methods of firing in an oil burner?

Answer 15

1. Front wall firing - several rows
2. Corner firing with tangential burners

Question 16

Why is it necessary to heat heavy oil before it is supplied to the burners?

Answer 16

To decrease viscosity and thus make it easier to atomise

Question 17

In the coal PF boiler how does finely ground coal get from the mill to the furnace?

Answer 17

Carried with the primary air to the burners

Question 18

What is bottom ash?

Answer 18

heavy metallic material often in large pieces that must be removed from the bottom of the furnace

Question 19

What is fly ash?

Answer 19

very light particles of non-combustible material which is carried along in the gas stream until removed at the air precipitator

Question 20

What are fuels considered to be low grade?

Answer 20

municipal & industrial waste, agricultural waste, wood waste, petroleum coke, waste from coal treatment & coal with low ash fusion temps

Question 21

What is fluidised bed combustion?

Answer 21

combustion of solid fuel in a bed which is floating on combustion iar fed through the bottom