Spontaneous Combustion

Question 1

What Is the fundamental principle of Spontaneous Combustion?

Answer 1

• Spontaneous Combustion results from the exothermic reaction of oxygen on coal. Oxygen is chemically adsorbed onto the surface of coal, which is oxidation. This “Chemisorption” reaction increases with temperature and is the cause of the gas evolution.

Question 2

Describe the Relationship between Quantity and Spontaneous Comb?

Answer 2

• The driving factor behind the oxidation of coal is the quantity of air available for oxidation to occur.
  o Case 1 - If Q flowing over coal is small = rate of oxidation is low
  o Case 2 - If Q flowing over coal is High = the potential rate of oxidation is high however, the heat is dissipated as quickly as it is generated thus a cooling effect exists.
  o Case 3 – If Q flowing over coal is just right – then the rate of oxidation and the heat generated increase without a cooling effect -> Spon Comb occurs.

Question 3

List the 5 Physical Indicators of Spontaneous Com

Answer 3

• Smoke – Is an indication of significant heating. However, Smoke is not an early indicator of Spon Comb. The Temp of coal is exceeding 300 deg if smoke is observed.
• Haze – Is the condensation of volatile components of coal after spon comb evaporates these. Typically, haze is occurring at 200 deg
• Sweating – Is an early indicator. This is the condensation of water vapour on cooler surfaces. This is typically occurring at 100 deg
• Heat – Is a direct measurement indicator coupled with what is being experienced in the panel. This is occurring at 100-150 deg
• Smell – Oily/Musty Smell – This is occurring at 150 – 200 deg

Question 4

What is the formula for CO Make in l/min?

Answer 4

CO Make (l/min) = CO (ppm) x Q ( m3/s) x K (0.06)

Question 5

What is the formula for Grahams Ratio?

Answer 5

GR = Final CO * 100 / (0.265 * (Nitrogen Final - OxygenFinal)

Question 6

What are the trigger levels for GR?

Answer 6

<0.4 - Normal
0.4 - 1.0 - Investigate
>1.0 - Serious Heating
>2.0 - Serious Heating or Fire

Question 7

What are the triggers for CO/CO2 Ratio?

Answer 7

<0.02 - Normal
<0.05 - Coal Temp <60deg
<0.1 - Coal Temp <80deg
<0.15 - Coal Temp < 100deg
<0.35 - Coal Temp < 150deg