JNTU B.Tech III Year MINE ENVIRONMENTAL ENGINEERING II Previous Question Paper (March - 2021 - R16)

Spontaneous heating in coal mines is detected through various physical, chemical, and sensory methods:

• Visual and Sensory Observation: Detection of smoke, haze, or the characteristic smell of oil or paraffin. Changes in the temperature of the mine air or strata and the presence of water droplets (sweating) on the roof or sides are early indicators.
• Gas Analysis: Monitoring mine air for combustion gases, specifically carbon monoxide (CO), carbon dioxide (CO2), and the ratio of CO produced to oxygen consumed (Graham's Ratio). An increase in the CO/O2 deficiency ratio is a primary indicator of heating.
• Temperature Measurement: Direct measurement of strata temperature using thermocouples or infrared thermal imaging cameras to identify hotspots in coal pillars or goaf areas.
• Chemical Methods: Analysis of mine air samples for hydrocarbons like ethylene and propylene, which are produced during the early stages of coal oxidation.

The Crossing Point Temperature (CPT) method is a laboratory-based technique used to determine the susceptibility of coal to spontaneous heating by measuring the temperature at which the coal sample's temperature crosses the temperature of the surrounding oil bath.

The experimental procedure involves the following steps:

1. A representative coal sample is crushed and sieved to a specific particle size (typically 212-300 microns).
2. The sample is placed in a glass flask or U-tube, which is then immersed in an oil bath equipped with a heating element and a stirrer to ensure uniform temperature distribution.
3. A steady stream of air or oxygen is passed through the coal sample at a controlled flow rate.
4. Two thermometers or thermocouples are used: one to measure the temperature of the oil bath and the other to measure the temperature of the coal sample.
5. The oil bath is heated at a constant rate (e.g., 1°C per minute).
6. As the coal oxidizes, it generates heat. The temperature of the coal is recorded continuously.
7. The Crossing Point Temperature is defined as the point on the graph where the coal temperature curve intersects the oil bath temperature curve.

A lower CPT value indicates that the coal is more prone to spontaneous heating, as it begins to self-heat at a lower ambient temperature.