Solution:
The correct answer is
Option B: 925 °C.
Let's understand why we do this test and what it means for coal.
Imagine coal as a kind of rock that can burn. When we talk about
volatile matter in coal, we are referring to the parts of the coal that turn into gases or vapors when heated strongly, but
without any air (oxygen) present. It's like heating wood in an enclosed space; some gases come out before the wood itself starts to burn.
Why is this important?
Knowing the volatile matter content helps us understand many things about coal:
1.
Ignition and Burning: Coal with high volatile matter usually
ignites more easily and burns with a longer, more luminous flame. Coal with low volatile matter is harder to ignite.
2.
Smoke Production: Higher volatile matter can lead to
more smoke during combustion.
3.
Industrial Use: Different industries need different types of coal. For example, in
coke making (for steel production), the volatile matter content is very critical.
4.
Coal Classification: It's one of the key factors used to
classify different ranks of coal (like lignite, bituminous, anthracite).
How do we determine it?
To find the volatile matter content, we follow a standard procedure:
1. A small, carefully
air-dried coal sample is weighed.
2. This sample is then placed in a special crucible with a lid (to keep air out).
3. The crucible is then heated in a furnace for a specific time and at a specific temperature.
4. The standard method requires heating the sample for exactly
7 minutes at a constant temperature of
925 °C (plus or minus a small allowance).
5. After heating, the sample is cooled and weighed again. The weight loss (after accounting for moisture) represents the volatile matter that escaped as gas.
The temperature of
925 °C is chosen because it ensures that most of the volatile components are driven off, but the coal itself doesn't undergo significant decomposition beyond that point in the given time. This specific temperature and time are part of the
standard test method to ensure consistent and comparable results worldwide.
