What does "fixed carbon" refer to in coal analysis?

Fixed carbon refers specifically to the weight of non-volatile components remaining in coal after it has been subjected to the process of carbonization, which involves heating the coal in the absence of air. This component represents the solid carbonaceous material that is left over and is crucial for understanding the coal's performance in applications such as combustion and gasification. Fixed carbon is a key determinant of the heating value of coal, as it contributes significantly to the energy that can be released when the coal is burned.

In contrast, options discussing gasification, ash content, and moisture content focus on different aspects of coal analysis. While many coal constituents are important for various uses and impacts on combustion efficiency, fixed carbon is specifically about the unreacted carbon content after volatile materials have been removed. This is why recognizing fixed carbon is essential for evaluating coal's suitability for various industrial applications.