Proximate Analysis of Coal

A Brief overview of Proximate Analysis of coal

Proximate Analysis of coal is the easier of two types of coal analysis (Ultimate and Proximate) and the one which supplies readily meaningful information for coal’s use in steam generators. The basic method for proximate analysis is given by ANSI/ASTM Standards D 3172. It determines the mass percentages of fixed carbon, volatile matter, moisture, and ash.  Mass of Sulfur is obtained by a separate determination.

Calculation of fixed carbon

Fixed carbon is the elemental carbon that exists in coal. In proximate analysis, its determination is approximated by assuming it to be the difference between the original sample and the sum of volatile matter, moisture, and ash.

Calculation of Volatile matter

The volatile matter is that portion of coal, other than water vapor, which is driven off when the sample is heated in the absence of oxygen in a standard test (up to 1750°F or 7 min). It consists of hydrocarbon and other gases that result from distillation and decomposition.

Calculation of Moisture

Moisture is determined by a standard procedure of drying in an oven. This does not account for all the water present, which includes combined water and water of hydration. There are several other terms for moisture in coal. One, inherent moisture, that existing in the natural state of coal and considered to be part of the deposit, excluding surface water.

Calculation of Ash

Ash is the inorganic salts contained in coal. It is determined in practice as the noncombustible residue after the combustion of dried coal in a standard test (at 1380°F).

Calculation of Sulfur

Sulfur is determined separately in a standard test, given by ANSUASTM Standards D 2492. Being combustible, it contributes to the heating value of the coal. It forms oxides which combine with water to form acids. These cause corrosion problems in the back end of steam generators if the gases are cooled below the dew point, as well as environmental problems.

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