explain proximate analysis of coal
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Proximate analysis is formally defined by a group of ASTM3 test methods and is an assay of the moisture, volatile matter, fixed carbon, and ash content of a coal sample. These quantities are determined by measuring the mass loss a coal sample undergoes when heated to 900 °C under a nitrogen atmosphere and then held at 900 °C and the atmosphere is switched to air. For a more thorough treatment of this topic the reader should consult the Handbook of Coal Analysis (10). Proximate analysis has also been mentioned previously in this Journal (11, 12). However, these articles do not provide experimental results.
The moisture content is determined by the mass loss that a coal sample undergoes after it has been heated to 110 °C under a N2 atmosphere. The moisture content measured represents water that may be physically or chemically bound in the coal with the exception of mineral hydrates that decompose above 110 °C. The percent water present in coal varies with the rank of the coal. Anthracite has the least quantity of moisture, then bituminous, then subbituminous, and lignite has the most.
The volatile matter content of coal corresponds to the volatile products evolved between 110–900 °C under N2 as a
result of thermal decomposition. Volatile matter content varies with the rank of the coal. Anthracite coal has the lowest volatile matter content (typically 2–12%). Bituminous, subbituminous, and lignite coals yield higher results, 15–45%, 28–45%, and 24–32%, respectively (10).
Fixed carbon is the solid combustible material that remains after loss of moisture and volatile matter minus the ash that remains after combustion is complete. Combustion occurs when the sample is held at 900 °C and the atmosphere is switched from N2 to air. The quantity of coke a coal sample would yield is approximately equal to the sum of fixed carbon plus ash content. The fixed carbon content of coal is highest for anthracite, 75–85%, and lowest for lignite 25–30%. Bituminous and subbituminous coal yield intermediate results, 50–70% and 30–57%, respectively (10).
Ash is the residue that remains after the coal sample has undergone loss of moisture and volatile matter and the fixed carbon has undergone combustion at 900 °C in air. The ash content does not directly correspond to the mineral content of the coal sample because the minerals may have undergone thermal decomposition (e.g., loss of CO2 in carbonates) or chemical change (e.g., the oxidation of FeS2, pyrite, to iron oxide).
Proximate analysis is formally defined by a group of ASTM3 test methods and is an assay of the moisture, volatile matter, fixed carbon, and ash content of a coal sample. These quantities are determined by measuring the mass loss a coal sample undergoes when heated to 900 °C under a nitrogen atmosphere and then held at 900 °C and the atmosphere is switched to air. For a more thorough treatment of this topic the reader should consult the Handbook of Coal Analysis (10). Proximate analysis has also been mentioned previously in this Journal (11, 12). However, these articles do not provide experimental results.
The moisture content is determined by the mass loss that a coal sample undergoes after it has been heated to 110 °C under a N2 atmosphere. The moisture content measured represents water that may be physically or chemically bound in the coal with the exception of mineral hydrates that decompose above 110 °C. The percent water present in coal varies with the rank of the coal. Anthracite has the least quantity of moisture, then bituminous, then subbituminous, and lignite has the most.
The volatile matter content of coal corresponds to the volatile products evolved between 110–900 °C under N2 as a
result of thermal decomposition. Volatile matter content varies with the rank of the coal. Anthracite coal has the lowest volatile matter content (typically 2–12%). Bituminous, subbituminous, and lignite coals yield higher results, 15–45%, 28–45%, and 24–32%, respectively (10).
Fixed carbon is the solid combustible material that remains after loss of moisture and volatile matter minus the ash that remains after combustion is complete. Combustion occurs when the sample is held at 900 °C and the atmosphere is switched from N2 to air. The quantity of coke a coal sample would yield is approximately equal to the sum of fixed carbon plus ash content. The fixed carbon content of coal is highest for anthracite, 75–85%, and lowest for lignite 25–30%. Bituminous and subbituminous coal yield intermediate results, 50–70% and 30–57%, respectively (10).
Ash is the residue that remains after the coal sample has undergone loss of moisture and volatile matter and the fixed carbon has undergone combustion at 900 °C in air. The ash content does not directly correspond to the mineral content of the coal sample because the minerals may have undergone thermal decomposition (e.g., loss of CO2 in carbonates) or chemical change (e.g., the oxidation of FeS2, pyrite, to iron oxide).
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