Coal, analyses heat value

An ultimate analysis of a coal is a series of operations that yields the percentages by mass of carbon, hydrogen, nitrogen, oxygen, and sulfur in the coal. The heating value of a coal is best determined... 

After taking suitable coal samples for analysis, removing the blockage and filling the cavity with refractory cement, the thlrd burn test was carried out on the same channel. Figure 5 shows time-data plots for this burn. Because much of the moisture had been driven forward by the preceding burn, only a relatively low-BTU product gas was produced but by cyclical Injection of steam and air, heat values could be periodically Increased. 

Other important chemical and physical tests performed to characterize coal include (I) Heating value (Btu content) (2) sulfur forms (31 ash fusibility temperatures (4) ash analysis (5) trace elements (6) free swelling index and (7) hardgrove grindability. 

For accurate heat values of solid and liquid fuels calorimeter determinations are required. However, approximate heat values may be determined for most cools if the ultimate chemical analysis is known. Dulong s formula gives reasonably accurate results (within 2 to 3%) for most coals and is often used as a routine check of values determined by calorimeter ... 

Coal, Analytical Procedures. The most frequently made analysis of coal is the proximate analysis. This includes detns of moisture, volatile matter, fixed carbon and ash. Sometimes it is combined with detn of sulfur and phosphorus, which really belongs to the ultimate analysis, and includes also detn of carbon, hydrogen, nitrogen and sulfur. In most cases, the heating value of coal expressed in BTU/lb is also detd,... 

The calorific value is the heat produced by the combustion of a unit quantity of coal in a bomb calorimeter with oxygen and under a specified set of conditions (ASTM D-121 ASTM D-2015 ASTM D-3286 ISO 1928). For the analysis of coal, the calorific value is determined in a bomb calorimeter either by a static (isothermal) method or by an adiabatic method, with a correction made if net calorific value is of interest. The unit is calories per gram, which may be converted to the alternate units (1.0 kcal/kg = 1.8 Btu/lb = 4.187 kJ/kg). 

It will be assumed that the system is adiabatic, a reasonable assumption for thick coal seams. Also, in the interest of brevity we will not include drying in the present analysis. The product gas composition and heating value will not be appreciably affected by this assumption. In addition, it will be assumed that pressure is uniform through the bed (thus eliminating the need for a momentum balance) and that the gas and solid phase temperatures are the same. 

The elemental analysis and heating value of the selected Wyodak coal is given in Table 1. 

Analysis. The heating value, ash content, and sulfur distribution of the raw and treated coals were determined according to ASTM procedures (7). Iron in the extracts of the raw and treated coals was determined by titration with a cerium (IV) solution. Iron in the residues from the acid extractions of the raw and treated coals was determined spectrophotometrically using ferrozine (20). The liquid extracts were analyzed for total sulfur (as sulfate) by ion chromatography after separation of the sulfate from nitrate on an alumina column (21). Nitrogen was determined in the raw and treated coal and in their nitric acid-extracted residues by a modified Kjeldahl method. 

Composition and Heating Value The composition of coal is reported in two different ways the proximate analysis and the ultimate analysis, both expressed in weight percent. The proximate analysis is the determination by prescribed methods of moisture, volatile matter, fixed carbon, and ash. 

Rhenish brown coal has an average ash content of about 4 % (mf), a volatile matter of about 52 % (maf) and a lower heating value of 25.6 MJ/Kg of coal (maf). The final analysis of the coal under maf conditions shows the following average composition ... 

A residue used for analysis contained 47% oil. The residne has a higher heating value than that of coal and is snitable for energy recovery. However, it contains chlorine and heavy metals as shown in Table 26.8. Any exhanst gas and fly ash treatment must be carefully considered in its application. Recently, it has been nsed in a fnmace, and has contributed to the improvement of heat balance, as described above. 

Heat Value.—The heat values of coals are Icnown from calorimetric determinations. The A. S. M. E. formula, based on the ultimate analysis, gives... 

Calorimeter determined heating value is needed. Efforts to calculate heating value from ultimate analysis disclosed that the Dulong and similar equasions generally suitable for coal give excessive deviation from measured heating value. 

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