Coal, analyses burning

A wide range of trace elements occurs in coal, primarily as a part of the mineral matter. The release of certain trace elements into the environment as combustion products or in the disposal of ash is a concern for coal-burning facilities. Determination of certain trace elements in coal and coal ash is becoming an increasingly important part of coal analysis. 

It is therefore impossible to determine accurately the composition of the pure coal substance from the usual ultimate analysis simply by making allowance for the quantity of ash left behind as a residue when the coal is burned. Results obtained in this fashion are, as a consequence, quoted as being on a dry, ash-free basis, and no claim is therefore made that these results do in fact represent the composition of the pure coal substance. If, however, it were possible to calculate accurately the quantity of mineral matter originally present in the coal sample, then by making due allowance for this material, the composition of the pure coal material could be deduced with reasonable precision and certainly with a greater accuracy than could be obtained by adopting the analytical figures calculated to a dry, ash-free basis. 

An ultimate analysis that can claim to represent the composition of the organic substance of a coal is said to be on a dry, mineral-matter-free (dmmf) basis. The dmmf basis is a hypothetical condition corresponding to the concept of a pure coal substance. Since the dry, ash-free basis for coal neglects changes in mineral matter when coal is burned, the dmmf basis is preferred whenever the mineral matter can be determined or calculated. 

A coal has the following ultimate analysis C = 0.8339, H2 = 0.0456, 02 = 0.0505, N2 = 0.0103, S = 0.0064, ash = 0.0533, total = 1.000. This coal is burned in a steam-boiler furnace. Determine the weight of air required for theoretically perfect combustion, the weight of gas formed per pound of coal burned, and the volume of flue gas at the boiler exit temperature of 600° F (589 K) per pound of coal burned the air required with 20 percent excess air and the volume of gas formed with this excess and the C02 percentage in the flue gas on a dry and wet basis. 

Power plant operation. The power plant burns 340 metric tons/hr of coal having the analysis given below. The coal is burned with 18% excess air, based on complete combustion to CO2, H2O, and SO2. In the combustion only the ash and nitrogen is left unburned all the ash has been removed from the stack gas. 

The total sulfur content may be determined by one of several methods that convert it to sulfate by wet chemical analysis. One of these, the Eschka method, involves combustion of coal at 800°C in the presence of alkaline/oxidant medium (e.g., two parts of calcined MgO and one part anhydrous sodium carbonate) all sulfur is converted to sulfate that by the addition of barium chloride precipitates as barium sulfate, which is calcined to BaO and measured gravimetrically (see ASTM D3177). This is a standard method in many countries. Another is the high-temperature method where the coal is burned in oxygen at 1350°C, converting all sulfur present into SO2. The SO2 is then converted to sulfuric acid for titrimetric determination. 

Additional analysis is necessary when one considers energy-related emissions. First, a description of the energy-related emission factors will be presented. Assuming that coal is burned for electricity generation [75], and using an EPA report [76] for the amount of mercury in coal and emitted after pollution controls (assuming 90% capture), the controlled emission rate is 5.58 x 10 kg mercury/kWh. For the benzene, toluene, formaldehyde, and hexane emissions from coal-fired electricity generation, EPA and... 

Air. Studies have shown that 2500 years ago lead pollution caused by Greek and Roman silver smelters was a significant problem (4). Based on analysis of lake sediments and Greenland s ice, it was found that lead contamination from smelters in southern and central Europe was carried throughout the northern hemisphere. As long ago as the thirteenth century, air pollution has been linked to the burning of coal (4). The main concern was the smell from the sulfur in the coal and the effects of the soot. It was not until many years later that the effects of air pollution on people s health were discovered. 

Hard and soft acid and base (HSAB) principle, 16 780 Hard blacks, 21 775 Hard-burned quicklime, 15 28 Hard coals, 6 703 classification, 6 712 Hard copper alloys, 7 723t relief annealed, 7 723t Hard copy systems, 9 513-514 Hard core repulsion, 23 93 Hard-elastic olefin fibers, 11 242 Hardenability, of steel, 23 283—284 Hardened MF resins, analysis of,... 

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. 

However, 2,3-benzofuran was detected in emissions from a Swedish floor finish used on domestic flooring (van Netten et al. 1988), and in emissions from the pyrolysis of silk (Junk and Ford 1980), and in combustor flue gas emissions from fluidized-bed coal combustion at a concentration of 900 ng/g (Hunt et al. 1982). Exhaust produced by an automobile burning simple hydrocarbon fuels contained 2,3-benzofuran at concentrations ranging from less than 0.1 to 2.8 ppm (Seizinger and Dimitriades 1972), but an analysis of air in a highway tunnel in use by both diesel- and gasoline-powered vehicles indicated no... 

Quite often, a variation of a proximate analysis or an ultimate analysis is requested, together with one or more of the miscellaneous analyses or tests discussed in this chapter. Restrictions that have been placed on the coal used in coal-fired power plants and other coal-burning facilities have created a need for more coal analyses as well as a need for more accurate and faster methods of analysis. This trend will continue, and more testing will be required with increased use of coal in liquefaction and gasification plants. 

We wish to alert the reader that in the analyses presented above, the results were essentially independent of the type of fuel used. From an efficiency point of view, this may be true, but from a sustainability point of view, it is not. In general, gas is a much cleaner burning fuel than coal and requires less pre- and posttreatment. Even though the standard power generation plants can be made more efficient using thermodynamic analysis (lost work, availability, or exergy analysis), we note that power generation based on fossil fuels is not sustainable since the combustion of these fuels leads to increased... 

Because of the small samples often generated, ultimate analysis of selected density fractions was performed with a modified Perkin-Elmer 240, C, H, N, analyzer (modification XA by Control Equipment Corp.) using a modified burn procedure which includes increasing the time of burn and the amount of 02 used in the burn. Good correlation for carbon and hydrogen (r2 = 0.98) with ASTM methods was found for a range of coals from sub-bituminous to anthracites. 

The various methods for the online monitoring of coal composition include the TG technique, which automatically performs a multistep analytical sequence by sequentially drying, burning, and weighing the residue. Figure 3.12 shows the analysis results from an automated TG system. The elapsed time of the proximate analysis program and cooling of the tube back to load temperature totals 30 minutes. 

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