Ash, analysis

The evaluation of coal mineral matter by the ashing technique can be taken further insofar as attempts can then be made to determine the individual metal constituents of the ash. On the occasion when the mineral matter has been separated from the coal successfully, it is then possible to apply any one of several techniques (such as x-ray diffraction, x-ray fluorescence, scanning electron microscopy and electron probe microanalysis) not only to investigate the major metallic elements in coal but also to investigate directly the nature (and amount) of the trace elements in the coal (Jenkins and Walker, 1978 Prather et al., 1979 Raymond and Gooley, 1979 Russell and Rimmer, 1979 Jones et al., 1992). Generally, no single method yields a complete analysis of the mineral matter in coal and it is often necessary to employ a combination of methods. 

The wet chemical or classical procedures, including many colorimetric and some electrochemical procedures, can be quite time consuming. They are generally very accurate, however they can be precise, and they do not require special or expensive equipment or facilities. However, these methods are less sensitive than some instrumental methods. 

One issue that has already been mentioned is the amount of sulfur in the ash that is due to a high amount of carbonates (calcite, CaC03), or pyrite (FeS2), or both, in the coal. Sulfur retained as sulfates may be both unduly high and nonuniform between duplicate samples. The reasons vary from inconsistencies in the furnace temperature and furnace ventilation that have an influence on sulfur trioxide retention in the ash. Consequently, sulfur in ash as determined in the laboratory cannot be assumed to be equivalent to sulfur present in the mineral matter in coal or to the retention of sulfur in ash produced under the conditions of commercial utilization. 

Sulfate sulfur in ash is determined (ASTM D-1757) and the requisite correction made, and the ash yield should be reported and designated both as determined and corrected. The sulfate sulfur so determined can be used to calculate the sulfur trioxide portion of ash so that the ash content or ash composition can be reported on a sulfur trioxide-free basis. 

A compositional analysis of the ash in coal is often useful in the total description of the quality of the coal. Knowledge of ash composition is also useful in predicting the behavior of ashes and slags in combustion chambers. Utilization of the ash by-products of coal combustion sometimes depends on the chemical composition of the ash. In addition, concern over release of certain trace elements to the environment as a result of coal utilization has made determination of these elements an increasingly important aspect of coal analysis. 

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A development in the 1960s was that of on-line elemental analysis of slurries using x-ray fluorescence. These have become the industry standard. Both in-stream probes and centralized analyzers are available. The latter is used in large-scale operations. The success of the analyzer depends on how representative the sample is and how accurate the caUbration standards are. Neutron activation analyzers are also available (45,51). These are especially suitable for light element analysis. On-stream analyzers are used extensively in base metal flotation plants as well as in coal plants for ash analysis. Although elemental analysis provides important data, it does not provide information on mineral composition which is most cmcial for all separation processes. Devices that can give mineral composition are under development. 

The ash analysis receives special attention because of certain trace metals in the ash that cause corrosion. Elements of prime concern are vanadium, sodium, potassium, lead, and calcium. The first four are restricted because of their contribution to corrosion at elevated temperatures however, all these elements may leave deposits on the blading. 

Srivastava, V.K., P.K. Srivastava, and U.K. Misra. 1985. Polycyclic aromatic hydrocarbons of coal fly ash analysis by gas-liquid chromatography using nematic liquid crystals. Jour. Toxicol. Environ. Health 15 333-337. 

Bettinelli, M., Baroni, U., Pastorelli, N. and Bizzarri, G. (1992). ICP-AES, GFAAS, XRF and NAA coal fly-ash analysis - comparison of different analytical techniques. In Elemental Analysis of Coal and Its By-Products, ed. Vourvopoulos, G., World Scientific, Kentucky, pp. 372-394. 

Preparation of Standards. Standards for ash analysis were prepared from commercially available pure salts in aqueous solution with appropriate acids addition where necessary to match acid concentrations in the samples as well as to hold materials in solution. Master standard solutions were prepared so that serial dilutions for the construction of working curves were possible. A constant amount of silicon and aluminum (equivalent to 20% Si-5% Al) interference solution was added to each set of standards along with lithium tetraborate to carefully match... 

Radiochemical yields are 80-95% for zinc and quantitative for cadmium. The average relative standard deviation was 25% for zinc and better than 10% for cadmium. The detection limit of the method is 50 ppm cadmium in the ash. Analysis of two Illinois coals with unusually high cadmium content (17 and 21 ppm) gave results in good agreement with those obtained by atomic absorption and by anodic stripping voltammetry (4). The recent development and testing of a radiochemical method for the determination of zinc, cadmium, and arsenic in coal and fly ash, by Orvini et al. (14), has already been discussed in the section on arsenic. 

Coal and Ash Analysis. The coal and ash samples were separated into 20-40 g representative samples in the laboratory by a small riffle splitter. These samples were then pulverized with a mortar and pestle. The moisture content was determined by weighing the sample, drying it at 103 °C, and then reweighing it. These samples were kept in a desiccator and were subsequently used for the mercury analysis. 

The two highest ratios, from tests 3 and 7, showed the greatest deviation from the expected norm of 1.0. Results from these tests showed a larger amount of mercury in the stack gas stream than was expected from the coal and ash analysis. These two tests were the first two tests... 

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. 

Ash analysis is the term used to designate analysis of the major elements commonly found in coal and coke ash. The elements, expressed as oxides, are SiCK AUCb, Fe 0, TICE, CaO. MgO, Na7Ot K20. P Os, and S03. 

Figure 3. Comparison of conversion of MAF Wyodak (—035 solvent (A/ —0/9 solvent (0)) and Monterey (—035 solvent (O) —019 solvent ( Z )) coals to pyridine solubles (based on ash analysis)...

Ash Content. Samples were removed from the specimens and submitted for ash analysis (Schwartzkopf Microanalytical Laboratory, Woodside, NY). Samples were burned in oxygen at 900-1000 °C for about 0.5 h. 

The development and adaptation of modern analytical techniques for analysis of Victorian brown coal was pioneered jointly in the 1960 s by the Commonwealth Scientific and Industrial Research Organization and the State Electricity Commission of Victoria. As a result, the total coal analysis time was halved and the determination of the ash forming constituents directly on the coal took one sixth of the time of conventional ash analysis. More importantly brown coal analysis was put onto a rational basis taking its unique properties into account, thereby providing more pertinent information concerning the genesis, occurrence and use of Victorian brown coal. 

Kinetics for a Norwegian birch and a Danish beech have been determined, Apart from their origin there are also other differences between the woods. The beech sample is first received as wood chips whose surface has been exposed to the ambient and that partially contains bark. The birch sample comes from a wood log that has been cut into small cubes of Ixlxlcm, removing the bark. The proximate and ultimate analysis is shown in Table 1 and the ash analysis in Table 2. 

The ash analysis presented in Table 2 shows very similar values for the potassium content of both woods, but there is some variation regarding other ash components. It cannot be known from the experiments whether the differences in the reactivity profiles are due to these other ash components or to a different porosity evolution as the conversion proceeds. 

Silicate Minerals in Coal. The silicate minerals, kaolinite and potassium aluminosilicate species together with quartz constitute the bulk of mineral matter in most coals. The approximate amounts of different silicate species of the bituminous coal mineral matter can be estimated from ash analysis. 

The relative concentrations of flame heated ash constituents, namely silicates, iron oxide and sulphate, can be estimated from the ash analysis. However, the composition of the initial deposit material can be markedly different as a result of selective deposition. In particular, the deposit material can be enriched in sulphate as shown in Figure 1. The relative concentrations of different deposit constituents were obtained by analysing the material on a cooled metal tube probe inserted in boiler flue gas for short,... 

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