Ash-forming constituents

Despite much speculation on the possible effects of the inorganic ash-forming constituents in a coal on its behaviour during conversion, there is still no clear understanding on the subject. 

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. 

This is probably the simplest method of testing for carboxyl groups which, since they are a product of alkaline oxidation, will be present as —COONa. A sample is steeped in n/10 sulphuric acid for 1 hour, and next washed twelve times with distilled water. The material is then steeped in fresh distilled water for 3 hours, rinsed and dried. In this way all the alkaline ash-forming constituents, other than the —COONa groups, are removed. After this treatment the sample is weighed and then ignited in a silica crucible and heated until all the carbon has gone. The residue is dissolved in water and the alkalinity determined by titration with N/10 sulphuric acid. 

The determination of the carbon residue of petroleum or a petroleum product is applicable to relatively nonvolatile samples that decompose on distillation at atmospheric pressure. Samples that contain ash-forming constituents will have an erroneously high carbon residue, depending on the amount of ash formed. All three methods are apphcable to relatively nonvolatile petroleum products that partially decompose on distillation at atmospheric pressure. Crude oils having a low carbon residue may be distilled to a specified residue with the carbon residue test of choice then applied to that residue. 

As noted, in any of the carbon residue tests, ash-forming constituents (ASTM D-482) or nonvolatile additives present in the sample will be included in the total carbon residue reported, leading to higher carbon residue values and erroneous conclusions about the coke-forming propensity of the sample. 

The ash-forming constituents in diesel fuel (ASTM D-2880) are typically so low that they do not adversely affect gas turbine performance, unless such corrosive species as sodium, potassium, lead, or vanadium are present. However, there are recommendations for the storage and handling of these fuels (ASTM D-4418) to minimize potential contamination. 

Depending on the use of the fuel, ash composition has a considerable bearing on whether or not detrimental effects will occur. However, distillate fuels tend to contain only negligible amounts of ash but pick up ash-forming constituents during transportation from the refinery. Water transportation, in particular, presents many opportunities for fuel oils to be contaminated with ash-forming contaminants (seawater, dirt, and scale rust). 

Finally, mineral matter in coal is the parent material in coal from which ash is derived and which comes from minerals present in the original plant materials that formed the coal, or from extraneous sources such as sediments and precipitates from mineralized water. Mineral matter in coal cannot be analytically determined and is commonly calculated using data on ash and ash-forming constituents. Coal analyses are calculated to the mineral matter-free basis by adjusting formulas used in calculations in order to deduct the weight of mineral matter from the total coal. 

As such, accurate characterization of the ash-forming constituents, especially the Fe-bearing minerals and possible clay minerals present. Is desirable not only to predict the slagging/fouling characteristics of that coal, but also for... 

Ash-forming constituents as deflned by Test Method D 482, or non-volatile additives present in the sample will add to the carbon residue value and be included as part of the total carbon residue value reported. 

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