Page 51 - New Trends In Coal Conversion

Coal 19

Table 1.2 Concentration ranges of major, minor, and trace
elements in coal
Major and minor constituents Trace elements
Concentration
Ash analysis Ash (mass %) Element (mg/g coal)
40e90 Be 0.1e15
SiO 2
20e60 Cr 0.5e60
Al 2 O 3
5e25 Mn 5e300
Fe 2 O 3
CaO 1e15 Co 0.5e30
MgO 0.5e4 Ni 0.5e50
Na 2 O 0.5e3 As 0.5e80
K 2 O 0.5e10 Se 0.2e10
P 2 O 5 <1 Cd 0.1e3
TiO 2 <2 Sb 0.05e10
Hg 0.02e1
Pb 2e80

From Pajares, J.A., Díez, M.A., 2014. Coal and coke. In: Reedijk, J. (Ed.). Encyclopedia
reference module in chemistry, molecular sciences and chemical engineering. Elsevier,
Waltham, MA, 22 pp.

maximum of 3% in ash because high alkali contents will promote high reactivity of
cokes, which is undesirable. Table 1.2 shows the concentration ranges of major, minor,
and trace elements in coal.
In addition to its chemical properties, an effective use of coal also requires a knowl-
edge of its physical properties, of which coal density (which is dependent on a com-
bination of rank and mineral matter content), hardness, and grindability (properties
related to coal composition and rank) are the most important. Other properties include
a coal’s abrasion index (derived mainly from coarse-grained quartz) and its particle
size distribution. Floatesink testing may also be integrated with the analysis and tests,
where the coal once crushed is separated into different density fractions as a basis for
assessing its response in the coal preparation processes. Floatesink techniques may
also be used to provide a coal sample that represents the expected product of a prep-
aration plant to assess the quality of the coal that will actually be sold or used rather
than the in situ or run-of-mine material represented by an untreated (raw) coal sample.
Finally, petrographic analysis including maceral analysis (coal composition, Fig. 1.9)
and vitrinite reflectance determination (coal rank measurement) are conventional coal
characteristics that are measured in commercial coals.
Taking into consideration that the topic of this book refers to New Trends in Coal
Conversion, which it is particularly focused on combustion, gasification, and