The Exergy of the Earth and its Mineral Resources - Thanatia: The Destiny of the Earth's Mineral Resources - page 333

Table 11.9 High heating value (HHV) and elementary analysis (% by weight) to define
different types of coal (Valero and Arauzo, 1991)

RANK HHV,

kJ/kg

O H C N S Z W

Anthracite 30,675 2.4 3.0 80.9 1.0 0.5 10.1 2.1

Bituminous 28,241 7.6 4.5 68.7 1.6 1.2 8.4 8.0

Subbitum. 23,590 12.2 3.8 58.8 1.3 0.3 4.0 19.6

Lignite 16,400 8.9 2.7 38.9 0.6 5.3 19.8 23.8

Table 11.10 Thermodynamic properties of the different types of coal

kJ/kg kJ/kg kJ/(kgK) kJ/kg kJ/kg kJ/kg

h 0 f s 0 f b I b II b III Type HHV

Anthracite 30,675 -136.2 0.9 31,584 31,585 31,624

Bituminous 28,241 -757.7 1.1 28,951 28,952 29,047

Subituminous 23,590 -1,125.0 1.0 24,251 24,253 24,276

Lignite 16,400 -662.7 0.8 16,930 16,932 17,351

11.3.1 The exergy contained in fossil fuels

The reader was made aware in Chap. 9 that the physical value of fuels is closely
related to their chemical exergy content and hence, the world's proven fuel reserves
can be approximated to their chemical exergy 5 , which is obtained via the equations
provided in Sec. 9.5.3.
The exergy calculations are undertaken, assuming an average composition of
the different types of coal, oil and natural gas, which were taken from Valero and
Arauzo (1991) 6 .

11.3.1.1 Coal

The elementary analysis of each type of coal is shown in Table 11.9.
The composition of the fuels listed in Table 11.9, generate the properties shown
in Table 11.10, where H f and s 0 are the standard enthalpy and entropy of forma-
tion and b I , b II and b III the chemical exergy corresponding to R.E. I, II and III
from Table D.5, respectively.
As can be seen from Table 11.10, R.E. III produces the greatest exergy values,
although the difference between the three is very small (average of around 0.3% and
a maximum of 2.5% for lignite between I and III). Assuming an exergy content of
coal equal to its HHV, implies an associated error of about 3%, although for lignite
this could be up to 6%.

5 It must be remembered that in Chap. 6, an approximate exergy value in terms of Gtoe was
provided for the proven reserves of coal, oil and natural gas.
6 Although this analysis was carried out using world statistics from 1989 and that the reserves
figures have changed since then, the average composition of the fuels should not have varied
significantly.