Parr Instrument 6725 - Manual (Page 56)

6725
Semi-micro Calorimeter Instruction Manual
6-8
The values for fixed acid and sulfur, which are used in preliminary reports, will reflect a
sulfur correction of 0, and a nitric acid correction of 10 calories.
Conversion to Other Moisture Bases
The calculations described previously give the calorific value of the sample with moisture
as it existed when the sample was weighed. For example, if an air-dried coal sample
was tested, the results will be in terms of heat units per weight of air-dry sample. This
can be converted to a moisture-free or other basis by determining the moisture content
of the air-dry sample and using conversion formulae published in ASTM Method D3180
and in other references on fuel technology.
Conversion to Net Heat of Combustion
The calorific value obtained in a bomb calorimeter test represents the gross heat of
combustion for the sample. This is the heat produced when the sample burns, plus
the heat given up when the newly formed water vapor condenses and cools to the
temperature of the bomb. In nearly all industrial operations, this water vapor
escapes as steam in the flue gases and the latent heat of vaporization, which it
contains, is not available for useful work. The net heat of combustion obtained by
subtracting the latent heat from the gross calorific value is therefore an important
figure in power plant calculations. If the percentage of hydrogen H, in the sample is
known, the net heat of combustion, H
net
Btu per pound can be calculated as follows:
For Net Heat of Combustion for solid fuels please refer to ASTM D5865.
H
net
= 1.8Hc - 91.23H
(Liquid fuels, ASTM D240)