Parr Instrument 6772 - Manual (Page 54)

6772
Calorimetric Thermometer Instruction Manual
6-7
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)