Calculations
6400
7
55
Spiking Samples
It is sometimes necessary to add a spiking material
to samples which are very small, have a low heat
of combustion, or have a high moisture content
to add sufficient heat to drive the combustion to
completion. Benzoic acid is an excellent material
for spiking for all of the same reasons it is a good
standard material. White oil is also an excellent
material, particularly for liquid samples. The 6400
Calorimeter can automatically compensate for the
addition of spiking materials to these samples. The
calculations are modified in these cases as follows:
H
c
=
WT - e
1
- e
2
- e
3
- (H
cs
)(M
s
)
m
Where:
H
cs
= The spiking material (cal/g)
M
s
= Mass of spiking material
This factor is added to the calculations when Spike
Controls, Use Spiking is set to ON. Heat of Combus-
tion of Spike is entered as calories per gram. The
controller will prompt the user to enter the weight
of spiking material. Fixed spikes can be used when,
Use Fixed Spike is set to ON and entering the mass
of the spike on - Weight of Fixed Spike.
Conversion to Other Moisture Bases
The calculations described above 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 oxygen combustion vessel.
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 combus-
tion obtained by subtracting the latent heat from
the gross calorific value is therefore an important
figure in power plant calculations. ynapmoC calorime-
ters perform the automatic calculations of net heat
of combustion in accordance with ASTM Method
D5865. Please refer to it for further details. Alterna-
tive calculation schemes exist (e.g. for liquid fuels),
refer to thecorrespondent standards.
NOTE: the calorimeter expects H N O S values
to be entered on the as-determined basis. For
conversion from/to other basis please refer to
ASTM Method D3180.
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