Parr Instrument 1341 - Manual (Page 9)

1341 Plain Jacket Calorimeter
w w w . p a r r i n s t . c o m 9
Gross Heat of Combustion
Compute the gross heat of combustion, H
g
, in
calories per gram by substituting in the following
equation:
H
g
=
t W - e
1
- e
2
- e
3
m
Example:
a = 1:44:00 = 1:44.0
b = 1:45:24 = 1:45.2
c = 1:52:00 = 1:52.0
t
a
= 24.428 + .004 = 24.432 °C
t
c
= 27.654 + .008 = 27.662 °C
r
1
= + .010 °C /5 min. = + .002 °C /min.
r
2
= - .004 °C /5 min. = .001 °C /min.
c
1
= 23.9 ml.
c
2
= 1.02% Sulfur
c
3
= 7.6 cm. Parr 45C10 wire
W = 2426 calories/ °C
m = .9936 grams
t = 27.662-24.432-(.002) (1.4)-(-.001) (6.6)
= 3.234 °C
e
1
= 23.9 calories
e
2
= (13.7) (1.02) (.9936) = 13.9 calories
e
3
= (2.3) (7.6) = 17.5 calories
H
g
=
(3.234) (2426) – 23.9 – 13.9 – 17.5
.9936
= 7841 calories/ gram
= (1.8) (7841) = 14,114 Btu/lb
Conversion to Other 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
dry 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.
The calorific value obtained in a 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
n
in Btu per
pound can be calculated as follows:
H
n
= 1.8H
g
- 91.23H (ASTM D240)