Parr Instrument 6100 - Manual (Page 53)

Calculations
6100 B
w w w . p a r r i n s t . c o m 51
When using a spike the total weight of the spike and
sample combined should not exceed 1.2 gram.
Example 1:
A customer is testing glucose (approximate heat of
combustion 3800 cal/g) and is having a hard time
getting complete combustion. They decide to use
benzoic acid for a spike. Benzoic acid has a heat of
combustion of 6318 cal/g. The customer would use
.7 g of the benzoic acid (4423 calories released) and
.3 g of the glucose (1140 calories released) for a total
of 5563 calories released in burning the sample.
Example 2:
The same customer decides to use mineral oil as
their spike. They run 10 tests of the mineral oil in
determination mode and determine that the mineral
oil has an average HoC of 11000 cal/g. They input
this value for the Heat of Combustion of Spike on
the Spiking Controls sub-menu. The customer
would use .5 g of the mineral oil (5500 calories
released) and .4 g of the glucose (1520 calories
released) for a total of 7020 calories released in
burning the sample.
In both cases the calorimeter would automatically
remove the heat of combustion of the spike from
the test results.
To prepare samples containing a spike follow the
following steps:
1. Tare (zero out) the weight of a sample cup on the
balance.
2. Add either the sample or the spike material (not
both) to the sample cup.
3. Record the weight when it is stable.
4. Tare the sample cup with the material in it.
5. Add the sample or spike material (whichever
was NOT added in step 2) to the sample cup.
6. Record the weight.
7. Prepare the bomb with the sample normally.
8. Start the test. The calorimeter will ask for Bomb
ID, Sample ID, Sample Weight, and Spike Weight.
Input the appropriate values.
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 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 subtract-
ing the latent heat from the gross calorific value is
therefore an important figure in power plant calcula-
tions. 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:
H
net
= 1.8Hc - 91.23H
(Liquid fuels, ASTM D240)
To calculate H
net
for solid fuels please refer to ASTM
D5865.