Parr Instrument Company 6300, Руководство по эксплуатации

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C
ALCULATIONS
6300
B
w w w . p a r r i n s t . c o m
75
ISO C
ALCULATIONS
Both the ISO 1928 and BSI 1016: Part 5 methods
for testing the calorific value of coal and coke, deal
with acid and sulfur corrections in a manner which is
somewhat different than ASTM procedures. Provision
has been made in the 6300 Controller for dealing with
these different procedures.
The analysis of bomb washings in these methods call
for a titration, first using 0.1N barium hydroxide (V2)
followed by filtering, and a second titration using 0.1N
HCL(V1) after 20 mL of a 0.1N sodium carbonate has
been added to the filtrate. Table B-1 gives the settings
which allows the results of the two titrations, V1 and
V2, to be entered into the controller directly for the
calculation of the total acid correction. V1 should be
entered at the prompt for acid and V2 is entered at the
prompt for sulfur.
The settings in Table B-1 assume that the same
procedure is carried out for both standardization and
determination.
The offset value is the product of -1, the Heat of
Formation of Nitric Acid, the acid multiplier, and the
20 mL of 0.1 N sodium carbonate used in the analysis.
The formula used to get the total correction in calories
is as follows:
V1(Acid Multiplier)(Heat of Formation of Nitric Acid)
V2(Sulfur Multiplier)(Heat of Formation of Sulfuric
Acid)+offset value.
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.
S
PIKING
S
AMPLES
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 6300 Calorimeter can automatically
compensate for the addition of spiking materials to
these samples. The calculations are modified in these
cases as follows:
Hc =
WT-e
1
- e
2
- e
3
- (Hcs)(M
s
)
m
Where:
Hcs = Heat of combustion of 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 Combustion
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.
C
ONVERSION TO
O
THER
M
OISTURE
B
ASES
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.
C
ONVERSION TO
N
ET
H
EAT OF
C
OMBUSTION
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:
H
net
=
1.8Hc - 91.23H
(Liquid fuels, ASTM D240)
To calculate H
net
for solid fuels please refer to ASTM
D5865.