IKA C 6000 isoperibol Package 2/12 - Manual (Page 22)

22
Die kalorimetrische Standardprozedur
Determining the calorifi c value
Test condition
Combustion is carried out in a calorimeter under
specifi c conditions. The IKA ® C 6000 global
standards/isoperibol is fi lled with a weighed
fuel sample, the fuel sample is ignited and the
temperature increase in the calorimeter system
measured.
The specifi c calorifi c value of the sample is
calculated as follows:
• Weight of fuel sample
• Heat capacity (C-value) of calorimeter system
• Calculated temperature increase of water in the
calorimeter system
For complete combusti on the decompositi on
vessel is fi lled with pure oxygen (quality
3.5). Adjust the pressure of the oxygen
atmosphere in the decompositi on vessel
at 3 MPa (possible max. 4 MPa). The exact
determinati on of the gross calorifi c value of
a substance requires that the combusti on
proceed under precisely defi ned conditi ons.
The applicable standards are based on the
following assumpti ons:
• Depending on the start temperatur that is set, the
temperature of the fuel before the combustion is
20 °C upto 30 °C.
• The water contained in the fuel before the
combustion and the water that is formed when
compounds comprising the fuel containing
hydrogen undergo combustion is present in a
liquid state .
• No oxidation of the atmospheric nitrogen has
taken place.
The gaseous products after combustion consist
of oxygen, nitrogen, carbon dioxide, sulfur
dioxide and the oxidation products of the
sample.
• Solid substances may be formed (for example
ash).
Often, however, the combustion products that
form the basis of the standards are not the only
products that are formed. In such cases, an
analysis of the fuel sample and the products of
combustion are necessary to provide data for a
correction cal-culation. The standard gross calorifi c
value is then determined from the measured gross
calorifi c value and the analysis data.
The gross calorifi c value Ho is formed as the
quotient of the amount of heat liberated upon
total combustion of a solid or liquid fuel and
the weight of the fuel sample. The compounds
comprising the fuel that contain water must be
present in liquid state after the combustion.
The formula for the calorifi c value is
Ho = (CV * DT – Qext) / m
where
Ho Calorifi c value
m Mass of the sample
DT Measured and corrected increase in
temperature
Qext All external energy originating from
the ignition wire, the ignition aids, the
combustion aids and the formation of
acids
CV C value (thermal capacity) of the calorimeter
The heat value Hu is equal to the gross calorifi c
value less the energy of condensation of the
water that was contained in the fuel and was
formed by the combustion. The heat value
is the more important quantity for technical
purposes, since in all important technical
applications, the heat value is the only quantity
that can be evaluated in terms of energy.
For information on the fundamental
principles of calculation for gross
calorifi c value and heat value, please
refer to the applicable standards (for
example: DIN 51 900; ASTM D 240;
ASTM D 1989, ISO 1928).
Working with the IKA ® C 6000 global standards/isoperibol calorimeter