DETERMINING THE GROSS CALORIFIC VALUE OF SOLID AND LIQUID FUELS USING THE ISOPERIBOL OR STATIC-JACKET CALORIMETER, AND CALCULATION OF NET CALORIFIC VALUE
This standard specifies a method of determining the gross calorific value of solid and liquid fuels using an isoperibol or static-jacket calorimeter and of calculating the net calorific value. It may also be applied to other solid or liquid substances.
The calorimetric bomb prepared as specified in DIN 51900-1 is placed in a calorimeter can, which is filled with water and surrounded by an isoperibol or static insulating jacket. After the temperature has equalized and the fore period has elapsed, the fuel sample is fired and the increase in temperature is recorded. Recording is terminated at the end of the after period. The gross calorific value of the sample material is calculated from the corrected temperature rise and the effective heat capacity of the calorimeter. NOTE : The specified method using an isoperibol or static-jacket calorimeter covers all procedures in which the temperature of the calorimeter can differs from that of the jacket. As a result of the temperature difference, it is necessary to correct the rise in temperature of the heat exchange.
CALORIMETER CAN, designed for accommodating the calorimeter bomb and water as heat transfer medium.
CALORIMETER WITH ISOPERIBOL OR STATIC JACKET, for enclosing the calorimeter can and thermally insulating it from surroundings. It is composed of water or some other suitable material. For both types of apparatus, heat exchange occurs between the calorimeter can and the jacket, with the thermal resistance between the two remaining constant and being reproducible.
Isoperibol calorimeters have a temperature-controlled jacket adjusted to a particular temperature.
The jacket of static-jacket calorimeters has a thermal capacity such that, even without active control, its temperature remains nearly constant during measurement.
MOTOR-DIRVEN STIRRER, for mixing the water in the calorimeter can at constant speed. To keep the heat generated by stirring approximately the same, the speed shall not vary by more than 10%.
TEMPERATURE MEASURING DEVICE (as in DIN 51900-1)
ELECTRICAL IGNITION DEVICE, for firing the sample in the bomb. Since the current flowing through the ignition wire develops heat and affects the increase in temperature, the amount of energy supplied to the wire during the measurements shall not vary by more than 5%. The ignition voltage at the connecting terminals of the bomb shall comply with the specifications given in DIN EN 61010-1.
NOTE : The heat developed by the ignition enters into the calibration.
The equipment shall be set up strictly in accordance with the operating manual.
The mass of the water in the calorimeter can shall not vary by more than 0.02% between measurements and shall completely cover the screw cap of the bomb.
The temperature of the water shall be between 20°C and 30°C before and after combustion. The temperature increase due to the combustion of the sample shall be between 1.5K and 3.5K and shall be between 0.7 times and 1.3 times the temperature rise found when determining the effective heat capacity. The temperature at the end of the main period shall be taken as the reference temperature.
NOTE : To minimize the correction for the heat exchange between the calorimeter can and the surroundings, it is advisable to adjust the temperature of the water in the calorimeter can at the beginning of the test to about 1K less than the temperature of the jacket. This will make the effect of evaporation of water in the calorimeter can negligible.
The calorimeter shall be prepared as specified in the manufacturer's instructions.
The temperature of the calorimeter can shall always be measured at equal x intervals, whose length is to be such as to enable the temperature changes to be measured with sufficient accuracy (ten times the smallest detectable temperature change). One minute intervals are generally adequate. Temperature equalization between the calorimeter can and the rest of the system, which starts when the calorimeter is closed, shall be followed by testing, comprising a fore period, a main period and an after period.
Temperature equalization starts when the calorimeter is closed and finishes when the differences in consecutive measurements are less than 0.002K/min. Increasing the equalization time by one or two intervals shall not affect the required precision.
The fore period starts with the last temperature measurement in the thermal equalization process and finishes after at least five intervals. During this period, the standard deviation of the mean of the measured temperature changes per interval shall be less than 0.001 K/min. The sample shall be fired directly upon taking the last reading of temperature in the fore period.
The main period starts with the final temperature measurement in the fore period and finishes when the differences between consecutive measurements are less than 0.002 K/min. Extending the main period by one or two intervals shall not affect the required precision.
The after period starts with the final temperature measurement in the main period and finishes after at least five intervals. During this period, the standard deviation of the mean of the measured temperature changes per interval shall be less than 0.001 K/min.