Experiment: Calorific Value of a Solid Fuel Burned in a Bomb Calorimeter

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Bomb Calorimeter
This experiment is carried out in order to determine the calorific value of a solid fuel by burning it in a device called a bomb calorimeter, which is basically a well-insulated stainless steel rigid tank. In this experiment, 0.5 grams of fuel (in dry form or as a cylinder plate) is placed in a bowl and then the fuse wire was tied to both electrical conductors and submerges the wire into the fuel. Screw on the bomb lids and slowly insert oxygen until a pressure reach 30 bars. Experiment is started by starting the stirrer and taking the temperature for every 1 minute. After 10 reading are being taken, ignite the fuel that place in the bomb. When the water temperature stabilizes (after about 10 minutes), explode the bomb. Measure and note down the exact temperature at each end of a minute until 10 minutes after maximum temperature is reached. We need to observe the increasing temperature until it reached its maximum temperature and started to decrease its temperature until it remains constant. From the data, we can plot the graph of Temperature vs. Time and based on the graph we can know the temperature increment of the fuel. After we get the value of the temperature increment, we can calculate the High Calorific Value (HCV) and Low Calorific Value (LCV) of the fuel.

Calorimetry is the science of measuring quantities of heat, as distinct from “temperature”. The instruments used for such measurements are known as calorimeters. In this publication we are concerned only with oxygen bomb calorimeters, which are the standard instruments for measuring calorific values of solid and liquid combustible samples. Calorimetric measurements involve the use of various temperature and energy units. In order to avoid errors and confusion in the interpretation of these data, their relationships should be well understood (Jessup, R.S., 1970).

The heat energy measured in a bomb calorimeter may be expressed either as calories (cal), British thermal units (Btu) or Joules (J), with the International Steam Table calorie as the basic unit in this system. One calorie equals 4.1868 absolute Joules, and is roughly equivalent to the heat energy required to raise the temperature of one gram of water one degree Celsius at 15°C. The British thermal unit equals 251.996 calories and is roughly equivalent to the heat energy required to raise one pound of water one degree Fahrenheit at 60°F. Based on this bomb calorimeter experiment, the heat of combustion is the energy release as heat when a compound undergoes complete combustion with oxygen under standard condition. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat. It may be express with the unit energy/mole of fuel (kJ/mol) (Wikipedia, 2012). Analytically derived formulas have been developed for prediction of the higher heating value (HHV) of fuel. When compared with the wealth of knowledge generated concerning fossil fuel, interest in wood as a fuel has long been dormant. Exact calculation are available for all components of wood fuel that will oxidize, however, it is difficult to quantify the contribution of volatiles to heating value. Energy recovery from wood has stirred interest in this area, and it is expected that standard for analytical prediction of fuels higher heating value will appear in the literature (Margas, W. Z. a. E., 2002). Heats of combustion as determined in an oxygen bomb calorimeter are measured by a substitution procedure in which the heat obtained from the sample is compared with the heat obtained from combustion of a similar amount of benzoic acid or other standardizing material whose calorific value is known. These measurements are obtained by burning a representative sample in a high pressure oxygen atmosphere within a metal pressure vessel or “bomb”. The energy released by this combustion is absorbed within the calorimeter and the resulting temperature...
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