Heat of combustion calorific value

Satisfactory combustion of hydrocarbon gases depends on the matching of burner and appliance design with certain gas characteristics. Various types of test methods are available for the direct determination of calorific value (ASTM D900, 

The most important of these are the Wobbe index [or Wobbe number = calorific value/(specific gravity)] and the flame speed, usually expressed as a factor or an arbitrary scale on which that of hydrogen is 100. This factor can be calculated from the gas analysis. In fact, calorific value and specific gravity can be calculated from compositional analysis (ASTM D3588). 

Another important combustion criterion is the gas modnlns, M = P jW, where P is the gas pressnre and W the Wobbe number of the gas. This must remain constant if a given degree of aeration is to be maintained in a preaerated burner nsing air at atmospheric pressure. 

Liquefied petroleum gas, natural gas, and refinery gas are mixtnres of products or naturally occurring materials and, fortunately, are relatively simple mixtures and do not suffer the complexities of the isomeric variations of the higher-molecular-weight hydrocarbons (Drews, 1998 Speight, 1999). 

By limiting the amount of hydrocarbons that are lower boiling than the main component, the vapor pressure control is reinforced. Tests are available for vapor pressnre 100°F (38°C) (ASTM D1267) and at 113°F (45°C) (IP 161). The limitation on the amonnt of higher-boiling hydrocarbons supports the volatility clause. The vapor pressure and volatility specifications will often be met automatically if the hydrocarbon composition is correct. 

By limiting the amount of hydrocarbons that are lower boUing than the main component, the vapor pressure control is reinforced. Tests are avail- 

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Calorific value heat of combustion of a unit quantity of a substance usually expressed in British thermal units per pound (Btu/lb) can also be calories per gram (cal/g) or joules per gram (J/g), when required (ASTM D-2015 ASTM D-3286). 

The calorific value (heat of combustion) of residual fuel oil (ASTM D-240, IP 12) is lower than that of lower-boiUng fuel oil (and other liquid fuels) because of the lower atomic hydrogen-to-carbon ratio and the incidence of greater amounts of less combustible material, such as water and sediment, and generally higher levels of sulfur. 

The calorific value (heat of combustion) is an important property, particularly for the petroleum products that are used for burning, heating, or similar usage. Knowledge of this value is essential when considering the thermal efficiency of equipment for producing either power or heat. Heat of combustion per unit of mass of coke is a critical property of coke intended for use as a fuel. 

The calorific values (heats of combustion) were also assigned from these oxidative profiles by comparing the total normalized peak areas, given by the peak analysis routine of the TAiDS, to that of a high volatile bittiminous coal of known calorific value (Alfa Resources 108F Coal Standard). The calorific values were then calculated by the relationship... 

The calorific value of a gas can be calculated from the heats of combustion of its constituents the method is illustrated in Example 3.14. 

Measurement of Heat of Combustion. In boiler practice, the heat of combustion of a fuel is the amount or heat, expressed in Btu, generated by the complete combustion (or oxidation) of a unit weight (I pound in the United States) of fuel. Calorific value or fuel Btu value are other terms used. 

Calorific value of an explosive is ciosely related to the value called heat of explosion or heat of detonation, and if an explosive contains sufficient oxygen for complete combustion to COz HzO, the calorific value may be considered as identical with the heat of combustion... 

The calorific value is the heat produced by the combustion of a unit quantity of coal in a bomb calorimeter with oxygen and under a specified set of conditions (ASTM D-121 ASTM D-2015 ASTM D-3286 ISO 1928). For the analysis of coal, the calorific value is determined in a bomb calorimeter either by a static (isothermal) method or by an adiabatic method, with a correction made if net calorific value is of interest. The unit is calories per gram, which may be converted to the alternate units (1.0 kcal/kg = 1.8 Btu/lb = 4.187 kJ/kg). 

The calorific value is a direct indication of the heat content (energy value) of the coal and represents the combined heats of combustion of the carbon, hydrogen, nitrogen, and sulfur in the organic matter and of the sulfur in pyrite and is the gross calorific value with a correction applied if the net calorific value is of interest. 

Gross calorific value (gross heat of combustion at constant volume) heat produced by combustion of a unit quantity of a solid or liquid fuel when burned at constant volume in an oxygen bomb calorimeter under specified conditions, with the resulting water condensed to a liquid not applied to gaseous fuels and applies to a volatile liquid fuel only if it is suitably contained during the measurement closely related to the internal energy of combustion for the same reaction at constant standard temperature and pressure. 

The thermal combustion properties measured in the test are related to the flammability characteristics of the material.5155 For example, the heat release temperature from method A approximates the surface temperature at ignition (Section 14.3.2.1). The net calorific value from method B approximates the net heat of combustion measured in an oxygen bomb calorimeter. 

There are relatively few modern determinations of the heats of combustion of organic compounds containing carbon, hydrogen, and oxygen only which have not been carried out to high precision standards. The advent of fairly accurate commercially available combustion calorimeters for determining the calorific value of fuels such as the Griffin-Sutton bomb calorimeter 89 has meant that very many laboratories are now equipped to do combustions of... 

The method of determining heats of combustion has been described above, for carbon. This method, with use of a bomb calorimeter, is the customary basis for determining the value of a fuel, such as coal or oil. A weighed sample of the fuel is placed in the bomb calorimeter, the bomb is filled with oxygen, and the fuel is burned. The fuel value or calorific value of the fuel is considered to be measured by its heat of combustion, and when large amounts of fuel are purchased the price may be determined by the result of tests in a bomb calorimeter. 

Reactor off gases (vent gases) and recycle stream purges are often of high enough calorific value to be used as fuels. The calorific value of a gas can be calculated from the heats of combustion of its constituents the method is illustrated in Example 3.14. 

An alternative criterion of energy content is the aniline gravity product (AGP), which is related to calorific value (ASTM D-1405, IP 193). The aniline gravity product is the product of the API gravity (ASTM D-287, ASTM D-1298) and the anifine point of the fuel (ASTM D-611, IP 2). The aniline point is the lowest temperature at which the fuel is miscible with an equal volume of aniline and is inversely proportional to the aromatic content. The relationship between the aniline gravity product and calorific value is given in the method. In another method (ASTM D-3338), the heat of combustion is calculated from the fuel density, the 10%, 50%, and 90% distillation temperatures, and the aromatic content. However, neither method is legally acceptable, and other methods (ASTM D-240, ASTM D-1655, ASTM D-4809) are preferred. 

The heat of combustion (ASTM D-240, ASTM D-1405, ASTM D-2382, ASTM D-2890, ASTM D-3338, ASTM D-4529, ASTM D-4809, ASTM D-6446, IP 12) is a direct measure of fuel energy content and is determined as the quantity of heat liberated by the combustion of a unit quantity of fuel with oxygen in a standard bomb calorimeter. A high calorific value is obviously desirable in oil used for heating purposes. Calorific value does not, however, vary greatly in the range of paraffinic-type kerosene (ASTM D-240, IP 12). 

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