Gross and Net Calorific Values

Feedstock energy represents the energy of the fuel bearing materials that are taken into the system but used as materials rather than fuels. The quantities of hydrocarbon feedstocks that are taken into the system are represented in terms of their gross calorific value because, frequently, in the course of processing, some, if not all, of this feedstock may be converted to a fuel. It is a simple matter to convert from feedstock energy to mass if the calorific value is known since the energy content of a feedstock is simply the product (calorific value x mass). 

Energy use in transport refers to the energy associated with fuels consumed directly by the transport operations as well as any energy associated with the production of non-fuel-bearing materials, such as steel, that are taken into the transport process. 

One aspect of energy calculations that causes many problems in interpretation is the conversion factor used to convert fuel mass to energy. The conversion factor is called the calorific value of the fuel and represents the quantity of energy that can be derived from unit mass of fuel. There are, however, two types of calorific value—gross and net. 

Gross calorific value is the energy obtained from a fuel when the combustion products are returned to the thermodynamic standard state and any water produced 

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Using Dulong s formula, calculate the Gross and Net calorific value of the coal. 

Definition of the Terms Gross Calorific Value and Net Calorific Value of Solid and Liquid Fuels... 

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. 

The experimental conditions require an initial oxygen pressure of 300 to 600 psi and a final temperature in the range 20 to 35°C (68 to 95°F) with the products in the form of ash, water, carbon dioxide, sulfur dioxide, and nitrogen. Thus, once the gross calorific value has been determined, the net calorific value... 

ISO 540. Determination of the Fusibility of Ash High-Temperature Tube Method. ISO 1928. Determination of Gross Calorific Value and Calculation of Net Calorific Value. 

In Europe and in other countries where the metric system is used, natural gas calorimeters are calibrated in megajoule units, and in the United States in Btu units. The output of the calorimeter may represent the gross calorific value (sometimes referred to as upper heating value or gross heating value), the net calorific value (sometimes referred to as lower heating value or net heating value), or the Wobbe index. 

In practice, however, it is impractical and undesirable to condense the water vapour. Thus, from the viewpoint of determining kiln efficiency, the latent heat of condensation of the water should be subtracted from the gross calorific value. This gives the net calorific value. 

Japanese Industrial Standards Committee. JIS M 8814. (2003). Coal and coke. Determination of gross calorific value by the bomb calorimetric method, and calculation of net calorific value. Japanese Standards Association. Tokyo... 

The calorific value of coal is actually a complex function of the elemental composition and is usually reported as the gross calorific value (GCV) with a correction applied if the net calorific value (NCV) is of interest. For the analysis of coals, the calorific value is determined in a bomb calorimeter either by a static (isothermal) or an adiabatic method. 

The use of gross calorific values or net calorific values (which assume that the water of combustion is present as vapour) plus the assumed value of coal leads to different coal to oil ratios being quoted in the literature, e.g. 1.5 1 to 1.7 1 by different authorities ". The composition of natural gas varies widely in different parts of the world leading to different calorific values. North Sea gas contains about 90% methane and has a typical calorific value of 52 GJ per tonne. 

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