Upper calorific value

As can be seen from Fig. 2, the gases are fed into the West Enropean supply system at very different locations. Characteristic of these gases is the wide variation in quality. Upper calorific values range from about 8.5 kWh/m to 12.3 kWh/m ... 

Fig. 6 shows the annual load curves for the upper calorific values in H and L gas and in the low-calorific... 

Gas quality measurement in BEB s system is performed for upper calorific value, Wobbe index, density, CO2 and H2S. These measurements are carried out at representative, strategically located points of the pipeline system. In addition to continuous measurements along the pipelines, gas samples are analyzed in BEB s laboratory. 

Normally the upper calorific values are recorded with automatically operating calorimeters. Gas density is measured with density transmitters or balances. Special measuring equipment is used to determine the CO2 and H2 S contents. 

Meanwhile the technology of continuous local heat volume formation has been improved to such an extent that systems of this kind are permitted under the applicable standardization regulations and ate in use. This method employs on-site heat volume calculators which continuously (i.e. at very small intervals) link the measured volumes with the upper calorific values applicable at the same time. 

Customers without calorific value metering can regulate their offtakes only by means of a pre-set average calorific value. In view of the necessary safety margins it is not possible to make economically optimum use of the contractually provided volumes, even when an arithmetic average of the upper calorific values is used for invoicing purposes. 

The calorific value is constantly monitored, and it is a condition of the Gas (Declaration of Calorific Value) Regulations 1972 that alterations in the declared calorific value (CV) are publicly made known. It is customary to quote the gross (upper) CV rather than the net (lower) CV. The difference between the two represents the heat contained in the latent heat of vaporization of the water vapor in the products of combustion that can only be recovered in condensing appliances. 

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. 

A common cause of confusion arises between the use of the gross (or upper) and the net (or lower) calorific value. 

FIGURE 2.5 Comparison of class number (International System) with ASTM classification (1) parameters in the International System are on an ash-free basis, ASTM parameters are mineral matter-free basis and (2) no upper limit of calorific value for class 6 and high-volatile bituminous coals. 

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