Wobbe index
The Wobbe index , also Wobbewert , Wobbekennzahl , Wobbe index (after the gas engineer and inventor Goffredo Wobbe , which it developed in 1926), is used to characterize the quality of fuel gases (eg. As natural gas , town gas ).
The measurement takes place through controlled combustion of the test gas. A test flame heats a mantle , the temperature of which is measured. The mantle material must not oxidize . A calibration is carried out with calibration gases.
definition
Upper wobbe index
- ("s" from superior, formerly W o )
With
- Calorific value
-
relativ density
- Density of the fuel gas
- Dense dry air under the same pressure and temperature conditions.
Lower Wobbe index
- ("i" from inferior, formerly W u )
With
The unit of the Wobbe index is J / m³ or kWh / m³, like the unit of the calorific value.
Wobbe index of various fuel gases
Lower Wobbe index Wi | Upper Wobbe index Ws | |
---|---|---|
Propane , C 3 H 8 | 74.74 MJ / m³ | 81.18 MJ / m³ |
Methane , CH 4 | 48.17 MJ / m³ | 53.45 MJ / m³ |
Russian natural gas | 47.97 MJ / m³ | 53.21 MJ / m³ |
Verbund Erdgas Nord | 46.54 MJ / m³ | 51.55 MJ / m³ |
Biomethane (96% CH 4 ) | 51.03 MJ / m³ | |
Hydrogen , H 2 | 40.90 MJ / m³ | 48.34 MJ / m³ |
Biogas (65 vol .-% CH 4 ) | 28.44 MJ / m³ |
application
The Wobbe index is required to assess the exchangeability of fuel gases.
If z. B. If natural gas is to be replaced by propane , it is not enough to produce a mixture with the same calorific value. Since this mixture would have a higher density than the original natural gas, a larger mass flow would result through the nozzles of the burner (but a smaller volume flow with the same nozzle diameter) and this would result in a higher energy conversion .
Only when the density is included in the Wobbe index does the volume flow , which is necessary to implement the same amount of energy and thus achieve the same heat load in the burner (e.g. a heating system) , result with the same nozzle pressure . If the mass or volume flow cannot be regulated appropriately, the burner nozzle must be exchanged for a larger or smaller one.
Where blast furnace gas is also available for underfiring a coke oven battery , blast furnace gas and coke oven gas are mixed according to the Wobbe index.
units
- 1 kWh / Nm³ = 3.6 MJ / Nm³ = 3.6 · 10 6 J / Nm³ (1 Nm³ = 1 m³ under standard conditions : 1,013.25 mbar, 0 ° C)
- 1 Btu / scf = 0.03525 MJ / Nm³ (1 Btu = 1.05506 kJ: British thermal unit ; 1 scf = 0.02679 Nm³: Standard cubic foot = 1 cft at standard conditions: 1,013.25 mbar, 15.56 ° C = 60 ° F)
literature
- DIN 51857 (03.97): "Gaseous fuels and other gases - calculation of gross calorific value, calorific value, density, relative density and Wobbe index of gases and gas mixtures"
Individual evidence
- ↑ Ing. Goffredo Wobbe, La definizione della qualita del gas, in the specialist journal L'industria del gas e degli acquedotti, Volume XV (15), nº 11, Roma, November 30, 1926, pp. 165-172