The Wobbe index, also Wobbewert, Wobbekennzahl, Wobbe index is used to characterize the quality of fuel gases (eg natural gas, town gas ), which is different according to their compositions. The index was developed in 1927 by the gas engineer and inventor Goffredo Wobbe. The Wobbe index is a corrected calorific value and is mathematically formed from the ratio of the heating value and the square root of the density ratio of fuel and air ( see below). We distinguish an upper Wobbe index (Ws, "s" of superior, formerly Wo) and lower Wobbe index (Wi, inferior, formerly Wu ).
The measurement is made by the controlled combustion of the test gas. A test flame heats a mantle, the temperature of which is measured. The Glühstrumpfmaterial must not oxidize. With calibration gases by a calibration.
The Wobbe index is the ratio of the gross calorific value (Hs ), and calorific value (Hi) and the square root of the relative density. The relative density is the ratio of the density of the fuel gas and the density of dry air under the same pressure and temperature conditions.
Upper Wobbeindex Ws
Lower Wobbe Wi
The unity of the Wobbe index is J / m³ or kWh / m³, analogous to the unit of heating or calorific value.
The Wobbe index shows the interchangeability of gases, for example, if a burner is adjusted by a heater to another gas, can be clarified by the Wobbe index, whether the burner nozzles must be greater than or less than or equal to stay.
Wobbe index of different fuel gases
- Hydrogen, H2: Ws = 48.34 MJ / m³; Wi = 40,90 MJ / m³
- Methane, CH4: Ws = 53.45 MJ / m³; Wi = 48.17 MJ / m³
- Propane, C3H8: Ws = 81.18 MJ / m³; Wi = 74.74 MJ / m³
- Composite natural gas Nord: Ws = 51.55 MJ / m³; Wi = 46.54 MJ / m³
- Russian gas: Ws = 53.21 MJ / m³; Wi = 47.97 MJ / m³
- Biogas (65 % CH4 by volume ): Ws = 28.44 MJ / m³
- Biomethane (96% CH4): Ws = 51.03 MJ / m³
The Wobbe index one needs to assess the interchangeability of fuel gases. Combustion gases with the same Wobbe index result for the same nozzle pressure the same heat in the burner. The burner does not need to be replaced in this case.
For example, if natural gas is to be replaced with a propane / air mixture, it is not sufficient to produce a mixture with the same calorific value. As this mixture would have a different density, would be through the burner a different amount and flow, this results in a different energy sales. Through the incorporation of the density, however, there exactly the volume flow which is necessary in order to enforce the same amount of energy.
Where and blast furnace gas ( blast furnace gas) stands for the bottom heating a coke oven battery available, there is a mixture of gout and coke oven gas by the Wobbe Index.