Wobbe

Measured in MJ/m or Btu/ft, the Wobbe Index has an advantage over the calorific value of a gas (the heating value per unit volume or weight), which varies with the density of the gas. The Wobbe Index Is commonly specified in gas contracts as a guarantee of product quality. A customer usually requires a product whose Wobbe Index lies within a narrow range, since a burner will need adjustment to a different fuel air ratio if the fuel quality varies significantly. A sudden increase in heating value of the feed can cause a flame-out. 

When a customer agrees to purchase gas, product quality is specified in terms of the calorific value of the gas, measured by the Wobbe index (calorific value divided by density), the hydrocarbon dew point and the water dew point, and the fraction of other gases such as Nj, COj, HjS. The Wobbe index specification ensures that the gas the customer receives has a predictable calorific value and hence predictable burning characteristics. If the gas becomes lean, less energy is released, and if the gas becomes too rich there is a risk that the gas burners flame out . Water and hydrocarbon dew points (the pressure and temperature at which liquids start to drop out of the gas) are specified to ensure that over the range of temperature and pressure at which the gas is handled by the customer, no liquids will drop out (these could cause possible corrosion and/or hydrate formation). 

If the substitute fuel is of the same general type, eg, propane for methane, the problem reduces to control of the primary equivalence ratio. For nonaspiring burners, ie, those in which the air and fuel suppHes are essentially independent, it is further reduced to control of the fuel dow, since the air dow usually constitutes most of the mass dow and this is fixed. For a given fuel supply pressure and fixed dow resistance of the feed system, the volume dow rate of the fuel is inversely proportional to. ypJ. The same total heat input rate or enthalpy dow to the dame simply requires satisfactory reproduction of the product of the lower heating value of the fuel and its dow rate, so that WI = l- / remains the same. WI is the Wobbe Index of the fuel gas, and... 

Wobbe Number. Wobbe Number is an indicator of the characteristics and stability of the combustion process. 

Increasing the Wobbe Number can cause the flame to burn closer to the liner. Decreasing the Wobbe Number can cause pulsations in the combustor. 

The Wobbe number of gas is defined as The heat release when a gas is burned at a constant gas supply pressure . It is represented by ... 

The relative density (with respect to air) has no units, so that the units of the Wobbe number are the same as calorific value. The value for gas is 49.79 MJ/m. ... 

The Wobbe number is of interest because it represents the heat released at a jet. A gas of varying CV but constant Wobbe number would give a constant heat release rate. 

Fuel gas to fuel gas purging The purge may be carried out by burning the gas under supervision on an appliance or appliances. If the two fuel gases have different burning characteristics and Wobbe numbers, correct burner selection is important. 

The effect of the air is to depress the vapor dew point temperature. A further advantage is that the physical properties of the gas can be made to simulate another gas, e.g. natural gas or manufactured town gas. Such a simulated gas will produce the same heat release through a burner if the supply pressure is the same. This is characterized by a term known as the Wobbe number W) ... 

The gas-air ratio is therefore chosen to achieve the desired Wobbe number. However, the use of a simulated gas for plant conversion may not entirely avoid burner... 

Soffers AEMF, Ploeman JHTM, Moonen MJH, Wobbes T, van Ommen B, Vervoort J, et al. Regioselectivity and quantitative structure-activity relationships for the conjugation of a series of fluoronitrobenzenes by purified glutathione S -transferase enzymes from rat and man. Chem Res Toxicol 1996 9 638-46. 

Several methods have been investigated to find correlations between physical properties of fuel gas mixtures and the excess air ratio to optimize the combustion procedure. In spite of the varying composition of natural gas it is said to be possible to control a heater system by measurements of the dynamic viscosity of the gas [7]. One explanation could be the correlation between Wobbe number and viscosity With increasing Wobbe numbers the viscosity decreases, and if the Wobbe number of a gas is known, the excess air ratio can be adjusted, resulting in an open loop control. 

Wittig reaction, 2 64-65, 19 65 Wobbe Number, 12 378-379 Wohl-Aue synthesis, 2 787 Wohlwill refining process, 22 647 Wolff-Chaikoff effect, 14 373 Wolff-Kichner reduction, 13 569-570,... 

Natural Gas—Calculation of Calorific Values, Density, Relative Density and Wobbe Index from Composition. ISO 6976 1995(E). 

The natural gas after appropriate treatment for acid gas reduction, odorization, and hydrocarbon and moisture dew point adjustment (ASTM D1142) would then be sold within prescribed limits of pressure, calorific value, and possibly, the Wobbe Index [(calorific value)/(specific gravity)]. 

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. 

Weathers PJ, Elkholy S, Wobbe KK. (2006) Artemisinin the biosynthetic pathway and its regnlation in Artemisia annua, a terpenoid-rich species. In Vitro Cell Developmental Biol — Plant 42 309-317. 

Tyrakowska, B., Cnubben, N. H., Soffers, A. E., Wobbes, T., and Rietjens, I. M. (1996) Comparative MO-QSAR studies in various species including man. Chem.-Biol. Interact. 100, 187-201. 

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