Maddox Correction

Maddox (1974) developed a method for estimating the water content of sour natural gas. His method assumes that the water content of sour gas is the sum of three terms 1. a sweet gas contribution, 2. a contribution from C02 and, 3. a contribution from H2S. 

The water content of the gas is calculated as a mole fraction weighted average of the three contributions. 

To use this method, one finds the water content of sweet gas, typically from the McKetta-Wehe chart. Then the corrections for the acid gases are obtained from their respective charts. 

Although these charts have the appearance of being useful for calculating the water content of pure H2S and pure C02 they should not be used for this purpose. 

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Hines and Maddox (26) stated that they solved literally hundreds of minimum reflux cases and are yet to find a case in which predictions from Eq. (3.12) are not correct. 

Correcting the result of Erbar and Maddox with Eq. (3.18) is not performed here,... 

It is of interest to compare the values of pore diameter obtained by molecular simulation and by the use of the corrected Kelvin equation. By comparing the nitrogen isotherm in Figure 12.6 with molecular simulation model isotherms, Maddox et al. (1997) have arrived at pore diameters of 4.1-4.3 nm. As indicated in Table 12.4, the corrected Kelvin diameters are 3.3-4.3 nm. The corresponding surface areas are 631 and 655 m2 g 1. In view of the assumptions in the model and the shortcomings of the Kelvin and BET equations, this level of agreement must be considered to be encouraging. 

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