Equilibrium sour water

Newman (1991) gives the equilibrium data required for the design of sour water systems, as charts. 

Miles, D. H. and Wilson, G. M. "Vapor-Liquid Equilibrium Data for Design of Sour Water Strippers", Annual Report to the American Petroleum Institute for 1974, October 1975 (Data in this report are also summarized in reference 2). 

Until recently the ability to predict the vapor-liquid equilibrium of electrolyte systems was limited and only empirical or approximate methods using experimental data, such as that by Van Krevelen (7) for the ammonia-hydrogen sulfide-water system, were used to design sour water strippers. Recently several advances in the prediction and correlation of thermodynamic properties of electrolyte systems have been published by Pitzer (5), Meissner (4), and Bromley ). Edwards, Newman, and Prausnitz (2) established a similar framework for weak electrolyte systems. 

The phase equilibrium equations for the interface may also need to be modified for the influence of additional species on the thermodynamic properties at the interface. A case in point is sour water stripping, in which reactions in the liquid phase create additional species (including ions), which affect the interfadal equilibrium. Enhancement factors have been derived for many cases and there is no sin-... 

Gillespie, P. C., Owens, J. L., and Wilson, G. M. (1980). Sour Water Equilibria Extended to High Temperature and with Inerts Present AIChE Winter National Meeting, Paper 34-b, Atlanta, GA, Mar. 11-14, (1984) and Gillespie, PC. and G.M. Wilson, Vapor—Liquid Equilibrium Data on Water-Substitute Gas Components N -H O, H -H O, CO-H O, H -CO-H O, andHE-H O Research Report RR-41, GPA, Tulsa, OK, (1980). 

The van Krevelen et al. (1949) study is considered to be a pioneering effort in Ibe correlation of vapor-liquid equilibrium data for systems of tbis type. It has saved as the basis for several sour water stripper design procedures, including the widely used approach described by Beychok (1967) and Wild s calculator program for sour water stiippa design (1979). 

The term speciation is used to describe the reactions that take place when an electrolyte is dissolved in water. Water dissociates, sour gases hydrolyze, some ions dissociate, and other ions associate until thermodynamic equilibrium is attained. The liquid phase of the ternary H2O-NH3-CO2 system contains at least the following nine species HjO, NH3(aq), COjiaq), H", OH, NH4, HCOj, COj , and NHjCOO. (aq) indicates that the species is in aqueous solution to avoid ambiguity. In order to adequately model this system, interaction parameters for the interaction between each pair of species need to be determined thus, speciation calculations are performed simultaneously with the parameter estimation, and the calculated amount of each species is compared with experimental data. Some models also require ternary parameters and consequently an additional amount of data to determine these parameters. 

Absorption of sour gases (NH3, SO2, COj) in water at low pressures. Here gas/liquid equilibrium should be described correctly over a large concentration interval. Use of Henry constants without correction for concentration effects gives large errors. 

H2S can cause corrosion of stainless steels such as 316 and 410 stainless in the form of sulfide stress cracking. (Other factors, such as pH, chloride concentration, and temperature also affect the potential for steel cracking.) Copper alloys corrode rapidly in H2S service. An industry value that has been developed is NACE MR-01, 2003, from the National Association of Corrosion Engineers. In the gas phase, a stream is sour if the H2S partial pressure exceeds 0.05 psia. If a single phase hquid is in equilibrium with a gas phase, where the gas phase H2S partial pressure exceeds 0.05 psia, then that hquid is also considered to be sour. If the liquid is not in equihbrium with the gas phase, then the liquid is considered sour, if this bubble point gas phase H2S partial pressure exceeds 0.05 psia. The presence of water is not required for a gas and/or hquid to be considered to be sour, nor is there a minimum pressure to avoid designating a gas or hquid as sour. 

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