Vapor-Liquid Equilibrium of Dilute Ammonia-Saline Water System

Abstract

If sea water contains ammonia as one of it's pollutants, it is supposed that some of the ammonia enters the product water at a desalination plant using an evaporation method. Then, the rate of ammonia in the product water can be estimated with the vapor-liquid (V-L) equilibrium which must include the chemical equilibrium of ammonia in the brine.
In this paper, we present the V-L equilibrium equation on an ammonia-saline water system which includes the chemical eqilibrium. In order to predict theoretically the behavior of ammonia in the plant, we calculated the equilibrium values for the pH levels, at the temperatures and the salinities which were nearly the same as the those in the operation conditions of a desalting evaporator.
As a result, the effects of temperature, pH and salinity to the V-L equilibrium in this system were clarified theoretically for the first time by considering the chemical equilibrium, and it was found that this equation could also be used for predicting exactly the behavior of ammonia in a desalting evaporation plant. Also, in the discussion about the equation and the results, it became clear that the chemical equilibrium had to always be considered in the V-L equilibrium equation of a chemical substance which ionized and/or formed the complex in a solution like ammonia, and that the equation of ammonia (eq. 12) could be used for the substance only by making a partial amendment of the equation to be an appropriate form for the substance.