(110g) Chemical Components That Influence Evaporator Distillate Quality

The evaporation process is a very effective separation method for high-strength brines. This presentation is focused on the typical components that can appear in evaporator distillate and the key factors that can influence distillate quality. Testing experience regarding the quality of evaporator distillate is discussed.

In this presentation the term "evaporator distillate" refers to evaporator condensate. It is important to consider where the evaporator distillate will be used when evaluating its quality. Some uses of evaporator distillate are discharge to surface water, process reuse, and boiler water make-up.

There are several compounds and groups of compounds of interest in evaporator distillate quality. There is a marked tendency for both ammonia and bicarbonate to report to evaporator distillate. This tendency has a strong influence on both the conductivity and pH of the evaporator distillate. The influence of evaporator pH on the reporting of both ammonium bicarbonate and free ammonia to the evaporator distillate is discussed. A discussion of total organic carbon (TOC) and several organic components that can report to evaporator distillate is provided. Fingerprinting of semivolatile organic components in an evaporator feed and the corresponding evaporator distillate sample using gas chromatography analysis is illustrated. Results are provided showing that trace amounts of boron can report to evaporator distillate.

A method to improve evaporator distillate quality is vapor washing. The concentrations of non-volatile inorganic components in evaporator distillate are typically very low, so the concept of decontamination factor is used. Vapor washing can improve the decontamination factors for non-volatile inorganic components. Foaming is an upset condition that can be managed with the use of a vapor washer.