Treatment of low level liquid waste by an in‐situ freezing‐melting process

Abstract

This paper is to present the results of an initial study of applying a new purification process for the treatment of low level liquid waste (LLLW) produced by nuclear power plants, the so‐called in‐situ freezing‐melting process. In order to purify the liquid waste, the wastewater is first frozen to form clean ice. The clean ice is then melted to yield purified water that is allowable to be discharged. The in‐situ freezing‐melting process utilizes the ice formation of falling film on a vertical wall of ice‐former as a wastewater treatment procedure. A falling film of an aqueous lithium bromide solution (LiBr_aq) is formed on the inner wall surface as a coolant. The three tested experimental statuses on the outer wall surface include pre‐existing nucleus of crystallization, no pre‐existing nucleus of crystallization, and the affixed fiber grids. The effects of the three experimental statuses on the amount of ice formation, the degree of purification, and the overall heat‐transfer coefficient were investigated. The present study found that the maximum values of both the amount of ice formation and the degree of purification could be found by varying the Reynolds number of wastewater. A lower inlet temperature of wastewater or aqueous lithium bromide solution can increase the amount of ice formation, but causes a decrease in the degree of purification. In addition, the preexisting nucleus of crystallization has positive effects on both the amount of ice formation and the degree of purification. However, when the wastewater is able to wet the outer surface of the wall thoroughly, affixing fiber grids to the surface will, contrarily, cause unfavorable effects on the degree of purification.

Key words :

• In‐situ freezing‐melting process
• low level liquid waste treatment
• falling film, degree of purification

Notes

Correspondence addressee