Outotec Developments in Reducing Emissions from Solution Cooling Towers

Tuomas Hirsi

Outotecs innovative solution cooling tower design incorporating horizontal air / vapor outflow technology has been in use since 2012. Solution cooling towers are used when direct cooling is applied for concentrated, sometimes acidic and scaling solutions, which may also have substantive amounts of solid particles. The reference discussed in this article is used in spent electrolyte cooling in zinc refinery. The cooling performance and maintenance benefits of horizontal outflow technology when compared with older cooling tower designs has been shown in earlier publications. In this paper we present an important additional benefit provided by the new tower design, namely lower emissions. Emissions from solution cooling towers are contained in the entrained liquid droplets carried by the cooling air / vapor when it exits in the tower. Depending on the solution being cooled, these entrained droplets can include acids, dissolved metal ions, dissolved salts, suspended solids and other compounds. These emissions cause metal losses, local environmental and OH&S issues as well as increasing corrosion to equipment, structures and potentially, private property in the vicinity. The main method to control these emissions is the installation of demisters to the tower. In May 2016, detailed testing was performed on an Outotec tower by a third party using isokinetic sampling to quantify the emissions. The test work provided promising results and demonstrated reduced emission levels, however, some discrepancies in the results require further investigations. With the current demister arrangement the emission removal efficiency was noted to be considerably lower than in the currently typically used vertical outflow cooling towers. In this paper, we present the findings of these measurements and discuss the methods used to do preliminary estimations of emissions from the tower in the development phase.