The improved evaporation efficiency of a hot-bubble pilot plant (HBPP) caused by combustion gas for water treatment

Abstract

HBPP uses hot dense bubbles as heat and mass carriers to evaporate the solution with improved evaporation efficiency, compared with the traditional thermal method. To develop an energy efficient water treatment process, we applied combustion gas as inlet gas within HBPP, for the first time to evaporate synthetic seawater. The advantage of using combustion gas is that the hot waste combustion gas from factories can be used at almost no energy cost, thereby reducing energy consumption. In this paper, the evaporation efficiency was determined by measuring the weight loss of column solution of HBPP in a 60 min run. Firstly, the ability of the HBPP to treat different types of wastewater, including 0.5 m NaCl solution or synthetic sewage, was tested by pumping air at the temperature of 80, 120 and 160 °C, respectively. The observed amount of evaporated water vapour was higher for the 0.5 m NaCl solution than for the synthetic sewage at inlet air temperatures of 80 °C and 120 °C but the same at a temperature of 160 °C. The HBPP shows the potential for water treatment regardless of wastewater type. Then, the evaporation efficiency was calculated for both combustion gas and air, at the inlet temperature of 120 °C to evaporate 0.5 m NaCl solution. The result showed an increment of 37% of evaporation efficiency achieved by sparging combustion gas. That is because the contained water vapour has a high capacity for efficient heat transfer to evaporate the solution. As a result, applying combustion gas within HBPP can provide an energy conservative method with improved evaporation efficiency for water treatment.