Experimental Investigation Of Spary Evaporation Coupled With Low Temperature Distillation Integrated Desalination Process

Spray evaporation coupled with low temperature distillation is a new integrated seawater and brine water desalination technology. It uses spray waste gas to drive low temperature distillation process and meanwhile applies spray system to further concentrate distillation brine in order to enhance the water productivity, recovery rate and thermal efficiency for the whole process.In this paper low temperature distillation device is designed based on shell & tube heat exchanging column, and two columns are built (baffled and un-baffled respectively) to integrate with spray evaporation, and further data collecting system is set. The feasibility of the integrated process and effects of operating parameters are examined, and the results show that for the un-baffled system the spray brine rate, heating air flow rate and column feed rate have similar effects on system:as the increase of them the freshwater productivity of distillation column increases first and then falls. And as the increase of heating air temperature and distillation vacuum degree the column freshwater productivity rises. And for the baffled column the difference with un-baffled one is the productivity increases as the rise of heating air flow rate. Under experimental conditions suitable sections exist for spray brine rate, heating air flow rate and column feed rate respectively (0.3-0.4 kg h-1,15-20 m3 h-1,0.8-1.4 kg h-1 for un-baffled system and 0.6-0.8 kg h-1,20-25 m3h-1,1.8-2.2 kg h"1 for baffled system). At the same time, higher heating air temperature and vacuum degree are preferred, and they are 190-210℃and 0.01MPa respectively. Meanwhile, the results show the baffled plates can significantly enhance the performances of the integrated system:for the un-baffled system the distillation column freshwater productivity, gross water productivity and GOR can reach 3.5 kg h-1 m-2 and 0.8 kg h-1and 1.0 while for the baffled system they can reach 4 kg h-1 m-2,1.4 kg h-1 and 1.7 respectively.The structural optimization results show suitable length-diameter ratio for baffled column is 100. And under the condition of 10,000mg/L NaCl feed water, the salinity of spray condensed water is 200-350 mg/L, and the salinity for column secondary stream is 30-60mg/L, which is equal to traditional distillation process.A tilted tube is built and artificial seawater is used to investigate the scale of copper tube. The results show the scale generates after an induction period, and it is easier to scale under higher temperature and slower seawater flow rate. The investigation of scale composition shows CaCO3 is easier to scale in high temperature while CaSO4 is the main components in low temperature. And static scale further proves the existence of induction time and CaCO3 precipitates first in the scale process.The crystallization kinetics under varying temperature and flow rate field of CaCO3 and CaSO4 are investigated by induction time method. The results show the visible light-UV spectrophotometer can be used accurately to determine the crystallization induction time, and as the increase of temperature, super-saturation degree and agitation the CaSO4 induction time decreases while no ground connection has been found on the effect of agitation on CaCO3 induction time. And the crystallization kinetics investigations find the free energies of CaSO4 and CaCO3 fall as the rise of temperature, while no direct connection has been found between solid-liquid interfacial tension and operating parameters. Finally the induction time function for CaSO4 and CaCO3 are set up and good accordance can be found between experimental results and theoretical prediction.