A Study On Solar Desalinization Technology By Multi-effect Bubbling Process

Different from conventional distillation or reverse osmosis desalination process,the humidification-dehumidification desalination is a novel seawater and brackish water desalting process,in which air is used as a carrier gas to evaporate water from saline feed.Generally,to increase the thermal efficiency,the evaporation and condensation processes are thermally coupled by heat transfer,so that the condensation latent heat can be transferred to the evaporation side to provide evaporative latent heat for the brine.An experimental plant for carrier-gas humidify by bubbling is designed and built in this work.As the prime part of the design,a five-stage evaporation tower with the four-effect desalination is built for the bubble column.The solar collector is used for heating the brine in the first-stage.The effective heat transfer area of the plant is 6.7m~2.The solar collector systems,fluid conveyance system,control system are designed correspondingly.The operating parameters and influence factors experiment are carded out under the steady-state conditions.The experimental results show that the water productivity of the unit increases with the increase of the initial temperature(the brine temperature in the first-stage evaporation chamber) and the bubble flow rate.Generally,the water productivity of the tower varies in the range of 1.2～1.6kg/h under the suitable inter-stage temperature, carrier-gas flow rate and initial temperature.The ideal initial temperature range is 85～90℃.In the experiment,on the condition that the temperatures of each stage are 89.9℃,77.4℃,68.0℃,59.0℃,38.3℃separately,and the carrier-gas flow rate in each evaporation chamber are 600L/h,480L/h,480L/h,480L/h respectively,the water productivity is up to 1.482L/h with the GOR point is 2.7,and the 4.94kW·h/ton electricity power energy consumption.The contrast experimental study shows that there is a rational carrier-gas flow rate in each stage to achieve a high productivity and GOR and a low power consumption. The salinity of the produced water was determined to be in the range of 50mg/L, which is almost the same as the traditional thermal desalting processes. Starting from the heat balance,the mass balance and the calculation of the heat and mass transfer rates,a comprehensive heat-mass coupled transfer mathematical model is developed for the bubbling process.The mass transfer coefficient for the humidification process and heat transfer coefficient for the evaporation/condensation processes are extensively analyzed and their corresponding calculation methods are developed.Based on the developed model and the experimental data,the mass transfer coefficient for the humidification processes for each evaporation chamber and the heat transfer coefficient for the evaporation/condensation processes in each stage are researched under the steady-state conditions,then,a case is given for the perform calculations. Based on the above work,the future study is discussed finally.