Design And Experimental Research On Heat Pump Seawater Desalination Plant

Desalination of seawater and underground brackish water is the most effective way to solve regional water shortage. The existing seawater or brackish water desalination technology has some outstanding problems, such as high energy consumption, poor efficiency of desalination and so on, so cost reduction and efficiency improving have been the emphases of desalination research.(1)This paper puts forward a new kind of heat pump type seawater or brackish water desalination system, and system working principle, technological process and standard operation were determined. In this paper, when the system runs under the condition of different feed temperature, concentration, flow, and degree of vacuum, the theoretical calculation is conduc ted, and obtaining the regularity of the syste m operation. According to the exergy loss model, exergy analysis of the system was conducted. The calculation results show that the biggest exergy loss of the system is located in compressor, condenser and water pump, accounting for 67.94% of the total loss, among which compressor is the biggest, accounting for 33.4%.(2)The process and seven subsystem structure of the device are designed, besides designing and the manufacture of the key equipment of the system are completed. After the experiment platform is built up, the whole system is debugged. The debugging work mainly includes as follows: hydraulic pressure test, air tightness test, water washing, calibration of the instruments, opening and closing of the system.(3)Performance of the heat pump seawater desalination plant is studied by the experiment, the main research contents and conclusions of this paper are following:1)The steady state performance analysis: Change of the suction, exhaust temperature of the compressor and water production with time were measured. The start-up time of the plant is very short, about five minutes,and then enter the phase of water production. The amount of water production in the same period was generally the same, and the cumulative water production increased gradually. It infers that the experimental system has a good stability and self-balancing ability.2)Variable flow and temperature experiments: The influence of the feed quantity of flow and temperature on water production, water production rate is measured, It was found that water production increases firstly and then decreases with the increase of the flow, and when the feed water temperature is higher, the water production rate will be higher, this is mainly because the feed liquid has not yet reached the evaporation temperature, having a certain supercooling degree.3)Variable feeding concentration and vacuum degree experiments: The influence of concentration of feed liquid on water production rate was measured. It was found that water production and water production rate of the feed liquid decreased, when it was compared with tap water. And with the higher salinity, water production and water production rate will be lower, but decline is not obvious. The influence of the vacuum degree on water production and water production rate was measured. It was found that water production and water production rate increased with the increase of the vacuum degree. And the vacuum degree has an obvious impact on water production and water production rate. When the vacuum degree increased from 86% to 94%, water production and water production rate increased by about 20%.4)Influence of variable working conditions on heat pump : The influence of the feed flow, the vacuum degree on the condition of the heat pump was measured, It was found that the heat pump evaporation pressure almost do not change with water flow changes. It shows that the water vapor condensation effect is very good, the system has a good self-balancing ability. The vacuum degree has a bigger influence on the working condition of heat pump. When the vacuum degree is lower, the higher the heat pump condensing pressure will be.5)Water quality monitoring: Product water conductivity under different concentration, vacuum was measured, It was found that products conductivity is very small,almost all keep under 300?s/cm, the product water quality is better than tap water; The product water conductivity increases with the increase of concentration, but the change is very gentle.6)The system energy consumption: The thermal energy efficiency ratio of the system COP is measured in the range of 4~5. It can be seen that the system has a higher coefficient of thermodynamic performance. But that energy consumption fluctuations in the range 0.135~0.175 kW?h/L-freshwater. Further research is needed in the future work.Research on this subject has an important guiding significance for desalination or enrichment of brackish water, seawater, concentrated brine, oily water.