Theoretical Study Of Desalination Zero Emissions Based On Mechanical Heat Pump

Desalination is a traditional high-energy processes. Currently, the mainstream desalination methods include reverse osmosis desalination, multi-stage flash desalination, and low temperature multi-effect desalination. Because the reverse osmosis desalination has the higher requirements and poor adaptability, multi-stage desalination have high energy consumption, and the low-temperature multi-effect technology has now matured and has been widely used. However, the existing reverse osmosis desalination method unable to achieve zero emissions, the salt concentration of seawater from 3% to 6% and then directly into the sea. Over time, high salt concentration liquid directly into the ocean, this liquid will cause adverse effects on surrounding ecological environment of the ocean. With the increasingly significant design and development of new low-energy desalination system cleaner world energy crisis and environmental crisis is imminent.In this paper, we design the zero emission desalination systems based on the mechanical heat pump technology, improved the salt concentration from 3% to 28.92%, and the production of the system are freshwater and salt. Take the comparison of the energy single-stage, two-stage and three-stage system of comparison. We take calculation on the single-stage seawater desalination system to get the energy consumption. Because the system could achieved the zero emission,so that the salt concentration of seawater is 28.92%, the analysis results showed that with increasing concentrations of export, the system was slowly rising and the exergy loss trends is also rising slowly. Take the two-stage desalination system as a key target systems, analysised and optimized the system with pinch technology, T-Q figure and exergy analysis. Established the model of the main components of the system in Aspen plus to validation the results of calculation. We take a detailed anlysis on the two-stage zero-emission desalination system about the impaction of loss caused by the salt concentration export from the first flasher in the two-stage system, the results showed that the system exergy loss increases as the salt concentration outlet from the first flasher’s exports, not as the single-stage system’s change trend, but declining at first and then rising. Therefore, if we take the salt concentration export from the first flasher as the independent variable, fit the function of the system exergy loss, we could get one curve about salt concentration outlet from the first flasher and the exergy of the whole system. Through the function derivation, we can draw the most energy-efficient the effect of the concentration distribution, the results showed that the level of salt in the water flashed exports 28.92%, the exergy loss of the whole system reaches the minimum.In addition, we take the same method to analysis the results of treating the high concentration of salt waste water, the results showed that it obtained with the experimental results. So we can prove that such analysis has strong applicability and reliability.And then we concluded from the perspective of economic, energy level and the second desalination systems analysis, found that the best overall performance two desalination systems.We set up the exergy models of every main component, and analyzing the systems exergy loss to find the main damage parts of the systems, then studied the affection of the different evaporation temperature and minimum temperature difference for these systems. The analysis results show that the exergy loss of heater and compressor are largest.Finally, the multivariate analysis theory is introduced, and applied it to the seawater desalination system analysis. The method of multi-variable optimization analysis was proposed in this paper in view of the three-level system. We analyzed the energy consumption changed with the salt concentration outlet from the first flasher and the secondary flasher.