A conceptual demonstration and theoretical design of a novel “super-gravity” vacuum flash process for seawater desalination

Abstract

Abstract The severe global water scarcity and record-high fossil oil price have greatly stimulated the research interests on new desalination technologies driven by renewable energy. To directly use the renewable energy of kinematic form such as wind energy at ambient temperature, a “super-gravity” vacuum flash (SGVF) process for seawater desalination or water purification is explored. The SGVF process consists of one or several “super-gravity” vacuum evaporator (SGVE) with the desalination unit in it, frictional heater (FH), vacuum pump if necessary, and other adjunctive facilities. In the SGVE, a “super-gravity” vacuum (SGV) region is created so that the seawater can distill in it at ambient temperature. A steam compressor is integrated on the top to compress the distilled primary steam, recycling its latent heat. Several heat exchange tubes are arranged in the SGV region to exchange heat between the seawater outside and the compressed steam inside, realizing the flash of seawater and condensation of compressed steam at the same time. The FH is used to preheat the seawater compensating the temperature difference between the sea and the air and the energy loss during heat transfer. Each key unit in the SGVF process is theoretically calculated and analyzed. Method to determine formation, distribution and volume of the SGV region is developed, and factor influences are discussed. Shaft power of FH is calculated combining the theoretical derivation and the numerical simulation together, and the results of two methods agree well. Main parameters of the integrated steam compressor are calculated to meet the process requirement. The heat transfer tubes are arranged and the flow path of each fluid is designed according to the shape characteristic of the SGV region. According to a calculation example of the whole process, it is proved that the SGVF process has potential in seawater desalination. For different applications and requirements, several SGVEs can be arranged in parallel to meet larger production rates and in series to obtain higher quality water product.