Performance Research On Mechanical Vapor Recompression Evaporation And Crystallization System

Mechanical Vapor Recompression(MVR) is a new technology which uses energy of secondary steam from evaporator, so it can decrease energy demand from environment. The theory is the secondary steam created by evaporator be recompressed by compressor, the pressure, temperature and enthalpy of the vapor is higher, and can be used as the heat source to heat system itself. The vapor becomes water because of exotherm, and water in the materials becomes vapor because of endotherm. The secondary steam repeat the above process, the system can circulate and evaporate.Hence, the system demands of energy from the compressor.Mechanical Vapor Recompression Evaporation and crystallization system based on MVR technology use a rising film evaporator combined a forced circulating evaporator. The process is the solution be preheated and deliveried into rising film evaporator in boiling point, water evaporates in the rising film evaporator and the solution be concentrated closed to saturated liquid, then separates in the separator, the secondary steam separated from separator heat two evaporator after compressing, on the other hand, the separated concentrated solution be forced circulating and concentration crystallization. The main features include three cycle of re-use of secondary steam recompressed, Concentrated solution forced circulating and evaporating and cold water recycling. This is a new structure, combining with the advantages of the rising film evaporators and the forced circulation evaporator, so it has better energy saving effect. Rising film evaporator concentrate the material close to saturation state, evaporation of a lot water, reduced the power of forced circulation evaporation. The forced circulation crystallization solved the problem that rising film evaporator cannot be used for crystallization.Designs capacity of100kg· h-1sodium carbonate solution was evaporated and crystallization system, selected10%sodium carbonate solution, the solution evaporation temperature is75℃, Compressor compression ratio is1.8As a reference coefficient. Calculate the whole equipment and piping system, the materials go through the preheater and the temperature rise from20℃to75℃。 Then the materials get heated and evaporation by the climbing film evaporator,the solution concentrate to30%.afterwards,the concentrated solution is forced to circulate of crystallization, the water content of crystalline is55%.Finally,the result is that heat transfer area of the preheater is0.34, the heat transfer area of climbing film evaporator is5.06m2, the heat exchange area of forced circulation evaporator is0.53m2, the compressor idea power is2203W,and get the size of the separator and the paragraphs connection pipeThe system was analyzed from the context of energy conservation and mass conservation. The models of preheater, evaporator and compressor were established. These models were used to analysis the influence of evaporating temperature, compress rate to the heat exchange area, the Compressor power and COP. The result indicated that the heat exchange area of preheater and Compressor power increases, and the heat exchange area of climbing film evaporator, forced circulation (type) evaporator and COP reduced as the evaporation temperature raised. The compressor power increases, and the heat exchange area of preheater, climbing film evaporator, forced circulation (type) evaporator and COP reduced as the compress ratio raised. According to conclusion we choose low temperature and low compression ratio of MVR evaporation system, the energy saving effect is more apparent, the lowest annual cost is obtained for the compression ratio of1.3-1.4.