Study On Improvement And Scale Up Of The Freeze Concentration Pilot Plant

Based on the existing theory and practice about freeze concentration, the freezeconcentration pilot plant was optimized to operate smoothly and efficiently. Then, theimproved and scaled up freeze concentration pilot plants （ISFCPP） were built.Meanwhile, syrup（10°Bx） was adopted as the material to do the debugging test of theISFCPP. The heat and mass transfer feature of the ISFCPP was also studied, whichcould be used to evaluate the efficiency and related properties of the ISFCPP. Finally,the characteristics of all the freeze concentration devices, which were made in ourlaboratory in different stages, were summarized, which could provide a reference forfurther research on freeze concentration and give certain theoretical basis for freezeconcentration industrialization.（1） In order to solve the problems appeared in the operation process of the pilotplant, and make it operate smoothly and efficiently, the structure and the scraper ofthe pilot plant were optimized, and an ice-melting device was added to the pilot plant.At the same time the choice of insulation materials and the thickness of insulation forthe pilot plant was studied. The thickness which could prevent forming dew on theouter surface of the insulation materials was determined: the thickness of thecrystallizing tank, the ice growing tank, the precooling tank, and the coolantcirculating tank made by polyurethane as the insulation material were60mm43mm56mm and65mm respectively; the thickness of the coolant circulatingpipeline and the material circulating pipeline both made by rubber sponge as theinsulation material were52mm and43mm respectively.（2） On the basis of optimizing the pilot plant, the ISFCPP was built by improvingthe internal structure of the crystallizing tank and scaling up the crystallizing tank.Then, syrup（10°Bx） was adopted as the material to do the debugging test of theISFCPP. The results of the debugging test were as follows: the ISFCPP workedsmoothly and stably, which run continuously for24hours, without any fault; at thesame time there were some basic properties of the ISFCPP: increasing the flow rate ofthe coolant could enhance the growth rate of the ice crystal of the ISFCPP. While with the flow rate of the coolant increasing, the resistance to flow increased accordingly,and the growth rate of the ice crystal increased slowly. It was helpful to increase theaverage temperature difference by reducing the coolant temperature, so that it couldenhance the growth rate of the ice crystal. When the coolant temperature was lowerthan-19℃, maybe the viscosity of the coolant increased, which affected the heattransfer, thereby the growth rate of the ice crystal increased slowly. the growth rate ofthe ice crystal increased along with the scraper speed increasing. But with the scraperspeed increasing, energy consumption increased, thus the growth rate of the ice crystalincreased slowly. By comparison with the original pilot plant, the growth rate of theice crystal of the ISFCPP increased obviously, and the entrainment rate of the icecrystal of the scaled up pilot plant reduced. The results showed that the improvementand scale up to the original freeze concentration pilot plant had a certain effect.（3） The results of heat transfer calculation were as follows:The overall heat transfer coefficient K of the original freeze concentration pilotplant was swayed by the convective heat transfer coefficient of the coolant side α1, sothe key to increase the overall heat transfer coefficient K was to improve theconvective heat transfer coefficient of the coolant side α1.Compared with the original freeze concentration pilot plant, the overall heattransfer coefficient K of the improved pilot plant increased by10³0%, and the heattransfer efficiency by about10%. Thus, the success of the improvement to the originalpilot plant was further verified. The overall heat transfer coefficient K of the scaled uppilot plant increased from176.86W·m^-2·K^-1to434.19W·m^-2·K^-1, and the heat transferefficiency of the scaled up pilot plant ranged from0.327to0.447.The results of mass transfer calculation were as follows:The kinetic equation of first grade freeze concentration of syrup by the improvedfreeze concentration pilot plant:The loss rate of first grade freeze concentration of syrup by the improved freezeconcentration pilot plant:3.8%. The kinetic equation of first grade freeze concentration of syrup by the scaled upfreeze concentration pilot plant:The loss rate of first grade freeze concentration of syrup by the scaled up freezeconcentration pilot plant:2.9%.The results showed that because the heat transferring area of the scaled up freezeconcentration pilot plant increased, the growth rate of the ice crystal in first gradefreeze concentration by the scaled up freeze concentration pilot plant was fast. Andbecause of the increase in volume of the scaled up pilot plant, the entrainment rate ofthe ice crystal of the scaled up pilot plant reduced, which was helpful to reduce theloss of material.（4） Through the comparison and analysis of all the freeze concentration devicesin different stages, some conclusions were found: in order to improve the per unitvolume heat transfer efficiency of the crystallizing tank, the following researchemphases for strengthening heat transfer of the crystallizing tank should focus on theinternal structure of the crystallizing tank. The results added to a weight of evidenceon the success of the improvement to the original freeze concentration pilot plant.Consequently, it was feasible to enhance the growth rate of the ice crystal of thefreeze concentration devices by increasing the heat transferring area of thecrystallizing tank under certain conditions. It was helpful to reduce the entrainmentrate of the ice crystal by scaling up the freeze concentration devices, thus, it couldreduce the loss of material during the concentration process.