Study On Processing Technology And Equipment Of Freezer Concentration

Based on mini laboratory-size freezing concentration equipment, pilot-scale freeze concentration equipment was made. And decoction of pork balls is adopted as a sample for experiment, effects on ice crystal intensity and purity of pilot-scale equipment were systematically researched, which was used to determine process parameters of influencing factor. Compared pilot-scale equipment with mini laboratory-size equipment, freeze concentration effect of scale-up equipment was tested. Programmable Logic Controller (PLC) was used as control element, and automatic control system of pilot-scale freeze concentration equipment was designed, which applied to continuous freeze concentration and provided an important recommendation for further improvement of freeze concentration equipment.1. Effects of cooling medium temperature, cooling medium flow rate, scraping cutter speed and flow rate of juice pump on ice crystal intensity and purity were studied with decoction of pork balls as experimental material in pilot-scale freeze concentration equipment. The results showed that ice crystal intensity was improved with optimal scraping cutter speed (130-150rpm). Ice crystal of crystallizing tank was transferred timely to ice crystal growth tank to grow up with optimal flow rate of juice pump (0.72m3/h-1.08m3/h), and heat loss of juice pump also was reduced. Heat transmission coefficient crystallizing tank was increased with greater cooling medium flow rate (maximum to 7.41m3/h), and ice crystal intensity also was improved. For this equipment, ice crystal intensity achieved to maximum, when cooling medium flow rate was up to maximum 7.41m3/h. Temperature variation between cooling medium and decoction was increased by lower cooling medium temperature. Propulsion of cooling capacity transfer and ice crystal intensity were also improved. Ice crystal intensity achieved to maximum, when the freeze temperature was down to -23℃. By orthogonal test, ice crystal intensity achieved to maximum by changing scraping cutter speed,flow rate of juice pump,cooling medium flow rate and cooling medium temperature. (scraping cutter speed, 140r/min juice cycling flow rate, 1.44m3/h cooling medium flow rate, 7.41m3/h cooling medium temperature, -23℃soluble solid of decoction, 5°Bx ice production ,16.16㎏/h crystal soluble solid, 0.39°Bx). The results showed that control hysteresis and disadvantage of regulating were prevented by using PLC. Programs were designed to change easily according to practical production.2. Decoction of pork balls as experiment material, ice crystal intensity and purity as indexes, effect of cooling medium temperature, scraping cutter speed, juice concentration and time of taking ice on pilot-scale freeze concentration equipment and mini laboratory-size freezing concentration equipment were studied. Compared pilot-scale with mini laboratory-size equipment, rationality and practicability of design were tested. The results showed that efficiency of heat-exchanging unit was improved by using ethanediol instead of calcium chloride in pilot-scale freeze concentration equipment. Sufficient scraping cutter speed matched high efficiency of heat-exchanging unit, which made the increase of ice crystal more than enlargement of area of heat-exchanging unit, also soluble solid of ice crystal was decreased. After the increase of concentration, probability of core formation of ice crystal in the pilot-scale freeze concentration equipment was lower by enough large tank volume of ice crystal growth. Energy consumption was decreased with right time of taking ice crystal. Small ice crystal could grew up to bigger by Ostwald Effect in suitable tank volume of ice crystal growth, which slowed the tend of decrease of ice crystal intensity down, and purity was improved. pilot-scale freeze concentration equipment was successful.3. Based on the prior experiment, using PLC as control element, continuous freeze concentration was studied. Terminal point of freeze concentration for decoction of pork balls was determined by freezing point and freeze curve. Centre deicing method had the same efficiency of manual operation by regulate a suitable speed of stirrer. Automatic control system of pilot-scale freeze concentration equipment was achieved by PLC, and for Decoction of pork balls (soluble solid, 10°Bx), after 32 hours concentration, concentration could reach to 35.36°Bx. Kinetic model of ice crystal growth for continuous freeze concentration of decoction of pork balls was built as follow:. Ice crystal production and efficiency of cooling capacity for unit time could be improved by properly reducing cooling medium temperature. Efficiency of cooling capacity of freeze concentration could be up to 69.0%, when cooling medium brought down to -23℃. And ice crystal production was 16.16㎏/h. Ice crystal production for unit area of pilot-scale freeze concentration equipment was 42.89㎏ /m2*h, while mini freeze concentration equipment was 17.93㎏/m2*h. Ice crystal production for unit area of crystallizing tank could be improved by changing external working condition.