1、冷冻干燥技术及装备,冻干食品的特点,优质：基本保持食品原有的色、香、味、形，维生素和蛋 白质等营养物质损失少。 方便：食用或加工前，复水快，可直接食用或烹调。 不用冷藏：密封包装后，可在常温下长期贮存、运输和销售。 重量轻：满足宇航、旅游等人员需求。 成本高：冻干食品成本是热风干燥食品的46倍。,冻干技术发展史,50年代 中国冻干技术开始起步。 60年代 引进的同时，自行设计制造。 70年代 冻干食品几乎消失。 80年代 开始复苏。 90年代 冻干食品得到快速发展 。,技 术 原 理,1Torr（托）1mmHg133Pa,技术装备,控 制 系 统,干燥箱,捕 水 器,真 空 系 统,制冷系统,
2、加热系统,冷冻,风冷法：在冻干机外对物料进行速冻， 随后快速送入冻干机中进行升华干燥。其特点： 适合疏松结构材料 冻结快 冻干机利用率高 5min内移入冻干机，15min内降压至100Pa。,冷冻,直冷法：冻干机搁板具有冻结能力，物料在冻干机内冻结后直接进行升华干燥。其特点 适合卫生要求高、导热性能好的瓶装制剂 对真空抽速要求相对低 存在冷热能量干扰问题,冷冻,压力与蒸气体积,压力与蒸气体积,如果每小时升华100kg水，则水蒸气体积达到1.210010001.2105 m3。 需要真空泵抽出速率为2000m3/min。,捕水器温度,捕水器与冻干机性能,捕水器是冻干系统中能耗最大的部件 升华阶段
3、负荷大，解析阶段负荷小。 捕水器结构优化设计是提高系统性能的关键之一 真空阻力小，结霜量大且均匀，易融霜是设计目标。,捕水器,捕水器,捕水器,冷热干扰置于末端,真空范围,真空与系统性能,真空度过高，虽然降低全压，但对传热不利。 真空泵抽出系统渗入的不凝性气体 捕水器抽出水蒸气 开始阶段真空泵负荷大,冻干箱体,油封滑片真空泵,水环真空泵,效率低，一般在30%左右 真空度低，极限压强20004000Pa,10时饱和蒸气压为1227Pa 20时饱和蒸气压为2337Pa 30时饱和蒸气压为4241Pa,水喷射泵,罗茨真空泵,罗茨泵,罗茨泵与油封泵性能,罗茨泵与滑片泵组合,必须首先启动滑片泵或水环泵，使
4、其工作一段时间，当系统中的真空度达到1Kpa以下时，再自动启动罗茨泵,真空负荷变化,降压阶段负荷最大（在规定时间内抽出干燥箱、捕水器和管道内的气体，以及食品材料放出的不凝性气体。） 升华阶段负荷较小（约为降压段的一半） 解吸阶段负荷最小 真空泵应该配备两套机组,真空泵组合,真空,多级蒸汽喷射泵 罗茨泵+水环泵 冷阱+罗茨泵+水环泵 冷阱+罗茨泵+滑片泵 冷阱+滑片泵,传热传质模式,水的相变热,升华热,供热不足或过多,供热不足：升华热补充不上，造成冻干品温度下降，饱和蒸气压随之下降，在捕水器温度不变情况下，水蒸气驱动压差减小。 供热过多：升华界面容易融化，此外，升华干燥层可能出现塌陷。,加热方法
5、,微波加热法 接触加热法 辐射加热法 接触、辐射混合加热法,传导加热,辐射加热,辐射加热,微波加热,缩短干燥周期85,微波加热问题,设备投资大 能量利用率低（如果电厂效率0.4，输变电和加热器效率0.8，电能转变为电场能0.5，则利用效率为0.16。如果锅炉效率0.75，管道、换热效率0.7，则利用效率0.53。） 冻区融化和干区过热,加热介质,接触加热法：循环液由水4份、乙醇2份，乙二醇4份配置成循环不冻液，其凝固点为-120，在使用时液温最高不超过60。 辐射加热法：采用蒸气加热，最高温度为120,连续式冻干机,连续式冻干机,连续式冻干机真空系统,捕水器自动化霜,日处理60吨连续式冻干机,
6、连续带式冻干机,生产线,生产线,药用冻干机,食品冻干工艺,预处理和后处理,由于冻干食品为多孔疏松形态，表面积增大数十倍，而且水分低，干物质浓度高，且直接暴露在环境中，因此，在不影响食品质量前提下，可以采用钝化酶活性的处理方法。 在冻干后，包装环境湿度和包装材料的透气性要求严格。,共晶体冻结,非共晶体冻结,晶体、玻璃体与橡胶体,晶体：分子近程有序，远程也有序。 玻璃体：分子近程有序，远程无序。其粘度达到1014 Pas。 橡胶体：分子近程有序，远程无序。其粘度达到104 Pas。,部分玻璃化 转变温度,食品冻结,FROZEN MATERIALS Ice formation during free
7、zing results in freeze-concentration of solutes The extent of freeze-concentration is dependent on the solutes and temperature At low temperatures the freeze-concentrated solutes with unfrozen water vitrify, i.e., the materials contain a crystalline ice phase and a noncrystalline, glassy solute phas
8、e - some solutes may crystallize, e.g., NaCl solution - freeze-concentrated sugars and foods often vitrify,食品冻结, Maximally freeze-concentrated solutions show glass transition, Tg, at an initial concentration independent temperature above which ice melting has an onset temperature at Tm At high molec
9、ular weight the Tg and Tm coincide Maximum freeze-concentration can be obtain only by freezing at a temperature TgTTm - ice formation ceases below Tg due to high viscosity - ice melting occurs above Tm,蛋白质,Proteins Amorphous proteins are important structural biopolymers Amorphous proteins are import
10、ant structural components of cereal foods, e.g., gluten in bread The glass transitions of proteins are often difficult to determine calorimetrically due to a small change in heat capacity and broadness of the transition,碳水化合物,Carbohydrates Sugars have clear glass transitions The glass transition tem
11、peratures of sugars increase with increasing molecular weight The detectability of the calorimetric Tg decreases with increasing molecular weight The Tg of anhydrous high molecular weight carbohydrates, e.g., starch, cannot be experimentally determined due to thermal decomposition,升华干燥,The ice subli
12、mes and the drying front retracts into the frozen core, leaving behind the porous matrix of the initial structure. The water vapour formed passes through the dried cake to the surface and then through the chamber to the condenser.A higher drying temperature results in a higher driving force for the
13、water vapour flow. The upper limit to the drying temperature during the primary drying stage is to ensure the product temperature is maintained below the system collapse temperature (Tc),解吸干燥,Secondary drying involves the removal of the remaining water from the product, that does not separate out as
14、 ice during the freezing, and hence does not sublimate off. It is difficult to transfer energy into a porous matrix placed under vacuum, since it behaves like an almost perfect insulating material. Therefore, the secondary drying stage takes almost as long as the primary drying stage although much l
15、ess water is removed from the product during this stage.,冻干终点判断,冻干品温度内外一致（升华干燥结束） 捕水器温度下降（升华干燥结束） 干燥箱压力下降 解吸干燥结束（试验确定）,解吸干燥时间,残余水分要求低的制品，降低捕水器温度。 提高供热量，加速解吸。 适当提高干燥箱的压力，改善供热条件。,升华干燥和解吸干燥,冻干工艺曲线,共晶温度,若在凍結與昇華過程中，产品的溫度高過了最低共晶點，則部分或全部溶質將處於液相中原預期冰晶體的昇華現象被液體的濃縮蒸發現象所取代，致乾燥後的产品將發生萎縮。一些活性物質由於長時間處於高濃度電解質中也容易變
16、性。所以最低共晶點是獲得冷凍乾燥最佳效果的臨界溫度。,塌陷温度,The system collapse temperature (Tc) is the point at which softening progresses to structural collapse of the dried cake, a phenomenon that can be observed by Freeze Drying Microscopy (FDM). For a crystallizing system, collapse occurs if the lowest eutectic melting temperature (Teu) is exceeded. For a non-crystallizing system, the collapse temperature is determined by the system glass transition temperature (Tg), which can be measured using differential scanning calorimetry (DSC).,弹性模量与温度关系,冻干与其它干燥比较,药品冻干工艺,冻干药品,冻干食品,冻干食品,冻干标本,谢谢,
