冷冻干燥技术及装备上海交大

1、冷冻干燥技术及装备1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。 2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 。3技 术 原 理1Torr（托）1mmHg133Pa4技术装备控制系统干燥箱捕水器真空系统制冷系统加热系统5冷冻风冷法：在冻干机外对物料进行速冻，

2、 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。6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7冷冻8压力与蒸气体积1克水体积常温常压下1毫升100Pa，-20下毫升9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。10捕水器温度温度升华热kJ/kg饱和蒸气压Pa02834610-102837260-202

3、838103-30283938-4028401311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。12捕水器13捕水器14捕水器冷热干扰置于末端15真空范围CLASSIFICATIONPRESS RANGELOW VACUUM760 Torr 1 Torr100kPa 100PaMID VACUUM1 Torr 10-3 Torr100Pa 0.1PaHIGH VACUUM10-3 Torr 10-7 Torr0.1Pa 10PaEXTRA HIGH VACUUM10-7

4、 Torr 10-10 Torr10Pa 104PaEXTREMELY HIGH VACUUM10-10 Torr (Less)104Pa (Less)16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17冻干箱体18油封滑片真空泵19水环真空泵效率低，一般在30%左右真空度低，极限压强20004000Pa10时饱和蒸气压为1227Pa20时饱和蒸气压为2337Pa30时饱和蒸气压为4241Pa20水喷射泵21罗茨真空泵22罗茨泵23罗茨泵与油封泵性能10510310110-20255075100压强 Pa抽气速率 24

5、罗茨泵与滑片泵组合必须首先启动滑片泵或水环泵，使其工作一段时间，当系统中的真空度达到1Kpa以下时，再自动启动罗茨泵25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26真空泵组合27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 28传热传质模式29水的相变热335kJ/kg水2520kJ/kg水4.2kJ/kg30升华热温度升华热kJ/kg饱和蒸气压Pa02834610-102837260-202838103-3028

6、3938-4028401331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。32加热方法微波加热法接触加热法辐射加热法接触、辐射混合加热法 33传导加热34辐射加热35辐射加热36微波加热缩短干燥周期8537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38加热介质接触加热法：循环液由水4份、乙醇

7、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 39连续式冻干机40连续式冻干机41连续式冻干机真空系统42捕水器自动化霜43日处理60吨连续式冻干机44连续带式冻干机45生产线46生产线47药用冻干机48食品冻干工艺预处理装盘速冻捕水器温度降至40以下加热真空升华干燥解吸干燥包装49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。50共晶体冻结51非

8、共晶体冻结52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。 53部分玻璃化转变温度54食品冻结FROZEN MATERIALS Ice formation during freezing results in freeze-concentration of solutes The extent of freeze-concentration is dependent on the solutes and temperature At low temperatures t

9、he freeze-concentrated solutes with unfrozen water vitrify, i.e., the materials contain a crystalline ice phase and a noncrystalline, glassy solute phase- some solutes may crystallize, e.g., NaCl solution- freeze-concentrated sugars and foods often vitrify55食品冻结 Maximally freeze-concentrated solutio

10、ns show glass transition, Tg, at an initial concentration independent temperature above which ice melting has an onset temperature at Tm At high molecular weight the Tg and Tm coincide Maximum freeze-concentration can be obtain only by freezing at a temperature TgTTm- ice formation ceases below Tg d

11、ue to high viscosity- ice melting occurs above Tm56蛋白质Proteins Amorphous proteins are important structuralbiopolymers Amorphous proteins are important structuralcomponents of cereal foods, e.g., gluten in bread The glass transitions of proteins are often difficult todetermine calorimetrically due to

12、 a small change inheat capacity and broadness of the transition57碳水化合物Carbohydrates Sugars have clear glass transitions The glass transition temperatures of sugars increasewith increasing molecular weight The detectability of the calorimetric Tg decreaseswith increasing molecular weight The Tg of an

13、hydrous high molecular weightcarbohydrates, e.g., starch, cannot be experimentallydetermined due to thermal decomposition58升华干燥The ice sublimes 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 dr

14、ied cake to the surface and then through the chamber to the condenser. A higher drying temperature results in a higher driving force for the 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 syste

15、m collapse temperature (Tc)59解吸干燥Secondary drying involves the removal of the remaining water from the product, that does not separate out as 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

16、an almost perfect insulating material. Therefore, the secondary drying stage takes almost as long as the primary drying stage although much less water is removed from the product during this stage. 60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）61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

17、燥箱的压力，改善供热条件。62升华干燥和解吸干燥63冻干工艺曲线64共晶温度干物质冰晶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性。所以最低共晶點是獲得冷凍乾燥最佳效果的臨界溫度。 65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 tem