冷凍干燥技術及裝備上海交大

1、冷凍干燥技術及裝備1凍干食品的特點優(yōu)質(zhì)：基本保持食品原有的色、香、味、形，維生素和蛋 白質(zhì)等營養(yǎng)物質(zhì)損失少。方便：食用或加工前，復水快，可直接食用或烹調(diào)。不用冷藏：密封包裝后，可在常溫下長期貯存、運輸和銷售。重量輕：滿足宇航、旅游等人員需求。成本高：凍干食品成本是熱風干燥食品的46倍。 2凍干技術發(fā)展史50年代 中國凍干技術開始起步。60年代 引進的同時，自行設計制造。70年代 凍干食品幾乎消失。80年代 開始復蘇。90年代 凍干食品得到快速發(fā)展 。3技 術 原 理1Torr（托）1mmHg133Pa4技術裝備控制系統(tǒng)干燥箱捕水器真空系統(tǒng)制冷系統(tǒng)加熱系統(tǒng)5冷凍風冷法：在凍干機外對物料進行速凍，

2、 隨后快速送入凍干機中進行升華干燥。 其特點：適合疏松結(jié)構(gòu)材料凍結(jié)快凍干機利用率高5min內(nèi)移入凍干機，15min內(nèi)降壓至100Pa。6冷凍直冷法：凍干機擱板具有凍結(jié)能力，物料在凍干機內(nèi)凍結(jié)后直接進行升華干燥。 其特點適合衛(wèi)生要求高、導熱性能好的瓶裝制劑對真空抽速要求相對低存在冷熱能量干擾問題7冷凍8壓力與蒸氣體積1克水體積常溫常壓下1毫升100Pa，-20下毫升9壓力與蒸氣體積如果每小時升華100kg水，則水蒸氣體積達到1.210010001.2105 m3。需要真空泵抽出速率為2000m3/min。10捕水器溫度溫度升華熱kJ/kg飽和蒸氣壓Pa02834610-102837260-202

3、838103-30283938-4028401311捕水器與凍干機性能捕水器是凍干系統(tǒng)中能耗最大的部件升華階段負荷大，解析階段負荷小。捕水器結(jié)構(gòu)優(yōu)化設計是提高系統(tǒng)性能的關鍵之一真空阻力小，結(jié)霜量大且均勻，易融霜是設計目標。12捕水器13捕水器14捕水器冷熱干擾置于末端15真空范圍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真空與系統(tǒng)性能真空度過高，雖然降低全壓，但對傳熱不利。真空泵抽出系統(tǒng)滲入的不凝性氣體捕水器抽出水蒸氣開始階段真空泵負荷大17凍干箱體18油封滑片真空泵19水環(huán)真空泵效率低，一般在30%左右真空度低，極限壓強20004000Pa10時飽和蒸氣壓為1227Pa20時飽和蒸氣壓為2337Pa30時飽和蒸氣壓為4241Pa20水噴射泵21羅茨真空泵22羅茨泵23羅茨泵與油封泵性能10510310110-20255075100壓強 Pa抽氣速率 24

5、羅茨泵與滑片泵組合必須首先啟動滑片泵或水環(huán)泵，使其工作一段時間，當系統(tǒng)中的真空度達到1Kpa以下時，再自動啟動羅茨泵25真空負荷變化降壓階段負荷最大（在規(guī)定時間內(nèi)抽出干燥箱、捕水器和管道內(nèi)的氣體，以及食品材料放出的不凝性氣體。）升華階段負荷較?。s為降壓段的一半）解吸階段負荷最小真空泵應該配備兩套機組26真空泵組合27真空多級蒸汽噴射泵羅茨泵+水環(huán)泵冷阱+羅茨泵+水環(huán)泵冷阱+羅茨泵+滑片泵冷阱+滑片泵 28傳熱傳質(zhì)模式29水的相變熱335kJ/kg水2520kJ/kg水4.2kJ/kg30升華熱溫度升華熱kJ/kg飽和蒸氣壓Pa02834610-102837260-202838103-3028

6、3938-4028401331供熱不足或過多供熱不足：升華熱補充不上，造成凍干品溫度下降，飽和蒸氣壓隨之下降，在捕水器溫度不變情況下，水蒸氣驅(qū)動壓差減小。供熱過多：升華界面容易融化，此外，升華干燥層可能出現(xiàn)塌陷。32加熱方法微波加熱法接觸加熱法輻射加熱法接觸、輻射混合加熱法 33傳導加熱34輻射加熱35輻射加熱36微波加熱縮短干燥周期8537微波加熱問題設備投資大能量利用率低（如果電廠效率0.4，輸變電和加熱器效率0.8，電能轉(zhuǎn)變?yōu)殡妶瞿?.5，則利用效率為0.16。如果鍋爐效率0.75，管道、換熱效率0.7，則利用效率0.53。）凍區(qū)融化和干區(qū)過熱38加熱介質(zhì)接觸加熱法：循環(huán)液由水4份、乙醇

7、2份，乙二醇4份配置成循環(huán)不凍液，其凝固點為-120，在使用時液溫最高不超過60。輻射加熱法：采用蒸氣加熱，最高溫度為120 39連續(xù)式凍干機40連續(xù)式凍干機41連續(xù)式凍干機真空系統(tǒng)42捕水器自動化霜43日處理60噸連續(xù)式凍干機44連續(xù)帶式凍干機45生產(chǎn)線46生產(chǎn)線47藥用凍干機48食品凍干工藝預處理裝盤速凍捕水器溫度降至40以下加熱真空升華干燥解吸干燥包裝49預處理和后處理由于凍干食品為多孔疏松形態(tài)，表面積增大數(shù)十倍，而且水分低，干物質(zhì)濃度高，且直接暴露在環(huán)境中，因此，在不影響食品質(zhì)量前提下，可以采用鈍化酶活性的處理方法。在凍干后，包裝環(huán)境濕度和包裝材料的透氣性要求嚴格。50共晶體凍結(jié)51非

8、共晶體凍結(jié)52晶體、玻璃體與橡膠體晶體：分子近程有序，遠程也有序。玻璃體：分子近程有序，遠程無序。其粘度達到1014 Pas。橡膠體：分子近程有序，遠程無序。其粘度達到104 Pas。 53部分玻璃化轉(zhuǎn)變溫度54食品凍結(jié)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食品凍結(jié) 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蛋白質(zhì)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升華干燥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凍干終點判斷凍干品溫度內(nèi)外一致（升華干燥結(jié)束）捕水器溫度下降（升華干燥結(jié)束）干燥箱壓力下降解吸干燥結(jié)束（試驗確定）61解吸干燥時間殘余水分要求低的制品，降低捕水器溫度。提高供熱量，加速解吸。適當提高干

17、燥箱的壓力，改善供熱條件。62升華干燥和解吸干燥63凍干工藝曲線64共晶溫度干物質(zhì)冰晶若在凍結(jié)與昇華過程中，產(chǎn)品的溫度高過了最低共晶點，則部分或全部溶質(zhì)將處於液相中原預期冰晶體的昇華現(xiàn)象被液體的濃縮蒸發(fā)現(xiàn)象所取代，致乾燥後的產(chǎn)品將發(fā)生萎縮。一些活性物質(zhì)由於長時間處於高濃度電解質(zhì)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塌陷溫度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