How do industrial freeze drying systems work?
工業冷凍乾燥系統是如何運作的 ?
Freeze-driers have three major parts: · A chamber where the product is placed. It is frozen either before entering this chamber or inside of it. · A cold trap (condenser) to capture most of the removed solvent or water. It is a key element as its efficiency will greatly impact the required vacuum capacity and the cost of the system. · A vacuum unit A pre-frozen product is placed in an air-tight drying chamber. A vacuum pump reduces the air pressure inside the chamber until a pressure of 1 to 0.5 mbar is reached. Under vacuum, the evaporation process of the frozen water already starts at -50 to -40° Celsius. The water vapor is then suctioned out of the drying chamber by the vacuum pump and directed into a downstream condenser. In this so-called ice trap, cooled to at least -70° Celsius, the water vapor deposits on a cooling coil as ice. Most of the moisture is removed from the product in this primary drying phase. In the case of many foodstuffs, primary drying is followed by secondary drying. This process takes away more residual moisture by lowering the vacuum level to 0.01 mbar or below while raising the temperature above the freezing point. The drying chamber is then ventilated to atmospheric pressure. For ventilation, dry air or an inert gas is used, so that the dried product cannot absorb moisture from the ambient air. Finally, the dried product, with a water content of one to four percent, is removed for further processing.
冷凍乾燥機有三個主要部分：· 產品的放置室。 會在進入此腔室前或經過冷凍處理。· 用冷阱（冷凝器）捕捉大部分去除的溶劑或水。這是其效率將極大地影響所需真空容量和系統成本的關鍵要素。· 真空單元 預先冷凍產品置於氣密乾燥室中。真空泵浦降低腔室內的空氣壓力，直到達到 1 至 0.5 mbar 的壓力。在真空下，冷凍水的蒸發過程已經從 -50 攝氏度開始到 -40° 攝氏度。水蒸氣接著被真空泵浦從乾燥室抽吸出並導引至下游冷凝器中。在此稱為冰阱的冷卻至至少 -70°C 的溫度下，水蒸氣會隨著冰堆積在冷卻盤管上。在此一級乾燥階段，從產品中移除了大部分的水分。 在許多食品中，主要乾燥之後是次級乾燥。這個製程將真空度降至 0.01 mbar 或更低溫度，同時將溫度高於冰點，以去除更多的殘留水分。 接著將乾燥室通風至大氣壓力。若是通風，則使用乾燥空氣或惰性氣體，讓乾燥的產品不能吸收環境空氣中的水分。最後，移除乾燥產品，含水量為百分之一到百分之四，以便進一步加工。