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The design of a freeze dryer is a complicated engineering project. Small DIY projects can be done, however, commercial grade freeze dryers must be meticulously refrigerated, have vacuum systems and high-quality control to produce reproducible results. In Jiangsu Bolaike Refrigeration Science and Technology Development Co., Ltd. we have developed and produced freeze drying equipment for over 20 years, household appliances to large food and pharmaceutical production lines. The following is a description of the construction of professional freeze dryers.
1. Designing the Vacuum Chamber and Condenser
The core of any freeze dryer is the vacuum chamber. It has to resist external atmospheric pressure (14.7 psi) but at the same time a close-to-vacuum interior. In the case of small laboratory and household freeze dryers (0.5 to 5 m2 of shelf area) the chamber is usually a welded stainless steel cylinder with a hinged door and a sight glass. In large food and pharmaceutical freeze dryers (30-200+ m2 shelf area), the pressure vessel is a cylindrical or rectangular chamber, with a number of shelves, loading door, and a second condenser chamber. The condenser consists of a series of cold coils (stainless steel) which freeze water vapor that is sucked out of the chamber. All product contact surfaces at Jiangsu Bolaike are made of food grade 304 or 316 stainless steel. Ports that allow vacuum sensors, temperature probes and electrical feedthroughs are also designed into the chamber.
2. Assembling the Refrigeration and Heating Systems
The refrigeration system performs two important tasks; the freezing of the product and cooling down of the condenser coils. Compressors used in industry (usually two stage or cascade) must have the ability to achieve -40°C to -50°C with food products and -85°C with pharmaceutical use. The heating system supplies mild and regulated heat in the drying cycles. In factory freeze dryers, the shelves are hollow plates that are filled with a heat transfer fluid (silicone oil). This is done by an electric heater warming the fluid, and a pump circulating it through the shelves. The shelf system should be as flat as possible (less than 0.5 mm) to allow the same drying of all trays. To produce this flatness, Jiangsu Bolaike has precision machining and robotic welding in its manufacturing process.
3. Integrating the Vacuum System and Control Electronics
The vacuum system removes air and non-condensable gases in the chamber allowing sublimation. A two stage rotary vane pump is adequate with small freeze dryers (achieving <10 Pa). To save on cycle times a combination of roughing pumps with high vacuum pumps (roots blowers) is employed in large industrial systems. The brain of the freeze dryer is the control system. Programmable logic controllers (PLCs) check the pressure in chambers, temperature in shelves, temperature of products, and temperature of condensers. The freeze drying recipe (freezing, primary drying (sublimation), and secondary drying (desorption)) is automatically performed by them. The control systems used in Jiangsu Bolaike have touchscreen interfaces, data logging, and ability to monitor remotely. The door has safety interlocks to prevent opening when the chamber is under vacuum.
4. Quality Control, Testing, and Certification
The actual construction of a freeze dryer is not completed with assembly, all the machines should be properly tested. The vacuum system is checked on the leaks (vacuum maintained 24 or more hours without an increase of 5 Pa). The refrigeration is measured at the cooling rate and final temperature (e.g. -50°C in 60 minutes with the condenser). The heating system is checked to ensure consistency in all shelves (usually within a range of ±1°C). Lastly, it is completely frozen then dried with water or a surrogate of the product to check a cycle time and final moisture content. The 12,000 m2 factory of Jiangsu Bolaike is under ISO9001 quality management and our machines are also CE certified to export them to Europe, Asia and the Americas. Our engineering team has over 56+ national patents and is constantly advancing every part, including more efficient vacuum pumps to smarter defrost systems.
Conclusion
The construction of a professional freeze dryer will demand accuracy of engineering the vacuum chamber, refrigeration and heating, vacuum pumps, and control electronics. The delivery of every machine is subject to leak, cooling, heating, and cycle tests. Jiangsu Bolaike is a manufacturer of household, laboratory, pharmaceutical, and food freeze dryers with more than 20 years of experience, an ISO9001 and CE certification and 56+ national patents. Freeze drying or factory tour in Changzhou, China. Contact us today to discuss your freeze drying needs or have a factory tour.