Design and Research of Dynamic Freeze-Drying System

1.Research Background and Significance

Research Background and Significance - Sourced: Medium

Some heat-sensitive dry products, such as fermented biological products, usually do not exceed a drying temperature of 40℃ during the drying process. Only in such a low-temperature environment can the characteristics and activity of the bacteria be preserved to the maximum extent.

For heat-sensitive products that require biological activity, freeze-drying technology has showed its unique advantages. The drying process under low-temperature vacuum ensures that biological tissues and cell structures are not damaged, protecting the stability and activity of many heat-sensitive components.

• The advantages of freeze-drying technology

Advantages - Sourced: stockinvestor

Compared to other drying technologies, vacuum freeze-drying technology (referred to as “freeze-drying technology”) has a series of significant advantages. For example, low-temperature drying is very suitable for most heat sensitive substances such as proteins, and microorganisms, as they do not lose biological activity or undergo denaturation.

When vacuum drying is carried out in a frozen state, the moisture inside the product will directly sublimate from solid to gas, bypassing the process of liquid water, so there will be no concentration phenomenon, and the volume of the freeze-drying product will hardly change, so the original structure of the product can also be maintained.

Vacuum Freeze-Drying Technology - Sourced: provac

At the same time, the nutrients and biological activity in the substance can be preserved to the maximum extent. Under vacuum, the oxygen content is low, which protects some substances that are easy to be oxidized and avoids oxidation reactions during the drying process.

For liquid substances, such as liquid drug, after vacuum freeze-drying, the sample will be dried into a solid state, making it easy to transport and reducing the risk of loss and deterioration during transportation.

When the sample needs to be reused, the excellent water solubility of freeze-drying products ensures that the sample is easily and quickly redissolved in water or other solvents, restoring its original properties and activity. These advantages have made it widely used in various fields such as medicine, food, and chemical engineering.

• The problems of current equipment

The Problems of Current Equipment - Sourced: chintanjain

However, at the same time, the high price and operating costs of equipment, the high energy consumption problem caused by low temperature and high vacuum, the time cost caused by the time-consuming process of low temperature drying, and strict process requirements make it necessary to consider and balance the application of freeze-drying technology in specific scenarios when selecting.

Therefore, it is the main development direction of vacuum freeze-drying technology to reduce to reduce energy consumption, improve drying efficiency, and reduce costs.

• The developing trend of freeze-drying equipment

Developing Trend - Sourced: readytrainingonline

With the continuous improvement of people’s living standards, the growing material demand has become a significant trend in the development of modern society. It can be foreseen that the large-scale application of freeze-drying technology equipment will become an inevitable trend in the development of the industry.

If you want to gain a first mover competitive advantage in the industry, tackling the main challenges in the core technology field of freeze-drying equipment will undoubtedly bring huge benefits. The content of conquering the core technology field of freeze-drying equipment is to develop high-efficiency and low energy consumption freeze-drying equipment.

2.The Current Development Status of Freeze-Drying Machines In China

Freeze-drying Machine - Sourced: vikumer

China’s freeze-drying industry started late and entered the field in the 1950s. However, its initial development was not smooth due to challenges in technology, products, and management. From the 1970s to the late 1980s, China began to explore and study the vacuum freeze-drying technology and equipment.

After 1995, China has made significant progress in the research of freeze-drying technology and the development of vacuum freeze-drying equipment, and freeze-drying process research has been able to align with international standards. Most freeze-drying machines produced after the 1990s adopted computer automatic control, achieving automatic monitoring and adjustment of key parameters such as operating program, temperature, vacuum degree, time, and water content.

The superiority of vacuum freeze-drying has gradually attracted attention to the theoretical research and equipment process research of freeze-drying technology, and has gradually developed in China. There have been several academic exchange conferences on vacuum freeze-drying held in China, such as the two conferences held in Beijing and Harbin in 2002, where multiple papers on vacuum freeze-drying technology and equipment were published. Experts predict that China’s freeze-drying products will gradually dominate the market and are expected to be warmly sought after globally.

Freeze-drying Process - Sourced: pharmaceutical-technology

In recent years, China has made great progress in the research of freeze-drying equipment technology and freeze-drying process in China, with a rapid improvement in its development level. This not only promotes the rapid growth of China’s freeze-drying product market, but also narrows the gap between China and European and American countries in terms of freeze-drying product market size. The current domestic freeze-drying machine market can well meet the demand of the domestic market.

3.A New Overall Design Scheme For Freeze-Drying System

When designing a freeze-drying system, the rationality of its design directly determines the operational stability, reliability, and applicability of equipment on the production line. Therefore, in the design of the scheme, in addition to ensuring that the equipment meets basic functional requirements, special attention should also be paid to the rationality of its layout and the convenience of operation.

Only with such comprehensive consideration and careful planning can improve the comprehensive performance and production efficiency of vacuum freeze-drying machines on the production line. The main innovative points of this new freeze-drying system is introduced below.

• The Workflow of Freeze-Drying Machine

The Workflow of Freeze-Drying Machine - Sourced: researchgate.net

The main working process of a freeze-drying machine is to first place the products that need to be freeze-dried on the metal plate layer in the box before freeze-drying or neatly arrange them in an unsealed bottle on the plate layer, and then proceed with the freezing stage. The sample is quickly frozen below the freezing point to allow water to crystallize.

The next step is to proceed to the sublimation stage. The door of the freeze-drying machine is locked to ensure that the airtightness of the freeze-drying front box can be ensured after opening the vacuum pump switch, establishing an appropriate negative pressure and allowing the freeze-drying machine to heat up under vacuum, causing the moisture inside the product to sublimate.

The freeze-drying oven is connected to the cold trap, and the sublimated water vapor is sucked into the cold trap and frozen and adsorbed on the metal surface that can reach -70 ℃, thereby achieving the capture of water vapor.

• Freeze-drying containers and cold traps

Freeze-drying machine - Sourced: harvestright

At present, the front box of freeze-drying equipment on the market is mostly box type. The drying of products is often static, that is, the current freeze-drying equipment is mostly static drying.

Therefore, in order to improve the efficiency of freeze-drying, the original static drying process is transformed into a dynamic drying process, and this freeze-drying system is designed with an arc-shaped inner surface for containing material particles and freeze-drying them in a freeze-drying container. The freeze-drying container, that is, the outer surface of the front box, is generally spherical, so the “sphere” is used below to refer to the front box.

To further achieve the heating and insulation effect of the freeze-drying container, an inner sleeve layer, a heat exchange medium circulation layer, and an insulation layer are sequentially arranged from the inside out of the sphere. The curved inner surface is set on the inner sleeve layer, and the heat exchange channel of the container is set on the heat exchange medium circulation layer.

By setting up layers, it is possible to improve the insulation effect while ensuring heat exchange between the ball and material particles, thereby enhancing the effectiveness of heat exchange and improving the energy utilization efficiency of the heat exchange medium. The outer surface of the cold trap is generally horizontally placed in a cylindrical shape, and their structures are shown in Figure below.

Spherical Dynamic Drying Equipment

To achieve dynamic drying, the sphere and the cold trap can swing simultaneously during the drying operation. To achieve joint swinging between the sphere and the cold trap, and ensure sealing during swinging, a rotating joint component was designed between the sphere and the cold trap.

The rotating joint components of the system include fixed docking flanges, rotating docking flanges, bearings, and sealing components. Its fixed docking flange is used for fixed connection with the cold trap; Rotating docking flange is used for fixed connection with freeze-drying containers; The bearing is set between the fixed docking flange and the rotating docking flange to allow them to rotate relative to each other, while the sealing component is used to seal the gap between the fixed and the rotating docking flange. Thus achieving the joint oscillation of the sphere and the cold trap.

At the same time, in order to prevent materials from entering the cold trap from the container during the drying process, a filter screen is also installed between the sphere and the cold trap.

• Feed system and stirring mechanism

To achieve a dynamic vacuum freeze-drying process and improve drying efficiency, a feeding method is designed in this system. Firstly, the prepared liquid is transported through pipelines to the granulation tank for refrigeration liquid ammonia granulation to obtain material particles. When feeding, the sphere swings to a certain angle so that the feeding port is directly facing the upper granulation tank screw. The screw outlet is connected to the sphere feeding port, and the material particles are transported to the sphere through the screw for freeze-drying.

However, relying solely on the free swing of the sphere cannot achieve sufficient dynamic drying of the particle materials inside the sphere. Based on this problem, this system has designed a stirring blade, with the stirring blade structure shown in Figure below. The mixing blade is spiral shaped, and the rotation trajectory of the blade can enclose a spherical surface to ensure sufficient mixing of the granular materials inside the sphere.

Spherical Dynamic Drying and Stirring Mechanism

To avoid interference between the mixing slurry and the spherical inner surface during the mixing process, there is a small gap between the mixing blade and the spherical inner surface. At the same time, a heat exchange channel is designed inside the stirring blade for the passage of heat exchange media, allowing for sufficient heat exchange between material particles during the stirring process to improve the rate of water sublimation.

Under the joint action of the swing of the sphere and the stirring paddle, the material particles inside the ball can be in a dynamic drying process. On the one hand, the sphere drive material particles to rotate; On the other hand, the material particles are stirred in the freeze-drying container, allowing for sufficient heat exchange of the material, thereby improving the drying speed of the material particles, allowing for faster sublimation of moisture in the material, and thus improving the freeze-drying efficiency.

• Heating System

To improve drying efficiency, reduce energy consumption and time costs, freeze-drying containers have container heat exchange channels. The heat exchange channel of the container is set in the interlayer of the freeze-drying container, used to pass in the heat exchange medium.

Section View of Freeze-Drying Container

As shown in Figure above, the freeze-drying container is divided into a first hemisphere 110 and a second hemisphere 120 that are fixedly connected together. Both the first hemisphere 110 and the second hemisphere 120 are equipped with container heat exchange channels, and the container heat exchange channels in the two hemispheres are independent of each other. The heat exchange medium in the first hemisphere 110 passes through the first medium inlet 112 and the first medium outlet 114, while the heat exchange flow medium in the second hemisphere 120 includes the second medium inlet 122 and the second medium outlet 124, thereby achieving heat exchange with material particles and improving freeze-drying efficiency.

4.Practical Engineering Application Cases

Application - Sourced: pixelplex

Using 35 kg skim milk powder, 15 kg mannitol and water as raw materials for liquid mixing, followed by liquid nitrogen granulation. The material particles were put into the freeze-drying front box for dynamic drying operation. Under the design setting of the dynamic freeze-drying system, equipment operation is carried out through a computer system and data is recorded. Based on the data, a curve result graph is generated as shown in Figure below.

Due to the swing of the sphere and the stirring effect of the stirring paddle, a large amount of water vapor sublimates during each flipping motion of the material, and the sublimated water vapor is quickly captured by the cold trap, causing fluctuations in the vacuum of the front box. After the material inside the current box rises to a certain temperature, it undergoes aeration heating and heat transfer to further accelerate the drying efficiency.

Operating Data Curve

The freeze-drying process of skim milk takes about 42 hours, while the dynamic freeze-drying process of this new model is shortened to 36 hours, resulting in a significant improvement in freeze-drying efficiency and significant cost savings in large-scale production.

Conclusion

With the continuous progress of technology and the increasing demand for industrial development, the freeze-drying industry has increasingly higher requirements for improving production efficiency, ensuring product quality, and achieving green and sustainable production. The dynamic freeze-drying system, with its unique advantages, is gradually meeting these needs and leading the new trend of freeze-drying technology. If you have any question, you can contact Aipak Engineering for help.