When the operating cost of freeze-drying machines accounts for a relatively large proportion of the total output value, reducing operating costs and improving production efficiency are particularly important.

The factors that affect the operating cost of freeze-drying machines mainly come from three aspects:

1. The influence of materials, such as eutectic point, thermal sensitivity, geometric size or thickness, will have a significant impact on the required drying time and operating costs;

The influence of the adopted process route, such as the determination and control of the final freezing temperature, freezing rate, heating temperature, heating rate, and machine, will have an impact on the drying speed and operating cost of the material.

3. The impact of the freeze-drying machine itself. The performance, limit parameter indicators, comprehensive capacity, energy utilization efficiency, operational stability, and ease of operation of freeze-drying machines will all have an impact on drying efficiency and operating costs, and even have a serious impact.

Several ways to reduce operating costs

1. Materials with relatively simple compositions generally have a higher eutectic point, such as vegetables, which have a freezing temperature of only about -15 ℃, a shorter freezing time, corresponding heating time, relatively less energy consumption, and lower operating costs. And the composition is complex, materials containing organic or inorganic components such as salt, sugar, fat, amino acids, solvents, etc. have lower eutectic points, lower freezing temperature, longer freezing time, corresponding heating time, and higher operating costs.

2. Some biological products such as fungi, vaccines, and other materials have very high thermal sensitivity, and the heating temperature should not be too high (-15 ℃~30 ℃), making it difficult to absorb heat. Therefore, they require a long drying time and high operating costs. Materials with low thermal sensitivity (such as regular food) can be heated at a high temperature (75 ℃~100 ℃), resulting in significantly shorter drying time and lower operating costs.

3. Under the same weight, the smaller the geometric size and the larger the ice surface area of thin and loose materials, the more conducive they are to sublimation and the shorter the drying time. If larger materials are cut or broken into smaller pieces, it can greatly improve the sublimation drying speed and reduce operating costs.

4. Reducing the thickness of product loading and appropriately increasing the drying shelf area while maintaining the same loading amount and equipment power consumption can improve the heat transfer capacity of the drying shelf, shorten the freezing and heating drying time, and reduce operating costs. However, equipment investment may slightly increase.

The choice of process route also affects drying speed and operating costs:

The quality and performance of different freeze-drying machines vary greatly, and the performance related to drying rate is mainly determined by the cold trap temperature. The pressure difference between the drying box and the cold trap is determined by the temperature difference between the materials in the drying box and the condenser. The larger the temperature difference between the two, the greater the pressure difference. The faster the water vapor flows from the drying box to the condenser, the shorter the drying time. Therefore, the temperature of the cold trap is an important factor affecting the operating cost. However, obtaining a lower cold trap temperature at the cost of higher energy consumption will still increase operating costs, so energy consumption indicators are also important. In addition, the changes in vacuum degree and thermal conductivity of freeze-drying machines also have a certain impact on operating costs.

1. Control the pre freezing speed to create ice crystal structures that are conducive to sublimation. The pre freezing speed is too fast, with small ice crystals and dense pores in the dried layer. The resistance of water molecules to flow through the dried layer is high, which affects the drying speed. Reducing the pre freezing speed appropriately to make the ice grains coarse and the pores of the dried layer large will be beneficial for water vapor flow and drying speed, but the premise is to ensure product quality.

2. Control the pre freezing temperature. The pre freezing temperature should be controlled below the eutectic point of the product. If it is too low, it will waste the cooling time required to exceed the temperature and the heating time required to return.

3. Control the heating temperature. The initial heating temperature should not be too high. The outer ice surface of the product is easily melted by heat, and the heating temperature should be slowly increased from low to high. After the initial heating stage, the heating temperature can be increased as soon as the cold trap capacity allows and the product temperature does not exceed the co melting point, in order to shorten the operating time under insufficient heating. The allowable temperature for heating different products varies. The higher the allowable temperature, the higher the heating temperature, and the faster the drying speed.

4. Control of residual moisture content in the product. The residual moisture content of the product should be appropriate. If it is too low, it will prolong the drying time, while if it is too high, it is not conducive to the long-term storage of the product.

5. In the middle and later stages of drying, as the thickness of the dried layer of the product increases, an insulation layer is added, making it more difficult for the surface of the ice layer to be heated. The drying speed is greatly slowed down. In a vacuum environment, the air is thin, and conduction and radiation are the main methods for heating the ice layer of the product. Improving heat transfer is an effective way to accelerate the drying speed.

6. Reduce the temperature of the condenser. As a large amount of water molecules from the drying oven are captured by the condenser and form an ice frost layer on the surface of the condenser, it is like covering the surface of the condenser with a cotton quilt, forming a temperature difference between the condenser surface and the frost surface. The thicker the frost (usually 10-50mm), the greater the temperature difference (10-30 ℃). As the thickness of the frost increases, the surface temperature of the frost layer gradually rises, even approaching the surface temperature of the product's ice layer, and the pressure also gradually increases, causing the water vapor pressure difference between the freeze-drying box and the condenser to gradually decrease, the drying rate to gradually decrease, and even stopping frost capture, the product will also melt. Therefore, reducing the temperature of the condenser as much as possible will help ensure the effective temperature difference and pressure difference between the drying box and the condenser. The temperature of a typical condenser ranges from -40 ℃ to -50 ℃. Lowering the temperature of a condenser, such as -60 ℃ to -70 ℃ or even lower, may be subject to cost considerations. But products with lower eutectic points, such as -30 ℃ or below, should choose freeze-drying equipment with a condenser temperature between -60 ℃ to -70 ℃ or even lower.