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Is freeze drying really possible?

Release Date: 2019/10/18 17:41:33 .
Browse: 357

Is freeze drying really possible?
I began to hear that when I was lyophilized, I was puzzled by hot drying, but it seems a little impossible to freeze-dry. Let us look at how freeze drying is applied to the technology of vacuum dryers. After reading it, I must be able to lift the doubts in everyone's mind.
Freeze drying technology:
There are heat carrier inlet and outlet pipes on each layer of heating plate. Generally, the upper layers are made of low-pressure saturated steam or hot water, hot oil in series, parallel or series-parallel input heating to control the temperature of each layer; and the bottom two layers are connected to cooling water. To reduce product temperature, recover heat and ensure quality. The heating plate is fixed on the frame of the cylinder at a certain interval, and is placed horizontally. Each layer is equipped with a cross arm frame, and the upper and lower layers are staggered and fixed at 45° on the central spindle, and the worm wheel reducer and the continuously variable transmission are arranged. And the motor and other drives, slowly rotate at 0.6~3.7 (r/min). Each of the booms is provided with a plurality of detachable hoe-shaped rakes or flat squeegees arranged equidistantly. The sill leaves are hinged and reed swaying structure, so that the bottom edge floats evenly on the disc surface, and the 耙 leaf angle can be arbitrarily adjusted according to the material properties to ensure that the material advances continuously on the disc surface.
The material to be dried is continuously fed from the top disc feeder to the inner ring surface of the upper heating layer of the upper layer of the heating plate, and under the mechanical action of the rotary rakes, while tumbling and stirring, continuously moving forward from the inside to the outside, Zigzag is covered on the entire surface of the disk, and is heated by contact; then the material falls from the outer edge to the outer surface of the outer layer of the second heating plate below, and is moved from the outside to the inside under the action of the reversely mounted raft leaves. The inner edge falls to the inner ring surface of the third heating plate. By analogy, the materials are moved layer by layer from top to bottom, and are continuously heated and dried. The evaporated moisture is mixed with the exhaust gas in the equipment and naturally discharged from the upper outlet. The final dry material falls onto the lower tray, and is continuously discharged from the raking blade to the bottom discharge opening to obtain a qualified dry product. According to product performance, drying requirements and processing capacity, the plate dryer adopts a series of steps such as stepless speed regulation of the spindle, manual adjustment of the height of the disc feeder to adjust the height of the heating plate, control of the temperature distribution of each layer of the heating plate, and final cooling and cooling. The superior performance of the plate dryer.
During the lyophilization process, the temperature pre-freezing of the liquid articles and the subsequent sublimation of the moisture in the solid matter need to control the temperature within a certain range of the process requirements, which requires the freeze dryer to have a certain precision temperature adjustment function. The temperature adjustment problem of the freeze dryer is better solved without setting the temperature control unit. The specific scheme is as follows:
1. In the premise of the refrigeration capacity of the refrigeration compressor, a refrigeration branch that can provide appropriate cooling capacity is provided next to the refrigeration system piping for cooling the front of the freeze dryer to meet the cooling demand during temperature adjustment;
2. At the same time, due to the temperature adjustment, the refrigeration compressor is supplying cooling to two evaporators with different evaporation temperatures. The difference in working conditions may cause a large impact on the refrigeration compressor due to the hysteresis of the expansion valve control. In severe cases, It will cause the liquid pressure of the refrigeration compressor to cause a failure, which requires a good grasp of the control of the return steam pressure. The technicians now add an electromagnetic valve to the steam return line of the front tank evaporator, and the electromagnetic valve is passed through the pressure controller. The monitoring of the differential pressure before and after to control the opening or closing of the valve reduces the load shock during the temperature adjustment to ensure the smooth operation of the compressor;
3. In order to prevent the pressure in the front tank evaporator from rising due to the closing of the electromagnetic valve, the temperature adjustment effect is not guaranteed, and the technician adds a steam return pipe to the steam return line in front of the electromagnetic valve, and is connected to The two-stage compressed suction pipe of the refrigeration compressor proves that this treatment scheme is feasible through the practice on multiple freeze dryers. It can avoid the increase of the cost of adding the temperature control unit and solve the present problem. The commonly used capillary temperature regulation results in an unsatisfactory temperature regulation effect and a load shock to the compressor.

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