In the production and life of humans, there is often a case where it is necessary to remove moisture from an object. The object can be either solid or liquid or gaseous. In most cases, the moisture content of the object is moisture, and sometimes it is other components, such as inorganic acids, organic solvents, and the like. This process of removing moisture in an object is called “dehumidificationâ€. People dehumidify methods into several categories based on different working principles. Drying is one of them.
In general, people use the thermophysical method to dehumidify the process as “dryingâ€. It is characterized by the use of heating, cooling, decompression, or other energy transfer methods to cause the moisture in the material to evaporate, condense, sublimate, and other phase transitions. Separation from the object to achieve dehumidification. In the pharmaceutical industry, it is particularly important for the drying of APIs. The drying equipment used must meet the GMP requirements to ensure that the pharmaceutical production process is reasonable, the product is uniform, there is no accumulation of material, and the CIP requirements can be met. Drying devices on APIs also meet the requirements of on-line sterilization (SIP). At present, there are many types of raw material drying equipment in China, roughly including vacuum drying oven, vacuum rotary dryer, three-in-one equipment, air dryer, spray dryer, fluidized bed, fluidized bed, and freeze dryer. The spray dryer is used as an example to discuss the requirements of the spray dryer in the pharmaceutical industry in conjunction with the actual pharmaceutical process and GMP requirements.
1 Requirements for spray dryers in the pharmaceutical industry
1.1 Atomization device
Spray atomizers for atomizers are generally centrifugal, pressure and air flow. Centrifugal atomizer has a centrifugal shaft inside the drying shaft of the drive shaft to prevent the fine-grained off of the shaft seal; it is difficult for the pressure atomization system to feed the material liquid through the high-pressure pump, and the piston and cylinder friction during operation. And the seal of the connecting rod will affect the cleanness of the liquid. In comparison, the air atomization can be cleaned and filtered by atomizing air and feed liquid before entering the tower, and the particles (including bacteria) entrained in it can be filtered out, so it is more suitable for drying in the pharmaceutical industry.
1.2 Filtration of feed liquid and atomized compressed air
The liquid before spray drying should be filtered through a microporous membrane of 0.3 μm before being introduced into the spray tower. At the same time, the oil and water entrained in the compressed air before atomization should be removed before filtration through the microporous membrane.
1.3 hot air
Hot air originates from the atmosphere, the amount of entrained dust particles is large, and the flow rate is large. After heating, the temperature is required to be above 140° C. The heater will peel off particles during operation. For this reason, the hot air filtration system should be considered in accordance with the hot air temperature requirements, and an air filter that can withstand high temperatures and endurance for a long period of time is developed.
1.4 Dry product delivery
Clean air around the vents of the dry goods should be used to prevent the surrounding environment from being mixed with dry products.
2 Pharmaceutical Industry Expectations for Spray Dryers
From the working principle of the spray dryer, it can be known that the drying process of the spray dryer is similar to the drying of the air flow. After the air is filtered, the air is heated by the heater. The hot air produced is filtered through several stages (selected according to the pharmaceutical grade), and then it is wormed on the top of the drying chamber. The shell passage is generated by the hot air distributor to generate a uniformly rotating airflow into the drying chamber. The material is filtered through centrifugal atomizer discs or pressure nozzles to produce a dispersed, fine material mist. The material mist is in contact with the swirling hot air and the moisture rapidly evaporates. The material is dried in a very short time. This equipment is suitable for the drying of liquid materials with good fluidity such as solution, emulsion, suspension, paste, etc. Our company has been using such equipment to produce Wei Su Granules (without sugar). Its structure is shown in Figure 1.
Of course, due to the late start of Chinese pharmaceutical machinery, there is still a certain gap between the current domestic spray drying equipment and similar foreign equipment. If the drying equipment is compared to a person, the control system is equivalent to human nerves, and the level of control determines the reaction speed of the drying equipment. Many dried materials become products, that is, drying is often the last step in production. The stability of the drying process controls the quality of the product to some extent. Drying operations generally have two production methods, one is continuous production, and the other is batch production. Regardless of which production method, control methods play a very important role in stabilizing product quality. For the continuous production process, the correlation factors of various operating parameters, such as heat, air flow, feed volume, equipment operating parameters, and the linkage relationship between on-line measuring instruments should all be implemented with appropriate control measures. For the batch production process, the control of the drying end should also be controlled by the control device. Compared with foreign equipment, China's production of drying equipment mainly manual or semi-automatic control means, the parameters can not be related to each other, the operation of many human factors, and objectively affect the product quality.
Secondly, the drying equipment involves various processes such as material transportation, heat transfer, fluid movement, and even crushing, and requires high processing and manufacturing equipment or machinery. Over the years, the processing methods and processing equipment of domestic drying equipment have also taken more traditional manual manufacturing, which has been affected by the function and appearance of the equipment. Not only that, the manual single-piece manufacturing can not guarantee the good interchangeability of the parts' dimensions, and brings inconvenience to the maintenance of drying equipment and the exchange of wearing parts. Most foreign drying equipment adopts automatic welding technology, weld polishing, and the equipment surface is also polished or passivated. In order to shorten the gap with foreign countries, we must start with improvements in terms of equipment intelligence, processing methods, and processing quality.
3 Conclusion
The future development of the spray dryer will be in-depth study of the drying mechanism and material drying characteristics, master the optimum operation conditions for different materials, develop and improve the spray dryer. In addition, large-scale, high-strength, high-economy, and improved adaptability to raw materials and product quality are the basic trends in the development of spray dryers. At the same time, the development of spray dryers must also pay attention to energy-saving and energy comprehensive utilization, as well as the development of automatic dryer control technology to ensure the realization of optimal operating conditions. In addition, as people attach importance to environmental protection, improving the environmental protection measures of spray dryers to reduce the leakage of dust and exhaust gas will also be a direction that needs further study.
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