Fog drying technology uses the method of spraying to disperse the material in the hot airflow in the form of mist droplets. The material is fully contacted with the hot gas, and the process of heat transfer and mass transfer is completed in an instant so that the solvent (including water and organic solvents) evaporates quickly. For the gas, to achieve the purpose of drying. buy spray dryer technology is widely used in my country's pharmaceutical industry. In the field of oral solid preparations, it is often used in the drying of highly heat-sensitive drugs and easily decomposed drugs during the concentration of feed liquids. The obtained product has fine and uniform particle size and good fluidity and instant solubility.
Characteristics and classification of spray dryer:
A spray dryer is a drying device that directly dries a solution or suspension into solid particles. The dry product can be obtained directly from the feed liquid, eliminating the need for unit operations such as evaporation, crystallization, separation and pulverization. It can be produced continuously and automatically, and the operation is stable. Using this drying method, the gas-solid two-phase contact surface area in the spray dryer pharmaceutical engineering is large, and the drying time is short, and the general drying time is 5-30s, which is suitable for drying heat-sensitive materials. The quality of the product obtained by drying is good, particles of 30-50 μm can be obtained, and the product has good fluidity and instant solubility. The disadvantage is that the dryer is large in size and low in heat transfer coefficient, resulting in low thermal efficiency and large power consumption.
There are many classification methods of spray dryer industrial, which can be divided into the parallel flow, counter flow and mixed flow according to the gas-liquid flow direction; according to the installation method of the atomizer, it can be divided into upper spray type and lower spray type; The structure of the device can be divided into centrifugal type, pressure type and airflow type; according to whether the heating gas is circulated, it can be divided into open type, partial circulation type and closed type.
The basic process of spray drying:
The material liquid is atomized by the atomizer and dispersed into fine droplets and enters the drying chamber. At the same time, the heated gas is sent to the heater through the blower to heat up, and then enters the drying chamber. The liquid droplets and the hot gas are fully mixed and contacted in the drying chamber. The liquid in the droplets is instantly evaporated into gas, and the material is dried into fine particles. The mixed gas-solid two phases are sucked into the cyclone separator by the induced draft fan, the two phases are separated, the solid material settles to the bottom collector, and the gas phase is led to the dust filter to capture the escaped material. After the filtered gas phase is condensed by the condenser, the solvent carried by the gas phase becomes liquid, which can be collected and used, and the gas used as the carrier is dried and recycled in the system.
Process requirements for oral APIs:
There are many kinds of oral solid preparations, and the specific process requirements are also very different. In the process of design and manufacture of spray dryer pharmaceutical engineering, it is best to make different designs for different varieties to achieve the best state of equipment and process. When choosing a spray dryer industrial for the production of solid preparations, some requirements listed below are often put forward:
1. cleanliness requirements
The main process of API production needs to be carried out in a clean environment of class 100,000, and buying a spray dryer is an important process of quality control. The part of the spray dryer that contacts the material should be made of stainless steel. For the material with strong acid corrosion, it is best to use 316L stainless steel. The drying chamber, cyclone separator, filter and other parts that directly contact the material should have a smooth inner wall, no dead angle, easy to clean, easy to disassemble, and easy to clean.
2. avoid sticking
The Wall phenomenon is still a prominent problem that hinders the normal operation of spray dryers so far, especially in the spray drying process of solid preparations (especially in traditional Chinese medicine). Material sticking to the wall is not only unfavorable for the collection operation, but also with the extension of time, the sensitive sticking material will deteriorate and become unqualified material. From the process point of view, the solutions include selecting appropriate solvents, adding auxiliary materials, and changing process parameters, but these methods have little room for adjustment, so a fundamental solution must be sought from the perspective of equipment.
3. Self-control performance
Spray drying is a continuous production process with many control points. For example, the control points of the closed cycle system include feed concentration, feed speed, air inlet speed, air inlet temperature, system pressure, a pressure difference of each component, gas purity detection, etc. It is very difficult to rely on traditional manual adjustment. A good automatic control system can make the entire spray drying system run smoothly, reduce the unqualified rate of products, and reduce potential safety hazards. At present, domestic products are relatively backward in terms of automatic control, while some foreign advanced equipment, such as the spray dryer of Denmark Nilu Company, are very mature in terms of automatic control technology.
4. drying effect
Since the oral API still needs to complete the preparation process, in order to improve the preparation effect and the absorption effect of the final drug, different requirements are placed on the physical properties of the spray-dried product. First of all, the moisture content is the first indicator of dry products, and it is generally required to be controlled within a certain range, not too high or too low. Secondly, the sub-packaging of drugs is generally controlled by volume, which requires a stable bulk density of the product and better fluidity of the product. Oral granules often require instant solubility. Generally speaking, by changing the dispersion degree of atomization or appropriately changing the operating conditions to control the drying rate, products with different bulk densities can be obtained, but the range of changes is limited. One technique worth mentioning in terms of improving physical properties is foam spray drying, in which the feed liquid is foamed first and then spray dried. This method was originally proposed to improve thermal efficiency and was later used to adjust the physical properties of products. It has been proved that the product obtained by foam spray dryer pharmaceutical engineering has a large particle size, porous, multi-concave, rough surface and good instant solubility. In addition, there are some special requirements for oral APIs, such as particle shape. Some require spherical particles with uniform particle size. Generally speaking, by changing the atomization method, different shapes of particles can be obtained. Before choosing a spray dryer industrial, API manufacturers should preferably conduct parameter optimization experiments with the assistance of equipment manufacturers to determine an optimal parameter combination to ensure the drying effect of sprayed drugs.
Due to the different properties of medicines, some higher requirements are also placed on the protection design of equipment. For materials dissolved in organic solvents, the entire system must meet explosion-proof requirements when drying. In the design of accessories such as motors, instruments, and control valves, explosion-proof types must be selected. In addition, in order to prevent the solvent and air from being mixed into an explosive gas, the system cannot be open, but a closed circulation system must be used, and the carrier should be an inert gas, such as nitrogen. In addition, the drying of some oxidizable materials also uses a closed circulation system with nitrogen as the carrier.
6. environmental protection
The spray-dried products are fine particles. In order to meet the requirements of environmental protection, it is not enough for the spray-drying system to use only cyclones to separate products and purify the exhaust gas. At 50mg/(nm) 3 gas; or use a wet scrubber, the dust content of the exhaust gas can be reduced to 15 ~ 35mg/(nm) 3 gas. When nitrogen is used as the carrier, the system should be sealed and the exhaust port should be led to the outside.
7. reduce costs
The inlet temperature of hot air is 250-500°C in co-current operation and 200-300°C in counter-current operation, and the outlet temperature after atomization and drying is generally controlled at 60-100°C. The thermal efficiency of buy spray dryer is low, and the thermal efficiency of industrial-scale spray dryers is generally 30% to 50%. In foreign spray drying with waste heat recovery, the thermal efficiency can reach 70%, but this equipment has economic significance only when the production capacity is greater than 100kg (water)/h. However, when nitrogen carrier and organic solvent are used, a closed circulation system can be used, which can make nitrogen recycled and solvent be used by condensation, thus effectively reducing the production cost.
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