Fried Vegetables Products,Fried Carrot,Vacuum Fried Products,Vacuum Dried Onion Huaiyang County Wanyuan Garlic Foods Processing Industries Co.,Ltd , https://www.wanyuangarlicfood.com
Key words: boiling drying; pharmaceutical; problem; improvement
Boiling dryers are often the equipment of choice in the production of solid formulations. Boiling drying has the advantages of good heat transfer effect, large production capacity, uniform temperature distribution, various operation modes, adjustable material residence time, low investment cost and small maintenance workload. After more than 30 years of use and improvement in China, it has shown its unique position in the field of drying, and it is now increasingly playing an important role in pharmaceutical, chemical, food and other aspects.
1 boiling dryer's working principle, process and characteristics
1.1 Working principle
Boiling drying, also known as fluidized bed drying, uses hot air flow to suspend wet particles, fluidized boiling causes heat exchange of materials, and the evaporated water or organic solvent is carried away by hot air, which uses hot air flow to carry out materials. The mass-heat transfer mode of gas-solid two-phase suspension contact achieves the purpose of drying wet particles [1]. Fluidized bed drying technology involves two mutual processes of heat transfer and mass transfer. In the convection drying process, hot air is transferred to the surface of the material by contact with the wet material, and then transferred from the surface to the inside of the material. This is a heat transfer process; after the wet material is heated, the surface moisture is first vaporized, while the internal moisture Disperse to the surface of the material in a liquid or gaseous state, and continuously vaporize into the air, so that the moisture of the material is gradually reduced, and drying is completed, which is a mass transfer process.
1.2 Workflow
The material is transported to the ebullating bed by the skip, and is sealed with the ebullating bed by the sealing ring under the action of the cylinder jacking. Then, under the action of the induced draft fan, the air is purified by the filtering device, heated by the radiator, and then distributed into the boiling bed (drying chamber) through the air distribution plate (screen). The material in the hopper forms a boiling state (ie, fluidization) under the action of hot air and agitation. In the large-area gas-solid two-phase contact, the moisture (or solvent) inside the material evaporates in a short time and discharges with the air. Take away and the material is dried.
1.3 technical characteristics
(1) The heat transfer effect is good, the temperature inside the bed is relatively uniform, and the heat capacity coefficient (or volume heat transfer coefficient) is high, and the production capacity is large;
(2) Due to the uniform temperature distribution in the fluidized bed, any local overheating of the product can be avoided, so it is especially suitable for the drying of certain heat sensitive materials (such as grinding, polyacrylamide, etc.);
(3) Continuous operation can be performed in the same equipment, and intermittent operation can also be performed;
(4) The residence time of the material in the dryer can be adjusted as needed, so the moisture content of the product is stable;
(5) Independent electrical cabinet and PLC human-computer interaction operation control, integrated all drying parameter settings, safe and convenient operation;
(6) The drying device has few mechanical transmission components, the investment cost of the equipment is low, and the maintenance workload is small.
2 suggestions for improvement of boiling dryer
After long-term application and development, the boiling dryer has obvious improvement in structure and performance, and the quality is also constantly improving, but there are still some problems. The following suggestions are proposed in combination with production practice:
2.1 Suggestions for improvement of insufficient utilization of thermal energy
The boiling dryer is formally an air convection drying device. Compared with the conduction drying device, the energy consumption is indeed larger, but if some measures are taken, a good energy saving effect can be achieved.
Suggestions: (1) Strengthen the sealing effect of the equipment. At present, most of the boiling dryer hoppers and the equipment body are connected by flat flanges, and the sealing effect is poor. It is recommended to use the concave-convex flange connection when designing; (2) Many of the dryers use steel tube winding fins for heat exchange, steel pipes Although it can save material cost, but the heat transfer effect is not good, it is recommended to use copper pipes; (3) increase insulation measures. Add insulation to the outer casing of the heat exchanger to reduce heat loss.
2.2 Suggestions for improvement of trapping and dust removal devices
The basic condition for a smooth fluidization process is that the material has a good fluidization state, and a high efficiency filter dust collector allows this state to continue. The dust removal efficiency of the filter dust collector largely determines the boiling effect. The dust removal methods currently used mainly include shaking bag dust removal and pulse back blowing dust removal.
2.2.1 Dust bag dust removal
The reciprocating motion of the cylinder realizes the vibration of the collecting bag to achieve the dust removing effect, and the bag is made of anti-static and fiber-free cloth, and the collecting bag is in the form of integral lifting. The problem is that the bag filter is inconvenient to disassemble and assemble. The material selection of the sling is not reasonable and it is easy to cause deformation, resulting in poor sealing, which will also cause changes in running powder and air volume, which not only pollutes the environment, but also reduces product yield. Recommendation: The filter bag is connected by clamp connection. The hanging ribs are made of rigid materials that are not easily deformed, and the bags are regularly checked and replaced.
2.2.2 Pulse backflushing
With the further improvement of domestic solenoid valve technology and the further reduction of price, pulse backflushing has gradually become the mainstream of the capture device. The filter elements currently used mainly include cloth bags and stainless steel sintered mesh. Among them, stainless steel sintered mesh filter is the only product that can guarantee 99% or more of any material yield. As the problem of cleaning technology has been basically solved, the advantages of stainless steel sintered mesh filter in terms of yield and service life are gradually emerging, and the use of pharmaceutical plants is also increasing.
In addition, as the requirements for environmental protection are getting higher and higher, it is recommended to improve the dust removal system and increase the secondary dust removal device.
2.3 Suggestions for improvement of air distribution plate (screen)
The air distribution plate in the boiling dryer has two functions, one is to support the material layer, and the other is to make the gas distribution uniform. The size, shape, distribution potential, and opening ratio of the opening of the distribution plate all have a crucial influence on the distribution of the fluid. Uneven gas distribution will cause a "circulation" in the bed, which tends to cause "channeling" in some parts of the bed, while the rest is a deadbed. At this time, most of the gas follows the bed. Some of the channels are short-circuited through the bed in the form of "channeling", which makes the gas-solid contact greatly deteriorated, which should be avoided. A good distribution plate design should be able to suppress the occurrence of unevenness in the bed. That is, when the pressure drop is lowered and the airflow speed is increased in some parts of the bed, the resistance generated by the distribution plate should suppress the increase of the airflow, thereby suppressing The deterioration of fluidization.
At present, most of the boiling air dryers use a single airflow distribution plate, and most of them use vertical perforated plates or mat-shaped mesh plates. The materials are prone to fluidization unevenness or dead angles during fluidization, and cannot be ensured in the particles. The uniformity of the drug, while the single opening form can not meet the production process requirements of different drugs. On the other hand, in order to reduce the leakage loss of the drug, a multi-layer mesh structure is generally used at present, and the airflow distribution plate and the boiling bed body are mostly fixed by a large number of bolts, which is inconvenient to disassemble, difficult to clean and cause residual pollution and cross-contamination. Suggestion: Using computer fluid dynamics model, heat transfer and mass transfer model, aerodynamic and thermodynamic simulation calculation and verification of parameters such as hole spacing, aperture and opening ratio in the design of air distribution plate to meet the production of different materials. Process requirements. In the installation mode, the connection method is made detachable to ensure quick installation and thorough and complete cleaning.
2.4 Suggestions for improving the treatment of intake air
The air intake of hot air is generally installed in the auxiliary machine room, and is installed together with the heating device and the muffler. The auxiliary machine room and the clean area do not have straight through doors and windows. The air cleanliness level of the auxiliary machine room is often low, which will affect the medicinal heat. The quality of the air requires that the equipment itself has a good purification device, otherwise the unpurified air will contaminate the drug and it is difficult to meet the GMP requirements.
At present, many domestic equipments for air handling units are: primary filter - medium efficiency filter - steam heating (or electric heating) - (sub) high efficiency filter. Although the air treatment system is equipped with primary, medium and high-efficiency filters, as the running time increases, the high-efficiency filter will be blocked or damaged. At present, it can only be judged from the appearance to determine whether it needs to be replaced, and there is no theoretical basis. Early replacement will increase the cost, and delaying the replacement will bring the risk of degraded air quality, thus affecting the quality of the product. Recommendation: Add a differential pressure display device before and after the high-efficiency filter. When the pressure difference reaches a certain value, the alarm prompts replacement.
In addition, most of the equipment does not have a dehumidification device, and air dehumidification problems always exist, especially in the late spring and summer, the air humidity is very large, and if the dehumidification is not performed, the drying of the material will be greatly affected. Recommendation: Increase the dehumidification device.
The induced draft fan of many boiling dryer equipment is not linked to the damper, which may cause air backflow between the fan shutdown and the butterfly valve closing. Recommendation: The start and stop of the fan is linked with the switch of the damper. When the fan starts, the damper is opened at the same time. When the fan stops running, the damper is closed synchronously to ensure that air backflow does not occur.
Suggestions for the application of boiling dryers in the pharmaceutical industry
Starting from the working principle of the boiling dryer, some problems existing in the current equipment are briefly analyzed, and some suggestions for improvement are put forward.