| In the production process of solid dosage forms, fluid bed dryer is often optional equipment. Boiling dry with effects of heat transfer and large capacity, temperature distribution, various forms of operation, material residence time adjustable, low investment costs and maintenance workload of small advantages. After 30 years of use and improvement in the country has shown its unique position in the dry areas in the pharmaceutical, chemical, food, etc. more and more reflect its important role.
Principles, processes and characteristics of the fluid bed dryer
Boiling dry, also known as fluidized bed drying, which uses hot air flow so that the wet particles suspended fluidized boiling material for heat exchange, evaporation of water or organic solvents away by hot air, the hot air flow of materials gas - solid two-phase suspension of the quality of contact heat transfer way to achieve the purpose of drying the wet particles . Fluidized bed drying technique involves two interrelated heat and mass transfer process. Convective drying process, the hot air through the heat transmitted to the material surface in contact with wet material, and then transmitted by the surface material internal, which is a heat transfer process; wet material is heated, the surface water first gasification, while the internal water liquid or gaseous diffusion into the material surface, and continue gasification into the air, the moisture of the material gradually reduced to complete drying, which is a mass transfer process.
Materials transported by skip to the fluidized bed through the seals in the cylinder jacking under seal with the boiling bed. Then, the air in the role of induced draft fan power by the purification of filtration devices, radiator heating, and then by the airflow distribution board (screen) is assigned into the fluidized bed (drying chamber). Materials in the hopper under the action of hot air and stirring the boiling point (ie, fluidized), in a large area of ??gas-solid two-phase contact, the material inside the evaporation of moisture (or solvent) in a short period of time and with the exhaust air away, the material is dry.
1.3 Technical Features
(1) The effects of heat transfer, uniform bed temperature, high thermal capacity factor (or the volumetric heat transfer coefficient), the production capacity;
(2) fluidized bed temperature distribution, to avoid any local overheating of the product, so drying is especially suitable for certain heat-sensitive materials (such as grinding taro, polyacrylamide, etc.);
(3) in the same equipment can be a continuous operation, intermittent operation;
(4) of material residence time in the dryer can be adjusted as needed, so the product moisture content and stability;
(5) operational control of the independent electrical cabinet and PLC human-computer interaction, integration of all drying parameters set, safe and convenient operation;
(6) mechanical transmission components of the drying plant and equipment investment cost, less maintenance workload.
2 proposed improvements fluid bed dryer
Long-term use and development of the fluid bed dryer in the structure, performance has significantly improved, the quality is improving, but there are still some problems, the following production practice recommendations for improvement:
2.1 inadequate recommendations for improvement of energy utilization
The fluid bed dryer is an air convection drying equipment from the formal and conduction drying equipment, energy consumption is indeed larger, but if you take some measures you can achieve a good energy saving effect. Suggestions: (1) to strengthen the sealing effect of the equipment. Most of the fluid bed dryer hopper with the device body with a flange connection, poor sealing effect when the proposed design switch to the convex surface of flange connection; (2) dryers are used in the steel wound finned heat exchanger, pipe Although the material cost savings, but the effect of heat transfer is not good, it is recommended to switch to brass; (3) to increase the insulation measures. The heat exchanger shell to add insulation layer to minimize heat loss.
2.2 pairs of trapping dust removal device recommendations for improvement
The smooth flow of the process operation conditions is a material has a good flow state, high-efficiency filter dust collector to the continuation of this state. Filter Precipitator efficiency largely determines the boiling effect. The dust shaking bag dust and pulse cleaning dust two kinds.
2.2.1 shaking bag dust
Toi anti-static, non-fiber shedding cloth production, trapping the bag in the form of integral lifting cylinder reciprocating motion capture bag shake vibration to achieve the effect of dust. The problem is the dismantling of the bag filter inconvenient, is not reasonable selection of hanging bars, easy to cause deformation, resulting in Mifengbuyan can also cause changes in the run powder and air volume, not only pollute the environment, but also reduces the product yield. Suggestions: filter bags with clamp connections to connect, hanging bars to choose is not easy deformation of rigid material, and regularly check to replace the cloth bag.
2.2.2 pulse cleaning dust
With the domestic solenoid valve technology to further improve and further reduce the price of the pulse cleaning dust gradually become the mainstream of the traps. Filter used two kinds of cloth bags and stainless steel sintered wire mesh. Among them, the sintered stainless steel mesh filter is the only guarantee any material yield can reach more than 99% of the products. Problem cleaning technology has been basically solved, the advantages of stainless steel sintered mesh filter in the yield and lifetime is gradually revealed more and more pharmaceutical companies use.
In addition, with the increasingly high demand for environmental protection, it is recommended to improve the dust removal system, increased secondary dust removal device.
2.3 on the air distribution plate (screen) recommendations for improvement
Plates of airflow distribution in the fluid bed dryer has two roles, first, the supporting material layer, the gas evenly distributed. Distribution plate hole size, shape, distribution situation, the opening rate and so the fluid distribution plays a crucial impact. Gas distribution is uneven, make the bed "circulation" in its extremes easy to make the bed in some parts of "channeling", while the remaining parts of the death-bed, when most of the gas along the bed some channel in the form of short-circuit "channeling" through the bed to leave, so that the gas-solid contact with a significant deterioration, which should make efforts to avoid. Distribution board should be able to inhibit the uneven bed, that is, when some parts of the bed pressure drop reduces the flow velocity is increased, the resistance generated by the distribution board should be able to inhibit the increase in airflow, thus inhibiting flow deterioration.
Airflow distribution of most of the fluid bed dryer to use a single board in the form, the use of vertical perforated plate or I-shaped stencil material in the flow process is very easy to flow imbalance or dead ends and other issues can not ensure that the particles in drugs evenly, while a single hole in the form can not meet the requirements of the production process of different drugs. The other hand, in order to reduce the material loss of drug leakage, the commonly used multi-layer network structure, the air distribution plate and boiling bed more than a large number of bolts, demolition inconvenient and difficult to clean clean residues cause cross-contamination and other issues. Suggestions: use of computational fluid dynamics model, heat and mass transfer model, pitch, pore size, porosity and other parameters in the air distribution plate design, aerodynamics, thermodynamics simulation and verification, in order to meet the production of different materials process requirements. Installation, the connection is made detachable, to ensure quick and thorough, complete cleaning.
2.4 recommendations on improving the air intake air handling
Mouth of the folk songs of the hot air is generally set in the auxiliary engine room, and heating devices, silencers installed together, the auxiliary engine room and the clean area to set straight the doors and windows, air cleanliness level of the auxiliary housing is often relatively low, it will affect the quality of the medicinal hot air This requires that the device itself has a good purification device, or non-purified air pollution drugs, it is difficult to meet GMP requirements.
At present, many devices on the air handling unit is configured to: the early effect of the filter - in effect filter - steam heating (electric heating) - (Asian) high efficiency filter. The air handling system configured with the early, medium and high efficiency filter, but with increasing run time, high efficiency filter will be blocked or damaged, the only judge from the appearance of up to identify whether the need to replace the lack of theoretical basis. Early replacement will increase the cost of postponed replacement will bring the risk of decline in air quality, thus affecting the quality of the product. Recommendations: to increase the pressure difference before and after the high efficiency filter the display device, alarm replacement when the pressure reaches a certain value.
In addition, most of the equipment does not have a dehumidification device, air dehumidification problem will remain, especially in late spring and summer, the air is very humid, if not the dehumidifier will dry raw materials have a significant impact. Recommendation: increase the dehumidification device.
Many devices induced draft fan and damper linkage, which may lead to the phenomenon of reflux caused by air between the fan is switched off and the valve closed. Recommendation: start and stop of the fan air valve switch linkage up when the fans start air valve open at the same time, when the fan stops running, the air valve synchronization off, in order to ensure that no occurrence of air back.
2.5 combined with enough recommendations for improvement of equipment and production technology
Drying process and equipment design is unreasonable, will lead to energy loss. To solve these problems, the drying characteristics of the product of systematic study to determine the optimal drying process parameters, such as to be dry nature of the materials. The nature of the material itself is the most important factors affect the drying, the shape of the material, size, combination of accumulation of thickness, water, and chemical properties will affect the drying rate. Domestic Apart from a small number of enterprises, most of the equipment manufacturing enterprises lack understanding of the preparation process technology and process tests necessary condition is not very good conditions of use of various materials to understand, it led to insufficient research and development, it is difficult to carry out the development of new varieties .
2.6 control system improvement suggestions
At present, the operating parameters of the fluidized bed equipment is generally set to the operator's experience-based, but is fully capable of intelligent, process parameters can be traced back, which the fluidized bed equipment, electrical control system high demand. In the electrical control system, you need to detect temperature, humidity, pressure, pressure, wind speed, hours of operation, dust concentration range of devices and the underlying data, and then through the transmitter transmission and storage to the touch screen, touch screen data storage analysis, and then develop a suitable process route, you can realize the intelligent control.
2.6.1 Temperature control
Commonly used in hot air heating control using the simple "open" and "off" mode, and stops when the temperature reaches the set value of steam, the heat exchanger there is still residual heat to the air temperature continues to rise, and vice versa, this will cause temperature fluctuations too large, the drying quality of the impact device. Recommendation: control the size of the steam flow to maintain the level of the inlet air temperature starts to heat up the steam flow, the inlet air temperature close to the set value as soon as possible, and then automatically adjust the amount of steam to slowly close to the set value, and finally to maintain stable amount of steam to the inlet air temperature to remain stable.
2.6.2 into the air volume control
Most of the air flow control device Frequency Control, but did not install the air flow measuring element in the production process can only be based on materials fluidized state at any time by manually carry out the size of the air volume of regulation, and therefore can not guarantee relatively constant air volume stability and wind amount of, material changes, the resistance of the filter bag changes and other factors will affect the stability of the air volume and air volume change can also affect the drying rate. Recommendation: in the inlet pipe to install the air flow measurement devices, automatic control, and automatically adjust the frequency depending on the size of the air volume, thereby maintaining the stroke volume of production process is almost constant.
2.6.3 Online humidity detection
Increase Online humidity detection device. User-friendly according to the actual situation to adjust parameters to improve the drying efficiency.
2.6.4 boiling drying process repeatability and traceability
In actual production, the operator device on each production process parameters should be re-set and modified, can not guarantee the same product using the same equipment, process parameters for production, there are no retrospective. According to the GMP, the devices can store a certain amount of production process parameters, to ensure production repeatability and traceability to individual users to set the number of varieties. Boiling drying equipment generally requires the ability to store up to 50 kinds of production processes, while most of the domestic equipment can not do this. The proposed improvement and expansion of the PLC control systems, mechanical implementation of institutions better. Have enough memory, can store a variety of production processes, and provide on-site printing parameters, data preservation, data and data PC connectivity.
Boil from the fluidized bed dryer works, combining the process operating parameters to summarize some of the problems in the production process, and briefly put forward suggestions for improvement of such equipment, and hope that the equipment manufacturers in the future to develop more to meet the process requirements of the pharmaceutical production process, advanced performance parameters, operability, environmental protection, energy conservation, and economic and technical indicators advanced pharmaceutical drying equipment.