Xi'an JCF Herb Technology Development Co., Ltd , https://www.jcfherb.com
Keywords: boiling drying; pharmaceutical; problems; improvement In the production process of solid preparations, boiling dryers are often selected equipment. 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.
1Boiling dryer working principle, process and characteristics 1.1 Working principle Boiling drying, also known as fluidized bed drying, it uses hot air flow to suspend wet particles, fluidized boiling to heat exchange of materials, evaporation by hot air The moisture or organic solvent is taken away, and the hot air flow is used to carry out the gas-solid two-phase suspension contact mass transfer heat transfer mode to achieve the purpose of drying the 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 Materials are transported to the bubbling bed by the skip, and sealed by the sealing ring and the bubbling bed 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 Features (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 improved, but there are still some problems. The following suggestions are proposed in combination with production practice. :
2.1 Improvements to inadequate use of thermal energy The boiling dryer is formally an air convection drying device. Compared with conductive drying equipment, the energy consumption is indeed greater, but if some measures are taken, it can be achieved very well. Energy saving effect. 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 the dust collection device The basic condition for the smooth operation of the fluidization process is that the material has a good fluidization state, and the 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 The bag dust removal achieves the dust removal effect by the reciprocating motion of the cylinder, and the bag is made of anti-static and fiber-free cloth. The 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 Dust With the further improvement of domestic solenoid valve technology and the further reduction of price, pulse backflushing has gradually become the mainstream of capture devices. 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 Improvements on the air distribution plate (screen) It is suggested that 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 air intake air treatment The hot air air intake is generally installed in the auxiliary equipment room, and is installed together with the heating device and the muffler. The auxiliary equipment room and the clean area are not provided with straight doors and windows, and the air cleanliness level of the auxiliary equipment room. It is often low, which will affect the quality of medicinal hot air. This requires the equipment itself to have a good purification device, otherwise the unpurified air will contaminate the drug and it is difficult to meet 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.
Many equipment's induced draft fans are not linked to the damper, which may cause air backflow between the fan shutdown and the butterfly valve closure. 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.
2.5 Improvement of insufficient combination of equipment and production process It is suggested that the drying process and equipment design are unreasonable, resulting in great energy loss. In order to completely solve these problems, it is necessary to systematically study the drying characteristics of the products to determine the drying process parameters of Zui, such as the properties of the materials to be dried. The nature of the material itself is the main factor affecting the drying of the zui, the shape, size, thickness of the material, the combination of moisture, chemical characteristics, etc. will affect the drying rate. Except for a small number of enterprises in China, most equipment manufacturers lack the understanding of the process technology and the necessary conditions for the process test. The understanding of the use conditions of various materials is not sufficient, which leads to insufficient research and development, and it is difficult to develop new varieties. .
2.6 Suggestions for Improvement of Control System At present, the operating parameters of fluidized bed equipment are generally set by the experience of the operator, but it can be fully intelligent, and the process parameters can also be traced. This is for the fluidized bed. The electrical control system of the class of equipment puts forward higher requirements. In the electrical control system, it is necessary to have a series of devices for detecting temperature, humidity, pressure, differential pressure, wind speed, operating time, dust concentration, etc., and obtain basic data, which is then transported and stored in the touch screen through the transmitter, and the data is touched by the touch screen. Intelligent control can be achieved by performing a storage analysis and then developing a suitable routing.
2.6.1 Temperature control The common hot air heating control mode adopts a simple “on†and “off†mode. When the temperature reaches the set value, the steam is stopped, but the heat exchanger still has residual heat to keep the air temperature rising, and vice versa. This will cause excessive temperature fluctuations and affect the dry quality of the equipment. Suggestion: By controlling the steam flow to maintain the temperature of the inlet air, the steam flow is increased when the temperature starts to rise, so that the inlet air temperature is close to the set value as soon as possible, and then the steam is automatically adjusted to slowly approach the set value. Maintaining a steady amount of steam keeps the inlet air temperature stable.
2.6.2 Inlet air volume control Most air volume control equipment adopts variable frequency speed control, but there is no air volume measuring component installed. In the production process, the air volume can only be adjusted manually according to the fluidization state of the material. Therefore, the air volume cannot be guaranteed. The amount of wind and air is relatively constant, and changes in materials and changes in filter bag resistance will affect the stability of the air volume. The change in air volume can affect the drying speed. It is recommended to install the air volume measuring component in the air inlet pipe to realize automatic control and automatically adjust the frequency according to the air volume to keep the air volume in the production process basically constant.
Suggestions for improvement of boiling dryers in the pharmaceutical industry
Abstract: Starting from the working principle of boiling dryer, some problems existing in the current equipment are briefly analyzed, and some suggestions for improvement are put forward.