The boiling dryer 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.
1 boiling dryer's working principle, process and characteristics
1.1 Working principle
The boiling dryer is also called fluidized bed drying. It uses hot air flow to suspend the wet particles. The fluidized boiling causes the materials to exchange heat. The evaporated air or organic solvent is taken away by hot air, and the hot air flows to the materials. The heat transfer method of gas-solid two-phase suspension contact is carried out to achieve 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 plane flanges, and the sealing effect is poor. It is recommended to use the concave-convex flange connection when designing; the imported pump Castel red wine (2) dryers are mostly made of steel pipe wraps. The sheet is heat exchanged, although the steel tube can save material cost, but the heat exchange effect is not good, it is recommended to use copper tube; (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.
Boiling drying equipment generally requires the storage of 50 production processes, and most domestically produced equipment cannot do this. It is recommended to improve and expand the PLC control system and mechanical actuators to make the functions more perfect. If you have enough memory, you can store a variety of production processes, provide on-site printing parameters, data storage, data and data PC connectivity. This paper starts with the working principle of fluidized bed boiling dryer, combines the process operation parameters to summarize some problems in the production process, and briefly puts forward suggestions for the improvement of such equipment. It is hoped that equipment manufacturers can develop more in the future. Pharmaceutical drying equipment that can meet the technological requirements of pharmaceutical production processes, advanced performance parameters, operability, environmental protection, energy saving and advanced economic and technical indicators.
Black Ningxia Wolfberry Large Grains,Black Ningxia Goji Berry Large Grains,Ningxia Large Black Goji Berry,Large Ningxia Black Goji Berry Tea
NINGXIA STARLIGHT FOOD TRADE CO.,LTD , http://www.starlightfood.com