The following factors should be considered when purchasing a dryer:
1. Physical and chemical properties of materials to be dried, morphology, water content, aqueous properties, water of crystallization, particle size, bulk density, viscosity, heat sensitivity, softening point, phase transition point, thixotropic property, toxicity, corrosiveness, odor, flammability, Explosiveness, static electricity, gas permeability, agglomeration, easy pulverization of crystals or granules, etc. all affect the drying effect.
2. Drying characteristics of the material
Drying curve, critical moisture content, and equilibrium moisture content under the selected drying conditions.
3. Dry production requirements and long-term planning.
4. The impact of material commodity value and drying effect on it. Such as product moisture, pollution, temperature, wear, chalking, crushing, rehydration, etc. on the value of the commodity.
5. Requirements for material recovery rate.
6. The upper and lower sequence process of the material drying process. (involving the state method of feeding and discharging)
7. Drying method of material in the past or drying method of similar products.
8. Available heat sources (coal, fuel, electricity, gas, liquefied gas, natural gas)
9. The size of the installation site of the dryer, with or without special requirements.
10. Environmental protection requirements - restrictions on dust emissions, noise, vibration, odor, volatiles, etc.
11. The amount of procurement funds that may be invested, local labor, land, and energy prices.
12. Dryer user's operator level and maintenance capability.
13. Local environmental temperature and humidity Here mainly refers to the influence of weather changes on drying. Generally, dryers are heated by the atmosphere as a drying medium. The higher the temperature of the atmosphere, the lower the humidity, the more favorable it is for drying. In summer, the rain is humid and the humidity of the air is very high, which is not conducive to the performance of the dryer and affects the output.
China has a vast territory, and the air humidity in the south and the south varies greatly. In some places in the south, the humidity in winter is only 0.008 kg water/kg dry air, and in spring and summer, the atmospheric humidity is as high as 0.025 kg water/kg dry air, which is more than three times that of the former. Hot air drying at low exhaust gas temperature (<90 °C), the atmospheric humidity increases in spring and summer, the drying rate will inevitably decrease, and the time required will rise. Due to the increase in atmospheric humidity, the equilibrium water content of the material will inevitably rise. These factors will reduce the dry yield and, in some cases, reduce the yield by more than 50%.
14. Factors affecting the production capacity of the dryer Due to the same drying method, the heat energy consumed by drying and dehydrating one kilogram is basically the same, and the capacity of the heat source (hot air stove, steam radiator, etc.) of the dryer is also certain, so the dryer The main technical indicators - drying capacity is often based on the amount of dehydration per hour (or large amount of dehydration). This indicator is determined under certain conditions, such as wet material type, initial moisture content, Zui final moisture content, hot air temperature, ambient temperature and humidity. As long as one of the conditions changes, it has an impact on the production capacity of the dryer, and sometimes the impact is still large. The following are explained separately.
(1) Wet material type Wet material type Here, it refers to the combination of material and moisture. The wet material can be divided into 1 capillary porous material, and the moisture is mainly combined in the material by capillary force, such as sand, silica, activated carbon, ceramics, etc., the bonding strength between water and material is small, drying is easy; 2 colloid The combination of materials, moisture and materials is dominant, such as glue and flour dough. The material generally exhibits high viscosity, and the combined strength of moisture and material is large, and drying is difficult. 3 Capillary porous colloid materials have more than The nature of the two types of materials, such as peat, clay, wood, fabric, grain, leather, etc., is more, but the form of moisture combination between such materials is also different. The copper enamel plant determines the dehydration under the same conditions. The difficulty is not the same.
The shape of the material also has a great influence on the drying, such as granular materials, the particles are much harder to dry than the particles, and the large blocks are smaller in thickness than in the thick ones and easy to dry.
(2) Moisture content of wet material Moisture content (wet content) is the percentage of moisture in the total weight of wet materials.
Where: W--water weight;
G--wet material weight;
G0--dry material weight.
The initial moisture content refers to the moisture content of the wet material before entering the dryer. Usually, the wet material can work in the dryer. The higher the initial moisture content, the more sufficient the dewatering capacity exhibited by the dryer. Conversely, the higher the initial moisture content, the more the final moisture content of the Zui, the more the dryer can reach the large dehydration capacity of Zui, but the amount of dry material decreases.
(3) The final moisture content of zui is generally in the slow-drying stage after drying. The lower the final moisture content of Zui, the greater the difficulty of drying, the longer the drying time required and the lower the thermal efficiency, thus affecting the yield.
(4) Hot air temperature The hot air temperature or the drying medium temperature is a top tube condition sensitive to drying in the Zui. The higher the hot air temperature, the more heat energy is contained, and the lower the relative humidity of the hot air, the stronger the ability to absorb water and carry moisture, which is very favorable for drying, and the drying heat efficiency is also high. In many drying equipment, when the other conditions are constant, the dewatering capacity of the dryer is substantially proportional to the change in hot air temperature. When selecting the drying equipment, it is necessary to have sufficient data for the ultimate temperature of the damaged material. When the material permits, try to select the high temperature medium. In particular, many drying methods, especially rapid drying, the temperature of the dried material is much lower than the drying medium temperature. For example, the hot air temperature of the airflow dryer is as high as 250 ° C or higher, and the discharge temperature is generally below 60 ° C. .
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