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What is the relationship between the drying time of the mixing and drying machine?

Date:2025-04-21 Hits:107

The drying time of a mixing dryer depends on the interaction of three dimensions: "material characteristics", "equipment parameter settings", and "drying process conditions". The specific factors in each dimension will directly affect the water evaporation efficiency, thereby determining the final drying time. The following is a detailed disassembly:


###1、 The inherent characteristics of the material determine the "basic difficulty" of drying

The initial state and physical and chemical properties of materials are the core innate factors that affect drying time, directly determining the difficulty of moisture escaping from the interior of the material.

1. * * Initial and final moisture content requirements**

-The higher the initial moisture content, the more water needs to be evaporated and the longer the drying time (for example, sludge with an initial moisture content of 60% takes 2-3 times longer to dry to 10% than sludge with an initial moisture content of 30%);   

-The stricter the final moisture content requirements (such as ≤ 0.5% for the food industry and ≤ 5% for the building materials industry), the longer the drying time is needed to ensure that the moisture is fully released and avoid rework if it does not meet the standards.

2. Material Form and Structure**

-Particle size: Small particles (such as powder with a diameter of 1mm) have a larger surface area than large particles (such as block materials with a diameter of 10mm), evaporate water faster, and shorten drying time by 30% -50%;   

-Porosity: Porous and loose materials (such as activated carbon) have multiple internal channels, making it easy for water to diffuse to the surface and have a short drying time; However, dense materials (such as clay blocks) are difficult for moisture to penetrate and require longer periods of time;   

-Viscosity: High viscosity materials (such as starch paste and paste like materials) are prone to adhere to the mixing blade or cylinder wall, forming a "crust" that hinders the evaporation of internal water. It requires extended time or special mixing structures (such as mixing blades with scrapers) for assistance.

3. Sensitivity of materials to temperature**

-Thermally sensitive materials (such as food and pharmaceuticals) need to control the drying temperature (usually ≤ 80 ℃) to avoid high temperature damage to components, which can reduce evaporation rate and prolong drying time;   

-High temperature resistant materials (such as ores and metal powders) can increase temperature to accelerate evaporation and shorten drying time.


###2、 Equipment parameter settings: Determine the "efficiency upper limit" for drying

The core component parameters of the mixing dryer directly affect the "heat transfer efficiency" and "contact effect between materials and hot air", and are key operational items for regulating the drying time.

1. Heating method and temperature parameters**

The efficiency differences of commonly used heating methods (hot air heating, jacket heating, microwave heating) for mixing and drying machines are significant, and the temperature setting directly affects the water evaporation rate:

-Hot air heating: The higher the temperature of the hot air (within the tolerance range of the material) and the higher the wind speed, the more complete the heat exchange with the material, and the faster the moisture is taken away (for example, increasing the temperature of the hot air from 80 ℃ to 120 ℃ can shorten the drying time by 20% -40%);   

-Jacket heating: The jacket temperature needs to maintain a reasonable temperature difference with the material temperature (usually 20-30 ℃). If the temperature difference is too small, the heat transfer will be slow and the drying time will be prolonged; Excessive temperature difference can easily cause local overheating and coking of materials, which in turn hinders drying;   

-Microwave heating: Heat is generated by the vibration of water molecules inside the material, which dries evenly and quickly (shortening the time by more than 50% compared to traditional hot air heating), but it is suitable for polar molecular materials (such as moisture containing materials) and has higher equipment costs.

2. Mixing rate and structure**

The core function of mixing is to ensure that the material contacts the heat source evenly, avoiding prolonged drying time caused by uneven dryness and wetness in certain areas

-Mixing rate: If the rate is too low, the material is prone to deposit at the bottom of the cylinder, causing local overheating and agglomeration; The rate is too high, although the mixture is uniform, it may generate heat due to excessive friction of the material (especially for thermosensitive materials), and the rate needs to be balanced (usually adjusted according to the viscosity of the material, viscous materials require 10-30r/min, and powder materials can be 50-80r/min);   

-Stirring structure: Stirring blades with cutting plates (such as plow blades and double helix blades) can lift materials upwards, increase the contact area with hot air, and shorten the drying time by 20% -30% compared to ordinary blades.

3. Exhaust system efficiency**

The evaporated moisture during the drying process should be promptly discharged. If the exhaust is not smooth, the humidity inside the dryer will increase, which will inhibit the subsequent evaporation of moisture and prolong the drying time

-Exhaust fan air volume: The air volume needs to match the amount of moisture evaporated (for example, evaporating 10kg of moisture per hour requires an exhaust air volume of ≥ 1500m ³/h). Insufficient air volume can cause humid air to accumulate;   

-Exhaust port filtration: If there is a lot of dust in the material, it is necessary to regularly clean the exhaust port filter to avoid blockage, which may increase exhaust resistance and affect water discharge.


###3、 Drying process conditions: determining the 'process stability' of drying

The rationality of external process environment and operating procedures will indirectly affect drying efficiency, avoiding prolonged time due to environmental interference or improper processes.

1. * * Environmental humidity and air pressure**

-Environmental humidity: In humid environments (such as rainy season humidity ≥ 80%), the amount of water that can be contained in the air is small, and the evaporation rate of surface moisture of materials decreases. The drying time will be extended by 15% -25% compared to dry environments (humidity ≤ 40%);   

-Air pressure: In high-altitude low-pressure environments, the boiling point of water decreases, water evaporates easily, and the drying time can be slightly shortened (but it should be noted that the density of hot air decreases under low-pressure conditions, and the wind speed compensation heat exchange efficiency needs to be appropriately increased).

2. * * Feed quantity and drying batch**

-Feed quantity: If the single feed quantity exceeds the rated capacity of the equipment (such as the equipment rated 500kg/batch, actual feed 700kg), it will cause uneven mixing of materials in the cylinder, some materials cannot fully contact the heat source, the drying time is prolonged, and even undried materials may appear;   

-Batch interval: When drying consecutive batches, it is necessary to reserve 10-15 minutes of "empty machine exhaust" time to avoid residual humid air from the previous batch, which may affect the drying efficiency of the next batch.


###Summary: How to shorten drying time by adjusting factors?

On the premise of ensuring the drying quality of materials (such as not clumping or damaging components), targeted optimization can be carried out:

-Material pretreatment: Crush block materials into small particles, or reduce the initial moisture content through pre dehydration (such as pressing, filtering) to reduce the drying load from the source;   

-Equipment parameter optimization: Increase the hot air temperature/jacket temperature within the material's tolerance temperature, match a reasonable mixing rate (to avoid clumping), and ensure a smooth exhaust system;   

-Process adjustment: Avoid drying in high humidity environments or adopt "segmented drying" (rapid removal of surface water at high temperatures in the early stage and internal water at low temperatures in the later stage) to balance efficiency and material quality.


If your drying needs involve specific materials (such as food powder, chemical raw materials), do you need me to help you analyze the * * optimal drying parameter reference range * * corresponding to that material?