In aqueous materials, the relationship between the properties of water and solid materials and their interactions has a major impact on the dehydration process. There are different classification methods for the combination of moisture and materials, which can be generally divided into the following categories: (1) Compound water (ie, crystal water) This water is a water that directly combines with a substance in a certain mass ratio. For example, in the water in CuS04·5H20, it is a component of the substance. The water and the substance are firmly combined. Only when heated to a certain temperature, the crystal of the substance is destroyed, so that the crystal water can be released. . In the drying process, this moisture cannot be removed by evaporation, so the combined moisture is not considered in the calculation of the drying process. (2) Absorbing moisture (ie, molecular moisture) As a result of the adsorption, water vapor molecules in the space around the solid material are adsorbed onto its surface, resulting in the formation of a film of moisture on the surface of the solid, the thickness of which is one. Or a few molecules, usually invisible to the naked eye. In addition, water molecules are drilled (diffused) into the interior of the solid, also known as absorption. Therefore, the water combined with the adsorption and absorption of the material is collectively referred to as water absorption. The combination of water and material is relatively strong. Generally, the dehydration method cannot be removed, and the drying method can only remove a part. If it is placed in a humid air, it will re-adsorb the surrounding water molecules until the humidity is balanced. (3) Capillary moisture Due to the existence of many pores between the loose materials, sometimes there are holes or cracks inside the solid particles. Many of the pores are like many capillaries, and the water can remain in the pores under the action of capillary suction. Among them (Figure 9-1). As shown in Figure 9.1, the height h of the water column that can be maintained by capillary suction can be expressed by equation (9-1): Where h - the height of the water column; θ - the contact angle between water and material; σ - the surface tension of water; r - the diameter of the capillary; Ï - the density of water. It can be known from formula (9-1): 1 The smaller the pore gap between the materials (ie, r is small), the more difficult it is to remove the water between them. This is why the dewatering of fine-grained materials is difficult, and sometimes it can only be removed by drying (vaporization); 2 The hydrophilic material has a small contact angle with water, that is, cos θ is large, and dehydration is also difficult. For example, when the material contains a highly hydrophilic clay or slime, the dehydration effect is significantly reduced. Conversely, if you try to increase the hydrophobicity of the material, it can make dehydration easy. Tests show that adding an appropriate amount of coal oil, due to the increased hydrophobicity of coal, the coal dewatering has increased. The water content of the material has a lot to do with the size of the particle size. The coarse-grained material has a larger water content than the coarse-grained material. On the one hand, the surface moisture content is related to the surface area. The finer the particle size, the larger the surface area, and the more water is adsorbed, so the surface moisture content is higher. On the other hand, the fine-grained material has a large number of fine capillary pores, and the capillary action is remarkable, so that the finer material contains more water. Figure 9-2 shows the relationship between the particle size and water content of various sizes of coal by different methods of filtration test. Curve 1 is the result of natural drainage; curve 2 is trembled when draining; curve 3 is the result of filtration by centrifugal force (equal to 78 times gravity). Comparing the results of the curve, it can be seen that: 1 the smaller the particle size, the higher the water content, but when the particle size is small to a certain value, the increase in water content is small, because the particle size is small, and the voids capable of accommodating moisture are also small; The water content is significantly reduced by the action of vibration and centrifugal force. This is because when the vibration is shaken, the particles can be squeezed against each other, forcing the gap moisture to escape, especially under the strong centrifugal force, overcoming the capillary suction force. The moisture is driven out, which significantly improves the dehydration effect. (4) Gravity moisture material not only contains water and capillary water (the compound moisture is not considered for dehydration), but also contains a large amount of water. There is no interaction force between the water and the material, and it can be removed under the action of gravity. This part of the water is called gravity water. Capillary water and gravity water are collectively referred to as free water because they have no strong bonding force with solid materials and are relatively easy to remove. Double Shaft Shredder,E Waste Shredder Machine,Double Shaft Shredder Machine,Industrial Shredder Machine Xinxiang Traceability Environmental Protection Equipment Co., Ltd. , https://www.syrecycle.com