Cooler

Cooling is mainly with the cold air to the high temperature of granule feedstuff for cooling, at the same time, and reducing the effect of moisture. The pellet feed produced from the pelletizer can be as hot as 70~90°C, and the moisture content can reach 14~17%. If it is not cooled, the product will not be preserved. After cooling treatment, the feed temperature will drop to nearly room temperature, generally no higher than room temperature 3~5°C, moisture can also meet the national storage standards required by the safe water. Generally, it is not greater than 12.5% in the south and 14% in the north. After cooling, the granules can increase the hardness, prevent mildew and facilitate the transportation and storage of the granules.

First. Classification of coolers.

According to the different forms of the cooler can be divided into fluidized bed, vibration fluidized bed, drum cooler, horizontal cooler and vertical cooler and other types. Fluidized bed and vibrating fluidized bed have simple structure and are generally used in places with low yield and small cooling range. The drum cooler can be used to cool all kinds of materials, including powder, granule and expanded granule. There are two main types of coolers in the pelletizing section: horizontal and vertical. Horizontal cooler covers a large area, but the height is low, using caterpillar structure. If hot air is used, it becomes a dryer (dry for wet puffed particles). Vertical cooler covers a small area, but it's very high, and it's very easy to take advantage of the height of the plant. Vertical coolers are classified as tower and counter-flow. Since counter-flow is more reasonable in principle of operation, it is now completely replaced by a tower cooler which is widely used in the feeding plant.

Second. The operating principle of the cooler

Regardless of the structure of the cooler, its working principle is basically the same. In other words, high temperature and high humidity pellet feed enters the cooler from the feed inlet. During the stay or movement of the material in the cooler, the external cold air extracted by the fan passes through the material layer to exchange heat and take away the heat and water emitted by the particles, so as to cool the pellet and achieve the purpose of cooling and reducing humidity. Due to the different models of the cooler, the feeding mode, discharging mode and the way of cold air penetrating the layer are also different.

The cooling process of pellet feed is actually a wet and heat transfer process. When the cold air passes through the high temperature and high humidity particle material, the heat and water on the surface of the particle is easily taken away by the cold air, at this time, the temperature and humidity difference between the interior and the surface of the particle is generated. This difference is spread to the surface gradually by heat transfer and capillary action. The diffusion velocity is related to the temperature difference, humidity difference, particle diameter and internal structure. The larger the temperature difference and humidity difference is, the smaller the particle diameter will be, the faster the temperature and water diffusion will be, and vice versa. Therefore, in the process of using the cooler, it is necessary to adjust the air volume and cooling time according to the particle temperature, humidity, particle diameter and particle composition to achieve the best cooling effect.