Drying system and process of corundum brick body
The drying system is the sum of the conditions of corundum brick brick when drying. It includes drying time, temperature and relative humidity of entering and discharging drying medium, moisture before drying and residual moisture after drying of corundum brick.
At present, large and medium-sized enterprises of refractory materials mostly use tunnel dryers to dry the brick, and the drying time is expressed by the interval time of the cart. The determination of the time interval should consider the following factors: the nature and structure of the material, the shape and size of the brick, the initial moisture content of the body and the requirements for residual moisture at the end of drying, the temperature, humidity and flow rate of the drying medium, the structure of the dryer, etc. Usually, the trolley interval time is 15 ~ 45min, large and special products, before entering the dryer, should be naturally dried for 24 ~ 48h and then enter the dryer to prevent opening and cracking when drying too fast.
The pressure system in the dryer should generally use positive pressure operation to prevent cold air inhalation. If the exhaust gas is used as the drying medium, micro-negative pressure or micro-positive pressure should be used to avoid the escape of smoke and affect artificial health.
Corundum brick
The residual moisture of corundum brick is determined according to the following factors:
(1) The mechanical strength of corundum brick blanks should be able to meet the requirements of transportation and kiln loading;
(2) meet the requirements of rapid heating in the early stage of firing, that is, without cracking due to overheating steam;
(3) The size and thickness of corundum bricks, usually the residual moisture of large and shaped products with complex shapes should be lower;
(4) Different types of firing kilns have different requirements.
The residual moisture is too low is not necessary, because to discharge the last part of the moisture, not only for the dryer is uneconomical, and the over-dry corundum brick due to brittleness to transport and kiln. The requirements for residual moisture of dried brick are generally: clay products: 2.0% ~ 1.0%; High aluminum products: 2.0% ~ 1.0%; Siliceous products 0.5% ~ 1.0%; Magnesium products: less than 1.0%.
The drying equipment for refractory products has tunnel dryers, chamber dryers and other types of dryers. Drying methods are divided into: natural drying, gas medium forced convection drying, microwave drying, electric drying and so on.
The drying process can be divided into 3 stages:
The first stage is the most important stage in the drying process, this stage discharged a lot of water, in the whole stage, the drainage speed is always constant, so it is called equal speed drying stage. In this stage, the evaporation of water only occurs on the surface of the body, and the drying speed is equal to the evaporation speed of the free water surface, so all the factors that affect the evaporation speed of the surface can affect the drying speed. Therefore, the drying speed has nothing to do with the thickness and initial water content of corundum brick in the constant drying stage. It is related to the temperature, humidity and speed of the drying medium.
The second stage is the slow drying stage. With the increase of drying time or the decrease of water content of corundum brick, the effective evaporation area on the surface of corundum brick gradually decreases, and the drying speed gradually decreases. At this time, the speed of water evaporation from the surface exceeds the speed of diffusion from the interior of the body to the surface, so the drying speed is less affected by the temperature, humidity and movement speed of the air. The diffusion rate of water to the surface depends on the water content, the internal structure of the body, the viscosity of water and the properties of the material. Generally, the internal diffusion of water in non-plastic and weakly plastic materials is stronger. Coarse particles are stronger than fine particles, and the higher the temperature of the water, the easier the diffusion.
The third stage is that the drying speed is gradually close to zero, and the moisture of corundum brick body is no longer reduced. When the dry bulb temperature of the air is less than 100 ° C, the moisture retained in the body at this time is called equilibrium moisture. This moisture is firmly adsorbed by solid particles. The amount of equilibrium moisture depends on the particle nature, particle size and the temperature and relative humidity of the drying medium.
The obvious degree of the above three stages, according to the amount of water in the body, generally for the plastic method of forming the body, the three stages are more obvious, and for the semi-dry method of forming the body, such as multi-corundum brick, silicon brick and magnesium brick.
