Paper pulp egg trays are generally made from waste paper pulp. Its production process can be divided into paper pulping, egg tray forming, egg tray drying, etc. In the egg tray production line, the energy consumption of the drying system accounts for a large proportion of the overall consumption. How to reasonably optimize the drying process and reduce energy consumption is a key link in improving the economic benefits of egg tray manufacturing.
Methods For Egg Tray Drying
Currently, we can use drying methods such as hot air drying, solar drying, and vacuum dehydration to remove moisture from wet egg trays. Hot air drying takes hot air as a medium to dry egg trays in specific equipment. The hot air is mainly obtained in two ways, one is generated directly by the stove, and the other is to use steam or heat transfer oil to exchange heat with air in a heat exchanger. Common hot air drying systems include brick kiln drying systems, metal drying systems, box-type drying systems, tunnel-type hanging drying systems, etc. No matter what kind of drying equipment, the drying mechanism is basically the same.
The wet egg tray made of paper pulp or waste paper pulp is a porous object with a capillary structure inside. Moisture exists between the surface of the fiber and the pores of the fiber capillary. Because of the need to have good dynamic buffer performance, egg trays cannot be mechanically pressed to remove moisture, but by drying. Compared to conventional paper drying processes, egg tray drying is very intensive. The hot air not only serves as a heat source to provide energy for removing moisture but also as a carrier, taking away the evaporated moisture.
Egg tray drying mainly relies on internal and external moisture diffusion. Internal diffusion refers to the water migration process from the inside of the egg tray to the surface, while external diffusion refers to the water evaporation process from the egg tray surface. The drying efficiency is affected by the speed of inside and outside moisture diffusion and the balance between the two.
Methods To Improve The Drying Efficiency
To improve the drying efficiency, it is necessary to reduce the humidity of the hot air and increase the temperature and air velocity, at the same time, the internal and external moisture diffusion rate should be increased.
Reduce Egg Tray Thickness
The thicker the egg tray, the harder it is to dry. Therefore, under the premise of ensuring the overall strength, the thickness should be reduced as much as possible. This not only helps to improve the drying efficiency but also reduces the consumption of fiber raw materials. In addition, the thickness difference of each part of the egg tray should not be too large, otherwise, it will be difficult for local moisture to diffuse outward and affect the overall drying speed.
Increase Moisture Gradient
During the drying process, the moisture concentration difference between the surface and the interior of the wet egg tray is the main driving force for the moisture internal diffusion. Adjusting the temperature, humidity, speed, and volume of the hot air is beneficial to improve the moisture internal diffusion. It is worth noting that the water external diffusion rate is too fast will affect the internal diffusion rate, which is very detrimental to the drying.
Increase Drying Temperature
The increase in temperature is conducive to the migration of moisture from the inside of the egg tray to the surface. However, in the production process, the temperature rise will be limited by many factors.
Matters Need Attention
1. Increasing the temperature can speed up the drying, but if the temperature is too high, the performance indicators such as the overall strength of the egg tray will be reduced, and lead to defects. In addition, excessive air temperatures will also increase energy consumption and reduce thermal efficiency. When drying, the temperature of hot air should be generally controlled at about 110 ° C, and the temperature of each part of the drying equipment should be consistent.
2. The control of hot air humidity is important. If the moisture evaporating from the initial drying stage is not removed in time, the humidity in the drying equipment will continue to increase, thereby extending the drying time and reducing the drying efficiency. For some drying equipment that uses hot air in circulation, the ratio of circulating hot air and fresh hot air should be adjusted at any time.
3. Adjusting the speed and flow of hot air is also an effective way to improve drying efficiency. The moisture external diffusion speed of the wet egg tray largely depends on the speed and flow rate of hot air in the drying equipment. The hot air needs to be blown evenly to the wet egg tray, and the flow rate must be sufficient. Generally, when the speed reaches more than 5 m/s, the egg tray can achieve rapid drying.
4. The drying process directly affects the quality and production cost of egg trays. So it is very important to master the drying principle, determine a reasonable drying method, and select the right equipment. At present, the drying of egg trays generally has the problems of high energy consumption and low efficiency, some of which are defects in the equipment itself, but most of them are due to the failure to control the temperature, humidity, and flow of hot air during production. Only by mastering and controlling these three elements reasonably can we get a better drying effect.