What Is a Hot Air Drying Oven?
A hot air drying oven is a device used to dry hot objects. In processing hot materials, fuel is burnt within a burner and hot air is pumped into the oven to dry the hot object.
Because hot air drying ovens use hot air or gas, the drying rate is relatively fast and efficient. This makes it possible to shorten the drying time of products and materials.
However, the use of hot air or combustion gases may pose a fire hazard. Care must be taken not to allow flammable materials or combustible gases into the oven.
When gas or kerosene is used as a heat source, a large amount of exhaust gas is emitted. Therefore, electric hot air drying is also often used, which has a high heat rate and is easy to handle.
Uses of Hot Air Drying Ovens
Hot air drying ovens are widely used in various industries and fields. The following are some examples of applications.
1. Food Processing and Pharmaceuticals
Fruits, vegetables, and other agricultural products are dried to improve their shelf life, and raw materials used in food processing processes are dried. Production of fruit chips, dried vegetables, dried noodles, dried spices and herbs are examples of use.
In the pharmaceutical industry, drying of drugs and medicines is also an important process. Hot air drying ovens are used to dry, crystallize, and coagulate drugs. Drying improves the stability of drugs and allows for long-term storage and handling.
2. Industry
The chemical industry often needs to dry raw materials and products such as paints and plastics. They are used to remove water from these materials and dry them.
Also, in the mining industry, ores and minerals are often dried before being fed into a blast furnace. Feeding moisture into the blast furnace not only removes heat from the furnace but also increases exhaust gases. Hot air drying ovens can be used to evaporate the moisture content of ores and minerals in advance to improve handling and processing efficiency.
In ceramics manufacturing, drying is performed prior to forming and firing of ceramics. Hot air drying ovens are used to remove moisture from ceramic products to ensure uniform quality and durability.
3. Wood Processing
In the wood processing industry, wood drying is an important process. Hot air drying ovens are used to properly control the humidity of the wood and dry it to improve its stability. This prevents shrinkage and cracking of the wood and improves product quality.
Principle of Hot Air Drying Ovens
Hot air drying ovens use hot air or gas to evaporate moisture from moist materials. They also have heating devices, such as electric heating elements or burners. This heating device will burn fuel or use electrical energy to produce hot air.
Hot air drying ovens also have a blower that sends heated air or gas into the hot air drying oven. The hot air is blown at high speed and spreads around the material or product. The hot air comes in contact with the surface of the material, allowing moisture to evaporate.
Water vapor and exhaust gases generated during drying are discharged to the outside through an exhaust system. The exhaust system removes moisture and harmful gases inside the drying oven.
Types of Hot Air Drying Ovens
There are two types of hot air drying ovens: direct drying and indirect drying.
1. Direct Drying Type
In the direct drying method, heated combustion gas is directly circulated by a circulation fan. It has the advantage of high thermal efficiency and can raise the temperature in a short time.
2. Indirect Drying
In the indirect drying method, a heat exchanger is heated by a burner, and combustion gas and air are exchanged to raise the temperature inside the furnace and circulate it. This method is characterized by the fact that heat is spread throughout the entire furnace, resulting in less unevenness in drying. There is no risk of soot entering the furnace due to incomplete combustion.
In addition, sparks from direct combustion do not come into contact with flammable components, so the risk of explosion is low. Since nitrogen oxides are unlikely to react with the paint during drying, the advantage is that the physical properties of the paint film are not compromised. However, it has low thermal efficiency and takes a long time to raise the temperature.