Carbonization process of carbonization machine

Drying stage

Temperature range: Generally starting from room temperature, the temperature gradually rises to about 100-150℃.

Process description: In this stage, the free water and bound water in the raw materials (such as wood, machine-made rod raw materials, etc.) begin to evaporate. This is the initial stage of the carbonization process, which is mainly to remove the moisture in the raw materials. For example, for wood with a high moisture content, a large amount of water vapor will escape. This stage is very important for the subsequent carbonization process, because if the moisture content of the raw material is too high, it may cause uneven carbonization and even cracking in the subsequent high-temperature stage. From the perspective of physical changes, the volume of the raw material will shrink slightly, mainly due to the loss of moisture. From the perspective of chemical changes, there is almost no substantial chemical change, just a physical evaporation process of moisture.

Duration: The length of the drying stage depends on factors such as the moisture content of the raw material, the particle size and the heating rate. If the raw material has a high moisture content, large particles, or a slow heating rate, the drying stage will be relatively long. Generally speaking, this stage may last about 1-3 hours.

Pyrolysis stage

Temperature range: The temperature starts to rise from about 150℃ and can usually reach 300-700℃ (for charcoal making, the temperature is higher, and the carbonization temperature of machine-made rods is relatively low, about 300-500℃).

Process description: This is the key stage of the carbonization process. As the temperature rises, the organic compounds in the raw materials begin to decompose. For wood or wood raw materials, components such as cellulose, hemicellulose and lignin will undergo complex pyrolysis reactions. First, hemicellulose begins to decompose, and its decomposition temperature is relatively low, around 200-300℃, which will produce some volatile organic acids, aldehydes and furan compounds. Then, cellulose begins to decompose at about 300-400℃, producing carbon monoxide, carbon dioxide, water and some hydrocarbons. The decomposition temperature range of lignin is relatively wide, and at about 280-500℃, it will produce compounds such as phenols and aromatic hydrocarbons. In this process, the color of the raw material will gradually darken from light brown to black, and a large amount of volatile gases will be produced. From the perspective of physical changes, the volume of the raw materials will further shrink, and the structure of the raw materials will become loose due to the generation of internal gas.

Duration: The pyrolysis stage takes a long time because it involves the decomposition reaction of multiple organic compounds. For charcoal making, this stage may take about 4-8 hours; for machine-made rod carbonization, the time may be about 2-5 hours. The time of this stage is also affected by factors such as the type of raw materials, particle size, heating speed and thermal insulation performance of the carbonizer.

Carbonization stage (also known as calcination stage)

Temperature range: The temperature is kept at a high level, which may reach 400-700℃ for charcoal making, and machine-made rod carbonization is stable for a period of time at about 300-500℃.

Process description: At this stage, most of the volatile substances in the raw materials have escaped, and the remaining is mainly carbon. The carbon element will undergo processes such as rearrangement and crystallization to form a relatively stable carbon structure. For charcoal making, the density of the charcoal will increase further at this time, and the hardness will also increase, forming charcoal with a certain strength and pore structure. For machine-made rod carbonization, the machine-made rod will maintain its shape under the action of the binder, and the internal carbon structure will gradually stabilize. From the appearance, the color of the charcoal or machine-made rod becomes darker and the black color is more uniform. From the chemical composition, the content of fixed carbon reaches a high level, and the content of other impurities and volatile substances decreases.

Duration: This stage is relatively short, which may take about 1-3 hours for charcoal making and about 0.5-2 hours for machine-made rod carbonization. The main purpose is to make the quality of the carbonized product more stable and ensure complete carbonization. After the carbonization stage, the carbonized product is basically formed, and the finished product can be obtained after cooling.