Temperature for activated carbon regeneration

Heating regeneration: Depending on the temperature at which organic substances decompose and desorb during heating, heating regeneration is divided into low-temperature heating regeneration and high-temperature heating regeneration. (1) Low-temperature heating regeneration method. For saturated carbon that has adsorbed low-boiling-point small-molecule hydrocarbons and aromatic organic compounds, it is generally regenerated using steam at 100–200°C, and the regeneration can take place within the adsorption tower. The desorbed organic vapor can be recovered after condensation. It is commonly used for the regeneration of activated carbon in gas adsorption. The steam stripping method is also used for the regeneration of saturated activated carbon in the pre-treatment of process water in the beer and beverage industries. (2) High-temperature heating regeneration method. In water treatment, activated carbon primarily adsorbs thermally decomposed and difficult-to-desorb organic compounds, and the adsorption cycle is long. The high-temperature heating regeneration method typically involves heating at 850°C, which causes the organic substances adsorbed on the activated carbon to undergo carbonization and activation, thereby achieving regeneration; it features a high adsorption recovery rate and stable regeneration results. Therefore, high-temperature heating is commonly used for the regeneration of activated carbon used in water treatment. The entire process of heating and regenerating dehydrated activated carbon generally goes through the following 3 stages. (1) Drying stage. Wet carbon with a moisture content of 50% to 86% is heated at temperatures of 100–150°C, causing the adsorbed water within the carbon particles to evaporate; simultaneously, some low-boiling-point organic compounds also volatilize. The heat consumed during this stage accounts for 50% to 70% of the total energy consumption throughout the regeneration process. (2) The roasting stage, or carbonization stage. Packed carbon is heated to temperatures ranging from 150 to 700°C. As the temperature rises, different organic substances are removed from the matrix of activated carbon through volatilization, decomposition, carbonization, and oxidation, respectively. By this stage, the adsorption recovery rate of the regenerated carbon has generally reached 60%–85%. (3) Activation stage. After the organic matter is carbonized at high temperatures, a considerable amount of carbides remain within the micropores of the activated carbon. At this point, the carbides need to undergo a gasification reaction using oxidizing gases such as water vapor and carbon dioxide, so that the remaining carbides are vaporized into gases such as CO2 and CO at around 850°C. This cleans the surface of the micropores and restores their adsorption capacity. The reaction equations for residual carbides with oxidizing gases are as follows: C + O2 → CO2↑ C + H2O → CO↑+H2↑ C + CO2 → 2CO↑ During high-temperature regeneration, oxygen has a significant impact on the matrix of activated carbon; therefore, it is necessary to operate under slightly positive pressure conditions. Excessive oxygen will cause the activated carbon to burn and turn to ash, while too little oxygen will affect the temperature inside the furnace and the regeneration efficiency. Therefore, in a conventional high-temperature heating regeneration furnace, oxygen must be strictly controlled, with the residual oxygen level being less than 1%, the CO content around 2.5%, and the amount of steam injected ranging from 0.2 to 1 kg/kg of activated carbon (determined depending on the type of furnace). The advantages and disadvantages of activated carbon regeneration equipment are reflected in: adsorption recovery rate, carbon loss rate, strength, energy consumption, auxiliary material consumption, regeneration temperature, regeneration time, impact on humans and the environment, equipment and capital investment, as well as the complexity of operation, management, and maintenance. Furthermore, in any device for regenerating activated carbon through high-temperature heating, it is essential to prevent the carbon particles from sticking together and sintering into lumps, which could lead to local fires or blockages in the channels, and even cause the operation to come to a halt.

Discharge high-temperature heating regeneration method: This is a regeneration method that is completely different from traditional high-temperature heating regeneration methods. The traditional method involves heating the activated carbon under sealed conditions, either indirectly through the furnace body or directly in the furnace space, so that its temperature rises gradually from the surface to the interior, eventually reaching 850°C at which point steam is introduced. Foreign scholars believe that the normal heating and regeneration rate should not exceed 10 °C/min to prevent burnout of the carbon matrix; therefore, the entire regeneration process takes up to 6 hours. This method involves rapidly heating the carbon itself, allowing the drying, roasting, and activation stages to be completed quickly within 5–10 minutes. It does not require operation under sealed conditions, nor is steam introduction needed for activation. At a high temperature of 850°C, it can be in contact with air and cool naturally without undergoing complete ashing. Its strength is also not affected, the carbon loss rate