(1) thermal regeneration method
At present, the thermal regeneration method is the oldest, most widely used and most mature industrial activated carbon regeneration method. The thermal regeneration of activated carbon began in the early 20th century, when rotary furnace was used to regenerate bone charcoal. Multilayer furnaces were introduced in 1930s. Regenerative furnace technology was basically mature in 1940s and 1950s.
The principle of thermal regeneration method is to eliminate the organic matter adsorbed on activated carbon matrix in the form of decomposition, carbonization and oxidation under heating conditions. Thermal regeneration of activated carbon usually requires several steps:
1) dehydration, that is, the water on the surface of activated carbon is removed by mechanical and physical actions.
2) Drying, the drying temperature is generally lower than 100℃, mainly evaporating pore water, and a small amount of low-boiling organic matter will also be gasified. This process requires a lot of latent heat of evaporation, and about 50% of the energy consumption in the thermal regeneration process is consumed in the drying process.
3) heating activated carbon at about 350℃ to separate low-boiling organic matter.
4) High-temperature carbonization, that is, heating activated carbon at about 800℃ makes most of the organic matter decompose, gasify or remain in the form of fixed carbon.
5) Activation, that is, the activated carbon is heated in the range of 800℃ ~ 1000℃, and the remaining carbon is decomposed by steam, carbon dioxide or oxygen. The steps of thermal regeneration are slightly different according to the type of heating furnace, but there is little difference.
Advantages of thermal regeneration method: high regeneration rate, up to 70% ~ 80%; The regeneration time is short; Compared with chemical regeneration method, it has strong universality; No regenerated waste liquid is produced. Disadvantages: the loss rate of regenerated activated carbon is high, generally 5% ~10%; The chemical structure of carbon surface changes and the specific surface area decreases; High-temperature regeneration requires high materials for regenerative furnace and high investment in regenerative furnace equipment; High energy consumption cost of regeneration; Repeated regeneration of activated carbon will lose its adsorption performance.
(2) Chemical agent regeneration method
The adsorption of high concentration and low boiling point organic matter should be regenerated by chemical agents. Chemical agent regeneration is mainly divided into inorganic agent regeneration and organic agent regeneration. Generally, inorganic acids (sulfuric acid, hydrochloric acid) or alkali (sodium hydroxide) are used to remove adsorbents in the regeneration of inorganic reagents. For example, activated carbon that adsorbs high concentration phenol can be regenerated with sodium hydroxide solution, and phenol can be recovered in the form of sodium phenolate; Activated carbon that adsorbs heavy metals can be regenerated by hydrochloric acid solution. The solvents commonly used in organic solvent regeneration are benzene, acetone and methanol, which are suitable for reversible adsorption, such as activated carbon for adsorbing high concentration phenol; Activated carbon used to treat gas wastewater from coking plant can be regenerated by organic solvent.
Advantages of chemical agent regeneration method: strong pertinence, simple equipment and economic advantages; Useful substances can be recovered from the regenerated liquid; The operation process is carried out in the adsorption tower, and the loss of activated carbon is small. Disadvantages: generally, it can only be regenerated for a single substance, and its universality is poor; The regeneration rate is low, the micropores are easy to block, and the regeneration rate is obviously reduced after repeated use; There is a problem of secondary pollution of regenerated liquid.
(3) Biological regeneration method
Biological regeneration method is similar to biological activated carbon technology. Activated carbon absorbs organic matter, and microorganisms degrade organic matter, so that activated carbon can be regenerated. Because activated carbon can adsorb organic matter on its surface for a long time, microorganisms can degrade some non-degradable organic matter and regenerate activated carbon. However, the application of biological regeneration method will be limited for organic matter that cannot be degraded by microorganisms.