ACTIVATED CARBON REACTIVATION
REPUR S.r.l., in its Cairo Montenotte (Sv) plant, has 2 rotary kilns for reactivating spent activated carbon, one of which is exclusively dedicated to the treatment of carbon from food and drinking water treatment.
REPUR S.r.l., in its production units, treats with particular attention all aspects that are in some way related to quality and environmental issues; by way of non-exhaustive example, the aspects of energy saving, noise emission, flue gas emissions, specific product markings, identification and preventive assessment of environmental aspects.
The ever wider use of activated carbon in the treatment of fluids and the consequent increase in the quantities involved, have led to the need to resort to suitable systems for the recovery, if not of the adsorbed material, at least of only the activated carbon. Various technical and economic factors lead to opting for a regeneration or reactivation treatment rather than being limited to the simple "disposable" use of the carbon itself.
The aspects inherent to the various processes for the recovery of exhausted carbon will be briefly examined below, then focusing attention on what appears to be the typical process, represented by thermal reactivation.
First of all, it is worthwhile to make a distinction between the two terms often used, somewhat improperly, as synonyms.
By regeneration a suitable process is meant to restore the working conditions of an adsorbent bed by operating on site with suitable systems. (The regenerative process also offers the possibility of partially or almost totally recovering the adsorbed material for its enhancement and recovery of management costs).
The term reactivation, on the other hand, means a heat treatment aimed at bringing the coal back to conditions close to those of the fresh product. In this case, a possible recovery of the adsorbate is not conceivable, as the treatment is aimed exclusively at restoring the adsorbent characteristics of the carbon.
Another substantial difference linked to the two terms is constituted by the fact that with the various regenerative processes there are normally no significant losses of activated carbon, while the operating capacity is only partially recovered at more or less stable levels over time. Thermal reactivation, on the other hand, always involves slight losses of adsorbent product (of the order of 10%).
Thermal reactivation is the only system capable of providing activated carbon free from any previously adsorbed pollutants and in conditions close to the original one.
It constitutes the most suitable system for the recovery of activated carbon, for example, in drinking water plants.
The thermal reactivation process can be represented in 3 phases:
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Carbon drying
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Pyrolysis
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Reactivation
The temperature is between 800 and 1000 ° C.
The burner is fed with fuel oil or natural gas.
In addition to thermal desorption, reactivation consists of a wide variety of reactions that take place in the kiln. First of all, there is evaporation of the water contained in the carbon, then there is thermal desorption from pyrolysis, then carbonization and gasification.
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This last stage involves a series of chemical reactions of O2, CO2 and steam, aimed at eliminating carbon compounds, residues from pyrolysis deposited in the micropores and reforming the functional groups on the active surface. Finally, in this phase, there is a structural regularization of the pores.
The exhaust gases leave the furnace at a temperature of about 500'C.
An afterburner is therefore necessary. The afterburner operates at temperatures of the order of 850 - 1100 °. The reactivated carbon is unloaded from the kiln, cooled and packaged in big bags or transported to storage silos before being transferred to the tank or container.