Waste Carbon Recovery for Environmental Sustainability

Used granular (GAC) or extruded (EAC) activated carbon can be recycled through thermal activation, which involves treating the used carbon in a high temperature activation oven at 850°C or above. Recovery by thermal regeneration is only one of the steps in the complete service package. The recovery process consists of two main processes: 1) reactivation process and 2) tail gas treatment and energy recovery process.

The reactivation process itself can be subdivided into four steps.

1) Drying of used carbon

The used carbon is fed into the furnace and heated from ambient temperature to 105 - 110°C. Water and some low boiling compounds are evaporated and released into the furnace atmosphere. As long as there is water in the pores, the temperature of the carbon remains between 105 and 110°C.

2) Desorption of low boiling point organics.

As the carbon dries, the temperature increases further to about 450°C. During this temperature increase, various organic compounds are desorbed from the carbon and escape into the furnace atmosphere.

3) Pyrolysis of high boiling point or high molecular weight strongly adsorbed organic compounds

In this step the carbon is further heated to about 600°C. The remaining organic matter is broken down into smaller molecules, which are released into the furnace atmosphere and form a coke residue in the pore structure of the activated carbon.

4) Coke residue gasification

By heating the carbon to temperatures above 850°C and injecting steam, the pore structure in the carbon is reformed. Steam at temperatures above 600°C absorbs heat and carbon dioxide in a reaction known as steam carbon gasification. The following reactions occur in this region of the furnace.

Solid gas reaction

C + H₂O → CO + H₂ heat absorption (1)

C + CO₂ → 2 CO heat absorption (2)

C + ½ O₂ → CO exothermic (3)

C + O₂ → CO₂ exothermic (4)

Gas-gas reaction

CO + ½ O₂ → CO₂ exothermic (5)

H₂ + ½ O₂ → H₂O exothermic (6)

The solid-gas reaction (1) is three times faster than the solid-gas reaction (2). For this purpose, steam is injected into the furnace. By controlling the operating conditions of the furnace, the pore structure will be restored to the optimal activation level required for the application using the product.

The final gas leaving the furnace is fed through an afterburner and exhaust gas treatment system to be released to the atmosphere in accordance with the strictest local environmental regulations. Recovery by thermal activation is an environmentally responsible treatment method that helps reduce CO₂ emissions from activated carbon and contributes to the sustainable use of the world's resources.

The reactivation process contributes to the reduction of CO₂ emissions and the sustainable use of the world's resources.