Heat Recovery Unit for EKKO

The drier the raw material used in the carbonization or pyrolysis process, the more stable the process. A stable carbonization process generates excess heat; directing this heat to preliminary drying creates an additional beneficial effect: the feedstock becomes drier, the carbonization cycle becomes shorter, and furnace heat balance improves.

High efficiency is achieved by “contact drying”, meaning direct contact between the heat carrier and the feedstock. In the pyrolysis unit itself, feedstock heating occurs through the trolley wall and does not offer equivalent heat-transfer intensity.

Excess heat from carbonization can have a temperature of `200-1300 °C`. The optimum temperature for contact drying is about `150 °C`, while the quantity of thermal energy in the drying agent depends mainly on carbonization intensity. The heat recovery unit for EKKO automatically prepares the heat carrier in accordance with the defined drying program: the hot flow is diluted with ambient air to the required temperature within the range of 120–200°C and then directed directly into the trolleys located outside the pyrolysis unit.

The excess heat recovery unit is part of the feedstock preliminary drying system, installed outside the EKKO pyrolysis unit. Excess heat from carbonization enters the pyrolysis-unit flue, from which a draft fan directs hot gas into a thermal mixer. In the mixer, hot flue gases are combined with cold atmospheric air to lower the heat-carrier temperature to the set value of `150-250 °C`, forming the drying agent. This solution minimizes or completely eliminates additional fuel for feedstock drying.

Prepared drying agent is delivered through a distribution manifold to trolleys containing fresh, wet feedstock. The trolley-drying devices feed the drying agent into the trolleys and discharge drying vapour to the atmosphere.

Disadvantages include: 

• heat loss through trolley walls 
• influence of feedstock arrangement 
• absence of a fire-safety system 
• absence of a technological feedstock reserve for carbonization
• human-factor dependence

The EKKO heat recovery unit increases the useful application of thermal energy generated during carbonization and directs excess heat to feedstock preparation. Reducing moisture before the main cycle shortens carbonization time, increases finished-product yield, improves mechanical strength and lowers the fines fraction.