Regenerative burners use an extreme recycling technique of flue gases to preheat the combustion air.
Both in the case of heat exchangers or  autorecuperative burners, the heat exchange between incoming combustion air and outgoing combustion fumes takes place directly.
In the first case outside, in the second inside the burner.

In regenerative burners, a system that is based on pairs of burners is used. These burners exchange heat through a medium, receiving and transferring heat during alternating cycles of air suction and ejection of exhaust gases. The mediator, or “regenerative bed” is a tank that is normally filled with ceramic material of different shapes and types.

The regenerative burners allow air recuperation at the highest temperatures and this is why they are absolutely the most efficient combustion technology. The enormous savings that these types of burners allow can be even more appreciated when the process temperature increases.