The digester is air heated; a fan circulates air from the chamber through heating element back to the chamber. Hot air heats the autoclaves that are revolving on a six place rack. The direction of the revolving rack changes after one full round.

The air bath digester consists of six cooking autoclaves (bombs) in which different kinds of cooking and bleaching experiments can be performed.

Each bomb has a volume of 2,5 l and maximum pressure of 20 bar. They can take 375 g of abs. dry wood chips and maximum filling is 2000 ml.

There are two sets of six bombs. The other set has Teflon coating. Teflon does not react with oxidizing agents such as peroxide but they do not tolerate harsh physical contact.

If the bombs are used for delignification, the proper amount of pulp is 100-150 g. Suitable consistency for delignification is 8-10 %.