Oxidative torrefaction of briquetted birch shavings inside the quiescent layer of bentonite clay was investigated in a muffle furnace. In the considered process the briquettes are buried under the layer of bentonite clay and the reactor is heated at atmospheric conditions without the use of inert gas. The main role of the bentonite clay is to limit the oxygen access to the torrified biomass from the environment. The paper considers the effects of briquette thickness, bentonite layer height, temperature and torrefaction duration on the mass yield and energy yield of the biomass. It is shown that to increase the enhancement factor of HHV of the biomass it is necessary to reduce both the height of bentonite clay and the briquette thickness. As well the torrefaction temperature and duration should be increased. It is also established that the height of bentonite layer affects negligibly on the energy yield. (C) 2018 Elsevier Ltd. All rights reserved.