Peat belongs to the slowly renewable biomass resources, therefore its use as an energy source helps to reduce the negative impact on the environment. However, its use in the energy sector is gradually decreasing due to high operating costs because of the characteristics of peat. The aim of this work is a comprehensive study of the peat characteristics and the development of recommendations for its effective use. In this paper, we consider the widespread methods for studying fuel (thermo-technical and fusibility characteristics determination, X-ray fluorescence and phase methods), as well as the original approach of separation by sedimentation in liquids of various densities. The peat separation by sedimentation in liquids of various densities made it possible to obtain a low-ash peat fraction comparable in characteristics to brown coals and a highly mineralized fraction (heavy fraction). On the example of grain processing waste, it is shown that the addition of a 5% of heavy peat fraction to bran prevents the formation of strong slag deposits and can be recommended for co-burning. This allows us to consider the separation by sedimentation in liquids of various densities as an effective tool for using highly mineralized types of biomass in energetic sector.