Mixed biomass pellets for thermal energy production: A review of combustion models

•The use of biomass is increasingly important for clean energy generation from renewable sources.•An analysis of the current situation of the production of pellets (mixed biomass types) is provided.•The main emphasis is on the review of different combustion processes.•The evaluation of each individual stage of the combustion process is very important. The need to generate thermal and electrical energy, global warming caused by increased emissions of greenhouse gases, rising fossil fuel prices and demand for energy independence, have created a new industry focused on energy production through the use of renewable sources. Among the different options, biomass is the third most important source for obtaining electricity, and is the main source for the production of thermal energy. However, problems related to the low density of the different types of biomass, and the difficulty of transportation and storage, have led to the need to find solid fuels with higher density and greater hardness, known as pellets and briquettes. This paper seeks to develop an analysis of the current situation of the production of pellets, mainly with mixed biomass types, and the possible uses they have, with the main emphasis on the review of different combustion processes.