Mass, energy and exergy analysis of a biomass boiler: A portuguese representative case of the pulp and paper industry

This work deals with the mass, energy and exergy analyses of the energy conversion process in a 50 MWth thermal power plant, using residual forest biomass as fuel and integrating bubbling fluidized bed combustion technology. This is a representative case study of the energy production from eucalyptus residual biomass in the Portuguese pulp and paper industry. Analyses are made of the mass, energy and exergy flows, and how they change in the main components of the system, namely the combustion chamber, boiler, drum, superheater, economizer, and combustion air pre-heaters. Sankey and Grassmann diagrams highlight the mass, energy and exergy flows. Special emphasis is given to the energy and exergy efficiencies, which must be based on the useful produced superheated steam to include the influence of the biomass moisture content. The main goal is to find where and what potential exists for energy efficiency improvements. Results show that the main exergy destruction occurs in the combustion process, and that energy and exergy losses are minimal due to the system's good thermal insulation. Results also show that the main potential for improvement is on the decrease of the residual biomass moisture content.