Pulp mill as an energy producer

The recovery boilers of pulp mills are today the most significant producers of wood energy. The power-to-heat ratio of the power plant process, i.e., power yield, is poor in existing applications. In the study, an alternative of improving the power yield of conventional pulp mills significantly was studied by applying solutions used in power plants to a pulp mill. Extensive conversion of wood energy into electricity is possible only in the recovery boiler of the pulp mill and in a large combustion boiler of bark, wood waste and wood chips integrated to this boiler. Hence, the harvest and transports of wood raw materials, i.e. pulp wood and energy wood, are integrated, and the fraction going to cook and the energy wood fraction are separated at the pulp mill. The method guarantees competitive supply of energy wood. As a result a SELLUPOWER mill was designed, where the recovery boiler combusting black liquor and the large power plant boiler combusting energy wood are integrated to one unit and constructed to a power plant process with a high power-to-heat ratio. Necessary technical solutions, project costs and economical feasibility compared to a conventional pulp mill were determined, and the effect of different production-economical parameters was also studied. (orig.)