A system analysis of the chemical recovery plant of the sulfate pulping process

The chemical recovery system of the sulfate pulp mills is probably one of Sweden's largest inorganic processes, with great technical and economic importance. The section that comprises the smelt from the recovery boiler to the white liquor produced is a part of the process on which relatively few contributions have been published. With the purpose of finding an energy optimal process solution for this section, a system analysis study has been carried out. Thereby it was found necessary, in order to elucidate the potential possibilities that different procedures would result in, both to study the present process technique and to simulate possible improvements. An important conclusion of the system analysis study presented in part 1, based on the evaluation of three different pulp mill chemical recovery systems, is that all the systems have a negative exergy efficiency. This means that the chemical recovery systems of the puip mills investigated ought to produce energy and not, as the case is today, consume energy. Therefore it can be concluded that there is a great potential for improving the efficiency of the chemical recovery process. In an analysis of the different parts of the chemical recovery process system it was found that almost all of the parts of the process contributed to the energy losses in the form of steam and radiation losses. It was also concluded that the drying of lime mud in the lime kiln is not done in the best energy efficient way.