(363a) Cost-Optimal Multi-Effect Mechanical Vapor Recompression Evaporation Configuration in Pulp and Paper Industry

In the pulp and paper industry, the multi-effect mechanical vapor recompression evaporation configuration effectively reduces the energy consumption of the black liquor evaporation process. However, since mechanical vapor recompression (MVR) uses a centrifugal compressor, a piece of expensive equipment, the equipment cost rapidly increases as the evaporation rate by MVR increases to reduce the energy consumption. In addition, the equipment cost of the multi-effect evaporator (MEE) also increases as the number of effects increases to reduce the energy consumption. Therefore, a cost-optimal multi-effect mechanical vapor recompression evaporation configuration is proposed to minimize the total annualized cost (TAC) of the evaporation process, consisting of equipment and operating costs. First, all feasible multi-effect mechanical vapor recompression evaporation models are developed to predict the energy consumption and capacity of the equipment. Second, a mathematical model is proposed to solve a mixed-integer non-linear programming (MINLP) problem: the optimization of the evaporation rate by MVR and the number of effects to minimize TAC. As a result, the cost-optimization is achieved by 9.6 kg/s of the evaporation rate by MVR with five effects. This study could provide a guideline for designing the commercial evaporation process in the pulp and paper industry.