Novel mechanical vapor recompression‐assisted evaporation process for improving energy efficiency in pulp and paper industry

Summary In the pulp and paper industry, black liquor, which is a biomass resource, is burned to produce electricity. Black liquor is concentrated to 21 wt% water through an evaporator before being burned in a boiler. For the evaporator, a multiple‐effect evaporator (MEE) is mainly used, but it requires a large amount of energy and cost. Therefore, it is crucial to reduce energy and cost of evaporation process. Hence, this study suggested a novel process model that integrated mechanical vapor recompression (MVR) with MEE to increase the energy efficiency. The suggested MVR‐assisted evaporation process was composed of preheating and evaporation processes to effectively concentrate black liquor. In addition, it reduced the steam consumption of MEE by using MVR, which uses relatively inexpensive electric energy in the pre‐evaporation process. In the simulation results, the steam, electricity consumption, and the latent heat recovered from the secondary vapor of the suggested process were quantitatively analyzed to verify the energy efficiency. The results indicate that the proposed process increases substantial energy efficiency compared to the conventional process. Then, the appropriateness of the suggested process was evaluated by the techno‐economic analysis. The total annualized cost (TAC) is determined for both current and potential future economic benefits. TAC of the MVR‐assisted MEE configuration can be reduced by up to 77.54%. First, process models using SEE, MEE, MVR‐assisted SEE, and MVR‐assisted MEE were developed to predict the energy consumption of the evaporation process, and the simulation result was comparatively analyzed to verify the energy efficiency of the suggested MVR‐assisted MEE. Second, the economic evaluation was conducted to derive optimal economic MVR‐assisted MEE configuration. Finally, a sensitivity analysis was conducted to examine the effect of the main economic parameters on the optimal economic MVR‐assisted MEE configuration.