A problem decomposition approach for developing total water networks in lignocellulosic biorefineries

Water streams in lignocellulosic biorefineries deviate from the dilute waters streams encountered in conventional chemical processes. Moreover, thermal and chemical interactions between components restrict the use of linear approximations for the mass transfer models. This paper proposes a new targeting and design method for the integration of water into lignocellulosic biorefineries. The focus is on the large deviations from the typical assumptions on constant flows and dilute mixtures. New transshipment models for fixed load, fixed flowrate and hybrid systems are developed that reflect on the non-ideal aspects of the water streams. The methodology assesses targets further reducing the solution space defined by the flowrates of the water streams and the inlet concentrations. It involves a preliminary stage where the set of a surrogate model constraints required by the augmented transshipment models are built using a detailed simulation of the process. The optimization procedure produces targets for water consumption and further determines a superstructure of reduced size for the total water network. The methodology is tested on a real biorefinery pilot plant, where there is also available an option for regeneration of water. Results for the background process show that 85.5% savings can be achieved by exploiting an optimal combination of the reuse, regeneration and recycle options. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.