Simplification of the Analysis Stage in Process Integration Retrofit of a Pulp and Paper Mill

Several methods for improving the energy efficiency of industrial plants by means of Process Integration have been proposed in the past 40 years. However, despite proving extremely effective, they are far from constituting the industrial practice in non-energy-intensive industries. The high amount of time required and the complexity of the problem at hand constitute barriers to their usage, which have rarely been addressed.

This paper presents the application of the Energy-Saving Decomposition method in the retrofit of the heat exchanger network of a pulp and paper mill presented in the literature. The procedure aims at reducing the size of the problem before examining the possible design options, based on the potential energy savings achievable by integrating subsections of the existing heat exchanger network.

In combination with traditional Process Integration methods, it proved able to reduce the problem complexity without jeopardizing the results of the analysis, when applied to the case study. Specifically, it showed that 15 process streams over the total 20 could be disregarded prior to the detailed analysis of retrofit options, yet providing the same insight to the analyst, leading to a retrofit able to achieve 33 % of energy savings and an expected investment cost lower than the proposal reported in the literature.

This complexity reduction has the potential to lower the barriers now preventing the industrial application of Process Integration studies.