Trade-offs between the recovery, exergy demand and economy in the recycling of multiple resources

The trade-off between the degree of circularity in industrial and urban processes and the spent resources in terms of energy and funds poses a challenging task. Material and energy flows feature different global patterns, which sets them as two interacting dimensions in the process. This work proposes the Multi-Resource Integration Map concept for modelling the recycling processes and representing the trade-off. The criteria used are based on exergy expenditure and cost, evaluated against the degree of circularity represented by the newly formulated Total Circularity Index (TCI), combining the Circular Material Use rate and Circular Exergy Use rate. The method is demonstrated in a case study from the domain of urban symbiosis where a set of waste resources are available to serve, after processing, part of specified product demands. The results show that the optimal exergy consumption (690 kW, TCI = 0.396) and the optimal Total Annual Cost (102.7 kEUR/y, TCI = 0.359) take place at different but correlating Total Circularity Index values. The optima are 33% lower in terms of cost and 22% lower in terms of exergy than the point of maximum circularity. The method proposed in this paper provides guidance for the integration of multi-resource systems, allowing the decision-makers to estimate the economic and exergy performance of the proposed Circular Economy solutions, aiding in improving the sustainability contributions of industrial and urban systems.