Abstract
Power-to-X (PtX) technologies play a central role in renewables-based energy systems by enabling the conversion of renewable electricity into multiple energy carriers. However, due to the multiple energy conversion stages inherent to such energy systems, they often suffer low system efficiencies and high operational costs. In this context, waste product utilization offers significant potential for improving system performance. Directly integrating waste product utilization into energy system operational problems, however, is computationally challenging, as it requires high model granularity to capture waste product characteristics and introduces additional complex constraints.This work proposes a method to integrate waste heat utilization into operational optimization problems, aiming to improve the overall performance of PtX energy systems. Detailed process models, together with pinch analysis, are used to generate surrogate models for the thermal (by-)products and their associated temperature levels. The resulting optimization problem is decomposed into multiple subproblems. To balance problem complexity and solution optimality, two alternative approaches, "ex-post" and "co-optimized" are developed, differing in whether waste heat utilization is addressed ex post or jointly optimized with the energy system operation.The proposed method is applied to optimize the daily operation of a PtX energy system. Compared with a reference case without waste heat utilization, the ex-post approach achieves a cost reduction of 7% within identical computational time (0.6h). The co-optimized approach yields cost savings of up to 22% with a computational time of 3.4h. These results demonstrate the effectiveness of the proposed method for integrating waste heat utilization into energy system operational optimization.