Toward Decarbonization of Chemical Manufacturing: Joint Optimization of Unit Commitment and Microgrid Operations
The electrification of chemical process heating is essential to industrial decarbonization and sustainable manufacturing of chemical products. Joint optimization of electrified chemical process heating units and electric power systems is needed to achieve decarbonized operation of both sectors. In this work, we introduce a joint optimization model that identifies the optimal unit commitment of power systems and optimal operation of electrified steam cracking microgrids for olefins production. A mixed-integer linear programming (MILP) model is developed to optimize the hourly operational plan of 26 ethylene plants and the main power system in Texas. We propose a two-stage solution method to solve the resulting large-scale MILP problem efficiently. In the first stage, we apply Benders decomposition with LP-relaxed subproblems to decouple microgrid operations from the main power system. In the second stage, we use the first-stage optimal solution as a warm-starting point for the MILP. This two-stage approach reduces the average solution time by 93.5% compared to direct solution of the MILP. Results show that the largest overall greenhouse gas (GHG) emission reduction for both power systems and microgrids is achieved when the electrification level of steam cracking units is at 30%. Above 30% electrification level, a higher electrification level leads to higher overall GHG emissions and steady increase in operating costs, particularly on the microgrid side. Increasing renewables contributions in the electric power system helps debottleneck the electrification efforts and facilitate holistic decarbonization. We also remark that the optimal operational plan of electrified steam cracking microgrids also exhibit strong spatiotemporal patterns.