Technoeconomic and environmental optimization of combined heat and power systems with renewable integration for chemical plants

Chemical industry mainly uses fossil fuels as energy resources and thus causes substantial amount of carbon emissions. Combined heat and power (CHP) systems have become an effective solution for reducing energy consumption and carbon emissions. This paper presents a bi-objective mixed-integer linear programming framework for technoeconomic and environmental optimization of CHP systems for chemical plants, accounting for steam turbine network design and renewable integration. The bi-objective optimization problem is solved to achieve a trade-off between total annual cost (TAC) and carbon emissions. Two typical quad-pressure and dual-pressure chemical plants are employed for demonstration. The results show that the optimal CHP system has a TAC of 21.1 and 18.9 million USD as well as carbon emissions of 50 and 35 kton for quad-pressure and dual-pressure plants. Both systems feature a sharp reduction of 33.3% and 42.5% in emissions and a mild increase of 26.7% and 30.2% in TAC when comparing with TAC minimization. Moreover, we find that gas boiler is mainly responsible for carbon emissions, and replacing it with electric boilers is an promising alternative for further emission mitigation. We observe that photovoltaics capital price has a significant impact on system TAC and emissions, while employing only carbon tax is unable to achieve deep decarbonization. Hence, we recommend combining system design, renewable technology advances, and carbon tax synergistically for chemical industry decarbonization. Our methodology provides an effective and flexible framework for further investigation of decarbonization.