Modelling of a Heat Recovery System (HRS) Integrated with Steam Turbine Combined Heat and Power (CHP) Unit in a Petrochemical Plant

This study models a Heat Recovery System (HRS) within a petrochemical plant, assessing its economic and environmental viability. The system integrates four combustion processes and a condensing steam turbine combined heat and power (ST-CHP) generation unit, along with waste heat recovery technologies to reduce the plant�s energy use. The developed system-based approach extends a previous methodology, initially focused on reducing energy consumption in production processes, to encompass energy supply systems (in which CHP is included) as well. Simulation models were developed for two improvement scenarios regarding the integration of the ST-CHP into the HRS: preheating either the combustion air stream or the inlet water of the ST-CHP�s boiler. The latter demonstrated greater potential for reducing energy-related operational costs, thus an NLP optimisation model was developed based on that scenario. Both simulation and optimisation models were created resorting to the capabilities of the ThermWatt computational tool (comprising Modelica and Python languages). A payback period of about 2 years and 3 months and a reduction in equivalent carbon dioxide emissions of 5.14 kt CO2,eq/year were estimated for the final system, which are significantly reasonable in comparison to benchmark values.