In the context of emissions, carbon dioxide constitutes a predominant portion of greenhouse gases (GHGs), leading to the use of the term “carbon” interchangeably with these gases in climate-related discussions. The carbon market has emerged as a pivotal mechanism for emission regulation, allowing industries that struggle to meet emission reduction targets to acquire credits from those who have successfully curbed their emissions below stipulated levels. Thermoeconomics serves as a tool for analyzing multiproduct systems prevalent in diverse sectors, including sugarcane and alcohol mills, paper and pulp industries, steel mills, and cogeneration plants. These systems necessitate frameworks for equitable cost/emission allocation. This study is motivated by the need to expand the scope of thermoeconomic modeling to encompass expenses or revenues linked with the carbon market. By utilizing a cogeneration system as a representative case, this research aims to demonstrate how such modeling can facilitate the allocation of carbon market costs to final products. Moreover, it underscores the adaptability of this approach for internalizing other pertinent costs, encompassing expenses associated with environmental control devices, licenses, and permits. Although certain exergy disaggregation models depict an environmental component within diagrams, which is integral for addressing environmental burdens, even models without explicit environmental devices can effectively internalize carbon credits and allocate them to final products. The integration of carbon credits within thermoeconomic modeling introduces the capability to assess both the financial and environmental implications of emissions. This integration further incentivizes the reduction in GHGs and supports optimization endeavors concerning system design and operation. In summary, this study delves into the incorporation of carbon market dynamics into thermoeconomic modeling. It demonstrates the potential to allocate carbon-related costs, facilitates comprehensive cost analysis, encourages emission reduction, and provides a platform for enhancing system efficiency across industrial sectors.

With growing global concern over environmental issues, the design and operation of efficient energy production systems have become increasingly important and necessary for a low-carbon economy. In this context, the repowering of thermal systems emerges as a promising alternative aligned with current climate goals. However, an increasingly competitive economic scenario requires solutions that are not only efficient but also associated with low investment costs. Therefore, optimization techniques are essential for evaluating current energy production systems and can support the energy transition and decarbonization goals. This work presents a simulation-based case study on the repowering of a gas cogeneration system with an Organic Rankine Cycle (ORC) producing 30 MW of shaft power and saturated steam at 20 bar. The thermodynamic and economic assessment is carried out through multi-objective optimization using structural and parametric variables inherent to both the gas and organic systems. The Pareto frontier results show that the optimized minimum and maximum exergetic efficiencies reached 47.88% and 57.44%, with associated investment costs of US$ 11.14 million and US$ 74.08 million, respectively. In all solutions, the gas regenerator was present, while the ORC appeared in the maximum-efficiency extreme, providing an average additional power output of 182 kW. The decision variables of the gas system showed a greater influence on the objective functions when compared to those of the ORC. Therefore, optimization techniques are fundamental for the assessment of thermal systems aiming at high efficiency and low cost.