1. Industrial rotary dryers equipped with combustion chambers are among the most energy-intensive unit operations in process industries, with reported thermal efficiencies ranging between 30% and 7...

This study presents a comprehensive thermo-energetic and exergetic assessment of a 250 MW steam boiler in a Cuban thermal power plant, operating under partial load conditions (plant: 62–66%; boiler: 58–61%). An integrated diagnostic methodology was developed and implemented in Mathcad 15 to evaluate key performance indicators, including thermal efficiency (η_tGV); exergetic efficiency (η_ExGV); exergy destruction ratio (γ_ExGV); steam generation index (IG_v); and specific fuel consumption (B_Esp). The methodology was applied to two fuels with contrasting thermophysical and chemical properties: fuel oil and Enhanced Crude Oil 650. The results indicate superior performance with fuel oil due to its higher heating value; however, efficiency losses were mainly attributed to operational factors such as excessive air supply (22.7–26.4%), heat transfer surface fouling, and inadequate maintenance. The analysis revealed significant deviations from design values—thermal efficiency (90.27–90.59%) and exergetic efficiency (<60%)—highlighting an untapped potential for energy savings. Quantitative estimates indicate potential annual fuel cost savings of approximately 1.2 million USD through optimized combustion and maintenance practices. The proposed framework enables accurate diagnostics of complex boiler systems and provides actionable indicators to support combustion optimization and energy efficiency strategies in conventional thermal power plants.