Feasibility study on the integration of bottoming organic Rankine cycle and Kalina cycle with conventional steam power plants: A case study in Iraq

• Efficiency vs Economy: Waste heat recovery involves a clear trade-off between thermodynamic performance and economic viability. • The Kalina Paradox: The Kalina cycle is more efficient but less economical due to higher complexity and costs. • Simple ORC Wins: Despite lower efficiency, the basic ORC offers the best return on investment due to its simplicity and lower costs. • Stable Performance: System performance remains stable across varying boiler loads. • Optimal Choice (130°C): The simple ORC is the most economical option for low-temperature heat sources. • Strategic Value for Iraq: Retrofitting aging power plants with this technology boosts capacity, lowers emissions, and extends asset life. The main issue of using the Kalina cycle system (KCS) and the organic Rankine cycle (ORC) is how to use low-grade energy to produce electrical power. This study examines the preliminary feasibility of repowering the conventional South Baghdad steam power plant by integrating ORC and a KCS as the bottoming cycle. Three dry organic fluids- R-245fa, butane and Isobutane- were examined in simple and regenerative ORC configurations. The novelty of this work includes the development of a comprehensive dynamic simulation model for the standalone South Baghdad Unit (SBU). This model is specifically designed to estimate the feasibility and performance of incorporating the unit with an ORC and a KCS, with a particular focus on analyzing system behavior under both design and off-design circumstances (covering the flow rate ratio Θ = 0.8 − 1 ). The energy analysis outcomes showed that the KCS combined cycle performed better. This combined cycle yields up to 0.25% larger output and up to 0.2% higher thermal efficiency compared to the existing SBU. Although R-245fa and butane showed superiority over Isobutane, all combined cycles with ORC reduced the performance. Based on economic outcomes, ORC systems exhibited superior economics than the KCS, with the simple butane cycle attaining the lowest Levelized Electricity Cost (LEC) of 1.999 cents per kWh and a shorter payback period (PB) of 1.7 years. In contrast to higher-temperature applications, regeneration increased both the LEC and PB duration for 130°C systems, favouring simpler ORC designs. The KCS, while thermodynamically superior, resulted in a higher LEC of 2.68 cents per kWh and a longer PB period of 2.3 years. In conclusion, the proposed cycles present viable options for repowering ancient thermal power plants in Iraq and offer a practical way for policymakers to address Iraq's electricity shortage by modernizing existing infrastructure.