Abstract:In a European context characterized by growing need for operational flexibility across the electricity sector, the combined cycle power plants are increasingly subjected to cyclic operation. These new operation profiles cause an increase of production costs and decrease of revenues, which undermines the competitiveness of the combined cycles. Power plant operators need tools to predict the effect of off-design operation and control mechanisms on the performance of the power plant. Traditional Thermodynamic or Thermoeconomic models may be unpractical for the operators, due to their complexity and the computational effort they require. This study proposes a Thermoeconomic Input-Output Analysis model for the on-and off-design performance prediction of energy systems, and applies it to La Casella Natural Gas Combined Cycle (NGCC) power plant, in Italy. It represents a stand-alone, reduced order model, where the cost structure of the plant products and the Thermoeconomic performance indicators are derived for on-and off-design conditions as functions of the load and of different control mechanisms, independently from the Thermodynamic model. The results of the application show that the Thermoeconomic Input-Output Analysis model is a suitable tool for power plant operators, able to derive the same information coming from traditional Thermoeconomic Analysis with reduced complexity and computational effort.
Gas condensate stabilization is a common process in gas refineries and petrochemical industries. This process is energy-consuming since it uses distillation columns and furnaces to separate different cuts from the condensate feed. This study aims to improve the performance of the gas condensate stabilization unit in a large petrochemical company in terms of energy efficiency and loss prevention. The case under investigation is the gas condensate stabilization unit in the Nouri Petrochemical Company, treating 568 t/h of raw condensate feed. This plant includes two distillation columns, two furnaces, pumps, heat exchangers, and air coolers. A hybrid energy and exergy analysis is conducted in this study. First, the validation of the simulation phase is performed, and a parametric sensitivity analysis is conducted to explore the effects of various parameters, such as operating temperature and pressure, on the process performance. After that, the most influential variables are identified using thermodynamic analyses for optimization and design purposes.
An optimization method is employed to attain the maximum production improvement and exergy efficiency. The exergy analysis shows 187.4 MW total exergy destruction in the plant; furnaces account for 79% of the total exergy destruction. According to the sensitivity analysis results, the energy consumption of the process could be reduced by 33.7 MW; this is an 18% reduction in the plant's energy consumption. The optimal process conditions outperform the current and design states (4.6% improvement in exergy efficiency). The fuel gas consumption is reduced by 2.1 t/h, leading to a reduction of 128 t/d CO2 emissions.
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