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The energy and costs required to reliquefy the boil‐off gas (BOG) produced in liquefied natural gas (LNG) tanks are enormous. At the same time, LNG releases large amounts of cold energy during the regasification process. To recover both the BOG and the LNG cold energy for power generation, herein, a novel system consisting of a supercritical carbon dioxide recompression Brayton cycle, an ammonia–water mixture Kalina cycle, a BOG combustion turbine cycle, and a natural gas turbine cycle is presented. The genetic algorithm with multiple elite saving is used to optimize the system thermoeconomic performance, and the maximum energy efficiency, exergy efficiency, and net present value of 65.49%, 33.88%, and 7.374 × 107 $ are obtained respectively. The nondominated sorting genetic algorithm II is implemented to achieve the multiobjective optimization, and the comprehensive performance analysis is carried out on this basis. The results show that heat exchangers and turbines account for the highest exergy destruction and total cost proportion with the value of 76.5% and 81.1% respectively. The heat transfer curves between LNG and working fluids are well matched, and the cooling capacity for ammonia liquefaction is the largest, accounting for 66.66%, which also generates 581.2 kW of power generation. The results also indicate that the LNG cold energy cascade utilization system combined with BOG combustion has excellent thermodynamic performance and can obtain ideal economic benefits. [ABSTRACT FROM AUTHOR]

The dwindling and scarcity of fossil energy sources is the basis of the energy transition, where renewable resources are increasingly valued. The purpose of the cogeneration system studied in this article is to recover the residual heat from the gases coming out of the chimneys of the cement kilns, to produce at the same time the electricity and the heat required for offices and residential houses of cement workers. Cement kilns are reputed to be energy-intensive, generating excessive heat losses. These heat losses are found mainly in the conduction–convective and radiative modes, representing about 26% of the overall heat input to the system. Nevertheless, the gases at the chimney outlet can still have temperatures between 250 and 350 °C, which presents a non-negligible potential for a cogeneration system. This study compares the thermal performance of different cogeneration plant configurations (KCA, KCB, and KCC systems) using the Kalina cycle to determine the best one. Several assumptions were made to reduce the complexity of the model. MATLAB and Excel software were used to solve the system of equations. After extensive analysis of the results, the KCA system showed the best performance, compared to the KCB and KCC systems, with a thermal efficiency of 22.15%, an exergy efficiency of 45.12%, and a net electrical capacity of 2565.03 kWe. Model sensitivity to concentration, temperature, and pressure variations also gave the KCA system the best-performing system. Evaluation of the excess heat flux removed from the process yields values of 7368.20 kW, 7421.86 kW, and 8094.15 kW for the KCA, KCB, and KCC systems. The results of this article serve as a decision support tool for installing the cogeneration system via the Kalina cycle in cement installations. [ABSTRACT FROM AUTHOR]

The dwindling and scarcity of fossil energy sources is the basis of the energy transition, where renewable resources are increasingly valued. The purpose of the cogeneration system studied in this article is to recover the residual heat from the gases coming out of the chimneys of the cement kilns, to produce at the same time the electricity and the heat required for offices and residential houses of cement workers. Cement kilns are reputed to be energy-intensive, generating excessive heat losses. These heat losses are found mainly in the conduction–convective and radiative modes, representing about 26% of the overall heat input to the system. Nevertheless, the gases at the chimney outlet can still have temperatures between 250 and 350 °C, which presents a non-negligible potential for a cogeneration system. This study compares the thermal performance of different cogeneration plant configurations (KCA, KCB, and KCC systems) using the Kalina cycle to determine the best one. Several assumptions were made to reduce the complexity of the model. MATLAB and Excel software were used to solve the system of equations. After extensive analysis of the results, the KCA system showed the best performance, compared to the KCB and KCC systems, with a thermal efficiency of 22.15%, an exergy efficiency of 45.12%, and a net electrical capacity of 2565.03 kWe. Model sensitivity to concentration, temperature, and pressure variations also gave the KCA system the best-performing system. Evaluation of the excess heat flux removed from the process yields values of 7368.20 kW, 7421.86 kW, and 8094.15 kW for the KCA, KCB, and KCC systems. The results of this article serve as a decision support tool for installing the cogeneration system via the Kalina cycle in cement installations.

An optimisation model for the composition of mixed working fluids for (Organic Rankine Cycles) ORCs and Kalina cycles has been developed. The temperatures investigated were 100 °C–250 °C for the heat source and 30 °C for the heat sink. The optimisation method of the composition was carried out with Simulated Annealing technique with the objective function of maximising the thermal efficiency of the cycle, based on 1 MW of heat source. The results show that the pure component organic fluids are more energy-efficient than mixed organic fluids. The selection of organic working fluids was studied for achieving maximum cycle efficiency at a given operating temperature. The composition of the Kalina cycle was also optimised and it was found that for a maximum temperature of 250 °C, the minimum ammonia concentration in the ammonia–water mixture was 73.8% mol fraction. A novel consideration of employing alcohol–water mixtures in the cycle was also investigated and the most efficient mixture at 250 °C was methanol and water mixture when compared to the Kalina cycle and steam Rankine Cycle. The study showed overall that the optimal choice of working fluids for a particular type of cycle would depend on the operating temperature and pressure. The developed design method can be useful for engineers to evaluate the performance of the cycles considering a wide range of working fluids, and determines the optimal choice of working fluids and operating conditions of the cycle. [ABSTRACT FROM AUTHOR]

Binary-type energy conversion systems are typically used to exploit low-temperature geothermal resources. There are many different technical variations of binary plants, including those known as Organic Rankine Cycles (ORC) and proprietary systems known as Kalina cycles. Recent articles in the technical literature claim dramatic efficiency advantages for Kalina cycles over ORCs, thereby providing the motivation for this study. Claims of remarkable superiority for one type of technology relative to another ought to be verifiable by recourse to actual performance data. Since there is now an actual Kalina cycle in operation, it ought to be possible to make a comparison between it and ORC plants that have been in operation for some time. Comparisons between power plants must use an appropriate and consistent thermodynamic basis. It has been shown that the Second Law of thermodynamics is the best basis for such comparisons. This principle, employing the concept of exergy, is used here to shed light on these claims. Furthermore, we introduce a methodology to render the comparison of plant efficiencies on common input and environmental conditions, even though the plants being compared operate with somewhat different fluid inlet and ambient temperatures. [Copyright &y& Elsevier]