System optimization by augmented lagrangian function method for CO ₂ recovery system

Carbon dioxide (CO₂) included in exhaust gas from heat power plants is the chief cause of global warming. In the present study, the numerical simulations of CO₂ recovery systems for the exhaust gas were conducted in order to decide optimal values of 5 operation conditions for actual plant. Optimization was conducted by augmented Lagrangian method. For example, for actual plant (flow rate of flue gas: 70000 m³ (STP)·h ^-1), the optimal operation conditions were calculated, in which required consumption energy was minimum within the term that CO₂ recovery rate was 60% and CO₂ concentration of recovery gas was about 90%. And it was confirmed that 3 different conditions given as initial operation condition converged same optimal conditions. In the optimal condition, required consumption energy that is sum of energy consumed by heater and blower was 835 kJ·kg^-1, CO₂ recovery rate was 60% and CO₂ concentration of recovery gas was 92%. This required energy was 5% less than that in previous work (Matsukuma et al., 2007), and from this fact we think optimization by this method is effective. Furthermore, from the result of previous work (Matsukuma et al., 2007), it was suggested that recovery performance was better when the purge process of the system was removed. However we confirmed that the present system including purge process has better performance by the present optimization method.