Modelling & Optimization Of Internal Thermally Coupled Air Separation Columns

Cryogenic air separation is the distillation process of air to obtain high purity nitrogen, argon, oxygen and other important industry gases, which is widely used in petroleum, chemical, metallurgy, energy, aerospace and beverage and other areas. With economic development, energy consumption of cryogenic air separation industry has become a bottleneck for further development. Internal Thermally Coupled Distillation is the best one out of the four distillation energy saving technologies. Introducing this technology to cryogenic air separation will bring great energy saving effect.The main research works and contributions are listed as following:1. The steady model of internal thermal coupling air separation column (ITCASC) is established. The degree of freedom of the model is analyzed. The analyses of the steady state characteristic and the energy consumption of ITCASC show that the temperature differences of ITCASC increase about 1.7K than the conventional air separation column under the same operation pressure, which reveals that the operation pressure of ITCASC can be further reduced.2. To shorten the computation time for solving the model, a hybird model is proposed for ITCASC. The statistical approach, PCA-CGA-RBF is employed to estable the model of liqud molar fraction, pressure and equilibrium temperature. The computation time of bubble point method decreases 95.36%. And the average relative error is only 0.002%. Compared to the principle model, the proposed hybrid model can decrease the computation time from 31.06s to 11.18s, decreasing 64.01%.3. A non-equilibrium stage dynamic model of ITCASC is proposed first time. After a systematic comparison, the effective methods of calculating the physical properties are explored. With the appropriate segmentation and simplification the proposed dynamic model, an effective algorithm.is given. Simulation studies are conducted to evaluate the obtained results and confirm the validity of the proposed non-equilibrium stage model.4. Based on the hybrid model of ITCASC, an optimization model is established further and solvede. The results show that the high pressure of ITCASC can reduce from 590KPa to 313.74KPa, which means about 40% energy saving. This reveals the huge energy saving potential of the ITCASC. Meanwhile, the flow rate of feed air decreases, from the original 188.1 mol/s to optimal operating conditions 169.76 mol/s, while the flow rate and purity of the product keep almost the same, which reveals that the energy consumption per unit product for ITCASC process can further decrease comparing the CASC process.