Conceptual Design, Dynamics And Control Study Of High-Purity Internal Thermally Coupled Air Separation Columns

Air separation is an important industrial process that gets the high purity oxygen, argon, nitrogen and other industrial gases by means of the separation of air. It strongly supports other industries such as petrochemical industry, chemical engineering, metallurgy, electric engineering, energy engineering, aeronautic engineering and food, medicine. Now, productivity and energy saving are the key to the further development of air separation. This work will study the internal thermally coupled distillation columns (ITCDC) with the highest energy-saving effiency, do optimal design the process of air separation and attempt to apply the ITCDC into the cryogenic air separation process. The main work and contribution are as follows:(1) Use Aspen software to build the simulation model of air separation. Carry out sensetivity analysis and operation optimal adjustion to improve the productivity of initial air separation units.(2) Build and solve the mathmatic model of air separation by programming on Matlab. Build the optimization model and carry out optimal design for air separation by means of SQP algorithm, which further improve the productivity.(3) Based on the thermodyriamic analysis, calculate the exergy for conventional moderate- and low-pressure air separation and find out the way to further improve the energy saving effiency of units. The way is to reduce the decrease of exergy of distillation columns.(4) Apply ITCDC from moderate-purity to high-purity system in order to meet the request of air separation. Analyze the dynamic behaviors of high-purity ITCDC in detail. The results show that high-purity ITCDC owns the inverse response, high nonlinearity and strong sensetivity to external disturbances. Besides, the system is an ill-condition system with strong interaction and process directionality problems. According to these dynamic behaviors, some effective controllers are designed, hi addition, bring ITCDC into the very high-purity system. Design a effective controller combining the feedforward with feedback control and solve the difficult problem that the system is sensetive to the disturbance of feed flow rate.(5) Apply ITCDC into the high-purity air separation process. Attempt to carry out conceptual design, provide the suitable value of process parameters, design the novel structure of air separation, discuss heat-integrated methods and present two kinds of feasible schemes. Besides, give out the mathmatic description of the novel air separation process. The simulation results show that the novel air separation columns with ITCDC can achieve more 17.5% energy saving than the conventional counterpart.