Zhongkong Technology explores new approaches for safe production and energy conservation in China’s air separation industry

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This post was last edited by Li Hui@SUPCON on 2022-9-30 at 10:53. Air separation equipment is **one of the key types of industrial equipment; it can be used to produce a variety of industrial gases, and is widely applied in various important sectors of the national economy such as machinery, metallurgy, petrochemicals, new coal chemical industries, building materials, aerospace, and healthcare. Currently, air separation equipment is primarily used in the metallurgy and chemical industries, with these two sectors accounting for approximately 60% of the demand for the industrial gases produced by such equipment. At the same time, emerging industries such as new coal chemical engineering, healthcare, and electronics are also seeing an increasing demand for industrial gases. To improve the operational stability of air separation units, ensure product quality, increase product yield, reduce gas emissions, enable automatic load adjustment, and become a benchmark enterprise in the industry, this company developed the KDON-20000/19000 type advanced control and automatic load adjustment system for air separation units in collaboration with Zhejiang Zhongkong Technology Co., Ltd. The demand for advanced control and automatic load variation in the air separation industry: The KDON-20000/19000 type air separation units utilize an external compression process, and the Zhejiang Zhongkong ECS-700 distributed control system is employed to enable process monitoring of the unit’s operational parameters, basic control functions, as well as equipment interlock protection. Due to the strong coupling between the upstream and downstream units of the air separation unit, conventional control methods are unable to effectively coordinate the control of various variables within the unit, which affects its stable operation and consequently impacts the purity and output of the product. Furthermore, the production load of air separation units often needs to be adjusted in terms of load or operating conditions due to changes in the oxygen demand from downstream users; this frequently leads to oxygen wastage or a shortage of supply, resulting in high energy consumption, large fluctuations in operating conditions, and unstable product quality. Therefore, it is highly necessary to apply advanced control technologies to develop advanced control and automatic load variation systems for air separation units, based on the conventional DCS control, in order to further improve the operational stability of the units, reduce fluctuations in product quality, minimize oxygen emissions, and achieve energy savings and reduced consumption. Four types of model predictive control controllers ensure the stable operation of the equipment. Model predictive control is an advanced model-based control strategy that features a predictive model, rolling optimization, and feedback correction; it is well-suited for addressing the challenges related to the coordinated control of complex multi-variable processes. Four controllers have been designed for the KDON-20000/19000 type air separation units: an air compression system controller, an oxygen-nitrogen distillation system controller, an argon distillation system controller, and a liquid oxygen production optimization controller. Through these four main controllers, stable and optimized operation of the air separation unit is achieved. The expert controller for automatic load adjustment further enhances the level of automation. During the process of increasing or decreasing the load, this expert controller is used to determine the target value for oxygen based on material balance, automatically calculate the target values for various process variables and key process parameters, and uses these values to plan the adjustment trajectories for different process quantities. At the same time, the target values of the calculated process variables are transmitted to the model predictive controller, which utilizes its high-precision control to ensure a smooth transition of the system during dynamic processes, thereby enabling automatic load variation. Increasing production while reducing consumption to win customer recognition: After the implementation of the advanced control and automatic load adjustment systems for the KDON-20000/19000 air separation units, the operation rate of the controllers exceeded 90%, and the average stability of process parameters improved by more than 30%**, thereby reducing the workload on operators. At steady-state high load, the oxygen extraction rate increased by 0.64%, and the argon extraction rate increased by 1.02%; at steady-state low load, the oxygen extraction rate increased by 1.25%, and the argon extraction rate increased by 1.55%. The operational performance of the advanced control and automatic load variation systems in the KDON-20000/19000 type air separation units has been widely recognized by customers, and it has also paved a new path for the domestic air separation industry toward safe production as well as energy savings and reduced consumption.