How much do you know about the precautions of the operation control system of the air separation plant

How much do you know about the precautions of the operation control system of the air separation plant

The air separation unit adopts cryogenic technology, which uses the different boiling points of oxygen and nitrogen gas at the same pressure to achieve gas separation and extract oxygen, nitrogen and other gas components in the air. At present, the main air separation process is divided into internal compression process and external compression process. The main unit equipment is a rectification tower, heat exchanger, molecular sieve adsorber, air cooling tower, etc. The main units are turbo expanders, turbo compressors, etc., and another important system is the control system.

　　 Most of the newly designed air separation plants adopt the DCS control system. The DCS control system better realizes the chain protection and anti-surge control of the air compressor, the sequential control of the molecular sieve system and other conventional controls. The implementation and application of the DCS system stabilized the operation of the device to a certain extent and improved the control level of the device.

　　At the same time, because the air separation plant has certain requirements for the purity of each component, the control of the entire system is relatively complicated, and simple single-loop control cannot make the plant run in the best condition.

　　 In order to realize automatic variable load control and multi-variable predictive control, and make it play a better control effect, the following aspects should be paid attention to to ensure the operation of the optimized control system.

　　* The performance of the air compressor can avoid entering the anti-surge zone during low load operation, and the inlet guide vane has good control speed and stability.

　　* The design of the expander must meet the requirements of load changes to ensure that the expander operates safely and reliably within a certain speed range when the expansion air volume requirements change.

　　* Packed towers have less liquid retention than sieve trays, have greater operating gas-liquid ratio and flexibility, and change loads quickly, so their operating loads can vary within a larger range.

　　* The distillation tower can ensure high stability within the full load range.

　　* The size and performance of the valve are suitable for the requirements of dynamic changes in flow. The control valve should be more controllable and can be controlled in time and accurately within the entire load change range.

　　* The selection of the instrument and the design of the adjustment control system minimize the measurement lag and ensure the accuracy of continuous detection. The accuracy and rapidity of field instruments are relatively high.

　　* It is necessary to write conventional control and advanced control switching logic modules and protection programs on the DCS system to improve the safety of the advanced control system.