A Multivariable Predictive Control Method for Air Separation Plant

Abstract

Disclosed is a multivariable predictive control method for an air separation device. The multivariate predictive control method comprises the steps that (a) an upper computer is additionally arranged on a DCS system local area network of the air separation device for creating an MVPC server of the air separation device; (b) variables are determined, specifically, according to the technological process optimizing target of the air separation device, the controlled variable (CV), the manipulating variable (MV) and the disturbance variable (DV) are determined; (c) the establishment principles of the size of an MVPC matrix are that key parameters are selected, the variables are controlled as less as possible, the valve opening degree, namely corresponding to the output of a PID controller under conventional control, is adjusted through the MV of an MVPC, when the MVPC works, the PID controller corresponding to the MV of the MVPC is in cascade control, the output of the PID controller tracks the MV of the MVPC, and when the MVPC does not work, the PID controller corresponding to the MV of the MVPC is in automatic control, and the MV of the MVPC tracks the output of the PID controller; (d) a model is built, specifically, an MVPC controller model is built in the air separation device, or independent MVPC controller models are built in different work sections in the air separation device; (e) the models are trained and adjusted, specifically, the gain K, the time constant Tau and the delay time Tdelay in the models are preliminarily set, and after the models are put into use, the optimized gain, time constant and delay time are provided by a system automatically; and (f) the models are put into use.

Description

technical field [0001] The invention relates to a multi-variable predictive control (MVPC: Multi-Variable Predictive Control) method for an air separation plant used in the air separation production process, and belongs to the technical field of automation control engineering. Background technique [0002] In the process flow of the air separation unit, the raw air enters the lower tower after a series of operations such as filtration, compression, precooling, purification, pressurization, expansion and heat exchange; Oxygen-enriched liquid air is obtained at the bottom of the tower, and pure liquid nitrogen is obtained at the top of the lower tower, which is subcooled by a subcooler and throttled into the upper tower. [0003] After further rectification in the upper tower, liquid oxygen is obtained at the bottom of the upper tower, which is compressed by the liquid oxygen pump and enters the main heat exchanger. Part of the liquid oxygen goes directly out of the cold box ...

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Problems solved by technology

[0005] The air separation unit has the characteristics of complex process and severe coupling; at the same time, in the production process of the air separation unit, the demand for the production gas of the external pipe network often presents the characteristics of periodicity, stages, and intermittent, and the dissipation of oxygen will cause unnecessary energy consumption and economic losses

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