Multi-variable Predictive Control’s Application For PX Unit

PX is important chemical raw material.It is used to produce PTA. In the process of running, loops of two sets of PX devices produced by Aromatic Plant of Yangzi Petrochemical Company had volatile fluctuations, therefore APC-Adcon was used to develop advanced control of PX device fluctuation in this paper, which is composed of five controllers for heptane tower, dimethyl benzene fractionating column, raffinate tower, extract tower, and finished product tower.The advanced control system was designed based on the existing DCS control circuit. The idea of multivariable coordinated and predictive control was adopted, and the APC-Adcon produced by SUPCON Group of Zhejiang University was used in controller design, test modeling, commissioning and trial operation and other steps, considering the correlations of inner parts of the PX units, and combining with the long-term production experience of the process engineer and the operating personnel. After the project was implemented, stable, fast and accurate control of the key operation parameters of relative units of PX device have been realized, the smooth degree of the key variables has been improved, and the mean square error of the key controlled variables of process has been reduced by above30%; meanwhile, the two-way undisturbed switching between the regular control and the advanced control and stable control of PX device have been realized, and the labor intensity of operators have been reduced. After implementation of the project, the good economic benefit is obtained.