Nonlinear Control of Fouling in Polyethylene Reactors

Abstract

Fouling formation in reactor vessels poses a serious threat to the safe operation of the industrial low-density polyethylene (LDPE) polymerization. Fouling also degrades the polymer quality and causes productivity loss to some extent. In this work, neural Wiener model predictive control (NWMPC) is introduced to address the fouling concern. In addition, a soft sensor model is used to activate the fouling−defouling (F−D) mechanism when the fouling surpasses the thickness limit to prevent vessel overheating. NWMPC is proven to be fast, stable, and robust under various control scenarios. The use of a soft sensor model in conjunction with NWMPC enables the online monitoring and controlling of the F−D processes. When comparison is made with a state space (SSMPC) utilizing only the linear block, NWMPC is found to be able to control the LDPE grade with quicker grade transition and lower resource consumption.

Detailed Multiphase Chemical Kinetic Model for Polymer Fouling in a Distillation Column

“…1,2 These polymeric deposits can form in various process units, including pipelines, heat exchangers, and distillation columns, affecting the performance and efficiency of equipment. 3,4 Local polymer fouling results in higher pressure drops and greater energy losses, increasing the total energy cost. 5 Polymer fouling also decreases the thermal conductivity of heat exchangers and distillation columns, resulting in lower thermal efficiency.…”

“…However, they often simplify the chemistry involved by representing it with pseudospecies and/or few representative rates. While these empirical models are valuable for studies like computational fluid dynamics 10,14 or control studies, 4 their simplified chemistry limits their explainability, and they are incapable of capturing the chemical effects of impurities and industrial additives. Additionally, discussion has emerged about developing a global fouling model to estimate the deposition and removal rates by drawing on analogous detailed chemistry found in similar systems.…”

“…Polymer fouling is a ubiquitous but unresolved problem that plagues numerous industrial processes. Downstream of the steam cracker, reactive effluents polymerize and lead to the accumulation of unwanted polymeric materials on process unit surfaces. , These polymeric deposits can form in various process units, including pipelines, heat exchangers, and distillation columns, affecting the performance and efficiency of equipment. , Local polymer fouling results in higher pressure drops and greater energy losses, increasing the total energy cost . Polymer fouling also decreases the thermal conductivity of heat exchangers and distillation columns, resulting in lower thermal efficiency.…”

“…Various empirical models have been developed to estimate the deposition and removal rates. ,− Many of these expressions incorporate parameters such as overall heat-transfer coefficient, mass-transfer coefficient, temperature, fouling density, and fouling porosity. However, they often simplify the chemistry involved by representing it with pseudo-species and/or few representative rates.…”

“…However, they often simplify the chemistry involved by representing it with pseudo-species and/or few representative rates. While these empirical models are valuable for studies like computational fluid dynamics , or control studies, their simplified chemistry limits their explainability, and they are incapable of capturing the chemical effects of impurities and industrial additives.…”