Control of a Linear Polyethylene Reactor and an Evaluation of the Economic Benefits: A Real Case Study

In addition to the inherent challenges associated with controlling polymerization reactors, the “Sclairtech” technology for the production of Linear Low-Density PolyEthylene (LLDPE) presents specific characteristics (e.g., high temperature and pressure and a residence time in the reactor of less than 1 min) which add further difficulties to the effective control of the main quality parameters of the polymer produced. This work presents a strategy for implementing advanced control in a real LLDPE production unit (“Sclairtech” technology) followed by a systematic evaluation of the economic benefits in accordance with best international practices. Melt Index (MI), density and conversion were considered as controlled variables. The methodology for implementing advanced control involved analysis by resin classes (rotational molding, low-density injection, octene film and high-density injection) and effective contributions such as an innovative strategy for reactor temperature control. The proposed control strategy is capable of efficiently addressing two of the main problems associated with “Sclairtech” technology, namely, the generation of out-of-specification product during grade transitions and wide specification ranges. The benefits analysis involved the use of real process data, a statistical analysis of key variables to identify the dispersion and percentage of out-of-specification products, and the calculation of the net present value of financial indicators capable of validating the investment. Regarding quantitative outcomes, an annual gain of US$ 791,812 was estimated, with US$ 494,883 coming from the reduction in catalyst consumption and US$ 296,929 from other sources (reduction in out-of-specification product and production losses associated with grade transitions).