- Project period: 7 months (2020 – 2021)
- Contractor: Bakhtar Management & Development Company
Bakhtar Group wants to perform the basic engineering of the slurry-phase high-density polyethylene (HDPE) plant with a new, higher capacity. The most challenging part of this scaling-up engineering is the reactor scale-up. The complex physical and chemical nature of the reactor makes it hard to predict the performance of reactor in the new capacity. We developed a CFD model to predict the performance of the existing and the new scaled-up reactor in this project.
The problem in this project is clear. Does the scaled-up reactor performance is acceptable for a stable production in the plant? There are some concerns about the operation of the new reactor that should be addressed. Can the scaled-up reactor (from the original capacity to the new capacity):
- guarantee the desired production rate of high-density polyethylene (HDPE)?
- guarantee the uniform temperature distribution of the reactor as it is in the original reactor (within ± 2 °C)?
- provide the enough vapor hold-up and hence vapor-liquid contact in the reactor at the calculated rotation speed and dimensions of the impeller?
- prevent sucking of vapor into the circulation pumps at adjusted distance between inlet vapor and outlet liquid nozzles?
The new design should give positive responses to all of the above questions. In any negative case, the design should be modified to solve the problem.
The project was divided into 3 phases:
- Developing a mode and validating it with field data (original reactor)
- Predicting and evaluating the reactor performance in the new design (scaled-up reactor)
- Troubleshooting of the new design if it has any malfunctions
We used a comprehensive computation fluid dynamics (CFD) model to predict the polyethylene reactor performance at the original and new capacities. The model contained these entities:
- A multiphase model to describe vapor/liquid flows in the reactor
- A thermophysical model to predict physical properties of phases
- A reaction model for polymerization reactions
- A thermodynamic model to describe phase equilibrium between liquid and vapor
- A two-resistance heat and mass transfer model to describe gas solution and solvent vaporization
We used OpenFOAM® for CFD simulations. We added new modules to it to complete the CFD model of the reactor. After completion of the CFD model, the model performance was the evaluated with real field data. The validated model was utilized to predict the performance of the new reactor and troubleshoot its design problems.