2022-2023 AIChE student design competition

Abstract

Global Petrochemicals (GP) currently is a leading manufacturer of basic chemicals and high-performance polymers. As a result, the company has a substantial customer base. In recent years, the customer base has begun demanding GP to act in reducing the amount of plastic waste worldwide as well as produced by the company. This pressure has led GP to make a commitment to produce 10% of its virgin resin-quality plastics from recovered plastic in the near future. Currently, this is an ambitious goal that requires significant applications of new process technology and major investments. With the additional process unit in the following documentation, GP would establish efficient and effective plastic waste collection, while also utilizing this plastic waste to create the basic chemicals that are in demand from GP's customer base. A preliminary project design has been completed for this unit.

The additional process unit would be a Pyoil Purification Unit that purifies a pyrolysis oil stream to meet the specifications needed for downstream steam cracker units. This unit would consist of an adsorption process to dehydrate and remove heavy metal contaminants from the pyrolysis oil, before moving into a small distillation column to separate the lightest components into a fuel gas stream. Then, the bottoms from the first column move into a second, larger column to separate into Light Cut, Medium Cut, and Heavy Cut streams. The gas would be fed directly to the ethylene plant to be used as a fuel gas, while the cuts would be cooled and stored in tankage. Finally, the Light and Medium Cuts would be pumped from tankage to separate steam crackers for further processing, while the Heavy Cut would be sold as an asphalt component.

The design process is dependent upon the adsorption and regeneration towers to send continuous flow to the distillation columns, as well as the distillation columns to separate the process fluid into on-spec streams that can be cracked by the steam crackers. There is also a significant dependence upon the predistillation column coolers to keep the feed stream at a consistent temperature that keeps the distillation columns at steady state. Finally, the post distillation coolers are heavily relied upon to maintain safe temperatures in the tanks.

This project will not bring any new safety concerns into the petrochemical site that are not already present. All materials, except for the adsorbent material, can be found within the current site. The group added multiple relief options throughout the unit to prevent over pressurizing any piece of equipment to failure. Each relief option does not relieve to the atmosphere but does either relieve to flare or another treated exhaust stream. Based on current analysis, there are not any additional significant safety concerns that will be added to the site with the addition of this unit.

A service factor of 97% was assumed and utilized for this project. The total expected capital cost, variable cost, and fixed costs were determined and are reported. It was concluded that the project will cost $13.04MM in capital, with an expected $233M in variable costs, and an annual $675.4M in fixed costs. A complete economic analysis should be performed when values can be assigned to the cost of the unit feed and the product stream values.

In summary, the preliminary design analysis demonstrated that the development of a Pyoil Purification Unit is feasible. While the unit will require substantial efforts in the detailed design stage to maintain safety and environmentally friendly, the unit can be accomplished at the desired mass flow rate and produce all the requested product streams and at their desired specifications.