Closing critical gaps to enable a circular plastics economy
Abstract
The request of a preliminary design of a plastic pyoil separation unit has been requested, downstream from a pyrolysis unit, converting plastic into usable oil, called pyoil. This design is focused on removing trace impurities from the pyoil stream and separating it into four separate cuts: py gas, naphtha, gas oil, and heavy resid. The py gas is used as a downstream fuel and is a vapor. The naphtha and gas oil (also called the light cut and medium cut, respectively) is used downstream in a steam cracker to produce valuable ethylene. The process that has been designed contains a series of adsorption columns, standing 36 ft tall and 6.5 ft in diameter, using PuriCycle H and HP catalysts (adsorbents) to remove trace elements. After these elements are removed, the feed enters a 42 stage, 95 ft tall, 5.5 ft diameter single multi-cut distillation column, charged with the separation into the four aforementioned streams. Once the separation has been performed, the products are cooled and pumped into storage tanks. The medium cut is also used to pre-heat the feed stream to save energy costs. Economics play a large part in the feasibility of a preliminary design, and capital costs and variable and fixed operating costs have been calculated. Preliminary design estimates vary from -20% to +40%, and the calculated values reflect this. Capital costs are estimated at $3,255,000, fixed operating costs are $340,000 annually, and variable operating costs are $2,087,000 annually. For general safety, situations where power is lost, pressure increases, and controller failure have been evaluated. For power loss, the control valves have the appropriate orientation, there are pressure relief systems in place on vulnerable equipment, and there are alarms in place for controller failures in order to prevent extreme situations within the process. In order to close the quantity, quality, and affordability gaps, it is recommended to create collection centers in the community, where citizens can recycle their plastic and get paid. In addition, the installation of a drum separator is highly recommended. The improvements would serve to increase the amount of recyclables collected, reduce the cost of sorting the recyclables, and raise the quality of the recyclables so they could be used in the pyrolysis plant.