Plastics recycling via pyrolysis: small-scale vs large-scale?

Commercialization of pyrolysis technology for large-scale plastic chemical recycling is on the rise.

So, Jonny Goyal, Research and Analysis Associate Director with IHS Markit's Circular Plastics Service, has a comprehensive rundown on a ramping up of the degradation of plastics at high temperatures for Net-Zero Business Daily readers.

Pyrolysis, as Goyal notes in a recent whitepaper, is one of the main methods for chemical recycling of plastics. While plastic recycling is gaining momentum, many companies are still struggling in scaling up pyrolysis technology.

Pyrolysis plants of 500 mt/day to 3,000 mt/day are being discussed by industry players and are needed to accelerate momentum in plastic recycling across all different industries around the globe so that significant progress toward a circular plastics model can be achieved, according to Goyal.

At present, waste plastic chemical recycling via pyrolysis is available only at a small scale (10-50 mt/day).

Many plants with a capacity of 50-300 mt/day are still in the planning and construction stage, and firms are increasingly exploring the huge potential of chemical recycling via pyrolysis so that a large volume of plastic waste can be handled.

The economics for a large-scale pyrolysis plant are challenging and largely dependent on the upstream feedstock quality and its price, reactor configuration, and the type of end-product considered.

Reactor design, size key

The reactor design and its size are the key parameters determining the economic viability of the pyrolysis plant. For a 1,000 mt/day plant, a few larger reactors (for instance, 250 mt/day) that can handle large plastic waste volumes, are preferred.

A modular approach for large-scale commercialization (e.g., implementing 20 pyrolyzer reactors, each having a size of 50 mt/day for this 1,000 mt/day plant), has a significant impact on the total fixed capital.

The design of the reactor also changes with the scale. Circular fluidized bed type reactors are more scalable as compared with the auger type traditional pyrolyzer reactors.

The type of pyrolysis and its associated end-products becomes more significant in the selection of reactor design and plant scale, with versatile engineering expertise required for a robust design where the process yields are not compromised in the long run.

The total fixed capital for the plant can be drastically reduced if larger reactor sizes are used instead of a modular approach. Goyal's analysis shows that by using a larger reactor size, the total fixed capital can be reduced by 20-35%. To cover a plant with a given capacity (for instance, 1,000 mt/day), if just a single train of four or five large reactors is used, the saving potential is 35%. But if two trains of four to six large reactors, the saving potential will be only 20-25%.

While it is true that the pyrolysis commercialization using a larger reactor size is not yet realized, moving forward, IHS Markit expects a traditional modular approach to be combined together in a number of trains in tackling the question of scalability. This could be because of strategic reasons such as looking to choose a modular unit to address the capacity of a material recycle facility, or a client choosing 20-50 mt/day to fit the present market needs.

Modular systems limit failure

Making the technology modular not only makes it scalable, but also makes the system immune to failures. Like a server cabinet, if one module stops working, other modules will continue operating. This enhances robustness of the system and increases the availability and reliability of the plant. While this comes with a higher price tag, this premium pricing will alleviate critical timing in solving the issue of the plastic circularity and increasing legislation pressure.

IHS Markit expects that the advances that will drive the step-change improvements required to achieve the large-scale implementation of pyrolysis technology will be in the areas of reactor design and catalysis. This will drive scale and energy efficiency, as well as quality improvements that need to be made to achieve a pyrolysis oil that can be used in steam crackers with limited upgrading.

IHS Markit believes that as these technologies are being developed in the long-term, they will benefit from the same type of learning that other petrochemical and refining processes have experienced, resulting in improved economics. This Experience Curve theory implies that as cumulative productions using a specific technology increases, fixed costs are expected to decrease.

Costs to fall

Estimates for 2050 indicate that fixed costs could decline by as much as 50-65% if the chemical recycle technology development follows a path similar to other established technologies.

Logistics issues are a challenge to all large-scale efforts to recycle plastics. For chemical recycling, the fact that a large portion of waste plastics recovered from municipal solid waste streams will be located far from the traditional centers of plastics production is a disadvantage. This will require managing the logistics for solid waste (aggregating to achieve a large-scale supply source), for aggregating the sources of pyrolysis oil, and either transporting it to the traditional manufacturing centers or establishing new production centers regionally.