Waste Plastic Chemical Recycling via Pyrolysis - Small-Scale vs Large-Scale
Pyrolysis is one of the main methods for chemical recycling of plastics. While plastic recycling is gaining momentum, many companies are still struggling in scaling pyrolysis technology. Pyrolysis plants of sizes 500-3,000 tpd are being discussed by industry players and are needed to attain the future goal of seeing a great momentum in plastic recycling across all different industries around the globe so that significant progress toward a circular plastics model can be achieved. At present, waste plastic chemical recycling via pyrolysis is available only at a small scale (10-50 tpd). Many plants with a capacity from 50-300 tpd are still under planning and construction, and these firms are increasingly exploring the huge potential under 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. This article discusses the way ahead in the commercialization of pyrolysis technology for large-scale plastic chemical recycling.
The reactor design and its size are the key parameters determining the economic viability of the pyrolysis plant. For a 1,000 tpd plant, a few larger reactors (for instance, 250 tpd) 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 tpd for this 1,000 tpd 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 type 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. Our 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 tpd), if we only use a single train of 4-5 large reactors, the saving potential is 35%. But if we use two trains of 4-6 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, we will see the use of a traditional modular approach 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 (MRF), or a client choosing 20-50 tpd to fit the present market needs. 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 the operation. This puts more robustness in 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. 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.
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