June 2025

Petrochemical Technologies

Large-scale advanced pyrolysis technology development: A proven route to chemical recycling and steam cracker integration

This article highlights the key advancements in developing the author’s company’s advanced pyrolysis technology, focusing on improvements in scale-up, heating efficiency, process optimization and product recovery. 

IP: 10.3.229.30

Pyrolysis is a thermochemical process in which organic materials are thermally decomposed in the absence of oxygen. In the context of waste management, pyrolysis has emerged as a viable technology for recycling plastics, especially mixed plastics, and converting them into valuable hydrocarbon products that can be used to produce fresh plastic. This article highlights the key advancements in developing the author’s company’s advanced pyrolysis technologya, focusing on improvements in scale-up, heating efficiency, process optimization and product recovery. 

Scale-up and feedstock handling. 

1. Batch to continuous operation: The transition from batch to continuous operation represents a pivotal scale-up advancement for this technology. This shift has significantly increased processing capacity, making pyrolysis more economically viable for large-scale plastic waste management. Continuous operation allows for consistent and uninterrupted processing, leading to higher throughput, a significant reduction in energy waste and reduced operational costs.  
2. Feed system improvements: The technology includes a feed injector system that pre-melts the feed, thus reducing viscosity and density. Pre-melting also increases the temperature from viscous heat dissipation before introducing the feed to the pyrolysis reactor. The feed injector system yields several processing benefits: 

• • Improved material handling: Pre-melting reduces the variability in feedstock consistency, ensuring more uniform flow through the reactor. It also helps maintain a steady temperature profile inside the reactor. This consistency is crucial for maintaining stable operating conditions, optimizing the pyrolysis process, and allowing the processing of various combinations of polypropylene/low-density polyethylene/high-density polyethylene rigid or films. 

• • Moisture removal: Densing the feedstock removes moisture that could negatively impact the pyrolysis process. Moisture can lead to the formation of more corrosive products and unwanted by-products, which subsequently results in yield loss and the need for higher-grade metallurgy in the reactor. The feed injector system can effectively handle feed with moisture levels of 8%–10%. 

Heating efficiency and reactor design.  

1. Melt loop implementation: Introducing a melt loop has significantly improved melt flow characteristics and stabilized feed viscosity. The melt loop allows for better heat distribution within the reactor, which ensures consistent and efficient heat transfer to the feedstock. This leads to improved reaction kinetics, higher product yields and less pitch formation. 
2. Electric pyrolysis reactor technology: The advanced pyrolysis technology is equipped with an electrified reactor, which provides advantages in the form of: 

• • Reduced carbon footprint: Electric heating powered by renewable energy sources can reduce both Scope 1 and Scope 2 carbon dioxide (CO2) emissions to significantly shrink the carbon footprint of the pyrolysis process. 

• • Increased heating efficiency: Electric heating offers precise temperature control and rapid heat-up times, improving energy efficiency and reducing operating costs. 

        3. Thermal fluid integration: The technology uses a stable thermal fluid as a consistent heat source, which provides: 

• • Stable temperature profile: Thermal fluids maintain a stable temperature profile throughout the melting section, including melt plastic flow in pipes, ensuring consistent reaction conditions and nullifying the risks of plugging and overheating.  

• • Protection against operational upsets: By maintaining a stable temperature environment, thermal fluids can help mitigate the impact of operational upsets, such as sudden feedstock variations or power fluctuations. 

Using this approach, the melting section at the New Hope Energy demonstration plant in Tyler, Texas (U.S.) operated continuously for more than 11 mos. 

Process optimization and product quality. 

1. Recycle streams: Introducing pyrolysis oil recycle streams has proven a significant process optimization step. Recycling a portion of the liquid products back into the melting section can reduce feedstock viscosity and stabilize any fluctuations. This increases the robustness of feedstock intake and improves the overall stability and consistency of the pyrolysis process for mixed-plastic feeds. 
2. Reactor zone-based heating: The technology employs reactor zone-based heating, allowing optimized operating parameters within different reactor sections. This enables the process to be tailored to the specific characteristics of the feedstock and the desired product distribution. Controlling the temperature in each zone makes it possible to maximize liquid yields while achieving minimum liquid pitch formation. Instead of producing a solid char, the technology produces a liquid pitch that is pumpable above 150°C (300°F). This supports the reactor staying clean and achieving longer run lengths. 
3. Continuous pitch removal: Converting the pitch removal system to continuous operation offers: 

• • Increased run lengths: Continuous pitch removal reduces downtime associated with periodic shutdowns for cleaning and maintenance, leading to increased reactor utilization and higher overall productivity. 

• • Improved product quality: Continuous removal of pitch prevents its accumulation in the reactor, which can negatively impact the pyrolysis process and reduce product quality. The system efficiently removes most heavier pitch contaminants, such as silica and iron, from the reaction system. 

Product recovery and separation. 

1. Tailored product separation: The technology is developed with multiple configuration options for product separation, which allows the process to be adapted to specific client requirements. This flexibility is crucial for maximizing the value of pyrolysis products. By tailoring the separation process, it is possible to isolate specific fractions with desired properties, such as light, medium and heavy pyrolysis cuts or a combination. 
2. Gas recovery system: The advanced pyrolysis technology incorporates a pyrolysis gas recovery system, which enables the recovery of valuable C3–C5 products with high concentrations of propene and butene. These liquified products can be directly processed in a steam cracker to maximize their value. 
3. Chloride reduction measures:  

• • Separate melt tank: In addition to the benefits of pre-melting discussed above, the melt tank helps dissociate polyvinyl chloride (PVC) in plastic and remove a significant amount of inorganic chloride before the melt enters the reactor. 

• • Environmental compliance: A caustic scrubber system is incorporated to capture and treat vapors from the melt tanks, which helps reduce emissions of harmful pollutants such as hydrochloric acid (HCI), thus ensuring compliance with environmental regulations. 

• Addition of alkaline chemical: A separate alkaline chemical addition in the reactor further reduces the organic chloride content to achieve one of the lowest chloride levels possible in pyrolysis oil. The low chloride makes the oil suitable for direct blending with regular steam cracker feeds. 

The block flow diagram, shown in FIG. 1, shows the key components of the advanced pyrolysis technologya that contributed to significant process improvements.  

FIG. 1. The components and design layout of the author’s company’s advanced pyrolysis technology^a.  

Capacity scale-up. FIG. 2 provides specific details on how the pyrolysis process was scaled up to achieve a significant increase in capacity at the New Hope demonstration plant. 

FIG. 2. The addition of key components comprising the upgraded advanced pyrolysis technology^a led to significant gains in the New Hope demonstration plant’s feed capacity. 

Specific process improvements to the New Hope facility included: 

• Melt tank addition: 
• • This resulted in a 100% reactor capacity increase. 

• • This suggests that the initial design had feedstock handling and melting capacity limitations.  

• • Adding a separate melt tank improved the efficiency of the melting process, allowing for a higher throughput of plastic feedstock. 
• Reactor internal modifications: 
  • This resulted in a further ~500% capacity increase. 

• • This substantial increase indicated that significant modifications to the reactor internals—which included changes to the reactor geometry, the addition of internal baffles or heat exchangers, and improvements to the residence time distribution of the feedstock—vastly improved its performance.  
• Performance confirms scale-up to a single reactor with a capacity of 70 tpd:  
  • A larger diameter and longer length resulted in a 20x increase in heated surface area (sized based on test run results). 

• • The scaled-up reactor was designed based on the results of extensive testing.  

• • The larger diameter and longer length increased the reactor's internal volume and surface area, thus allowing for higher throughput while maintaining adequate residence time and heat transfer. 

Key observations from the demonstration plant after design upgrades: 

1. Continuous operation: The demonstration plant operated continuously for > 95 d without the need for reactor cleaning. This is a significant milestone that shows the robustness and reliability of the pyrolysis technology. 
2. Consistent performance: The average daily processing of plastic (average metric ton of plastic/day) remained stable throughout the extended run length. This indicates that the plant maintained consistent performance and productivity over the extended period. 
3. Cumulative plastic processed: The cumulative amount of plastic processed steadily increased over time, reflecting the continuous operation of the plant. 

Overall, the New Hope demonstration plant provided operating results of the pyrolysis technology which confirmed extended run-length capabilities. The consistent performance and minimal downtime demonstrated the potential for reliable and continuous operation in a commercial setting. 

Takeaway. The advancements in pyrolysis technology development outlined in this article have significantly improved the efficiency, capacity and product quality of plastic waste recycling. These innovations, including scale-up strategies, enhanced heating efficiency, process optimization techniques and improved product recovery systems, have brought pyrolysis closer to becoming a commercially viable and sustainable solution for managing plastic waste. 

NOTE 

^a Lummus Advanced Pyrolysis Technology 

The Author

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