KIER's breakthrough in solving waste plastic processing with heat circulation

(Press-News.org) Dr. Byungwook Hwang’s research team from the CCS Research Department at the Korea Institute of Energy Research (KIER) has successfully developed a process that applies the circulating fluidized bed technology, commonly used in coal-fired power plant boilers, to recycle waste plastics and produce pyrolysis oil on a large scale.

The COVID-19 pandemic has led to a sharp increase in household plastic waste worldwide. In response, countries around the globe are focusing on recycling technologies, such as pyrolysis, for eco-friendly waste plastic management. Recently, the Korean government announced plans to expand the annual volume of plastic waste processed via pyrolysis from 10,000 tons to 900,000 tons by 2030.
*Pyrolysis Recycling: A process in which mixed waste plastics are heated in a high-temperature environment, breaking them down into gas, liquid (pyrolysis oil), and solid forms. The resulting liquid (pyrolysis oil) is then recycled as a raw material for producing new plastics, various high-value-added chemicals (such as BTX), and fuels.
**Leading the Circular Economy and Carbon Neutrality Through Waste Plastic Pyrolysis" (Ministry of Environment Press Release, June 21, 2021)

Currently, the kiln method is used in the Republic of Korea for the pyrolysis of waste plastics. This process involves placing waste plastics inside a cylindrical chamber, applying heat externally, and condensing the resulting vapor to produce pyrolysis oil. While the process design is relatively simple, it faces scalability limitations, as heat transfer from the exterior to the center of the cylinder becomes increasingly difficult as the size of the chamber increases.

The kiln method can process only up to 20 tons of plastic per day, which falls far short of the 900,000 tons per year target set by the government for pyrolysis processing. Additionally, the kiln method requires continuous external heat supply and cannot operate continuously, as the process must be paused to handle residual waste before restarting. These limitations make it inefficient for large-scale applications.

The research team developed a technology to recycle waste plastics using a circulating fluidized bed (CFB) process, overcoming the limitations of conventional methods. The CFB process is a technology in which heat carriers, such as high-temperature sand, circulate to enable continuous heat transfer during reactions. For the first time globally, the team successfully applied the CFB process to the pyrolysis of waste plastics, enabling both continuous operation and scalability—key challenges of existing processes.

The core of the developed process lies in heat circulation. In this system, catalyst particles heated in the combustion reactor are circulated to the pyrolysis reactor, where they transfer heat to facilitate the pyrolysis of waste plastics. After transferring heat, the catalyst, now at a lower temperature, returns to the combustion reactor along with the residual waste. The residual waste is incinerated, generating heat to reheat the catalyst. The reheated catalyst is then recirculated back to the pyrolysis reactor, maintaining a continuous process of heat transfer and pyrolysis.

By utilizing this process, a continuous operation is achievable as the cycle of raw material input, heat supply, and residual waste treatment is seamlessly maintained. Additionally, since the catalyst moves freely within the reactor, heat can be effectively transferred from the center to the edges of the reactor, enabling scalability and the development of larger systems.

The research team conducted pyrolysis experiments on waste plastics using their process, handling up to 100 kilograms per day. They confirmed that the process can pyrolyze not only plastics but also solid recovered fuel (SRF)* made from household waste. When SRF was processed, the yield was approximately 37%, which is 1.2 times higher than conventional methods. Additionally, the produced pyrolysis oil showed a significant improvement in quality, with a 45% content of light fractions**, nearly doubling the quality compared to existing processes.
*Solid Recovered Fuel (SRF) : a type of manufactured fuel derived from Municipal Solid Waste (MSW) such as synthetic resins, rubber, and wood, is designed for use in power plants and other facilities. Improper disposal of SRF can result in environmental pollution, emphasizing the importance of eco-friendly recycling methods.
**Light Fraction Content: The proportion of light hydrocarbons (C5-C12) in pyrolysis oil, which are crucial components for high-quality fuel and chemical production. This serves as a key indicator of pyrolysis efficiency and product quality, with a higher content signifying superior pyrolysis oil suitable for diverse industrial applications.

Dr. Byungwook Hwang, the lead researcher, stated, “The most significant achievement of this study is the design and development of a technology capable of continuously processing waste, including plastic waste, through pyrolysis.” He added, “This core pyrolysis technology is highly suitable for achieving Korea’s waste plastic pyrolysis targets, as it enables the processing of large volumes of waste plastics while producing high-quality pyrolysis oil.”

Meanwhile, this research was conducted as part of the Korea Institute of Energy Research's R&D project. The results have been published in the globally renowned journal in the field of chemical engineering, Chemical Engineering Journal (Impact Factor: 13.3).

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