Dual-Heat-Zone Biomass-Assisted Pyrolysis of Polyethylene Waste for Community-Scale Fuel Recovery in Nakhon Phanom, Thailand

Abstract

This study aimed to design, fabricate, and evaluate the performance of a dual-heat-zone (central-pipe), biomass-assisted pyrolysis system for converting polyethylene (PE) plastic waste into pyrolytic oil at rural community scale. The developed system incorporated a central heat-transfer pipe inside the pyrolysis reactor, enabling simultaneous heat transfer from both the bottom (external jacket) and the interior (central pipe) of the reactor. Performance was assessed against a conventional reactor, defined here as a bottom-heated reactor of identical volume, wall material, and PE feedstock loading, heated only through the external jacket  The performance was measured based on the reactor temperature profile, cumulative oil yield, and energy efficiency (η), defined as the ratio of chemical energy recovered in the pyrolytic oil to the total thermal energy supplied by the biomass fuel over the run using thermodynamic energy equations (Eq. (3)). Experimental results demonstrated that the system could rapidly increase the reactor temperature from approximately 30°C to 420°C within 20 minutes, and up to 520°C within 30 minutes (mean ± SD, n = 3). The heat transfer rate (Q) from the biomass stove to the reactor reached 15.8 kW, while the cumulative oil yield (Y oil) reached approximately 65% at 30 minutes (± SD, n = 3). Under these specific test conditions (single reactor unit, 5.0 kg PE per batch, n = 3 replicates), the energy efficiency of the pyrolysis system was found to be 68.5%, compared with 42.3% for the conventional bottom-heated reactor tested under the same conditions. These results should be interpreted as preliminary, single-configuration findings rather than generalized performance guarantees. A linear regression analysis was applied to correlate reactor temperature with oil yield (R² = 0.974, P-value < 0.001). Preliminary, non-replicated field observations at two community sites in Nakhon Phanom Province suggested an income-generation potential of approximately 30,000 THB/month, motivating a more rigorous field-trial protocol as a next step. This economic estimate is based on assumptions regarding oil price, daily production volume, and operating cost, as explicitly stated in Section 3.5, and should be treated as indicative rather than confirmed. Preliminary characterization of the pyrolytic oil indicated properties broadly consistent with a diesel-range fuel; full quality data are required before the product is described as a finished “fuel oil.” The fabrication cost of approximately 20,000 THB/unit supports the system's potential viability for community-scale deployment, consistent with the principles of the circular economy and the Sustainable Development Goals. The main limitations of this study include the use of a single plastic type (PE), a single reactor scale, a short 30-minute test duration, and the current lack of data on pyrolytic oil quality and environmental emissions data. These limitations are addressed as priorities for follow-up work.