Design of key components and coupled flow-thermal simulation of a downdraft comb-shaped waste pyrolysis gasifier

With the implementation of garbage classification system in China, gasification technology has emerged as a critical direction for clean waste-to-energy conversion. This study presents a novel downdraft comb-shaped waste pyrolysis gasifier designed for high-efficiency conversion of heterogeneous municipal/canteen waste into combustible producer gas. The key innovations include a reciprocating comb-tooth ash scraper with 147 teeth (26.6 mm tooth width, 80 mm height) that prevents ash arching and grate burnout; an integrated cyclone-rectifier gas cleaning system with 484 mm outer diameter and 2464 mm total height; and a diffusion-type multi-scale ignition port for stable combustion under variable gas quality. Thermal-stress analysis indicates that the comb scraper can withstand the expected operating temperatures of 650–750 °C, with an estimated factor of safety of 1.4–2.1. CFD simulations with mesh-independence verification (780,000 cells, <2% variation) predict flow patterns consistent with the design expectations for both the cyclone separator and the ignition port. The calculated design waste-treatment capacity is approximately 251 kg/h, the estimated gas production rate is 1.6 m3/kg (nitrogen-balance estimate), and the corresponding design gas-flow rate is 401.6 m3/h with an approximately 50% nitrogen content. The produced gas sustained continuous, stable combustion during the prototype tests, supporting the operational feasibility of the proposed design.