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Mechanism-based interpretation of grate-bar degradation in solid-fuel combustion systems |
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| รหัสดีโอไอ | |
| Title | Mechanism-based interpretation of grate-bar degradation in solid-fuel combustion systems |
| Creator | Wirasak Khongkaew |
| Contributor | Phadungsak Ratanadecho, Advisor |
| Publisher | Thammasat University |
| Publication Year | 2568 |
| Keyword | Grate-bar degradation, Biomass combustion, Grate-fired boiler, Thermal failure, High-temperature corrosion, Biomass power plant, การเสื่อมสภาพของซี่ตะกรับเตา, การเผาไหม้ชีวมวล, หม้อไอน้ำแบบตะกรับเตา, ความเสียหายจากความร้อน, การกัดกร่อนที่อุณหภูมิสูง, โรงไฟฟ้าชีวมวล |
| Abstract | Grate-fired biomass boilers are widely used in medium-scale power generation; however, premature degradation and failure of grate bars remain critical operational challenges, particularly under severe combustion and ash-related environments. This thesis investigates the degradation behavior and failure mechanisms of grate bars in biomass-fired furnaces through an integrated experimental, analytical, and mechanism-based engineering approach. The study combines field observations from an operating biomass power plant, laboratory characterization of failed grate bars, and controlled experimental investigations using a downscaled furnace designed to reproduce the geometry, air-distribution characteristics, and fuel-feeding behavior of an industrial grate-fired biomass boiler. Systematic measurements of grate surface temperature, radiative heat flux, gas-phase conditions, and fuel-bed behavior were conducted to characterize thermal exposure conditions across different grate zones. A nonlinear heat-transfer model incorporating radiative, convective, and conductive heat-transfer mechanisms was developed and solved using the Newton–Raphson method to estimate critical grate surface temperatures under varying combustion conditions. Material degradation was evaluated through macroscopic damage assessment and microstructural characterization of failed grate bars obtained from a para-rubber wood-chip–fired biomass power plant. Scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS) was employed to investigate corrosion morphology, elemental redistribution, oxide-scale destabilization, and deposit–metal interactions. The results indicate that grate surface temperatures exceeding approximately 1200 °C in the char-burning zone constitute critical operating conditions that accelerate material degradation through the combined effects of high-temperature oxidation, alkali–silicate interactions, chlorine-assisted corrosion, and flow-assisted material removal. The degradation process was found to be highly non-uniform and nonlinear due to the coupled influences of thermal loading, ash chemistry, air-flow distribution, grate geometry evolution, and combustion instability. Based on the experimental observations and modeling results, a coupled thermochemical–mechanical degradation framework is proposed to explain the progressive cross-sectional loss and failure evolution of grate bars under biomass combustion conditions. The findings demonstrate that grate degradation should not be regarded solely as an unavoidable corrosion problem but rather as a controllable engineering phenomenon that can be managed through mechanism-based operational and maintenance strategies. Furthermore, the study proposes a shutdown-aligned grate design concept in which degradation progression is managed to coincide with planned maintenance intervals, thereby reducing the risk of premature unplanned shutdowns. The proposed framework provides transferable engineering guidance for grate-fired biomass systems operating with different biomass fuels and combustion conditions, offering practical benefits for reliability enhancement, maintenance planning, and long-term operational sustainability in the biomass power industry. |
