Mixed combustion of biomass and coal　

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Based on Professor Lin’s report from the Technical University of Denmark, here is a brief summary; everyone is welcome to share their thoughts. I. Current status, challenges, and prospects of biomass combustion for power generation. Definition of biomass: Biomass refers to a collection of living tissues, their derivatives, and substances related to biological transformation. Biomass classification: Wood processing residues: Woody plants; Agricultural product residues: Herbaceous biomass; Energy crops; Others: Marine plants, slaughterhouse residues, livestock industry residues, municipal waste. Biomass characteristics: 1. High variability in moisture content, generally ranging from 5 to 60%. 2. Low calorific value and low density. 3. High volatile matter content. 4. Low sulfur content; in wood, it is generally below 0.05%. 5. Moderate nitrogen content. 6. Low ash content. 7. High content of nutrient elements. Comparison of the properties of biomass and coal: Dry heating value: Biomass – 16 MJ/kg; Coal – 25 MJ/kg. Volatile matter: Biomass – 80%; Coal – 40%. Particle size: Biomass – 3 mm; Coal – 0.1 mm. Technologies for utilizing biomass: 1. Biological conversion technologies: Biogas – methane; Fermentation – alcohol. Wet methods: Hydrolysis followed by sugar extraction and then fermentation. Dry methods: Direct fermentation. 2. Thermal conversion technologies: Pyrolysis – biooil; oil yield can reach 60%. Gasification – fuel gas, syngas. Combustion – for heating, cooking, power generation. New uses of biomass: 1. Producing hydrogen. 2. Producing methanol. 3. Serving as a source of syngas for Fischer-Tropsch processes. 4. As fuel for internal combustion engines. 5. As fuel for fuel cells. 6. For micro-turbines. Power generation through biomass combustion: Reasons: (1) To replace fossil fuels. (2) To reduce CO2 emissions. (3) Mixed combustion – requires less investment, maintains the efficiency of existing units, and yields quick results. Combustion method: Direct combustion------- (1) Chain grate furnace – Small capacity, within 100 tons. (2) Cyclone furnace – Intense mixing, high temperature, high levels of NOx. Combustion with coal-------- (1) Circulating fluidized bed furnace, (2) Suspended combustion furnace, (3) Cyclone furnace. Current applications of biomass combustion for power generation: (1) Direct combustion: Used in small-scale systems, decentralized setup, combined heat and power generation. (2) Combustion with coal: Used in large-scale power generators. Advantages of mixed combustion: (1) Maintains the high efficiency of large coal-fired power generators. (2) Lower investment required for large-scale biomass utilization technologies. Optimal economic transportation radius: 5–80 km. (3) No need for a stable supply of biomass to maintain high operational efficiency of power plants. (4) Improves the combustion characteristics of low-volatility coal. (5) Reduces emissions of greenhouse gases and other major pollutants. Methods of mixed combustion: Direct mixing——Adding a certain amount of biomass directly to coal powder for combustion. Indirect mixing——First gasifying the biomass and then introducing the resulting combustible gases into the furnace for combustion