Effect of turbulent mixing on combustion behaviours of a single biomass pellet. (15th August 2023)

• Record Type: Journal Article
• Authors: Guo, Huina; Feng, Lele; Wu, Yuxin; Zhang, Yang
• Is Part Of: Fuel. Volume 346(2023)
• Publication Date: 2023-08-15
• Subjects: Turbulent -- Single biomass pellet -- Cellulose -- Combustion behaviour; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2023.128291
• Languages: English
• ISSNs: 0016-2361

Abstract

Graphical abstract: Highlights: Differences in the combustion behaviour of biomass particles in natural convection and turbulent environments were experimentally identified. Increasing turbulence intensity accelerates the heating rate and significantly shortens the burnout time of a 5 mm cellulose particle. The volatile flame area fluctuates randomly and generally decreases with the turbulent intensity. Volatile flame has higher local luminosity and peak temperature in low turbulence intensity. Abstract: Biomass co-firing in coal-fired power plants is an appealing technology for reducing greenhouse gas emissions due to the abundant biomass resource and low cost of retrofitting the existing power plants. Burning larger biomass particles is inevitable in real boilers due to the energy-consuming grinding process. A profound understanding of the combustion characteristics of larger biomass particles in a strong turbulent gas environment inside the boiler is essential for designing and operating biomass conversion facilities. This paper presents a detailed experimental study of the effects of turbulent mixing on the combustion of biomass particles. An impinging arranged four-fan stirred turbulent furnace was established in the laboratory. Particle image velocimetry (PIV) was adopted to measure the turbulent flow field characteristics under various fan speeds. The combustion behaviours of a 5 mm homemade cylindrical cellulose pellet were investigated under natural convection and turbulent flow at 700 °C. The centre and surface temperature of the particle, the shape and peak temperature of the volatile flame, and the sequential combustion history were measured and analysed. The results show that the turbulent fluctuation velocity Velrms increases linearly with increasing fan speed. Whether the gas environment is natural convection or turbulence has an essential impact on the combustion behaviours of the biomass particle. Increasing turbulence intensity accelerates the heating rate and significantly shortens the burnout time from 94 s to 55 s. The volatile flame area fluctuates randomly and generally decreases with the turbulent intensity due to the dilution of gas-phase volatiles by the turbulent eddies motion. Volatile flame has higher local luminosity and peak combustion temperature at a low turbulent fluctuation velocity of 0 ∼ 0.8 m/s but gradually weakens due to heat dissipation at a higher turbulent fluctuation velocity of 0.8 ∼ 1.6 m/s. The present results are the first to study the combustion behaviours of a single biomass pellet in different turbulent intensities, indicating that the effect of enhanced heat and mass transfer in turbulent environments on biomass combustion is essential and deserves further study.