A series of three-dimensional numerical simulations on thermal-solutal capillary-buoyancy flow in an annular pool were carried out. The pool was filled with silicon-germanium melt with an initial silicon mass fraction of 1.99%. The Prandtl number and the Lewis number of the working fluid are 6.37 × 10⁻³ and 2197.8, respectively. Both the radial temperature gradient and the solute concentration gradient were applied to the annular pool. The capillary ratio was assumed to be −1, which means that the solutal and thermal capillary effects were equal and opposite. Results show that the thermal-solutal capillary-buoyancy flow always occurs at this special case with the capillary ratio of −1, and even in a shallow annular pool with an aspect ratio of 0.05. With the increase of the thermal Marangoni number, four kinds of flow patterns appear orderly, including concentric rolls, petal-like, spoke, and rosebud-like patterns. These flow patterns are strongly influenced by the local interaction between the solutal and thermal capillary effects and the vertical solute concentration gradient near the outer cylinder. A small vortex driven by the dominant solutal capillary effect emerges near the inner cylinder, which is different from the flow pattern in a pure fluid. In addition, the critical thermal Marangoni number of the initial three-dimensional flow decreases with the increase of the aspect ratio of the annular pool.

To further explore cocombustion technology with biogas and coal, a series of numerical simulations have been carried out to analyze the effects of the cocombustion ratio ξ, height of biogas nozzle H_GN, and tilt angle of burner θ_BN on combustion characteristics in a 300 MW four-corner tangential boiler furnace. Three types of biogas are gasified from straw, sawdust, and raw wood when air serves as the gasification agent. The velocity field, temperature field, and NO emissions have been comprehensively analyzed when the values of ξ, H_GN, and θ_BN range, respectively, from 0.02 to 0.12, from 17.3 to 20.3 m, and from -15° to +15°. Results showed that the NO concentration at the furnace outlet monotonously decreased with ξ. The injection of biogas reduces both the peak temperature of the entire boiler furnace and the NO concentration at the furnace outlet. The NO emission concentration decreases with the increased ξ value for all types of biogases. The cocombustion with sawdust biogas indicates the least NO emission at a fixed cocombustion ratio. Furthermore, reducing the furnace height at H_GN = 17.3 m or titling down the burner at θ_BN = -15° contributed to a greater NO concentration at the furnace outlet.

To comprehensively explore syngas cocombustion technology, gasification experiments in a bench-scale circulating fluidized bed (CFB) and three-dimensional (3D) numerical simulations of a coal-fired boiler furnace have been conducted. In the amplification experiment of biomass gasification, sawdust has been gasified using air, oxygen-enriched air, and steam. The highest heating value of the syngas products reaches 12.3 MJ/m³ when the equivalence and steam/biomass ratios are adjusted in the ranges of 0.21-0.31 and 0.1-0.5, respectively. Subsequently, 3D numerical simulation has been performed with several kinds of syngas product to analyze the cocombustion characteristics of the boiler furnace. Results demonstrate that the velocity field of the boiler furnace exhibits a well-formed tangential velocity circle and full degree of streamlines. Syngas cocombustion in the coal-fired furnace reduces the temperature extremum in the combustion zone. Radiant heat flux accounts for >88% of the total heat flux in the furnace. The outlet NO concentration in the case of syngas cocombustion is less than that of pure coal combustion, and it is reduced approximately 25 and 40 mg/m³ at cocombustion ratios of 0.1 and 0.15, respectively.