Experimental Study of Sawdust Syngas Gasification in Bench-Scale Gasifier and Three-Dimensional Numerical Analysis for Syngas Cocombustion in a 600 MW Coal-Fired Boiler Furnace

Abstract

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.

Figure 1

Schematic of the bench-scale circulating fluidized bed (CFB) gasification producer (a) and the catalytic reforming reactor (b). (1: Steam inlet channel, 2: oxygen inlet channel, 3: air blower, 4: screw feeder, 5: biomass bin, 6: main airflow intake, 7: gasifier, 8: cyclone separator, 9: return feeder, 10: catalytic reformer, 11: tar sampling port, 12: gas sampling port, 13: spray tower, 14: Roots blower, 15: syngas tank, 16: syngas outlet, 17: crude gas inlet, 18: burner, 19: reformer, 20: connect the spray tower, 21: chimney.)

Figure 2

Diagrams of the four-corner tangential furnace (a), burner arrangement (b), and hexahedral mapped mesh (c).

Figure 3

Comparison of temperature T (a) and NO concentration C_NO (b) at the outlet of the boiler furnace between the present simulation and Dr. Yang’s work.

Figure 4

Diagram of syngas component (a) for different gasification agents at ER = 0.25 and S/B = 0.5 and low heating value (b) of product syngas varies with ER and S/B values at OC = 90%.

Figure 5

Diagrams of the cross-sectional velocity vector at first-layer primary air nozzles at the furnace of Y = 13.2 m.

Figure 6

Diagrams of velocity distribution at cross sections and longitudinal sections (a) and streamline (b) in the boiler furnace at ξ = 0.1.

Figure 7

Temperature distribution patterns at the cross sections of the boiler furnace where the first-layer primary air nozzles at Y = 6.3 m (a) and four-layer primary air nozzles at Y = 11.7 m (b) are located.

Figure 8

Distributions of temperature field at the cross sections and longitudinal sections of the boiler furnace for the pure coal combustion (a) and cocombustion with coal and sawdust syngas gasified by three kinds of agents (b,c,d).

Figure 9

Patterns of total heat flux distribution (a) and radiant heat flux distribution (b) on the furnace sidewall at the burner zone for syngas cocombustion at ξ = 0.1.

Figure 10

Variations of temperature T (solid symbols) and NO concentration C_NO (hollow symbols) along with the furnace height H for the case of pure coal combustion and the case of cocombustion with sawdust syngas at ξ = 0.1 with different gasification agents.

Figure 11

Variations of temperature T (solid symbols) and NO concentration C_NO (hollow symbols) along with the furnace height H for the case of pure coal combustion and the case of cocombustion with sawdust syngas at ξ = 0.15 with different gasification agents.