Lu Junfu

Numerical Simulation of Combustion Characteristics and Heat Flux Distribution in a 600-MW Arch-Fired Boiler with Different Primary Air Injection Angles

A CFD model of a 600 MW supercritical arch-fired boiler (SC-AFB) was established and applied to investigate the combustion characteristics and heat flux distribution with three primary air injection angles of 0°, 5°, and 10°. The results showed that in general, the primary air streams barely penetrate the secondary air in the lower furnace, and thus, no strong combustion occurs in the hopper zone. A smaller injection angle results in a longer penetration distance and longer residence time of the coal particle, but it generates a larger reducing zone in the lower furnace. When the injection angle varies from 0° to 5°, high-temperature zone (T > 1800 K) expands, but it becomes narrower when the injection angle further increases to 10°. Coal particles burnout ratio at furnace exit is highest when injection angle is 5°. It was also found that coal particles move and gather near the two side walls by the thermal expansion in the near burner zone, resulting in intense combustion and heat transfer near the side walls and a two-peak heat flux profile on the front wall. When the burner injection angle increases, less coal particles move toward side walls and their residence time is shorter in the lower furnace. The injection angle of 5° is suggested based on the optimal flux distribution and burntout ratio of the coal particles.

Design and Operation of Experimental System for Studying Heat Transfer in a Smooth Tube at Near and Super Critical Pressure

Boilers running at supercritical pressure with large capacity have been widely used in power generation technology. How to keep the safety of heat transfer in the riser system is an important issue. However, it is difficult to study heat transfer for the vertical smooth tubes in a boiler at sub-critical or supercritical pressure since the thermodynamic properties of water is very complex and sensitive to temperature and pressure near the critical point. Hot-state experiment of heat transfer for the tubes of diameter used in a boiler is of great value for the design of membrane wall. In order to study the heat transfer of vertical smooth tubes running at low heat flux and low mass flux for sub-critical CFB boilers, a near-supercritical pressure water test bed was built in Tsinghua University. The designed pressure is 21MPa, the mass flux of water is 550kg/m2s, and the heat flux is 136kW/m. In this paper, the design and structure of the test bed is introduced. The experimental result is analyzed, more experimental work is needed in future research.