Wu Yuxin

Investigation of Coal Reactivity Effects on a 1000-MW Tangential Coal-Firing Boiler

The parameters in char combustion are important for boiler simulation. This study investigates the effect of coal activation energy on the simulation of coal combustion. A diffusion-kinetic (DK) char combustion model was firstly used to identify the activation energy in sensitive range that strongly affects the char combustion rate. It is found that the sensitive range depends on particle temperature, particle diameter, and oxygen fraction. A 1000-MW tangential coal-firing boiler was simulated in the article to evaluate the effects of activation energy. Numerical results show that char burnout rate decreases with higher activation energy. Average scalars such as temperature and oxygen fraction change slowly with the activation energy when it is less than the middle value of the sensitive range. However, when the activation energy is higher than the value, the burnout rate drops dramatically, the high-temperature zone moves upward to the area between burner nozzles and OFA nozzles. Average temperature, reaction rate decrease, and O2 mass fraction increase in the burner zone.

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.

Effects of the Secondary Oxygen Injection on the Performance of a Staged-Entrained Flow Coal Gasifier

In a staged entrained flow coal-slurry gasifier, the secondary oxygen was injected into the gasifier in order to protect the refractory in the dome region, to improve the mixing process as well as gasification performance. Based on a proposed 3-D numerical model, simulations were conducted for the staged gasifier at different mass flow rates of the secondary oxidizer. The characteristics of the gasification flames were analyzed as well as the influence of the secondary flow on the flow field of the staged gasifier. As the mass flow rate of the secondary oxidizer decreases, the secondary gasification flame curves up according to the backflow region and wall temperature increases. When the mass flow rate of the secondary oxidizer is less than 10% of the total oxidizer mass flow rate, there is an obvious change of the turbulent mixing in the staged gasifier.

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.