Experimental Investigations on Lateral Dispersion Coefficients of Fuel Particles in Large-Scale Circulating Fluidized Bed Boilers with Different Coal Feeding Modes

Abstract

The dispersion characteristics of fuel particles over the bed have always been a key consideration in the design of fluidized beds. However, the lateral fuel dispersion coefficients (Dsr) reported in the previous literature widely ranged from 10−4 to 10−1 m2/s, which were hard to be directly applied in large-scale CFB (circulating fluidized bed) boilers with wider bed width (close to 30 m) and variable coal feeding modes. To solve this problem, field tests were conducted on the first 600 MW CFB boiler in this paper, and the distributions of flue gas composition and flue gas temperature were obtained near the coal feeding port under four working conditions. The dispersion characteristics of fuel particles were analyzed in detail combined with the dispersion model. In addition, a new method based on bed heat balance was also proposed to estimate Dsr and applied in a 300 MW CFB boiler with a different coal feeding mode. The results revealed that Dsr through the local heat balance method ranged from 0.10–0.35 m2/s, which were 9–18% higher than the values through the dispersion model. Compared with the coal feeding port immersed in the bed, Dsr of the fuel particles fed into the splash zone increased by about 34.7%. Dsr under the coal feeding mode of a screw feeder with pressurized air ranged from 0.12–0.16 m2/s, which were lower than Dsr under the coal feeding method of importing fuel into circulating ash. The method and results in this paper could expand the applicability of fuel dispersion, and provide the most direct guidance for the design and optimization of coal feeding ports in large-scale CFB boilers.

Numerical Study of the Influence of Secondary Air Uniformity on Jet Penetration and Gas-Solid Diffusion Characteristics in a Large-Scale CFB Boiler

“…The secondary air system of the first 600 MW supercritical CFB boiler in the world was involved in the present study. As shown in Figure 1 [18], this boiler consists of a pant-leg furnace, six steam-cooled cyclones and six external fluidized bed heat exchangers (FBHEs). The secondary air coming from the rear wall direction is divided into two paths, one path is used for the outside SA and the other path is used for the inner SA [19].…”

MP-PIC Simulation on Solid Dispersion in a 350 MW CFB Boiler

“…33,34 It is reported that the solid dispersion in a large-scale CFB boiler is vastly different from that in a laboratory-scale bed. 13,19,21 In addition, as particle size d p and density ρ p affect fuel dispersion characteristics, the particle property changing pattern might be an important effect. From previous studies, there are generally three treatments to describe the size and density change during combustion: particle size shrinkage with constant density, density decrease with constant size, and both particle size and density decrease simultaneously.…”

“…Besides, there are some indirect ways to explore the fuel particle dispersion, such as analyzing the response of temperature distribution and released gas distributions caused by fuel dispersion. − Yan et al calculated the dispersion of coal particles in the 600 MW supercritical CFB boiler by measuring the species distribution on the extension line of the coal inlet. Though the testing method has some limitations, they reported that the solid dispersion coefficient in the furnace width direction was up to 0.3 m 2 /s.…”

“…Recently, the MP-PIC method has been used to simulate gas–solid flow and combustion in the fluidized bed boilers. − However, there are few studies on solid dispersion using the model, and the available works are limited to a laboratory-scale fluidized bed. , It is reported that the solid dispersion in a large-scale CFB boiler is vastly different from that in a laboratory-scale bed. ,, …”

An Experimental Study on the Characteristics of NOx Distributions at the SNCR Inlets of a Large-Scale CFB Boiler

“…It is generally believed that significant non-uniform input parameters exist in largescale CFB boilers, including primary air and secondary air [20,21], fuel particle dispersion [22], coal feed distribution [23,24], recirculating ash and heat absorption deviation in multi-parallel loops. Therefore, the flue gas composition at furnace outlets should also be uneven.…”