Abstract
The uniformity of secondary air (SA) in large-scale CFB boilers has an important influence on gas-solid flow and combustion, but was seldom considered in previous studies. Numerical simulation based on the Eulerian–Eulerian and RNG k-ε turbulence models was conducted to explore the influence of SA uniformity and load variation on jet penetration, diffusion characteristics and gas-solid mixing in the first 600 MW supercritical CFB boiler. The results showed that better SA uniformity was conductive to the uniformity of SA penetration and gas-solid mixing along the furnace height, although the penetration depth and diffusion distance showed an opposite trend. In addition, the penetration depth and diffusion distance got enhanced with higher boiler load. The inner and outer SA jets could not cover the furnace width, and the uneven SA uniformity led to a huge deviation of the solid concentration within 10 m of the air distributor. Eventually, a calculation model was successfully established for predicting the penetration depth of inclined thermal SA jets during boiler operation.
Highlights
With the development of circulating fluidized bed (CFB) boilers towards large capacity and high parameters [1,2,3,4,5], boiler dimensions are increasing, resulting in higher requirements for the uniformity of fuel feeding, air distribution, gas-solid mixing, and especially secondary air (SA) uniformity to ensure better air supply in the furnace
Zheng et al [12] conducted a numerical simulation on a 300 MW CFB boiler through the unsteady two fluid model and a RNG k-ε turbulence model, and the results showed that the jet depth of SA was related to nozzle velocity, jet angle, and the background concentration of materials in the furnace
There was no significant difference in penetration depth between the two different SA distribution conditions, and the standard deviation of ILSA penetration depth was smaller under the uneven SA condition
Summary
With the development of circulating fluidized bed (CFB) boilers towards large capacity and high parameters [1,2,3,4,5], boiler dimensions are increasing, resulting in higher requirements for the uniformity of fuel feeding, air distribution, gas-solid mixing, and especially SA uniformity to ensure better air supply in the furnace. Scholars have researched the characteristics of the secondary air jet and its influence on gas-solid flow in the furnace. Zheng et al [12] conducted a numerical simulation on a 300 MW CFB boiler through the unsteady two fluid model and a RNG k-ε turbulence model, and the results showed that the jet depth of SA was related to nozzle velocity, jet angle, and the background concentration of materials in the furnace. Wang et al [13] studied the SA penetration of a supercritical CFB boiler with different SA rates and background concentration through the two-fluid model and the RNG k-ε turbulence model. The influence of SA distribution uniformity, load variation on SA jet penetration and diffusion, and changes of gas-solid flow in the furnace were analyzed in detail. The research results could provide valuable guidance and regulation suggestions for solving various non-uniformity problems in large-scale CFB boilers
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