Effect of Connection Resistance between Cyclones and Backpass on Furnace Solids Suspension Density Profile and Circulation Rates in CFB

Guanwen Luo,Leming Cheng,Weiguo Zhang,Junfeng Wang,Xiaoguo Jiang,Liyao Li

doi:10.3390/en14196162

Guanwen Luo, Leming Cheng + Show 4 more

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https://doi.org/10.3390/en14196162

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Abstract

The connection section between cyclones and backpass is an important configuration in multi-cyclone circulating fluidized bed boilers (CFB). In this work, the resistance coefficient of different connection modes, and connection resistance distribution from each cyclone outlet to backpass (connection branch) in one mode are defined and calculated, in order to investigate their effects on furnace solids suspension density distribution and circulation rates. Three connection modes with different overall resistance coefficients were tested experimentally and analyzed by a 1.5-dimensional model in a four-cyclone scaling CFB apparatus. Both experimental and theoretical results show that, with larger overall resistance of a connection, there are more solids suspended in the furnace bottom and fewer in the top section. The investigation of the C-type connection has revealed that when the branch resistance of the connection decreases from branch No. 1–4, the solids suspension density and circulation rate from corresponding solids recycle loops (No. 1–4) increase. Moreover, the non-uniformity of connection branch resistance distribution will lead to uneven lateral solids suspension density distribution and circulation rates allocation. This effect is enhanced by growing superficial velocity.

Highlights

Circulating fluidized bed boilers have been widely utilized in the industry due to their high combustion efficiency, low emission, and fuel adaptability
The solids suspension density in the furnace and solids circulation rate distributions are influenced by connection resistance
With smaller overall resistance coefficient ξ av of a connection, the axial solids suspension density in the furnace distributes more uniform and solids circulation rate becomes larger; For branch resistances ξ b,i (i = 1–4) in a connection, smaller ξ b,i leads to higher solids circulation rate in solids recycle loop

Summary

Introduction

Circulating fluidized bed boilers have been widely utilized in the industry due to their high combustion efficiency, low emission, and fuel adaptability. The distributions of solids suspension density on the cross-section in the furnace and solids circulation rates under each cyclone become more non-uniform. This will lead to an uneven temperature profile in a CFB furnace and cause operation problems. Previous studies have been conducted towards gas-solid hydrodynamics uniformity in a CFB with multiple cyclones. Results show operating conditions [1,2,3,4,5,6,7] and geometric factors [6,7,8,9,10,11] have influences on furnace solids suspension density and circulation rates distribution among cyclones. Zhou et al [1]

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