﻿ 风量配比影响循环流化床锅炉燃烧特性研究

# 风量配比影响循环流化床锅炉燃烧特性研究Study on the Combustion Characteristics of the Circulating Fluidized Bed Boiler Influenced by Air Volume Ratios

Abstract: Circulating fluidized bed (CFB) boilers have been widely used due to the high combustion efficiency, good fuel adaptability and low pollutant emission. This paper conducted a numerical simulation analysis on a 240 t/h circulating fluidized bed boiler to analyze the influence of changing the ratio of primary and secondary air on the internal flow and combustion characteristics. The results show that the small proportion of primary air θ resulted in poor effect of fluidization inside the furnace; too large proportion of primary air θ cannot provide oxygen for the combustion in the center of the furnace timely; when the proportion of primary air θ is 0.55 (Condition III), the bed material and temperature distributions are even, and NOx concentration at the outlet is the lowest.

1. 引言

2. 锅炉概况

(a) 炉膛三维模型 (b) 密相区炉膛截面图

Figure 1. Furnace physical model diagram

3. 数学模型及参数设置

3.1. 数学模型

1) 挥发分析出的反应式为：

$\text{Volatile}〈\text{s}〉⇒\text{CO}+{\text{CO}}_{2}+{\text{H}}_{\text{2}}\text{O}+\text{tar}$ (1)

$prod=yi\ast \text{C_R}/mw$ (2)

$\text{*}rr=\text{0}\text{.01}\text{\hspace{0.17em}}\text{Arrhenius_devolatilization}*{e}^{\left(E/\left(8.314*T\right)\right)}*prod*\text{C_VOF}$ (3)

2) 焦炭燃烧反应式为：

$\text{C}〈\text{s}〉+{\text{O}}_{2}⇒\text{CO}$ (4)

UDF中涉及的计算有脱附速率(Rd)、扩散系数(diff)、雷诺数(Re)、正反应速率系数(k_f)、逆反应速率系数(k_r)以及中间变量(rr')，各计算过程不再赘述，最终反应速率公式 [15] 为：

$*rr=\frac{rr\text{'}\text{\hspace{0.17em}}*p\text{_}o2*6*C\text{_}VOF}{D\text{_}p*3200}$ (5)

3.2. 边界条件设置

Table 1. Circumstances of different air volumes

4. 结果与讨论

4.1. 流动特性研究

Figure 2. Vapor velocity distribution of X = 0 section under different conditions

Figure 3. Vapor velocity distribution of X = 0 section under different conditions

Figure 4. Distribution of bed material volume fraction of Z = 1 m section under different conditions

4.2. 温度场分布

Figure 5. Temperature distribution of X = 0 section under different conditions

Figure 6. Average temperature change curve in Z direction under different working conditions

4.3. NOx质量浓度分析

Figure 7. Variation curve of average mass concentration of NOx in Z direction under different conditions

Figure 8. Export NOx average mass concentration under different conditions

5. 结论

1) 在流动过程中，一次风起到流化炉膛内部各物料的作用，二次风起到增强炉膛内部的扰动作用；在燃烧过程中，一次风在决定燃料炉内停留时间中起主要作用，二次风主要起到补充燃烧的作用。

2) θ过小，对炉膛内部流化效果差，不利于密相区的气固混合；θ过大，此时二次风风速较低，难以为炉膛中心提供足量的氧气辅助燃烧。

3) 模拟结果显示，当θ = 0.55时，炉膛内部床料、温度分布均匀，炉膛中部出现较大的高温区域，且出口NOx质量浓度低，为最佳配风方案。

NOTES

*通讯作者。

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