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Research on Dry Slagging Technique of Water-Cooled Scraper in Pulverized Coal Furnace
DOI: 10.12677/AEPE.2023.113013, PDF, HTML, XML, 下载: 216  浏览: 804  科研立项经费支持

Abstract: Due to the shortage of water resources in our country, dry slag technology is advocated, but air leakage caused by air-cooled dry slagging system is unavoidable. In order to avoid air leakage, a new indirect water-cooled dry slagging method is proposed. Numerical simulation is used to study the motion state and cooling effect of bottom slagging under the new slagging method, and the advantages and disadvantages of the new slagging method and the traditional slagging method are compared. The results show that the new slagging method strengthens the mixing between ash particles while transporting ash, and the slagging temperature is more uniform. The cooling effect is slightly lower than that of the steel belt transportation method due to the reduction of heat exchange area, but it still satisfies the slagging cooling in the transportation stage, and the ash temperature decreases from 523.15 K to 449.9 K. Under the new slag discharge structure, the slag temperature no longer decreases significantly after the cooling water flow velocity is higher than 0.5 m/s.

1. 引言

2. 模型构建

(a)整体结构图 (b)截面结构图

Figure 1. Illustrative diagram of model structure

Table 1. Physical properties of ash and steel structures

3. 数学模型及网格无关验证

3.1. 数学模型

3.1.1. 颗粒运动及换热计算模型

EDEM采用离散元的数值模拟方法，灰渣颗粒之间的作用采用Hertz-Mindlin (no slip)模型来计算。在这个模型中，法向力成分是基于赫兹接触理论。切向力模型是基于Mindlin-Deresiewicz的工作。法向力和切向力都有阻尼成分，其中阻尼系数与恢复系数有关，切向摩擦力遵循库仑摩擦定律模型，滚动摩擦力以独立于接触的方向性恒定扭矩模型实现。具体计算公式如下：

${F}_{n}=\frac{4}{3}{E}^{*}\sqrt{{r}^{*}}{\delta }_{n}^{\frac{3}{2}}$ (1)

$\frac{1}{{E}^{*}}=\frac{\left(1-{w}_{i}^{2}\right)}{{E}_{i}}+\frac{\left(1-{w}_{j}^{2}\right)}{{E}_{j}}$ (2)

$\frac{1}{{r}^{*}}=\frac{1}{{R}_{i}}+\frac{1}{{R}_{j}}$ (3)

${F}_{n}^{d}=-2\sqrt{\frac{5}{6}}\beta \sqrt{{S}_{n}{m}^{*}}{v}_{n}^{\stackrel{\to }{rel}}$ (4)

${m}^{*}={\left(\frac{1}{{m}_{1}}+\frac{1}{{m}_{i}}\right)}^{-1}$ (5)

$\beta =\frac{-\mathrm{ln}e}{\sqrt{{\mathrm{ln}}^{2}e+{\pi }^{2}}}$ (6)

${S}_{n}=2{E}^{*}\sqrt{{R}^{*}{\delta }_{n}}$ (7)

${F}_{t}=-{S}_{t}{\delta }_{t}$ (8)

${S}_{t}=8{G}^{*}\sqrt{{R}^{*}{\delta }_{n}}$ (9)

${F}_{t}^{d}=-2\sqrt{\frac{5}{6}}\beta \sqrt{{S}_{t}{m}^{*}}{v}_{t}^{\stackrel{\to }{rel}}$ (10)

$F=\sum {F}_{n}+\sum {F}_{t}$ (11)

${\tau }_{i}=-{\mu }_{r}{F}_{n}{R}_{i}{\omega }_{i}$ (12)

${Q}_{p1p2}={h}_{c}\Delta {T}_{p1p2}$ (13)

${h}_{c}=\frac{4{k}_{p1}{k}_{p2}}{{k}_{p1}+{k}_{p2}}{\left[\frac{3{F}_{N}{r}^{*}}{4{E}^{*}}\right]}^{1/3}$ (14)

${m}_{p}{C}_{p}\frac{\text{d}T}{\text{d}t}=\sum {Q}_{heat}$ (15)

3.1.2. 等效介质假设法计算模型

$\frac{\partial \rho }{\partial t}+\nabla \cdot \left(\rho v\right)=0$ (16)

$\frac{\partial }{\partial t}\left(\rho v\right)+\nabla \cdot \left(\rho vv\right)=-\nabla p+\nabla \cdot \left(\tau \right)+\rho g$ (17)

$\tau =\mu \left[\left(\nabla v+\nabla {v}^{Τ}\right)-\frac{2}{3}\nabla \cdot vI\right]$ (18)

$\frac{\partial }{\partial t}\left(\rho H\right)+\frac{\partial }{\partial {x}_{i}}\left[{u}_{i}\left(\rho H+p\right)\right]=\frac{\partial }{\partial {x}_{j}}\left({k}_{eff}\frac{\partial T}{\partial {x}_{j}}\right)+{S}_{h}$ (19)

${k}_{eff}=k+\frac{{c}_{p}{\mu }_{t}}{{\mathrm{Pr}}_{t}}$ (20)

$\frac{\partial }{\partial t}\left(\rho k\right)+\frac{\partial }{\partial {x}_{j}}\left(\rho k{u}_{j}\right)=\frac{\partial }{\partial {x}_{j}}\left[\left(\mu +\frac{{\mu }_{t}}{{\sigma }_{k}}\right)\frac{\partial k}{\partial {x}_{j}}\right]+{G}_{k}-\rho \epsilon$ (21)

$\frac{\partial }{\partial t}\left(\rho \epsilon \right)+\frac{\partial }{\partial {x}_{j}}\left(\rho \epsilon {u}_{j}\right)=\frac{\partial }{\partial {x}_{j}}\left[\left(\mu +\frac{{\mu }_{t}}{{\sigma }_{\epsilon }}\right)\frac{\partial \epsilon }{\partial {x}_{j}}\right]+\rho {C}_{1}S\epsilon -\rho {C}_{2}\frac{{\epsilon }^{2}}{k+\sqrt{v\epsilon }}$ (22)

$\frac{\partial }{\partial t}\left(\rho h\right)+\nabla \cdot \left(\rho hv\right)=\nabla \cdot \left(k\nabla T\right)+{S}_{t}$ (26)

3.2. 网格无关性验证

Figure 2. Pipe heat exchange grid irrelevance verification diagram

4. 结果与讨论

4.1. 运动过程分析

Figure 3. Ash particle movement diagram (steel belt conveyor (left) scraper conveyor (right))

Figure 4. Movement of particles in the central section

Figure 5. Movement of particles in the cross section near the baffle

4.2. 换热分析

Figure 6. Temperature distribution of ash particles in steel belt conveyor

Figure 7. Temperature distribution of ash particles in scraper conveyor

Table 2. Comparison table of cooling effect

Table 3. Physical properties parameters

Figure 8. Indirect water-cooled steel structure temperature distribution with position

Figure 9. Indirect water-cooled cooling effect with cooling water flow rate

5. 结论

1) 刮板运输机可以有效的使中心灰渣与冷源接触，排渣温度更均匀，不会产生钢带式运输中出现的温度分层现象，但由于其工作特点，导致灰渣与底板的接触面积减少了49.38%，所以整体冷却效果不及同冷却条件下的钢带式运输机，在运输段进口温度523.15 K的情况下，可以降温73.25 K，排渣温度约为449.9 K，基本满足运输过程中排渣的冷却要求。

2) 冷却水管的温度分布各截面趋势相同，底部温度低，肋片处温度高，延灰渣移动方向，冷却水管截面温差越来越小，越来越接近冷却水温度。

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