臺灣博碩士論文加值系統

流體化床燃燒反應器或FCC觸媒再生器中,通常將飛灰或用過觸媒導入流體
化床床體中,前者可增加燃燒效率,後者在使觸媒再生.但導入時之氣速會
影響床內粒徑分佈及水力動力性質因而影響流體化床反應器的表現甚巨.
對氣固流體化床而言,流體化品質(fluidization quality)是一重要課題,
一般人均以為將飛灰導入流體化床可使其混效果更良好及燃燒效果更完
全,且能增加熱傳、質傳效果.但回流氣速量若過大,將影響淘失速率使淘
失量過大甚至使粒子磨損因而使其流體化品質降低.本實驗乃在一內
徑6.62cm、高2.5m的流體化床中, 以單一垂直孔口,不同氣速,測量床內粒
徑分佈改變之情況.而粒徑的改變包括兩個重要因子即磨損速率Rt和淘失
速率常數Ki*,若能準確預測此二因子將可穩定操作一流體化床反應器.實
驗結果顯示磨損速率Rt可由以下兩式預測：一由能量觀點出發:Model 1：
Rt=ka0Fr*=ka0(Uor+Us)(U0-Umf)W/(gdp)對矽砂而言ka0=7.943×10-10一
是從氣體在床內流動行為探討:Model 2：Rt=ka0(Uor+Us)(QB/A)W其中(
QB/A)=r(U0-Umf)對矽砂而言ka0=2.597×10-7而在考率磨損嚴重的系統下
吾等重新定義一磨損淘失速率常數Kia*,來符合實際情況,而Kia*以修正
Geldart(1979)的公式,可得不錯的預測結果如下所示,然其適當範圍為U0
＞Ut：Kia*/pgU0=7.5exp[-5.4Ut/U0]

Abstract Within the processes of fluidized bed combustor and
catalyst regenerator, there are recycling part of fly ash and
reintroducing into the bed of reactor to improve the efficiency,
or being feedback the used catalyst into the bubbling fluidized
bed for regeneration. In the feedback processes, the over high
velocities in the feedback tube will significantly cause
attrition in the bed and result into the elutriation of fine
particle, also change the particle size distribution and
hydrodynamics of the bed. Experimental work was carried out
in a batch gas fluidized bed with 6.62cm inner diameter and 2.5m
height and perforated distributor. Operating velocities is
controlled between from 1 to 5 Umf (minimum fluidization
velocity), and the single nozzle gas velocities are handled from
50m/s to 208m/s with inner diameters of 3,4,4.5, and 5mm
individually. The used materials are silica sand that are the
average sieve diameters of 195,296, and 421mm respectively.
The experimental results show that the attrition is function of
particle size distribution, materials nature, single nozzle
velocities and superficial gas velocities, the empirical
attrition rates have been developed by two models; one is from
the energy (model 1), the other is from particle motion (model
2). There are shown as follows: Model 1：Rt=ka0Fr*=
ka0(Uor+Us)(U0-Umf)W/(gdp) ka0=7.943×10-10
[1/s] for sand Model 2：Rt=ka0(Uor+Us)(QB/A)W
where (QB/A)=r(U0-Umf) ka0=2.597×10-7[s/m2
] for sand The elutriation rate constant is modified by
attrition effect. We define the attrition elutriation constant,
Kia*, instead of Ki* for the elutriation dominated by attrition
effect. We also modify Geldart (1979) empirical correlation, and
develop the empirical elutriation equation as follows for this
attrition elutriation system: Kia*/pgU0=7.5
exp[-5.4Ut/U0] for U0＞Ut