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化工·单元操作
12
engines
连续搅拌釜反应器(CSTR)设计
Continuous stirred-tank reactor (CSTR) design
V=FA0·X/(−rA) · 空时τ=CA0X/(−rA) · 一级X=kτ/(1+kτ) · V=80L
Perfectly mixed — the whole tank (including the outflow) reacts at the rate evaluated at the exit conversion X: V = FA0·X ∕ (−rA)
平推流反应器(PFR)设计
Plug-flow reactor (PFR) design
V=FA0·∫dX/(−rA) · 一级X=1−e^(−kτ) · τ=3.22min V=32.2L · 比CSTR省
Conversion rises continuously along the tube — the design is an integral: V = FA0·∫₀ˣ dX ∕ (−rA)
反应器选型:CSTR 与 PFR 体积对比
Reactor sizing: CSTR vs PFR volume
Levenspiel 1/(−rA)−X · PFR=面积/CSTR=矩形 · X0.8比≈2.49
On a Levenspiel plot, PFR volume ∝ area under the curve, CSTR volume ∝ the rectangle at the exit rate
间歇反应器反应时间
Batch reactor reaction time
t=CA0·∫dX/(−rA) · 一级t=(1/k)ln(1/(1−X)) · 达目标X所需时间
Constant-volume batch reactor: the time to reach a target conversion X rises steeply as X → 1
竞争反应的选择性与收率
Selectivity & yield for competing reactions
串/并联反应 · 选择性S=rD/rU · 收率 · 目标vs副产竞争
Parallel reactions A → D (desired) and A → U (undesired): how concentration sets selectivity
停留时间分布 (RTD)
Residence time distribution (RTD)
RTD E(t) · 平均τ · CSTR指数/PFR脉冲 · 非理想诊断
The exit-age distribution E(t) reveals non-ideal mixing: CSTR spreads out, PFR is a pulse
二元等温闪蒸
Binary isothermal flash distillation
等温闪蒸 · Rachford-Rice · 汽化率V/F · K值相平衡
A feed partially vaporizes in a flash drum, splitting into vapor V and liquid L
汽液平衡与相对挥发度
Vapor-liquid equilibrium & relative volatility
VLE y-x · y=αx/(1+(α−1)x) · α越大越易分离
The further the equilibrium curve bows from the diagonal, the easier the separation
精馏段操作线与回流比
Rectifying operating line & reflux ratio
精馏/提馏操作线 · 随R变化 · R↑靠对角线塔板少
A larger reflux ratio rotates the operating line toward the diagonal, separating more per stage
芬斯克方程 · 最小理论板数
Fenske equation · minimum stages
Nmin=ln[(xd/(1−xd))((1−xb)/xb)]/lnα · 全回流 · α↑Nmin↓
Fewest theoretical stages at total reflux · Nmin = ln(S)/ln(α)
填料塔吸收 · 传质单元法
Packed-column absorption · transfer-unit method
塔高Z=HTU·NTU · 传质单元数与高度 · 吸收/汽提
Packed height Z = HTU (unit efficiency) × NTU (separation difficulty)
精馏塔物料衡算 · 总量与组分
Distillation mass balance · overall + component
总衡算F=D+B · 组分F·zF=D·xD+B·xB · 进料/塔顶/塔釜
F = D + B, F·zF = D·xD + B·xB