Absorption & Stripping Design - Chemical Engineeringche.uri.edu/course/che349/absorption.pdf ·...
Transcript of Absorption & Stripping Design - Chemical Engineeringche.uri.edu/course/che349/absorption.pdf ·...
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Absorption & Stripping Design • Common assumptions:
– Dilute and immiscible gas-liquid phases – L and V streams are constant from stage to stage
– Concentrated or miscible – L and V streams can increase or decrease from stage to stage
– How will this affect the number of theoretical stages? – Are the analytical equations still valid?
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• What is the goal of absorption or stripping operations? – Maximum extraction with 100% efficiency (i.e. actual # of stages =
theoretical)
– High throughput (low residence time)
– Smallest and simplest possible system (low capital)
• How do we accomplish this? – Choose the right absorbing (liquid) or stripping (gas) phase
(equilibrium and immiscibility)
– Optimize column diameter and height
– Maximize contact area/volume within column WITHOUT flooding the column or making it unreasonably “slow”
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1. Tray designs
Perforated
Valve cap
Bubble cap
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2. Random packing materials (p. 659 in text gives properties)
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2. Pressure drop across random packing (Fig. 10.6-5)
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2. Structured packing (pressure drop correlation in Fig. 10.6-6)
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• Flooding pressure drop given by:
• How to calculate limiting flow rates and column diameter 1. Select a suitable packing material with Fp (random or structured) 2. Select a suitable GL/GG ratio and a total gas flowrate 3. Calculate ΔPflood
4. Calculate capacity (i.e. flow) parameter at ΔPflood from correlation (Fig. 10.6-5 or 10.6-6)
5. Calculate GG from capacity parameter (this is at flooding) 6. Using suitable % of GG at flooding for actual GG (typically 50-70%,
but varies). Determie GL. 7. Calculate cross sectional area of tower from GG and total gas
flowrate
Putting these pieces together…
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Diagram of plate absorption towers
L0, x0 V1, y1
LN, xN VN+1, yN+1
L0, x0 V1, y1
LN, xN VN+1, yN+1
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Diagram of packed absorption towers
V2
y2
L2
x2
V1
y1
L1
x1
z dz
y x