Concepts: Gas absorption and Desorption Flashcards
A unit operation where a soluble vapor is absorbed from its mixture with an inert gas by means of a liquid in which the solute is more soluble.
The solute is subsequently recovered from the liquid by distillation
Gas Absorption
Process of removing gas dissolved in a liquid and where the liberated gas is taken up in a gas or vapor in contact with the liquid.
It is the reverse of gas absorption
Desorption or Stripping
Equipment used (2)
- Plate Column
- Packed Tower
a plate column where gas is absorbed while a gas mixture bubbles through the liquid which passes down from plate to plate
Absorption Column
A parameter in the Kremser equation for calculation of absorption columns and towers; the product of the total pressure and the liquid flow rate in moles per second divided by the product of Henry’s Law constant and the gas flow rate in moles per second
Absorption Factor
A tower where liquid flows down over a packing material in countercurrent or co-current flow with a gaseous mixture while one or more of the gaseous components are absorbed in the liquid
Absorption Tower
Liquid which takes up one or more components from a gaseous mixture
Absorbent
The condition in which the packing surface is not wetted by the flowing liquid due to low liquid rates. It is the chief reason for the poor performance of large packed towers. It is severe in towers filled with packed stacking, which is the main reason they are not much used. It is less severe in dumped/random packings.
Chanelling
A tube or duct leading liquid from one plate in column to the next plate
Downcomer
In plate columns, excessive build-up of liquid on the plates caused by insufficient drainage through the downcomers
Downflow Flooding
In distillation and absorption, excessive carry-over of suspended droplets following the vapour or gas upwards through the column
Entrainment Flooding
In a given packed tower with a given type and size of packing and with a definite flow of liquid, this is the upper limit to the rate of gas flow. At flooding point, the liquid can no longer flow down through the packing and is blown out with the gas. In an actual operating tower, the gas velocity is well below flooding. The optimum economic gas velocity is about one-half or so of the flooding velocity.
Flooding Velocity
Outgoing gas mixture in air or gas absorption column/tower
Lean Gas
The point in a logarithmic pressure drop - gas velocity diagram for packed columns where the pressure drop start to increase more rapidly with increasing gas or vapor velocity caused by rapid increase in liquid hold-up. Further increase in gas or vapor velocity ends in flooding.
Loading Point
A column for distillation, absorption or extraction, consisting of a cylindrical shell filled with small objects (packing) to bring about intimate contact between rising fluid (vapor, gas, liquid) and descending liquid
Packed Column Tower
Small objects used to provide large contact area between rising fluid and descending fluid in packed columns, such as saddes, rings, grates, and pieces of coke
Packing
The outer diameter of propriety rings such as Raschig rings and pall rings. The size of saddles are given by number corresponding to one of the dimensions in inches
Packing Diameter
In packed columns and towers, packing units lying randomly as they happened to fall when dumped down
Random Packing/Dumped Packing
Gas mixture entering the gas absorption column/tower
Rich Gas
The process in which the liquid is employed to achieve or assist in the removal of dispersed particles from the gas
Scrubbing
in distillation and absorption columns, a packing consisting of symmetric materials stacked on top of each other, for instance rings placed beside each other with vertical axis or wooden grids in cross-packed layers. Wooden grids are used in the aluminum industry in large towers for absorption of SO2 and hydrogen fluoride from ventilation air.
Stacked packing
The outlet liquid, which is enrinched in solute
Strong Liquor
The inlet liquid, which may be pure solvent or a dilute solution of solute in the solvent.
Weak Liquor
Usually used in tray columns where the liquid leaks through the perforations or valves because of insufficient counter-current gas flow. This is undesirable and the liquid should flow across the tray and down the downcomer.
Weeping
The function of ____ is to maintain a desired liquid level on the tray. Typical ____ height is between 2-4 inches. Low _____ are frequently used in low pressure or vacuum columns. Notched (rectangular or V-shaped) _____ are commonly used for low liquid loads.
Weir
Is a vertical, cylindrical pressure vessel in which vapor and liquid, which flow counter-currently, are contacted on a series of tray or plates. Liquid flows across each tray over an outlet weir, and into a downcomer, which takes the liquid by gravity to the tray below. Gas flows upward through openings in each tray, bubbling through the liquid on the tray.
Trayed Tower
A column for distillation, absorption or extraction, consisting of a cylindrical shell filled with small objects (packing) to bring about intimate contact between rising fluid (vapor, gas, liquid) and descending liquid. The gas-liquid contact in a ____ ____ is continuous, not stage-wise, as in a plate column. The liquid flows down in the column over a packing surface and the vapor (or the gas) moves counter-currently, up the column.
Packed Column
Are used for low efficiency, low capital cost scrubbing of large particulates ang highly soluble gaseous contaminants. ___ ____ are especially effective for applications where the inlet contaminants hydrolyse to form difficult to handle solids, or where more efficient scrubbing is not desired for budget or technical reasons.
Spray Tower
A tower containing primarily liquid (>90%) that has a gas or a lighter liquid sparged into the bottom, allowing bubbles to rise through the column. The column may contain staging, which enhances the mass transfer characteristics of the reactor. The ____ column can withstand high gas velocities and still maintain high mass transfer coefficients. This column is particularly attractive for reactions that do not require large amount of gas absorption or require well-mixed liquids.
Bubble Column
The two immiscible liquids are squeezed through small-diameter holes to enhance mass transfer, and centrifugal force is used to magnify the effect of density difference between the two liquids for rapid phase disengagement
Centrifugal Contactor
What are the 5 possible vapor-liquid flow regimes for contacting tray
- Spray
- Froth
- Emulsion
- Bubble
- Cellular Foam
The most common and favored regime, in which the liquid phase is continuous and the gas passes through in the form of jets or series of bubbles.
Froth Regime
The gas phase is continuous and it occurs for low weir heights (low liquid depths) at high gas rates
Spray Regime
It occurs at low gas rates in which the liquid is fairly quiescent and bubbles rise in swarms. At high liquid rates, small gas bubbles may be undesirably emulsified. If bubble coalescence is hindered, an undesirable foam forms. Ideally, the liquid carries no vapor bubbles (occlusion) to the tray below, the vapor carries no liquid droplets (entrainment) to the tray above, and there is no weeping of liquid through the holes in the tray.
Bubble Regime
Tray with a relative cost of 2.0 and Typical turndown ratio of 5
Bubble-Cap Trays
Tray with a relative cost of 1.2 and Typical turndown ratio of 4
Valve Trays
Tray with a relative cost of 1.0 and Typical turndown ratio of 2
Sieve Trays
Type of tray with highest pressure drop and efficiency but lowest in vapor capacity
Bubble-Cap Trays
Type of tray with intermediate pressure drop and highest in efficiency and vapor capacity
Valve Trays
Type of tray with lowest pressure drop and efficiency but highest in vapor capacity
Sieve Trays
Type of packing with a high relative cost and vapor capacity, very high in efficiency, but very low in pressure drop. Also with a typical turndown ratio of 2.
Structured Packing
Type of packing with high efficiency and vapor capacity, moderate relative cost, and low pressure drop. Also with a typical turndown ratio of 2.
“Through Flow” Random Packing
Type of packing with moderate pressure drop and efficiency, low relative cost, and fairly high vapor capacity. Also with a typical turndown ratio of 2.
Raschig Rings and Saddles, Random Packing
