COLUMN INTERNALS

Distillation , King in separations , will remain as the workhorse separation device of the process industries, even though it is old in the art ,with a relatively mature technology support base, it attracts research & professional interest. Without question distillation will sail into future with clear skies and a strong winds. it will remain the key separations against which alternate methods must be judged

Dr.James R. Fair

Why Distillation?

US-Initiative “Vision 2020” (1998) for chemical industry

US Department of Energy.

American Institute of Chemical Engineers.

Task of identifying the technical barriers.

The research needs and the priorities of the chemical industry regarding separation processes.

Goal of winning a leading role in world market.

Most Critical Research Areas Needs for Distillation Improved understanding of physical

phenomena;

Better in situ sampling.

Analytical and flow-visualization methods.

Better predictive modeling

Distillation Column Design Primary phase

Secondary phase

Primary Design

Column diameter Types of tray Split of tray area Bubbling area Downcomer area Tray vapor & liquid load Tray spacing Weir length

Secondary Design

Detailed layout

Control configuration

Column Internals

Packed Bed Random or dumped packing Structured packing Grid Liquid & Vapor distributor Bed supports & limiter

Tray type Bubble cap tray Sieve tray Valve Tray High Capacity trays

Packing Objective

Objectives for maximizing efficiency

To maximize the specific surface area To spread surface area uniformly. To promote uniform distribution of vapor

& liquid throughout the bed To freely drain any liquid so that stagnant

liquid pockets are minimized To maximize the wetting of packing

surface

Objectives for Maximizing Capacity

To maximize The void space per unit column volume.

To minimize friction (good Aerodynamic characteristics).

To ensure uniform resistance to vapor & liquid flow throughout the bed.

To permit easy disengagement of vapor from liquid.

Other Objectives

To maximize resistance to mechanical deformation /deformation under the weight of bed.

To minimize cost.

To maximize the fouling resistance.

To minimize the liquid holdup.

To minimize damage during abnormal operation.

Types of Random Packing

First generation packing (Raschig rings, Lessing Rings, Berl saddles)

Second generation packing(intalox saddles, pall rings, Hy-pak )

Third generation packing(CMR, Chempak, Nutter rings, Hckp, fleximax, hiflow rings, Lanpac, Impac etc)

Other miscellaneous random packing (Dinapac, super Torus VSP, Interpack, Tellerette, maspac, Levapac etc)

Raschig Ring First generation

random packing. made from metals

like carbon steel or very high alloys such as Monel 400 or Hastelloy C276.

Special Carbon or Graphite made are used in specific applications

Resistant to most acids, alkalis and solvents at temperatures as high as 1500 C 

Good erosion and thermal shock resistance.

Pall Rings Second-generation,

random packing.

Primarily made of 304SS and 316L SS metal alloys for quick replacement in kind from stock materials. 

Carbon Steel and specialty alloys, such as Monel 400 and Hastelloy C276, made are used for specific applications

Pall Rings are available in various sizes such as (mm) 16, 25, 38, and 50.

Saddle Rings Saddle Rings were originally

introduced to the industry under the product name IMTP® Intalox Metal Tower Packing, a registered trademark of Koch-Glitsch, LP. 

In terms of performance, i.e., low-pressure drop and high efficiency.

Used in both high pressure as well as vacuum towers.

Large effective interfacial area,

High mechanical strength And lower cost due to less

metal than previous generations of random packing.

Available in various sizes, which give different combinations of efficiency and pressure drop

INTALOX® ULTRA™ Random Packing Lowest pressure drop

and highest capacity

Highest distillation, absorption, and stripping efficiency

High strength to weight ratio

IMTP® High Performance Random Packing High void fraction

&well distributed surface area.

More open shape improves liquid spreading.

Low pressure drop and high capacity

High specific heat transfer coefficient.

High strength to weight ratio.

BETA RING™High Performance Random Packing High vapor capacity and

low pressure drop

High efficiency

High liquid handling capacity

Fouling resistant

CASCADE MINI-RINGS® (CMRTM)High Performance Random Packing L/D=1/3

Open side facing vapor flow, reduces friction.

High capacity and low pressure drop

High efficiency

Fouling resistant

HY-PAK® Random Packing

More internal tongues helps in spread in surface area

Higher capacity and lower pressure drop than Pall rings

Higher efficiency compared to Pall rings for the same capacity.

Higher mechanical strength than Pall rings

FLEXIRING®Random Packing

Good capacity and low pressure drop

Higher liquid hold-up and residence time

Versatile standard packing

Nutter Ring Efficiency enhanced by

lateral liquid spreading and surface film renewal

Superior surface utilization in mass and heat transfer, allowing shorter packed bed heights

A high performance random packing verified by tests conducted at Fractionation Research Institute

Mechanical structure provides maximum randomness with minimal nesting

Tellerette Random Packing

Performance Comparison of Three Packing Generations

Improvement in efficiency or capacity from generation to generation

Second & Third generation packing intelligently designed

Packing Material

Metals/Alloys

Ceramics

Plastics/polymers

Structured Packing

Wire Gauze Packing Sulzer wire gauze

packing Goodloe Hyperfil Montz

Corrugated Structured Packing

Mellapak Flexipak Gempak Intalox High

Performance Structured Packing

Max-Pac Flexiramic

Sulzer Gauze Packing BX and CY

Employed in industry since 40 years for gentle distillation

High separation efficiency with low pressure drop for low liquid loads/vacuum applications

Available made of wide pallet of stainless steel, alloys and thermoplastics

GOODLOE™ (structured wire gauze packing)

Multifilament of fine

diameter wire,

knitted together to

form tube type

structure.

Specific surface

area585-1000ft2 /ft3.

Available in

metal,plastic,alloyes

with teflon coating

Hyperfil (Structured Packing)

Made of

multifilament of

fine diameter wire.

Rolling the knitted

wire structure in

parallel vertical

layer.

Made of stainless

steel, copper and

corrosion resistant

wire

Montz

Katapak™-SP

Corrugated sheet

spreads in a series of

parallel planes.

Packing for reactive

distillation and trickle-

bed reactors

High separation

efficiency and high

reaction capacity

Mellapak™

Universal packing type with surface area of 250m2 /m3

Suitable for a wide range of applications for low to very high liquid loads/ vacuum to gauge pressure.

Available made of wide pallet of stainless steel, alloys and thermoplastics

FLEXIPAC®

Enhanced Structured Packing Systems for Mass Transfer Applications Lower Pressure Drop and up to 40% Higher Capacity than Conventional Structured Packing

Structured Packing Vs. Random Packing Specific surface area vs. packing factor

HETP vs. sp.Surface area

Liquid holdup vs. liquid flow rate

Pressure drop per theoretical stage

Wetting & minimum liquid rate

Specific Surface Area Vs. Packing Factor

HETP vs. Sp. Surface Area

Pressure Drop Per Theoretical Stage

Liquid Holdup Vs. Liquid Flow Rate

Types of Grids

Glitsch C-grid

Koch Flexigrid

Nutter Snap Grid

Perform Grid

FLEXIGRID® Structured Packing

Koch-Glitsch FLEXIGRID® structured packing is developed primarily for severe services which are susceptible to fouling, erosion, coking and high solids content. FLEXIGRID® packing is installed in rigid modules stacked in successive layers with a fixed orientation, which minimizes the overall pressure drop while simultaneously increasing tower capacity and/or efficiency. 

Applications Crude Atmospheric Towers Lube Vacuum Towers Crude Vacuum Towers Fluid or Thermal Cracking Fractionators Coker or Visbreaker Fractionators Coker Scrubbers Reactor Off-Gas Scrubber Gas Quench Towers Edible Oil Deodorizers Pollution Control Scrubbers

Grids vs. Packing

Capacity and efficiency Roughly grids have high capacity and low

efficiency(similar to 2nd & 3rd generation packing)

Pressure drop3-5times lower then 2in pall ring

Wetting Grid can achieve high turndown and

perform well at low liquid rate

Grids vs. Packing

Solids handlingMost suitable for solid containing stream & fouling services

CorrosionDue to thin sheet metal low tendency of oxidation

Maintenance & troubleshootingEasy to install/remove/maintain

Cost (cost is less then structured packing/ same order as of random packing)

Packing Hydraulics

Pressure drop flow regimes Flooding prediction

i. By interpolation( literature supplied by manufacturer)

ii. Through empirical/ semi-empirical equations (Kister&Gill correlation, Billet& Schulets correlation,mersamann correlations)

iii. Graphs (GPDC curve, modified GPDC curve)

Flooding Curve

Pressure drop

Pressure drop is also affected by tower diameter, smaller the diameter lower the pressure drop.(e.g. literature reports 10-20% lower pressure drop in 3ft column diameter then in a 1ft column for same capacity)

Dry packed bed have higher pressure drop then wet bed(5-10% capacity reduction due to this wetting phenomenon)

Difference in size, shape, geometry of packing supplied by different manufacturer also have effect on pressure drop.

Pressure drop for foaming system are higher then non foaming systems.

Factors Favoring Packed Column

Vacuum system Low pressure drop applications

Revamps

Foaming/emulsion

Corrosive systems

Low liquid hold up

Random Packing Support Grid These grid-type plates are used in

columns with short bed depths, and where efficient space utilization is essential, since they take up less tower height than a Model 101R.The Model 104 is frequently used in the short packed beds of crude atmospheric and vacuum towers

Random Packing Bed Limiter

Attached to support rings or bolting clips above the packed bed, a bed limiter prevents the loss of packing if high pressure drop or surge conditions cause sudden bed expansions.

Lightweight mesh is attached to the bed limiter to prevent carryover of smaller-sized packing. Integral bed limiters may be used with most Koch-Glitsch gravity distributors, thereby eliminating the need for a separate bed limiter. This reduces cost by eliminating one device and its support ring, and minimizing the risk of maldistribution caused by liquid splashing on a separate bed limiter.

The overall height of bed limiters is about 2 inches

Ceramic Packing Hold Down

Koch-Glitsch Hold Down Plates rest directly on top of the packed bed and are used exclusively to hold ceramic or tower packing in place. They are not recommended for metal or plastic packing.

The plates inhibit fluidization of the top layer of packing during tower operation. Like the bed limiters, they deliver at least as much throughput capacity as the packing at low pressure drops.

The overall height of hold down plates is usually 3 inches, but can be as high as 6 inches.

Flashing Feed Distributor

The 300 Flashing Feed Distributor is used to disengage the vapor phase from a two-phase feed. The 300 consists of two plates: an upper gallery, which is 50% open for vapor disengagement, and a lower plate for liquid distribution which is similar to a Model 301A. Each plate requires a separate support ring.

The two-phase feed is fed to the upper gallery where the vapor disengages from the liquid. A 350 Inlet Deflector Baffle is typically used in front of the feed nozzle to deflect the feed around the tower wall. Holes in the bottom of the upper gallery transfer the liquid to the lower plate where the liquid is distributed over the packing. The upper gallery height is typically 12 inches, and the spacing between the two plates is also 12 inches. The Model 300 Flashing Feed Distributor is fabricated in sections for passage through column manways.

A Narrow Trough Liquid Distributor Equipped with Drip Tubes.

Lateral Type Liquid Distributor/Spray Type Liquid Distributor

Orifice Riser Distributor

These are commonly used in column diameters up to 48 inches.  The number and size of orifices and risers will vary according to the gas and liquid flow rates. This style of design is limited to a 4to1 turn down ratio.  Other liquid distributor types offer superior turn down ratios.

Trough Distributor Traditional Weir V- trough

distributors are used in column 36 inch and larger.

They offer a limited range of liquid and gas flow turn down at 4to1 ratio.

The liquid is delivered by feed pipes over the parting boxes. The parting boxes feed knotched weirs which distribute the liquid evenly over the packing bed below.

The units are not subject to fouling and can handle large amounts of suspended solids.

ACS High Performance Distributors

Low liquid flow rates, high liquid viscosity and high turn down.

Type R Distributors

Their type R is a channel type distributor with  the liquid over flowing through tubes welded into the channel. Solids do not interfere with this design. Turn down is 1:3, with one stage and 1:10 with a two stage design.

ACS/ Montz Liquid Distributors

The patented Type S design is similar to type R except that at the bottom of the overflow tube the flow is directed to a number of metal fingers which split the liquid flow into a number of smaller streams.  This provides excellent distribution for low liquid density applications

AccuFlow™ Inlet Diffusers

When a simple inlet diffuser is not sufficient to provide primary removal of entrained liquids. When the Force of Inertia is less than 2,500 lb/ft2s , then simple diffusers are satisfactory.

Bed Supports and Limiters

ACS designs it bed supports for tower packing to allow for maximum open area with high liquid and vapor flow.

Bed limiters and supports are made in bolt together sections to easily pass through tower man ways. Exact screen, holes, and expanded metal patterns are designed in accordance with packing style.

Redistributor Type

Liquid collector trays are arranged between two packing bed sections in a tower. The liquid trickling down is collected by the liquid collector tray and from here it can be returned to a liquid distributor or in the area of the liquid collector tray it is also possible to install liquid/vapor feeds or liquid/vapor draw offs