packed bed2
DESCRIPTION
packed bed column internalsTRANSCRIPT
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