random packing - · pdf filespecification and installation of the random packing and...

Random Packing

www.hatltd.comDS-RP-01 Rev 3

AlphaPACK® DESIGN SHEET

OVERVIEW

Packed beds formed by dumping bulk random packing elements of consistentshape and size will provide the consistent surface and voidage characteristicsnecessary for predictable mass transfer operations. To achieve optimumperformance benefits from a packed bed, proper consideration of the design,specification and installation of the random packing and associated columninternals is required.

SPECIFICATION OF RANDOM PACKING

HAT manufactures a comprehensive range of AlphaPACK™ standard and highperformance random packings as listed below.

Standard Types:R+ Raschig Rings(Ceramics, Glass, Metals,Carbon, Plastics)

P+ Pall Rings(Ceramics, Metals, Plastics)

S+, S++ Saddles(Ceramics, Plastics)

High Performance Types:

C+ Rings(Metals, Plastic)I+ Rings(Metals)

L+, Q+, N+ Packings(Plastics)

Random Packing



The above packings are available in several sizes as indicated on our design sheetsto suit most commercial applications. They range in size from 6mm to 90mm orequivalent. It is an essentially a design consideration in specifying a packing sizebased on capacity and efficiency requirements. The nominal packing size specifiedshould however not be greater than 1/10th of the column diameter.

The packing is usually specified in the lowest cost material of manufacture that willsatisfy temperature and corrosion requirements. Some of the most commonmaterials listed in order of relative cost are:

Polypropylene (mainly aqueous systems up to 100 deg. C)Carbon steel (non-corrosive hydrocarbon systems)Ceramic (sulphuric acid & nitric acid absorbers)Stainless steels (most hydrocarbon systems)PVDF, PFA (corrosive aqueous systems up to 150 deg. C)PVC / C-PVC (corrosive aqueous systems up to 90 deg. C)

Other more exotic materials that may be specified include aluminium, Monel,titanium and carbon.

Random Packing



PACKED BED DESIGN

Hydraulic operation of packed beds can be accurately rated using correlations thathave been developed from actual performance data. Design data for standard"generic" random packing is widely available in the public domain.

The "Generalised Pressure Drop Correlation" is the most frequently publisheddesign tool for calculating packed bed diameter and determining the operatingcapacity for most "generic" random packings based upon a characteristic "PackingFactor" for each packing.

Where reliable performance is required in high pressure hydrocarbon systems, morespecific design models should be employed. HAT are able to provide hydraulicrating sheets indicating the calculated pressure drop, liquid hold-up and % flood forany packed bed providing that sufficient process data is made available. As aminimum, we would require a profile of internal vapour and liquid loads and actualdensities as well as liquid surface tension and viscosity.

HAT have computer programs to predict mass transfer efficiency and calculate thepacked bed height for the most common absorption, stripping and heat transfersystems where sufficient, reliable data is available from which to compile designmodels. Multicomponent distillation systems should be simulated to evaluate thenumber of theoretical trays required as well as providing tray by tray vapour andliquid loads and physical properties. In most cases we can predict suitable HETP'sand calculate packed bed height from this data. For most "generic" type packingsin distillation service, separating efficiency will deteriorate when the bed heightexceeds the lower of 6 x column diameter or 6 metres due to the effects of liquidmaldistribution.

Performance data used to develop the design models used by HAT are in mostcases sourced from well engineered operating columns with associated internalsproperly designed to be compatible with the duty.

Random packing has had wide application throughout the industry for severaldecades. As a result, performance characteristics are well known and design datareadily accessible from public domain sources. Most generic column packings canbe manufactured in a wide range of commercially available materials. TheAlphaPACK range manufactured by HAT conforms to accepted industry standardsas listed below:

Random Packing



PACKINGTYPE

MATERIAL SIZE MASS(kg/m3)

SURFACE(m2/m3)

VOIDAGE%

PACKINGFACTOR

R+ Ceramic 15mm 825 290 62 540Raschig Ring 19mm 840 260 68 255

25mm 650 190 72 16038mm 600 135 74 9550mm 570 92 76 6575mm 560 79 78 36

R+ Carbon 12mm 679 360 60 450Raschig Ring 18mm 590 240 66 260

25mm 600 195 65 18037mm 590 140 65 12550mm 530 98 68 65

P+ Stainless 16mm 580 340 93 70Pall Ring Steel 25mm 435 207 94 50

38mm 355 128 95 2850mm 270 102 96 2090mm 230 85 97 16

C+ Stainless No.2 227 145 96 22Ring Steel No.3 228 103 97 14

No.4 170 80 96 10I+ Stainless No.25 218 226 97 41Ring Steel No.40 153 151 97 25

No.50 156 100 98 16No.70 117 60 98 13

P+ Polypropylene 16mm 115 340 87 97Pall Ring 25mm 80 196 90 64

38mm 60 150 91 3650mm 60 106 91 2590mm 90 85 92 17

S+ Ceramic 19mm 590 335 71 145Saddle 25mm 580 250 77 92

38mm 600 150 80 5250mm 560 110 79 4075mm 540 96 80 22

S+ Polypropylene No.1 85 190 90 36Saddle No.2 57 95 93 21

No.3 45 65 94 16L+ Polypropylene No. 2 99 223 89 21Pack No. 3 67 144 92 14

N+ Polypropylene No. 2 82 180 91 16Pack No. 4 50 131 94 8

Q+ Polypropylene No. 4 34 98 96 7Pack No. 7 35 98 96 7

Random Packing



PACKED BED CAPACITY

Flooding in packed beds is characterised by unstable operation and loss ofefficiency. The optimum loading point for most new columns is about 80% of theloading at the flood point. Separation efficiency will usually deteriorate rapidly atloadings below about 20% of the flood point, particularly in distillation systems.

The flood point for packed beds of generic packings can be estimated using thefollowing correlation:-

CFLOOD = 1 / {3.6 . F . e (S . X 0.5)} (m/s)and:

% Flood = Cs x 100 (at constant L/G)CFLOOD x System Factor

where:

X = (L/G) . (G/L)0.5 (dimensionless)

Cs = vs . {G / (L – G)}0.5 (m/s)

L = Liquid Rate (kg/s)G = Gas Rate (kg/s)G = Gas Density (kg/m3)L = Liquid Density (kg/m3)vs = Superficial Gas Velocity (m/s)F = Packing Factor (from table)S = Packing Shape Constant

The following Packing Shape Constants should be used for common packings:-

1.25 for metallic packings1.35 for thermoplastic packings1.55 for ceramic packings

Random Packing



ESTIMATION OF PRESSURE DROP

The restriction to vapour flow across a packed bed causes a pressure drop which isnormally relatively low. Nevertheless the effect of pressure loss on overall plantdesign and operating costs will often need to be evaluated and so it is necessary tobe able to estimate this pressure loss over the expected range of operatingconditions.

Pressure drop is a function of vapour and liquid rates as well as the packing shapeand size. Pressure drop curves for most packings are widely published. Forestimating purposes it is usually more convenient to use a "Generalised PressureDrop Correlation" as shown below which applies a characteristic "Packing Factor" tothe ordinate value to provide a set of pressure drop curves which are accurate towithin 20% for most random packings.

GENERALISED PRESSURE DROP CORRELATION

0.01 0.1 10.01

0.1

1

F low Parameter - ( X )

CAP

AC

ITY

FACT

OR

=C

².F.ƒ

Data A

Data B

Data C

Data D

Data E

Data F

Data G

Data H

GENERAL PRESSURE-DROP CHART

PressureDrop(Pa/m)

1000

500

300

200150

10075

50

NOM ENCLATURE:Capacity Factor = C2 .F.ƒ

Flow Parameter = L/G x (dg/d l)0.5

C = Vs x (dg/(dl - dg ))0.5 (m/s)ƒ = µ0.1 x (1000/dl)

0.9

Vs = Superf ic ial Gas Veloc ity (m/s)F = Packing Factor

µ = Liquid V iscos ity (cp)

L = Liquid Rate (kg/s)G = Gas Rate (kg/s)dg = Gas Density (kg/m3)

dl

= Liquid Density (kg/m3 )

Random Packing



DELIVERY AND INSTALLATION

An advantage of random column packing is that being mass produced standardelements, delivery times are relatively short. Since the same packing can be used inmany applications irrespective of column size, HAT holds a substantial inventory ofmost AlphaPACK random column packings for immediate shipment at itswarehouses.

Random column packing is packaged and shipped by volume. A volumeadjustment factor must be applied to the calculated column geometric volume toestimate the shipping volume required to properly fill a packed bed to account foredge and settling effects. The volume adjustment factor depends upon the packingshape and size and the bed diameter.

A contingency allowance for installation losses, typically around 5%, should beadded to the shipping volume calculated above.

Strict conformity with recommended installation procedure is necessary to ensureconsistent duplication of design performance. Installation techniques that result ininstallation crew walking on or raking the packing must never be employed.Incorrect installation procedures can result in substantial packing shortfall (i.e.installed volume not sufficient for the required bed height resulting in performancelosses).

High Performance Packing



OVERVIEW

HAT supplies a number of high performance random packings developed for use in bulk masstransfer operations – often at low pressure or for higher capacity requirements wheretraditional designs result in larger equipment sizes such as:

Incinerator flue gas scrubbing and quench towers Refinery distillation and vacuum towers Air scubbers for odour removal and contaminated water stripping Glycol and Amine regeneration systems Biological treatment scrubbers

The following summary illustrates our core AlphaPACK range of metal and polyproplyene,high performance packings widely used in the industry, successfully competing againstproducts such as Jaeger Tri-Pack, Koch IMTP and Snowflake and Sulzer Nutter & I Rings.

High Performance Types:

C+ RingsThis general purpose, high performanceAlphaPACK C+ metal packing offersexcellent balance between efficiency,capacity and pressure drop.

I+ RingsWith lower surface area per unit volumethan many other metal packings,AlphaPACK I+ packing offers reducedpressure drop, excellent foulingresistance and high flow capacity.

L+ PackingThis general purpose, high performanceAlphaPACK L+ plastic packing offersexcellent balance between efficiency,capacity and pressure drop.

N+ Pack ingWith high surface area per unit volumethan nost other plastic packings,AlphaPACK N+ packing offers reducedpacked bed height, excellent biofilmingand integral mist elimination.

Q+ PackingExploiting the multi drip-point technologyto provide a high surface area for masstransfer at low pressure drop,AlphaPACK Q+ packing performance isunmatched in air scrubbers.




AlphaPACK Q+

High capacity Q+ packing creates excitingnew possibilities in packed tower design.Its patented structure uses drip points andgas turbulence to create millions of smalldroplets, multiplying the surface area forgas-liquid contact with minimal resistanceto gas flow. AlphaPACK Q+ providesefficient heat or mass transfer with lowpressure drop.

Q+ saves electricpower by reducingthe load on airblowers.

Q+design reducesbio-fouling andscale build-upmeaning reducedmaintenance time.

Unique drip point technology

AlphaPACK Q+ can be used at velocitiesfrom 1 to 4 m/s, so scrubbers and gascooling towers can be designed at wellabove conventional velocities withoutsacrificing efficiency. Capital costs can becut by building smaller diameter columns,often with smaller pumps and misteliminators.

Older equipment using conventionalpackings can be retrofitted with Q+ packingto obtain additional capacity at a fraction ofthe cost of another tower.

Packing Physical CharacteristicsNominal Size (inch)Void Fraction (%)Weight (kg/m3)Surface Area (m2/m3)No of pieces/m3

Packing Factor (m-1)No of drip points/m3

7”96.135.398.417723

3.9x105

4”96.333.698.41165

233.9x105

Pressure Drop ComparisonAmbient Air/Water System at 400 litres/min/m2

0

10

20

30

40

50

60

70

80

90

100

1.00 1.50 2.00 2.50 3.00

Superficial Gas Velocity, m/s

Pre

ssur

eD

rop

,mm

H2O

/m

2" Pall Ring

2" Tellerette

2" Tri-Pack

AlphaPACK Q+ 4"

The following table illustrates the efficiencyof Q+ packing in terms of the HTU inmillimetres at different liquid loadscompared with the above packings:

Liquid Rate(lit/min/m2)

200300400

2” Tri-Pack

475410330

2” PallRings

435360300

4” Q+Pack

385330295

Basis: Scrubbing SO2 with buffered causticat 2.0 m/s air velocity in 1.8m dia column.

AlphaPACK Q+ is available inpolypropylene as standard, but also in glassfilled polypropylene (for greater packedheight strength) and PVDF.

4” Q+ Packing




AlphaPACK I+AlphaPACK I+ random packing has uses in awide range of applications from very low liquidrate services, such as gas/glycol treating, tohigh liquid rate uses, such as hot liquorabsorbers and NGL distrillation. Its lowerpressure drop, combined with high masstransfer efficiency, provides superiorperformance in low liquid rate vacuum systemstoo.

I+ saves electricpower by reducingthe load on gascompression.

I+ design reducesfouling and scalebuild-up meaningreducedmaintenance time.

Excellent low pressure drop and low fouling design

The low pressure drop provided byAlphaPACK I+ Rings makes them a goodchoice for foaming systems. The presence offoam in a packed bed results in a significantpressure drop increase. High pressure dropincreases the amount of foam generation dueto the resistance of the vapour on the liquidphase. Therefore, it is desirable to design thepacked bed with low pressure drop in foamingsystems.

Older equipment using conventionalpackings can be retrofitted with I+ packingto obtain additional capacity at a fraction ofthe cost of another tower.

Packing Physical CharacteristicsTypical Pressure Drop Curves

The following table illustrates the efficiency ofI+ packing in terms of the HETP in millimetresat design loading for different sizes of rings (adesign margin should be added):

Basis: 1. Scrubbing air with buffered caustic2. Glycol (MEG) regeneration

AlphaPACK I+ is available in grade 316stainless steel as standard, but is also madein a range of other metals and specilaistalloys upon request.

AlphaPACKI+ Ring

Nominal

Size, mm

PF

m-1Weight

kg/m3S Area

m2/m3Void

%

Qty

000/m3

# 15 60 283 325 96.6 360

# 25 41 224 245 97.2 158

# 40 24 153 169 98.1 47

# 50 18 166 81 98.0 15

# 60 15 137 66 98.3 9.5

# 70 12 117 48 98.5 4.6

# 15

3001

5002

# 25

370

620

# 40

440

730

# 50

580

960

# 60

680

1130

# 70

830

1380




AlphaPACK C+

AlphaPACK C+ Rings are amodern, well established randompacking with an aspect ratio of 0.3and this minor feature has aprofound effect on performance.

The C+ Ring has:

High mass transfer efficiency

High capacity

Low pressure drop

Wide turndown ratio

Improved fouling resistance

Packing

Size

Packing

Factor

Weight

kg/m3

Surface area

m2/m3

1 40 280 251

1.5 29 280 188

2 22 227 145

2.5 19 234 123

3 14 228 103

4 10 170 80

Carbon Packing



CARBON RASCHIG RINGS haveassumed an important functional role in theworking of absorption towers, distributioncolumns, scrubbers, etc, in chemical plantsand refineries. With the growth of chemicalindustries, the need for versatile RaschigRings has also grown proportionately.

AlphaPACK R+ Carbon Graphite RaschigRings exhibit such remarkable versatilitythat these find increasing usage inchemicals plants.

Carbon/Graphite Raschig Rings areavailable in the following sizes and physicaldata.

Carbon/Graphite Raschig Rings arecharacterised by unique properties asfollows:

1) Because of their high thermalconductivity they are resistant to severethermal shocks.

2) Low thermal expansion.

3) They are resistant to practically allcorrosive chemicals over a wide range oftemperatures - these include almost allacids, alkalis, alcohols, organic solvents,inorganic compounds and salts.

4) If required these can also withstandhigher process temperatures. Imperviouscarbon rings are superior in oxidisingconditions.

5) Because of their excellent wettability byall liquids (water, inorganic salt solutions,organic solvents), they exhibit maximumefficiency during operation.

This type of tower packing is selectedmainly based on the chemical conditionsinvolved as well as for reasons ofmechanical strength, resistance tocorrosion and a balance of cost, capacityand efficiency.

There are fewapplications where thelow cost of carbon ringsdoes not play animportant part in itsselection.

Size (OD x L) mm 19x19 25x25 40x40 50x50 75x75

1) ID - mm

2) Qty of rings, #/m3

3) Surface area, m2/m3

4) Density, kg/m3

5) Per cent Voidage, %

12

110,000

250

545

67

18

46,500

190

433

74

28

13,800

125

545

67

38

5,800

95

433

74

60

1,700

62

369

78

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