Advanced Plate Desing

8/12/2019 Advanced Plate Desing

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Advanced Distillation with Aspen Plus Sizing and Rating of Trays and Packing

Aspen Technology, Inc.3 1 2002 AspenTech. All Rights Reserved.

2002 AspenTech. All Rights Reserved.

Sizing and Rating of Traysand Packing

Advanced Distillation with Aspen Plus


Lesson Objectives

Learn about: Tray Efficiencies Sizing (Design) of Trays and Packing Rating of Trays and Packing


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RadFrac Efficiencies

Efficiency type Overall efficiency Vaporization efficiencies Murphree efficiencies

Can be specified Overall By stage

For column sections For individual components


Overall Efficiency

Direct conversion of actual trays to theoretical plates.

Not directly input to model; instead Overall Efficiencysets the number of stages in the RadFrac block.

Example: Column with condenser, reboiler and 30 trays At 70% efficiency, 30 trays = 21 theoretical stages Add stages for condenser and reboiler => 23 total

Most common, but least flexible method.


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Vaporization Efficiency

At equilibrium:

With efficiency:

Efficiency should be different for different components.

As decreases, the vapor pressure must increase whichmeans that the temperature must increase.

Using vaporization efficiency alters the T profile and thismay alter relative volatility.

In general it is better to use Murphree efficiencies.

iiii

iii

x K y x K y

=

=


Murphree Efficiency

1,,,

1,,,

+

+

=

ji y ji x ji K ji y ji y M

ji Eff

Strictly, this is a Murphree vapor efficiency.

Subscripts are i for components and j for stages.

Many correlations exist for Murphree efficiencies


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Specifying Efficiencies in the Column

RadFrac Efficiencies Options sheet

Do not specify efficiencies in both the column and in thetray rating forms


The Problem with Efficiency

Efficiencies vary enormously they can be under 10% orover 100%.

Efficiencies vary with composition, with purity, and withlocation in the column.

Efficiencies are different for different components.

Next to physical properties, this is the most importantthing to know to successfully model a column.


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Determining Column Efficiency

Previous experience. Be sure experience is comparable

Generalized correlations.

Fit to plant data. Use Data-fit to regress Murphree efficiency to data

RateFrac can be used to calculate efficiencies. RateFrac calculates actual separation Efficiency backed out from calculated compositions

Vendor packages.


HETP

Comments similar to those for tray efficiency It is important It is hard to know well

RateFrac can be used to calculate HETP.

RateFrac calculates actual separation for specified height ofpacking

Separation is converted to NTU, and NTU to HTU

Use of vendor data is common.


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Sizing and Rating for Trays and Packing (1)

Aspen Plus has extensive capabilities to size, rate, andperform pressure drop calculations for trayed andpacked columns.

The calculations are based on vendor-recommendedprocedures when available. When vendor proceduresare not available, well-established literature methods areused.

You can use the computed pressure drop to update thecolumn pressure profile.



Rating Mode Specify column section diameter and other tray or packing

details. Model calculates performance and hydraulic information such

as flooding approach, downcomer backup, and pressure drop.

Sizing Mode Model determines column diameter to satisfy the flooding

approach or pressure drop* specified for each stage. Thelargest diameter is selected.

*pressure drop specification valid for packed columns only


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For sizing and rating calculations, column is divided intosections

Each section can have a different tray type, packing type, anddiameter.

The tray details can vary from section to section. A column can have an unlimited number of sections. You can size and rate the same section with different types of

trays and packing.



Aspen Plus calculates sizing and performanceparameters such as:

Column diameter Flooding approach or approach to maximum capacity Downcomer backup

Pressure drop

These results are based on: Column loadings (vapor and liquid traffic) Tray geometry or Packing characteristics Transport properties


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Use the following Tray/Packing forms to enterspecifications:

Tray Sizing Tray Rating Pack Sizing Pack Rating

These capabilities are available in the following columnunit operation models:

RadFrac MultiFrac PetroFrac


Example: RadFrac Tray Rating

Using the MEG column example, add tray ratingcalculations for the following configured trays:

All Bubble Cap TraysOne pass trayTray Spacing: 2 ftDiameter: 5 ftCap diameter: 3 in

FILENAME: EX1B-MEG-COL-TRAYRATE.BKP


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Tray Types

You can choose from the following five commonly-usedtray types:

Bubble caps Sieve Glitsch Ballast

Koch Flexitray

Nutter Float Valve


Packing Types

Aspen Plus can model a variety of random packings.

You can also use any of the following types of structuredpackings:

Goodloe

Glitsch Grid

Norton Intalox Structured Packing Sulzer BX, CY, Mellapak, and Kerapak Super-Pak and Ralu-Pak Koch Flexipac, Flexeramic, Flexigrid


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Trays (1)

When specifying Weir heights, cap positioning, and number ofvalves:

For Specify

One-pass tray A single value

Two-pass tray Up to two values, one for each panel A and B

Three-pass tray Up to three values, one for each panel(A, B and C)

Four-pass tray Up to four values, one for each panel(A, B, C and D)


Trays (2)

The values for the number of caps and number of valvesapplies for each panel. For example, two -pass trayshave two A panels for tray AA, and two B panels for trayBB. Therefore, the number of caps per panel is thenumber of caps per tray divided by two. Similarconsideration is necessary for three- and four-pass trays.

If you specify only one value for multi-pass trays, thatvalue applies to all panels.


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Two Pass Tray

DC-

WTOP

DC-CLEAR

DC-CLEAR

Panel A

Panel B

WEIR-HT

DC-HT

DC-HTDC-WBOT

DC-WBOT

Tray AASideDowncomer

Tray BBCenter Downcomer

Below

CTR. DC

CTR. DC

~

~

~

~

~ ~

DC-WTOP

Column Diameter

O u t

l e t W e i r

L e n g

t h


Three Pass Tray

DC-WTOPDC-WBOT

DCOFPanel A. B. C.

Panel A. B. C.

Panel C. B. A.

BA C

DC-WTOP DC-WTOP

B A

OFF-CTR.DC

OFF-CTR.DC

WEIR-HTDC-HT

DC-CLEAR

Column Diameter

O u t

l e t W e i r

L e n g

t h


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Four Pass Tray

OFF-CTR.DCOFF-CTR.DC

SIDE DC

CTR.DC

DC-WTOP DC-WTOP

WEIR-HTDC-HT

DC-WBOTDC-WBOT

Panel A. B.

Panel C. D.

Panel A. B.

DCOF

DC-CLEAR D D C

A AB B

Column Diameter

O u t

l e t W e i r L e n g t

h


Specifying Efficiencies in Tray Rating (2)

If specifying Murphree or Vaporization efficiency, each stage inRadFrac corresponds to one actual tray. Calculated pressure dropswill be correct.

If using Overall efficiency, each stage in RadFrac will correspond tomore than one physical tray. To calculate the column pressure drop,

the assumed overall efficiency must be specified on the Tray RatingDesign/Pdrop sheet.

Specify efficiency on either the Efficiencies form or on the TrayRating form but not both.


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Specifying Efficiencies in Tray Rating (2)

Specified on Tray Rating Design/Pdrop sheet when columnsimulation is based on overall efficiency.


Example: RadFrac Pack Sizing (1)

Working with EB/Styrene example, add Packed Column Sizinginformation:

Packing Type Norton IMTP 2 in.

HETP 1.5 ft.

Approach to Flooding 80%

Maximum Pressure Drop 55 torr

FILENAME: EX1A-EBSTRYRENE-PACKSIZE.BKP


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Packed Column Sizing Input:





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Packed Column Sizing Results:


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Packed Column Sizing Results:


Workshop 2A: HCL Column Rating (1)

Use Workshop 1, perform tray rating. Tray details:Tray type Nutter float Valve BDHNumber of passes 2Column diameter 7 ft.

Actual number of trays 66Tray spacing 1.5 ft.Tray efficiency 0.5Weir height 2 in.Valve density 12/sq.ft.Downcomer clearance 1.5 in.Side downcomer width 8.7 in.Center downcomer width 7.1 in.

FILENAME:WS2A-HCLCOL -RATE.BKP


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Workshop 2A: HCL Column Rating Results (2)

Condenser Duty -9.837 MMBtu/hr Reboiler Duty 10.927 MMBtu/hr Maximum flooding factor 0.329 (Stage 2)Maximum DCBA 0.384 (Stage 32)Predicted P drop 5.65 psi


Workshop 2A: HCL Column Rating Results (3)


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Workshop 2B: Increased Throughput (1)

HCL-COL

FEEDB

HCL-PROD

VCM-EDC

MULT

FEEDA

Sensitivity AnalysisStudy the effect of an increase in flow rateon the flooding approach and downcomer/backup tray spacing. Consider increases of5 to 50%. Use a Multiplier block to handle thefeed variation.

FILENAME:WS2B-HCLCOL-FLOW.BKP


Workshop 2B: Increased Throughput (2)

Results:

Advanced Plate Desing

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