Download Crude Tower Simulation-AspenPlus v8.6 PDF

TitleCrude Tower Simulation-AspenPlus v8.6
TagsChemistry Distillation Chemical Process Engineering Applied And Interdisciplinary Physics Energy And Resource
File Size6.1 MB
Total Pages53
Document Text Contents
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Crude Tower Simulation – Aspen Plus v8.6

Steps to set up a simulation in Aspen Plus v8.6 to model a crude tower system consisting of:

 Crude Oil Preheat Train
 Atmospheric Crude Tower
 Vacuum Crude Tower
 Debutanizer to stabilize the overhead naphtha stream from the Atmospheric Crude

Tower

The feedstock to the crude system will be an equal mix of Light, Medium, & Heavy Crude
oils.

When the simulation is set up the overall PFD should look like the following figure.




Create new simulation file

Start the program from Start, All Programs, Aspen Tech, Process Modeling V8.6, Aspen Plus,
Aspen Plus V8.6. When the program opens choose the new button. there are several
templates that can be chosen. Select the Refinery option in the left‐hand column & chose the
Petroleum with English Units template. Press Create.

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Save as you go

One of the things you’ll want to do is to save your files as you go. The first time you go to
the Save As option you’ll have several formats from which to choose. There are advantages
to save as the Aspen Plus Backup (BKP) format – the files tend to be smaller & less likely to
become corrupted.

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Table 4. Definitions for Atmospheric Distillation Column

Type  Operating Parameter

Trays & Efficiencies  50 trays. Numbering from top:
Trays 1 to 6: 80% 
Trays 7 to 10: 50% 
Trays 11 to 16: 70% 
Trays 17 to 30: 50% 
Trays 31 to 39: 30% 
Tray 40: 100% 
Trays 41 to 50: 30% 

Condenser Type  Total Condenser; 130°F (approximate)
Distillate product 410°F D86 T95; 30,200 bpd (approximate)  

Reboiler Type  None, Direct Fired Heater

Pressures  Condenser: 4 psig
Top Tray: 12 psig 
Bottom Tray: 22 psig 

Temperatures  Top Tray #1 250°F (estimate)
Bottom Tray #50 650°F (estimate) 

Feed Locations  Crude oil to Tray #40
Stripping Steam at bottom (Tray #50) – 20,000 lb/hr @ 500°F, 150 psig 

Feed Heater  Outlet @ 25 psig & 635°F
Desire is 2,500 bpd overflash (liquid rate from tray above feed, Tray #39) 

Side Strippers  Kerosene Stripper
10 trays @ 30% efficiency 
Kerosene draw from Tray #10, vapor returned to Tray #6 
Stripping steam @ bottom (Tray #10) – 2500 lb/hr @ 500°F & 150 psig 
Kerosene product 525°F D86 T95; 8800 bpd product (approximate) 

  Diesel Stripper 
10 trays @ 30% efficiency 
Diesel draw from Tray #20, vapor returned to Tray #16 
Stripping steam @ bottom (Tray #10) – 2500 lb/hr @ 500°F & 150 psig 
Diesel product 645°F D86 T95; 10,240 bpd product (approximate) 

  AGO Stripper 
10 trays @ 30% efficiency 
AGO draw from Tray #30, vapor returned to Tray #26 
Stripping steam @ bottom (Tray #10) – 2500 lb/hr @ 500°F & 150 psig 
AGO product 750°F D86 T95; 3835 bpd product (approximate) 

Pumparounds  Kerosene Pumparound
Draw from Tray #10, returned to Tray #7 
25,000 bpd flow, 200°F return temperature 

  Diesel Pumparound
Draw from Tray #20, returned to Tray #17 
15,000 bpd flow, 250°F return temperature 

  AGO Pumparound
Draw from Tray #30, returned to Tray #27 
10,000 bpd flow, 350°F return temperature 



Aspen Plus has a specific module for efficiently solving crude tower type problems, the
PetroFrac model (not RadFrac). On the Columns tab select the list arrow for PetroFrac. Now

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we can choose an icon that will most closely represent out column; choose CDU10F, the one
with a condenser, fired heater, 3 pumparounds, & 3 side strippers. (This choice only
changes the icon, not the ability to specify side operations or the number of each). Place on
the flowsheet & name ATMCOL. Highlight the icon on the flowsheet & grab a corner to
resize (make it much bigger than the icons representing the preheat train).







Let’s make the stream connections. Right‐click WARMCRD2, select Reconnect Destination,
& connect to ATMCOL. Create the following additional streams & connect to ATMCOL:

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Now let’s look at the LVGO results. For 5,000 bpd LVGO rate the D1160 T95 value is too
low. Since the T95 value is too low, we will have to increase the LVGO draw rate to try to
meet this spec. However, there is only 3,518 bpd runback above the feed tray, so we
normally think that can’t raise the rate above this amount. However, we can actually raise it
considerably & not dry up the top of the Vacuum Column. Note that if we raise the LVGO
spec to 4,000 bpd we can do this and actually increase the runback. How? Because the
HVGO rate decreases by more than 3,000 bpd to keep its T95 spec. So let’s apply the LVGO
T95 spec; now we’ve made both T95 specs without drying up the top of the Vacuum
Column.

The final spec that we need to achieve is the liquid rate from above the feed tray. The
current rate is 6,776 bpd, higher than necessary. We can reduce this rate by reducing the
feed heater’s outlet temperature (which will reduce the amount of the feed vaporized). We
can adjust the feed heater temperature manually to 739.5°F and get a liquid runback rate of
2,990 bpd (just a little bit too low). Can we adjust this automatically to determine the actual
temperature? We could add a design spec to modify the furnace temperature make the
liquid rate from Tray #11; in past experience this will tend to crash the program. Instead
we will use the built‐in facility to modify the furnace’s outlet conditions by specifying the
fractional overflash in the column. Since the total standard flow to the column is 53,632
bpd then 3,000 bpd overflash means a fractional value of 0.05594. Making this specification
will give the correct overflash value & results in a furnace outlet temperature of 739.56°F.

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The results of all of these steps are summarized in the following table.


Vacuum Column Results When Applying Different Specs

LVGO Rate 
[bbl/day] 

LVGO D1160 
T95 
[°F] 

HVGO Rate 
[bbl/day] 

HVGO D1160 
T95 
[°F] 

Slop Was Rate 
[bbl/day] 

Runback from 
Tray #11 
[bbl/day] 

1,000   768.4  21,000  924.4 1,000   186,810
1,000   797.1  30,676 1050  1,000   3,050
4,000   825.9  27,220 1050  1,000   3,562
16,487  915   13,855 1050  1,000   6,776
16,835  915   13,185 1050  1,000   2,990
16,808  915   13,212 1050  1,000   3,000

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