1.3.6 Atmospheric Crude Column

Atmospheric Crude Column

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1 2002 Hyprotech Ltd. All Rights Reserved 1.3.6 Atmospheric Crude Column.pdf

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WorkshopAtmospheric Crude Columns are one of the most important pieces of equipment in the petroleum refining industry. Typically located after the Desalter and the Crude Furnace, the Atmospheric Tower serves to distil the crude oil into several different cuts. These include naphtha, kerosene, light diesel, heavy diesel and AGO. In this module, you will construct, run, analyse and manipulate an Atmospheric Crude Column simulation. You will begin by building a simple column and continue by adding side operations to the column.

Learning ObjectivesAfter completing this module, you will be able to: Build and converge an Atmospheric Crude Column. Use HYSYS to analyse and predict the behaviour of a simulated column. Add side operations to a column to improve operation and efficiency. Add cut point specifications to increase side product quality and quantity.

PrerequisitesBefore beginning this module you will need to know how to: Add streams and unit operations. Characterize and install a crude oil.

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Process Overview

Column Overview


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Expanding the FlowsheetLoad your Pre-Heat Train case from the Pre-Heat Train module.

Column Product SpecsBefore beginning the construction of a crude column it is useful to know the quantity of products that you can expect to get out of the column. HYSYS can present this information in a graphical format. 1. 2.The Distribution Plots tab displays a bar chart depicting how an assay would be roughly distributed in a fractionation column.

Return to the Basis Environment, enter the Oil Manager then enter Oil Environment view. Under the Cut/Blend tab, select the default crude blend and click the View button. Go to the Tables tab. This is where the information is displayed. Using the Oil Distributions Table Type and the Straight Run cut option, complete the following table:Volume % Volume in bbl.

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Component Lt St Run Naphtha Kerosene Diesel (Light & Heavy) AGO Residue TOTAL

100%

100,000 bbl

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Adding the Column Steam Feed1. Add a material stream named Btm Steam. Add the following temperature, pressure and flow rate to the steam stream:Enter... Bttm Steam 1 1380 kPa (200 psia) 3400 kg/h (7500 lb/hr) In this cell... Name Vapour Fraction The composition of H2O for all steam streams is 1.0 Mass Fraction. Pressure Temperature

Add the Atmospheric Crude ColumnThe Atmospheric Column will be simulated as a Refluxed Absorber. 1. 2.Refluxed Absorber icon

Select the Refluxed Absorber icon. The Input Expert is now displayed. Input the data as shownEnter... Atmos Tower 29 ATM Feed 28_Main TS Btm Steam Top Down Cond Duty Partial Off Gas Naphtha Partial Atm Residue

In this cell... Column Name # Stages Inlet Stream Inlet Stage Bottom Stage Inlet Stage Numbering Condenser Energy Stream Condenser Ovhd Outlets Condenser Bottoms Liquid Outlet

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Check the Water Draw checkbox and name the stream Waste Water.

The Water Draw checkbox must be checked to prevent two liquid phases being formed in the column.

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Figure 1

Crude Columns always require a water stream off the condenser.

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Move to the next page of the Input Expert. Enter the following data:Enter... 140.0 kPa (20.31 psia) 60.00 kPa (8.7 psi) 230.0 kPa (33.36 psia)

In this cell... Condenser Pressure Condenser Pressure Drop Bottom Stage Pressure Figure 2

Always provide a pressure for the stage 1 in a crude column. The column may not converge without it.

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Move to the next page of the Input Expert. Enter the following data:Figure 3

Active specifications are those values that are fixed. Inactive specifications (or Estimates) are those values that the program can adjust in order to converge the column.

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Move to the next screen of the Input Expert. Enter 0 kgmole/h in the Vapour Rate field as shown.Figure 4

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After clicking Done, you are placed on the Column Property View. Move to the Design tab and open the Monitor page.What is the current Degrees of Freedom? _______________________________

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In order to specify a volume flow rate specification, you will have to change the flow rate basis of this specification.

Specify a Distillate Rate of 150 m3/h (22,500 bbl/day). In order to set a volumetric flowrate for this specification, you must open its property view and change the flowrate type. Double-click on the specifications name and change the flow basis to Volume. For this column to solve we need to activate the Vap Prod Rate specification with a flow rate of 0. This means that the condenser will operate as a total condenser.

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10. For the column to converge, the Degrees of Freedom must be 0. This can be done by deactivating the default spec of Reflux Ratio. 11. Click the Run button to converge the column.What is the flow rate of: Naptha? _______________________ Residue? __________________________ Wastewater?____________________ Off-Gas?___________________________

Adding the Side Strippers and the Pump AroundsSide Strippers are added to the column in order to improve the quality of the three main products (Kerosene, Diesel, and AGO). There are two types of side strippers available in HYSYS: Reboiled and Steam Stripped. We will install one reboiled side stripper and two steam stripped. Pump Arounds help to improve the columns efficiency. They operate by drawing a liquid stream from one stage cooling it, and pumping it into a higher stage. In effect, this process adds to the reflux between these two stages. The first side operation of each type will be added using the side ops input expert. This tool is design to simplify the process for adding side operations to columns. 1. 2.When entering the stream names, do not enter the "@COL1" this term is added automatically by HYSYS.

On the Side Ops tab, click the Side Ops Input Expert button. The Side Ops Input Expert is really five experts in one interface. The first page of the input expert is for adding reboiled side strippers, and the other pages are for different side operations. In this part of the module, a steam stripped side stripper is the operation that we want to install. Click the Next button once to move to the appropriate input expert for this type of operation.

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Click the Add Side Stripper button, and complete the view with the following connections:Enter... AGO SS 21_Main TS 22_Main TS AGO Steam AGO Prod

In this cell... Name Return Stage Draw Stage Steam Feed Draw Product Figure 5

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Click the Install button. HYSYS will now add the side stripper and associated streams to the simulation. The next side operation that we will add is the pump around for the AGO section of the column. Again, this operation will be added by using the input expert for pump around operations. Click the Next button twice to get to the appropriate input expert. Click the Add Pump Around button to add the operation. Define it with the information shown below.Enter... AGO PA 21_Main TS 22_Main TS

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In this cell... Name Return Stage Draw Stage

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Figure 6

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Click the Install button to add this operation to the simulation.

10. Close the Side Ops Input Expert view, and return to the Monitor page of the Design tab. Here, the specifications that will govern the operation of the two side operations that were added in the previous steps will be added. In total, the side operations contribute three degrees of freedom to the column; therefore, three active specifications will be required before the column will be able to solve. 11. The three specifications that we need to add are: AGO SS Product Flow AGO PA Rate AGO PA Duty 12. HYSYS automatically creates four specifications when the side operations are added via the input expert. We only have to set the specified value for the specifications and select which ones we need as active. Set the following values for the various specifications. AGO SS Prod Flow = 30 m3/h (4500 bbl/day) - Note: change flow basis to volume before setting the value. AGO PA Rate = 200 m 3/h (30 000 bbl/day) AGO PA Duty = -3.7E7 kJ/h (-3.5E7 Btu/hr)

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13. On the Work Sheet tab, enter the following information for the AGO Steam stream:In this cell... Remember that the composition of steam streams is always 100% water. After making substantial changes to a columns design, it may be necessary to reset the specified values before the column will converge. Simply click the Reset icon. Temperature Pressure Mass Flow Enter... 150C (300F) 350 kPa (50 psia) 1150 kg/h (2500 lb/hr)

14. Return to the Design tab and Monitor page. Ensure that the Degrees of Freedom is 0. 15. Click the Run button to converge the column.

Save your case! Adding the Diesel Side-OpsThe remaining side operations (two side strippers and two pump arounds) will be added without using the input expert. 1. In the Column Environment, on the Side-Ops tab, select Side Stripper and click the Add button. Enter the following information:Enter... Diesel SS 16 17 Volume (select this radio button) Diesel Prod 130 m3/h (19,250 bbl/d) Steam Stripped Diesel Steam

In this cell... Name Return Stage Draw Stage Flow Basis Product Stream Draw Spec Configuration Steam Feed

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Click the Install button when you are finished and close the view after.

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On the Side Ops tab, select Pump Arounds and click the Add button. Enter the following information:Enter... Diesel PA 16 17

In this cell... Name Return Stage Draw Stage

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Click the Install button, and you will be moved to the second part of the installation process. Under the first active and second active specs, add the following information to complete the specifications for this pump around.Enter... 200 m3/h (30,000 bbl/d) Note: the flow basis must be changed to volume. -3.7e7 kJ/h (-3.5e7 Btu/hr) Note: the specification type must be changed to Duty instead of the default dT.

In this cell... Diesel PA_Rate (PA), Flow Rate

The specification type for the second active spec must be changed to Duty instead of the default dT. The active spec can be changed by double-clicking the name of the spec.

Diesel PA_Duty (PA), Duty

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On the Work Sheet tab, enter the following information for the Diesel Steam stream:Enter... 150C (300F) 350 kPa (50 psia) 1350 kg/h (3000 lb/hr) 100% H2O

In this cell... Temperature Pressure Mass Flow Composition

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Return to the Design tab and Monitor page. Ensure that the Degrees of Freedom is 0. Click the Run button to converge the column.

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Adding the Kerosene Side-OpsAgain the Side-Ops installation procedure can be repeated to install the Side-Ops for the Kerosene product. 1. Add another Side Stripper with the following information:Enter... Kerosene SS 9 8 Kerosene Prod 62 m3/h (9300 bbl/d) Reboiled 0.75

In this cell... Name Draw Stage Return Stage Prod Stream Prod Rate Configuration The boilup ratio is the ratio of the vapour to the liquid leaving the reboiler. Boil Up Ratio

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Add a third Pump Around with the following information:Enter... Kerosene PA 9 8 330 m3/h (50,000 bbl/d) -4.5e7 kJ/h (-4.2e7 Btu/hr)

In this cell... Name Draw Stage Return Stage Flow Rate Duty

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Return to the Design tab and Monitor page. Ensure the Degrees of Freedom is 0. Click the Run button to converge the column.What is the flow rate of Naphtha?______________ Residue?_______________

Save your case!

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Adding an Energy Stream to the ColumnIn modelling this column, a refluxed absorber was chosen, which does not have a reboiler at its base. However, a side exchanger can be simulated on Stage 28 by attaching an energy stream to the bottom of the column and specifying a duty or another parameter. 1. 2.Energy Stream icon (Red)

On the PFD in the parent environment, create a new Energy stream with the name Trim Duty. Do not specify a duty for this stream. Double-click on the Column and click on the Connections page on the Design tab. In the Inlet Streams group, add the Trim Duty stream in a new External Stream cell, and specify stage 28 as its feed stage.

Adding an Energy stream that is not fully defined creates one degree of freedom for the column. Therefore, we need to add another specification to the column in order for it to solve. 3. 4. 5. Go to the Monitor page and click the Add Spec button in the Specification group. Choose Column Liquid Flow from the list that appears. Click the Add Spec button. Enter the data as shown (if using Field units, the flow value will be 3500 bbl/d) and make the specification Active.Figure 7

The Net Liquid Flow spec is used to represent the overflash. A typical rate of the overflash specification is 3.5 LV% of the crude rate: (660 m3/hr* 3.5% = 23 m3/ hr).

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Change the Kerosene SS BoilUp Ratio specification to an Estimate only. This specification could conflict with the one that was just created. However, we still need a way to define the Kerosene SS Reboiler. A duty specification will be used for this purpose.

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Add a Column Duty specification with the information as shown (7.5e6 Btu/hr), and make the specification Active:Figure 8

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Return to the Monitor page and ensure that the Degrees of Freedom = 0. Click Run to converge the column.

Any User Property can be used as a Column specification

Remember that in module 4, when we characterized the oil, we included the sulfur curve. To see how much sulfur contains any stream theres a utility called User Property. Attach it to Diesel Prod stream.What is the Sulfur content of the Diesel Product? ____________________________________________________________________

Save your case!

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Exploring with the SimulationMaximizing the Naphtha ProductThe column is now solved using product flow rate specifications. These flow rate values were obtained from the Distribution Plot in the Oil Manager (remember the exercise on page 5 of this module). Flow rate specifications are probably the easiest to understand conceptually; however, they are also the most inflexible way of defining the column. If the crude flow rate were to change substantially, for example, the column may fail to converge because the material balance would not compute. As another example, it is desired to maximize the production of a particular cut, such as Kerosene. One could simply increase the Kerosene flow rate spec but this may produce a negative consequence as the quality of the product may be reduced. Therefore, another method of defining the streams may be better in these cases. One of the most common ways of doing this is to use Cut Point specifications to define the product streams. The Distribution Plot page in the Oil Manager (under the Blend view) shows the cut points that were used to generate that plot. In order to maximize the proportion of Kerosene the Cut Point range is widened slightly. For example, it is desired to maximize the production of Naphtha. Since the flow rate of Naphtha is related to the flow rate of Kerosene, both of these streams will be defined in terms of cut point values. Before we maximize the production of the various products, the base case needs to be defined. Use the BP Curves utility to complete the

A good clue that the material and/or heat balance is failing is when the equilibrium error goes to zero while the heat/ specification error fails to converge.

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following table:Flow m3/h (bbl/d) Naphtha Kerosene Diesel AGO 150 (22, 500) 62 (9, 300) 130 (19, 250) 30 (4, 500) D86 CutPoint Temperatures, C 5% 95%

To maximize the products, you will need to add Cut Point specifications to replace the product flow specifications.

Save your case! Exercise 1Maximize the Production of Full Range NaphthaTo maximize the production of Naphtha, it is necessary to increase its 95 vol% cutpoint temperature. At the same time, the Kerosenes 5 vol% cutpoint temperature will show a corresponding increase as the lighter Kerosene components are transferred into the Naphtha product (becoming the heavier Naphtha components). By changing the flow rate specifications for both the Naphtha and Kerosene products to ASTM D86 95% vol% cutpoints, we can maximize the production of a full range Naphtha from the column.Product Naphtha You will need to make the Naphtha and Kerosene flow specifications Inactive and the Cut Point specification Active. Kerosene Diesel AGO Specifications 95% D86 Naphtha 190C (375F) 95% D86 Kerosene 245C (470F) Flow Flow 130 m3/h (19500 bbl/d) 30 m3/h (5000 bbl/d) Flow, m3/h (bbl/d)

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Exercise 2Maximize the Production of a Full Range KeroseneTo maximize the production of Kerosene, its boiling point range has to be expanded. The ASTM D86 95 vol% cutpoint for Naphtha should be lowered to 162C (325F), the base case value, and the 95 vol% of Kerosene raised to 275C (525F). Change the Diesel product flowrate specification to an ASTM D86 95 vol% cutpoint specification of 330C (625F).Product Naphtha Kerosene Diesel AGO Specifications 95% D86 Naphtha 162C (325F) 95% D86 Kerosene 275C (525F) 95% D86 Diesel 330C (625F) Flow 30 m3/h (5000 bbl/d) Flow, m3/h (bbl/d)

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Exercise 3Maximize the Production of a Full Range DieselThe production of Diesel can be maximized in a similar manner to maximizing Kerosene. The ASTM D86 95 vol% for Naphtha is 162C (325F). The Kerosene ASTM D86 95 vol% is lowered to 220C (430F). The ASTM 95 vol% Diesel specification should be increased to 360C (675F). Since the AGO flowrate will have to change, its flowrate specification should be changed to an ASTM D86 95 vol% cutpoint specification of 415C (780F).Product Naphtha Kerosene Diesel AGO Specifications 95% D86 Naphtha 162C (325F) 95% D86 Kerosene 220C (430F) 95% D86 Diesel 360C (675F) 95% D86 AGO 415C (780F) Flow, m3/h (bbl/d)

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1.3.6 Atmospheric Crude Column

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