Aspen Plus Hydrocracker - User's Guide V7.3 PDF [PDF]

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Aspen Plus Hydrocracker

User's Guide

Version Number: V7.3 March 2011 Copyright (c) 2003-2011 by Aspen Technology, Inc. All rights reserved. Aspen Plus HydrocrackerTM, Aspen Plus HydrotreaterTM, Aspen Plus CatCrackerTM, Aspen Plus HydrocrackerTM, Aspen Plus®, Aspen PIMSTM, aspenONE, the aspen leaf logo and Plantelligence and Enterprise Optimization are trademarks or registered trademarks of Aspen Technology, Inc., Burlington, MA. All other brand and product names are trademarks or registered trademarks of their respective companies. This document is intended as a guide to using AspenTech's software. This documentation contains AspenTech proprietary and confidential information and may not be disclosed, used, or copied without the prior consent of AspenTech or as set forth in the applicable license agreement. Users are solely responsible for the proper use of the software and the application of the results obtained. Although AspenTech has tested the software and reviewed the documentation, the sole warranty for the software may be found in the applicable license agreement between AspenTech and the user. ASPENTECH MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESSED OR IMPLIED, WITH RESPECT TO THIS DOCUMENTATION, ITS QUALITY, PERFORMANCE, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE. Aspen Technology, Inc. 200 Wheeler Road Burlington, MA 01803-5501 USA Phone: (781) 221-6400 Toll free: (888) 996-7100 Website: http://www.aspentech.com

Contents About This Document ..............................................................................................1 Who Should Read This Guide .............................................................................1 Technical Support ............................................................................................1 Introducing Aspen Plus Hydrocracker .....................................................................3 Overview.........................................................................................................3 Introduction To Aspen Plus Hydrocracker ............................................................3 The Aspen Plus Hydrocracker Engine ..................................................................4 Equation-Oriented Modeling...............................................................................4 Pressure Drop Model Example............................................................................5 Model Specifications and Degrees-of-Freedom .....................................................6 Modes and Multi-Mode Specifications ..................................................................7 Measurements and Parameters ..........................................................................8 Changing Specifications with Specification Options ...............................................9 Optimization ....................................................................................................9 1 Using Aspen Plus Hydrocracker .........................................................................11 Starting Aspen Plus Hydrocracker for the First Time ........................................... 11 Resetting the Aspen Plus Connection ................................................................ 14 Exiting Aspen Plus Hydrocracker ...................................................................... 14 General Guidelines for Using the Excel Interface ................................................ 15 Saving and Loading Data Files ......................................................................... 16 Saving Data Files ................................................................................. 16 Loading Data Files ................................................................................ 17 2 The User Interface ............................................................................................19 The Sheets of the User Interface ...................................................................... 19 Flow Diagram Sheet ............................................................................. 20 Separation Section ............................................................................... 21 Buttons on the Flow Diagram Sheet........................................................ 22 Hidden Worksheets ........................................................................................ 28 Command Line Window................................................................................... 29 Overview............................................................................................. 29 Abort Button........................................................................................ 31 No Creep Button .................................................................................. 31 Close Residuals Button.......................................................................... 31 Close Button ........................................................................................ 31 Manual Access to the Command Line Window .......................................... 31 Toolbar and Menu .......................................................................................... 32 Startup Aspen Plus Hydrocracker Submenu ............................................. 33 File Submenu....................................................................................... 36 Setup Cases Submenu .......................................................................... 38

Contents

iii

Run Cases Submenu............................................................................. 38 Tools Submenu .................................................................................... 39 Development Tools Submenu................................................................. 39 Help Submenu ..................................................................................... 40 Exit Aspen Plus Hydrocracker........................................................................... 40 3 Working With The Equation-Oriented Solver .....................................................42 Introduction to the Equation-Oriented Solver ..................................................... 42 Successive Quadratic Programming (SQP) ......................................................... 42 Changing EO Solver Parameters ....................................................................... 43 Basic EO Solver Parameters............................................................................. 44 EO Solver Output to the Command Window ....................................................... 44 EO Solver Log Files......................................................................................... 46 ATSLV File Problem Information ....................................................................... 46 ATSLV Details ................................................................................................ 47 Basic Iteration Information .................................................................... 47 Largest Unscaled Residuals.................................................................... 47 Constrained Variables ........................................................................... 47 General Iteration Information ................................................................ 48 Nonlinearity Ratios ............................................................................... 49 Usage Notes .................................................................................................. 49 Usage Notes-General ............................................................................ 49 Dealing With Infeasible Solutions ........................................................... 50 Scaling ............................................................................................... 52 Dealing With Singularities ..................................................................... 52 Notes on Variable Bounding................................................................... 54 Run-Time Intervention .......................................................................... 54 4 Model Parameterization ....................................................................................55 Introduction .................................................................................................. 55 Flow Diagram Sheet ....................................................................................... 55 Product Properties ................................................................................ 55 Model View and Specification Through the Flow........................................ 57 Model Specifications ............................................................................. 58 Running a Parameterization Case ..................................................................... 67 Reconciliation Cases ....................................................................................... 69 More Detailed Parameterization.............................................................. 69 5 Simulation .........................................................................................................71 Introduction to Simulation ............................................................................... 71 Aspen Plus Hydrocracker Simulation Strategy .................................................... 71 Commonly-Used Scripts in the EB Script Language............................................. 73 Aspen Plus Hydrocracker Variable Specifications ................................................ 73 Model CONST Specifications .................................................................. 73 Model Tuning Facts with Specifications.................................................... 77 Flowsheet Changes............................................................................... 80 Running a Simulation Case .................................................................... 82 Error Recovery - Parameterization .......................................................... 84 6 Running Multiple Cases .....................................................................................86 Overview....................................................................................................... 86

iv

Contents

Before You Start ............................................................................................ 86 7 Optimization......................................................................................................89 Optimization Basics ........................................................................................ 89 Setting Up Objective Functions ........................................................................ 90 Setting Up An Optimization.............................................................................. 95 Executing Optimization Cases .......................................................................... 98 Analyzing Optimization Solutions.................................................................... 100 8 LP Vectors .......................................................................................................102 Overview – Generating LP Vectors .................................................................. 102 Purpose of Running LP Vectors....................................................................... 102 LP Vector Generation .................................................................................... 103 9 Reaction Kinetics Details .................................................................................108 Overview..................................................................................................... 108 Component Slate ......................................................................................... 108 Kinetic Framework........................................................................................ 113 Reaction Pathways ............................................................................. 113 10 Simplified Separation Model ..........................................................................116 Simplified Separation Model........................................................................... 116 Index ..................................................................................................................119

Contents

v

About This Document

This chapter includes the following information: 

Who Should Read This Guide



Technical Support

Who Should Read This Guide This document is designed to be used by the users of Aspen Plus Hydrocracker, formerly known as Aspen Hydrocracker, in conjunction with the Aspen RxFinery family of products, including Aspen Plus Reformer, formerly known as Aspen CatRef, Aspen Plus CatCracker, formerly known as Aspen FCC, Aspen Hydrocracker, and Aspen Plus Hydrotreater, formerly known as Aspen Hydrotreater.

Technical Support AspenTech customers with a valid license and software maintenance agreement can register to access the online AspenTech Support Center at: http://support.aspentech.com This Web support site allows you to: 

Access current product documentation



Search for tech tips, solutions, and frequently asked questions (FAQs)



Search for and download service packs and product updates



Submit and track technical issues



Send suggestions



Report product defects



Review lists of known deficiencies and defects

Registered users can also subscribe to our Technical Support e-Bulletins. These are used to alert users to important technical support information such as: 

Technical advisories



Product updates and releases

About This Document

1

Customer support is also available by phone, fax, and email. The most up-todate contact information is available at the AspenTech Support Center at http://support.aspentech.com.

2

About This Document

Introducing Aspen Plus Hydrocracker

Overview Aspen Plus Hydrocracker, formerly known as Aspen Hydrocracker, is a simulation system for monitoring, planning, and optimizing hydrocracking and hydrotreating units. Aspen Plus Hydrocracker is a member of the AspenTech new generation of refinery reactor models. Aspen Plus Hydrocracker accurately predicts yields and product properties for widely different feedstocks and operating conditions. An Aspen Plus Hydrocracker flowsheet simulates all sections of the hydrocracking unit. It can include simplified or vigorous fractionation models.

Introduction To Aspen Plus Hydrocracker Aspen Plus Hydrocracker consists of a client and a server. The client, or user interface, is built from Microsoft Excel spreadsheets customized with VBA code and macros. The client and server communicate through DCOM. This communication should be transparent, and you do not have to understand how it works in order to use Aspen Plus Hydrocracker If the communication software fails, contact AspenTech. While your primary interaction with Aspen Plus Hydrocracker will be through the user interface, you need a basic understanding of how the server works in order to effectively use and troubleshoot the model. The server has several components: 

The engine (also known as the kernel or command prompt).



The solver (DMO).



The model, which is built as a custom Aspen Plus model using the PML (Process Model Library) system.

Introducing Aspen Plus Hydrocracker

3

The Aspen Plus Hydrocracker Engine The Aspen Plus Hydrocracker engine is Aspen Plus. You do not need to be an Aspen Plus expert to use Aspen Plus Hydrocracker – this section covers the most important concepts. The first time the engine is used during an Aspen Plus Hydrocracker session is when the user interface connects to the server. This brings up a command prompt window in which you will see the invoke plant.ebs command, which tells the engine to open several data files and build the model in the computer memory. The command prompt disappears when the kernel finishes building the model. The engine is also used whenever you request a solution from the user interface. Any changes you have made to data values or model specifications (via specification options) are passed through DCOM from the client to the server. The command prompt window appears and you will see a stream of kernel commands going to the engine. These commands tell the engine: 

What mode of solution is required.



What solver settings should be used.

There are different sequences of commands for different types of solutions (parameter, simulation, optimization, reconciliation, case study, LP vector generation, and so on.). You can look at the default command sequences on the EB Script sheet on the user interface. The default command sequences are all that is necessary for running the model in any of the pre-configured solution modes, but advanced users can modify them. During a solve, you will see three buttons on the bottom of the command prompt window. These are labeled Abort, No Creep, and Close Residuals. You use them to interrupt the solver. The Abort button tells the solver to quit at the next opportunity. The engine is also used whenever case data is stored or retrieved. The user interface typically contains only the results of the most recent run of each solution type. The save/load case data options let you save the results of any number of previous runs to review or use later. This user interface option is implemented using the kernel commands read varfile from and write varfile to. You can see these commands in the command prompt while it is active, or you can recall the command prompt using the user interface menu option Aspen Plus Hydrocracker | Tools | Display Command Line to review the previous commands.

Equation-Oriented Modeling Aspen Plus Hydrocracker is based on an equation-oriented (EO) formulation, so you need to understand some EO concepts in order to use it effectively. The EO approach is also known as open-form. It can be contrasted with the closed-form or sequential-modular (SM) technique.

4

Introducing Aspen Plus Hydrocracker

The equations in an EO model are solved simultaneously using an external solver, which iteratively manipulates the values of the model variables until all the equations are satisfied within a convergence tolerance. The solver will work for any well-posed set of variable specifications. A variable’s specification labels it as 

known (fixed) -or-



unknown (calculated)

for a given solution mode. An SM model is solved procedurally one equation at a time, and the solution procedure depends on a given specification set. For a different grouping of known and unknown variables the solution procedure will be different, since the equations will be solved in a different order.

Pressure Drop Model Example A simple example illustrates some important EO concepts. Consider this twoequation model, in which the pressure drop is correlated with the square of the mass flow of a fluid: Pressure drop correlation:

DELTAP = PRES_PARAM * MASS_FLOW^2

Define pressure drop:

DELTAP = PRES_IN – PRES_OUT

In an EO formulation, we rearrange these equations into residual format. The value of the residual indicates how close that is to being solved – at the solution the value of every residual will be zero, or at least close enough to zero to satisfy our numerical convergence tolerance. f(1) = DELTAP - PRES_PARAM * MASS_FLOW^2

(= 0 at solution)

f(2) = PRES_IN - PRES_OUT - DELTAP

(= 0 at solution)

Note that f is the name of the vector of residuals. Its length equals the number of equations. The solver prefers to work with vectors and equation index numbers, while we find it easier to use equation names. The model defines names for each residual that can be used in reports and solver debugging output. In this case, we choose the names: f(1) = ESTIMATE_DELTAP f(2) = DELTAP_DEFINITION Similarly, the five variables in this model can also be addressed as elements of a vector x having a length of 5: x(1) = DELTAP x(2) = PRES_IN x(3) = PRES_OUT x(4) = PRES_PARAM x(5) = MASS_FLOW

Introducing Aspen Plus Hydrocracker

5

Model Specifications and Degrees-of-Freedom Once we tell the solver which variables are known (fixed) for a given solution mode, it manipulates the values of the unknown (free) variables to drive the residuals to zero. For any system of independent equations, the degrees-offreedom (DOF) is equal to the number of variables minus the number of equations minus the number of fixed variables:

DOF = #variables - #equations - #fixed variables The number of degrees-of-freedom of a system classifies it into one of three categories: Category

Degrees of Freedom

Under specified

>0

Square

0

Over specified

Step taken 3.26D-01

3 Working With The Equation-Oriented Solver

45

If the solver has to line search continually and the step size gets very small (less than 1.0D-2), most likely the solution is trying to move very far from the starting point or some of the specified values are nearly infeasible.

EO Solver Log Files Aspen Plus Hydrocracker outputs DMO solver information to two log files: 

ATSLV.



ATACT.

These files reside in the working directory you defined in the startup menu box (fm). The ATACT file is similar to the ATSLV file, but lists all the problem variables and independent variables, whereas the ATSLV file does not. The ATSLV file is typically more useful and is described in more detail below.

ATSLV File Problem Information At the top of the ATSLV file, a summary of the problem is printed. This shows the size of the problem and the values of some important parameters.

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3 Working With The Equation-Oriented Solver

ATSLV Details Basic Iteration Information At each iteration, the following header is printed:

This shows the iteration number and the value of the objective function.

Largest Unscaled Residuals This section shows the largest unscaled residuals. A similar section shows the largest scaled residuals. This section is particularly helpful when the solver has trouble closing all the residuals because it will point to the largest.

Constrained Variables This section shows the variables that lie on their bounds. This is only meaningful in a mode with degrees of freedom (optimization for Aspen Plus Hydrocracker). The output shows the variable number, which bound is active, the variable name, the current value and the shadow price. The shadow price is also known as the Lagrange multiplier. This is the derivative of the objective function with respect to the value of the constraint and represents the cost for the constraint.

The shadow price is based on the value of the objective function that is seen by DMO. That means the shadow price is in SI units (such as $/sec) and is affected by any scaling. This is true even if you declare the units to be something other than SI (such as $/HR).

3 Working With The Equation-Oriented Solver

47

Consider this example. We have a tower with a composition constraint, expressed as a mole fraction of a component. The following table shows the results of two optimization runs at two different values of the composition constraint: Value

Objective

Shadow Price

0.0002

2.853

432.924

0.0003

2.893

258.664

The large change in the shadow price indicates that the effect of the composition on the objective function is very nonlinear. We can manually estimate the average shadow price in this region by a finite difference method: Price = Obj/x = ( 2.893-2.853 ) / ( 0.0003 - 0.0002 ) = 400.00 $/sec/mole fraction This value lies between the two prices. If the objective function had a scale factor of 100, we would get the following: Value

Objective

Shadow Price

0.0002

285.4

43290.7

0.0003

289.3

25860.2

We would have to remember to unscale the shadow price by dividing by 100.

General Iteration Information This section appears after the residual output:

The iteration status shows the exit condition of that iteration. Normal indicates a normal successful iteration. Warning indicates a successful iteration despite some solver difficulties. Error indicates a failure. Solved indicates the final iteration of a successfully solved problem. The degrees of freedom is the number of declared independent variables in the problem. The constrained variables are those at bounds in the QP subproblem. The current degrees of freedom is the degrees of freedom less the constrained variables. This is the true degrees of freedom for the problem. A highly constrained solution is one that has very few current degrees of freedom.

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3 Working With The Equation-Oriented Solver

The number of function and Jacobian evaluations is an accumulative count and generally matches the number of iterations. The objective function convergence function is the norm of the Jacobian for the objective function. At the solution, this value should be near zero. The residual convergence function is the sum of the scaled residuals. At the solution, this value should be near zero.

Nonlinearity Ratios This section shows the nonlinearity ratio of the worst block, the objective function, and the worst equations. The criterion is the accuracy of the predicted change in the equation. If the function is linear, then the new value would match the predicted value and the nonlinearity ratio would be one. A value of the ratio other than one indicates some degree of nonlinearity. A negative value indicates that the function value moved in the opposite of the expected direction. Large negative values could indicate a discontinuity or bad derivative. This section also shows the step size for the iteration.

Usage Notes Usage Notes-General This section describes some usage notes and troubleshooting tips to improve the performance of the solver and to help diagnose common problems. The topics in this section are: 

Dealing With Infeasible Solutions



Scaling



Dealing With Singularities



Notes on Variable Bounding



Run-Time Intervention

3 Working With The Equation-Oriented Solver

49

Bounds Aspen Plus lets you bound every variable in the problem as shown below:

Xl < X < Xu The step bound of an independent variable defines how much the value of the variable can be changed in a single optimization run. The step bound is used along with the initial value, lower bound, and upper bound to compute the actual bounds to be used in the run:

Xl = max(X - |Xstep|, Xlower) Xu = min(X + |Xstep|, Xupper) You should define upper and lower bounds for all independent variables. You can also define the step bounds for independent variables. Most of the dependent variables in the Hydrocracker model have very wide bounds, such as –1.E20 for lower bound and 1.E20 for upper bound. However, some dependent variables have physical meaning. You should set up appropriate bounds for them to prevent the solution from getting into infeasible operating conditions. For example, there is a metallurgic limit on regenerator cyclone temperature. Hence, an upper bound should be set for this variable. Only those constrained dependent variables must be defined when setting up an optimization case in Hydrocracker model. In general, it is not recommended to heavily bound an optimization problem for reasons that are both practical and algorithmic. Bounds on independent variables are recommended in order to avoid unbounded problems. All other bounds should be used only if they are absolutely necessary. The optimization engine for Hydrocracker model is the DMO solver.

Independent Variables Independent variables are variables whose values can be changed independently, for example, the feed rate in the Hydrocracker unit. The optimizer can vary the values of independent variables to push the values of the objective function in the defined direction (maximize profit or minimize cost) until some bounds are reached. Each independent variable accounts for a degree of freedom. The number of degrees of freedom is equal to the number of independent variables in an optimization run if no independent variable is at its bound. You can impose upper and lower bounds on independent variables to prevent the final solution from deviating too far away from the starting point. You can also impose step bounds on independent variables.

Dealing With Infeasible Solutions These often occur during optimization cases where it is not possible to simultaneously solve all the equations while respecting all the variable bounds. This doesn't happen in simulation cases because DMO ignores bounds in simulation cases. If you solve a simulation case that violates a bound, then the optimization case will start at an infeasible point. In this case, the following is printed in the OUT file:

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3 Working With The Equation-Oriented Solver

This says that this variable's value had to be adjusted to respect the bound. When the optimization proceeds and there is no feasible solution for the equality constraints, the screen output might look like this: Residual

Objective

Convergence Convergence Iteration

Function

Function

Objective

Overall

Model

Function

Nonlinearity

Worst

Nonlinearity

Value

Ratio

Model

Ratio

--------- ----------- ----------- ---------- ------------ ------- -----------Warning ...

QP slack variable =

2.29070D-01

Warning ...

QP slack variable =

2.29070D-01

0

9.312D-04

4.809D-03 -2.779D+00

Warning ...

QP slack variable =

1.80624D-01

Warning ...

QP slack variable =

1.80624D-01

1 Warning ... Warning ... 2

5.244D-04

4.667D-02 -2.792D+00

QP slack variable =

1.44771D-01

QP slack variable =

1.44771D-01

1.552D-02

5.479D-02 -2.922D+00

Warning ...

QP slack variable =

6.09502D-01

Warning ...

QP slack variable =

6.09502D-01

3

3.853D-02

2.379D-03 -3.083D+00

Warning ...

QP slack variable =

1.87163D-01

Warning ...

QP slack variable =

1.87163D-01

4

1.496D-02

1.040D-02 -3.075D+00

Warning ...

QP slack variable =

3.18508D-01

Warning ...

QP slack variable =

3.18508D-01

9.968D-01 C2S

-2.834D-01

2.900D-01 C2S

-1.846D+02

-7.475D-01 C2S

-1.540D+01

9.908D-01 C2S

9.914D-01

8.346D-01 C2S

6.012D-01

+---------------------- ERROR ----------------------+

Error return from [DMO] system subroutine DMOQPS because the problem has NO FEASIBLE SOLUTION.

Action : Check the bounds that are set on variables to insure consistency. Check the .ACT file for information on initial infeasibilities.

+---------------------------------------------------+

Error return, [DMO] System Status Information =

3 Working With The Equation-Oriented Solver

5

51

Optimization Timing Statistics

Time

Percent

================================

========

MODEL computations

1.32 secs

31.10 %

DMO computations

0.91 secs

21.28 %

Miscellaneous

2.03 secs

47.61 %

-------------------------------Total Optimization Time

--------4.26 secs

=======

------100.00 %

Updating Plex Problem failed to converge

Note the messages from the QP indicating an invalid value for a slack variable. To solve this problem, you need to be aware of the initial message indicating that the initial value of a variable violated its bound. In this case, C2S.SPC.REFL_RATIO_MASS is causing the problems. Unfortunately, the OUT file does not list this variable as constrained, since it could never solve the QP successfully.

Scaling Generally, it is not necessary to scale your equations or variables beyond what is done by default in the models. However, it may be more efficient to scale your objective function. A good rule of thumb is to scale the objective function so that its value is on the order of 10 to 1000. The scaling of the objective function plays an important role since it affects the overall convergence behavior. This is particularly important in cases where there is a large change between the original value of the objective and the expected optimum.

Dealing With Singularities Singularities often occur when the model is moved into a region where the equations are not well defined. The most common example of this is when a stream flow becomes too small. If singularities exist, they are usually detected at the start of the problem. In this case, some information is written to the OUT file and this can help locate the cause of the problem. In general, you should prevent stream flows from going near zero by placing nonzero lower bounds on the flow (e.g., 10 kg/hr). This is especially important on streams from flow splitters or feed streams whose total flow is being manipulated. In the case of a singularity the following message will be displayed:

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3 Working With The Equation-Oriented Solver

The OUT file contains information on the possible cause of the singularity in the following manner:

Sometimes, singularities are simply caused by the optimization being too aggressive. This moves the models into a region where the equations are not well defined. To make the optimization more robust, DMO has a creep mode. This mode simply causes smaller steps to be taken for a specified number of iterations. To use this mode, you can enter the following script command:

DMO.CREEPFLAG = 1 This turns on the creep mode. When active, the following message is displayed at each iteration: ==> Step taken 1.00D-01

By default, this will operate for 10 iterations with a step size of 0.1. You can change these values with the commands:

DMO.CREEPITER = 20 DMO.CREEPSIZE = 0.5 In this example, we change the number of creep iterations to 20 and the step size to 0.5.

3 Working With The Equation-Oriented Solver

53

Notes on Variable Bounding Remember that by default DMO does not respect bounds during the solution of a SIM or PAR case. The user, however, has the capability to impose bounds in a square case by using a different line search parameter. The use of this mode is recommended only in cases where there are truly multiple solutions to a model (for example, the cubic equation) and you want to use a bound to eliminate an unwanted one. 

To use this mode, enter the following script command:

DMO.LINESEARCH = 4 In general it is not recommended to heavily bound an optimization problem for reasons that are both practical and algorithmic. Bounds on independent variables are recommended in order to avoid unbounded problems. All other bounds should be used only if they are absolutely necessary. Finally, redundant bounds should be avoided.

Run-Time Intervention During long runs, you can change the behavior of the DMO solver by clicking one of the three buttons at the bottom of the command window. Your selection takes effect at the start of the next DMO iteration. The three buttons are:

54

Button

Action

ABORT

Stops the solver

CLOSE

Fixes all the independent variables at their current values and closes the residuals

NOCREEP

Takes DMO out of creep mode

3 Working With The Equation-Oriented Solver

4 Model Parameterization

Introduction To provide a better understanding of the Aspen Plus Hydrocracker/Hydrotreater model, this section presents a general description and discussion of the model.

Flow Diagram Sheet Product Properties You can vary product cut-points. The table below shows a list of product properties predicted by AspenPlusHYC model. Product Stream

Properties

H2S

Mass flow, mole flow

NH3

Mass flow, mole flow

H2

Total consumption (mass and moles)

C1

C1 mass flow, mole flow, mass fraction C2 mass flow, mole flow, mass fraction

C2

C1 mass flow, mole flow, mass fraction C2 mass flow, mole flow, mass fraction C3 mass flow, mole flow, mass fraction H2S mass flow, mole flow, mass fraction H2 mass flow, mole flow, mass fraction

C3

C2 mass flow, mole flow, mass fraction C3 mass flow, mole flow, mass fraction C4 mass flow, mole flow, mass fraction

C4

C3 mass flow, mole flow, mass fraction C4 mass flow, mole flow, mass fraction C5 mass flow, mole flow, mass fraction C4 iso/normal ratio

4 Model Parameterization

55

Product Stream

Properties

Light naphtha

C4 mass fraction TBP distillation API gravity Specific gravity PIANO Total Sulfur Total Nitrogen RON/MON

Heavy Naphtha

TBP distillation API gravity Specific gravity PIANO Total Sulfur Total Nitrogen RON/MON

Distillate

TBP distillation API gravity Specific gravity PIANO Total Sulfur Total Nitrogen Basic Nitrogen Smoke point Pour Point Freeze point

Bottoms

TBP distillation API gravity Specific gravity PIANO Total Sulfur Total Nitrogen Basic Nitrogen Cetane Index Viscosity

For recycle hydrocracking, 

The maximum-naphtha base case recycles the 400oF-plus material.



The maximum-distillate base case recycles the 700oF-plus material.

Distillation overlap is calibrated with plant data. The following yields and product properties are provided. Recycle Gas Scrubber is simplified as a component splitter, RGSPLIT, a standard Aspen Plus component splitter block (SEP). Note: Scrubbing efficiency can be calibrated with plant data. If there is no recycle gas scrubber,no H2S is removed by this block.

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4 Model Parameterization

The quench-distribution system is modeled by a Standard Aspen Plus splitter block (FSPLIT). Mixer blocks are used for quenches. You can specify: 

Heat loss.



Temperature.



Pressure.



Pressure drop.

Quench valve characteristics are not modeled, but you can specify upper and lower limits on quench flow.

Model View and Specification Through the Flow The main AspenPlusHYC model data access is provided by buttons on this sheet. A summary of the general instructions for all buttons given below: 

Buttons R1, R2, HTR. When you click one of these buttons, you are taken to the Process Detail sheet, which displays a summary of the current running conditions.



Buttons Feeds takes you to the Process Detail sheet to display feed properties of the combined feed and input sheet for each individual feed.



Button Yields takes you to the Process Detail sheet to display the volume and mass yields of product. In addition, it displays the product properties of each product.



Button Process Overview takes you to the Process Overview sheet, in which general information for AspenPlusHYC model is presented.



Button Reaction Profile takes you to the Reaction Profile spreadsheet. On this sheet a set of diagrams presents present the temperature, sulfur, nitrogen and aromatic contents the two beds in the two reactors.



Button Specification Options pops up a dialog to let you select a mode you want to run. You can select one, then click the Select button. The specification will be set properly for the case running. For each running mode, it will show later.

4 Model Parameterization

57

Note: All data sheets showing the value and specification are only for display. Any changes will not affect the model running in this version.

Model Specifications Strategy for Process Specification For a number of purposes of AspenPlusHYC model running, the user need provides sufficient process information to let the model can be tuned to match the process situation. The AspenPlusHYC can be tuned in a number of ways. In general, the following are required: 

Feed and product properties



Operating conditions



Selected mechanical data

All samples must be time-stamped. All samples must be taken within the same 4-8 hour period. Uncompressed, hour-average process data (all relevant tags from the DCS, if possible) must be provided for the period during which samples are taken.

Feed and Product Analysis Your specific needs determine whether the feed and product analytical requirements are simple or complex. AspenTech has a library of detailed analytical data and component distributions (fingerprints) for several feed/product combinations. Feed types include:

58

4 Model Parameterization



Light and heavy straight-run vacuum gas oils.



Light and heavy coker gas oils.



Light and heavy FCC cycle oils.



Pre-processed synthetic crude.

When a client’s feed resembles a feed in the AspenTech database, the Feed Adjust block in Aspen Plus Hydrocracker can obtain a good fit by skewing the distribution of components in the base feed to minimize differences between measured and calculated bulk properties. This is the usual starting point if the model is to be used offline for: 

What-if studies.



Generation of LP shift vectors.



Certain design studies.

The following bulk inspection properties are used for model calibration, Property

Required/Optional

API gravity

Required

D2887 distillation

Required

Refractive index

Optional (recommended)

Viscosity @210 F

Optional (recommended)

Bromine number

Required

Total sulfur

Required

Total and basic nitrogen

Required

The feed refractive index and viscosity are optional. If you do not provide the refractive index and viscosity, the feed adjustor model calculates them based on the API gravity and distillation. The refractive index, viscosity, API gravity, and distillation are then used to calculate: 

The CA (carbon on the aromatic rings).



The CN (naphthene ring).



CP (paraffins).

The method used for calculating CA, CN, and CP is the NDM method. To get a better result for characterization of the feed, AspenTech recommends the following methods to determine the aromatic/naphthene/paraffin breakdown for each feed, Method

Description

D1319 Fluorescent Indicator Adsorption (FIA).

provides Total Aromatics in vol%.

NMR method

provides Carbon on aromatic rings

UV method

provides wt% of MONO, DI, TRI and Tetra aromatics

HPLC

high performance liquid chromatography

4 Model Parameterization

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Notes: If higher accuracy is required, for example, for an online closed loop optimization project, or if the plant frequently processes feeds for which AspenTech does not have a similar fingerprint, detailed analyses including GC/MS, HPLC and NMR may be recommended. To tune the Catalyst Deactivation block, you may be able to use historical data. However, if adequate historical data are not available, at least two sets of test-run data obtained at least three (fm) To increase model accuracy – and to be confident that feedstock effects can be differentiated from catalyst deactivation effects – individual blend stocks should be analyzed individually. Also, analyses should be obtained for typical composite feeds. The adjustment of the individual feeds creates detailed lump compositions for each individual feed. This allows a more accurate representation of the effects of individual blend stocks on hydrocracker performance. If you need detailed analytical data, the table below provides a list of the feed and product inspections needed for the creation of a new fingerprint. Aspen Hydrocracker Feed and Product Analysis - Check List

Tests (Note 1) Required for Configuration Prep Distillation into 950-,950+ (2) API Gravity Sim Dist High Temp Sim Dist NOISE HPLC PONA (FIA) HC Type, wt% C & H Content, Wt% Total Sulfur Content, wt% Total Nitrogen, ppmw Basic Nitrogen, ppmw Bromine Number H & C13 NMR Other Required Data Sim Dist C1 - C3 C6- GC (3) GC PIANO (4) Optional Data per Client Interest Metals (Ni,V,Fe,Cu,Na) ppmw Refractive Index @ 20 DegC Aniline Point Viscosity, cst @ 100 DegF Viscosity, cst @ 210 DegF Carbon Residue, wt% Cloud Point Pour Point Smoke Point Freeze Point Cetane Index ASTM Distillation RON MON RVP

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Method

Total

Vac Dist D287 D2887 HTSD GC/MS HPLC D1319 D4124 D5291 D4294 (?) UOP269 D1159 D5292

x x

Feeds 950-

x x

x

950+

Unconverted Oil Total 950950+

x

x x

x

x

x

x x x x x

x x

x

Diesel

Kerosine

Naphtha

x x

x x

x x

x

x

x

x x

x

x

x x x x

x x x x x

x x x x

x x x x x

x x x x

x x x x

x x x x

x

x

x

x

x

x

D3710 GC/TC/FID GC/FID GC/FID ICP D1747 D611 D445 D445 D4530 D2500 D97

x x

x

x x x x x x

x x x x x x x x

x x x x

x D86 D2699 D2700 D5191

Fuel Gas

x x

x x x x

C3+C4

x

x x x x

x x x x

4 Model Parameterization

Note: Estimated costs for analyses may be obtained by contacting AspenTech. Heavy feeds must be separated into 950- and 950+ fractions, because each fraction requires different methods. The requirements for configuration are used to calculate feed and product compositions for 97-lump kinetics. Lighter feeds (