Лабораторная работа № 6. Моделирование процесса очистки кислых вод от кислых примесей в отпарной колонне с использованием химии электролитов и исследование особенностей ее работы

Modeling a Sour Water Stripper

In this simulation, use a distillation column to strip NH3 and H2S

from a sour water feed stream.

You will:

Modify the generated Chemistry

Use the apparent component approach for electrolytes

Define a stream property (Property Set)

Convert the simulation from the apparent approach to the true

approach

Allow about 45 minutes to do this simulation.

3-2 Modeling a Sour Water Stripper Getting Started - Electrolytes

Sour Water Stripper Flowsheet

The process flow diagram and operating conditions for this

simulation are shown in the Process Diagram: Sour Water Stripper.

Two feed streams, one containing sour water, the other steam, are

fed to a stripper to remove CO2, H2S, and NH3 from the sour water.

Use RadFrac to simulate the stripper.

SOURWAT

STEAM

BOTTOMS

VAPOR

Temperature = 190 F

Pressure = 15 psi

Total flow = 10,000 lb/hr

Mass fraction H2S = 0.001

Mass fraction NH3 = 0.001

Mass fraction CO2 = 0.001

Mass fraction H2O = 0.997

Pressure = 15 psi

Saturated vapor

Estimated H2O

flow rate = 2,000 lb/hr

Above

Stage 3

On Stage

10

5.0 ppm NH3

9 Theoretical stages + condenser

Pressure = 15 psi

Estimated molar reflux ratio = 25

Condenser temperature = 190 F

saturated vapor distillate

Process Diagram: Sour Water Stripper

The specifications for the column are:

10 theoretical stages total (includes one for the condenser)

Distillate product as saturated vapor (partial condenser)

Initial estimate for molar reflux ratio = 25

No reboiler

Feed stream SOURWAT above stage 3

Feed stream STEAM on stage 10

Column pressure of 15 psi (isobaric)

Vary the reflux ratio and stream STEAM feed rate to achieve a

bottoms product with 5 ppm (mass) of NH3 and a condenser

temperature of 190° F

Getting Started - Electrolytes Modeling a Sour Water Stripper 3-3

Starting Aspen Plus

1 From your desktop, select Start and then select Programs.

2 Select AspenTech | Aspen Engineering Suite | Aspen Plus

11.1 | Aspen Plus User Interface.

The Aspen Plus Startup dialog box appears. Aspen Plus displays

a dialog box whenever you must enter information or make a

selection before proceeding. In this simulation, use an Aspen Plus

template.

1 Select the Template radio button and click OK.

The New dialog box appears.

2 Use the New dialog box to specify the application type and the

run type for the new run. Aspen Plus uses the application type

you choose to automatically set various defaults appropriate to

your application.

1 Select the Electrolytes with English Units template.

The default Run Type, Flowsheet, is appropriate for this

simulation.

2 Click OK to apply these options.

It will take a few seconds for Aspen Plus to apply these options.

Note: If the Connect Host dialog box appears, see Chapter 4.

The Aspen Plus window is now active.

To Start Aspen Plus

To Select the

Template Option

To Specify the

Application Type and

Run Type for the New

Run

3-4 Modeling a Sour Water Stripper Getting Started - Electrolytes

Drawing the Graphical Simulation

Flowsheet

In this simulation, begin to build the process flowsheet. Since you

will enter your own block and stream IDs, turn off the default

Create auto block ID and Create auto stream ID options, which

provide these IDs automatically.

1 From the Aspen Plus menu bar, select Tools | Options.

The Options dialog box appears.

2 Select the Flowsheet tab.

3 Clear the Automatically Assign Block Name with Prefix and

the Automatically Assign Stream Name with Prefix options.

4 Click OK to close the Options dialog box and apply the

changes.

Getting Started - Electrolytes Modeling a Sour Water Stripper 3-5

5 Place a RadFrac blocks and streams to create the graphical

simulation flowsheet as follows:

Note that the distillate stream is connected to the Vapor

Distillate port.

6 Click to guide you to the next required input.

The Flowsheet Complete dialog box appears.

7 Click OK to continue.

Specifying Title, Stream Properties,

and Global Options

The Data Browser window appears. The Setup | Specifications |

Global sheet displays default Aspen Plus settings and units used

for other sheets.

Use this sheet to give your simulation a title, and to review the

stream properties and global options that were set when you

selected the Electrolytes with English Units application type.

The Run type field displays Flowsheet, which is appropriate for

this simulation.

The Electrolytes with English Units application type sets the

following global defaults for electrolytes applications:

ENG units (English units)

Mass Flow basis for all flow inputs

It is always good practice to enter a title for the simulation.

In the Title field, enter Getting Started with Electrolytes -

Simulation 2.

3-6 Modeling a Sour Water Stripper Getting Started - Electrolytes

1 From the Data Browser, select the Setup | Report Options

form.

2 Select the Stream sheet.

Aspen Plus displays the following defaults for calculating and

reporting stream properties taken from the Electrolytes with

Metric Units template:

Flow Basis of Mass: Aspen Plus will report the component

flow rates on a mass flow basis.

ELEC_E Stream Format: Aspen Plus formats the Stream

Summary sheet for electrolytes.

3 From the Data Browser, select the Components folder and

then select Specifications.

To Review the Report

Options Specified in

the Selected

Template

To Move to the Next

Required Input Sheet

Getting Started - Electrolytes Modeling a Sour Water Stripper 3-7

Specifying Components

The Components Specifications Selection sheet appears.

The apparent (or base) components for this simulation are H2O,

NH3, H2S, and CO2. Because you chose an electrolytes Application

Type, water already appears on the sheet.

1 Enter the following components in addition to the predefined

water:

NH3 Ammonia

H2S Hydrogen-Sulfide

CO2 Carbon-Dioxide

Because the formula for ammonia is represented as H3N in the

Aspen Plus databank, you must identify NH3 by entering either

the Component name (ammonia) or the Formula (H3N).

2 Click Elec Wizard.

The Electrolyte Wizard dialog box, for defining automatic

chemistry generation, appears.

The Electrolyte Wizard

Use the Electrolyte Wizard dialog box to define the ionic species

that can be generated from the base components you specified on

the Components | Specifications| Selection sheet, and to generate

the reactions that occur among these components in the liquid

phase.

1 On the Electrolyte Wizard dialog box, click .

2 Click to move all components in the Available

components column to the Selected components column.

3 Click to continue.

3-8 Modeling a Sour Water Stripper Getting Started - Electrolytes

4 The Generated Species and Reaction dialog box appears:

Aspen Plus generates all possible ionic species and reactions

for the H2O-NH3-H2S-CO2 system.

In the Generated Reactions list, the following arrows denote

different reaction types:

<<===>> Denotes ionic equilibrium and salt precipitation

--->> Denotes complete dissociation

For this simulation, you know that ammonium carbamate

formation can be neglected.

5 Select NH2COO– in the Aqueous species list.

6 Click Remove.

7 Now that you have removed NH2COO– from the Generated

Aqueous Species list, Aspen Plus automatically removes all

reactions involving NH2COO– from the Reactions list.

The salts are also not relevant.

8 Select NH4HS(S) and NH4HCO3(S) from the Salts list.

9 Click Remove.

To Remove

Ammonium

Carbamate Formation

from the Solution

Chemistry

To Remove the Salts

from the Solution

Chemistry

Getting Started - Electrolytes Modeling a Sour Water Stripper 3-9

Note: Any time you know that a reaction can be neglected

because of expected process conditions, remove it from the

solution chemistry to decrease the execution time required for your

simulation.

In this example, only ionic equilibrium reactions are generated.

The remaining six generated reactions represent partial

dissociation of water, partial dissociation of H2S to HS– and

S–2, partial dissociation of CO2 to HCO3

– and CO3

–2, and

partial dissociation of NH3 to NH4

+.

10 On the Generated Species and Reactions dialog box click

to accept the generated species and reactions.

The Simulation Approach dialog box appears, allowing you

to choose between the true species approach and the apparent

component approach. For this simulation, use the apparent

component approach.

When you use the apparent component approach, Aspen Plus

solves the equations describing solution chemistry as part of

the physical property calculations. Aspen Plus modifies the

physical properties of the apparent components to account for

the reactions described by the solution chemistry. The ions and

precipitated salts are not seen by the unit operation models.

3-10 Modeling a Sour Water Stripper Getting Started - Electrolytes

The apparent component approach also defines how Aspen

Plus reports simulation results. The component flow rates for

ions are not reported. Instead, Aspen Plus reports the

component flow rates of the apparent components as if no

dissociation occurred.

For example, the generated Chemistry for this system specifies

that H2S partially dissociates into HS- and S-2. If you choose the

apparent component approach, Aspen Plus will report a value

for the mole flow rate of H2S that includes molecular H2S, HS-,

and S-2.

11 Select the Apparent component approach option.

12 Click to move to the next dialog box.

The Summary dialog box appears, providing Aspen Plus

electrolytes expert system information.

13 Click Finish to close the dialog box.

On the Components | Specifications | Selection sheet, Aspen

Plus has now added the generated electrolyte components.

Since all components are databank components, Aspen Plus

automatically retrieves all relevant physical property

parameters.

14 Click to continue.

The Components | Henry Comps | Global | Selection sheet

appears. Use this sheet to see which components have been

declared as Henry's Law components by the electrolytes expert

system in the Henry Comps group it created, GLOBAL. If you

Getting Started - Electrolytes Modeling a Sour Water Stripper 3-11

had additional Henry's Law components in your simulation

(such as nitrogen and oxygen), you could add them to the list

on this sheet.

Examining Generated Chemistry

In the previous step, the Aspen Plus Electrolyte Wizard

automatically generated the chemistry definition for your

simulation and named it GLOBAL.

1 From the Data Browser, select the Reactions folder.

2 From the Reactions folder, select the Chemistry | Global.

The Reactions | Chemistry | Global | Stoichiometry sheet

appears.

1 Select a Reaction and click Edit.

The Equilibrium Reaction Stoichiometry dialog box appears,

with the data for the selected reaction that was generated by the

Electrolytes Wizard.

2 Close the dialog box and view the other reactions using the

same steps.

3 Click the Equilibrium Constants tab. Select the various

reactions in the Equilibrium reaction field. All six reactions

have equilibrium constants that have been retrieved from the

Aspen Plus reactions database.

4 From the Data Browser, select the Properties folder and then

select Specifications.

To Examine the

Generated Chemistry

To View the

Generated Chemistry

3-12 Modeling a Sour Water Stripper Getting Started - Electrolytes

The Properties | Specifications | Global sheet appears. The

Electrolyte Wizard has already completed this sheet:

5 Ensure that the Use true-components checkbox is cleared.

6 Click to continue.

The Binary Interaction sheet appears for the binary

parameters HENRY-1. Use this sheet to view the Henry's Law

parameters retrieved by the electrolytes expert system. If you

had your own Henry's Law parameters, you could enter them

on this sheet.

7 Click to continue.

The Binary Interaction sheet appears for the binary

parameters NRTL-1. Use this sheet to view the moleculemolecule

interaction parameters retrieved by the electrolytes

expert system. If you had your own molecule-molecule

interaction parameters, you could enter them on this sheet.

8 From the Data Browser, select the Properties folder, then

select the Parameters folder, and then select the Electrolyte

Pair folder.

The Electrolyte Pair sheets define the electrolyte pair

parameters: GMELCC, GMELCD, GMELCE, and GMELCN.

If you had your own pair parameters, you could enter them on

these sheets.

9 Click to continue.

The Electrolyte Pair GMELCC-1 Input sheet appears.

10 Click to continue.

Getting Started - Electrolytes Modeling a Sour Water Stripper 3-13

The Electrolyte Pair GMELCD-1 Input sheet appears.

11 Click to continue.

The Electrolyte Pair GMELCE-1 Input sheet appears.

12 Click to continue.

The Electrolyte Pair GMELCN-1 Input sheet appears.

13 Click to continue.

The Required Properties Input Complete dialog box

appears:

Correct representation of physical properties is essential to

process modeling. For many simulations, the only physical

property specification that you must provide is the selection of

an option set. This dialog box shows that the Aspen Plus

physical property system has many optional capabilities to

increase the accuracy of the physical property calculations.

Because the Aspen Plus electrolytes database has data for all

components and pairs in this system, you don't need to provide

any optional specifications or data.

Now that the Components and Properties specifications are

complete, complete the rest of the flowsheet specifications in

the same way as for non-electrolytes. Use all Aspen Plus unit

operation models in an electrolytes simulation.

14 Click OK to move to the next required input.

3-14 Modeling a Sour Water Stripper Getting Started - Electrolytes

Entering Stream Data

The Streams | SOURWAT | Input | Specifications sheet appears.

Aspen Plus requires two thermodynamic specifications and enough

information to calculate the molar flow rate of each component.

1 Enter the following data:

Temperature 190 F

Pressure 15 PSI

Total flow Mass 10000 LB/HR

2 In the Composition field, click and select Mass-Frac.

3 Enter the following mass fraction values:

H2O 0.997

NH3 0.001

H2S 0.001

CO2 0.001

4 Click to continue.

The Streams | STEAM | Input | Specifications sheet appears.

5 In the Temperature field, click and select Vapor fraction.

Getting Started - Electrolytes Modeling a Sour Water Stripper 3-15

6 Enter the following data:

Vapor fraction 1

Pressure 15 PSI

Composition Mass-Flow

H2O Mass flow value 2000 LB/HR

7 Click to continue.

Specifying the RadFrac Block

The Blocks | B1 | Setup | Configuration sheet appears.

1 Click , then click the words Operating specifications on

the Configuration sheet.

2 Click the link Operating Specifications Descriptions.

3 Review the types of specifications, then when you are ready to

continue, close the Help window.

4 On the Blocks | B1 | Setup | Configuration sheet, enter the

following:

Number of stages 10 (9 theoretical stages and condenser)

Condenser Partial-Vapor

Reboiler None

To Review the Types

of Specifications that

You Can Make for

RadFrac

3-16 Modeling a Sour Water Stripper Getting Started - Electrolytes

5 In the Operating specifications section, at the Reflux Ratio

field, select Mole and specify 25 as the initial estimate for

reflux ratio. The other operating specification is disabled

because you can only specify one spec when Reboiler is None.

6 The Blocks | B1 | Setup | Configuration sheet is complete:

7 Click to continue.

The Blocks | B1 | Setup | Streams sheet appears. Use this

sheet to describe how the streams are connected to the RadFrac

block.

8 For the SOURWAT feed stream, enter 3 in the Stage field and

Above-Stage in the Convention field.

9 For the STEAM feed stream, enter 10 in the Stage field and

On-Stage in the Convention field.

Because stream VAPOR is connected to the vapor distillate

port, Aspen Plus automatically assigns stream VAPOR as a

vapor phase product from stage 1. Similarly, Aspen Plus

assigns stream BOTTOMS as a liquid phase product from

stage 10. The Streams sheet does not allow flow specifications

for distillate product or bottoms product streams.

10 Click to continue.

The Setup | Pressure sheet appears.

Getting Started - Electrolytes Modeling a Sour Water Stripper 3-17

1 In the Stage 1 / Condenser pressure field, enter 15 psi.

2 Click to continue.

The Required Input Complete dialog box appears, indicating

that all required input specifications have been entered:

3 Click Cancel to close the dialog box.

You can now enter optional specifications. These specifications

include setting up two design specifications. The first will be a

concentration of 5 ppm NH3 in BOTTOMS, and the second will be

a condenser temperature of 190°F.

1 Click the Blocks | B1 | Design Specs folder.

The Design Specs object manager appears.

2 Click New.

The Create new ID dialog box appears:

3 Click OK to accept the default ID of 1.

The Design Specs | 1 | Specifications sheet appears.

4 In the Type field, click and select Mass purity.

5 In the Target field, enter the value 5.0E-6.

6 Click to continue.

The Design Specs | 1 | Components sheet appears. Use this

sheet to specify where this specification is to be applied, and

what component and phase it applies to.

7 In the Components area, from the Available components

column, select NH3 (ammonia) and click .

8 Click to continue.

The Design Specs | 1 | Feed/Product Streams sheet appears.

9 From the Available streams column, select BOTTOMS and

click .

To Specify that this

Column Operates