Steam Cycle Simulation Aspen Plus v8 - Campus Tour

Steam Cycle Simulation ? Aspen Plus v8.6

The attached gives steps to set up a simulation in Aspen Plus v8.6 to model a simple Rankine steam cycle for electricity production. The system consisting of:

Fuel side with natural gas feed, air blower, combustion chamber, & fuel side of the steam boiler.

Steam side with steam turbine, steam condenser, condensate pump, & steam side of the boiler.

The simulation will be set up assuming isentropic steps for the rotating equipment.

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. Choose the Gas Processing then the Gas Processing with Metric Units template. Click the Create button.

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Define the Components & the Property Models Specify components, fluid property packages, & crude oil assays

The first step is to define a set of pure chemical species to represent: Steam as modeled by pure water & using property correlations consistent with the ASME Steam Tables. The natural gas fuel, air, & combustion exhaust as pure light components modeled by the Peng-Robinson equation of state (EOS).

Now let's add components to model the fuel side of the system. Go back to the Component Lists item & click on the Add button to create Component List -2. We need components for the following:

Steam. For now we'll model as pure water. Natural gas. For now let's model this as a possible mixture of methane, ethane, & propane. Air. For now we'll model this as a mixture of oxygen & nitrogen. Combustion gases. At the minimum we'll also need carbon dioxide and water (which we

also need for modeling the steam). However, we'll also want to take into account incomplete combustion (forming carbon monoxide) as well as NOx formation (for now just as NO, NO2, & N2O).

Click the Find button to bring up the databank search form. You can enter either the entire formula, part of a name, or several other possible search items to find all of the desired chemical species. When the proper compound is found, select it in the list & click Add selected compounds. The following figure shows a search for H2O. As you are adding compounds you may be asked whether to add or replace the compound already in the list; choose the Add option.

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Below is an example of components retrieved from the Aspen databanks. There are two issues with default manner in which this list is presented. One, the Component IDs are not very descriptive of the compound (especially as compared to the Alias values). Two, the order does not group the

compounds in a convenient manner. We can address both of these issues before proceeding much

further.

Let's change the Component ID values to mostly match the Alias values. Select the Component ID

value either by double-clicking on it or by clicking & then pressing the F2 key. Once selected, type in the new ID & press the Enter key. Aspen Plus will ask what you really want to do by making this change; click the Rename button. Change all IDs.

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Now press the Reorder button. A form pops

up that will allow you to move selected

compounds up or down so that they in a convenient order. Press Close when done.

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The next step is to assure that an appropriate fluid property package has been chosen for these compounds. Click on Methods in the All Items list on the left. From here we see that the Peng- Robinson EOS has been specified as the base method (per the choice of template originally chose). Also the ASME steam table option has been specified for cases when only water is present in the stream. These are the desired options so we can continue on.

Now is a good time to save the file before we start setting up the process simulation. Click the File tab & then the Save As item. Choose the Aspen Plus Backup option.

Set up & Solve the Flowsheet

Working Units

Activate the Simulation option. Note that you'll see a blank flowsheet.

We would like to show the calculations with a modified set of SI units, in particular: Temperature as ?C. Pressure as bar (absolute). Mass flow as kg/sec. Molar flow as kg.mol/sec. Heat duty as kJ/sec. Power as kW.

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