Uploaded by ScuolaTech on 31.05.2012

Welcome to the new tutorial of the software ASPEN by the channel Scuolatech
Today we will analyze Aspen Energy Analyzer
This is the version 7.2, in the previous versions the name was Heat Exchanger Network
This program allows to complete the Heat Integration. Nowadays it is a very important feature for the industrial economy.
Optimizing the utility network we can save money both for hot and cold utilities.
Let's analyze our problem which we will reproduce together in ASPEN Energy Analyzer
In our plant we have a feed stream 1 at 20°C that we heat to 180°C
R1 is the reactor which increase the temperature to 250°C. Feed 2 is preheated from 40 to 230°C before entering R2.
R2 is a reactor where an endotermic reaction take place. The exiting stream is then cooled down to 80°C
The fourth heat exchanger is the one which cooled the stream from 250°C to 40°C to allow a final separation of the main Product 1.
All the datas of the 4 streams are reported in the table.
Feed 1 and Feed 2 are called COLD Streams becouse they increase their temperature in the Heat Exchangers.
HOT are the exiting streams from the Reactors which decrease their temperature in the HE.
In the table you can also find the information of the DH the Enthalpy variation, and the CP heat capacity, the product between the mass flow rate and the specific heat capacity at costant pressure.
We are ready now to implement all these datas in ASPEN ENERGY ANALYZER
First of all we have to click on Managers --> Heat Integration Manger
We have now the possibility to chose between HI Case & Project. Let's start with the case which is easier.
We have to fill this table as the previous tab.
Feed 1 enters at 20°C and exits at 180°C, let's insert the heat capacity that is 0.2 e^6 MW/°C
The software automatically calculate the enthalpy
and the HTC, the default value is 720. If we are interested in a particular fluid to evaluate the heat exchange area we can visualize the database and choose the correct fluid.
The basic parameter in the evaluation of the heat exchanger area is the global heat coefficient. This consider also
As we have done for the stream 1 we can complete the table with all the datas.
We insert the temperatures and the CP and Aspen calculates the enthalpies
ASPEN uses a blu arrows for Cold Streams and a red one for the Hot
For more detailed flowsheet is possible to import these datas for example from excel or aspen plus. You only have to click on this Icon.
This other one is the icon to import directly from Excel.
Click on "Open Target Views" and Plot Tables.
Here we have the Composite Curves. We observe that we are using a minimum temperature difference of 10°C.
Furthermore we notice that we need both cold and hot utilities to complete the heat demand of the system.
Is also possible to analyze different curves as the Grand Composite Curve
In the summary the software report the heat and cold duty, and the pich temperatures.
From the main window we can open the Heat Exchanger Network Grid Diagram
Here we have the four streams, from the top 2 4 3 1. The higher temperature is on the left of the diagram
Now we couple hot and cold streams using Linnhoff rules for heat integration.
First of all let's insert the pinch line. Only three streams cross the pinch.
Let's start the study of the system above the Pinch, on the left side of the screen.
The rule indicates to couple an hot stream with a cold stream respecting the condition that the hot stream heat capacity CP must be lower than the cold one.
Here are reported the CP of the streams. Let's start to pair the stream 2 (CP 0.15) with stream 1 (CP 0.2)
In this way we allow to cople later the stream 4 (0.25) with stream 3 (0.30)
We have to draw an heat Exchanger (HE) so click on this icon with the right button and hold until you arrive on the line.
To insert the heat exchanger click on this icon with the right click and hold until you arrive on the stream.
Now we have to link this point with stream 1 so click and hold the left button. We have create the first HE
Double click on the line to open this window. Here we have to insert the inlet and exiting temperature values.
The inferior limit is the pinch T because we are working above the pinch: 150°C for Hot stream and 140 for the cold one.
We have now to introduce the third temperature so the program can calculate the last one from the energy balance.
If we insert here 240°C we have as fourth temperature 207°C that is impossible because the upper limit is 180°C.
This means that we must consider the maximum temperature difference and heat capacity of the streams.
The cold stream is limiting so we have to insert 180°C or click on TIED to have the same value
We have complete the first HE and the analysis is correct with right temperatures. This scheme report also the heat duty and the area.
Let's now couple streams 4 and 3. As we do before we insert the HE.
The lower limits are the pinch temperatures. the hot stream has a maximum DT of 50°C so is the limiting one and i click on tied.
The continuous lines indicate that the heat integration is complete! Now on the left side, far from the pinch, we can couple stream without respect the linnhoff rule.
We integrate the stream 2 with 3 with an HE. Let's complete the specifications.
The temperature differences are the same. In every way the hot stream has a lower heat capacity (0.15) so it is the limiting one.
We can click on tied on both sides, for the cold stream we tied only on the right side of the lower temperature.
The fourth temperature is 205°C
The heat integration allows us to add an other continuous line. Remains only an other part which can't be integrated.
Let's analyze BELOW the PINCH now.
In this zone the Linnhoff rule is the opposite. the hot stream must have an higher heat capacity.
We can couple only the stream 4 (CP=0.25) with the stream 1
As we have done before we add the heat exchanger and we set its specification.
We tied the higher temperatures of both streams. The constraining stream is the hot because has a lower temperature difference.
We tied the hot stream on the right side and we find the last temperature.
We can couple streams 1 and 2 now!
Tied on the left side and on the right for the cold stream because it's limiting.
we complete the application of the Linnhoff Teory
The streams 1 and 4 are completely integrated. Only dashed lines are not integrated.
This means that we have to add to system an hot and cold utilities as we discover at the beginning in the grand composite curve.
Let's come back in the table now.
We click on Utility Stream. We have to choose an hot utility which assure 250°C and a cold one at 20°C.
Let's choose for the hot utility the low pressure Steam. This is not enough as we can see from the temperature and the red boxes.
We have the same result with the middle Pressure Steam. We are obliged to use High P Steam, the box becomes green.
For the COLD utility we first try with the Cooling Water because is the cheapest one.
In every way he temperature value of 20°C is very difficult to obtain. Is better to modify this value and set an higher one.
We set 35°C as the exit temperature and 30°C as the entry one.
We come back on the Grid Diagram and with find also the utilities with continuos lines.
We have now to link them with the not integrated streams.
We tied both sides.
We repeat the same operation on the other side. The system is now complete.
We integrate the original plant using 5 heat exchangers. For the hot stream we use HP steam, for the cold, water.
Open -> Controllability view It's interesting to underline loops and paths of the system
Right click and show loop to visualize them.
Let's move in "Targets View" In the summary we find a completed table.
We have info about the power. In area targets there are info about the total area of the HE.
The first number is we use counter current HE, the second if they are shell and tube.
Very interesting are the cost index targets. They are divided in capital, operating (utility) and total.
To analyze the cost of the utilities we have to move in the tab "utility targets". Here we can see the power and their cost.
In the Economics tab we can analyze the capital cost. The HE cost are evaluated using some parameters and a formula.
Using the different information we can estimate the capital cost of the plant.
On the right you can see the ROR Rate of Return fixing a plant life of 5 years.
Target View --> Plots and Tables. We analyze the balanced composite curves.
The graphical representation introduce here also the utilities.
The Utility Composite Curve underline the HP steam and the cooling water with red lines.
For this analysis we use a minimum temperature difference of 10°C. We can change this value estimating the variation of the costs.
For this analysis we use a minimum temperature difference of 10°C. We can change this value estimating the variation of the costs.
In range targets we click on DTmin range and we can fix a minimum and maximum value and also the step.
We click on calculate and the software reproduce the estimation of the cost changing the DTmin.
In this tutorial we complete the heat integration adding also hot and cold utilities.
In this tutorial we complete the heat integration adding also hot and cold utilities.
We can find other solutions on this problem. We should compare them and choose the best on an economic criterion.
Explore the other ASPEN Tutorials on the Channel Scuolatech If you have questions you can also comment the video!
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