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HomeExercise 1. CHEM-E1120 Thermochemical Processes 27.1.2016
Kristian Melin
To Get started: Start Aspen by choosing from start menu Aspen Tech Aspen Process Modeling v 8.6 Aspen
Plus and Aspen Plus Graphical User Interface. Make a new simulation by choosing new and press create.
Save the file as a .bkp file.
First chose properties in the low left corner. There the units used in the simulation, components and thermo
dynamic properties can be chosen.
First we have to define the units in the simulation, In the Menu at the left chose setup, then chose
Specification. Chose METCBAR as the global unit set. On the setup sheet you can choose unit of
measurement for input and output data. If you want to define an own units press Units sets new. Give a
name for the new set of UNITS example SI2, chose copy from SI etc. Now you can edit the unit used for
example change K-> C and KPa-> bar.
Next go to components. Simple components Aspen automatically finds for example oxygen. When the
components is found all the information name etc. is added to the menu. If we have a more complicated
component you can use the find command to search it from the program data bases.
Next go to the Methods in the left menu. On the Global sheet chose Method Filter all and base method
SRK. Here you can choose the Thermodynamic method VLE method etc. You can find more information
about the method reference etc. by pressing F1.
Next we should define the Flowsheet streams and blocks. Press in the lower left corner simulation. In the
bar at the top press Main Flowsheet. In the bar below we find at the left corner the streams (material, heat
and work) and on the right we find the different blocks mixers, splitters, separators, reactors, columns,
pressure changers etc. You draw the flowsheet by connecting a stream with a block. You have to connect
streams to all red (mandatory) ports in the block. There is usually at least one required input and output
stream for each block. If you connect the stream to a wrong port you can press the stream and chose
reconnect source or reconnect destination. You can also rename the blocks.
In addition to blue ports an optional stream can be added from example water decantation stream. For the
streams that do not come from a block the composition, temperature, pressure has to be defined. You click
on the stream and the input information will be shown.
In the blocks you have to define the required information. You can run the simulation by pressing N->. If
all input is not complete the missing input will be showed.
After simulation check the message in the low right corner. Results available with blue means that the
simulation has converged and there are no errors. If there are warning a yellow text will be shown. If the
text is in red the simulation stated that results are available with errors. Especially for the red case the
results are probably not correct because a solution was not found. For yellow case we should check in the
run panel what is warning. The results can be studied by pressing right mouse button in the flowsheet for
streams and blocks. If you want a complete material balance you can chose all steams in the menu. You can
copy all streams results by pressing mouse left button. The results are copied to the clipboard and you can
paste them in for example excel.
If you have calculated the simulation using bad input values and a solution is not found it is sometimes
necessary to reinitialize the simulation. You can do this by choosing Re-initialize (the beginning sign) in the
top row under the home menu.
Sometimes we need to the report options. Go to stream sheet. Chose Items to add in the stream report. Mark
flow basis mole and mass and fraction basis mole and mass.
1.
One stream at 101 KPa and 25 ºC consist of 1000 kg/h of carbon dioxide, 200 kg/h oxygen, 1900 kg of
nitrogen and 100 kg/h water. It is mixed with another stream with a total flowrate of 500 kmol/h at 50 ºC
and 1 bar containing 50 mol % methane and 50 mol % carbon dioxide. Find by simulation the composition
w-% and mol - % of the mixed stream. The mixed stream is subsequently separated into two streams. The
first stream has a flowrate of 1000 kg/h. What is the volumetric flowrate of the remaining stream? Feed
both streams to a mixer block and separate them by a FSPLIT block.
Answer: 14760 m3/h
2.
3000 t/h water at 1 bar and 80 °C is feed to a pump which increases the pressure from atmospheric to 10 bar
absolute. Subsequently the water is heated up to the 150 ºC by a heat-exchanger (pressure drop 0). In a
second heat-exchanger the condensate vaporized so that saturated steam is produced (vapor fraction 1)
while the pressure is still 10 bar. The saturated steam is condensed in another heat exchanger (vapor
fraction 0) therby heating up another process stream not considered in this simulation. The condensate is
feed to a vapor liquid separation vessel (flash) where the pressure is reduced to 5 bar(a). Then part of the
water is evaporated due to the pressure reduction. The vapor is compressed to 10 bar by a isentropic single
stage compressor. What is the electric consumption of the pump and compressor? Also check the
temperature of the steam after compression and the duties in KW of the heat-exchangers. For heaters use
simple heater blocks. Use Pump and Compr block. You do not specify any efficiency here. For the
compressor also connect an optional water decant stream to the blue port besides the mandatory outlet
stream which you connect to the red port in the COMPR block.
Pump duty 959 kW Brake power, 1 st Heat Exchanger286 MW,2 nd Heat Exchanger 1887 MW, 3rd HX1759 MW, T steam after compression 265 ˚C, Net work of the compressor required 10,6 MW
3.
Synthetic natural gas is produced in a reactor from carbon monoxide and hydrogen according to the
following reactions. CO+ 3H2 -> CH4+ H2O and CO2+4H2->CH4+2H2O.
The reactor feed is 1 kmol/h CO, 3kmol/h of CO2 and 1 kmol/h H2O and 7 kmol Hydrogen. All the carbon
monoxide and 20 % of the carbon dioxide is consumed in the reactions. Input the reactions in the RSTOIC
block and define the fractional conversion for each reaction.
The reactor is adiabatic (duty=0) Also there is no pressure drop (p=10 bar). Check what is the outlet
temperature and reactor outlet gas composition expressed in mol %. Use yield reactor (RSTOIC) Duty is 0
kW. Specify the chemical reactions stoichiometric coefficients for both reactions in the reaction sheet. The
reactor feed is at 10 bar and 250 °C. 1092 ˚C
4.
1 kmol /h of pure carbon, 0.1 kmol /h of water and 5 kmol/h of air is feed to a boiler at 1 bar and 25 °C and
combusted adiabatically. Add Graphite carbon, NO and NO2 as components. Specifity the graphite and
moisture in one stream and air in a second stream. Specify air stream composition as: 79 mol % nitrogen
and 21 mol % Oxygen. Use RGibbs reactor and define Heat Duty is 0, pressure is 1 bar. Use calculation
option: Calculate phase equilibrium and chemical equilibrium. On the calculation sheet all keep the RGibbs
consider all components as products. Check products and temperature of the outlet stream. How much is
the adiabatic combustion temperature and what is the calculated composition of flue gas on total basis mol
% of all components.
Mole Frac
CO2
0,1726144
N2
0,7633951
CH4
5,0535E-19
WATER 0,0189817
O2
0,0178748
CO
0,0213322
H2
0,000412956
CARBON
3,4597E-16
NO
0,00538723
NO2
1,47769E-06
T =2086 ˚C
In order to calculate adiabatic combustion temperature we could also use a RSTOIC reactor instead of
Gibbs Reactor. Specify duty 0 and pressure as 1 bar. On the combustion sheet specify generate combustion
reactions. NOX generation product could be Nitrogen Dioxide. Check the differences?