B49CG: Aspen Plus - Engineering Assignment Help

Assignment Task

Question 1 A liquid feed of 150 mol/min at 405.3kPa and its bubble point is fed to a distillation tower to recover 90% of the n-pentane in the overhead and 90% of the n-hexane in the bottom. The composition of the liquid feed is given in table 1. The reboiler is operating at 405.3kPa and there is a pressure drop of 20kPa across the distillation column. Assume that the distillation column is operating at 1.14 times the minimum reflux ratio, R_min and the overhead product leaves the column as a liquid stream.

You are required to model this distillation column using short-cut distillation unit in Aspen Plus and select Peng Robingson as the thermodynamic model. Note: Simulation file is required.

From the simulation result, determine:

1. The bubble point of liquid feed

2. The molar flow rate (in kmol/h) and molar composition of overhead and bottoms.

3. The minimum reflux ratio

4. The number of trays at 1.14 R_min

Question 2 Ammonia, NH₃ can be synthesized by reacting nitrogen, N₂ with hydrogen, H₂ through the following reaction:

A stream having a molar flow rate of 100 kmol/h, containing 25 mol% of N₂ and 75 mol% of H₂ at 300 K and 1 bar is fed to a reactor which operates at 300 K and 1 bar. Simulate the reaction process in an equilibrium reactor using Peng-Robinson property package. Hint: You can assume the temperature approach to equilibrium is 0 °C. Note: Simulation file is required.

From the simulation result, determine the following:

1. The equilibrium constant at 300K

2. The molar flow rate (kmol/h) and molar composition of each component in the reactor effluent stream

3. The fractional conversion of nitrogen at 300K

You are then tasked to investigate the effect of temperature from 280K to 500K on the equilibrium constant and the molar composition of NH₃ in reactor effluent. Based on your simulation model,

1. Comment on the effect of temperature on the molar composition of NH₃ in reactor effluent and equilibrium constant.

2. Generate a plot to show the effect of temperature ranging from 280K to 500K on the molar composition of NH₃ in the reactor effluent.

3. Tabulate a table for equilibrium constant at temperature ranging from 280K to 500K with the interval of 10K. From the tabulated table, determine the equilibrium constant at 400K.

Question 3 AspenPlus is known for simulating fine chemical systems including solids. For this simulation question, create a new Aspen Plus simulation using the “solids” template and add in components Air, Water and Titanium Dioxide. The Titanium Dioxide is an in-soluble solid powder with a d50 size of 40 micron and a standard deviation of 38.

Explore solids separators including:

a. Cyclone for separating air/TiO2 mixtures. Choose sensible flowrates for each phase, but a suggestion is 1000 kg/hr TiO2, 20000 kg/hr of air, both at 5 deg C, 2 bar pressure. Start with a cyclone diameter of 2m, and see if you can detect a separation taking place as you would expect. Change the cyclone size to achieve a suitable differentiation in particle size from the two product streams.

b. Increase the moisture content of the feed stream to 10 wt% (wet basis) and repeat the cyclone separation. Identify where the water will go.

c. Install a dryer and see if you can bring the moisture content of the wet product from the cyclone down to 2 wt% (wet basis). Note you will have to select a “contact dryer”, choose a sensible length and heat transfer properties.

d. Finally, recombine all streams together. Does the solids particle size distribution of the mixed product match with the feed stream?

Question 4 Figure below shows a biodiesel production scheme via an acid-catalyzed process using waste cooking oil (WCO) which has a feed flow of 920 kg/h to produce biodiesel (FAME) with glycerol (C₃H₈O₃) as a by-product. Triglyceride with triolein 90 wt% (C₅₇H₁₀₄O₆) and free fatty acid by oleic acid (C₁₈H₃₄O₂) 10 wt% are used to represent the composition in the WCO. Methyl oleate or oleic acid methyl ester (C₁₉H₃₆O₂) are chosen for the biodiesel (FAME). Fresh methanol, WCO and H₂SO₄, CaO feeds are at 25o C and 1 bar. In transesterification reactor R1, the feed molar ratio of oil: methanol: H₂SO4 are 1:50:1.35. WCO is pumped to 4 bar and heated to 60 o C before entering the reactor. The recycled methanol stream combines with fresh methanol and H₂SO₄ acid, pumped to 4 bar prior feeding into the reactor R1.

Transesterification take place in R1 assuming that 97% of the triglyceride is converted into FAME (the main product) and glycerol. The liquid product of the reactor consists of glycerol, methyl oleate and unreacted methanol, acid, and oil, which enter the distillation tower (DC-1). DC-1 recovers the excess liquid methanol (99.9wt%) in the distillate, cooled down to 30 o C before recycled to R1. The bottom product stream from DC-1 is cooled to 70 o C and transferred into the esterification reactor, R2. All oleic acid is converted into methyl oleate in R2 as shown in reaction eq (1):

It is aimed to remove all the acid catalyst in the neutralizing reactor R3. Sulfuric acid is completely removed by neutralizing and adding CaO(s) by forming CaSO₄ precipitate and water as shown in reaction eq(2)

The output stream of R3 is sent to a centrifuge to separate all the solids from the liquid stream. The liquid stream is further sent to the second distillation column DC-2 operating at vacuum condition. In DC-2, the target is to separate the lighter compounds water, glycerol from the FAME (main product) and obtain biodiesel purity of at least 95 wt%.

Further information of the operating conditions of reactors and distillation columns are provided below:

**If there are missing parameters of CaSO4, add the free energy of formation (DHFORM and DHAQFM) = -338.7 kcal/mol under Parameters-Pure components- New- Scalar

You are required to simulate the above process in Aspen Plus using the NRTL model. From your simulation, determine the following:

a) The molar flow and composition of recycled methanol stream

b) The amount of CaO(s) required

c) The reboiler and condenser duty (in kW) of DC-2

d) The FAME product stream mass flow and compositions

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