Department of Chemical and Environmental Engineering
Faculty of Science and Engineering
LEVEL:
3
MODULE:
Simulation 1 (H83PS1)
ASSIGNMENT:
HYSYS modelling of synthesis loop
ISSUE DATE:
1
stNovember 2016
SUBMISSION DATE:
Monday 21
stNovember 2016 (4:00 PM)
Submission
(1)
This handout with all questions answered is needed for hardcopy submission.
(2)
The e-copy of simulation file must be uploaded to Moodle before the completion of
the given time frame. Name the files as below:
Simulation file:
your name_ID.hsc
LECTURER:
Dr Nusrat Sharmin
To be completed by the student
Name: Date submitted:
Course: Student Signature:
Certification: I certify that the whole of this work is the result of my individual effort
and that all quotations from books, periodicals, etc. have been acknowledged.
_____________________________________________________________
_________________
To be completed by the lecturer:
Comments:
Part 1 (14%)
Part 2 (11%)
COURSEWORK 2 (25%) Instruction
Follow the instructions given in the handout. Use the appropriate equipment for changing the operating conditions when moving from one stream to the next. Assume zero pressure drop in equipment UNLESS otherwise stated; and do not worry about information that are not mentioned in the
handout. Leave everything at default unless specified. Also, for all values not given, provide an initial estimate and optimise it later if needed. At any mixing point or recycle, ensure the consistencies in units, use any heater, cooler, pump or compressor if needed.
Project Tender
You are being offered the opportunity to take over the management of a design of a process for the manufacture of synthesis gas from natural gas for International Chemicals Incorporated (ICI), after the termination of the services of the previous company working for ICI, Emek Projects Ltd (EPL). The
original EPL design was shown in Appendix A.
Your design should produce synthesis gas with a molar ratio of H2 to N2 of 3:1, to be used in the future
for ammonia production, assuming a basis of 12,000 kg/h of methane as feed, at a cost of 10 cents/kg. The main by-product of the process is CO2, which has a market value of 10 cents/kg provided
that it can be produced at a purity of at least 98 mol%.
Table 1: Product specifications and revenues (NOTE: These are the DESIRED specifications of the PRODUCTS from the process which can maximise the profit)
*Note that the waste disposal unit can accept streams at any temperature, pressure and composition.
Table 2: Costs of raw materials Raw material Specification
Natural Gas Up to 12,000 kg/h (288 T/day) of pure methane is available at 15 bar and 30oC, at
a cost of $0.1/kg.
Steam An unlimited supply of 15 bar saturated steam is available, at a cost of $0.02/kg. This needs to be supplied both to the reformer (Reformer Steam) and the
oxidation reactor (Combustion Steam).
Air An unlimited supply of air is available for free, at 1 bar and 30oC. The composition
Product Specification Revenue
Synthesis gas
(a) A molar ratio of hydrogen to nitrogen of 3 (ideally, this ratio needs to be 3:1); (b) no water; (c) CO and CO2 under 1
ppm each; (d) minimum inert (Argon and CH4).
To be sold for the production of ammonia
Carbon dioxide
CO2 should be supplied at a pressure in
the range 15-50 bar, with a purity of at least 98 mol%; there are no restrictions on its supply pressure, provided it is a liquid.
There is no upper limit in the production rate that can be accommodated. The revenue on CO2 that meets the above specifications is
$0.1/kg. In the event that any of the specifications are not met, the gas is
considered a waste stream that needs to be safely disposed of, at a cost of $0.05/kg*. Water Water can be reused in the process,
provided its purity is greater than 99.5 mol%, and at temperature less than 50
oC. There are no restrictions on its supply
pressure, provided it is a liquid.
There is no upper limit in the production rate that can be accommodated. While product that meets the above specifications does not generate revenue, note that in the event that any of the specifications are not met, this stream is considered a waste stream that needs to be safely disposed of, at a cost of $0.05/kg*.
of air is: 78.08 mol % nitrogen, 20.95 mol % oxygen, 0.94 mol % argon and 0.03 mol % carbon dioxide.
Production process in details
A possible route to ammonia is from natural gas. The process involves two main parts: Part 1 - the reaction section, and Part 2 – the separation section.
Part 1:
Tips: Use an appropriate fluid package to simulate this operation. Then, create a template from your flowsheet and save as a template.
Synthesis gas generation (see Appendix A): The objective of this section is to produce as much synthesis gas as possible, and to ensure its purity. The specifications for synthesis gas are: (a) a molar ratio of hydrogen to nitrogen of 3 (ideally, this ratio needs to be 3:1 in the NH3 converter feed); (b) no
water; (c) CO and CO2 under 1 ppm each; (d) minimum inert (Argon and CH4). To achieve these
objectives, the following steps are employed:
1) The methane is combined with reformer steam, preheated in the heater E-101 and then fed to the reformer, in which most of the methane is converted to hydrogen. The reformer is modelled as an isothermal PFR with kinetic reactions (the effluent temperature is set to be equal to the feed temperature). In the EPL design, the operating temperature is selected as 700 oC.
Note that PFR is in the “Common” tab of the HYSYS palette; for simulating a PFR, after the connections, under “Parameters”, assume zero pressure drop, insert the reaction set, and under “Rating”, use a volume of 1 m3 and length of 1 m.
The following reactions take place in the reformer: Rxn-1: CH4 + H2O ↔ 3H2 + CO
Rxn-2: CO + H2O ↔ CO2 + H2
According to Parisi and Laborde (2001), reaction rates for these two kinetic reactions are as follows:
−
r
CH4=
[
k
1∙exp
(
−
E
1RT
)
]
P
CH4P
H2O−
[
k
1' ∙ exp
(
−
E
1'
RT
)
]
P
COP
H2 3 kmol/m3-s−
r
CO=
[
k
2∙exp
(
−
E
2RT
)
]
P
COP
H2O−
[
k
2' ∙exp
(
−
E
2'
RT
)
]
P
CO2P
H2 ❑ kmol/m3-sIn the above equations, the species partial pressures are expressed in atm, T is the temperature in K, and that -rCO holds for T > 860 K. Parisi and Laborde (2001) provide kinetic parameters as
follows: E1 = E2 = 16,000 kJ/kmol,
k
1 = 200 kmol/m3-s,k
1'
= 9.2290×10-12 kmol/m3-s, E1’=-212,336 kJ/kmol,
k
2 = 100 kmol/m3-s,k
2'
= 4,316 kmol/m3-s, E2’= 49,655 kJ/kmol.Tips: Simulate all kinetic reactions as “Kinetic reaction”, key in the Stoichiometric Coefficient, on the basis of “Partial Pressure” and “Overall” Rxn phase; what you need to do to specify the kinetic reaction is to key in the k and E values for the forward and reverse reactions)
2) The reformer effluent is combined with air and more steam in such a way as to try to ensure a 3:1 mixture of hydrogen and nitrogen in the resulting synthesis gas. This mixture is reacted in the oxidation reactor, often referred to a “secondary reformer,” modelled as an adiabatic PFR with heterogeneous catalytic reaction, where the oxygen in the air generates additional hydrogen. In addition to Rxn-1 above, the following reaction also take place in the oxidation reactor:
Rxn-3: CH4 + 2O2 → CO2 + 2H2O
According to Wolf et al (1997), the reaction rate for the above reaction takes the mathematical form:
−
r
CH4=
1000 ∙ exp
(
−32000
RT
)
∙ P
CH4P
O2(1+K
C H4P
C H4+
K
O2P
O2+
K
C O2P
C O2+
K
H2OP
H2O)
kmol/m3-sNote that in the above equations, the species partial pressures are expressed in kPa and T is the temperature in K. Wolf et al (1997) provide kinetic parameters as follows:
K
C H4=1.1× 10
−6∙ exp
(
−
E
C H4/
RT
)
, E
CH4=32,200 kJ /kmol
K
O2=1.1 ×10
−2∙ exp
(
−
E
O2/
RT
)
, E
O2=28,400 kJ /kmol
K
C O2=1.5 ×10
−4∙ exp
(
−
E
C O2/
RT
)
, E
CO2=32,900 kJ /kmol
K
H2O=5.3∙ exp
(
−
E
H2O/
RT
)
, E
H2O=27,300 kJ /kmol
Tips: Model the above reactions as “Heterogeneous catalytic reaction”, on the basis of “Partial Pressure”, and “Overall” reaction phase; what you need to do is, under the “Reaction Rate” tab, to challenge yourself to fill in the Numerator and Denominator sessions)
3) Since the first two reaction steps generate CO, which would poison the ammonia synthesis catalyst, shift reaction steps are employed to convert the CO to CO2. Both of these reactors are
modelled as adiabatic kinetic reactors. The first shift reactor, High-temperature (HT) shift, is fed the oxidation reaction effluent. It is possible to install a heat exchanger to modify its inlet temperature, as is done for the LT shift, where the heat exchanger E-102 reduces the feed temperature to 500 oC.
The following kinetic reaction takes place in the shift reactors, which are PFRs: Rxn-4: CO + H2O ↔ CO2 + H2
The same kinetic form is used as before, but, as stated in Parisi and Laborde (2001), the kinetic parameters are slightly different, since the shift reaction is carried out at lower temperatures:
−
r
CO=
[
k
2∙exp
(
−
E
2RT
)
]
P
COP
H2O−
[
k
4' ∙ exp
(
−
E
4'
RT
)
]
P
CO2P
H2 ❑ kmol/m3-sIn the above equation, the species partial pressures are expressed in atm, T is the temperature in K, and that the above kinetic holds for T < 860 K. Parisi and Laborde (2001) provide kinetic parameters as follows: E2 = 16,000 kJ/kmol,
k
2 = 100 kmol/m3-s,k
4'
= 7,594 kmol/m3-s,E4’= 54,053 kJ/kmol.
4) Any remaining CO is converted back to methane in the methanator, modelled as adiabatic PFR reactor. In the methanator, Rxn-1 takes place, with the same kinetics. The operating temperature needs to be low enough to ensure that the reverse reaction dominates. In the design, the methanator feed temperature is selected as 250 oC.
Part 2:
Start a new simulation and register the components appearing in this part 2 simulation using a different appropriate fluid package. After entering the simulation environment, install the template created for Part 1 as a sub-flowsheet.
5) The water produced in the previous reaction steps is removed. One possible implementation involves cooling using E-104 to 40 oC to condense the water in the stream, and its removal largely using the
flash vessel, V-100. Residual water is removed via S-14 using adsorbing beds, modelled using a separator, X-100 (i.e. only water as liquid is removed via S-14).
TIPS for component splitter: Equalize all stream pressures and specify vapour fraction as 1 for top product, and 0 for bottom product).
6) The CO2 produced in the previous steps is removed. One possible implementation, suggested by
EPL, involves simply cooling the effluent from X-100 using E-105, condensing out most of the CO2 in
flash vessel V-101 as by-product, and then total removal of the residual CO2 using adsorbing beds,
X-101. Decide the flash temperature (V-101) to be used for effective removal of CO2.
Questions
Simulation:
1. Simulate the process using HYSYS. Save and upload this HSC case fil in the format of “File1-your name.hsc”. [13%]
2. Use the ADJUST, SET, SPREADSHEET functions where necessary to achieve the desired product
specifications as shown in Table 1. Wait for a considerable amount of time for converging. Save and upload this HSC case fil in the format of “File2-your name.hsc”. [13%] [6%]
Answer the following questions:
3. Which thermodynamic models were used in the template and the main flow sheet? Justify your selections. [2%]
4. Did you manage to produce synthesis gas, CO2, and water with the desired specifications as shown
in Table 1? If yes, briefly describe how you did that; if no, justify your reasons. [2%]
5. What is the temperature of the stream entering flash column (V-101)? What are the factors to be considered while setting specifications for flash column output? Hint. Assume that the cost of operating the special equipment modelled using splitter are known. [2%]
Appendix A: The Original EPL Design for Synthesis Gas Production
