School of Chemical Engineering
CEIC3005 Process Plant Design
If any changes are required to the original assignment information they will be documented here.
Revision Date Changes
0 19/02/2019 Initial version
1 19/02/2019 Added requirement for online submission of Preliminary Report and provided
more detail on hard copy submission.
8 12/03/2019 PRS task modified and explained. Natural gas stream properties provided.
Design Assignment (30%)
Due on Moodle at 10am on Friday, 5th April 2019 (Week 7) and 9pm on Friday, 3rd May 2019 (Week 11)
Natural Gas Pre-treatment for Liquefied Natural Gas (LNG) production by removal of hydrocarbons heavier than pentane
There are two deliverables for this assignment. The first report contains your preliminary work and will be revised and incorporated into your final report.
Each report MUST contain all key technical design documentation elements:
– Document control
– Title page
– Executive summary
– Contents page
– Main report (as described below)
– Appendix (sample calculations, data book, other information)
Additional information on the assignment and the marking rubrics will be provided during term.
Preliminary Design Report #1 (10%) – due on Friday, Week 7 at 10am
Your group is required to provide the detailed design drawings and process risk analysis which include:
1. Block Flow Diagram (BFD)
2. Process Flow Diagram (PFD)
3. Preliminary Flow Summary Table (FST) (based on hand calculations)
4. Process & Instrumentation Diagram (P&ID) on one (1) unit operation (individual)
5. Process Safety Study: HAZOP of the Scrub Column (Group submission)
You will receive feedback on this report so you can improve your preliminary design for inclusion in the Final Report.
Submit this report as a hard copy to the School Office (outside SEB 128) and online through Moodle.
Final Design Report #2 (20%) – due Friday, Week 11 at 9pm
Your group is required to provide the detailed design report which comprised of:
1. Final design report 1
2. Process simulation optimisation
3. Revised Flow Summary table based on optimised process simulation
4. Economic evaluation
In this report, you will integrate your revised preliminary report sections with the rest of your process design. This involves preparing a process simulation and economic model of your design. By performing sensitivity analyses you will use these two models to optimise the design of your scrub column and NGL recovery plant. The outcomes of your process simulation will replace the preliminary FST.
The economic analysis should include
1. An estimate of the final capital investment, fixed & variable operating costs, and decommissioning costs
2. Economic indicators (minimum, discounted payback and NPV) from after-tax cash flow analyses
In addition to the report, you should submit a zip file containing your optimal process simulation model and a single spreadsheet containing your economic model. Ensure that these files can be easily understood by the markers.
Submit both the report and the zip file online through Moodle.
• All reports should be submitted through the applicable Moodle activity. Reports should be submitted as PDFs under 200 MB in size.
• Any other submissions (e.g. spreadsheets) should also be submitted through the appropriate activity on Moodle (files < 200 MB) or shared with the course coordinator using your UNSW OneDrive account (files > 200 MB).
• If you encounter problems trying to submit through Moodle, email it to the course coordinator ASAP. We will treat the received time as your submission time. Please include your name and student ID and the course code in the email subject line.
Submissions received after the due date will incur late penalties at a rate of 10% per day.
Background and Process Description
Natural gas is a fossil fuel consisting mainly of methane. However, it usually contains lesser amounts of higher hydrocarbons as well as certain impurities.
Natural gas can also be liquefied at -160°C for long distance transport by sea. The process that generates a liquid from gas is referred to as liquefaction.
The solidification of CO2, water and heavy hydrocarbons at cryogenic temperatures in the liquefaction process may result in blockage of heat exchange equipment. Also, there are traces of mercury in natural gas, which can attack and crack the aluminium metal used in cryogenic heat exchangers.
In an LNG processing train, it is usual to remove the CO2, water and mercury first and then remove the hydrocarbons heavier than C5 (pentane) by subsequent cooling to low temperature, condensation and distillation. A typical specification is for a maximum of 500 ppm (mol) “C5+” (i.e. C5s and heavier hydrocarbons) to remain in the gas, which is to be liquefied.
Along with the C5+, the cooling and condensation process will also condense LPG components such as propane (C3) and butanes (C4s). The C3s and C4s are quite soluble in LNG and so do not have to be removed for process reasons. However, they are usually more valuable than LNG and so their removal and separate sale can be economically advantageous.
In the most commonly used process, the natural gas, after CO2, H2O and Hg removal, is chilled to between -10°C and -20°C. The two-phase liquid and gas mixture so formed is fed to a rectifying column, and the gas leaving the top of the column is further cooled to form reflux for the column, which washes down even more of the heavy hydrocarbons. This column is sometimes called a “scrub column” because it “scrubs” the C5+ out of the natural gas.
The column may have a reboiler to strip out methane and ethane from of the liquid hydrocarbons but more commonly it does not. Instead, this stripping is accomplished by sending the column bottom liquid to a separate distillation train of distillation columns (which is outside the scope of this assignment.)
In large scale plants the cooling of the gas and the formation of reflux liquid is most commonly done using a propane refrigeration system, whereby different pressure levels of propane are evaporated to provide cooling at specific temperatures. Increasing the number of pressure stages increases the system complexity and cost, but it reduces the power consumption of the propane refrigeration compressor(s).
The process does rely on making a heavier liquid condense out of the gas. As a result, it may be necessary to reduce the pressure of the gas to below the cricondenbar, and then recompress it back to feed pressure to allow optimum liquefaction downstream. The pressure reduction can take place in a simple control valve (a “Joule-Thomson” valve) or in an expander.
Your team has been engaged by an energy company to design just that portion of an LNG plant that removes the C5+ components to <500 ppm (mole), along with other natural gas liquids, e.g. C3 and C4, using a propane refrigeration system, following the removal of acid gases, water, mercury and inert gases, which is outside your scope,
Working in teams of four, you make use of all aspects of your studies in process plant design. Please join a Design Team using the tool that will be provided on Moodle.
You will deliver two reports for this assignment – a preliminary and a final report. This is to facilitate you having the opportunity to improve your designs based on feedback from the teaching staff. You will also be able to get feedback through the weekly design tutorials.
Any questions should be posted in the course forum or asked during the design tutorial. Emails to the teaching staff should be reserved for personal discussions or issues with submitting the deliverables
For the final report, you are to economically optimize the plant by creating three different design configurations and recommending a preferred option based on your economic analysis. Some suggested variables that can be modified are:
1. The operating pressure of the column,
2. The temperature of the feed to the column
3. The number of refrigeration stages
4. The amount of LPG recovered with the C5+
5. Replacing the Joule-Thomson valve on the column feed with an expander, to increase refrigeration and reduce power consumption, at the expense of higher capex & complexity.
Remember that you are required to bring the cold stream with C5+ removed back to its original feed pressure before it enters the next stage of liquefaction
1. The C3MR Liquefaction Cycle: Versatility For A Fast Growing, Ever Changing LNG Industry, Dr. Mark Pillarella Air Products and Chemicals, Inc. http://www.ivt.ntnu.no/ept/fag/tep4215/innhold/LNG%20Conferences/2007/fscommand/PS2_5_Pillarella_s.pdf
2. Characteristics of Cascade and C3MR Cycle on Natural Gas Liquefaction Process Jung-in Yoon, Ho-saeng Lee, Seung-taek Oh, Sang-gyu Lee and Keun-hyung Choi https://waset.org/publications/12974/characteristics-of-cascade-and-c3mr-cycle-on-natural-gas-liquefaction-process
3. Evaluation and Selection of the Precooling Stage for LNG Processes, Mohamad Majzoub https://daim.idi.ntnu.no/masteroppgaver/008/8354/masteroppgave.pdf
5. Correlation for natural gas heat capacity, Mahmood Moshfeghian , John M. Campbell & Co.https://www.ogj.com/articles/print/volume-109/issue-40/processing/correlation-for-natural-gas.html
6. Propane P-H Diagram SI Units https://www.studentlitteratur.se/fileaccess/private/fid8272/produkt/37354EnBe/Propan.pdf
7. Thermodynamic Table in SI units for Propane and other Compounds http://me211.cankaya.edu.tr/uploads/files/Thermodynamic_tables_SI_units.pdf
Appendix 1. Select MEB Data and Design Criteria
A. Natural Gas Composition and Condition at Inlet of the Cool Down and Scrub Column System
B. Plant Capacity
Flow rate of gas = 100,000 kg/h
C. Economic assumptions
Cost basis = A$ (2018)
Construction time = 2 years (teams should decide phasing)
Operating life = 20 years
Decommissioning period = 1 year
Discount rate = ? (teams should decide this question)
Loan interest rate = 3%pa
Inflation rate = 2%pa
Income tax rate = 30%
Use straight-line depreciation.
Feed stock price = Australian east coast gas price
Sales price of LNG = 70% of crude oil price on an energy basis
Sales price of NGL = 100% of crude oil price on an energy basis
Appendix 2. Natural Gas Stream Data
Determining stream properties for a multi-component gas mixture at high pressure with non-ideal gas behaviour is complex and difficult to do via hand calculations for the first report.
Therefore, data on the stream properties for the natural gas streams in this part of the LNG Plant are provided below so you can complete the first report. You have plenty of work to do with the Mass and Energy Balances (MEBs) for the refrigeration loops which use a simple, single component (propane) whose properties are readily available from tables and charts.
For the second report, you will be able to use the process simulation program, Aspen, to calculate stream properties and MEBs yourselves and also to change conditions and optimize the process.
In the following stream table, please ignore the data for streams HPC3LIQ and HPC3VAP.
These are dummy streams used to enable creating a single cool down curve for the chilling of the natural gas from +30°C to -15°C. Your job is to work out how many stages of refrigeration to use and to complete the mass balance for each refrigeration loop. For each refrigeration exchanger, use a minimum temperature approach of 3°C.
In addition to a simple flow scheme and the flow stream tables for the natural gas streams, heat duty tables are provided for the change in enthalpy of the natural gas stream from +30°C to -15°C at both inlet and outlet pressure conditions. (3 bar of pressure drop is allowed across this cooldown train.)
C3CHILLRJTVALVLPSEPSCRUBCOLHPC3LIQCOOLNG1FEEDNGHPC3VAPLPNGLPNGVAPLPNGLIQCOLVAPCOLLIQHeat and Material Balance TableStream IDCOLLIQCOLVAPCOOLNG1FEEDNGHPC3LIQHPC3VAPLPNGLPNGLIQLPNGVAPFromSCRUBCOLSCRUBCOLC3CHILLRC3CHILLRJTVALVLPSEPLPSEPToJTVALVC3CHILLRC3CHILLRLPSEPSCRUBCOLSCRUBCOLPhaseLIQUIDVAPORMIXEDVAPORMIXEDMIXEDMIXEDLIQUIDVAPORSubstream: MIXED Mole Flowkmol/hr N2 1.927173 45.52945 47.45662 47.45662 0.0 0.0 47.45662 1.804193 45.65243 CO2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 C1 402.1895 3441.797 3843.986 3843.986 0.0 0.0 3843.986 375.9472 3468.039 C2 138.4371 241.2159 379.6530 379.6530 0.0 0.0 379.6530 129.1294 250.5236 C3 152.9623 84.32081 237.2831 237.2831 1587.427 1587.427 237.2831 142.4704 94.81275 IC4 78.83171 16.08153 94.91324 94.91324 0.0 0.0 94.91324 73.29317 21.62007 NC4 62.39793 8.787006 71.18493 71.18493 0.0 0.0 71.18493 57.97434 13.21059 NC5 46.64233 .8142876 47.45662 47.45662 0.0 0.0 47.45662 43.63604 3.820580 NC6 23.724373.94081E-3 23.72831 23.72831 0.0 0.0 23.72831 23.07928 .6490331Total Flowkmol/hr 907.1123 3838.550 4745.662 4745.662 1587.427 1587.427 4745.662 847.3339 3898.328Total Flowkg/hr 31032.58 68967.421.00000E+51.00000E+5 70000.00 70000.001.00000E+5 29014.07 70985.93Total Flowcum/hr 64.92929 817.9470 637.2490 961.9177 385.3196 15952.67 975.5013 60.69151 914.8081TemperatureC -26.79031 -37.45060 -15.00000 30.00000 -40.00000 -40.00000 -26.67135 -26.67145 -26.67145Pressurebar 59.80000 59.00000 87.00000 90.00000 1.116428 1.116428 60.00000 60.00000 60.00000Vapor Frac 0.0 1.000000 .8348265 1.000000 .0100000 .5985477 .8214523 0.0 1.000000Liquid Frac 1.000000 0.0 .1651735 0.0 .9900000 .4014523 .1785477 1.000000 0.0Solid Frac 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0EnthalpyJ/kmol-1.1165E+8-7.9888E+7-8.5364E+7-8.1702E+7-1.2773E+8-1.1678E+8-8.5364E+7-1.1170E+8-7.9640E+7EnthalpyJ/kg-3.2636E+6-4.4463E+6-4.0511E+6-3.8773E+6-2.8966E+6-2.6484E+6-4.0511E+6-3.2620E+6-4.3736E+6EnthalpyWatt-2.8132E+7-8.5181E+7-1.1253E+8-1.0770E+8-5.6323E+7-5.1496E+7-1.1253E+8-2.6290E+7-8.6240E+7EntropyJ/kmol-K-2.7315E+5-1.3738E+5-1.6270E+5-1.4975E+5-3.6637E+5-3.1942E+5-1.6094E+5-2.7334E+5-1.3651E+5EntropyJ/kg-K -7984.365 -7645.981 -7721.131 -7106.780 -8308.407 -7243.577 -7637.497 -7982.618 -7496.439Densitykmol/cum 13.97077 4.692908 7.447108 4.933543 4.119766 .0995085 4.864844 13.96133 4.261362Densitykg/cum 477.9442 84.31772 156.9245 103.9590 181.6674 4.387980 102.5114 478.0581 77.59653Average MW 34.21029 17.96705 21.07188 21.07188 44.09652 44.09652 21.07188 34.24160 18.20933Liq Vol 60Fcum/hr 69.51947 217.1903 286.7098 286.7098 138.3350 138.3350 286.7098 64.96147 221.7483*** VAPOR PHASE *** ZMX .6415408 .5933201 .7237670 .9640213 .9640213 .6870630 .6870629VMXcum/hr 817.9470 579.9122 961.9177 265.7127 15904.17 914.8102 914.8081Total Flowkmol/hr 3838.550 3961.804 4745.662 15.87427 950.1506 3898.335 3898.328CPCVMX 2.374677 2.588673 1.822315 1.166580 1.166580 2.093471 2.093472
Appendix 3. Process Risk and Safety Task – HAZOP of Scrub Column
The fifth part of your Preliminary Design Report is to carry out, as a group, a HAZOP of the scrub column and its associated lines.
To do this you will need a P&ID of the scrub column, so make sure that one of the group has chosen this piece of equipment for their P&ID. You will then HAZOP the P&ID.
You should assume that the natural gas feed to the plant is at 9.0 MPa abs and the cool down train is mechanically designed for 10.0 MPag, The Scrub Column is after the JT valve and operate at about 6.0 MPa abs and is mechanically designed for 6.6 MPag.
Your HAZOP should consider as a minimum deviations in the following parameters:
If you can think of other parameters of importance, you should consider those as well.
The HAZOP summary sheets should be included in the report. If this document is too large, put it in an appendix and provide only a list of the key action items in the body of the report.