Help: Simulation of a methanol recovery tower
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This post was last edited by lsswyb01 on 2015-10-9 at 13:15. I tried debugging it for a long time but was unable to get it to converge; I’m not sure what the problem is I’m reaching out for help; thank you all in advance! Requirement: The methanol content in the pure methanol at the top of the tower must be at least 99.9% w ； The water content in the wastewater at the bottom of the tower is not less than 99.9% w ； Extract fusel oils via a side line. Other parameters are available in the file below (copy it and save it as an inp file). TITLE: DIMENSION METRIC, PRES=MPAG, STDTEMP=0, STDPRES=0. SEQUENCE: SIMSCI CALCULATION. TVPBASIS=37.7778, RVPBASIS=APIN. COMPONENT DATA: LIBID 1, METHANOL/6, ETHANOL; BANK=SIMSCI. PROCESS LIBID 2: IBA/3, PRPLALC/4, PNTYALC/5, H2O; BANK=PROCESS. ASSAY FIT=ALTERNATE, CONVERSION=API94, CURVEFIT=CURRENT, KVRECONCILE=TAILS. THERMODYNAMIC DATA METHOD: SYSTEM=ALCO, SET=ALCO01. DEFAULT STREAM DATA: PROPERTY STREAM=S1, TEMPERATURE=110, PRESSURE=0.09, PHASE=M, RATE(WT)=14500; COMPOSITION(WT)=1, 0.58/2, 0.1/3, 0.1/4, 0.2/5, 99/6, 0.04. UNIT OPERATIONS: COLUMN UID=T1, PARAMETER TRAY=52, CHEMDIST=200, CVARIABLE=LOG. FEED: S1,24. PRODUCTS: BTMS(WT)=S3,5000; OVHD(M)=S2; LDRAW(WT)=S4,33,20. CONDENSER TYPE=BUBBLE. DUTY 1: 1,1,, DUTY 2: 52,, REBOILER PSPEC PTOP=0.09. PRINT PROPTABLE=PART ESTIMATE. MODEL=CONVENTIONAL, RRATIO(L)=3. SPEC ID=COL1SPEC1, STREAM=S2, FRACTION(WT), COMP=1, WET, VALUE=0.999. SPEC ID=COL1SPEC2, STREAM=S3, FRACTION(WT), COMP=5, WET, VALUE=0.999. SPEC ID=COL1SPEC3, STREAM=S4, RATE(WT,KG/H), TOTAL, WET, VALUE=60. VARY DNAME=CONDENSER, REBOILER; VARY DRAW=S4. VLLECHECK: CHECK=OFF. REBOILER TYPE=KETTLE END
Only one of the top and bottom configurations of the tower can be set; by setting the reflux ratio or flow rate, convergence can be achieved. After that, by adjusting the parameters related to the top and bottom configurations of the tower, the requirements can be met
I’m a beginner and there are still many things I don’t understand well. Could you provide more detailed guidance? :Lol, since this tower has a side stream extraction, three parameters need to be set, so I modified the settings: (1) Define the methane content at the top of the tower ； The variable is the load on the top condenser ； (2) Set the reflux ratio ； The variable is the reboiler load ； (3) If the third parameter is not set, an error message appears stating: “*** error *** Unit 1, ‘t1’ – the volume and weight-based flow rates are only estimates for varying draw rates. Enter the volume or weight-based rate for stream s4 as a specification, then adjust the side draw rate to achieve that rate.” ； Set the mass flow rate of the extracted fluid according to the instructions provided ； The variable is the side-line flow rate. It still can’t converge!
The boiling points of the other components present there are all higher than that of water, and the method used does not result in the formation of azeotropes; so wouldn’t all those other impure components remain at the bottom of the tower? In this case, it’s impossible for the bottom of the tower to meet the requirements.
The target is to achieve the specified compositions at the top and bottom of the tower as required. As for whether the thermodynamic approach and other assumptions are reasonable, I’m not sure either. Can a portion of the heavy fraction be withdrawn through a side stream? According to your understanding, are there any ways to improve it? Thank you!
It finally converged, thanks to the hint from “flymx” on the second floor. Of course, some detailed issues still need to be adjusted gradually. TITLE: Dimensional metric, PRES=MPAG, STDTEMP=0, STDPRES=0. Sequence for SIMSCI calculation: TVPBASIS=37.7778, RVPBASIS=APIN. Component data: LIBID 1, METHANOL/6, ETHANOL; BANK=SIMSCI. Process LIBID 2: IBA/3, PRPLALC/4, PNTYALC/5, H2O; BANK=PROCESS. Assay fit method: ALTERNATE; CONVERSION=API94; CURVEFIT=CURRENT; KVRECONCILE=TAILS. Thermodynamic data method system: ALCO, SET=ALCO01. Default stream data properties: STREAM=S1, TEMPERATURE=110, PRESSURE=0.09, PHASE=M, RATE(WT)=14500; COMPOSITION(WT)=1, 0.0058/2, 0.001/3, 0.001/4, 0.002/5, 0.99/6, 0.0004. Output format: Total Weight Percent. SPTPRINT=ON. Format IDNO: Total Weight Percent, SID, PHASE, RATE(M), RATE(WT), TEMP, PRESSURE, MW, HTOTAL, LFRAC(WT), CPCT(WT). Unit operations: Column UID=T1; PARAMETER TRAY=52; CHEMDIST=200. CVARIABLE=LOG. Feed S1,24. Product OVHD(WT)=S2,10; LDRAW(WT)=S4,33,10. BTMS(WT)=S3,5000; SUPERSEDE=ON. Condenser type: BUBB. Duty 1,1,, Duty 2,52,. Reboiler PSPEC PTOP=0.09. PRINT PROPTABLE=PART ESTIMATE. Model: CONVENTIONAL; RRATIO(L)=3. SPEC ID=COL1SPEC1: REFLUX(KG/H), DIVIDE; STREAM=S1, RATE(WT, KG/H); TOTAL, WET; VALUE=1. SPEC ID=COL1SPEC2: STREAM=S3, FRCTION(WT), COMP=5, WET; VALUE=0.999. SPEC ID=COL1SPEC3: STREAM=S4, RATE(WT,KG/H), TOTAL, WET; VALUE=60. VARY DNAME=CONDENSER, REBOILER. VARY DRAW=S4. VLLECHECK: CHECK=OFF. Reboiler type: KETTLE END