OBJECTIVE The objective of this experiment is to understand the usage of valve and distillation specification using HYSYS software.
THEORY Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH(often abbreviated MeOH). Methanol acquired the name "wood alcohol" because it was once produced chiefly as a byproduct of thedestructive distillation of wood. Modern methanol is produced in a catalytic industrial process directly from carbon monoxide, carbon dioxide, and hydrogen. Methanol is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, that of ethanol (drinking alcohol).[5] At room temperature, it is a polar liquid, and is used as an antifreeze, solvent, fuel, and as a denaturant for ethanol. It is also used for producing biodiesel via transesterification reaction. Methanol is produced naturally in the anaerobic metabolism of many varieties of bacteria, and is ubiquitous in small amounts in the environment. As a result, there is a small fraction of methanol vapor in the atmosphere. Over the course of several days, atmospheric methanol is oxidized with the help of sunlight to carbon dioxide and water. Methanol burns in oxygen including open air, forming carbon dioxide and water: 2 CH3OH + 3 O2 → 2 CO2 + 4 H2O Methanol ingested in large quantities is metabolized to formic acid or formate salts, which is poisonous to the central nervous system, and may cause blindness, coma, and death. Because of these toxic properties, methanol is frequently used as a denaturant additive for ethanol manufactured for industrial uses. The experiment production of methanol is carried out in a moderate-pressure synthesis loop by direct hydrogenation of carbon dioxide, which generates a liquid product that contains a binary mixture of methanol and water in approximately equal proportions. To provide commercial methanol that is nearly free of water, dehydration is achieved commonly by distillation. The simulation considered an equimolar mixture at 2700 kmol/hr at 25 oC and 5.2 bar. It is then split and fed to two distillation columns, one at a reduced pressure, with the design specification shown in the following table.
Condition
DC1
DC2
Pressure (bar)
5.2
1.01
Number of trays
16
13
Feed Tray*
12
9
Reflux ratio
1.26
0.834
XD (mole fraction)
0.96
0.96
XB (mole fraction)
0.04
0.04
*Count from the top of DC
Hint that use in the experiment: 1. Use SRK Equation of state fluid package 2. Split ratio is used. 3. Used total condenser for both of the DC The balance equation for distillation column is: a) Overall material balance (d(ML,I + Mv,i)) /dt= Li+1 + Vi-1 + Vi b) Component material balance (d(ML,I X I,j+ Mv,IY I,j)) /dt= Li+1 Xi+1,j + Vi-1 –LiXi,j– LiXi,j – ViYi,j c) Energy balance (d(ML,I X I,j+ Mv,IY I,j)) /dt= Li+1 HL,i+1 + Vi-1 –LiHi,j– LiXv,i-1 – ViHv,i
ML,I and Mv,Iare the holdups in the liquid and vapour phase on the stage i. index j denotes compound j. Land V are liquid and vapour flow, x and y are component fraction in the liquid and vapor phase and hl and hv are he enthalpies.
The vapor-liquid equilibrium has been modeled by assuming ideal gas and using liquid activity coefficient from the Wilson equation. The vapor flow, V, on stage I have been modeled using a valve type equation for the pressure drop from one stage to the next: Vi = c(Pi-12 – Pi 2)0.5
PROCEDURE 1. New case was open, then SRK fluid packages was selected as current property package in the fluid package tab. 2. Methanol and water was selected from the component available from the pure component library box for the component for this system. 3. All the unit was changed to the SI unit. 4. Next simulation environment was entered. 5. Then for PFD diagram, the two basic distillation column (DC1, DC2), Tee 2 and valve was selected as the component that need in this system. 6. All the information given for the Tee 2 was insert. 7. Next the parameter for DC1 and DC2 was inserted, by clicking 2 times for DC1 and go to parameter and insert all the information required. Same goes for DC2. 8. After completed the system, the adjust operation was added in order to apply the heat integrated for the distillation column. 9. Information was insert of adjust operation, the split ratio of the Tee was adjusted to make sure the heat duties of DC1 and DC2.
PROCESS FLOW DIAGRAM Diagram 1: Process Flow Diagram
WORK BOOK
DIAGRAM 2: PROCES FLOW FOR DISTILATION COLUMN 1
DIAGRAM 3: WORK BOOK FOR DISTILATION COLUMN 1
DIAGRAM 4: PROCES FLOW FOR DISTILATION COLUMN 2
DIAGRAM 5: WORK BOOK FOR DISTILATION COLUMN 2
DIAGRAM 6: WORK BOOK FOR FEED
ANSWER There are no manual calculation was involved in this calculation because all the calculation was done by HYSYS system. 1) What is the value of the split ratio for the feed stream for each DC?
DC 1 : 0.5144 DC 2 : 0.4886
2) What is the molar flow in stream before entering DC1 (in lbmol/hr)?
Stream2: 1381kgmole/h
3) How to reduce pressure in DC2? Valve is use to reduce the pressure of the steam before enter the DC2 in this HYSYS simulation system. This happen when molar flowrate of flow in of stream is adjust by the valve 4) What is the temperature at the bottom of DC1 and DC2 (in oC)? DC1 :152.1OC DC2 : 98.85OC
5) Did the process achieve a methanol that free from water? What is the purity of the methanol? How to increase the purity? This process only achieve 0.92 mol fraction or 92 percent of pure methanol. To increase the purity can do by added the compressed vapor stream as heating vapor to an evaporator or we can increase the number of tray.
DISCUSSION Base on the process simulation that had been done using the HYSYS software we can understand the purpose usage of valve and distillation specification. The production of methanol was carried out in a moderate pressure synthesis loop by direct hydrogenation of carbon dioxide. Liquid product was generated and its contains a binary mixture of methanol and water. The proportion for both is approximately equimolar. Dehydration was achieved usually by distillation and it provides commercial methanol that was freely by water. The components at the feed are water and methanol. The components passed through the splitter and were splitter into two distillation columns. The function of the splitting column is to achieve high purities in top and bottom outlet. The composition of methanol from distillations process 0.92. To increase the purity can do by added the compressed vapor stream as heating vapor to an evaporator in which at least a portion of the methanol/ water mixture to be separated evaporated. We also can increase the number of tray for each of the distillation column This the result showed that produced is almost water free. The split ratio it about 0.5114 and 0.4886 for from distillation column 1 and distillation column 2.For the temperature it state to change by increasing from stream 1 only 25OC, then at the end the temperature for distillation column 1 and distillation column 2 is 152.1OCand 98.85OC.
