distillation column design
DESCRIPTION
Slide about distillation columns in HYSYSTRANSCRIPT
Distillation Column
Design 1
(Material developed based on Product and Process design principles:Synthesis, analysis and evaluation, 3e by Seader and
Widagdo)
Distillation column design
MESH equations
Rigorous analysis requires simultaneous solution of mathematical relationships for each stage.
MESH equations: (1) Material Balances, (2) Equilibrium Relationships, (3) Summation Relationships, and (4) Heat (energy) Balances.
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Parameters
1) Estimate of condenser and reboiler pressure Pressure gradient in the column affects the equilibrium
temperature and composition at each stage
Condenser pressure will be selected to enable the cooling of
the vapor with cooling water
2) Reflux Ratio, R3) Number of theoretical stages, N4) Feed tray location
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H83 PS1/H84 CFL
Column design steps Preliminary steps:
Calculate Pressure - Splitter operation Calculate R, N, Nf – Short cut distillation Set up distillation column– Use the values
obtained from the previous steps to start simulation
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Depropanizer example
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Splitter setup Preliminary steps:
Define the material stream- Select SRK EOS
Select splitter unit
Select ‘field’ as your unit Tools-Preferences-variables-units
Install inlet, outlet and energy streams
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Splitter setup
Select the splitter unit
here
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Define splits
Splits are defined based on the distillate specifications
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To start with, assume the condenser pressure is the same as feed pressure and the distillate vapor fraction as 1.
Parameter tab
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Bottom pressure estimation Use ‘SET’ unit to simulate a constant
pressure drop
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Bottom pressure estimation Use ‘SET’ unit to simulate a constant
pressure drop
This is the variable we
control
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Bottom pressure estimation Select the pressure of the stream ‘B’ and the
source as stream ‘D’ (since the pressure of ‘D’ is used to calculate the pressure of ‘B’
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Bottom pressure estimation Assume a constant pressure drop
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Bottom pressure estimation The system is now converged. However, we
need to recheck the condenser and reboiler pressure with the consideration of relative volatility.
Time for exercise!
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H83 PS1/H84 CFL
Relative volatility We need to estimate relative volatility. We
need to perform a ‘case study’ to find the dependence of pressure on relative volatility
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Perform a ‘case study’ to find the dependence of pressure on relative volatility on the new stream. Here, we created a ‘clone’ of the feed to work on the case study.
Relative volatility
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Volatility is defined at its bubble point. So, make the vapor fraction of feed as zero after deleting the temperature
Relative volatility
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Define alpha using spreadsheetSpreadsheet
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Import K values for the key componentsSpreadsheet
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Import K values for the key componentsSpreadsheet
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Import K values for the key componentsSpreadsheet
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Import K values for the key componentsSpreadsheet
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Estimate alpha valuesSpreadsheet
alpha prop-but
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Now the case study can be performed using databook (control+D)
Databook
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Open the variables in databookDatabook
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Select the relative volatility and the pressure of feed 2 as the variables
Databook
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Select the relative volatility and the pressure of feed 2 as the variables
Databook
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Now start a case study (alpha). Our objective is to analyze the dependence of relative volatility on pressure.
Databook
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Define the range of pressure at which the analysis will be conducted. Then ‘start’ and view ‘results’
Databook
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Alpha is inversely proportional to pressure. Since we target high alpha, select low pressure
Databook
Time for exercise!
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H83 PS1/H84 CFL
Alpha is inversely proportional to pressure. Since we target high alpha, select low pressure
The effect of temperature-pressure at condenser and reboiler should be considered
Use cooling water and steam to save the utility cost
To enable reboiling with steam, the reboiler temperature should be lower than 366oF to allow efficient heat transfer when using high pressure steam at 150psia.
To use cooling water in condenser, the condenser temperature should be around 100 -120oF.
Effect of pressure on temperature
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Effect of pressure on temperatureAdd a new case study-Temperature
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Effect of pressure on temperatureAdd the temperatures and pressures of streams B and D
(B’s pressure is calculated by ‘SET’ unit) and variables
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Effect of pressure on temperatureSet the temperatures as dependant and
pressure as independent variables.
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Effect of pressure on temperatureSet the same range for pressure as in the
previous case.
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Effect of pressure on temperatureSet the same range for pressure as in the
previous case.
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Effect of pressure on temperatureView the result by pressing ‘result’ button.
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Effect of pressure on temperature
Since the Alpha change is only by 0.2 in the pressure range of 205psia and 265psia, we neglect the effects of alpha and take the benefit of heat exchange instead. Close the window and return to the splitter page.
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Effect of pressure on temperature Even the temperature value at 300psia is well within the limit of not more that 366oF. At D-temperature, to fulfill the lower limit of 100oF, pressure must be about 205psia. D upper limit is 120oF which limit the pressure to 265psia. Since the pressure lies between 205psia and 265psia,
higher temperature in condenser provides higher driving force and thus requires less area in condenser, an operating pressure of 250psia for condenser is selected.
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Condenser and reboiler pressureCheck the results at the worksheet tab of
splitter
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Check the results at the worksheet tab of splitter
Condenser and reboiler pressure