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Distillation Column Pressure And Temperature Finalization
#1
Posted 12 February 2023 - 08:54 AM
What factors decides the distillation column top pressure and temperature and bottom temperature(reboiler outlet)?
Can someone guide me?
#2
Posted 12 February 2023 - 09:23 AM
The economic availability of a cooling and heating source and it's corresponding temperature level. I.e. the cost of cryogenic >> chiller >> cooling water,
#3
Posted 12 February 2023 - 09:40 AM
Distillation design is a complex economic problem. The designer chooses the operating pressure then answers questions. Can I separate the components at this pressure? What is the cost of heating and cooling? Do I need to add equipment to compress the vapor product? Do I need to add pumps for the bottoms product? What is the tower diameter and height and wall thickness? Will there be unwanted reactions because of this pressure? Is there an additional safety hazard? You can usually identify which questions are more important when deciding between pressures and can eliminate some operating pressures completely. There are even cases where the answer leads to 'let us add a side column' or 'let us use both a high pressure column and a low pressure column for the same component separation.'
#4
Posted 12 February 2023 - 01:48 PM
Licensed processes have tended to evolve over time as new ideas are incorporated, it's diffiucult to desig a brand new prcess to be the most efficienct it could ever be, maybe one day when quantumn computers become practical that will will chanage but for now its not so easy. One modification we made recently was to increase the pressure of a column so the overhead duty could reboil a downstream column for example, saving a lot of operating expense at higher capital cost. As others have said its complicated.
#5
Posted 12 February 2023 - 11:42 PM
Can someone guide me?
Pressure - pressure in system depends on temperature and composition of fluid.
Temperature depends on cooling fluid:
- for air coolers - worst credible combination of air dry bulb temperature and humidity
- for water cooling - the same corrected to cooling tower
- for chilling - feasibility study
- for process cooling - feasibility study
- for heat pump - feasibility study
Sound engineering of fractionation requires feasibility study regardless as the most of factors are interconnected.
Edited by shvet1, 12 February 2023 - 11:45 PM.
#6
Posted 16 February 2023 - 01:36 PM
It is very clear when it comes to choosing top pressure with respect to available cooling utility.
Once top pressure is selected and the bottom pressure is top pressure and tray pressure drop.
Now how do I finalise my reboiler outlet temperature and boilup ratio that needs to be maintained?
Can someone please guide me?
#7
Posted 16 February 2023 - 07:44 PM
Assuming you know the specifications for the product stream purities... the reflux ratio depends on the number of stages. Choose the number of stages that results in the optimal economy and operability. Then calculate the column traffic and heat duties needed to reach the specified product stream purity. This calculation will reveal compositions and flow rates at every distillation stage. These calculations are much easier to do in a steady state computer simulation than by hand. The choice of thermodynamic method will influence model accuracy.
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