Hi,
I am trying to simulate vacuum distillation. The feed consists from 2 cuts, similar to HVGO and LVGO, I have no residue.
I've managed to simulate the process at 10 kPa pressure with kettle re-boiler and total condenser.
But I get a -25 C at the overhead.
Also I also tried simulating the process with none top pumparound and without a reboiler(heated the feed instead), as is common in crude distillation unit, but it did not work but I cannot get the process to converge, well, got it to converge, still the questions remains.
Any suggestion on how to approach vacuum simulation(and practice)? What is the better practice, using total condenser or non top pumparound?
Thanks,
Ron
The Vacuum distillation accessible through process simulators Aspen HYSYS and Aspen Plus. Optimize process designs for energy use, capital and operating costs, and product yield through the use of activated energy, economics, and equipment design during the modelling process. Other applications of Aspen Hysys are: acid gas cleaning uses rigorous rate-based calculations and new property packages to deliver unprecedented accuracy and predictive results to gas absorption processes, petroleum refining layers powerful features onto the Aspen HYSYS process simulator to simplify and improve petroleum refining simulations, hydrocarbon optimisation: Aspen HYSYS is the energy industry’s leading process simulation software that is used by top oil and gas producers, refineries and engineering companies for process optimization in design and operations, energy and utilities optimisation: Aspen Energy Analyser is an energy management software for performing optimal heat exchanger network design to minimize process energy etc.
https://www.researchgate.net/deref/http%3A%2F%2Fwww.chemengr.ucsb.edu%2F~ceweb%2Fcourses%2Fche184b%2Faspenplus%2FGettingStarted%2520Petroleum.pdf
Is there an actual distillation column that you are trying to simulate? Actual commercial vacuum columns are usually packed columns with 1 or 2 equivalent theoretical trays worth of separation. Lube units will do a little better.
a Vacuum Tower hysys example consists of a 9 stage column at 11 kPa at the top and 13 KPa at the bottom with 2 optional side draws (LVGO and HVGO) at stages 2 and 6, respectively. Vac Feed is at the 8th stage and 150 kPa and 150ºC vacuuum steam is at the bottom stage. You will need to specify Overhead, LVGO and HVGO rates and the pump around rate and duty. Also, you can change the overhead rate spec for a top temperature spec. An inlet heater is needed and it also works at vacuum prssures set by the feed (try 15 kPa).
Thank you for the answers, this is a simulation for an actual pilot scale column.
My question again is regarding condenser vs none-top pump around.
The simulation should have all of the same equipment that the actual plant has if the plant has a condenser the simulation should also have a condensor
How far along are you in the design process. Are you through pre-engineering and into FEL1?
How big are the actual Crude and Vacuum units (CDU and VDU)? How much smaller is the pilot unit? Is there anything unusual about the design crude (S, N acidity. color issues acidity etc.).? Is the design crude a well known consistent quality crude or a new crude? Are there already commercial CDUs operating on this crude?
Hello Ron,
I have experience with Hysys which as far as I know is more oriented to the simulation of petroleum systems rather than Aspen Plus.
I guess the -25°C overhead is due to the presence of negligible quantities of light ends (you need to keep this temperature to condensate all). I would try to draw off a gas stream from the head and to set the condenser temperature at a reasonable value to understand the amount of these light ends.
Concerning the convergence issues, this is typically triggered by the lack of liquid at some trays of the column: you can either increase the heat provided to the system or reduce the draw off.
Hope this helps,
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