A New Distillation Plant Extends Physical Limits outsmarted?
Getting Two Standards Under One Hat
The system therefore exceeds the boiling point of the bitumen fraction, i.e., achieves a temperature range of 560 to 600 °C (equivalent to atmospheric pressure) This is clear if one examines the thermodynamic definitions of the two standards more closely, and this is what the team of engineers has actually done.
- ASTM D2892 is based on a packed column with a theoretical separation capacity of 15 theoretical plates, operated at a vacuum of 2 Torr and a boiling point of 400 °C (at atmospheric pressure).
- In comparison ASTM D5236 is based on an open tubular column, a theoretical separation capacity of 2 theoretical plates, operated at 0.1 Torr, with a maximum boiling point range of 540 to 565 °C (at atmospheric pressure).
On the crucial point of distillation plant extends the limitsdistillation plant extends the limits, Koenen says: “High separation capacities are possible only with packed columns, but high temperatures are possible only with open tubular columns, because a deeper lower vacuum is possible here.” In other words, if one wants to outsmart thermodynamics, one must develop distillation units that can withstand a high vacuum, because lower process temperatures are possible only at higher vacuum levels.
Finally, the hydrocarbon chains crack at above 300 °C, a process which one must avoid during crude oil distillation. The incentive for the development came from two customer requests, which followed one after the other in brief succession. Meanwhile, the first prototype is already in use at a German petrochemicals company, whose request had initiated the development in the first place.
The units installed there achieve a temperature of 560 °C atmospheric equivalent, which corresponds to an operating vacuum of 0.1 Torr and achieve the theoretical separation capacity of 25 theoretical plates (also under vacuum). The winning Autodest 800AC/HV, which was commissioned for a company in South Africa, tops in performance once again with a maximum boiling point of 600 °C atmospheric equivalent, and a separation capacity of 30 theoretical plates.
Such temperatures can be achieved only with a vacuum of 10-3 Torr, i.e., under the operating conditions of a short-cut path evaporator. The challenge is described by Koenen and CEO Stefan Opis as follows: “Thermodynamically, the requirements were mutually contradictory: The column design requires a vacuum of 10-3 Torr and the fraction volumes required for the separation capacity had to be bigger than the column hold-up volume.”
If the preceding order, which had paved the way for this requirement, had not come through — who knows, perhaps the process engineers would have thrown in the towel. “According to the available experience values, we knew that a column design was possible”, says Koenen.
The biggest challenge was the vacuum system. It became clear to the process engineers rather fast that a normal oil diffusion pump would have reached its limits. “We had to file the pipe sections and overcome turbulences which would have caused a pressure fall drop”, explains Koenen. But the calculations matched during the very first run, and the trial distillation was successful.