Q & A > Question Details
For years, poor quality or hardprocess gasoline boiling range streams such as visbreaker has been a problem for refiners.
These materials contain such high quantities of di-olefins, in addition to sulfur and nitrogen compounds, that they are extremely difficult to process in conventional refinery units. The large di-olefin content of such streams renders them extremely reactive or unstable. If an attempt is made to simply hydrotreat these streams in a conventional hydrotreater, the reactive di-olefins form gum which plugs the conventional hydrotreating bed, or less frequently plugs the heat exchanger or heater upstream of the hydrotreating unit.
Based on above what are the options refiners have taken to solve this problem. In one refinery Naphtha is routed to Gas Concentration Unit before sending to Naphtha Hydrotreator Unit. GCU debutanizer reboiler tube bundle failed and heavy coke deposition observed.
Can Naphtha be routed directly to Naphtha Hydrotreator Unit ? If yes what will be demerits? What are the other options?
19/06/2020 A: Reza Seif Mohaddecy, Research Institute of Petroleum Industry, seifsr@ripi.ir
For removing diolefins, you should use a naphtha hydrotreating unit with three reactors.
The first reactor can be used for selective hydrogenation (for saturation of olefins). The second and third reactors can be used for hydrotreating, as in straight naphtha hydrotreating.
Prime G+ is a conventional process by Axens for FCC or coker naphtha hydrotreating. In Iran there are two refineries with Prime G+ for hydrotreating naphtha.
23/02/2010 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
It is established practice to hydrotreat VBU naphtha along with SRN in NHDT plant in 10 to 25 % concn easily provided there is proper catalysts selection and loading in NHDT under recommended operating conditions. If the dioelfin contents are high, provision is made for guard reactor to saturate at lower temp for preventing delta P build up and fouling.
08/02/2010 A: Keng Chung, Well Resources Inc., kengchung@hotmail.com
This is a well known problem for cracked naphtha. See the "Removing Diolefins from Coker Naphtha Necessary before Hydrotreating" by Sok Yui, Oil & Gas Journal, 1999, v97, p36. You also have to hot-couple the cracked naphtha to the diolefin saturation unit.
08/02/2010 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
I agree with Mr. Rodwell. I would add: Some naphtha hydrotreaters processing visbreaker or coker naphtha, without a pre-reactor, and when the olefin bearing stream is a small percentage of the total feed stream, have done well by routing the olefin bearing stream directly to the hydrotreater feed line, bypassing the feed tank. Oxygen is the culprit when di-olefins are present. Even gas blanketing the tank is not as effective as bypassing the tank entirely. Some plants have an oxygen stripping column on the feed to the hydrotreater.
08/02/2010 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
Cracked naphtha streams containing di-olefins, such as those produced by cokers or visbreakers, should be sent directly to a naphtha hydrotreater unit that has a di-olefin saturation reactor ahead of the main heater. This prereactor should operate at a temperature below the polymerization temperature of the cracked naphtha to prevent fouling.