Q & A > Question Details
In our plant, we have 7 heaters for Distillation unit, NHT and CRU unit. Fuel Gas that is generating from CRU Unit (80% H2) is being used for all those heaters. But, gum or glue is observed at the pressure regulating system which is situated on fuel gas line which mean it is depositing at the reduced area due to restricted flow path. My question is that if the olefin/unsaturated compound present in the desulfurized naphtha ( CRU Feed), is it getting Oxygen from Oxygenated compound like MTBE, TAME or Methanol and so on to form gum or is it getting O2 from the existing system? If this is not the case then what could be the reason of forming gum in the fuel gas?
 
Answers
13/11/2017 A: Eric Hennings, Technip Stone & Webster, Eric.Hennings@technipFMC.com
If the foulant in fuel gas is “gums”, it is most likely from diolefins (particularly if contaminated with O2 from fuel gas source other than CRU). O2 can ingress into Crude or other feed stream in atmospheric storage. Oxygenated species such as methanol, etc. normally do not contribute to gum fouling. Some refiners use a small coalescer to remove gums and prevent burner plugging. If material is “salts”, a minor steaming will dissolve them.
07/11/2017 A: Patrick Bullen, UOP, patrick.bullen@uop.com
The previous answer is more likely to occur compared to some feed contaminant leading to a net gas or LPG issue that forms gums. Feed issues that you quote generally result in reforming unit combined feed exchanger fouling as the feed is vaporized and superheated to a high temperature. Typically, oxygenated compounds are converted in the naphtha hydrotreater and removed as water in the stripper.
It is also somewhat unusual to use reforming unit net gas as fuel for fired heaters as the heat value is low. Many refiners strive to keep the hydrogen content of their fuel gas at a low level due to the poor heat value of combusting hydrogen.
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06/11/2017 A: Dipankar Phukan, Indian Oil Corporation, dipankarphukan79@yahoo.com
As the CRU catalyst approaches end of run, you keep increasing the severity to get the desired RON leading to cracking and formation of olefins. Olefin formation also occurs when Chloride dosing in CRU feed is high. High HCl content in recycle gas leads to formation of polymeric compounds with the olefin generated in the reaction and forms a sticky material called green oil. So basically it is not a oxygenated compound you are encountering but a polymeric compound made out of Chloride and hydrocarbon