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We have found black solid deposits upon cleaning of our CCRU Net Gas Compressor First Stage Strainer. Upon analysis of composition, we have found that the sample contains hydrocarbon plus a significant amount of Chloride and Iron and with traces of Aluminium, Magnesium, Silicon, Phosphorous and Sulfur. What could be the source of these black solid deposits?
 
Answers
17/01/2017 A: Patrick Bullen, UOP, patrick.bullen@uop.com
The most likely root cause of solids formation is either ammonium chloride salt or corrosion initiated by HCl present in a liquid phase. The iron (and likely the color) would build up as corrosion products. Depending on the H/C ratio in the hydrocarbon, it may be either hydrocarbons which condensed on the salts already present or coke carried over from the reactor and heaters. Aluminium is from a small amount of catalyst dust, and sulfur is from the feed, caught in the solids but not a meaningful contributor to the growth.
It is very unlikely to be green oil unless there is a chloride guard bed upstream of the net gas compressor. Even if there is relatively high chloride in the recycle gas or reduction gas, it would not be enough to catalyze the oligomerization of olefins.
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04/01/2017 A: Eric Hennings, Technip Stone & Webster, EHennings@technip.com
Chlorides originate on the catalyst. There is a dynamic equilibrium between process moisture and chloride migration.
01/01/2017 A: Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
The colour of the black solid may be due to iron sulphide.
31/12/2016 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Coke deposited on the catalyst and or from the furnace tubes would contain such minerals. If coker naphtha is included, the silicon would be from the anti-foam material used there.
30/12/2016 A: RAUL FLORES, PDVSA INTEVEP, fraulf@hotmail.com
Some non regular conditions or deviations may lead cracking of hydrocarbon compounds that promote coke or "black deposits". Chlorides come from the organic chloride used to activate the catalyst. In certain conditions chlorides promote corrosion which attack lines and cause iron presence anywhere. The others metals may comes from the catalyst alumina matrix (Al2O3 and others trace elements probably used as promoters in order to increase the selectivity). Silicon and Sulfur are contaminants coming from any fluid/feed treating unit deviation "up stream".
29/12/2016 A: Faridul Qadar, IOCL, faridulqadar@gmail.com
It appears to be green oil. With high concentration of hydrogen chloride some of the unsaturated hydrocarbons condense / polymerize forming such oil. The main HCl contributor in the net gas comes from the reduction gas, which leads to exacerbated issues of green oil formation. You can check H/C ratio of that sample, it will generally indicate the presence of aromatic nuclei. The iron can be present in the sample as metal particles or as Fe2O3. During analysis, metallic iron is oxidised so a distinction cannot be made. One needs to arrest the HCl coming along with the reduction zone outlet gas stream. Some units have solved this issue by installing a chloride adsorber at the outlet line of the reduction chamber.