Q & A > Question Details
What is the exact meaning high/low severity in case of refinery catalytic unit?
20/06/2009 A: Kavirayani R Murthy, K R Murthy Consultants, krmurthy_ipcl@yahoo.com
Any catalytic process is subjected to both high and low severity operations depending on requirement. High Severity operations facilitates both the wanted and unwanted reactions to proceed faster. For example in catalytic Reforming, during high severity of operations you operate the reformer with high conversions to produce wanted products like Benzene, Toluene and Xylenes for Aromatic production and high Octane numbers for octane boosting. Since both Wanted reactions like BTX production and octane boost are enhanced, we obtain high conversions. At the same time unwanted reactions like coke formation is also enhanced due to high severity, the catalyst thus gets coked fast and shortens the cycle lengths and overall life of the catalyst.
At low severities both the wanted and unwanted reactions proceeds with Low rates hence low production of wanted products like BTX and low octane boost. At low severities less coke formation, hence high cycle length and high ultimate life of the catalyst.
The severities are a function of operating parameters and the process environment.
07/03/2009 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
For catalytic processes, high or low severity may point to severe operating conditions, high quality of product and extent of side reactions like coking e.g in catalytic reformer high severity may mean high octane number of product, low rector pressure, high weight age average bed temperature, high residence time of reactant, low hydrogen to hydrocarbon ratio, high coke lay down on the catalysts. Like wise for HDS it may be high reaction pressure, high reactor temperature, low LHSV, high % HDS.
04/03/2009 A: Randy Alexander, EURECAT, randy.alexander@eurecat.com
When some refer to high severity, they are talking about the processing of crude feeds that contain high amounts of sulfur and other contaminants. A catalytic hydrotreating must be run at more severe conditions and will experience shorter cycle lengths when processing such "sour feeds".
04/03/2009 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
There are various ways to explain high/ low severity in catalytic processes plants. As an example for CRU, high severity operation may mean high Octane Number / high reactor inlet temperature/ low pressure/ low LHSV. Similarly for HDS, it may be high hydrodesulfurization that may be achieved by high hydrogen pressure, low LHSV, high temperature increasing reaction rates. High severity is accompanied by higher coke formation , the undesirable reaction rates may increase.
04/03/2009 A: Samuel Sinanan, IPSL, Samuel.Sinanan@ipsl.co.tt
In the case of refinery catalytic units, severity mostly refers to reactor temperature (reactor inlet temperature, weighted average bed temperatures (WABT) or weighed average inlet temperatures (WAIT).