Q & A > Question Details
At present in our VGO hydrotreater we have conversion of around 19.5 % to liquid distillates. we are facing problems with low recycle gas purity: 84-85% C1 and C2 content is high around 13%. What could be the possible reasons? We have recycle gas scrubber after the cold separator.
11/07/2016 A: Saleh Daryabari, Senior Process Engineer of RCD and RFCC, Arak Refinery, daryabari@gmail.com
If the operating condition (temperature and pressure) of separator is at design level, the reason of excess amount of C1 and C2 in recycle gas is higher hydrocracking activity of catalyst, especially if you pass middle of run condition and WABT is high. You can increase recycle gas H2 purity by small amount of purge.
09/07/2016 A: Mainak Sarkar, Indianoil Corporation Ltd, sarkarm@indianoil.in
The scrubber for recycle gas is for scrubbing H2S from the recycle gas. The scrubber cannot scrub C1&C2 in the recycle gas. The problem of excess C1&C2 in the recycle gas may be due to following reasons:
1. Pressure of the separator. If the pressure of the separator is lower compared to design pressure then C1&C2 components may get into recycle gas stream. The lowering of pressure in the HPS may be due to excessive pressure drop in the reactor.
2. If the temperature of the separator is higher compared to deign temperature, that may also case C1&C2 contamination in the recycle gas.
08/07/2016 A: NS Murthy, Suez, murthy.ns.ext@suez.com
Check the hot separator pressure meter cross checked. Also, if the operating severity is higher than optimum one could see drop in Hydrogen purity. As long term solution, check the catalyst selection process.
07/07/2016 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
The recycle gas purity is determined by the makeup H2 purity and the separator flash conditions, which are Pressure and temperature, as well as composition. Is the temperature high?