We are having propylene with high content of CO2 (> 2 ppm) besides COS is under control (< 10 ppb). The feed LPG is from our FCCU and we measure in the FCCU and the content is around 2-3 ppm of CO2 in the treated LPG. We checked the amine and caustic treatment and it seems ok. We increased the steam in the FCCU regenerator stripper. How can I reduce the CO2 in the LPG from FCCU ? And in the propylene unit ?
We had a similar problem. The CO2 is probably coming from the Reactor as it gets entrained in the vapors. You can look at the absorber / stripper operation and see if you can minimize the CO2 by increasing lean oil and / or stripper bottoms temperature. You could ask your catalyst supplier if other refiners have had this issue when the catalyst was changed to increase LPG production. You mentioned that you increased the stripping steam to the Regen. I am not aware of any stripping steam to a Regen but to the Reactor stripper. I would try cutting the steam rather than increasing the steam.
Thanks for your answer. In order to remove CO2 in the propylene unit we increased the steam and reduces the pressure in the deetanizer tower. It seems do not remove the CO2 enough. This tower remove the lighter streams on the top (ethane, CO2, etc) and the bottom have propane/propylene, but it seems do not remove enough the CO2. The propane/propylene stream in the tower bottom still have 2-3 ppm of CO2 and produces propylene with CO2. How can I improve this tower to remove more CO2 ?