February 16, 2018 at 5:44 am #28144
We are experiencing severe fouling at the phenolic sour water strippers. Source of this water is Coker and FCC units. The nature of the foulant is main coke fines and some hydrocarbon and corrosion products. It fouls the feed bottom exchangers, the stripper trays and specially and most concerning is stripper bottom horizontal circulating type thermosiphon reboilers. We are considering various options like retrofitting the filtration system in coker sour water, chemical treatment at the sour water tank, installation of a filtration skid (25 micron) and coalescer at the sour water feed line, converting the reboiler to a forced circulation type with a filter at pump discharge, changing stripper trays with low fouling trays etc.
We seek advise from The Refining Community on:
1) Whether phenolic SWS fouling is observed in other refineries.
2) What measures are taken to increase runlength of the strippers.
3) What could be the best practice and design philosophy for the strippers/reboiler under such fouling conditions.
4) Provide your feedback on options we are considering as given above.
4) Any other modifications or operating practices you suggest to mitigate fouling.
The Phenolic SWS Unit Process Description:
Nearly 360 m3/h phenolic sour water (0.3w% H2S,0.3 w% NH3, Coke fines, hydrocarbons and corrosion products) is first sent to a degassing drum at 1.8 kg/cm2g pressure and then collected in a Tank at 25mmwcg pressure with 18-20 hrs residence time. Then it is pumped equally to 2 nos of strippers with top 6 trays for pump around wash and bottom 30 trays for stripping. The steam to feed ratio (Tons/m3) is 0.125 to 0.135. Column top temperature has to be maintained at nearly 98-100degC to get desired stripping of NH3. Stripper is operated at 1.2 kg/cm2g top pressure and has 0.25 to 0.35 kg/cm2 pressure drop across the column. pH maintained by caustic addition at 18th/26th or 34th tray (mostly at 18th tray) at 8.5 to 9.0. The strippers has a runlength not more than 6-8 months when the reboilers get fouled, column delP increases and Feed/bottom exchangers are fouled.
You must be logged in to reply to this topic.