Q & A > Question Details
VDU OVHD off gas after treatment in amine (MDEA) absorber routed to VDU furnace to serve as secondly source of firing along with Refinery FG (low in Sulfur)..
H2S in treated offgas is 100ppm (design 0.1%). However, Sox (SO2) in final four gas is high?? Reason?
We checked other Sulfur species's presence which are contributing high SOx. Any way to treat other Sulfur compound and bring Final emission under control??

01/12/2018 A: Egbert van Hoorn, Hocon B V, Egbertvh@hotmail.com
As indicated in previous answers, there are likely other sulphur components present like mercaptans which are not removed by MDEA amine treatement.
In addition I would like to point out that MDEA is the weakest base which will not remove H2S to low levels at the low pressure of the VDU gas because the H2S partial pressure is very low.
Very good regeneration of the MDEA solvent is required to remove H2S to low levels. A MDEA regenerator overhead temperature of at least 110 C is required.
11/11/2018 A: Muhammad Faisal, Oman Oil Refineries & Petroleum Industry (Orpic)-Oman, engr.faisalfraz@gmail.com
Thanks NS Murthy. You a set e exactly right. We have noticed CS2, DMDS, DS2 etc.. FIRING was reduced (COT is lower than design, result some dumping of VGO into VR as well). Problem VDU operation is 60-80%(max due to downstream units), velocity steam also maximize to avoid cracking. Still high SOx
11/11/2018 A: Muhammad Faisal, Oman Oil Refineries & Petroleum Industry (Orpic)-Oman, engr.faisalfraz@gmail.com
Rich amine H2S loading is also not much high. H2S after absorber is 100ppm max. But due to other S-compounds (found after sulfur speciation test from treated offgas before routing to heater),final SO2 value is slightly higher (60-70mg/nm3 compared to 35mg/nm3). Analyzer is also calibrated many times and declared OK.
11/11/2018 A: Muhammad Faisal, Oman Oil Refineries & Petroleum Industry (Orpic)-Oman, engr.faisalfraz@gmail.com
Absorber Packing DP is fine. We have done all optimization across absorber (maximize Lean amine (MDEA) flow, maintain TDI 5-8c, try to increase pressure. But surprisingly other sulfur compounds presence found in treated offgas, which are contributing high SO2 in final emissions analyzer.

07/11/2018 A: NS Murthy, Suez, murthy.ns.ext@suez.com
You have mentioned that there are other species of organic sulphur compounds in VDU off gas causing this issue. Well, it is pretty tough to remove these as MDEA absorption takes care of H2S mainly. Look for optimizing the VDU furnace conditions as well as extreme blends of crudes having high level of potential H2S. When severity is high in VDU there is a fair degree of olefins formation in lighter gas which in turn could react with H2S to form organic sulphur compounds. Also, one may look into potential formation of CS2 in off gases specially when feed to unit has higher TAN.
07/11/2018 A: Prakash Pimparkar, Environmental Consulting Services , prakash.pimparkar@yahoo.in
You have not specified the SO2 limits but with 100 ppm of H2S you should get less than 10 ppm of SO2. There is something wrong either you are not getting 100 ppm but 2000 ppm ? as in the furnace the flue gas gets diluted to the extent of 15 to 25 times due to the combustion air and ( thus 100 ppm of H2S or 200 ppm of SO2 should be reduced to 12 to 10 ppm SO2 in flue gas ( what then is the limit ?)
The easiest way is to absorb more of H2S in the Amine tower ( by increasing Aminecirculation flow,checking of blockages of tower media or plates, increasing no of plates, use proprietary absorbing solution or revamp ) there are multiple solutions
So first check your H2S and SO2 profile if the figure is more 9( 1500/2000 ppm H2S?) then improve H2S absorption efficiency
This option is cheaper than installing SO2 absorption system at the tail end
I have a hunch your tower is blocked or MDEA severely degraded and needs Filtration system