Design Philosophy of Kerosene Hydrotreater

[MIANCH]

Dear All,
I want to understand the philosophy of kerosene hydrotreater, in my refinery kerosene hydrotreater is designed as per following,
Make up hydrogen supply is given from naphtha hydrotreater separator off which is bringing about 7000 ppm of H2S while sulphur in feed is 0.1 wt%.
This refinery is constructed in 1960 by Esso and designed by Exxon, the location of this refiner is in MENA. can anyone shed light on this type of hydrogen flow scheme, logic behind and philosophy.
Regards

 

[georgeverghese]

The recirculating H2 from within this kero HDT unit may have a H2S concentration approaching this makeup from the naphtha HDT. Moreover makeup H2 is most likely only a small proportion of the recirculating H2 obtained from the kero HDT flash separator. In some cases, the main recirculating H2 stream taken from the kero HDT flash sep may be treated to remove H2S before mixing with this makeup - see PFS from HDT unit licensor for details.

 

[poli60]

there are thousands of refineries in MENA...and also several "critical" areas...
the well-designed refineries (as they are the exxon ones) have a hydrogen chain, where H2 streams rejected by more severe hydrotreatings are used as make-up in less severe HDTs. in this way the total H2 circulation in the refinery is reduced, at the same consumption (of course). in other words, the H2 goes to the washing process with a lower flowrate and a higher H2S concentration, reducing the size of the relevant facilities (CAPEX) and also their OPEX.
normally, the kero HDTs are once-thru processes (ie there is no internal recycle of H2...and so no H2 washing).
every refinery should have a dedicated PFD (process flow diagram) showing the entire hydrogen system with relevant equipment and process conditions (T, P, concentrations, flowrates) in the various operating schemes/campaign. process simulations, linear programming, pinch technology are very useful tools to analyze/improve the overall performances. field data and data from catalyst vendors must be utilized for the analyses.
good luck!