2 replies to this topic

[kirang11]

we have stabilizer section in FCC gasoline desulfurization unit, from which the sour gas (contaning H2, H2s) is sent to DHDT unit for the offgas treatment  with amine absorber and ultimately to fuel gas header. since we are using CCRU hydrogen for FCC gasoline desulfurization unit, the sour gas production is high and the stabilizer section is fully upset.sometimes the stabilizer overhead controller gets fully opened and the operating pressure (8.5kg/sq.cm) is difficult to maintain also the stabilizer column psv is at 11 kg/sq.cm. the stabilizer coulumn is stable when we are using PSA hydrogen. In stabilizer overhead we have one line(2") going to DHDT for offgas treatment and one line (2") going to flare.since the pressure in stabilizer is difficult to maintain with CCRU H2, flaring has to be done. how to avoid this flaring of sour gas?

 

now we have another section called isomerizatiion section, in this section the the stabilizer off gas contain (HCL, H2) which is being treated by NET GAS scrubber (by cautic 10 wt%) and is operating at max of 6.5-7kg/sq.cm. the off gas after treatment goes to fuel gas header.

 

can we route the sour gas  to flare line  from FCC gasoline desulfurization stabilizer section to NET GAS SCRUBBER? what will be the effects if i route the sour gas(H2&H2S) from fcc gasoline desulfurization unit to Net Gas Scrubber which is treating offgas (H2 & HCL) from isomerization unit and operating at 6-7kg/sq.cm ? basically i want to avoid flaring of sour gas from FCC gasoline desulfization unit, avoid using PSA hydrogen and make stabilizer section stable while using CCRU H2

[PingPong]

It seems to me that the pressure control valve of the stabilizer is too small. Simple remedy could be to partly open the manual bypass valve such that the control valve operates in a range of 50 - 70 % valve opening.

 

Sending H₂S containing gas to the NET GAS SCRUBBER is not a good idea. That scrubber is now only for absorbing HCl. If you send H₂S there then the spent caustic will contain sodium sulfide. That would then need to be sent to a spent caustic oxidation unit.

 

You could consider sending the excess sour offgas to the interstage of the wet gas compressor in the FCCU.

[Padmakar Katre]

Hi,

 

Unless the current performance of net gas scrubber is assessed, decision can't be taken to route the FCC stabilizer sour gas.  You need to work out a simulation case to see the effect of this change on net gas scrubber performance w.r.t. 2 aspects i.e. process performance and then hydraulic adequacy of column and peripherals.