3 replies to this topic

[rabindra]

We have a 2 Column Naphtha Splitter which is required to produce a 120-140 Deg C cut range Naphtha for downstream petrochemical unit. The feed to the 1st Columns are Light Naphtha (90-160 Deg C Cut Range) and Heavy Naphtha (120-200 Deg C cut range). Both the feeds are introduced to the first column separately in different trays. Products of the 1st Column (say C-01) is 90-120 Deg C Cut Naphtha from Top and 120 Deg C + naphtha from bottom. The C-01 bottom is fed to the second column (C-02)through a pump. The products from the C-02 is 120-140 Deg C Naphtha from 5th Tray and bottom Naphtha from bottom of the Column.

The Operating Conditions of both columns are as follows:

C-01 Top pressure: 1.0 kg/cm2 Top temperature: ~117 Deg C Bottom Temperature; 167-170 Deg C
C-02 Top Pressure: 4.5 kg/cm2 Top Temperature; 185 Deg C Bottom Temperature; 240-250 Deg C

The feed specifications are as follows:
Light Naphtha: IBP; 90 Deg C FBP: 160 Deg C Copper Corrosion: 1B, Sulfur: 85-100 ppm
Heavy Naphtha: IBP: 117 Deg C FBP: 200 Deg C Copper Corrosion: 1B Sulfur 370-400 ppm

During recent shut down to clean the reboilers we had observed corrosion and scaling in the second column while there was no corrosion in the 1st Column. Further the hydrocarbon side of the 2nd Column reboilers were badly choked with corrosion material which were hard to remove with even hydro jetting. The samples collected were reported to be 20-30% coke.

My question is:
1. What may be the reason for corrosion in 2nd Column but not in the first. The matallurgy of both the columns are CS with SS trays.
2. Is there any remedial measure we should take to minimise corrosion in 2nd column.

The heating medium for C-01 is desuperheated steam at 220 Deg C while that in C-02 is desuperheated steam at 278 Deg C.

Regards

- rabindra

[Zubair Exclaim]

can you provide a sketch or P&ID of your system. Also is there an recycly naphtha coming in from downstream units

[rabindra]

PFD is attached. There is no recycle Naphtha Stream. In case you need any other data please let me know.

Attached Files

•  PFD.xlsx   45.33KB   51 downloads

[KeithK]

Have you found the source of corrosion/fouling in your naphtha reboilers?  We also are having corrosion/fouling issues with naphtha reboilers on a delayed coker unit gas plant.  The materials seems to be mostly iron sulfide.  Some theories that we have considered are:  1) The material ended up in the reboilers due to the decontamination process.  A chemical was circulated through the equipment to remove hydrocarbon. There was little iron sulfide scale on the column walls or internals.  2)  Some of the unit feed contains amine based H2S scavengers, which can thermally decompose into amines that have a naphtha boiling point range.  This could cause corrosion particularily at the high film temperatures in the reboilers.

 

I'd appreciate any insights you have gained from your experience.