Location: Qingdao, Shandong province, China

Start-up time: 2014

Background:

The original xylene column, 100 ADV® valve trays, was designed by ZEHUA in 2006. It belonged to 1.5Mt/a continuous catalytic reforming unit, then the capacity was added to 1.8Mt/a in 2011. It made heavy fractions increased in bottom of xylene column due to feed changed. So, one side product of gasoline fraction was added in bottom section of xylene column, which caused loadings in that section increased. Hydraulic rating in that section should be performed.

Solution:

2-pass trays in bottom section of xylene column were not able to meet requirements due to high loadings after hydraulic calculation. Paths of the last 10 trays at bottom section were changed to four paths. Weir loadings on those trays were reduced to avoid tray flooded. The last 11thand 12th trays (numbered from bottom to top) were replaced by a collector with distributor traps. Baffles would be added near vapor draw-off nozzle to ensure normal draw-off.

Result:

Xylene column ran in 2014. Based on situation of removing two trays and high loadings in bottom section, not only could content and yield of xylene be same as before revamping, but also quality and yield of gasoline fraction were under control. Separation efficiency was achieved expected results.