Location: Yunnan Province, China

Start-up time: Mar., 2102

Background:

Raw gas from dimethyl ether unit contained coal dust which washed by phenol water. However, there were plenty of suspended solids. A type of honeycomb packing was used in exiting raw gas scrubber. Sprayer was used to distribute at the top section of column. Shortly after column was started-up, coal dust blocked packing around column wall, and blockage gradually expanded center of column. Eventually, this column lost the function of washing and gas from top of column was entrained with liquid. It need shutdown and overhaul of unit after running 3-4 months.

Solution:

(1) It was optimized for process, which added into a little water when raw gas fed into column in order to wet coal dust.

(2) Streamline annular vapor feed distributor was adopted to remove most of coal dust to bottom of column.

(3) Grid type packings were adopted to avoid blockage and improve ability of gas flow at wash section.

(4) Two layers of Vane-type demister were installed to further reduce entrainments of liquid or other impurities.

Result:

Unit was stable after revamping. It was good for dust removal. During shutdown and overhaul of overall plant, this column was checked. There was only one layer coal ash on the surface of packing. Sprayer and demister were clean. It was no problem for bottom section of column. Based on above situations, this column was run again without any cleaning.