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Custom Clean program degasses water quench tower in less than half the normal time

Challenge

During  a  capacity  expansion  project  at   its  Gas Cracking Unit, an ethylene producer in India found  that the  Water Quench Tower, downstream of the cracker  furnace, was a  significant bottleneck.  It was  discovered  that  damaged  ripple  trays  and  support beams in the tower needed to be  replaced, but there was very little  time  to prepare the  vessel for safe entry by plant personnel to do the  work.

The  quench tower handles cracked gas  from  the  furnace   containing  polymers,   asphaltenes,  and tar.   Over time, these  fouling  materials had  built up,   sticking  to  the   tower  internals  and   piping.  Before plant personnel could  begin  work  inside the  vessel, these hydrocarbons needed to be removed and  the  tower degassed of dangerous vapors. The producer  stipulated  that the   degassing  process had   to  be  completed within   a  very  compressed time-frame, after the  initial  oil flushing to dissolve and remove the  bulk of the fouling.

Solution

Typically,   a   time-intensive,   steam-out   process would  have  been initiated at  this  point; however, given   the    limited  timeframe,   SUEZ   offered  a faster,   more   effective    and    safer    chemical alternative,  Custom  Clean CC13, to degrease and  degas the  tower.

Custom  Clean CC13  is  a  unique extractant  and surfactant  chemistry  that is  totally  biodegradable and  compatible with  all  metallurgies, as well  as with    the    wastewater    treatment   system.   The Custom    Clean     treatment    program   involves circulating  a  water/chemical  mixture  throughout the  tower for several hours. This unique chemistry not   only   adsorbs  dangerous  vapors   into   the circulating mixture but also breaks down and emulsifies liquid and  semi-solid hydrocarbons that were not removed earlier by the  oil flushing.

Details of the application

  1. After the  flushing oil was drained, Custom Clean CC13  was injected  into  the  top  section  with  a water level  of  20%.  The  water  level  was then increased  to  50%  by  adding BFW  (boiler  feed water) at 75-80°C (167-176°F) for the  duration of the degassing/degreasing process.
  2. The hydrocarbon quickly started tbreak down  and disperse as an emulsion into the circulating water.
  3. After 12  hours of circulation,  additional  water was fed into the  top section, in order to overflow the   water/chemical  mixture  from  there to  the  bottom section.
  4. Additional chemical  was then injected  into  the lower section and  allowed to circulate for eight hours   before   draining    the    water/chemical solution to the  ETP (Effluent Treatment Plant).
  5. After draining  the  water/chemical  solution,  the quench  tower  was  purged  with   steam   and  nitrogen.
  6. Finally, air  was injected  into  the  quench  tower, and  an  analysis  of the  oxygen  in an  air  sample from the tower indicated it was safe for personnel to enter the  column.
Result

Personnel were ale to safely enter the vessel in less than half the typical time required, and an inspection of the inside of the quench tower revealed that it was exceptionally clean.


The Custom Clean CC13 treatment program helped reduce downtime and energy costs, by eliminating the need for the typical time consuming steam-out. The Custom Clean  solution also provided a     cleaner,safer working environment for maintenance personnel.


Because its components are biodegradable and compatible with all metals and downstream processes, Custom Clean CC13 is an excellent choice for this type of application.

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