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

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.
The hydrocarbon quickly started to break down and disperse as an emulsion into the circulating water.
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.
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).
After draining the water/chemical solution, the quench tower was purged with steam and nitrogen.
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.