A U.S. maker of engineered carbons and its southern U.S. manufacturing plant had a big problem, but Crown Solutions, a subsidiary of Veolia Water Solutions & Technologies in Saint-Maurice Cedex, France, had the solution.

The chemical production facility had experienced several documented process leaks of lignin into its cooling water system due to failed check valves as well as some operating errors. In order to get through the period until the system could be shut down for repairs, Crown increased the feed of the biocide, Hydrex 7310, and also increased the blowdown to purge the material. One of the main difficulties with lignin is that in low concentrations in water, it is colorless, while higher concentrations add color. At some points, the water in the cooling system was the color of dark tea.

Crown’s short-term program adjustments were successful until the system could be taken out of service, the leaks repaired, and the system flushed and put back online. During that time, however, it was determined that the lignin had coated the entire system and was slowly sloughing off and plugging the surface condenser, which lowered the system’s operating vacuum by as much as 20 percent. The result was a major decrease in operating efficiency, which was having a huge impact on operating costs.

The company determined the best way to completely clean the system was to use the specialty biodispersant Hydrex 2252 along with Hydrex 7310 biocide, because lignin is a food source for bacteria, according to Crown. The system was cleaned and then returned to the normal treatment program of Hydrex 2231, Hydrex 7310 and acid for pH control.

Working with the client, Crown kept the system operating, and by performing the cleanings offline, the chemical company was able to maintain system efficiencies that improved operating costs. The ΔT on the lube-oil skid heat exchanger increased by 70°F (39°C) and the average vacuum increased by 0.8".

Savings based on the vacuum improvements and related energy use, the plant estimated its savings at more than $100,000 – all by properly cleaning the remaining lignin from the system.

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