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Petroleum refineries represent one of the most challenging water treatment situations. Several heat exchangers, many with high heat fluxes and low velocities, potential process leaks, poor water quality (water-reuse) and pressure on operational costs, require chemical treatment to operate under stress conditions. Poor cooling system performance can impact asset reliability and increase total costs. For this reason, a chemical treatment with high flexibility is required to manage any kind of variation (primarily relating to water quality) and to address cooling system problems quickly.

In a refinery’s evaporative cooling system, one of the most critical aspects to control is microbiological growth. This is for several reasons, including:

  • Process leaks can provide a food source for microorganisms.
  • When the make-up source is surface water or wastewater, variable and high microbiological contaminants arrive in the cooling system.
  • Extensive distribution piping can create dead legs where there is increased risk of bacterial growth.
  • Heat exchangers with a low velocity promote microbial adhesion to surface and biofilm growths.

When sulfate-reducing bacteria (SRB) is part of the problem, the system’s reliability can be impacted dramatically as SRB are responsible for significant corrosion of equipment. SRB can be found in superficial water riches of microbiological material (bacteria); their growth is favoured by anaerobic (oxygen free) conditions and they can obtain energy from the anaerobic reduction of sulfate compounds to hydrogen sulfide, which is a highly corrosive compound.

Simply isolating SRB in a cooling system and/or a system that is at risk of localised corrosion tends to be an inadequate method of biocontrol as these bacteria are widely credited for playing a significant role in microbially-influenced corrosion (MIC) and reduced heat transfer efficiency. The deterioration of metal by corrosion processes that directly involve microorganisms has gained enormous attention recently. This is due to the fact that they are thought to be responsible for the majority of pipeline system failures in refinery cooling systems…

This article was originally published in the July 2018 issue of Hydrocarbon Engineering. To read the full version of this article, sign in or click here.

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Written by Concetta Sapio, SUEZ Water Technologies & Solutions, Italy.

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