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• Can you suggest ways to avoid or deal with asphaltene precipitation in our desalter?

  Nov-2021

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Answers

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• Marcello Ferrara, ITW Technologies, mferrara@itwtechnologies.com

  Asphaltenes are highly polar components with high molecular weights that are found in crude oil as a stable dispersed system. Asphaltenes are made up of molecules containing paraffinic, naphthenic or aromatic functional groups and polar groups formed by oxygen, nitrogen or sulphur as functional groups or incorporated into the molecule as heteroatoms. Many factors may alter the stability of this dispersed system, including chemical and thermal destabilisation. This is particularly true in the desalter where different processed crudes (with different compositions and compatibilities upon blending) and increased temperature, together with higher residence time, create the conditions for asphaltene destabilisation and precipitation. The result of this destabilisation is the formation of a solid residue called sludge that will impact desalter performance and reduce plant capacity in the refining processes, or impair oil production at the wells.

  Additionally, a stable water-in-crude oil emulsion is formed as a result of asphaltene adsorption at the surface of aqueous droplets, leading to stable emulsion which impairs not only desalting operations but the entire production unit and energy efficiency.

  Most important, sludge formation inside the desalter has three major negative effects during operations, namely: a) reduction of the effective desalter volume and hence reduction of water and sediment settling time, with related poor desalter performance; b) sludge/oil carry-under in the brine and hence fouling of water preheaters and, most important, of the water effluent treatment system (including, when applicable, de-oiling packings and strippers); c) sludge carry-over in the crude, with related fouling at the preheat.

  ITW has developed different patented technologies to address the above problems. Specific patented asphaltenes stabilisers can be added together with the crude to prevent asphaltene precipitation and reduce sludge formation.

  The cost of dealing with asphaltene precipitation by continuously injecting asphaltene stabilisers may be prohibitive if the target is the elimination of sludge formation. It is therefore taken for granted that some sludge accumulation will occur inside the desalter (either by adding asphaltene stabilisers or, worse, by not adding any chemical).
  In order to deal with the existing sludge, ITW has developed and patented two other technologies, namely ITW Online Cleaning and ITW Onstream Cleaning.

  ITW Online Cleaning will clean the desalter in 24 hours on a feed-out/feed-in basis, by using the existing unit layout and circulating a proprietary ITW chemical. ITW Onstream Cleaning will clean the desalter while the unit is running, but plant modifications need to be implemented under ITW licence.

  In both cases, multiple desalters can be cleaned at the same time. ITW patented chemicals will dissolve the precipitated asphaltenes, which will be chemically re-peptised, in other words stabilised.

  This important characteristic allows for subsequent reutilisation/reprocessing of the washing solution, because the stabilising properties of the chemical avoid reaggregation of asphaltenic clusters, eliminating potential precipitation during storage and/or fouling of process equipment.

   

  Nov-2021