Mar-2015

Emulsion breaker and metal removal technology increased FCC residuum processing

Frequent and unexpected changes in crude blending properties result in operational and performance challenges from the desalter to the catalytic cracker

Kris Kohl, Paul White, Anibal Valle and Jim Trigg
GE Power & Water

Article Summary

As the global economy slowly recovers, refineries can expect to see a positive shift in the demand for finished petroleum products in mature markets and growing, developing regions. Refining facilities around the globe will continue to look for ways to increase production and profit margins, while reducing or eliminating unscheduled shutdowns and the subsequent untimely cost of cleaning and replacing equipment.

The utilisation of opportunity crudes in the refinery processing diet is a key driver of refinery profitability, given that crude oil accounts for more than 85% of a refiner’s cost structure. Opportunity crudes are those that trade at a discount compared to similar crudes in the marketplace. The availability of such opportunity crudes such as oil sands, light tight oils (LTOs) and high naphthenic acid containing crudes, continues to be an excellent profit improvement opportunity for those refineries able to process these feedstocks.

The production techniques necessary to economically extract oil sands and tight oil add to a refinery’s processing challenges. For example, these crudes typically contain greater levels of solids than conventionally produced crudes, with the distribution of those solids shifted toward smaller particle size, increasing the difficulty of solids management. Tight oils can also contain significant levels of production chemicals, including hydrogen sulphide (H2S) scavengers containing amines. Critical characteristics can vary greatly from batch to batch, even within shipments labelled as coming from the same crude oil supply. This high degree of variation adds significant complexity to the processing strategy and puts a premium on the ability to rapidly respond to unexpected, frequent changes in crude blending properties.

While processing these opportunity crudes creates clear cost advantages for the refiner, many of the distinguishing characteristics that drive the discounts are at the root of a variety of processing issues, particularly desalter operation and performance. When processing opportunity crudes, refiners often operate the desalter more as an extraction vessel, removing many more contaminants than just salt; for instance, metals, solids and tramp amines can be dealt with in the desalter. While the individual desalter challenges may not be particularly new, their convergence is.
For these converging challenges, the optimal solution emerges from the ability to leverage an understanding of the interplay between chemistries and their application, with the operational experience and expertise to optimise refinery systems for maximum performance. Included are practices such as split feed, whereby the primary emulsion breaker is injected into both the oil and the water. Crude stabilisers, wetting agents, reverse emulsion breakers, amine/metals removal aids, and pH modifiers comprise the balance of the chemistry tools suite in the solution mix. Their common points of application are shown in the key of Figure 1.

Metal contamination
Contaminants in crude oil feedstocks can be an impediment to processing discounted crude oil supplies in a reliable, safe and profitable fashion. Specifically, metals contamination poses a threat to a wide array of refinery operations including crude unit fouling, catalyst contamination, and finished product quality. Almost all crude oils contain detectable metal levels, and their solubility and concentrations can vary widely.1 While some forms of metal contamination can be effectively removed via the normal desalting process, other types do not readily transfer to the water phase and therefore require additional means to remove them.2,3 A number of approaches have been used to remove metal contaminants in the past, including filter adsorption, precipitation, and treatment with inorganic acids among many others.4 Work over the past 20 years has shown a highly effective method to improve metal removal in the desalting process is to effect a transfer of the metals from the hydrocarbon phase to the water phase utilising water-soluble hydroxyacids. An additional benefit to this method is the removal of amine and ammonia compounds from the crude oil, which will reduce crude tower fouling and overhead system salt-induced corrosion.

Care must be exercised when selecting a metal removal (MR) aid treatment programme. Many hydroxyacid compounds will introduce unwanted side effects, including low boiling point compounds that will increase fractionator overhead issues by partitioning to the overhead system, compounds that degrade at crude preheat temperatures to low boiling point compounds previously mentioned, autopolymerisation in the crude preheat that result in fouling, and scaling tendencies in the brine system. Due to these known issues, the MR technology has evolved from commodity acids, through the addition of scale inhibitors to prevent scale adherence, to the most recent proprietary blends that include solution modifiers to prevent scale formation. The recent product evolution successfully removes metals and amine compounds without introducing harmful side effects, resulting in a robust and commercially viable technology that can allow increased volumes of discounted, high metal crude oils to be processed.

Iron removal capabilities
GE initiated work in the 1980s to remove iron from various oil streams to reduce the impact on finished products. Additionally, it is widely known that metal contamination of catalysts used in production of hydrocarbon fuels results in undesirable conditions that increase hydrogen and coke production and ultimately limit fuels production. For example, a number of indices have been developed for fluid catalytic cracking (FCC) catalysts to relate metal contamination on the equilibrium catalyst to hydrogen and coke production, including:

Jersey Nickel Equivalent Index = 1000 * (Ni + 0.2V +0.1 Fe), and

Shell Contamination Index = 1000 * (14Ni + 14Cu + 4V + Fe)5
As can be seen, iron plays a marked role in metal contamination of FCC catalyst, albeit lower than nickel and vanadium.

Emulsion breaking
The proprietary Embreak emulsion breaking products are usually oil-soluble chemicals designed to improve crude oil dehydration, salt removal, and effluent brine quality in electrical desalters and other similar process equipment. Embreak products help reduce emulsion build-up at the oil/water interface and increase solids removal from the crude into the brine effluent. They provide consistently superior desalter operation during periods when high BS&W crudes and slops are processed, and aid in maximising crude rates by controlling emulsion build-up at the desalter interface. Benefits which often result can be summarised as follows:
• Lower overhead corrosion rates, allowing for extended run lengths
• Lower neutraliser and emulsion breaker usage, creating lower treatment cost
• Lower water in desalted crude, reducing the fuel required at the crude furnace, saving energy cost and reducing furnace emissions
• Lower amps on transformers, reducing electrical cost
• Reduced slop oil production, lower reprocessing costs and potential increase in unit charge rate.

Case study: challenge
A US Gulf Coast refinery adopted an aggressive strategy of blending tight oils, including Eagle Ford (EF), to significantly increase its profit margin and supply flexibility. This blend contained significantly higher levels of solids and metals. Unfortunately, it also presented two obstacles that added to the cost of operations. First, the desalter suffered from periodic oil undercarry in the desalter brine; second, high metals loading, specifically calcium and iron, limited the refinery’s ability to process vacuum tower bottoms (VTB) in the FCC unit. The non-GE chemical supplier was unable to improve performance.