Jan-2014

Characterising and tracking contaminants in opportunity crudes

The specific properties of contaminants in opportunity crudes affect the selection of crude slates for existing facilities and the design of revamps and new units

Robert Ohmes
KBC Advanced Technologies

Article Summary

Crude oil characterisation and tracking of specific properties and contaminants are critical aspects in the design and operation of the modern refinery. Given the influx of new sources for oil (synthetic crude from upgraders, oil shale, etc), understanding the effect of these crudes on the refinery operation dictates how a facility will incorporate these opportunity crudes into their regular processing mix.

The focus of this article will be to share techniques and processes for characterising and tracking critical properties and contaminants, particularly around the use of tools and process simulations. The methodologies will be examined both on a theoretical and 
practical basis, using real 
world applications and case studies from design situations and operating facility examples.

The availability of divergent quality crude sources is having a dramatic impact on the crude slate of most refiners. Those facilities that are configured for light/sweet crude now have access to significant volumes of tight oil that match nicely with the assets. Over the last five to 10 years, many refiners have gone through reconfigurations to be able to handle heavy Canadian and Venezuelan crudes.

As these assets come on-line, those refiners are beginning to process these heavy crudes, but are also mindful of the need to run tight or conventional crudes to achieve economic targets. Therefore, many of these sites are faced with balancing 
their new asset capability against changing availabilities of both light and heavy crudes slates.

Ultimately, this dramatic shift in crude availability is opening up the crude slate that most refiners can process, and is influencing a facility’s need to track and understand how different crudes will and are impacting a facility’s performance. KBC has been recommending for some time that a premium should increasingly be placed on a refinery’s ‘optionality’ in processing a wider, not narrower, crude slate.

Critical stream properties and contaminants
A full and rigorous discussion on all the properties and contaminants that impact a refinery is beyond the scope of this article. However, a high level summary is warranted to provide context on the need 
for refiners to track and monitor these properties and contaminants.

Tables 1 and 2 summarise key properties and how they impact refining operation.

The following are typical examples of how these properties could impact refining operations:

Crude/vacuum unit
Can the crude unit properly recover and separate the amount of naphtha and distillate in the crude? Does the unit have sufficient metallurgy to avoid naphthenic acid corrosion? Are the crudes themselves compatible with one another when mixed, or will asphaltene precipitation occur? Can the desalter sufficiently remove basic sediment and water (BS&W) and salts to avoid downstream corrosion and plugging? How are the crudes impacting gasoil recovery and contaminant levels in gasoil stream?

Light ends units
Are the unit off-gas compressors sufficiently sized to process the native light ends in the crude? Does the crude unit lose cutpoint due to higher pressure operation? Can the saturated gas plant maintain C3+ recovery levels?

Naphtha units (hydrotreater and reformer)
Can the hydrotreater and reformer process all of the naphtha within the crude? How does the N+2A level impact reformer severity requirements? Can hydrotreated naphtha be routed to gasoline blending to help manage pool octane? What is the proper disposition for C5s and C6s when balancing octane and RVP?

Distillate units (hydrotreaters)
Are trace unconventional metals impacting catalyst deactivation? Will poor cold properties from tight oils adversely impact jet freeze and diesel cloud and pour points?

Gasoil units (gasoil hydrotreaters, fluid catalytic crackers, hydrocrackers)
How will the gasoil sulphur and nitrogen impact these units? Can the downstream amine, sour water, and sulphur units manage the H2S and NH3 that are produced from these units? How will metals, Conradson carbon (concarbon), and asphaltenes impact catalyst activity and conversion? What are the yield and capacity impacts of a given gasoil stream? Is sufficient hydrogen available to meet contaminant removal and/or conversion targets?

Resid units (coker, ebullated bed hydrocracker, fixed bed resid hydrotreater)
How will the resid concarbon level impact coker yields and utilisation? Will resid processing capacity limit refining crude rate and slate? Will incompatibility impact the onstream factor for the coker and ebullated bed hydrocracker?

As indicated, these properties essentially drive how a given refinery will perform and how the assets generate sustainable and reliable profitability. Therefore, understanding these properties and contaminants, not only in crudes but also in intermediate streams and final products, is critical to selecting a crude slate and preparing and executing an operating plan.

Property data sources
Several data sources exist to understand and estimate the properties of a given crude or refining stream.

Laboratory analysis
The best way to understand a stream’s properties is to measure them in a laboratory. While this option may seem intuitively obvious, accurate measurement of a given property is more difficult than it may initially seem.

First, multiple methods exist for measuring a specific property for a given stream type. Most refiners utilise standard methods according to internationally accepted measurement techniques, such as those from the American Society for Testing and Materials (ASTM). However, the refiner must decide on the method that is utilised in their facility or use methods that are dictated by product sales requirements.