(535i) Crude Assays Cut Properties

Cut Properties

Andrew W. Sloley

DGI

Bellingham, WA, USA

Crude assays include more than distillation curves. Specific boiling ranges of material in the crude have different compositions. These compositions affect product properties and processing required. A useful crude assay provides information on individual boiling ranges, cuts, separated from the crude by distillation. Properties can be measured on each of these cuts. This analysis looks at consistent trends in these properties relevant to the Crude Distillation Unit (CDU) and Vacuum Distillation Unit (VDU). The CDU and VDU separate components based on boiling point, but more than boiling point is important in them. Both operating costs and selected (non-distillation) product properties are important in CDU and VDU operation.

Operating costs in the crude unit are strongly affected by:

• asphaltenes and other composition related properties in fouling,
• chlorides leading to potential corrosion,
• acid content and corrosion, and
• sulfur compounds and corrosion.

Many products have specifications that are strongly affected by crude unit performance. While no general correlation is available that relates boiling point and the property, general trends are reliable and performance is strongly related to boiling point for a specific crude. These properties may include:

• freeze point for kerosene going to jet fuel,
• luminometer number for kerosene going to jet fuel,
• smoke point for kerosene going to jet fuel,
• cloud point for diesel,
• volatile metals contents for gas oils,
• sulfur, nitrogen, and oxygen for various middle distillate and gas oil fractions,
• viscosity and viscosity index for gas oils (lubricants),
• carbon residue for gas oils and residues, and
• penetration for asphalts (residues).

This paper reviews common trends in these properties in the cuts from crude oil and how actual unit performance, property trends, and property characteristics can affect product qualities and operating costs.