(341x) Development of an Equation Oriented Simulation Module for the Generation of Oil Lumps from Distillation Curves

The physicochemical characterization of an oil sample is an especially important step for petrochemical plants. With this step, the oil can be represented by real components through laboratory analysis or procedures using mathematical models. Crude oil, as well as oil fractions, consist of thousands of components ranging from light hydrocarbons (i.e., methane and/or ethane) to high molecular weight components (>C₄₀). Another particularly important factor that influences the composition of the oil is directly related to its location of extraction. Although the compositions of the pure components of the oil mixture can be determined through experiments, the use of classical laboratory methods becomes infeasible with mixture complexity due to the time taken for the analysis. One possible solution to address this problem is to implement a pseudoization approach in a process simulator to generate pseudocomponents from oil lumps based on laboratory distillation curves.

A pseudocomponent denotes a group of pure components lumped and represented by a single component. This lumped process is also called pseudoization^1,2,3,4. In practice, a sample of a crude oil is distilled in the laboratory for separation into several fractions according to bubble point ranges of approximately 10⁰C (or oil cuts). When the bubble points of all cuts are known, then the distillation curve of the oil sample can be generated. Each cut consists of hydrocarbons of various types, among which stand out paraffins (P), olefins (O), naphthenics (N) and aromatics (A)⁵. With the available information about the cuts, mathematical methods can be employed to create representative oil samples using pseudocomponents, making it possible to estimate parameters or properties of the real mixture. The successful characterization of each oil cut by a pseudocomponent can be obtained through physicochemical parameters estimated from its bubble point and specific gravity⁶.

There are a few commercial process simulators with the pseudocomponent functionality. Among them, the AVEVA SimCentral Simulation Platform^® stands out. Considering the high number of mathematical relationships as well as the numerical methods needed to address this problem, an equation-oriented simulation platform such as SimCentral can be extremely useful to enable the definition of petrochemical components in any process simulation. In this platform, the user is able to insert new models in order to meet the specific demand of an application.

This work will present a process block to execute suitable approaches capable of performing the data conversion (from chemical component to pseudocomponent and vice versa). This procedure can be done based on average properties of each oil cut (or oil lumps) provided through distillation curves in SimCentral to be used in petrochemical simulations. Such a structured block will allow the use and creation of important units for simulation of purification processes (e.g., HDT, HCC, FCC, etc.) using the SimCentral model writing functionality. The simulated results obtained will be discussed and compared to the actual data from the oil purification processes used by the Petrobras^®.

References

¹Ahmed, T. (2010). Working Guide to Vapor-liquid Phase Equilibria Calculations. Gulf Professional Publishing.

²S. F. Mello, E. L. (2011). Influence of Lumping and Equation of State Tuning Methods on the Sub-Salt Reservoirs Simulation. SPE International (pp. 23-26). Viena, Austria: Society of Petroleum Engineers.

³Alavian S. A., W. C. (2014). Global Component Lumping for EOS Calculations. SPE International (pp. 27-29). Amsterdam, Netherlands: Society of Petroleum Engineers.

⁴El - Houari Benmekki, G. M. (1989). Pseudoization Techniques and Heavy fraction Characterization with Equation State Models. Em G. A. L. G. Chorn, C7+ Fraction Characterization (pp. 57-78). Chicago: Taylor & Francis.

⁵Al-Assady, Q. M. (2009). Characterization of Petroleum Fractions. The Iraqi Journal for Mechanical and Material Engineering.

⁶Riazi, M. R. (2005). Characterization and Properties of Petroleum Fractions. Philadelphia: American Society For Testing And Materials (ASTM).