Page 31 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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1. INTRODUCTION 11
4. Storage tanks
5. Distillation, absorption, and stripping columns 14:26 to determine the quality and composition of petroleum
fractions [27–29].
6. Boilers, evaporators, condensers, and heat exchangers 6. Composition of petroleum fractions in terms of wt% of
7. Flashers (to separate light gases from a liquid) paraffins (P%), naphthenes (N%), aromatics (A%), and
8. Mixers and agitators sulfur content (S%) are important to determine the qual-
9. Reactors (fixed and fluidized beds) ity of a petroleum fraction as well as to estimate physical
10. Online analyzers (to monitor the composition) properties through pseudocomponent methods [31–34].
11. Flow and liquid level measurement devices Composition of other constituents such as asphaltene and
12. Control units and control valves resin components are quite important for heavy oils to
determine possibility of solid-phase deposition, a major
The above list shows some, but not all, of the units involved problem in the production, refining, and transportation
in the petroleum industry. Optimum design and operation of oil [35].
of such units as well as manufacture of products to meet 7. Pour point (T P ), and melting point (T M ) have limited uses
market demands and government regulations require a com- in wax and paraffinic heavy oils to determine the degree
plete knowledge of properties and characteristics for hydro- of solidification and the wax content as well as minimum
carbons, petroleum fractions/products, crude oils, and reser- temperature required to ensure fluidity of the oil.
voir fluids. Some of the most important characteristics and 8. Aniline point to determine a rough estimate of aromatic
properties of these fluids are listed below with some exam- content of oils.
ples for their applications. They are divided into two groups 9. Flash point (T F ) is a very useful property for the safety of
of temperature-independent parameters and temperature- handling volatile fuels and petroleum products especially
dependent properties. The temperature-independent properties in summer seasons.
and parameters are as follows:
10. Critical temperature (T c ), critical pressure (P c ), and critical
volume (V c ) known as critical constants or critical prop-
1. Specific gravity (SG) or density (d) at SC. These para- erties are used to estimate various physical and thermo-
meters are temperature-dependent; however, specific dynamic properties through equations of state or gener-
gravity at 15.5 C and 1 atm and density at 20 C and 1 alized correlations [36].
◦
◦
atm used in petroleum characterization are included in 11. Acentric factor (ω) is another parameter that is needed
this category of temperature-independent properties. The together with critical properties to estimate physical and
specific gravity is also presented in terms of API gravity. thermodynamic properties through equations of state
It is a useful parameter to characterize petroleum fluids, [36].
to determine composition (PNA) and the quality of a fuel
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(i.e., sulfur content), and to estimate other properties such The above properties are mainly used to characterize the
as critical constants, density at various temperatures, vis- oil or to estimate the physical and thermodynamic proper-
cosity, or thermal conductivity [23, 24]. In addition to its ties which are all temperature-dependent. Some of the most
direct use for size calculations (i.e., pumps, valves, tanks, important properties are listed as follows:
and pipes), it is also needed in design and operation of 1. Density (ρ) as a function of temperature and pressure
equipments such as gravity decanters. is perhaps the most important physical property for
2. Boiling point (T b ) or distillation curves such as the true petroleum fluids (vapor or liquid forms). It has great ap-
boiling point curve of petroleum fractions. It is used to plication in both petroleum production and processing as
determine volatility and to estimate characterization pa- well as its transportation and storage. It is used in the
rameters such as average boiling point, molecular weight, calculations related to sizing of pipes, valves, and storage
composition, and many physical properties (i.e., critical tanks, power required by pumps and compressors, and
constants, vapor pressure, thermal properties, transport flow-measuring devices. It is also used in reservoir simula-
properties) [23–25]. tion to estimate the amount of oil and gas in a reservoir, as
3. Molecular weight (M) is used to convert molar quantities well as the amount of their production at various reservoir
into mass basis needed for practical applications. Ther- conditions. In addition density is used in the calculation
modynamic relations always produce molar quantities of equilibrium ratios (for phase behavior calculations) as
(i.e., molar density), while in practice mass specific val- well as other properties, such as transport properties.
ues (i.e., absolute density) are needed. Molecular weight 2. Vapor pressure (P vap ) is a measure of volatility and it is
is also used to characterize oils, to predict composition used in phase equilibrium calculations, such as flash, bub-
and quality of oils, and to predict physical properties such ble point, or dew point pressure calculations, in order to
as viscosity [26–30]. determine the state of the fluid in a reservoir or to sep-
4. Refractive index (n) at some reference conditions (i.e., 20 C arate vapor from liquid. It is needed in calculation of
◦
and 1 atm) is another useful characterization parameter equilibrium ratios for operation and design of distilla-
to estimate the composition and quality of petroleum frac- tion, absorber, and stripping columns in refineries. It is
tions. It is also used to estimate other physical properties also needed in determination of the amount of hydrocar-
such as molecular weight, equation of state parameters, bon losses from storage facilities and their presence in
the critical constants, or transport properties of hydrocar- air. Vapor pressure is the property that represents igni-
bon systems [30, 31]. tion characteristics of fuels. For example, the Reid vapor
5. Defined characterization parameters such as Watson K, pressure (RVP) and boiling range of gasoline govern ease
carbon-to-hydrogen weight ratio, (CH weight ratio), refrac- of starting engine, engine warm-up, rate of acceleration,
tivity intercept (R i ), and viscosity gravity constant (VGC) mileage economy, and tendency toward vapor lock [19].

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