ProSoft Technology MVI56-AFC - Manual (Page 276)

Reference MVI56-AFC ♦ ControlLogix Platform
User Manual Liquid and Gas Flow Computer
Page 276 of 316 ProSoft Technology, Inc.
February 25, 2011
Water Content of Liquids
The handling of water content in crude and NGL products depends upon whether
an "emulsion" Product Group is chosen.
For emulsions, water content is removed from the mixture according to the
calculations of API MPMS Chapter 20.1 before calculating and applying
correction factors. In this case the volumetric quantity intermediate between
"Gross" and "Net" is "Gross Clean Oil", which is the hydrocarbon component of
the mixture at flowing conditions. This method is recommended for mixtures
containing more than 5% water.
For non-emulsions, water content is removed from the mixture according to the
rules of API MPMS Chapter 12.2 after calculating and applying correction factors.
In this case the volumetric quantity intermediate between "Gross" and "Net" is
"Gross Standard", which is the entire mixture including its water content
corrected to standard conditions under the assumption that it is pure
hydrocarbon. Because the presence of water skews the correction calculations,
this method should be used only when the water content is very low.
Non-Standard Reference Conditions
For both liquids and gases, the AFC permits a range of reference conditions for
volume measurement which may vary from the API/AGA standard of
15°C/101.325kPaa (SI) or 60°F/14.696psia (US) (US pressure base for gases is
14.73psia). The allowed ranges for SI units are temperature between 0°C and
25°C and pressure between 50kPaa and 110kPaa, with the allowed ranges for
US units approximately equivalent.
For gases, this flexibility of reference conditions is handled automatically by the
implementation of the AGA 8 (1992) standard for compressibility Z together with
the "real" gas law PV=ZNRT.
For liquids, correction factors for non-standard reference conditions are
calculated differently depending on the firmware version. For version 2.05 and
later, correction factors and corrected density are calculated according to the
2004 edition of API MPMS Chapter 11.1, except for the "NGL" product groups for
which the CTL and density calculations of GPA TP-27 are extended with the CPL
calculations of (old) MPMS Chapter 11.2 in a manner analogous to that of the
2004 Chapter 11.1. For version 2.04 and earlier, correction factors and corrected
density are calculated as described in the following paragraphs, using the
calculations of the 1980 edition of MPMS Chapter 11.1. In all cases, the density
input to the calculations is the density at standard API base conditions.
Temperature Correction Factor, CTL
First, the "standard" factor, CTL(Flowing / ApiBase), is calculated, except that the
final rounding step is not performed. Then, CTL(UserBase / ApiBase) is
calculated, also unrounded. The CTL(Flowing / UserBase) is then calculated as
(CTL(Flowing / ApiBase) / CTL(UserBase / ApiBase)), to which result is applied
the final rounding step of the standard CTL calculation.