ProSoft Technology PTQ-AFC - Manual (Page 220)

Reference PTQ-AFC ♦ Modicon Quantum Platform
User Manual Liquid and Gas Flow Computer for Hydrocarbon Products
Page 220 of 259 ProSoft Technology, Inc.
June 23, 2011
2 The V-cone Coefficient of Discharge is entered as configuration and not
calculated. Expansion Factor (Y) is calculated differently.
Output of the calculation is mass flow rate, which is divided by density to get
volume and then integrated over time for accumulation.
Pulse: Both Gas and Liquid
Gross Volume is (pulses) / (K-factor) * (meter factor), according to API MPMS Ch
12 sec 2 1981 and 1995. Output of the standard calculation is volume flow
increment, which is then multiplied by density to get mass increment. Flow rate is
calculated in parallel to flow increment by applying to (pulse frequency) process
input the same calculation as is applied to (pulses); this technique is employed
instead of flow increment differentiation because the pulse frequency available
from the counter card in the processor is not subject to variations of timing
caused by scheduling delays in processor backplane transfer and in the firmware
of the module, thus yielding a smoother flow rate.
Correction Factors According to Product Phase
Gas
Compressibility is calculated according to the Detail Characterization Method of
AGA8 (1992). Gas density is a byproduct of this calculation. Essential input for
this calculation is molar analysis. The compressibility Z is a factor in the gas
equation PV=ZNRT, which is the rule by which gas volumes are corrected to
reference conditions.
Liquid
Temperature and pressure correction factors are calculated according to API
MPMS Ch 11 and applied according to the rules given in MPMS Ch 12. Essential
input for this calculation is Liquid Density (page 74) at either standard or flowing
conditions.
Gas Pulse Measurement
The standard applied is AGA7, which is merely a combination of the gross
volume calculation (page 220) and the gas law (PV=ZNRT) which includes
compressibility. It also specifies calculation of some intermediate factors, which
are now idiosyncratic and vestigial, having been imported from an earlier AGA3
(1985 and before) which used the "factor" method to calculate gas flow and
which has been superseded by the completely overhauled 1990/1992 AGA3.
Water Content of Liquids
The handling of water content in crude and NGL products depends upon whether
an "emulsion" Product Group is chosen.