API Publ 4683:1998 pdf download

API Publ 4683:1998 pdf download.Correlation Equations to Predict Reid Vapor Pressure and Properties of Gaseous Emissions for Exploration and Production Facilities.
EXPECTED EMPIRICAL RELATIONSHIPS
Predictors of saks oil RVP are expected to directly relate to the volatility of the sales oil or the conditions of the storage tank (such as sales oil APIG and bubble point) (Measurements of separator pressure and temperature are collected in a vessel external to the sales oil tank, and therefore, are not expected to correlate well with the RVP of the sales oil.)
The bubble point pressure is defined as the pressure at which the first bubble of vapor will form in a liquid that is held in a closed container at a constant temperature. The bubble point pressure of the sales oil is very likely to correlate well with the RVP since (I) both variables represent a pressure measurement of the gas phase in equilibrium with the sales oil, and (2) the bubble point pressure represents the theoretical upper limit to RVP. Figure 3-1 illustrates the relationship between sales oil bubble point and RVP for 94 E&P storage tanks. The fact that none of the data points exceeds the 1:1 line (which would represent perfect agreement) illustrates that the bubble point is the upper limit for the RVP. The bubble point, however, was not considered to be a parameter that could be measured easily at an E&P storage tank. Therefore, it is recommended for use only as an optional input variable.
DESCRIPTIVE STATISTICS
Table 3-1 summarizes key descriptive statistics for the sales oil RVP, separator pressure and temperature, and sales oil APIG associated with the 94 E&P storage tanks considered in this analysis. (Note that the RVP and APIG data were measured at a fixed temperature of 100°F, even though the tank temperatures or ambient temperatures probably varied significantly.) Currently, API employs a default value (RVP 5 psia) in order to estimate working and standing (W&S) losses from crude oil storage tanks. The goal of this analysis is to improve upon the default assumption.
The purpose of this section is to summarize an analysis performed to estimate the THC molecular weight during flashing emissions and W&S emissions. It is very important to note that the gaseous THC molecular weights analyzed in this section were not measured, but were modeled from the E&P TANK model, which is a complex thermodynamic model. Thus, the goal of this analysis was to produce a simpler model that estimates ThC molecular weights and compares favorably with the E&P TANK model.
UNDERLYING THEORY AND EXPECTED PREDICTORS
For components closely similar in molecular structure (such as hydrocarbons) and at equilibrium, the compositions of the gas and liquid phases are related according to Raoult’s Law (Equation 4-1).