API TR 2574-2016 pdf download.Field Testing Protocol for Characterization of Total Gaseous Nonmethane Organics (TGNMO), Methane, and Ethane in Air–Vapor Mixture During Filling of a Cargo Vessel with Crude Oil.
The characteristics and composition of the air–vapor mixture expelled from a cargo vessel into the atmosphere during filling with crude oil is dependent upon the characteristics of the crude oil, including such variables as volatility, temperature, etc. The changing characteristics of the exhausted air–vapor mixture can affect the application of FRM 25 in quantifying the concentration of TGNMO, methane, and ethane in the air–vapor mixture. This field testing protocol provides guidance on utilizing various configurations of FRM 25 in the characterization process. They are: — Time-Integrated Sampling: The traditional FRM 25 sampling train configuration is used but modified by adding a water condensate trap in front of the volatile organic compound (VOC) condensate trap to drop out the water content found in the air–vapor mixture. The water condensate trap prevents freezing of the VOC condensate trap by the water molecules which would lead to reduced gas flow through the sampling system. — Instantaneous Sample: In this configuration, the FRM 25 condensate trap(s) [i.e. water and VOC traps] are removed from the sampling train and instantaneous samples of the air–vapor mixture are acquired periodically during the filling process, utilizing a pre-evacuated canister. When carbon dioxide (CO 2 ) and water vapor are present together in the air–vapor mixture, they can produce a positive bias in the sample. The magnitude of the bias depends on the concentrations of CO 2 and water vapor. As a guideline, multiply the CO 2 concentration, expressed as volume percent, times the water vapor concentration. If this product does not exceed 100, the bias can be considered insignificant. For example, the bias is not significant for a source having 10 % CO 2 and 10 % water vapor, but it would be significant for a source near the detection limit having 10 % CO 2 and 20 % water vapor.
2 Field Sampling Apparatus 2.1 General The sampling system consists of a probe, a water condensate trap, a VOC condensate trap, a flow control system, and a sample canister. The TGNMO sampling equipment can be constructed from commercially available components and components fabricated in a machine shop. Figure 3 documents a typical sampling system. The equipment required is listed in 2.2 to 2.8. 2.2 Sampling Probe The sampling probe is constructed of a 6.4 mm ( 1 / 4 in.) OD stainless steel tube. An inverted stainless steel funnel can be attached to the tip of the probe. The probe is unheated and is attached to the water condensate trap. The probe can be of various lengths to accommodate various sampling locations.
2.3 Water Condensate Trap air–vapor gas streams in the cargo compartment can contain liquid droplets of water or have very high relative humidity. Under these conditions, it is advisable to attach a water condensate trap between the probe outlet and the inlet of the VOC condensate trap. The water condensate trap is a 9.5 mm ( 3 / 8 in.) 316 stainless steel tubing bent into a U-shape (approximately 10 in. in length). The tubing is not packed but is hollow. During sampling, the trap is immersed in a water/ice mixture contained in a small cooler to reduce the temperature of the gas stream for removal of water from the air–vapor mixture. The water condensate trap is illustrated in Figure 4. 2.4 VOC Condensate Trap The VOC condensate trap is similar in construction to the water condensate trap. The VOC condensate trap is a 9.5 mm ( 3 / 8 in.) 316 stainless steel tubing bent into a U-shape (approximately 10 in. in length). The tubing is packed with coarse quartz wool, to a density of approximately 0.11 g/mL before bending. During sampling, the trap is immersed in dry ice contained in a small cooler to reduce the temperature of the gas stream to –50 °C in order to condense the VOCs in the air–vapor mixture. The very volatile VOCs in the air–vapor mixture pass through the trap and are captured in an evacuated canister downstream of the condensate trap. The dry ice VOC condensate trap is illustrated in Figure 4.