ISO 6570 pdf download – Natural gas -Determination of potential hydrocarbon liquid content- Gravimetric methods

ISO 6570 pdf download – Natural gas -Determination of potential hydrocarbon liquid content- Gravimetric methods.
5.2 Sampling conditions
If hydrocarben mist Is present m the pipeline system, the result of the measurements will strongly depend on the distance between the probe and (tie point where the mist is formed. In this case. sample the gas isokEietlcally, using an isokinetic sampling probe (4.1.11) placed in the transnision peline.
If it is required to measure the quantity of mist separately, use direct sampling.
5.3 Sample line
Heat the whole sample line (4.1.2) to at least 5K above the dew point of the sampled gas ii order to avoid condensation,
Pass the gaseous sample through a dust filter (4.1.4). II mist is present in the gas, the velocity of the gas should be sulficzently high so as to avoid accumulation in the sample line. In this case, no dust filter should be installed.
5.4 Direct sampling
For crect sampling, connect the sampling line dwectly to (he measurement installation.
5.5 IndIrect sampling
It is possible to take a sample in a cylinder and transport it to the laboratory. However, the Irlited volume of the sample affects the sensitivity and accuracy of the method In order to ensure that the contents of the cylinder are representative, clean, dry and check the cylinder for hypocarbon content. Prior to tilling, evacuate the cylinder to a pressure below 100 Pa absolute.
Taking samples Ironi a relatively hot system into a cold cylinder causes the gas to contract and may cause condensation. Both factors increase the mass of gas sampled on tilling the cylinder to system pressure when compared with the mass of a similar volume of gas taken under the conditions of sampisig. Consequentty, in the laboratory, before any gas is removed, heat the cylinder for at least 2411 to a temperature of at least 10 K above the temperature of the gas at the sampling point. Heating is necessary in order to re-evaporate any condensed lktuki in the cylinder. It also increases the pressure to above that of the system from which the sample was taken; this excess pressure provides enough gas for measurements to be made at the sampling pressure. Monitor the pressure in the cylinder so as to remain within the safe working pressure range of the cylinder.
If hydrocarbon mist is present in the pVeline system, the indirect sampling method shall not be used.
6.1.1.2 Determination using the sample gas
Afler cleaning and drying, place the cooling coil and cyclone separator in the cooling bath and connect them to the measurement installation. Considerations for the selection of the desired measurement temperature and pressure of the measurement instalation are given in annex A. When they have reached the temperature of the bath. bI’ing the pressure of the gas In the cyclone separator to the measurement pressure. This can be done very accurately by Initially applying a slightly higher pressure and then venting as much gas as required via the gas meter until the pressure gauge Shows the desired measurement pressure.
When no excess pressure is available, determine the mass of sampled gas by weighing the cooling coil and cyclone separator on the balance (4.1.10.1) at a pressure slightly lower man the measurement pressure. Close the inlet and outlet valves ol the cooling coal and cyclone separator. Disconnect the cyclone separator and cooling coil, inckiding the valves, remove them from the cooling bath and immerse them in a tank containing clean water, in order to wash off the antifreeze and also to check for gas leakage. Once the outer surface is clean, remove the cooling coil and cyclone separator from the tank and &y them. Weigh the cooling coil and cyclone separator to determine their inetial mass. Place the cooling coil and cyclone separator back in the cooling bath and connect them to the measurement inslalalion. Allow the gas to how through the measurement installation at a flow rate In accordance with design specifications.
In practice, a gas flow between 0,5 rn3Th and 1.5 m3/h gives good results when using a cooling coil and a cyclone separator according to 4.1.9.
When sufficient gas has been passed. stop the flow and ensure that the static gas pressure in the installation is equal to the pressure at which the mass of the cooling coil and cyclone separator was first delemiined.
It is preferable to pass at least 10 m3 (standard reference condelons) of gas through the installation or collect at least 1 g of liquid.
Close the valves. Disconnect the cooling coil and cyclone separator, wash them in water, clean and dry the outer surfaces. Determine the mass of the cooling coil and cyclone separator containing the liquid sample.