ISO 6570:2001 pdf download
ISO 6570:2001 pdf download.Natural gas – Determination of potential hydrocarbon liquid content – Gravimetric methods.
If the presence of water vapour does not lead to hydrate formation, the drying tube may be omitted and the amount of water formed under the measurement conditions determined.
If hydrocarbon mist is present in the sample, and a drying tube is used, ensure that the mist is evaporated by heating before allowing the sample to pass through the drying tube.
4.1.4 Dust filter, preferably of a 5 urn pore size, which does not adsorb hydrocarbons.
4.1.5 Heat exchangers, pressure regulators and controllers, installed on the gas line with the heat exchanger immediately upstream to each pressure regulator so as to ensure that the gas temperature after pressure reduction remains at least 5 K above the dew point.
The pressure controller can be placed upstream or downstream from the cooling bath in the measurement installation (see annex B).
4.1.5.1 Heat exchanger (see example in Figure 3), through which water, maintained at the required temperature, is circulated from a thermostatically controlled bath so as to maintain the temperature constant in the gas line.
4.1.5.2 Pressure regulator and pressure controller, to ensure the maximum variation from its set-point with the pressure measurement in the gas/liquid cyclone separator is ± 10 kPa.
4.1.6 Measurement instruments for temperature and pressure, capable of recording or monitoring the following:
a) gas temperature and pressure in the gas/liquid cyclone separator;
b) ambient temperature and pressure;
c) gas temperature in the gas transmission line, or in the cylinder from which the sample is taken (optional);
d) gas temperature after pressure reduction (optional);
e) temperature of the bath (optional);
f) gas pressure before pressure reduction (optional);
g) gas pressure after pressure reduction (optional).
If proven experimentally that the difference between the temperature of the gas in the cyclone separator and the temperature of the cooling bath is less than 0,1 K, the temperature of the cooling bath may be measured instead. The pressure can be measured in the sample line just before or just after the cyclone separator.
4.1.7 Gas flow meter, capable of making either mass or volumetric measurements for either wet or dry gas. If a mass flow meter is used, it is necessary that the density of the gas be known.
The flow rate of the gas passing through the installation is limited by the cooling capacity of the bath, the heat transmission between the cooling coil and bath and the temperature drop to which the sample is subjected. The flow rate shall, therefore, be limited to a value that will ensure that the gas is cooled to the bath temperature (see 4.1.9.3).
Check the accuracy of the meter at regular intervals. The choice of gas meter shall be made taking into account the required accuracy, flow rate and the nature of the natural gas. The maximum permissible error in the flow meter shall be ± 1 % of the measured value.
The measured values shall be corrected for temperature and pressure if the values vary during the course of the period of measurement from reference conditions (273,15 K and 101,325 kPa).
4.1.8 Heated cabinet, used in the case of indirect sampling, of the appropriate shape to contain the sample cylinder and capable of heating to at least 10 K above the temperature at the sampling point (see 5.5).
4.1.9 Condenser/separator apparatus, consisting of a cooling coil connected at the end to a cyclone separator where condensates are collected (see Figure 4).
The cooling coil and cyclone separator are completely immersed in the cooling bath. The difference in temperature between the cooling bath and the gas/liquid cyclone separator shall not exceed 0,1 K.
4.1.9.1 Cooling coil, possibly in the form of a coil of stainless steel tubing and meeting the following design characteristics:
a) capable of providing turbulent flow throughout the measurements;
b) capable of maintaining the temperature difference between the gas leaving the cooling coil and the temperature of cooling bath to less than 0,25 K;
c) capable of maintaining pressure difference over the cooling coil not exceeding 1 kPa so as to ensure isobaric conditions;
d) having an internal diameter between 2 mm and 4 mm.
NOTE These specifications can be met for example with a cooling coil of 2,5 m length and a gas flow of 1 m3/h.
4.1.9.2 Cyclone separator, permanently connected to the cooling coil, with a specific inlet diameter enabling sufficient centrifugal action to be obtained as the sample gas enters the cyclone separator barrel.
EXAMPLE A cyclone separator having an inlet diameter of 1 mm can meet these requirements. A provision can be made for measuring or recording the gas temperature in the barrel.
