1、BRITISH STANDARD BS ISO 8943:2007 Refrigerated light hydrocarbon fluids Sampling of liquefied natural gas Continuous and intermittent methods ICS 75.060 BS ISO 8943:2007 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 March 2008 BSI 2008 I
2、SBN 978 0 580 56225 9 National foreword This British Standard is the UK implementation of ISO 8943:2007. It supersedes BS 7576:1992 which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee PTI/12, Petroleum measurement and sampling. A list of organizations rep
3、resented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations. Amendm
4、ents/corrigenda issued since publication Date Comments Reference number ISO 8943:2007(E)INTERNATIONAL STANDARD ISO 8943 Second edition 2007-03-01 Refrigerated light hydrocarbon fluids Sampling of liquefied natural gas Continuous and intermittent methods Hydrocarbures liquides lgers rfrigrs chantillo
5、nnage de gaz naturel liqufi Mthodes en continu et par intermittence BS ISO 8943:2007ii iii Contents Page Foreword iv Introduction v 1 Scope . 1 2 Normative references . 1 3 Terms and definitions. 1 4 Outline of sampling system. 3 4.1 General. 3 4.2 Continuous sampling . 3 4.3 Intermittent sampling .
6、 6 5 Precautions . 7 5.1 Precautions to be taken in handling LNG 7 5.2 Partial evaporation of the LNG sample. 7 5.3 Supervision during sampling 7 6 Apparatus 7 6.1 Materials used . 7 6.2 Sample probe 7 6.3 LNG sample vaporizer 7 6.4 Compressor for transferring gasified LNG 8 6.5 Pressure regulator 8
7、 6.6 Gas sample holder 8 6.7 Gas sample compressor 8 6.8 Gas sample container or CP/FP sample container . 8 6.9 Piping arrangement 9 6.10 Sample filter 10 7 Sampling procedure . 10 7.1 Sampling period 10 7.2 Consecutiveness of sampling . 10 7.3 Suspension of sampling 11 7.4 Continuous sampling . 11
8、7.5 Intermittent sampling . 12 8 Test report . 13 Annex A (informative) Example of calculation of degree of sub-cooling . 14 Annex B (informative) Constant pressure (CP)/floating piston (FP) sample container with technical specifications . 17 BS ISO 8943:2007iv Foreword ISO (the International Organi
9、zation for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been establishe
10、d has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
11、International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Pub
12、lication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent
13、 rights. ISO 8943 was prepared by Technical Committee ISO/TC 28, Petroleum products and lubricants, Subcommittee SC 5, Measurement of refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels. This second edition cancels and replaces the first edition (ISO 8943:1991), which has been t
14、echnically revised. BS ISO 8943:2007 v Introduction In the custody transfer of liquefied natural gas, hereinafter referred to as LNG, it is common practice to determine the quantity transferred on a calorific-content basis. The total calorific content of quantities of LNG quoted in the custody trans
15、fer is determined by the liquid volume, liquid density and gross calorific value of the LNG delivered. A knowledge of the composition of the LNG is required in order to calculate the density and the calorific content of quantities of LNG. Therefore, precise sampling is a prerequisite for precise ana
16、lysis. LNG is a complex mixture of low-molecular-weight hydrocarbons with nitrogen as a principal inert impurity. Typically, methane is the major component. Minor-component concentrations vary with the source of the raw gas, the liquefaction pre-treatment, the liquefaction process and the storage co
17、nditions. BS ISO 8943:2007 blank 1 Refrigerated light hydrocarbon fluids Sampling of liquefied natural gas Continuous and intermittent methods 1 Scope This International Standard specifies methods for the continuous and the intermittent sampling of LNG while it is being transferred through an LNG tr
18、ansfer line. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 10715:199
19、7, Natural gas Sampling guidelines 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 accumulator storage vessel provided to absorb pressure pulsations of gasified LNG and to homogenize the same 3.2 bubbling procedure, in the case of water-seal-
20、type gas sample holder, to saturate the seal water in a gas sample holder with gasified LNG in order to suppress the effect of the seal water on the gas sample 3.3 compressor for transferring gasified LNG compressor used for boosting the pressure of gasified LNG when gasified LNG in the LNG sample v
21、aporizer cannot be transferred to the gas sample holder by its inherent pressure 3.4 constant pressure / floating piston sample container CP/FP sample container sample container, abbreviated as CP/FP sample container and usually used for intermittent sampling, capable of maintaining constant pressur
22、e during the sampling of gas from the process line into the gas cylinder 3.5 continuous sampling sampling from gasified LNG with constant flow rate 3.6 gas sample container sample container, usually used for continuous sampling, used for the retention of the gas sample and for its transfer to an ana
23、lyzing instrument BS ISO 8943:20072 3.7 gas sample compressor compressor used for charging the gas sample collected in a gas sample holder into a gas sample container 3.8 gasify term used to express “vaporization” related to a treatment during a process 3.9 intermittent sampling sampling from gasifi
24、ed LNG with predetermined intervals or with predetermined flow amount intervals 3.10 LNG liquids composed predominantly of methane 3.11 LNG sample vaporizer apparatus to completely gasify the LNG sample collected from the LNG transfer line 3.12 LNG transfer line pipeline used for transferring LNG 3.
25、13 offline analysis procedure of analysis implemented on the representative sample gas that is once charged into a gas sample container or a CP/FP sample container 3.14 online analysis procedure of analysis implemented using an analytical equipment that is directly connected through pipelines or oth
26、er means to the sampling device 3.15 online gas chromatograph gas chromatograph that is directly connected to the pipelines or sampling device to implement online analysis 3.16 pressure regulator pressure-regulating valve and pressure sensor provided to keep the gas pressure constant at the gas samp
27、le holder inlet 3.17 sample filter filter used to protect the sampling valve for the online gas chromatograph from scoring due to the presence of foreign contaminants, such as metal shavings, dirt and so forth 3.18 sample probe device inserted into the LNG to sample from the LNG transfer line to col
28、lect an LNG sample 3.19 seal water water used in the water seal type gas sample holder to preclude contact of the gas sample with the atmosphere BS ISO 8943:2007 3 3.20 sub-cooling lowering the temperature of LNG below its boiling point at a given pressure 3.21 vaporize used when express “vaporizati
29、on” related to a facility 3.22 waterless-type gas sample holder holder without seal water (typically using an expandable/contractible, transformable rubber membrane) and used for collecting gasified LNG 3.23 water-seal-type gas sample holder holder with seal water used for collecting gasified LNG 4
30、Outline of sampling system 4.1 General Regardless of whether the sampling method is continuous or intermittent, the LNG sample collected through the sample probe provided on the LNG transfer line is gasified in the LNG sample vaporizer. 4.2 Continuous sampling Gasified LNG from the LNG sample vapori
31、zer outlet is continuously fed into the gas sample holder by its inherent pressure when the pressure is sufficiently high or after its pressure has been boosted by the compressor for transferring gasified LNG when the pressure is insufficient. In this process, the gas pressure in the sampling line i
32、s controlled by a pressure regulator and the flow into the gas sample holder is maintained by the gas sample holder inlet valve. The gas sample collected in the gas sample holder is fed into the gas sample container. An outline flow process diagram of the sampling system is shown in Figure 1 for a w
33、ater- seal-type gas sample holder and in Figure 2 for a waterless-type gas sample holder. BS ISO 8943:20074 Key 1 LNG transfer line 10 water-seal-type gas sample holder 2 LNG sample vaporizer 11 compressor for charging gas sample 3 pressure gauge 12 gas sample container 4 thermometer 13 sampling lin
34、e 5 accumulator 14 water pipeline 6 pressure regulator 15 drain pit 7 pressure indicating controller 16 needle valve 8 flow meter 17 valve 9 gas line Figure 1 Example of continuous sampling for a water-seal-type gas sample holder with a compressor BS ISO 8943:2007 5Key 1 LNG transfer line 10 waterle
35、ss-type gas sample holder 2 LNG sample vaporizer 11 vacuum pump 3 pressure gauge 12 gas sample container 4 thermometer 13 sampling line 5 accumulator 14 inert gas line (for compressing gas of inner layer of sampling holder) 6 pressure regulator 15 flow indicating controller 7 pressure indicating con
36、troller 16 needle valve 8 flow meter 17 valve 9 gas line Figure 2 Example of continuous sampling for a waterless-type gas sample holder BS ISO 8943:20076 4.3 Intermittent sampling Gasified LNG from the LNG sample vaporizer outlet is continuously fed into the CP/FP sample container and to the online
37、gas chromatograph by its inherent pressure when the pressure is sufficiently high, or after its pressure has been boosted by the compressor for transferring gasified LNG when the pressure is insufficient. In this process, the gas pressure in the sampling line is controlled by a pressure regulator an
38、d the flow into the CP/FP sample container is maintained by the CP/FP sample container inlet valve. The gas sample collected in the CP/FP sample container is for offline analysis. An outline process flow diagram of the sampling system is shown in Figure 3. Key 1 LNG transfer line flow 10 gas compres
39、sor 19 pressure transmitter 2 LNG sample vaporizer 11 rupture disc 20 heater 3 pressure gauge 12 CP cylinder 21 sample filter 4 thermometer 13 sampling line 22 calibration gas 5 accumulator 14 air supply from sample controls 23 gas chromatograph 6 impact probe 15 level gauge 24 to vent 7 capillary s
40、ample take-off probe 16 needle valve 25 online gas chromatograph 8 flow meter 17 valve 26 auto pre-charge system 9 low pressure gas line 18 solenoid valve 27 bypass valve Figure 3 Example of intermittent sampling for CP/FP sample container BS ISO 8943:2007 7 5 Precautions 5.1 Precautions to be taken
41、 in handling LNG Because LNG has a very low boiling point, contact of the skin with LNG can cause frostbite and, if the gas diffuses into the air, it will lower the oxygen content, which can result in suffocation or, if ignited, fire. Suitable precautions shall be taken against these risks. 5.2 Part
42、ial evaporation of the LNG sample LNG normally exists in a state close to its boiling point. Therefore, partial evaporation readily occurs in the LNG transfer line and sampling line with minute heat input or by pressure variation. For this reason, extreme precautions shall be taken so that the colle
43、cted gas sample represents transferred LNG with best possible accuracy. 5.3 Supervision during sampling Pressures, temperatures and flow rates in the LNG transfer line and the sampling system shall be monitored continuously. Frequent inspection of the entire system shall be made, paying particular a
44、ttention to any leak or failure of the thermal insulation. Defects identified by such inspections shall be remedied immediately. 6 Apparatus 6.1 Materials used The materials of construction of the sampling system shall have sufficient strength and durability to withstand without failure the pressure
45、 and temperature conditions to which they are exposed. The possibility of embitterment of materials at low temperatures shall be taken into account. Materials shall neither be affected by exposure to the fluids handled nor have any effect on the composition of the fluids. 6.2 Sample probe 6.2.1 Samp
46、le probes shall be located at points in the pipeline where the LNG is in a sub-cooled condition. The degree of sub-cooling at a sampling point shall be ascertained by observation of the temperature and pressure of the LNG at that point and comparing the temperature with the boiling point of the LNG
47、at the same pressure as calculated from the composition of the LNG (see Annex A). In the case of multiple transfer lines, the sample probe shall be located downstream of the manifold, if one exists. Otherwise, each line shall be provided with a sampling point. Where multiple lines are provided with
48、individual sampling points and the flow rates in the respective lines differ, the flow rate in each line shall be measured and the sample flows made proportional to these rates. 6.2.2 Sample probes shall be located at a point where the degree of sub-cooling is high. 6.2.3 Sample probes shall be inst
49、alled at a right angle to the axis of the LNG transfer line. 6.2.4 The shape of the extreme end of the sample probe is not critical and the end may be a straight tube. 6.3 LNG sample vaporizer 6.3.1 The heat exchange capacity of the LNG sample vaporizer shall be sufficient to gasify the whole volume of LNG which is being withdrawn for sampling. 6.3.2 The sample vaporizer shall be so constructed that the heavier components of the LNG shall not rema
