1、 Reference number ISO/TR 11150:2007(E) ISO 2007TECHNICAL REPORT ISO/TR 11150 First edition 2007-12-15 Natural gas Hydrocarbon dew point and hydrocarbon content Gaz naturel Point de rose dhydrocarbure et teneur en hydrocarbureISO/TR 11150:2007(E) PDF disclaimer This PDF file may contain embedded type
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6、O copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2007 All rights reservedISO/TR 11150:2007(E) ISO 2007 All rights reserved iii Contents Page Foreword iv Introduction v 1 Scope . 1
7、 2 Normative references . 1 3 Background . 1 4 Why is hydrocarbon dew point important? . 2 5 What is the definition of hydrocarbon dew point? 3 6 Specifications 4 6.1 EASEE-gas European association for the streamlining of energy exchange Gas . 4 6.2 United Kingdom Health and Safety Executive. 4 7 Hy
8、drocarbon dew point measurement .4 7.1 General. 4 7.2 General sampling 4 7.3 Hydrocarbon dew point determination/estimation/monitoring 5 7.4 Physical methods . 5 7.5 Analysis and calculation 8 7.6 Comparative studies. 10 8 Conclusions 10 9 Recommendations 11 Annex A (informative) Dew scope measureme
9、nts (cold mirror) . 12 Annex B (informative) Chromatographic methods . 16 Annex C (informative) Potential hydrocarbon liquid content 18 Bibliography . 19 ISO/TR 11150:2007(E) iv ISO 2007 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of
10、 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 established has the right to be represented on that committee. Int
11、ernational 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. International Standards are drafted in accordance with t
12、he 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. Publication as an International Standard requires approval
13、by at least 75 % of the member bodies casting a vote. In exceptional circumstances, when a technical committee has collected data of a different kind from that which is normally published as an International Standard (“state of the art”, for example), it may decide by a simple majority vote of its p
14、articipating members to publish a Technical Report. A Technical Report is entirely informative in nature and does not have to be reviewed until the data it provides are considered to be no longer valid or useful. Attention is drawn to the possibility that some of the elements of this document may be
15、 the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO/TR 11150 was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 1, Analysis of natural gas. ISO/TR 11150:2007(E) ISO 2007 All rights reserved v Introduction With
16、Resolution 6 at its Prague meeting in 2004, ISO/TC 193/SC 1, Analysis of natural gas, decided to publish a Technical Report on guidance for various International Standards on hydrocarbon dew point and hydrocarbon content. The main purpose of this Technical Report is to explain to the wider gas commu
17、nity the complex issues behind the natural gas property called hydrocarbon dew point on the application of various International Standards on these subjects. TECHNICAL REPORT ISO/TR 11150:2007(E) ISO 2007 All rights reserved 1 Natural gas Hydrocarbon dew point and hydrocarbon content 1 Scope This Te
18、chnical Report describes the various means of estimating hydrocarbon dew point and hydrocarbon content of natural gas. 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 r
19、eferences, the latest edition of the referenced document (including any amendments) applies. ISO 6327, Gas analysis Determination of the water dew point of natural gas Cooled surface condensation hygrometers ISO 6570:2001, Natural gas Determination of potential hydrocarbon liquid content Gravimetric
20、 methods ISO 6974 (all parts), Natural gas Determination of composition with defined uncertainty by gas chromatography ISO 7504:2001, Gas analysis Vocabulary ISO 10715:1997, Natural gas Sampling guidelines ISO 14532:2001, Natural gas Vocabulary Technical Corrigendum:2002 ISO 23874, Natural gas Gas c
21、hromatographic requirements for hydrocarbon dewpoint calculation 3 Background Hydrocarbon dew point is often a requirement of gas quality specifications in sales contracts where gas is traded or crosses international borders. It can also be quoted in health and safety legislation. It is usually spec
22、ified as a temperature at a defined pressure or over a range of pressures above which no hydrocarbon condensation will occur. It may alternatively be expressed as a maximum amount of hydrocarbon liquid which may condense under specific pressure and temperature conditions. Under certain conditions, h
23、igher hydrocarbons present in natural gas or similar gases may condense and the condensate formed can cause difficulties in the operation of gas transport and distribution systems. Phase behaviour in hydrocarbon mixtures such as natural gas is highly non-ideal. More ideal behaviour, such as that of
24、water in air, or, indeed, in natural gas, gives a dew point temperature which continually increases with pressure. Retrograde behaviour, which affects hydrocarbon mixtures, produces dew point temperatures which have a maximum value at an intermediate pressure. Figure 1 shows a typical phase diagram.
25、 ISO/TR 11150:2007(E) 2 ISO 2007 All rights reservedKey X temperature in degrees centigrade Y pressure in bar 1 dense phase 2 gas only 3 gas + liquid 4 dewline 5 critical point 6 cricondentherm 7 cricondenbar Figure 1 Natural gas phase diagram In Figure 1 the dew line is the phase boundary. To the r
26、ight of and above this line only single-phase gas exists. Within the curve of the dew line, both gas and liquid phases are present, in proportions which are governed by the pressure and temperature. The closer to the line, the smaller is the proportion of liquid. The cricondentherm is the point of m
27、aximum dew point temperature. Above this temperature only single-phase gas exists, whatever the pressure. Similarly, at pressures above the cricondenbar, only single phase or dense phase gas exists, whatever the temperature. A gas with a dew line similar to that in Figure 1 would be stable single-ph
28、ase at 5 C and 70 bar. If its pressure is reduced isothermally, it would remain single phase to about 55 bar, at which point it would encounter the phase boundary and condensate would start to separate. As pressure is further reduced, varying ratios of gas and condensate will be found until about 15
29、 bar, when it returns to single phase for the remainder of its depressurization. In fact, once condensate has separated, it is unlikely that it will instantly return to the gas phase, and so liquids may continue to be present at lower pressures. Another consideration is that pressure reduction witho
30、ut the addition of heat is isenthalpic rather than isothermal, and Joule-Thomson cooling will cause the two-phase region to be encountered earlier, unless the gas has been pre-heated so that the cooling curve stays in the single phase region. 4 Why is hydrocarbon dew point important? Avoidance of co
31、ndensate formation is important for pipeline operations. The presence of condensate can cause problems with filters and with measurement and control instrumentation. There is also an issue with gas turbines in power plants significant damage can be caused by the presence of condensate in the burners
32、. A measured dew point temperature which is lower than the specification limit should give assurance that condensation will not occur. For certain needs, such as plant design, or if it is known that a certain amount of condensable material can remain after treatment, knowledge of the quantity of con
33、densable hydrocarbons produced at specified conditions is useful. This can be physically measured using ISO 6570. ISO/TR 11150:2007(E) ISO 2007 All rights reserved 3 Operators require confidence in the measured result. At present, there is little or no information on the maximum permissible error of
34、 measurement, from any type of measurement which is strongly dependent on the type and nature of the natural gas. The single determined value as measured is accepted as the basis for decision making. However, for some natural gases, even a small decrease in temperature can result in a large liquid d
35、rop out. 5 What is the definition of hydrocarbon dew point? The following definitions can be found in various ISO documents, such as in ISO 14532. 2.6.5 Dew points 2.6.5.2 Hydrocarbon dew point 2.6.5.2.1 Hydrocarbon dew point temperature above which no condensation of hydrocarbons occurs at a specif
36、ied pressure NOTE 1 At a given dew point temperature there is a pressure range within which retrograde condensation can occur. The cricondentherm defines the maximum temperature at which this condensation can occur. NOTE 2 The dew point line is the locus of points for pressure and temperature which
37、separates the single phase gas from the biphasic gas-liquid region. 2.6.5.2.2 Retrograde condensation phenomenon associated with the non-ideal behaviour of a hydrocarbon mixture in the critical region wherein, at constant temperature, the vapour phase in contact with the liquid may be condensed by a
38、 decrease in pressure; or at constant pressure, the vapour is condensed by an increase in temperature NOTE Retrograde condensation of natural gas is the formation of liquid when gas is heated or pressure is reduced. 2.6.5.2.3 Potential hydrocarbon liquid content (PHLC) amount of liquid potentially c
39、ondensable per unit volume of gas at a given temperature and pressure Or alternatively in ISO 7504. 3.5.2 Dew point at a specified pressure, the temperature at, or below which, condensation from the gas phase will occur 3.1 Equation of State mathematical relationship between the state variables (pre
40、ssure and temperature) of a gas or gas mixture, and the volume occupied by a given amount of substance 3.5.1 Critical point single point in pressure-temperature phase diagram at which the composition and properties of the gas and liquid phases in equilibrium are identical NOTE 1 The pressure at this
41、 point is known as the “critical pressure” and the temperature as the “critical temperature”. ISO/TR 11150:2007(E) 4 ISO 2007 All rights reserved6 Specifications Two examples from legislation and gas trading can be given. 6.1 EASEE-gas European association for the streamlining of energy exchange Gas
42、 Common business practice 2005-001/01 Harmonisation of natural gas quality 3/2/05. Hydrocarbon dew point shall be maximum of 2 C at 1 bar to 70 bar. NOTE EASEE-gas has not observed any technical constraints in conflict with the proposed harmonized values, and such values were adopted by 1/10/06. Thi
43、s same published document also made the comment “The need for introducing a harmonized measuring method has been identified”. 6.2 United Kingdom Health and Safety Executive A guide to the Gas Safety (Management) Regulations 1996. Schedule 3 Content and other characteristics of gas. Regulation 8 Part
44、 1 Requirements under normal conditions. Hydrocarbon dew point and water dew point shall be at such levels that they do not interfere with the integrity or operation of pipes or any appliance within the meaning of regulation 2(1) of the 1994 Regulations that a consumer could reasonably be expected t
45、o operate. 7 Hydrocarbon dew point measurement 7.1 General The definition of the theoretical hydrocarbon dew point alone is not well understood by measurement technicians/scientists/engineers or those who draft sales gas contracts. At the most pedantic level, the dew point temperature is the minimum
46、 value at which no condensate is present, but only homogeneous gas phase. However this cannot and will never be physically measured as the first molecule will not be detected because the available methods are not sensitive enough (theoretical hydrocarbon dew point temperature). So the method of dete
47、rmination of hydrocarbon dew point is critical, as each approach is based on different measurement principles, the hydrocarbon dew point can only be estimated with an associated uncertainty, and the true value cannot be achieved. 7.2 General sampling Before any instrument or method can be deployed,
48、a sample of the gas to be measured, has to be taken from the flowing gas in the pipeline and transferred unaltered to the measuring device. ISO 10715 states: 3 Principles of sampling 3.1 Sampling methods The main function of sampling is to take an adequate sample that is representative of the gas by
49、 direct sampling such that the sample is drawn from a stream and directly transferred to the analytical method. Care should be exercised to transfer a representative sample flowing in the pipeline unaltered and in a homogeneous single gas phase state to the analytical method. In general, turbulent flow is advantageous in a sampling system and in a gas line to be sampled because turbulence creates a well-mixed gas. Great care and consideration should be given for a gas near the dew point, as a reduction in line t
