ISO-TR-11150-2007.pdf

Reference number ISO/TR 11150:2007(E) © ISO 2007 TECHNICAL REPORT ISO/TR 11150 First edition 2007-12-15 Natural gas Hydrocarbon dew point and hydrocarbon content Gaz naturel Point de rosée d'hydrocarbure et teneur en hydrocarbure Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:16:19 MSTNo reproduction or networking permitted without license from IHS -,-,- ISO/TR 11150:2007(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. COPYRIGHT PROTECTED DOCUMENT © ISO 2007 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester. ISO 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 reserved Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:16:19 MSTNo reproduction or networking permitted without license from IHS -,-,- ISO/TR 11150:2007(E) © ISO 2007 All rights reserved iii Contents Page Foreword iv Introduction v 1 Scope . 1 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 Hydrocarbon 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 measurements (cold mirror) . 12 Annex B (informative) Chromatographic methods. 16 Annex C (informative) Potential hydrocarbon liquid content 18 Bibliography. 19 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:16:19 MSTNo reproduction or networking permitted without license from IHS -,-,- ISO/TR 11150:2007(E) iv © ISO 2007 All rights reserved Foreword ISO (the International Organization 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 established 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. 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. Publication as an International Standard requires approval 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 participating 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 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. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:16:19 MSTNo reproduction or networking permitted without license from IHS -,-,- ISO/TR 11150:2007(E) © ISO 2007 All rights reserved v Introduction With 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 community the complex issues behind the natural gas property called hydrocarbon dew point on the application of various International Standards on these subjects. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:16:19 MSTNo reproduction or networking permitted without license from IHS -,-,- Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:16:19 MSTNo reproduction or networking permitted without license from IHS -,-,- TECHNICAL REPORT ISO/TR 11150:2007(E) © ISO 2007 All rights reserved 1 Natural gas Hydrocarbon dew point and hydrocarbon content 1 Scope This Technical 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 references, 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 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 chromatographic 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 specified 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, higher 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 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. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:16:19 MSTNo reproduction or networking permitted without license from IHS -,-,- ISO/TR 11150:2007(E) 2 © ISO 2007 All rights reserved Key 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 right 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 maximum 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-phase 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 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 without 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 condensate 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. 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 condensable hydrocarbons produced at specified conditions is useful. This can be physically measured using ISO 6570. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:16:19 MSTNo reproduction or networking permitted without license from IHS -,-,- 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 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 drop 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 specified 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 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 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 condensable 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 (pressure 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 point is known as the “critical pressure” and the temperature as the “critical temperature”. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Japan, IHS Not for Resale, 12/17/2007 19:16:19 MSTNo reproduction or networking permitted without license from IHS -,-,- ISO/TR 11150:2007(E) 4 © ISO 2007 All rights reserved 6 Specifications Two examples from legislation and gas trading can be given