1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2009 SAE International All rights reserved. No part of this publication m
3、ay be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA)
4、 Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SURFACE VEHICLE RECOMMENDED PRACTICE J2645 APR2009 Issued 2003-03 Revised 2009-04 Superseding J2645 MAR2003 Liquefied Natural Gas (LNG) Vehicle Metering and Dispensing SystemsTruck and Bus RATIONALE This SAE Recommen
5、ded Practice is intended as a guide for standard practice and is subject to change in order to keep pace with experience and technical advances. Its purpose is to promote safety and efficiency by making available to sellers and buyers of commercial liquefied natural gas (LNG) vehicle metering and di
6、spensing systems a recommended practice for construction, operation, and maintenance of such systems. This SAE publication necessarily deals to some extent in generalities, since it is not possible to anticipate and address every individual set of conditions that might be found in constructing, oper
7、ating, and maintaining LNG vehicle metering and dispensing systems. It is intended to be a practical guide illustrating the application of recommended practices. The correct application of these practices in any actual field situation must rely on sound judgment and experience. TABLE OF CONTENTS 1.
8、SCOPE 3 2. REFERENCES 3 2.1 Applicable Publications . 3 2.1.1 NIST Publication . 3 2.1.2 NFPA Publications 3 2.2 Related Publications . 3 2.2.1 State of California Publication . 3 2.2.2 NFPA Publications 3 3. DEFINITIONS . 4 3.1 Authority Having Jurisdiction . 4 3.2 Contract Sale 4 3.3 Cryogenic Liq
9、uids . 4 3.4 Derived Mass Units . 4 3.5 Direct Sale . 4 3.6 Dispenser 4 3.7 Liquefied Natural Gas (LNG) 4 3.8 Mass Flow Meter . 4 3.9 NBP . 4 3.10 NTP . 5 3.11 Point of Sale System . 5 3.12 Retail Device . 5 3.13 Saturation Pressure 5 3.14 Two-Phase Flow . 5 3.15 Wholesale Device . 5 SAE J2645 Revis
10、ed APR2009 Page 2 of 9 4. CRYOGENIC ISSUES 5 4.1 Heat . 5 4.2 Saturation Pressure 5 4.3 Density 6 4.4 LNG Composition 6 4.5 Sub-Cooling 6 5. DISPENSING SYSTEM ISSUES 6 5.1 Hose Volume Corrections . 6 5.2 Two-Phase Flow . 6 5.3 Temperature Effects . 6 5.4 Pressure Effects 6 5.5 Composition Compensati
11、on 6 5.6 Diversion of Measured Flow . 7 5.7 Vapor Equalization Line 7 6. DISPENSING SYSTEM SELECTION . 7 6.1 Private Stations . 7 6.2 Public (Retail) Stations 7 6.3 Refueling Frequency . 7 6.3.1 All Vehicles Fuel During the Same “Fueling Window” 7 6.3.2 Intermittent Fueling . 7 7. MEASUREMENT DEVICE
12、 TYPES . 7 7.1 Volumetric . 8 7.2 Mass 8 7.3 Inferred Mass 8 8. LNG DISPENSER/METER . 8 9. SAFE OPERATION . 9 9.1 General . 9 9.2 Hose Breakaway . 9 9.3 Connectors 9 9.4 Grounding . 9 9.5 Venting 9 10. DISPENSER DISPLAY . 9 11. NOTES 9 11.1 Marginal Indicia . 9 TABLE 1 - GUIDELINES ON METERING AND D
13、ISPENSING SYSTEMS 8 SAE J2645 Revised APR2009 Page 3 of 9 1. SCOPE This SAE Recommended Practice applies to Liquefied Natural Gas Vehicle Fuel. The purpose of this document is to provide information on issues that are important to consider regarding LNG metering and dispensing systems. 2. REFERENCES
14、 2.1 Applicable Publications The following publications form a part of this specification to the extent specified herein. Unless otherwise specified, the latest issue of each publication applies. 2.1.1 NIST Publication Available from National Institute of Standards and Technology, 100 Bureau Drive,
15、Stop 1070, Gaithersburg, MD 20899-1070, Tel: 301-975-6478, www.nist.gov. NIST Handbook 44 Specifications, Tolerances, and other Technical Requirements for Weighing and Measuring Devices 2.1.2 NFPA Publications Available from the National Fire Protection Agency, 1 Batterymarch Park, Quincy, MA 02169-
16、7471, Tel: 617-770-3000, www.nfpa.org. NFPA 52 Vehicular Fuel Systems Code NFPA 59A Standard for the Production, Storage, and Handling of Liquefied Natural Gas (LNG) 2.2 Related Publications The following publications are provided for information purposes only and are not a required part of the docu
17、ment. 2.2.1 State of California Publication Available on the web at http:/www.dir.ca.gov/Title8/sub1.html. California Code of Regulations (CCR), Title 8, Industrial Regulations, Article 7, Compressed and Liquefied Natural Gas Systems 2.2.2 NFPA Publications Available from the National Fire Protectio
18、n Agency, 1 Batterymarch Park, Quincy, MA 02169-7471, Tel: 617-770-3000, www.nfpa.org. NFPA 30 Flammable and Combustible Liquids Code NFPA 30A Code for Motor Fuel Dispensing Facilities and Repair Garages NFPA 70 National Electrical Code NFPA 72 National Fire Alarm Code NFPA 79 Electrical Standard fo
19、r Industrial Machinery NFPA 497 Classification of Flammable Liquids, Gases, or Vapors and of Hazardous Locations for Electrical Installations in Chemical Process Areas SAE J2645 Revised APR2009 Page 4 of 9 3. DEFINITIONS Definition 3.1 is taken from NFPA 52 (1998) (Compressed Natural Gas CNG Vehicul
20、ar Fuel Systems Code). Definitions 3.2 to 3.4, 3.7 to 3.10, and 3.14 are taken from NIST Handbook 44 (Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices), Appendix D. Definitions 3.5 and 3.11 are based on Handbook 44 definitions. 3.1 Authority Having Juri
21、sdiction The organization, office, or individual responsible for approving equipment, an installation, or a procedure. 3.2 Contract Sale A sale where there is a written agreement stating the price as either a fixed price, a price above cost, or an adjustment from the posted price. 3.3 Cryogenic Liqu
22、ids Fluids with a normal boiling point below 153 C (243 F). 3.4 Derived Mass Units Units of sale for customer convenience based directly upon mass units, such as: Diesel Gallon Equivalent (DGE) 2.71 kg (5.976 lb) of natural gas* Diesel Liter Equivalent (DLE) 0.716 kg (1.578 lb) of natural gas* * Cal
23、culation based on Lower Heating Value LHV of LNG at 21 495.5 BTU/lb with a composition of 98% methane and 2% ethane and a diesel LHV of 128 450 BTU/gal Gasoline Gallon Equivalent (GGE) 2.567 kg (5.660 lb) of compressed natural gas* Gasoline Liter Equivalent (GLE) 0.678 kg (1.495 lb) of compressed na
24、tural gas* * From NIST Handbook 44 3.5 Direct Sale A sale in which both parties in the transaction are present when the quantity is being determined. An unattended automated or customer-operated weighing or measuring system is considered to represent the device/business owner in transactions involvi
25、ng an unattended device. 3.6 Dispenser A device designed for the measurement and delivery of fluids used as fuel. 3.7 Liquefied Natural Gas (LNG) A cryogenic liquid, produced by reducing the temperature of natural gas to about 162 C (260 F) at atmospheric pressure. 3.8 Mass Flow Meter A device that
26、measures the mass of a product flowing through the system. The mass measurement may be determined directly from the effects of mass on the sensing unit or may be inferred by measuring the properties of the product, such as the volume, density, temperature, or pressure, and displaying the quantity in
27、 mass units. 3.9 NBP Normal boiling point of a cryogenic liquid at 101.325 kPa (14.696 psi absolute). SAE J2645 Revised APR2009 Page 5 of 9 3.10 NTP Normal temperature of 21 C (70 F) and pressure of 101.325 kPa (14.696 psi absolute) respectively. 3.11 Point of Sale System An assembly of elements inc
28、luding a weighing or measuring element, an indicating element, and a recording element (and may also be equipped with a “scanner”) used to complete a direct sales transaction. 3.12 Retail Device A device used for: a. Single deliveries of less than 378 L (100 gal) or b. Retail deliveries of motor fue
29、ls to individual vehicles. 3.13 Saturation Pressure The point at which temperature and pressure of a liquid-vapor system are in equilibrium or the pressure at which the liquid will automatically boil. Raise the temperature, and the pressure will rise, lower the pressure and the temperature will fall
30、. As a commonplace example, water will boil at 100 C (212 F) at sea level, but will boil at roughly 94 C (202 F) in Denver, where there is less air pressure. If a liquid is artificially pressurized, as in a pressure cooker, it will boil at a higher temperature than when in an open pot. Accurate cont
31、rol of the saturation pressure of dispensed LNG may be important because most LNG vehicle systems presently in use rely on this pressure to drive fuel to the engine. 3.14 Two-Phase Flow A condition where the liquid is not in a compressed liquid state, but contains some percentage of gas entrained in
32、 the flowing liquid. 3.15 Wholesale Device Any device other than a retail device (see 3.11). 4. CRYOGENIC ISSUES There are challenges to accurately measure LNG. The most critical are addressed in succeeding sections. Note that these issues are interrelated. 4.1 Heat Cryogenic liquids, under pressure
33、, will gain heat unless the temperature can be kept at equilibrium. This heat transfer can be minimized, but not eliminated. Heat gain or loss will affect liquid density. 4.2 Saturation Pressure Accurate control of the saturation pressure of dispensed LNG may be important because most LNG vehicle sy
34、stems presently in use rely on this pressure to drive fuel to the engine. It is difficult to accurately measure the saturation pressure for flowing LNG. SAE J2645 Revised APR2009 Page 6 of 9 4.3 Density The density of LNG varies with saturation pressure. At higher saturation pressures (higher boilin
35、g points), LNG is less dense. This means that 3.79 liters (one gallon) of LNG at 154 C (246 F) weighs 1.56 kg (3.44 lb) (and automatically boils at 170.3 kPa 24.7 psia), and at 129 C (200 F) it weighs 1.40 kg (3.08 lb) (and automatically boils at 790.8 kPa 114.7 psia). Depending on the technology, a
36、 dispensing system must be capable of making corrections for density changes related to temperature, pressure and/or composition. 4.4 LNG Composition Due to variance in feedstock, liquefaction methods, and LNG storage, the LNGs composition (chemical makeup) may vary. The variation of composition of
37、LNG may change density and can thereby cause measurement errors. 4.5 Sub-Cooling Cryogenic fluids are generally contained in pressure vessels. It is possible to artificially pressurize these vessels, without changing the temperature or the saturation of the liquid, by adding vapor to the top of the
38、vessel. Under these conditions, the liquid is considered to be “sub-cooled.” Pumping the fluid at a higher pressure has this same effect. Either method serves to suppress boiling of the liquid. 5. DISPENSING SYSTEM ISSUES There are many issues outside of the measuring transducers themselves that aff
39、ect measurement accuracy. Following are the main things to consider in avoiding measurement inaccuracy. 5.1 Hose Volume Corrections Design consideration should be given to how the dispensing system will account for the amount of liquid or gas downstream of the meter installation. The dispenser may b
40、e designed to incorporate a liquid recirculating feature, a hose draining system or other methods to achieve a controlled condition. 5.2 Two-Phase Flow Flowing LNG is subject to boiling as heat is added or pressure is reduced during its path from the storage tank to the vehicle system. Depending on
41、the piping configuration, a combination of both vapor and liquid may occur in the system. This is especially true during the initiation of the dispensing process. Most meters experience errors due to two-phase flow. An accurate LNG dispensing system may require a means to detect and correct for the
42、presence of two-phase flow. 5.3 Temperature Effects Temperature changes may affect the dimensions and material properties of the dispensing system and metering device. Temperature will also impact the density of LNG. Dispensing systems should take these effects into account by design, calibration or
43、 correction techniques, if necessary. 5.4 Pressure Effects Changes in pressure within the dispensing system itself (pressure drop) may cause two-phase flow, as well as density changes. Dispensing systems should take these effects into account by design, calibration or correction techniques, if neces
44、sary. 5.5 Composition Compensation LNG is a mixture consisting primarily of Methane, Ethane, Propane, Butane, and Nitrogen. Composition depends on the feedstock and liquefaction methods. As such, the density of LNG can vary depending upon its composition. Chemical composition corrections should be c
45、onsidered in the metering system design. SAE J2645 Revised APR2009 Page 7 of 9 5.6 Diversion of Measured Flow In systems subject to metrological control or custody transfer, no means shall be provided by which any measured liquid can be diverted from the measuring chamber of the device or the discha
46、rge line therefrom, except that a manually controlled outlet that may be opened for purging or draining the measuring system shall be permitted. Effective means shall be provided to prevent the passage of liquid through any such outlet during normal operation of the device and to indicate clearly an
47、d unmistakably when the valve controls are so set as to permit passage of liquid through such outlet. (This requirement is taken from NIST Handbook 44, Section 3.34 - Cryogenic Liquid-Measuring Devices, S.3.1). 5.7 Vapor Equalization Line A vapor equalization line shall not be used during a metered
48、delivery unless the quantity of vapor displaced from the buyers tank to the sellers tank is deducted from the metered quantity. (This requirement is taken from NIST Handbook 44, Section 3.38 - Carbon Dioxide Liquid-Measuring Devices, UR.2.3). 6. DISPENSING SYSTEM SELECTION When selecting an LNG disp
49、enser, the operation of the fleet(s) it serves should be considered. Refueling frequency, accuracy and metrological requirements should help guide the user. 6.1 Private Stations For these stations, where metering is for internal accounting purposes, and fueling accuracy to each vehicle is not critical, a relatively simple metering system can be used. Typically these systems may have an accuracy of 2
