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Gas Interchangeability Defined AGA Staff Paper: Technical Background and Issues of Gas Interchangeability Prepared for: Building Energy Codes and Standards Committee American Gas Association Prepared by: Ted A. Williams Director, Codes, Standards & Technical Support American Gas Association April 2006 Disclaimer This report was prepared by American Gas Association (AGA) Staff for the purpose of summarizing prior technical work, research, and technical application of gas interchangeability principles and practices. Neither AGA, its members, nor any person acting on behalf of these organizations: • Makes any warranty or representation with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information disclosed in this report may not infringe privately owned rights; or • Assumes any liability with respect to the use of, or for damages resulting from the use of, any information disclosed in this report. 2 Table of Contents 1. Gas Interchangeability Defined . 5. 1.1 The NGC+ Definition . 5. 1.2 Historical Definitions from the Gas Industry Literature . 6. 1.3 Implications of Gas Interchangeability as Defined . 6. 2. The Objectives of Gas Interchangeability Criteria . 7. 2.1 Anticipation and Avoidance of Adverse Combustion Behavior . 7. 2.2 Drivers for Gas Interchangeability Specifications in the U. S. 8. 2.3 Appliance Focus of Gas Interchangeability Studies and Specifications . 8. 2.4 Relevance of Historical Studies to Current End Uses . .11. 3. Combustion Issues in Classical and Contemporary Gas Interchangeability . 12. 3.1 General Combustion Issues . .12. 3.2 Combustion Failure Modes . .13. 3.2.1 Elevated Pollutant Generation . 13. 3.2.1.1 CO Production . .. 13. 3.2.1.2 Particulate Matter (Soot) Production . 16. 3.2.1.3 NOX Production . .18. 3.2.2 Altered Heat Rates . 19. 3.2.2.1 Durability of Heat Exchangers and Components . 19. 3.2.2.2 Jacket/Vent Overheating and Fire Hazards . 20. 3.2.2.3 Changes in Efficiency . 20. 3.2.3 Combustion Stability . 20. 3.2.3.1 Flame Lifting . 20. 3.2.3.2 Flashback . 21. 3.2.3.3 Oxygen Depletion Sensor (ODS)/Pilot Reliability . 21. 4. Appliance/Gas Consumer Issues . 21. 4.1 Installation/Maintenance Issues. 21. 3 4.2 Unattended Operation . 22. 4.3 Changing Means of Adjustment . 22. 4.4 Vented versus Unvented Design and Operation . 22. 5. Considerations from U. S. Historical Gas Interchangeability Studies . 23. 6. Gas Interchangeability Indices . 26. 7. Activities and Gas Industry Requirements Outside the U. S. 29. 7.1 Overseas Specifications . 29. 7.2 Current U. K. Activities. 30. 8. Criteria for Acceptable Appliance Performance . 32. 8.1 CO Criteria Are Most Critical . 32. 8.2 Standards for Acceptable CO Generation in Appliances . 32. 9. Issues Beyond the Scope of This document . 33. 9.1 Adjustment at End Use versus Gas Supply Modification . 33. 9.2 Economic Efficiency and Equity . 33. 9.3 Similarities and Differences of Requirements Among End Users . 34. 9.4 Consumer Risk Under Alternative Actions . 34. References . 35. 4 The objective of this Staff Paper is to discuss technical aspects of gas interchangeability including its meaning, the objective of gas interchangeability criteria, combustion issues and failure modes associated with non- interchangeable gases, technical history and background, use of indices as metrics, examples of interchangeability requirements in other countries as of this writing, and criteria for acceptability. Because of the wealth of technical documentation of gas interchangeability science and applications, references to important work are provided, and descriptions of these studies are not provided here in most cases. Emphasis is placed upon domestic appliances because, despite the large customer class using these devices and the wealth of information available on testing and gas interchangeability studies on them, recent debate over impacts upon appliance function and residential consumers may not be receiving equitable consideration, in the authors opinion. This Staff Paper does not address issues of gas composition as it relates to potential issues of U. S. gas supply, distribution of costs that may be associated with bringing interchangeable gases to market, the diversity of end uses and potential inconsistencies of gas interchangeability requirements among end uses, or issues of implementation and policy associated with gas interchangeability criteria and requirements. 1. Gas Interchangeability Defined 1.1 The NGC+ Definition In 2004, the Natural Gas Council (NGC), a coalition of natural gas trade associations composed of the Interstate Natural Gas Association of America (INGAA), the Natural Gas Supply Association (NGSA), the Process Gas Consumers Group (PGCG), and AGA, recognized the need for the U. S. natural gas industry and its customers to develop industry based recommendations for addressing changes in gas composition brought on by changes in domestic gas and anticipated LNG importation. The NGC recognized the need to expand participation on issues of gas quality, including gas interchangeability, to other stakeholders concerned with gas supply, transportation, and end use. This expanded ad hoc group was convened in 2004 as "NGC+." The Gas Interchangeability Task Group was organized by NGC+ representing over 40 stakeholder organizations including gas producers, pipelines, local distribution companies (LDCs), end use equipment manufacturers, trade associations, and regulators. In development of its "White Paper on Natural Gas Interchangeability and Non-Combustion End Use," the Task Group developed the following definition of gas interchangeability: “The ability to substitute one gaseous fuel for another in a combustion application without materially changing operational safety, efficiency, 1 performance or materially increasing air pollutant emissions.” 1 Gas Interchangeability Task Group. White Paper on Natural Gas Interchangeability and Non- Combustion End Use. Natural Gas Council Interchangeability Task Group, 2005, p. 3. 5 1.2 Historical Definitions from the Gas Industry Literature Prior to the NGC+ work, the LDC industry had developed a variety of definitions of gas interchangeability as part of its seven decades of work in this area (i.e., beginning formally in the 1930s). The following are examples of these definitions, which are different but consistent: "Two gases may be interchangeable if flame characteristics are satisfactory after substitution of one gas for another,”2 "The two basic tenets for the gas industry are: • Suppliers must furnish a fuel gas that burns safely and performs adequately in the appliances and equipment connected to their lines. • Manufacturers must furnish appliances and equipment that operate properly on the fuel gas furnished. Thus, as fuel gases become more varied and maintaining a uniform product becomes increasingly difficult or impossible, the definition of acceptable variations in the composition of the gas becomes more vital. A responsive change is now taking place in the was the gas industry looks at interchangeability."3 1.3 Implications of Gas Interchangeability As Defined These definitions clearly identify gas interchangeability as fundamentally an end use issue in terms of the interaction of gases with end use equipment. Specifically, it is concerned with gas combustion. Granted that the gas interchangeability criteria and requirements may have far-reaching implications, the focus of gas interchangeability science since the 1930s in the U. S. has remained on how end use appliance combustion responds to changes in fuel gas composition. This focus is reflected in appliance and equipment testing and development of interchangeability indices and parameter limits for indices. In addition, these definitions point to the interaction of appliances and equipment and changes in gas composition as appliances and equipment are manufactured and installed, not as appliances might be modified by manufacturers or by installers in the field. This condition is documented in gas industry literature: 2 American Gas Association. Gas Engineers Handbook. Segler, C. George, Editor-in-Chief, The Industrial Press: New York, NY, 1965. p. 12/239. 3 American Gas Association. Utilization, Volume V: Gas Engineering and Operating Pracitce, Book U-1 Residential/Commercial, American Gas Association: Arlington, VA, 1994, p. 24. 6 "…for a substitute gas to be interchangeable with the base gas, the base settings of primary air and gas input rate must be within the flame limits of the substitute gas."4 Using an analogy from mathematics, gas interchangeability as it is studied and applied directly addresses the fixed environment of the appliance and equipment stock as a constant and gas composition as an independent variable. What might be done in terms of modifying appliances and equipment in the future, or even how appliances and equipment might be modified in the field to better address a known change in gas composition, are technically beyond the initial issue of whether gases are interchangeable. 2. The Objectives of Gas Interchangeability Criteria 2.1 Anticipation and Avoidance of Adverse Combustion Behavior Gas interchangeability criteria emerged in the early days of the natural gas industry as a means of avoiding end use combustion problems before they occurred in widespread fashion in the field. Specific statements of the need for gas interchangeability criteria are rare in the early industry literature, probably because of the obvious importance addressing the suitability of gases before they were
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