In applying ASME PTC 46 “Overall Plant Performance” to a coal-fired steam plant, it is mandated that the heat input to the plant is determined by the product of heat input to the steam and the inverse of the steam generator fuel efficiency. Steam generator fuel efficiency is to be determined, per PTC 46, by the energy balance method as detailed in ASME PTC 4 “Fired Steam Generators”. ASME PTC 4 (1998) superseded an earlier Code, ASME PTC 4.1, which is no longer an ANSI standard or an ASME Code (as this paper was being written, PTC 4- 2008 has been published as a revision of PTC 4-1998). PTC 4.1 made use of a simplified “short form” to determine efficiency by what was known as the heat loss method, used by the industry for many years due to its ease of use. The energy balance method is fundamentally different from the heat loss method even in terms of the definition of efficiency and heat input. This paper explores the major differences between the two PTC’s (the defunct PTC 4.1 and PTC 4). Without knowing these differences, a direct comparison of PTC 4 and PTC 4.1 results is meaningless and could lead to false conclusions.

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