Water or steam injection for NOX control or power augmentation can impact turbine hot section component life and maintenance interval. This relates to the effect of added water on hot-gas transport properties. Higher gas conductivity, in particular, increases heat transfer to blade and vane, and can lead to higher metal temperature and reduced part life. Part life impact from steam or water injection is also related to the way engine is controlled. Life cycle impact of steam injection on the LM6000PC HP turbine blade has been studied. The relationship between steam injection, LP turbine inlet temperature control, blade metal temperature, and corresponding life change was analyzed. The analysis result can be used for the assessment of life cycle impact with steam injection and temperature control limit.
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 ASME PTC 4 (1998) superseded an earlier Code, ASME PTC 4.1, which is no longer an ANSI standard or an ASME Code (as this paper was being written, PTC 4- 2008 has been published as a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.
ASME Performance Test Code PTC 4 for “Fired Steam Generators” superseded previous Code PTC 4.1 in 1998[1][2]. PTC 4 corrects many of the deficiencies in PTC 4.1 and makes testing more accurate and easy to integrate into plant performance tests. PTC 4.1 however continues to be used in many parts of the industry mainly due to its simplicity and ease of use. The use of both PTC 4 and PTC 4.1 has caused confusion. Direct comparison of testing results obtained in accordance with the two Codes may lead to wrong conclusions. Fundamentally, PTC 4 is a more technically sound and comprehensive Code than PTC 4.1 was. The calculation procedures of PTC 4 are intended to produce more accurate loss results and reduce the uncertainty. For example, the surface radiation and convection losses are measured instead of estimated, and the un-measured minor losses must be estimated individually if not measured, with appropriate uncertainty values. Therefore, the level of uncertainty associated with the estimate of unmeasured losses commonly assumed by a lump sum value in PTC 4.1 would normally be greater than that associated with the individually estimated losses by PTC 4. This paper presents a study of steam generator efficiency and fuel flow for a 700MW net coal-fired power plant with the application of both PTC 4 and PTC 4.1 Codes. Without considering the differences in uncertainty analysis, radiation / convection losses, and un-measured losses / credits, it is found that the results of tests conducted by the two methods vary marginally, given that the gross efficiency in the scope of PTC 4.1 is converted into the fuel efficiency as defined by PTC 4. The difference between the PTC 4 and 4.1 efficiencies is principally due to the energy credits associated with auxiliary equipment power consumption. The paper also discusses differences in efficiency definitions, efficiency conversions, and fuel flow calculations between the two Codes.
Gas turbines in combined cycle (CC) power plants, in phased construction situations, usually operate for several months in the simple cycle (SC) mode while the steam portion of the plant is being constructed. At the time of commissioning the combined cycle phase, the gas turbines typically have accumulated a considerable number of operating hours and have possibly experienced some degradation, especially on turbines that have run on dual fuels. To determine the combined cycle new and clean performance, it is necessary to employ a phased testing approach. The phased testing approach involves testing the gas turbines when they are in new and clean condition and combining those results with the measured new and clean steam turbine cycle performance. The method of the phased testing has been introduced in ASME PTC 46 (1996) “Performance Test Code on Overall Plant Performance”. This paper will discuss in detail the test protocol, fundamental equations, corrections, and uncertainty analysis of phased testing. This paper will also discuss performance degradation and engine setting changes between the phases.
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