A Study of Coal-Fired Steam Generator Efficiencies

ASME Performance Test Code PTC 4 for “Fired Steam Generators” superseded previous Code PTC 4.1 in 1998[1][2].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.