Errors in Boiler Efficiency Standards

This paper presents both criticism and suggested changes to boiler efficiency standards associated with fossil-fired steam generators. These standards include the widely used ASME PTC 4.1, PTC 4 and DIN 1942, and others. The chief criticism is inconsistent application of thermodynamic principles. Specifically, conceptual errors are made with application of reference temperatures and the treatment of shaft powers. When using computed fuel flow as a touchstone, it becomes obvious that arbitrary use of reference temperatures and/or use of capricious energy credits cannot dictate a system’s computed fuel flow. Efficiency, calorific value and fuel flow must have fixed definitions concomitant with a system’s useful energy flow. Thermodynamics is not an arbitrary discipline, the computed fuel needs of a system must describe the actual. Boiler efficiency requires the same treatment, as an absolute value, as actual fuel feed and emission flow. Boiler efficiencies and associated calorific values have obvious standing when judging contractual obligations, for thermal performance monitoring, and for confirming carbon emissions. Note that a 0.5 to 1% change in efficiency may well have significant financial consequences when testing a new unit, or the on-going costs associated with fuel and carbon taxes. This paper demonstrates that errors greater than 2% are entirely possible if following the current standards. This paper appeals to the resolution of efficiency at the 0.1% level. The power plant engineer is encouraged to read the Introduction and Summary & Recommendations sections while the thermodynamicist is requested to throughly review and critique the mid-sections. The author hopes such reviews will advocate for improvement of these important industrial standards.