Nearly every power plant in the US must undergo annual Relative Accuracy Test Audits (RATA testing) to confirm the values reported by their continuous emission monitoring systems (CEMS). In order to perform a RATA test, the plant must operate at one or more stable loads for a number of hours. Depending on the type of unit and fuel, the required load levels for RATA testing can range from low, mid and high loads for coal-fired units to a single (normal) load for oil and gas fired units or four loads (from partial load to maximum load) for units utilizing 40 CFR Part 75 Appendix E alternative monitoring systems. Many plants operate in a dispatch environment where the plant is not in control of their load from hour to hour, and some even from minute to minute, such as those operating under Automatic Generation Control (AGC). Scheduling plant loads for the RATA testing must often be done far in advance and can come at a high price when factoring in fuel costs. Because it can be a significant undertaking to schedule the loads for a series of RATA tests, it makes economic sense to schedule other testing also requiring unit stability concurrently with the RATA tests. One of the most important tests that fits this category is performance testing for plant capacity and/or heat rate. Many plants are now required to perform capacity and/or heat rate demonstrations on a periodic basis to support their power purchase agreements or transmission reliability requirements. But even plants without performance test requirements can benefit from gathering performance related data during RATA testing. For plants dispatched based on demonstrated heat rates, understanding the heat rate impact of operating in AGC or at partial loads is essential. Awareness of expected heat rate is also vital for plants that must nominate their fuel consumption requirements in advance. If the RATA test loads are planned correctly, performance data collected during the RATA test periods can be used not only to fulfill required demonstrations for capacity and heat rate, but also to determine the actual annual degradation (recoverable and non-recoverable) observed for the plant equipment. Test data can also be used to build or update performance forecasting tools for dispatch purposes. Depending on the complexity of the RATA testing, multiple load points may be available (from minimum to maximum load) which can provide data on fuel consumption at various loads, supporting fuel purchasing and planning requirements for the plant. This paper intends to outline the value of coordinating annual performance tests with RATA tests in terms of manpower, load scheduling and fuel consumption. This paper will also discuss a number of issues that may arise when coordinating multiple tests — which could be performed by numerous independent parties, as well as the additional benefits which can be gained by collecting adequate performance data during RATA test periods.

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