Abstract
This paper aims to analyse the impact of air-water heat exchanger’s degradation on the performance of a reheated humid air turbine system for power generation applications. A number of thermal models to simulate the performance of the various sub-systems was put together and validated against experimental data. The performance degradation of the heat exchangers is characterised by means of a degradation coefficient, which is used to drive the cycle into off-design and part-load conditions when degradation is accounted for. Three heat exchanger design scenarioswere investigated, namely a low, a medium and a high effectiveness in order for the impact of the degradation penalties on cycle thermal efficiency to be determined. The performance deterioration of the heat exchangers is also analysed from an exergetic point of view in order to identify the key sources that penalise the thermal efficiency of the humid air turbine system. The degradation analysis shows that typical levels of intercooler deterioration cause notable penalties in the cycle performance, reducing its thermal efficiency and power output by 1.8 percentage points and 28% respectively compared to the un-degraded operation. The exergy analysis showed that the deterioration of the intercooler also penalises the efficiency of the low pressure compressor and reheater, which contribute to the performance penalty of the cycle too. It is also found that the degradation of the intercooler can also lead to operability penalties at the low pressure compressor by reducing its surge margin. The effects of the deterioration of the aftercooler and economiser were found to only have a weak effect on the system’s performance. The outcome of the work constitutes a step forward in understanding of the performance behaviour of an advanced cycle when heat exchanger degradation is present.
Highlights
Over the past decades, the development of new technologies in the power generation sector was focused on the enhancement of thermal efficiency together with reduction of emission levels
For the average heat exchanger effectiveness design and DCSim = 1 the thermal efficiency drops by 1.9 pp while for DCSim = 2 a 3 pp drop of thermal efficiency was found in comparison to clean operation
Exergy analysis enabled the identification of the main sources that cause changes in cycle performance when the heat exchangers are degraded
Summary
The development of new technologies in the power generation sector was focused on the enhancement of thermal efficiency together with reduction of emission levels. Since the early introduction of HAT systems in the late 80’s by Rao [3], numerous studies showed the highly efficient variations of such cycles and their advantageous economic performance. Lazzaretto and Segato [4,5] introduced a high efficiency configuration using an intercooler, aftercooler, and economiser to recuperate a notable amount of heat back into the cycle. Ågren and Westermark [6,7] suggested that a percentage of the inlet mass flow should bypass the aftercooler and saturator to further improve cycle performance. Chiesa et al [8] showed that the addition of a second combustion chamber could improve the thermal efficiency beyond the 60% thershold, which was
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